243 results on '"Southward, Steve C."'
Search Results
2. Pulse Train Fx-LMS Algorithm for Drive File Identification
- Author
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Balasubramanya, Bharath, Southward, Steve C., Balasubramanya, Bharath, and Southward, Steve C.
- Abstract
A novel time-domain algorithm is proposed in this paper for the iterative estimation of drive files. A drive file is a synchronized batch of dynamic time series commands that are simultaneously sent to one or more actuators in a test rig that is designed for service environment replication (SER). When drive file commands are input to an SER test rig, the response of the article under test is similar to what was measured in a service environment. The proposed Pulse Train Filtered-X Least Mean Square (PT-Fx-LMS) algorithm is based on methods developed for active noise and vibration control (ANVC). A time-domain PT-Fx-LMS algorithm is shown through several simulation studies to rapidly converge to a dynamic solution in a small number of iterations for a one degree-of-freedom nonlinear suspension. The PT-Fx-LMS algorithm is also shown to enable targeted iteration over isolated time slices within the data set, which challenges conventional frequency-domain techniques.
- Published
- 2024
3. Pulse Train F x -LMS Algorithm for Drive File Identification.
- Author
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Balasubramanya, Bharath and Southward, Steve C.
- Subjects
ACTIVE noise & vibration control ,ADAPTIVE signal processing ,ALGORITHMS - Abstract
A novel time-domain algorithm is proposed in this paper for the iterative estimation of drive files. A drive file is a synchronized batch of dynamic time series commands that are simultaneously sent to one or more actuators in a test rig that is designed for service environment replication (SER). When drive file commands are input to an SER test rig, the response of the article under test is similar to what was measured in a service environment. The proposed Pulse Train Filtered-X Least Mean Square (PT-Fx-LMS) algorithm is based on methods developed for active noise and vibration control (ANVC). A time-domain PT-Fx-LMS algorithm is shown through several simulation studies to rapidly converge to a dynamic solution in a small number of iterations for a one degree-of-freedom nonlinear suspension. The PT-Fx-LMS algorithm is also shown to enable targeted iteration over isolated time slices within the data set, which challenges conventional frequency-domain techniques. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
4. An Anthropomimetic Approach to High Performance Traction Control
- Author
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Kirchner William and Southward Steve C.
- Subjects
traction control ,anthropomimetic ,vehicle dynamics ,human in the loop ,adaptive control ,Technology - Abstract
The ability to learn and adapt to changing environmental conditions, as well as develop perceptive models based on stimulus-response data, provides expert human drivers with significant advantages. When it comes to bandwidth, accuracy, and repeatability, automatic control systems have clear advantages over humans; however, most high performance control systems lack many of the unique abilities of a human expert. This paper documents our first step toward the development of a novel automatic traction control algorithm using an anthropomimetic approach. The primary objective of this approach was to synthesize a high performance longitudinal traction control system by incorporating desirable human behavior distilled from human-in-the-loop (HIL) testing on a 6-DOF driving simulator. The proposed control algorithm was developed in a general framework, and applied to the specific task of longitudinal traction control. Simulation results confirm that the proposed anthropomimetic traction control algorithm provides improved performance relative to a well-tuned conventional PID-based traction control algorithm. Results are also compared with the HIL response data from a behavioral study.
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- 2011
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5. Active vibration control using optimized modified acceleration feedback with Adaptive Line Enhancer for frequency tracking
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Nima Mahmoodi, S., Craft, Michael J., Southward, Steve C., and Ahmadian, Mehdi
- Published
- 2011
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6. Adaptive vehicle traction control: combined longitudinal and lateral motion
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Kirchner, William T. and Southward, Steve C.
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- 2013
- Full Text
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7. On controlling an uncertain system with polynomial chaos and [H.sub.2] control design
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Templeton, Brian A., Cox, David E., Kenny, Sean P., Ahmadian, Mehdi, and Southward, Steve C.
- Subjects
Mathematical optimization -- Research ,Chaos theory -- Research ,Polynomials -- Research ,Engineering and manufacturing industries ,Science and technology - Abstract
This paper applies the [H.sub.2] norm along time and parameter domains. The norm is related to the probabilistic [H.sub.2] problem. It is calculated using polynomial chaos to handle uncertainty in the plant model. The structure of expanded states resulting from Galerkin projections of a state space model with uncertain parameters is used to formulate cost functions in terms of mean performances of the states, as well as covariances. Also, bounds on the norm are described in terms of linear matrix inequalitys. The form of the gradient of the norm, which can be used in optimization, is given as a Lyapunov equation. Additionally, this approach can be used to solve the related probabilistic LQR problem. The legitimacy of the concept is demonstrated through two mechanical oscillator examples. These controllers could be easily implemented on physical systems without observing uncertain parameters. [DOI: 10.1115/1.4002474] Keywords: polynomial chaos, orthogonal polynomials, parametric uncertainty, optimal control, [H.sub.2] control, LQR
- Published
- 2010
8. A sensor placement strategy for the hybrid adaptive feedforward observer
- Author
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Tran, Chau M. and Southward, Steve C.
- Subjects
Sensors -- Research ,Dynamical systems -- Research ,Engineering and manufacturing industries ,Science and technology - Abstract
A sensor placement technique is proposed for implementing the hybrid adaptive feedforward observer. The observer is a conventional dynamic observer augmented with an adaptive feedforward component for estimating the effect of persistent, nonstationary disturbances. The placement technique searches for the least possible number of sensors that satisfy two criteria, the observability of the plant, and the lowest condition number of the error dynamic system's state matrix. Demonstration was performed on a one-dimensional acoustic duct. The results show that the proposed technique is an effective guideline for identifying the optimal sensor locations. [DOI: 10.1115/1.2196421]
- Published
- 2006
9. No-jerk skyhook control methods for semiactive suspensions
- Author
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Ahmadian, Mehdi, Song, Xubin, and Southward, Steve C.
- Subjects
Vibration -- Research ,Mine roof bolting -- Research ,Science and technology - Abstract
This paper presents two alternative implementations of skyhook control, named ' skyhook function' and 'no-jerk skyhook, 'for reducing the dynamic jerk that is often experienced with conventional skyhook control in semiactive suspension systems. An analysis of the relationship between the absolute velocity of the sprung mass and the relative velocity across the suspension are used to show the damping-force discontinuities that result from the conventional implementation of skyhook control. This analysis shows that at zero crossings of the relative velocity, conventional skyhook introduces a sharp increase (jump) in damping force, which, in turn, causes a jump in sprung-mass acceleration. This acceleration jump, or jerk, causes a significant reduction in isolation benefits that can be offered by skyhook suspensions. The alternative implementations of skyhook control included in this study offer modifications to the formulation of conventional skyhook control such that the damping force jumps are eliminated. The alternative policies are compared to the conventional skyhook control in the laboratory, using a base-excited semiactive system that includes a heavy-truck seat suspension. An evaluation of the damping force, seat acceleration, and the electrical currents supplied to a magnetorheological damper, which is used for this study, shows that the alternative implementations of skyhook control can entirely eliminate the damping-force discontinuities and the resulting dynamic jerks caused by conventional skyhook control.
- Published
- 2004
10. A virtual sensing method for tonal ANVC systems
- Author
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Tran, Chau M. and Southward, Steve C.
- Subjects
Dynamics -- Testing ,Sensors -- Testing ,Engineering and manufacturing industries ,Science and technology - Abstract
Virtual Sensing (VS) is considered to be an extension for feedforward Active Noise and Vibration Control (ANVC) systems when, for example, it is desired to minimize the response at one or more spatial locations where it is either physically impossible or undesirable to place an actual error sensor. In this context, VS is an estimation technique for predicting the appropriate system response using available measurements and a dynamic system model. A hybrid adaptive feedforward observer is proposed which has the ability to overcome the limitations of conventional dynamic observer designs. The hybrid observer utilizes a conventional dynamic observer augmented with an adaptive feedforward element for estimating the effect of the persistent disturbance. For simplicity, we restrict this development to a single tonal disturbance for which a coherent reference is assumed available. It will be appreciated that this technique may be extended to handle disturbances that contain multiple tones as well as broadband noise, as long as suitable reference signals are available. Numerical simulations and real-time experiments were performed on a one-dimensional acoustic duct. The results demonstrate that the hybrid adaptive feedforward observer is an effective method for predicting the virtual sensor response in an ANVC system. [DOI: 10.1115/1.1435642]
- Published
- 2002
11. Elastic Response of Acoustic Coating on Fluid-Loaded Rib-Stiffened Cylindrical Shells
- Author
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Doherty, Christopher Gilles, primary, Southward, Steve C., additional, and Hull, Andrew J., additional
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- 2018
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12. System Identification and Optimal Control of Half-Car Active Suspension System Using a Single Noisy IMU With Position Uncertainty
- Author
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Attia, Tamer, primary, Kochersberger, Kevin, additional, Bird, John, additional, and Southward, Steve C., additional
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- 2017
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13. Active Control of Low Frequency Modes in an Aircraft Fuselage Using Spatially Weighted Arrays
- Author
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Lane, Steven A., Clark, Robert L., and Southward, Steve C.
- Subjects
Aircraft cabins -- Research ,Frequency modulation -- Research ,Array processors -- Usage ,Science and technology - Abstract
Acoustic enclosures such as aircraft cabins often display lightly damped modal behavior at low frequencies where passive treatments are impractical due to mass and volume constraints. This work presents a feedback control approach using dynamic [H.sub.2] controllers implemented with spatially weighted arrays of collocated pressure sensors and constant volume-velocity actuators. The open-loop system is shaped using spatially weighted transducer arrays to yield increased pole-zero separation, which results in better closed-loop performance. The transducer arrays are weighted to emphasize coupling to a particular acoustic mode or modes, which facilitates global control of the targeted dynamics. This work presents a method to determine the spatial weighting vectors for the transducer arrays from frequency response measurements. The development and implementation of low-order, dynamic [H.sub.2] control laws is also discussed. Experimental results are presented for a single-mode and a multiple-mode controller implemented on an aircraft fuselage section, and demonstrate significant reduction of the targeted acoustic modes. To the best of the authors' knowledge, this is the first experimental implementation of a feedback controller of this type capable of achieving such levels of global reduction in a three-dimensional acoustic system. [S0739-3717(00)02303-5]
- Published
- 2000
14. Sensitivity Analysis and Optimization of Multibody Systems
- Author
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Mechanical Engineering, Sandu, Adrian, Sandu, Corina, Southward, Steve C., Dopico Dopico, Daniel, Bohn, Jan Helge, Zhu, Yitao, Mechanical Engineering, Sandu, Adrian, Sandu, Corina, Southward, Steve C., Dopico Dopico, Daniel, Bohn, Jan Helge, and Zhu, Yitao
- Abstract
Multibody dynamics simulations are currently widely accepted as valuable means for dynamic performance analysis of mechanical systems. The evolution of theoretical and computational aspects of the multibody dynamics discipline make it conducive these days for other types of applications, in addition to pure simulations. One very important such application is design optimization for multibody systems. Sensitivity analysis of multibody system dynamics, which is performed before optimization or in parallel, is essential for optimization. Current sensitivity approaches have limitations in terms of efficiently performing sensitivity analysis for complex systems with respect to multiple design parameters. Thus, we bring new contributions to the state-of-the-art in analytical sensitivity approaches in this study. A direct differentiation method is developed for multibody dynamic models that employ Maggi's formulation. An adjoint variable method is developed for explicit and implicit first order Maggi's formulations, second order Maggi's formulation, and first and second order penalty formulations. The resulting sensitivities are employed to perform optimization of different multibody systems case studies. The collection of benchmark problems includes a five-bar mechanism, a full vehicle model, and a passive dynamic robot. The five-bar mechanism is used to test and validate the sensitivity approaches derived in this paper by comparing them with other sensitivity approaches. The full vehicle system is used to demonstrate the capability of the adjoint variable method based on the penalty formulation to perform sensitivity analysis and optimization for large and complex multibody systems with respect to multiple design parameters with high efficiency. In addition, a new multibody dynamics software library MBSVT (Multibody Systems at Virginia Tech) is developed in Fortran 2003, with forward kinematics and dynamics, sensitivity analysis, and optimization capabilities. Several di
- Published
- 2015
15. Parametric Optimal Design Of Uncertain Dynamical Systems
- Author
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Mechanical Engineering, Ross, Shane D., Southward, Steve C., Sandu, Adrian, Sandu, Corina, Hong, Dennis W., Hays, Joseph T., Mechanical Engineering, Ross, Shane D., Southward, Steve C., Sandu, Adrian, Sandu, Corina, Hong, Dennis W., and Hays, Joseph T.
- Abstract
This research effort develops a comprehensive computational framework to support the parametric optimal design of uncertain dynamical systems. Uncertainty comes from various sources, such as: system parameters, initial conditions, sensor and actuator noise, and external forcing. Treatment of uncertainty in design is of paramount practical importance because all real-life systems are affected by it; not accounting for uncertainty may result in poor robustness, sub-optimal performance and higher manufacturing costs. Contemporary methods for the quantification of uncertainty in dynamical systems are computationally intensive which, so far, have made a robust design optimization methodology prohibitive. Some existing algorithms address uncertainty in sensors and actuators during an optimal design; however, a comprehensive design framework that can treat all kinds of uncertainty with diverse distribution characteristics in a unified way is currently unavailable. The computational framework uses Generalized Polynomial Chaos methodology to quantify the effects of various sources of uncertainty found in dynamical systems; a Least-Squares Collocation Method is used to solve the corresponding uncertain differential equations. This technique is significantly faster computationally than traditional sampling methods and makes the construction of a parametric optimal design framework for uncertain systems feasible. The novel framework allows to directly treat uncertainty in the parametric optimal design process. Specifically, the following design problems are addressed: motion planning of fully-actuated and under-actuated systems; multi-objective robust design optimization; and optimal uncertainty apportionment concurrently with robust design optimization. The framework advances the state-of-the-art and enables engineers to produce more robust and optimally performing designs at an optimal manufacturing cost.
- Published
- 2011
16. Probabilistic control using H2 control design and polynomial chaos: Experimental design, analysis, and results
- Author
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Templeton, Brian A., primary, Ahmadian, Mehdi, additional, and Southward, Steve C., additional
- Published
- 2012
- Full Text
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17. Neural Control of Posture During Small Magnitude Perturbations: Effects of Aging and Localized Muscle Fatigue
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Davidson, Bradley S, primary, Madigan, Michael L, additional, Southward, Steve C, additional, and Nussbaum, Maury A, additional
- Published
- 2011
- Full Text
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18. Traction Control Using an Anthropomimetic Approach
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Kirchner, William T., primary and Southward, Steve C., additional
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- 2011
- Full Text
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19. Estimating Changes in Speech Metrics Indicative of Fatigue Levels
- Author
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Shahidi, Parham, primary, Soltan, Reza A., additional, Southward, Steve C., additional, and Ahmadian, Mehdi, additional
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- 2010
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20. Estimating Crew Alertness From Speech
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Shahidi, Parham, primary, Southward, Steve C., additional, and Ahmadian, Mehdi, additional
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- 2010
- Full Text
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21. A Methodology for Laboratory Testing of Truck Cab Suspensions
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Marcu, Florin M., primary, Ahmadian, Mehdi, additional, Southward, Steve C., additional, and Jansson, Stefan B., additional
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- 2009
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22. A Methodology for Accounting for Uneven Ride Height in Soft Suspensions with Large Lateral Separation
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Marcu, Florin M., primary, Ahmadian, Mehdi, additional, Southward, Steve C., additional, and Jansson, Stefan B., additional
- Published
- 2009
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23. Nonlinear MR model inversion for semi-active control enhancement
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Reader, Daniel, primary, Southward, Steve C., additional, and Ahmadian, Mehdi, additional
- Published
- 2009
- Full Text
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24. Fuzzy Analysis of Speech Metrics to Estimate Conductor Alertness
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Shahidi, Parham, primary, Southward, Steve C., additional, and Ahmadian, Mehdi, additional
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- 2009
- Full Text
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25. Identification and Stability Analysis of the Postural Control System During Small Magnitude Perturbations
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Davidson, Bradley S., primary, Madigan, Michael L., additional, Southward, Steve C., additional, and Nussbaum, Maury A., additional
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- 2008
- Full Text
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26. Real-Time Estimation of Temporal Word Boundaries Without Linguistic Knowledge
- Author
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Shahidi, Parham, primary, Southward, Steve C., additional, and Ahmadian, Mehdi, additional
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- 2008
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27. No-jerk semi-active skyhook control method and apparatus
- Author
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Lord Corporation, Virginia Tech Intellectual Properties, Inc., Ahmadian, Mehdi, Southward, Steve C., Reichert, Brian Anthony, Song, Xubin, Lord Corporation, Virginia Tech Intellectual Properties, Inc., Ahmadian, Mehdi, Southward, Steve C., Reichert, Brian Anthony, and Song, Xubin
- Abstract
A method of controlling a controllable force generator within a controllable suspension system interconnected between a first member M.sub.1 and a second member M.sub.2. The method includes the steps of obtaining a first signal (V.sub.abs) representative of the absolute velocity of the first member M.sub.1, obtaining a second signal (V.sub.rel) representative of the relative velocity between the first and second members, and setting a desired damping force for the generator based upon a control policy which defines a control surface. The control policy includes a preselected gain, an absolute velocity, and a shaping function of relative velocity wherein said control surface exhibits only continuous first derivatives for V.sub.rel *V.sub.abs >0 and wherein the control surface is devoid of any surface discontinuities. This control policy effectively eliminates the jerkiness in certain prior art control methods, such as skyhook.
- Published
- 2000
28. Vibration Confinement by Minimum Modal Energy Eigenstructure Assignment
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Rastgaar Aagaah, Mohammad, primary, Ahmadian, Mehdi, additional, and Southward, Steve C., additional
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- 2007
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29. Real-Time Parameter ID Using Polynomial Chaos Expansions
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Southward, Steve C., primary
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- 2007
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30. Effect of the Actuators’ Location on Vibration Suppression Using Minimum Modal Energy Eigenstructure Assignment
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Aagaah, Mohammad Rastgaar, primary, Southward, Steve C., additional, and Ahmadian, Mehdi, additional
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- 2007
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31. Development of a General Use Quarter-Vehicle Test Rig
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Langdon, Justin, primary and Southward, Steve C., additional
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- 2007
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32. Acoustic Beamforming Enhancement of Locomotive Cabin Speech
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Muecke, Karl, primary and Southward, Steve C., additional
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- 2007
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33. Scale-Model Test Rig for Passive and Active Suspension Control Comparison
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Annis, Nathanael D., primary and Southward, Steve C., additional
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- 2007
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34. Comparison of Static and Dynamic Models for the Force Output of Magnetorheological Dampers
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Richards, Russell J., primary, Sandu, Corina, additional, and Southward, Steve C., additional
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- 2007
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35. Detecting Crew Alertness With Processed Speech
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Shimp, Samuel K., primary, Southward, Steve C., additional, and Ahmadian, Mehdi, additional
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- 2007
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36. Modeling Magnetorheological Dampers with Application of Nonparametric Approach
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Song, Xubin, primary, Ahmadian, Mehdi, additional, and Southward, Steve C., additional
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- 2005
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37. Eliminating the Unwanted Dynamics From the Controllable Suspensions for Vehicle Applications
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Song, Xubin, primary, Ahmadian, Mehdi, additional, and Southward, Steve C., additional
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- 2002
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38. A Virtual Sensing Method for Tonal ANVC Systems
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Tran, Chau M., primary and Southward, Steve C., additional
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- 2001
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39. Commercialization of Active Isolation for Jet Aircraft
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Southward, Steve C., additional, Ivers, Douglas E., additional, and Nicholson, Geoff C., additional
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- 1997
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40. Feedforward control with the higher‐harmonic, time‐averaged, gradient (H‐TAG) descent algorithm
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Kewley, Dorene, primary, Clark, Robert L., additional, and Southward, Steve C., additional
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- 1993
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41. A Property of Stick-Slip Friction Models which Promotes Limit Cycle Generation.
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Radcliffe, Clark J. and Southward, Steve C.
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- 1990
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42. A modified Luenberger observer for the inverted pendulum
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Southward, Steve C.
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- 1985
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43. Elastic Response of Acoustic Coating on Fluid-Loaded Rib-Stiffened Cylindrical Shells
- Author
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Doherty, Christopher Gilles, Southward, Steve C., and Hull, Andrew J.
- Abstract
Reinforced cylindrical shells are used in numerous industries; common examples include undersea vehicles, aircraft, and industrial piping. Current models typically incorporate approximation theories to determine shell behavior, which are limited by both thickness and frequency. In addition, many applications feature coatings on the shell interior or exterior that normally have thicknesses which must also be considered. To increase the fidelity of such systems, this work develops an analytic model of an elastic cylindrical shell featuring periodically spaced ring stiffeners with a coating applied to the outer surface. There is an external fluid environment. Beginning with the equations of elasticity for a solid, spatial-domain displacement field solutions are developed incorporating unknown wave propagation coefficients. These fields are used to determine stresses at the boundaries of the shell and coating, which are then coupled with stresses from the stiffeners and fluid. The stress boundary conditions contain double-index infinite summations, which are decoupled, truncated, and recombined into a global matrix equation. The solution to this global equation results in the displacement responses of the system as well as the exterior scattered pressure field. An incident acoustic wave excitation is considered. Thin-shell reference models are used for validation, and the predicted system response to an example simulation is examined. It is shown that the reinforcing ribs and coating add significant complexity to the overall cylindrical shell model; however, the proposed approach enables the study of structural and acoustic responses of the coupled system.
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- 2019
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44. Probabilistic control using control design and polynomial chaos: Experimental design, analysis, and results
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Templeton, Brian A., Ahmadian, Mehdi, and Southward, Steve C.
- Subjects
- *
PROBABILITY theory , *POLYNOMIAL chaos , *EXPERIMENTAL design , *ELECTRIC oscillator design & construction , *PERFORMANCE evaluation , *COMPARATIVE studies - Abstract
Abstract: This work presents an experimental investigation of recently developed design methods that combine polynomial chaos with control. The experiment utilizes a mechanical oscillator with different amounts of mass added in order to create an experimental parametric uncertainty. The uncertain mass is described in the system model by a polynomial chaos representation of a probability distribution function (PDF). Four different controllers using different variance weightings, are optimized using the and polynomial chaos technique. A comparable standard design and open loop performance are presented for comparison. The motivation for the work includes validating the proposed technique as well as contributing an experimental investigation to the polynomial chaos literature, which is predominately limited to simulation studies. The paper covers the experimental design and setup. A practical overview of the control design method is given. Standard control analysis tools showing responses for a selection of parameter values allow visualizing some of the properties of the controllers. Further, the experimental results from the test allow better conceptualization of the effects of the method as well as illustrating practical limits. Of particular interest, the defined norms used for designing the optimal controllers also provide an elegant way to quantitatively compare the theoretically expected performance with the obtained experimental performance. [Copyright &y& Elsevier]
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- 2012
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45. Investigation of Multiphase Coupled Inductor Topologies for Point-of-Load Applications
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Zhu, Feiyang, Electrical Engineering, Li, Qiang, Southward, Steve C., Zhang, Yuhao, Centeno, Virgilio A., and Lee, Fred C.
- Subjects
nonlinear inductor ,multiphase buck converter ,Multiphase coupled inductor ,fast transient response ,point-of-load application ,magnetic integration - Abstract
As a scalable, high-efficiency, and simple converter topology, an interleaved, multiphase buck converter has been widely used to power microprocessors in information industry. As modern microprocessors continuously advance, the required current for high-performance microprocessors used in data center applications could be several hundreds of amperes with a current slew rate larger than 1000 A/μs. This poses great challenges for a high-efficiency, high-power-density voltage regulator design with a fast transient response. On the other hand, the design challenges of voltage regulators in mobile applications are also increasing due to the stringent requirement on the device thickness and the battery life. In a multiphase buck converter, discrete inductors are widely used as energy storage elements. However, this solution has a limited transient response with a large size of magnetic components. To overcome these issues, coupled inductor is proposed to realize a small steady-state current ripple, a fast transient response, and a small inductor size at the same time. Although lots of studies have been conducted in the topic of the coupled inductor, there are still several challenges unsolved in this area. These challenges are addressed through a comprehensive study in this dissertation. First, a comprehensive analysis of different coupled inductor structures is crucial to identify the benefits and limitations of each inductor structure and provide design guidance under different application requirements. Based on the coupling mechanism, different coupled inductor structures are categorized as a direct-coupled inductor (DCL), an indirect-coupled inductor (ICL) or a hybrid-coupled inductor (HCL) in this work. The performance of these three types of coupled inductors is analyzed in detail through the equivalent inductance analysis and the magnetic flux analysis. For the applications that require a small phase number, a DCL can achieve the smallest inductor size with a given inductance requirement. As the phase number increases, it is beneficial to use an ICL and an HCL due to their symmetrical, simple, and scalable inductor structures. As compared to an ICL, an HCL can achieve a smaller inductor size due to the flux-cancellation effect. The difference between a DCL, an ICL and an HCL are revealed quantitively with several design examples through this study. Second, the steady-state inductance (Lss) and the transient inductance (Ltr) are two key design parameters for coupled inductors. A large Lss and a small Ltr are preferred from the circuit performance point of view. However, there is a design conflict in an ICL and an HCL under the inductor size constraint, where reducing Ltr also results in a smaller Lss. A variable coupling coefficient concept is proposed to overcome this issue. With the same Lss, the proposed method can achieve a smaller Ltr during load transients as compared with the conventional method. This concept is realized by applying a nonlinear inductor in the additional winding loop with the current in this loop as the control source. Compared with the conventional structure, the proposed structure can achieve a great output voltage spike reduction and output capacitance reduction. Third, although an ICL and an HCL are promising candidates for multiphase coupled inductors, an extra inductor is required in the additional winding loop to adjust the coupling coefficient. This additional inductor occupies extra space. To shrink the total inductor size, several improved magnetic core structures are proposed to achieve the controllable coupling through the magnetic integration for an ICL and an HCL. Furthermore, the thickness of the core plate can be significantly reduced by the improved core structure for an HCL. Overall, it is demonstrated that the inductor footprint is greatly reduced by the proposed core structure, as compared with the conventional solution. Lastly, a novel PCB-embedded coupled inductor structure is proposed for a 20MHz integrated voltage regulator (IVR) for mobile applications. To achieve a small inductor footprint and a low profile, the inductor structure with a lateral flux pattern and direct coupling is adopted. Compared with the state-of-the-art solution, the proposed structure can adjust the coupling in a simple core structure by changing the inductor winding pattern. The proposed structure integrates multiple inductors into one magnetic core and is embedded into PCB with a total thickness of 0.54 mm. In contrast to prior arts, the proposed inductor structure features a large inductance density and quality factor with a much smaller DC resistance (DCR), thus is seen as a promising candidate for IVR applications. Doctor of Philosophy As modern microprocessors continuously advance in the information industry, the required current for high-performance microprocessors used in data center applications could be several hundreds of amperes with a current slew rate larger than 1000 A/μs. This poses great challenges for the power converter design. On the other hand, the design challenges of power converters in mobile applications are also increasing due to the stringent requirement on the device thickness and the battery life. As a scalable, high-efficiency, and simple converter topology, an interleaved, multiphase buck converter has been widely used to power these processors. In a multiphase buck converter, discrete inductors are widely used as energy storage elements. However, this solution has a limited transient response with a large size of magnetic components. To overcome these issues, coupled inductor is proposed to realize a small steady-state current ripple, a fast transient response, and a small inductor size at the same time. Although lots of studies have been conducted in the topic of the coupled inductor, there are still several challenges unsolved in this area. These challenges are addressed through a comprehensive study in this dissertation. First, a comprehensive analysis and comparison of different coupled inductor structures is crucial to identify the benefits and limitations of each inductor structure and provide design guidance under different application requirements. Based on the coupling mechanism, different coupled inductor structures are categorized as a direct-coupled inductor (DCL), an indirect-coupled inductor (ICL) or a hybrid-coupled inductor (HCL) in this work. The performance of these three types of coupled inductors is analyzed in detail through the equivalent inductance analysis and the magnetic flux analysis. The difference between a DCL, an ICL and an HCL are revealed quantitively with several design examples through this study. Second, the steady-state inductance (Lss) and the transient inductance (Ltr) are two key design parameters for coupled inductors. A large Lss and a small Ltr are preferred from the circuit performance point of view. However, there is a design conflict in an ICL and an HCL under the inductor size constraint, where reducing Ltr also results in a smaller Lss. A variable coupling coefficient concept is proposed to overcome this issue. This concept is realized by applying a nonlinear inductor in the conventional structure. Compared with the conventional structure, the proposed structure can achieve a great output voltage spike reduction and output capacitance reduction. Third, although an ICL and an HCL are promising candidates for multiphase coupled inductors, an extra inductor is required in the additional winding loop to adjust the coupling coefficient. This additional inductor occupies extra space. To shrink the total inductor size, several improved magnetic core structures are proposed to achieve the controllable coupling through the magnetic integration for an ICL and an HCL. Lastly, a novel PCB-embedded coupled inductor structure is proposed for a 20MHz integrated voltage regulator (IVR) for mobile applications. Compared with the state-of-the-art solution, the proposed structure can adjust the coupling in a simple core structure by changing the inductor winding pattern. In contrast to prior arts, the proposed inductor structure features a large inductance density and quality factor with a much smaller DC resistance (DCR), thus is seen as a promising candidate for IVR applications.
- Published
- 2023
46. Design and Integration Techniques for High-Frequency PCB-Based Magnetics in Resonant Converters
- Author
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Ahmed, Ahmed Salah Nabih, Electrical Engineering, Li, Qiang, Southward, Steve C., Lee, Fred C., Centeno, Virgilio A., and Dong, Dong
- Subjects
high-frequency ,DC-DC converter ,LLC converter ,transformer design ,EMI ,gallium nitride ,magnetic integration - Abstract
In today's industrial power converters, converter reliability is essential, and converter topologies are well-established. Without a doubt, the power electronic industry continues to seek efficient power delivery and high power density. Resonant converters, especially LLC converters, have been intensively studied and applied in DC-DC converters. One of the most demanding applications for LLC converters is data centers. To date, LLC Resonant converters, are deployed in many applications for improved efficiency, density, and reliability. With the introduction of WBG devices coupled with the soft switching feature, the switching frequency can be extended beyond Mega-Hertz. With the significant increase in operating frequency, complicated magnetic components can be broken down into a cellular structure, each with a few number of turns. They can be easily implemented using 4-6 layers of PCB windings. Moreover, integrating the cellular cores using flux cancellation can further improve the power density. The proposed integrated magnetics can be automated in the manufacturing process. The magnetic size is reduced at this frequency, and planar magnetics using PCB winding become more relevant. PCB magnetics feature multiple advantages over Litz wire. The benefits are summarized as follows: The labor-intensive manufacturing process can be automated, thus reduction of cost. There is much reduced CM noise by using the shield layer. They have parasitics with much-improved reproducibility in large quantities. PCB windings feature less leakage between transformer windings because of the flexibility of the winding interleaving and the reduced number of turns. There is better thermal management due to the increased surface-to-body ratio. The design has a low profile and high-power density. However, it is not without its own limitations. There are challenges for high frequency PCB-magnetic magnetic design for the LLC converter. Firstly, With the recently developed high frequency core material, a phenomenon referred to as the dimensional resonant is observed. The effects of dimensional resonance were discussed in the literature when using an unusually large core structure; however, it can be observed more frequently under high excitation frequency, particularly with integrated magnetics. This dissertation discusses the dimensional effects of core loss on a PCB-based magnetics structure. A case study is presented on a 3-kW 400-to-48-V LLC prototype running at 1 MHz. The converter utilizes a low-profile matrix of two integrated transformers with a rectangular and thin cross-section area for reduced core loss. Specific solutions are presented. % Secondly, The matrix transformer is suitable for an LLC converter with high output current. However, the matrix transformer also increases the core size and core losses. The core loss degrades the LLC converter's light load and peak efficiency. In this dissertation, We discuss the design process and implementation of the DC-DC stage of the power supply unit for narrow range 48 V data center bus architecture. The optimization takes into account the number of elemental transformers, number of transformer turns, switching frequency, and transformer dimensions, namely winding width and core cross-section area. The optimization process results in a nearly 99% efficient 400-to-48-V LLC with a very high-power density and low profile fully integrated on PCB. A matrix of four transformers is used to reduce the termination loss of the secondary synchronous rectifier and achieve better thermal management. The number of secondary turns is optimized to achieve the best trade-off between winding loss, core loss, and power density. Another challenge arises for magnetic integration when multiple magnetic components with different characteristics come together. For instance, in the case of a transformer and an inductor on the same PCB. The PCB transformer is designed with perfectly interleaved primary and secondary layers to utilize the full PCB layer thickness. As a rule of thumb, the transformer winding layer is designed within 1 to 2 times the skin depth. On the other hand, the inductor's winding lacks interleaving and suffers from high MMF stress on layers. This makes the inductor prone to high eddy currents and eddy loss. Furthermore, this dissertation addresses the challenges associated with the high winding and core loss in the Integrated Transformer-Inductor (ITL). To overcome these challenges, we propose an improved winding design of the ITL by utilizing idle shielding layers for inductor integration within the matrix transformer. This method offers full printed circuit board (PCB) utilization, where all layers are consumed as winding, resulting in a significant reduction in the winding loss of the ITL. Moreover, we propose an improved core structure of the ITL that offers better flux distribution of the leakage flux within the magnetic core. This method reduces the core loss by more than 50% compared to the conventional core structure. We demonstrate the effectiveness of our proposed concepts by presenting the design of the ITL used in a high-efficiency, high-power-density 3-kW 400-to-48-V LLC module. The proposed converter achieves a peak efficiency of 98.7% and a power density of 1500 W/in3. This dissertation presents the concept of matrix inductors to solve such problems. A matrix of four resonant inductors is also designed to reduce the proximity effect between inductor windings and reduce inductor PCB winding loss. The matrix inductor provides a solution for high thermal stress in PCB-based inductors and reduces the inter-winding capacitance between inductor layers. This dissertation solves the challenges in magnetic design in high-frequency DC-DC converters in offline power supplies and data centers. This includes the transformer and inductor of the LLC converter. With the academic contribution in this dissertation, Wide-bandgap devices WBG can be successfully utilized in high-frequency DC-DC converters with Mega-Hertz switching frequency to achieve high efficiency, high power density, and automated manufacturing. The cost will be reduced, and the performance will be improved significantly. Doctor of Philosophy Industrial power converters need to be reliable and efficient to meet the power industry's demand for efficient power delivery and high power density. Research should focus on improving existing converter designs to improve fabrication, efficiency, and reliability. Resonant converters have been found to be effective in power conversion, especially in data centers where energy consumption is high. Three-element Resonant converters (LLC) are already used to improve efficiency, density, and reliability. By using Wide Bandgap devices and soft switching, the switching frequency can be extended beyond MHz, simplifying magnetic components and improving power density. The proposed integrated magnetics can be automated during the manufacturing process, further improving power density. At higher frequencies, planar magnetic components made with PCB winding are more effective than Litz wire. They are cheaper to make because of automation, have less common-mode noise, and are more reproducible in large quantities. PCB winding also has a low profile, high-power density, and better thermal management. However, it is not without its own limitations. There are challenges for high frequency PCB-magnetic magnetic design for the LLC converter. Firstly, With the recently developed high frequency core material, a phenomenon referred to as the dimensional resonant is observed. The effects of dimensional resonance were discussed in the literature when using an unusually large core structure; however, it can be observed more frequently under high excitation frequency, particularly with integrated magnetics. This dissertation discusses the effects of core loss on a PCB-based magnetics structure and presents solutions, including a case study on a 3-kW 400-to-48 V LLC prototype running at 1 MHz. Another challenge arises for magnetic integration when multiple magnetic components with different characteristics come together. For instance, in the case of a transformer and an inductor on the same PCB. The PCB transformer is designed with perfectly interleaved winding and low Ohmic loss. On the other hand, the inductor's winding lacks interleaving and suffers from a high proximity field. This makes the inductor prone to high eddy currents and eddy loss. This dissertation presents the concept of matrix inductors to solve such problems. A matrix of four resonant inductors is also designed to reduce the proximity effect between inductor windings and reduce inductor PCB winding loss. The matrix inductor provides a solution for high thermal stress in PCB-based inductors and reduces the inter-winding capacitance between inductor layers. Furthermore, this dissertation addresses the challenges associated with the high winding and core loss in the Integrated Transformer-Inductor (ITL). To overcome these challenges, we propose an improved winding design of the ITL by utilizing idle shielding layers for inductor integration within the matrix transformer. This method offers full printed circuit board (PCB) utilization, where all layers are consumed as winding, resulting in a significant reduction in the winding loss of the ITL. Moreover, we propose an improved core structure of the ITL that reduces the core loss by more than 50% compared to the conventional core structure. We demonstrate the effectiveness of our proposed concepts on a high-efficiency, high-power-density 3-kW 400-to-48-V LLC module. The proposed converter achieves a peak efficiency of 98.7% and a power density of 1500 W/in3. This dissertation solves the challenges in magnetic design in high-frequency DC-DC converters in offline power supplies and data centers. This includes the transformer and inductor of the LLC converter. With the academic contribution in this dissertation, Wide-bandgap devices WBG can be successfully utilized in high-frequency DC-DC converters with Mega-Hertz switching frequency to achieve high efficiency, high power density, and automated manufacturing. The cost will be reduced, and the performance will be improved significantly.
- Published
- 2023
47. Autonomous Vehicle Perception Quality Assessment
- Author
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Zhang, Ce, Mechanical Engineering, Eskandarian, Azim, Abaid, Nicole, Southward, Steve C., Asbeck, Alan Thomas, and Ahmadian, Mehdi
- Subjects
Deep Learning ,Computer Vision ,Neural Network ,Autonomous Vehicle ,Image Quality Assessment ,Point Cloud Quality Assessment - Abstract
In recent years, the rapid development of autonomous vehicles (AVs) has necessitated the need for high-quality perception systems. Perception is a fundamental requirement for AVs, with cameras and LiDARs being commonly used sensors for environmental understanding and localization. However, there is a research gap in assessing the quality of AVs perception systems. To address this gap, this dissertation proposes a novel paradigm for evaluating AVs perception quality by studying the perception quality of cameras and LiDARs sensors. Our proposed paradigm aims to provide a comprehensive assessment of the quality of perception systems used in AVs.To achieve our research goals, we first validate the concept of surrounding environmental complexity through subjective experiments that rate complexity scores. In this study, we propose a neural network to classify complexity. Subsequently, we study image-based perception quality assessment by using image saliency and 2D object detection algorithms to create an image-based quality index. We then develop a neural network model to regress the proposed quality index score. Furthermore, we extend our research to LiDAR-based point cloud quality assessment by using the image-based saliency map as guidance to generate a point cloud quality index score. We then develop a neural network model to regress the score. Finally, we validate the proposed perception quality index with a novel designed AVs perception algorithm. In conclusion, this dissertation makes a significant contribution to the field of AVs perception by proposing a new paradigm for assessing perception quality. Our research findings can be used to improve the overall performance and safety of AVs, which has significant implications for the transportation industry and society as a whole. Doctor of Philosophy This dissertation delves into the fundamentals of autonomous vehicles (AVs), which is perception, with the aim of developing a new paradigm for evaluating the quality of perception algorithms. AVs are the dream of humanity, and perception is the fundamental requirement for achieving their full potential. Our research proposes a new approach to assessing the quality of perception algorithms, which can have significant implications for the performance and safety of AVs. By studying the perception algorithm quality, we aim to identify areas for improvement, leading to better AV performance and enhancing user trust. Our findings highlight the importance of perception in the development of AVs and demonstrate the need for continuous evaluation and improvement of the perception algorithms used in AVs.
- Published
- 2023
48. PCB-Based Heterogeneous Integration of PFC/Inverter
- Author
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Wang, Shuo, Electrical Engineering, Lee, Fred C., Orlowski, Mariusz Kriysztof, Li, Qiang, Southward, Steve C., and Centeno, Virgilio A.
- Subjects
balance technique ,near field effect ,high frequency ,PCB winding-based inductor ,EMI ,Wide-bandgap devices ,PFC/inverter - Abstract
State-of-the-art silicon-based power supplies have reached a point of maturity in performance. Efficiency, power density, and cost are major trade-offs involved in further improvements. Most products are custom designed with significant non-recurrent engineering and manufacturing processes that are labor intensive. In particular, conventional magnetic components, including transformers and inductors, have largely remained the same for the past five decades. Those large and bulky magnetic components are major roadblocks toward an automated manufacturing process. In addition, there is no specific approach to reduce electromagnetic interference (EMI) in conventional practices. In certain cases, EMI filter design even requires a trial-and-error process. With recent advances in wide-bandgap (WBG) power semiconductor devices, namely, SiC and GaN, we have witnessed significant improvements in efficiency and power density, compared to their silicon counterparts. In a power factor correction (PFC) rectifier/inverter, the totem-pole configuration with critical conduction mode (CRM) operation to realize zero-voltage switching (ZVS) is deemed most desirable for a switching frequency 10 times higher than current practice. With a significantly higher operating frequency, the integration of inductors with embedded windings in the printed circuit board (PCB) is feasible. However, a PCB winding-based inductor has a fundamental limitation in terms of its power handling capability. The winding loss is proportional to the magnetomotive force (MMF), which is Ni. That is to say, with the number of layers (turns) and currents increased, winding loss is increased nonlinearly. Furthermore, for a large-size planar inductor, flux distribution is usually non-uniform, resulting in dramatically increased hysteresis loss and eddy loss. Thus, current designs are challenged by the capability to increase their power range. To address those issues, a modular building block approach is proposed in this dissertation. A planar PCB inductor is formed by an array of pillars that are integrated into one magnetic core, where each pillar handles roughly 750 W of power. The winding loss is reduced by limiting the number of turns for each pillar. The core loss is minimized with a proposed planar magnetic structure where rather uniformly distributed fluxes were observed in the plates. The proposed approach has a similar loss to a conventional litz wire-based design but features a higher power density and can be easily assembled in automation. A 3 kW high frequency PFC converter with 99% efficiency is demonstrated as an example. Furthermore, PCB-based designs up to 6 kW are provided. Another challenge in a WBG-based PFC/inverter is the high common-mode (CM) noises associated with the high dv/dt of the WBG devices. Symmetry and cancellation techniques are often employed to suppress CM noises in switching power converters. Meanwhile, shielding technique has been demonstrated to effectively suppress CM noises in an isolated converter with PCB-based transformer design. However, for non-isolated converters, such as PFC circuits, none of the techniques mentioned above are deemed applicable or justifiable. Recently, the balance technique has been demonstrated to effectively suppress CM noises up to a point where the parasitic ringing between the inductor and its winding capacitor is observed. This dissertation presents an improved balance technique in a PCB-based coupled inductor design that compensates for the detrimental effect of the interwinding capacitors. A CM noise model is established to simplify the convoluted couplings into a decoupled representation so as to illustrate the necessary conditions for realizing a balanced network. In the given 1 kW PFC example, CM noise suppression is effective in the frequency range of interest up to 30 MHz. The parasitic oscillation of inductors, known to be detrimental for CM noise reduction, is circumvented with the improved magnetic structure. By applying the balance technique to a PFC converter and the shielding technique to an LLC DC/DC converter, significant noise reductions were realized. This provides the opportunity to use a simple one-stage EMI filter to achieve the required EMI noise attenuation for a server power supply. This dissertation further offers an in-depth study on reducing the unwanted near-field couplings between the CM/DM inductors and DM filter capacitors, as well as unwanted self-parasitics such as the ESL of the DM capacitors. An exhaustive finite element analysis (FEA) and near field measurements are conducted to better understand the effect of frequency on the polarization of the near field due to the displacement current. The knowledge gained in this study enables one to minimize unwanted mutual coupling effects by means of physical placement of these filter components. Thus, for the first time, a single-stage EMI filter is demonstrated to meet the EMI standard in an off-line 1 kW, 12 V server power supply. With the academic contributions in this dissertation, a PCB winding-based inductor can be successfully applied to a high-frequency PFC/inverter to achieve high efficiency, high power density, automation in manufacturing, lower EMI, and lower cost. Suffice it to say, the proposed approach enables a paradigm shift in the designing and manufacturing of a PFC/inverter for the next generation of power supplies. Doctor of Philosophy State-of-the-art silicon device-based switching power supplies have reached a point of maturity in performance. Efficiency, power density, and cost are major trade-offs involved in performance improvements. Most products are custom designed, requiring significant non-recurrent engineering and labor-intensive manufacturing processes. In particular, conventional magnetic components, including transformers and inductors, have largely remained the same for the past five decades. Those large and bulky magnetic components are major roadblocks toward an automated manufacturing process. In addition, there is no specific approach to reduce electromagnetic interference (EMI) in conventional practices. In consequence, a large multi-stage EMI filter is usually adopted between the power converter and the grid to reduce the EMI noise. It generally occupies 1/4-1/3 of the total converter volume. In certain cases, EMI filter design even requires a trial-and-error process. Suffice it to say, EMI is still regarded as both science and art. With recent advances in wide-bandgap (WBG) power semiconductor devices, namely, SiC and GaN, we have witnessed significant improvements in efficiency and power density, compared to their silicon counterparts. With GaN devices, the switching frequency of a PFC converter is able to be increased by 10 times compared to the state-of-the-art design without compromising efficiency. With a significantly higher operating frequency, the integration of inductors with embedded windings in the printed circuit board (PCB) is feasible. However, the state-of-the-art PCB winding-based inductor has a fundamental limitation in power range. Its winding loss and core loss increase dramatically in high powers. To address this issue, a modular building block approach is proposed in this dissertation. A planar PCB inductor is formed by an array of pillars that are integrated into one magnetic core, where each pillar handles roughly 750 W of power. The winding loss is reduced by limiting the number of turns for each pillar. The core loss is minimized with a proposed planar magnetic structure where rather uniformly distributed fluxes have been observed in the magnetic core plates. A 3 kW high-frequency PFC converter with a 99% peak efficiency is demonstrated as an example. Furthermore, PCB-based designs up to 6 kW are provided. Another challenge in a WBG-based PFC/inverter is the high common-mode (CM) noises caused by the high switching speed of the WBG devices. Symmetry and cancellation techniques are often employed to suppress CM noises in switching power converters. Meanwhile, shielding technique has been demonstrated to effectively suppress CM noises in an isolated converter with PCB-based transformer. However, for non-isolated converters, such as PFC circuits, none of the techniques mentioned above are deemed applicable or justifiable. Recently, the balance technique has been demonstrated to effectively suppress CM noises up to several MHz. However, the CM noise reduction is not effective beyond that. This dissertation presents an improved balance technique in a PCB-based coupled inductor to circumvent the limits. In the given 1 kW PFC example, CM noise suppression is effective in the frequency range of interest up to 30 MHz. By applying the balance technique to a PFC converter and the shielding technique to an LLC DC/DC converter, significant noise reductions were realized. This provides the opportunity to use a simple one-stage EMI filter to achieve the required EMI noise attenuation for a server power supply. It features a smaller volume compared to a conventional multi-stage filter. To further enhance the filter's performance at high frequencies, an exhaustive finite element analysis and near field measurements are conducted to better understand the effect of frequency on the polarization of the near field due to the displacement current. The knowledge gained in this study enables one to minimize unwanted mutual coupling effects through physical placement of these filter components. Several approaches for improving the filter performance at high frequency are conducted. With these approaches applied, a single-stage filter is demonstrated in an off-line 1 kW, 12 V server power supply. Thus, for the first time, a single-stage EMI filter can be contemplated to meet the EMI standard in server power supplies. With the academic contributions in this dissertation, a PCB-winding based inductor can be successfully applied to a high-frequency PFC/inverter to achieve high efficiency, high power density, automation in manufacturing, lower EMI, and lower cost. Suffice it to say, the proposed approach in this work enables a paradigm shift in the designing and manufacturing of a PFC/inverter for the next generation of power supplies.
- Published
- 2023
49. PCB-Based Heterogeneous Integration of LLC Converters
- Author
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Gadelrab, Rimon Guirguis Said, Electrical Engineering, Lee, Fred C., Li, Qiang, Southward, Steve C., De La Reelopez, Jaime, and Ha, Dong S.
- Subjects
high-frequency ,DC/DC converter ,LLC converter ,transformer design ,three-phase LLC ,Wide-band-gap ,EMI ,magnetic integration - Abstract
Rapid expansion of the information technology (IT) sector, market size and consumer interest for off-line power supply continue to rise, particularly for computers, flat-panel TVs, servers, telecom, and datacenter applications. Normal components of an off-line power supply include an electromagnetic interference (EMI) filter, a power factor correction (PFC) circuit, and an isolated DC-DC converter. For off-line power supply, an isolated DC-DC converter offers isolation and output voltage adjustment. For an off-line power supply, it takes up significantly more room than the rest; thus, an isolated DC-DC converter is essential for enhancing the overall performance and lowering the total cost of an off-line power supply. In contrast, data center server power supplies are the most performance-driven, energy-efficient, and cost-aware of any industrial application power supply. The full extent of data centers' energy consumption is coming into focus. By 2030, it is anticipated that data centers will require around 30,000 TWh, or 7.6% of world power usage. In addition, with the rise of cloud computing and big data, the energy consumption of data centers is anticipated to continue rising rapidly in the near future. In data centers, isolated DC-DC converters are expected to supply even higher power levels without expanding their size and with much greater efficiency than the present standard, which makes their design even more challenging. LLC resonant converters are frequently utilized as DC-DC converters in off-line power supply and data centers because of their high efficiency and hold-up capabilities. LLC converters may reduce electromagnetic interference because the primary switches and secondary synchronous rectifiers (SRs) both feature zero-voltage-switching (ZVS) and zero-current-switching (ZCS) for the SRs. Almost every state-of-the-art off-line power supply uses LLC converters in their DC-DC transformations. However, LLC converters face three important challenges. First, the excessive core loss caused by the uneven flux distribution in planar magnetics, owing to the huge size and high-frequency operation of the core. These factors led to the observation of dimensional resonance within the core and an excessive amount of eddy current circulating within the core, which resulted in the generation of high eddy loss within the ferrite material. This was normally assumed to be negligible for small core sizes and lower frequencies. This dissertation proposes methods to help redistribute the flux in the core, particularly in the plates where the majority of core losses are concentrated, and to provide more paths for the flux to flow so that the plates' thickness can effectively be reduced by half and core losses, particularly eddy loss, are reduced significantly. Second, the majority of power supplies in the IT sector are needed to deliver high-current output, but the transformer is cumbersome and difficult to build because of its high conduction losses. In addition, establishing a modular solution that can be scaled up to greater power levels while attaining a superior performance relative to best practices is quite difficult. By increasing the switching frequency to several hundred kilohertz using wide-band-gap (WBG) transistors, printed circuit board (PCB) windings may include magnetics. This dissertation offers a modular and scalable matrix transformer structure and its design technique, allowing any number of elemental transformers to be integrated into a single magnetic core with significantly reduced winding loss and core loss. It has been shown that the ideal power limitations per transformer for PCB-based magnetics beat the typical litz wire design in all design areas, in addition to the unique advantages of PCB-magnetics, such as their low profile, high density, simplicity, and automated construction. Alternatively, shielding layers may be automatically put into the PCB windings between the main and secondary windings during the production process to reduce CM noise. A method of shielding is presented to reduce CM noise. The suggested transformer design and shielding method are used in the construction of a 3 kW 400V/48 V LLC converter, with a maximum efficiency of 99.06% and power density of 530W/in3. Thirdly, LLC converters with a matrix transformer encounter a hurdle for extending greater power, including the number of transformers needed and the magnetic size. In addition to the necessity of resonant inductors, which increase the complexity and size of the magnetic structure, there is a need for a resonant inductor. By interconnecting the three-phases in a certain manner, three-phase interleaved LLC converters may lower the circulating energy, but they have large and numerous magnetic components. In this dissertation, a new topology for three-phase LLC resonant converters is proposed. Three-phase systems have the advantage of flux cancellation, which may be used to further simplify the magnetic structure and decrease core loss. In addition, a study of the various three-phase topologies is offered, and a criterion for selecting the best suitable topology is shown. Compared to the single-phase LLC, the suggested topology has less winding loss and core loss. In addition, three-phase transformers have a lower volt-second rating, and smaller core sizes may be used to mitigate the impact of eddy loss in the ferrite material. In contrast, three-phase systems offer superior EMI performance, which is shown in the loss and size of the EMI filter, and much less output voltage ripple, which is reflected in the size of the output filter. Finally, several methods of integrating resonant inductors into transformer magnetics are presented in order to accomplish a simple, compact, and cost-effective magnetic architecture. By increasing the switching frequency to 500 kHz, all six transformers and six inductors may be achieved using four-layer PCB winding. To decrease CM noise, additional 2-layer shielding may be implemented. A 500 kHz, 6-8 kW, 400V/48V, three-phase LLC converter with the suggested magnetic structure achieves 99.1% maximum efficiency and a power density of 1000 W/in3. This dissertation addresses the issues of analysis, magnetic design, expansion to higher power levels, and electromagnetic interference (EMI) in high-frequency DC/DC converters used in off-line power supply and data centers. WBG devices may be effectively used to enable high-frequency DC/DC converters with a hundred kilohertz switching frequency to achieve high efficiency, high power density, simple yet high-performance, and automated manufacture. Costs will be minimized, and performance will be considerably enhanced. Doctor of Philosophy The IT industry, market size, and customer interest in off-line power supply continue to grow quickly, especially for computers, flat-panel TVs, servers, telecom, and datacenter applications. Off-line power supplies usually have a DC-DC converter, an EMI filter, and a PFC circuit. A DC-DC converter is needed for an off-line power supply. An isolated DC-DC converter makes an off-line power supply work better and cost less, even though it takes up more space than the rest. But power supplies for data center servers are the most performance-driven, energy-efficient, and cost-conscious industrial applications. It's becoming clear how much energy data centers use. By 2030, data centers will use 7.6% of the world's power, or 30,000 TWh. With the rise of cloud computing and big data, energy use in data centers is likely to go up by a lot. In data centers, isolated DC-DC converters are expected to have much more power without getting bigger and to be much more efficient than the current standard. This makes their design even harder. LLC resonant converters are often used as DC-DC converters in data centers and off-line power supplies because they are very efficient and easy to control. LLC converters may have less electromagnetic interference because both the primary switches and the secondary synchronous rectifiers (SRs) have zero-voltage-switching (ZVS) and zero-current-switching (ZCS). Almost every modern off-line power supply uses LLC converters for DC-DC stage. LLC converters have to deal with three big problems. Due to the large size of the core and the high frequency of operation, the uneven distribution of flux in planar magnetics causes too much core loss. This dissertation suggests ways to redistribute flux in the core, especially in the plates where most core losses are concentrated and provide more flux paths to reduce plate thickness by half and core losses, especially eddy loss. Second, most IT power supplies need to put out a lot of current, but transformers are bulky and hard to build because they lose a lot of current. It is hard to make a modular solution that can scale up to higher levels of power and perform better than best practices. With wide-band-gap (WBG) transistors, the switching frequency can be raised to several hundred kilohertz so that magnetics can be added to PCB windings. This dissertation describes a modular and scalable matrix transformer structure and design method that lets any number of elemental transformers be put into a single magnetic core with much less winding loss and core loss. PCB-based magnetics have a low profile, a high density, are easy to build, and can be built automatically. Their ideal power limits per transformer beat the typical litz wire design in every way. Shielding layers can be added automatically between the main and secondary PCB windings to cut down on CM noise. CM noise is lessened by shielding. The suggested transformer design and shielding method are used to build a 3 kW 400V/48 V LLC converter with a maximum efficiency of 99.06% and a power density of 530W/in3. Third, LLC converters with matrix transformers can't get more power without more transformers and a bigger magnetic size. Resonant inductors, which add to the size and complexity of a magnetic structure, are also needed. By connecting the three phases, three-phase interleaved LLC converters use less energy, but they have a lot of magnetic parts. In this paper, a three-phase LLC resonant converter topology is proposed. In three-phase systems, flux cancellation makes magnetic structures easier to understand and reduces core loss. There is also a study of three-phase topologies and a set of criteria for choosing one. Compared to the single-phase LLC, the topology cuts down on winding and core loss. Three-phase transformers have a lower volt-second rating, and ferrite material eddy loss can be reduced by making the core smaller. The size and loss of the EMI filter show that three-phase systems have less output voltage ripple and better EMI performance. Finally, several ways of putting resonant inductors into the magnetics of a transformer are shown to make a magnetic architecture that is simple, small, and cheap. At 500 kHz, all six transformers and all six inductors can be wound on a four-layer PCB. CM noise can be cut down with 2-layer shielding. With the suggested magnetic structure, a 500 kHz, 6-8 kW, 400V/48V, three-phase LLC converter can reach 99.1% maximum efficiency and 1000 W/in3. This dissertation presents analysis, magnetic design, expanding to higher power levels, and electromagnetic interference (EMI) in high-frequency DC/DC converters used in off-line power supplies and data centers. WBG devices can be used to make high-frequency DC/DC converters with a switching frequency of a few hundred kilohertz that are powerful, easy to use, and can be automated. Both cost and performance will get better.
- Published
- 2023
50. Theoretical Analysis and Design for the Series-Resonator Buck Converter
- Author
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Tu, Cong, Electrical Engineering, Ngo, Khai D., Southward, Steve C., Manteghi, Majid, De La Reelopez, Jaime, and Zhang, Yuhao
- Subjects
Multiphase converter ,Series-Resonator Buck (SRB) converter ,resonant inductor ,power delivery ,soft switching ,high ac flux ,resonant converter ,one-turn inductor ,data center ,48V ,series-capacitor buck (SCB) converter - Abstract
High step-down dc/dc converters are widely adopted in a variety of areas such as industrial, automotive, and telecommunication. The 48 V power delivery system becomes increasingly popular for powering high-current and low-voltage chips. The Series-Capacitor Buck (SCB) converter doubles the duty ratio and equalizes the current between the two phases. Hard switching has hindered efforts to reduce volume via increased switching frequency, although a monolithically integrated SCB converter has boosted current density. A Series-Resonator Buck (SRB) converter is realized by adding a resonant tank in series with the series capacitor Cs. All switches turn on at zero-voltage (ZVOn), and the low-side switches turn off at zero-current (ZCOff). The design of the SRB converter includes characterizing the design variables' impacts on the converter performances and designing low-loss resonant components as the series resonator. The Series-Resonator Buck converter belongs to the class of quasi-resonant converters. Its resonant frequency is higher than the switching frequency, and its waveforms are quasi-sinusoidal. This work develops a steady-state model of the SRB converter to calculate voltage gain, component peak voltages, and resonant inductor peak current. Each switching cycle is modeled based on the concept of generalized state-space averaging. The soft-switching condition of the high-side switches is derived. The ZVS condition depends on the normalized control variable and the load condition. The gain equation models the load-dependent characteristic and the peak gain boundary. The theoretical peak voltage gain of the SRB converter is smaller than the maximum gain of the SCB converter. A smaller normalized load condition results in a larger peak voltage gain of the SRB converter. The large-signal model of the SRB converter characterizes the low-frequency behavior of the low-pass filters with the series capacitor and the high-frequency behavior of the resonant elements. A design recommendation of t_off f_r
- Published
- 2023
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