Search

This paper addresses the complex constraints and multi-objective requirements faced in the operation process of the Cascade Canal System (CCS), and proposes the Multi-Objective Model Predictive Control (CCS-MOMPC) method that can simultaneously consider the gate control constraints and gate regulation frequency. The proposed method modifies the original predictive control objective function by incorporating a gate regulation penalty term, and directly constrains both the gate deadband and the gate regulation frequency. Furthermore, the multi-objective function is converted into a single-objective function using the weighted method, which is then solved employing the Particle Swarm Optimization (PSO) algorithm. The proposed method is applied in the last eight canal pools of the Middle Route Project of South-to-North Water Diversion (MRP-SNWD). The results show that under the experimental conditions, compared with the traditional method, the proposed method can reduce the maximum water level deviation at control point from 0.15 m to 0.10 m, and decrease the total gate control frequency by 37.1%. In the case of unknown secondary disturbance, the proposed method can reduce the final action time of the gate by 77.5%. The results of this paper show that the improved control method can significantly improve the water level control accuracy and reduce the frequency of gate regulation. • An improved predictive control model for cascade canal systems has been proposed. • The gate control penalty is introduced and the gate deadband is directly constrained. • An intelligent optimization algorithm is used to solve the model. • Proposed model performs better in control accuracy and control frequency. [ABSTRACT FROM AUTHOR]

Electrical power conversions are common in a large variety of engineering applications. With reference to AC/DC and DC/AC power conversions, a strong research interest resides in multilevel converters, thanks to the many advantages they provide over standard two-level converters. In this paper, a power-oriented model of single-phase Modular Multilevel Converters (MMCs) is first provided, followed by a detailed harmonic analysis. The model is given in the form of a Power Oriented Graphs block scheme that can be directly implemented in the Matlab/Simulink environment. The performed harmonic analysis gives a deep and exact understanding of the different terms affecting the evolution of the voltage trajectories in the upper and lower arms of the converter. Next, a new model-based cascade control architecture for MMCs is proposed. Combined with the real-time calculation of the ideal average capacitor voltages reference, the proposed control architecture allows to properly track the desired load current while minimizing the tracking error and the harmonic content in the generated load current itself. [Display omitted] • Power-Oriented Modeling of Modular Multilevel Converters. • Full Harmonic Analysis of Modular Multilevel Converters. • Calculation of the Ideal Voltage Tracking Reference for the Capacitors Voltages. • Model-Based Cascade Control of Modular Multilevel Converters. • Load Current Tracking Error and Harmonic Content Reduction. [ABSTRACT FROM AUTHOR]

A comprehensive autolanding design for a representative model of a twin-engined commercial aircraft is presented in this paper. To facilitate the design task and minimize control law switching, a cascaded control structure is selected which resembles integrator chains. Classical loopshaping and robust control techniques are used to design the individual control loops. The emphasis is on providing a complete and comprehensive qualitative design strategy. The control system’s ability to safely land the aircraft despite strong crosswind in a variety of possible scenarios is demonstrated in an industry-grade verification campaign. Nonlinear Monte Carlo simulations of the airliner model are used to assess the risk of unsafe landing conditions and provide insight into the performance characteristics and limitations of the proposed control system. [ABSTRACT FROM AUTHOR]

This paper presents a robust parameterization method for the well-established cascaded control structure of feed drives and applies it to both proportional (P) and sliding mode (SMC) position controllers. The controller parameterization is based on the structured μ -synthesis technique, which allows direct robust tuning of fixed control structures with respect to the conflicting goals of tracking and disturbance rejection over different frequency ranges. The proposed strategy explicitly takes into account both matched and unmatched uncertainties and considers the dynamics of the Kalman filter and feedforward control, ensuring robust stability and performance based on a simple low-order plant model with only two parameters. To ensure industrial applicability, the parameterization problem is formulated in a signal-based manner and the tuning complexity is limited to the selection of only two hyperparameters by directly extracting the information from measurements. Extensive experimental results are performed on an industrial feed drive to validate the performance and robustness of the proposed approach. For example, compared to P-PI cascade control with feedforward and nominally tuned SMC position control, the robustly parameterized SMC position controller reduces the root-mean-square tracking error by 79% and 61% during high-speed milling experiment. Even under variation of model parameters by 20%, the robustly parameterized SMC still cuts the tracking error by more than 44% in the comparison. • Robust control parameterization with stability guarantee based on low-order model. • Trade-off strategies considering uncertainties by selection of two hyperparameters. • Maintained dynamic accuracy despite variation of model parameters by ± 20 %. • Tracking error is 79% less than P-PI cascade control during high-speed milling. [ABSTRACT FROM AUTHOR]

Control performance assessment techniques are widely studied and many performance assessment indices have been proposed. In this paper, a control performance assessment technique for multi-loop control systems is presented based on the decision fusion strategy. Since decisions based on individual indices can lead to erroneous results, decision fusion of different indices can improve the assessment accuracy, especially in multi-loop control systems in the presence of loop interactions. Performance assessment indices are individually evaluated and decisions based on these indices are fused. The results of simulation and practical implementation on series cascade control structures illustrate the effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

This work presents an adaptive image-based visual servoing approach for uncertain robot manipulators using an eye-to-hand camera configuration, which does not require any calibration procedure and image velocity measurement. A monocular camera provides visual feedback for the robot's joint control, allowing successful tracking of the translational trajectory, prescribed in image space, for a given target object attached to the robot end-effector. As our contribution, an indirect adaptive control approach is proposed to deal with the uncertain parameters of the camera–robot system and any camera misalignment concerning the robot frame. The indirect adaptive visual servoing approach is then combined with a direct adaptive motion controller using a cascade control framework to consider the uncertain robot dynamics in our stand-alone robot vision system. Lastly, an adaptive model-based state observer is designed to avoid the need for measuring the image feature velocity in the interconnected control loops. The Lyapunov stability theory and the passivity paradigm are synergized to demonstrate the stability properties of the overall closed-loop system. Experimental results, obtained with a 4-DoF robot manipulator carrying out translational trajectory tracking tasks using a commercial webcam, illustrate the performance and effectiveness of the proposed adaptive control methodology. [ABSTRACT FROM AUTHOR]

This paper presents a framework for the multivariable robust control of perfusion animal cell cultures. It consists of a cascade control structure and an estimation algorithm, which provides the unmeasurable variables needed in the design of the control law, and ensures the regulation of the cell and glucose concentrations at imposed levels by manipulating the bleed and the dilution rates. The cascade control structure uses a feedback linearizing controller in the inner loop and linear (PI) controllers in the outer loops, and requires the measurement of the cell concentration and the glucose concentration in the bioreactor. Two approaches are provided: the first one assumes the availability of an approximate model of the process kinetics and uses an extended Kalman filter (EKF) to estimate the system states; the second approach does not require the prior knowledge of the process kinetics. These are estimated from the available measurements using sliding mode observers (SMO). A receding horizon optimization algorithm is employed to (periodically) tune the gains of the outer loop controllers. The proposed framework is easy to implement and tune, and may be applied to a general class of perfusion cell culture systems. Its effectiveness and robustness are illustrated by means of simulation results. [ABSTRACT FROM AUTHOR]

Abstract: The problem of controlling single-phase shunt active power filters is addressed in presence of nonlinear loads. The control objective is twofold: (i) compensation of harmonic and reactive currents absorbed by the nonlinear load, this objective is referred to as power factor correction (PFC); (ii) regulation of the inverter output capacitor voltage. A two-loop cascade control strategy is developed that includes an inner-loop designed, using the Lyapunov design approach, to cope with the compensation issue and an outer-loop designed to regulate the capacitor voltage. The controller performances are formally analysed using system averaging theory. The theoretical results are illustrated by simulation. [Copyright &y& Elsevier]

Abstract: This article presents the development to reliably seal copper canisters containing the Swedish nuclear waste, using friction stir welding. To avoid defects and welding tool fractures, it is important to control the welding temperature within a span of 790–910°C. A cascade controller is used to efficiently suppress fast power input disturbances reducing their impact on the temperature. The controller is tuned using a recently presented method for robust PID control. Results show that the controller keeps the temperature within during the 40min long joint line sequences. Apart from the cascaded control structure, good process knowledge and control strategies adapted to different weld sequences have contributed to the successful results. [Copyright &y& Elsevier]

Abstract: This paper details the design and implementation of a robust controller that stabilizes an unmanned motorcycle. A linearized model and Quantitative Feedback Theory (QFT) are used to derive a low order cascaded controller that stabilizes the motorcycle for velocities ranging from 2.5 to 6.5m/s. Stabilization is achieved by measuring roll angle and roll rate and controlling the steering torque. The approach is validated through simulations and experiments with a 50cc scooter whose throttle, brakes, and reference roll angle are radio-controlled. [Copyright &y& Elsevier]

Abstract: A cascade-control algorithm based on a sliding mode in the legspace is proposed to realize the trajectory tracking control of a hydraulically driven six degrees of freedom (6-DOF) parallel robot manipulator. The cascade controller, which consists of an inner loop and an outer loop, is applied to separate the hydraulic dynamics from the mechanical part so that the designed controller takes into account not only the mechanical dynamics but also the hydraulic dynamics of the manipulator. The experimental results investigate the effectiveness of the proposed approaches and demonstrate the satisfactory position tracking behaviour of the parallel manipulator for the proposed cascade controller based on a sliding mode. [Copyright &y& Elsevier]

This article is concerned with a classical problem of how to design an inferential control system for enhancing the performance of distillation composition control. In this article, a new inferential control, termed “predictive inferential control,” is proposed. In the predictive inferential control system, future compositions predicted from on-line measured process variables are controlled instead of the estimates of current compositions. The key concept of the predictive inferential control is to realize feedback control with a feedforward effect by the use of the inherent nature of a distillation column. The detailed dynamic simulation results show that the proposed predictive inferential control scheme integrated with cascade control works considerably better than other control schemes. Furthermore, the improvement of the control performance through iterative modeling or control-relevant identification is also demonstrated. [Copyright &y& Elsevier]

A real-time HVAC system is proposed which implements real-time control of thermal environment for virtual reality. It consists of a pair of hot and cold air loops that serve as thermal reservoirs, and a mixing box to mix the hot and cold air streams supplied from the loops. Their flow rates are controlled to meet the set temperature and flow rate. Cascade control algorithm and gain scheduling was applied to the system. Test results showed that the controller approaches a set temperature and flow rate within 2 or 3 s, thereby satisfying the requirement of implementing real-time thermal environment. [Copyright &y& Elsevier]

In this paper, a modified uncertainty and disturbance estimator (MUDE)-based attitude controller for quadrotors based on a high-accuracy actuator dynamic model is proposed. The actuator dynamics are approximated by a first-order plus time-delay dynamic model, and both static and dynamic models of the actuator are identified using a motor test platform. The actuator model is further exploited as a virtual sensor to provide the actuator-generated torque estimates for the controller. By these estimates, an MUDE is constructed to compensate for not only the uncertainties and disturbances in attitude dynamics but also the time delay and disturbances in actuator dynamics. The systematic consideration of actuator disturbance rejection significantly improves the overall attitude tracking performance during maneuvers, which is clearly distinguished from other existing solutions assuming ideal actuators. Furthermore, the stability and performance analysis of the closed-loop system is presented, showing that the estimation error and the closed-loop tracking error can be reduced by tuning a single parameter. Finally, the proposed control, as well as classic uncertainty and disturbance estimator-based control and cascade PID controller, are implemented and compared on a real quadrotor platform. The experimental results show the effectiveness and advantage of the proposed control method with respect to signal tracking and disturbance rejection. [ABSTRACT FROM AUTHOR]

This paper is devoted to the development of the magnetic plasma control system for the Globus-M/M2 spherical tokamak (ST) when minor disruptions occur. The novelty of the research is the design of robust cascade multivariable control systems for time-varying plasma models in the presence of nonlinear thyristor current inverters as actuators for plasma position control. A new architecture of coordinated control of plasma position and shape is proposed. Quantitative Feedback Theory is used for the synthesis of robust Single-Input Single-Output (SISO) controllers for plasma position and PF-currents. Multiple-Input Multiple-Output (MIMO) H ∞ control is applied to control the plasma shape. The simulation results of the gaps-based MIMO plasma shape control system with the plasma equilibrium reconstruction code in the feedback are shown. The robust stability of the control system is estimated. [ABSTRACT FROM AUTHOR]

It is a challenge to achieve fast altitude control for hypersonic flight due to the inherently insufficient sensitivity of air density to the near-space altitudes. A dominant open-loop feedforward term and a minor altitude error correction term are combined together to obtain the elevation angle command in this paper. A cascade control strategy is used to calculate the elevation command while ensuring the attitude stability. Moreover, an extended state observer is employed to achieve precise and robust attitude control simultaneously, and a stability margin tester is used to tune the controller explicitly. Extensive simulations are conducted to validate the effectiveness, robustness and measurement noise sensitivity of the proposed method. • An efficient cascade altitude control is presented for hypersonic vehicles. • A feedforward term, which triggers no mathematical singularity, plays a crucial role. • An extended state observer based attitude control is provided with explicit tuning. • Extensive simulations demonstrate the effectiveness and superiority of the proposed method. [ABSTRACT FROM AUTHOR]

Since the characteristics of the industrial heat exchange system (HES) are drastically affected by variations of the steam pressure, ambient temperature and water quality, it is difficult for the classical cascade PI control system to meet the desirable control objectives. Therefore, in this paper, a deterministic linear model with unmodeled dynamics is used to describe the dynamic characteristics of the HES. It should be noted that the unmodeled dynamics at the previously sampled instant can be calculated using actual measurements and that the tracking error, which includes effects of the rate of changes of unmodeled dynamics on the controlled model, can be accurately determined. An additional compensating signal is obtained with the feedforward control together with a one-step optimal control law. Consequently, the cascade PI control strategy with the signal compensation is established. The simulation and industrial application show that the proposed method can effectively improve the performance of the cascade PI control system, especially when the unmodeled dynamics is subjected to unknown variations. [ABSTRACT FROM AUTHOR]