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© 2023 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting /republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works This article presents two algorithms to control the speed of doubly-fed induction motors. The controllers are designed using the complex-valued sliding mode methodology to track either the rotor or the stator current. An outer loop controls the mechanical speed. The control schemes are validated experimentally and compared in a laboratory setup.

Cascading blackouts are the oldest major unsolved technical problem in power system engineering, highly visible since the Northeast Blackout of 1965 in North America. In this article, we review some cascading blackouts and past work on the problem. New metrics measure network stress to identify and reduce the risk of cascading failures.

This article considers the control problem for a motor/generator set, where a prime mover drives a generator and the electrical power produced drives a motor. Both the generator and the motor are assumed to be doubly fed induction machines with direct ac connection between their stators. The rotors are controlled by three-phase converters, so that operation is possible with motor and generator speeds that are different from each other, and not synchronized with the electrical frequency of the stator voltages. The strong couplings between the two machines motivate the design of an integrated controller. This article proposes a general framework for such a design based on a joint model of the two machines. A specific method is also developed for the control of the stator voltages and the motor velocity. In its simplest form, the proposed algorithm does not rely on current sensors. A current command option is also developed that ensures closer tracking and limiting of the rotor currents. The algorithm is relatively simple and all its parameters can be computed based on the estimates of the machine parameters. Practical implementation and testing can be performed rapidly. Experiments performed on a small-scale laboratory testbed show very good tracking performance of a speed reference profile.

This paper presents a method to control the speed of doubly fed induction motors. The motivation lies in the possible use of such motors for hybrid electric propulsion. The stator of the motor is assumed to be supplied by three-phase voltages with frequency and magnitude that may vary. The rotor is supplied by a bidirectional converter. Two versions of the algorithm are presented. The first version does not rely on inner current loops, but instead commands directly the voltages applied to the rotor. These voltages are computed using an open-loop controller for torque and for stator reactive power, which is augmented to follow a speed reference profile. The second version uses stator and rotor current measurements to ensure tracking and limiting of the rotor currents. All the parameters of the control systems can be computed based on estimates of the machine parameters together with a desired time constant of the speed response. The alignment of an incremental encoder is integrated in the initialization of the algorithm. Practical implementation and testing are performed easily and rapidly. Experiments performed on a small-scale laboratory testbed show very good tracking performance of a speed profile in tests involving one motor, as well as two motors on a single three-phase supply. Improved current limiting is observed with the version incorporating current feedback.

Routh's treatise [1] was a landmark in the analysis of the stability of dynamic systems and became a core foundation of control theory. The remarkable simplicity of the result was in stark contrast to the challenge of the proof. Many researchers devoted much effort to extend the result to singular cases, with some of the earlier techniques shown to be inadequate [2]. Together with the extensions to singular cases, shorter proofs were also proposed. The proof of [3] is noteworthy, which followed the root locus arguments of [4]. A key feature of the proof is a continuity argument used in an earlier derivation [5]. In [6], the more conventional approach using Cauchy?s principle of the argument is followed. A relatively simple proof is proposed, considering the extension to complex polynomials and singular cases.

This paper considers a hybrid electric propulsion architecture where most of the electric power is transmitted from the generator to the motors without conversion. Doubly fed induction machines are...

A multiple-reference complex-based controller is proposed for three-phase power converters feeding nonlinear and unbalanced loads. The control scheme incorporates a stable multiple-complex coefficient filter with bandwidths that are set arbitrarily and independently for every harmonic under consideration. The multiple-reference complex-based control scheme is applied to an uninterruptible power supply system with a voltage source converter. Each harmonic is controlled using a standard complex proportional-resonant controller that is designed for stability and robustness using the Nyquist criterion. Similar stability and robustness properties follow for the overall system due to the frequency-domain properties of the filter and of the controllers. The proposed methodology is validated in simulation and experimental tests.

The paper considers the problem of sub-synchronous resonances (SSR) in doubly fed induction generators connected to the grid through series-compensated lines. The existence of oscillations is observed on a laboratory test-bed in various conditions, with instabilities developing in the worst-case scenario. Despite the limitations of a small-scale test-bed, the ability to investigate problems and solutions in ways that would not be possible on a full-scale system is very valuable. In particular, the paper demonstrates the significant effect of the choice of dq reference frame on the severity of SSR. Stator-aligned algorithms are found to be significantly more resonant than grid-oriented algorithms, as evidenced in experiments as well as using an analysis method proposed in the paper. From this observation, an algorithm is proposed to emulate a grid-alignment using stator voltages and currents, but without measurements of the grid and series-capacitor voltages. Two control laws are then presented to regulate the active and reactive powers generated, resulting in well-damped transient responses. SSR oscillations are found to be eliminated in experime, as well as simulations of a full-scale system and using a frequency response analysis of the closed-loop system. The effectiveness of the proposed control schemes is verified through experiments for different compensation levels and varying speeds. Within the assumptions made in the design, the proposed controllers are global.

The paper presents three algorithms to synthesize a dynamic controller for a doubly-fed induction generator (DFIG). In each case, the pole placement approach is used to compute the parameters of a feedback controller that regulates the active and reactive powers produced using the rotor voltages. Due to the special structure of the DFIG's model, the analysis and design of the feedback control loop are simplified by transforming its representation into an equivalent system with complex coefficients and half the number of states. This approach yields analytic solutions of the problem with remarkable simplicity. The complex framework facilitates the direct placement of the DFIG system poles in the left half-plane, which ensures stability and performance of the closed-loop system. Additionally, this framework can be used to evaluate the robustness properties of the closed-loop systems. The ability of the synthesized controllers to provide a desirable dynamic and steady-state response is investigated through experiments on a laboratory testbed.

A new controller for a grid-connected inverter with an LCL filter is proposed in this paper. The system is described by its complex representation, and the controller is designed using the complex root locus method. The complex representation allows a considerable reduction in the order of the system, simplifying the design task and making it possible to use advanced techniques, such as the complex root locus. The new complex controller adds an extra degree of freedom that makes it possible to move the poles of the systems and to improve the stability and speed of response compared with the conventional controls. This paper includes a detailed discussion of the effect of the gains of the controller on the root locus. The proposal is validated with simulation and experimental results.

International audience; This paper presents a new state-space model (SSM) to represent the four types of currents flowing through a Modular Multilevel Converter (MMC). In line with the converter topology, the model itself is modular. In other words, its configuration adapts itself to the number of AC phases, to the active or passive nature of the AC-side grid, to the connection between the AC and DC neutral points, and to the number of submodules. The model describes the influence of the MMC arm voltages on the currents using an average behavior of the submodules. Simulations performed using a software dedicated to electrical engineering systems demonstrate the value and the accuracy of the proposed model.

This paper presents a modeling of the modular multilevel converter (MMC) which is modular, inline with its topology. The modeling of the MMC is made of two parts, a low-level part which deals with the description of the sub-modules (SM) connected to the arms of the MMC and a high-level part which represents the behavior of the MMC with its interfaces, it is this high-level part which is studied here. Two state-space models are developed, they describe the influence of the arm voltages of the MMC on the different types of currents flowing within the converter. These models are scalable to the number of phases and to the number of sub-modules composing the MMC. The first model is derived in the stationnary m-phase reference frame while a reduction of order is performed to obtain the second one which is developed in the rotating frame, making the order of the latter independent of the number of phases and the number of sub-modules. Simulations show the value of these models in terms of simulation time and accuracy., Cet article présente une modélisation du convertisseur modulaire multiniveaux (MMC) qui se veut modulaire à l'image de sa topologie. La modélisation du MMC est composée de deux parties, une partie bas-niveau qui traite de la description des sous-modules (SM) qui composent le MMC et une partie haut-niveau qui représente le comportement du MMC avec ses interfaces, c'est cette partie haut-niveau qui est traitée ici. Deux modèles dans l'espace d'état sont développés, ils décrivent l'influence des tensions propres aux bras du MMC sur les différents types de courants qui le traversent. Ces modèles sont capables de s'adapter au nombre de phases et au nombre de sous-modules composant le MMC. Le premier modèle est réalisé dans le repère fixe m-phasé tandis qu'une réduction d'ordre est opérée pour obtenir le second qui est rattaché au repère tournant, rendant alors l'ordre de ce dernier indépendant du nombre de phases et du nombre de sous-modules. Des simulations mettent en évidence l'intérêt de ces modèles sur le plan du temps de simulation et de la précision obtenue.

The improper use of artificial light causing skyglow is detrimental to many types of wildlife and can potentially cause irregular human sleeping patterns. Studies have been performed to analyze light pollution on a global scale. However, light pollution data on a local scale is not of ten available and the effects at local scale have rarely been studied. Herein, a new custom-designed autonomous light assessment drone (ALAD) is described for evaluating light pollution at local scale. The ALAD is designed and equipped with a sky quality meter (SQM) to measure skyglow and a low-cost illuminance sensor to measure light from artificial sources. Outdoor field tests are performed at a remote site in central Utah and the measured results are validated against data from lightpollution-map.info. The SQM measurements are in agreement with the estimates from the light pollution map, and the initial results demonstrate feasibility of the ALAD for local-scale skyglow assessment.

© 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works In this work, a complex-valued controller for a three-phase VSC with an LC output filter is proposed. The system is first transformed into its complex representation with the consequent order reduction and simpler analysis. The proposed complex controller places all the poles at desirable locations in the complex plane. Unlike classical controllers with an inner current-control loop and outer voltage-control loop, the proposed controller considers the complete dynamics of the system, thus ensuring the closed-loop stability. Furthermore, the complex representation facilitates the pole placement in the complex plane compared to the real domain. The performance of the proposed controller is validated through simulations and experiments.

This brief proposes an optimization formulation of the control problem for power electronic converters. A benefit of the approach is a systematic method for the control of high-switch-count static converters. In the case of the three-phase, four-leg, two-level inverter, the framework provides a characterization of all the possible solutions that yield a maximal extension of the inverter linearity range. The method makes it possible to recover well-known modulation strategies as well as to discover some new ones having different properties and distinct advantages. The characteristics resulting from different design choices are evaluated in simulations, with consideration being given to the linearity range, total harmonic distortion, and switching losses. Key principles of extension of the proposed method to multilevel, multileg converters are given, as well as motivations for a field-programmable gate array-based hardware implementation enabling real-time pulsewidth modulation control.

An elegant way to exploit redundancies available in multilevel converters is through a constrained optimization formulation. An interesting connection can be made with the so-called control allocation problems defined in over-actuated constrained systems. Redundancies and constraints are taken into account to achieve the best performance. In this paper, we introduce the first result of an investigation of control allocation methods for multilevel conversion. The method is dedicated to the flying-capacitor inverter with focus on the active balancing of capacitor voltages to ensure admissible blocking voltages for the switches. A linear program is formulated and solved by using the well-established simplex algorithm. Fast variations of the DC-bus voltage were applied in simulations. Disturbances are well rejected, resulting in an increased bandwidth and a safe switching operation for the semiconductors.

The paper proposes an optimization formulation of the control problem for modular multilevel converter (MMC). The main control stage computes arm voltages on average over a fixed switching period by minimizing control errors in order to satisfy as best as possible the desired references of input, circulating and output currents, while taking into account arm voltage limits. Then, mean-values of required arm voltages are achieved by phase shift pulse-width modulation (PSPWM) by computing duty cycles for each submodule while taking into account the issue of active balancing of the capacitor voltages in a secondary control stage. The proposed optimization problems are solved by using a numerical method based on the simplex algorithm and simulation results are shown in order to support the validity of the approach.

International audience; This paper presents a control algorithm for the parallel interconnection of heterogeneous power converters. A single resistive load is assumed to be fed by an arbitrary number of buck converters via a common DC bus. The approach is based on control allocation theory and a constrained quadratic optimization algorithm. The strategy achieves a fast voltage response with an optimal current distribution among the converters, while taking into account the current limits, the dynamic response, and the efficiency of the individual converters. An interesting by-product of the approach is the ability to put converters in and out of service through trivial adjustments of the code. The benefits of the approach are assessed through simulations and an experimental evaluation.

Une maniere elegante d'exploiter efficacement les redondances de commande disponibles pour les convertisseurs statiques multi-niveaux est de formuler des problemes d'optimisation contraints. Ces problemes sont similaires aux problemes dits d'allocation de commandes rencontres pour les systemes mecaniques sur-actionnes. Les redondances et les contraintes sont prises en compte pour obtenir les meilleures performances. Dans ce papier, nous presentons un des premiers resultats de l'etude de methodes de commande par allocation pour la conversion statique multi-niveaux. Nous proposons une nouvelle methode pour l'onduleur a condensateurs flottants avec une attention particuliere portee sur l'equilibrage actif des tensions des condensateurs afin de maintenir des tensions de commutation admissibles pour les interrupteurs. Nous formulons un probleme d'optimisation lineaire dont la resolution repose sur le celebre algorithme du simplexe. En simulation, nous faisons subir de fortes variations de la tension continue d'entree. Grâce a notre methode, ces perturbations sont rapidement rejetees, garantissant une meilleure securite des interrupteurs de puissance et une bande passante elevee.

Advances in sensors and avionics computation power suggest real-time structural load measurements could be used in flight control systems for improved safety and performance. A conventional transport flight control system determines the moments necessary to meet the pilot’s command while rejecting disturbances and maintaining stability of the aircraft. Control allocation is the problem of converting these desired moments into control effector commands. In this paper, a framework is proposed to incorporate real-time structural load feedback and structural load constraints in the control allocator. Constrained optimal control allocation can be used to achieve desired moments without exceeding specified limits on monitored load points. Furthermore, certain criteria can be minimized, such as loads on certain parts of the aircraft. Flight safety issues can be addressed by using system health monitoring information to change control allocation constraints during flight. The framework to incorporate structural l...

The Special Issue presents results of current research on adaptive methods designed for periodic signals with unknown frequency. The first group of papers presents new methods for parameter estimation, while the second group focuses on practical applications involving active noise and vibration control problems. These papers are compiled in a special virtual issue of the journal at the journal homepage. To access all of the papers please follow the following link http://onlinelibrary.wiley.com/journal/10.1002/ISSN1099-1115/homepage/virtual_issue_-_recent_advances_in_adaptive_methods_for_frequency_estimation_wit.htm. Copyright © 2016 John Wiley & Sons, Ltd.

The Convergent Aeronautics Solutions (CAS) High Voltage-Hybrid Electric Propulsion (HVHEP) task was formulated to support the move into future hybrid-electric aircraft. The goal of this project is to develop a new AC power architecture to support the needs of higher efficiency and lower emissions. This proposed architecture will adopt the use of the doubly-fed induction machine (DFIM) for propulsor drive motor application.The Convergent Aeronautics Solutions (CAS) High Voltage-Hybrid Electric Propulsion (HVHEP) task was formulated to support the move into future hybrid-electric aircraft. The goal of this project is to develop a new AC power architecture to support the needs of higher efficiency and lower emissions. This proposed architecture will adopt the use of the doubly-fed induction machine (DFIM) for propulsor drive motor application. DFIMs are attractive for several reasons, including but not limited to the ability to self-start, ability to operate sub- and super-synchronously, and requiring only fractionally rated power converters on a per-unit basis depending on the required range of operation. The focus of this paper is based specifically on the presentation and analysis of a novel strategy which allows for independent operation of each of the aforementioned doubly-fed induction motors. This strategy includes synchronization, soft-start, and closed loop speed control of each motor as a means of controlling output thrust; be it concurrently or differentially. The demonstration of this strategy has recently been proven out on a low power test bed using fractional horsepower machines. Simulation and hardware test results are presented in the paper.

In this paper, we evaluate the usefulness of metrics that assess susceptibility to cascading blackouts. The metrics are computed using a matrix of Line Outage Distribution Factors (LODF, or DFAX matrix). The metrics are compared for several base cases with different load levels of the Western Interconnection (WI). A case corresponding to the September 8, 2011 pre-blackout state is used to compute these metrics and relate them to the origin of the cascading blackout. The correlation between the proposed metrics is determined to check redundancy. The analysis is also used to find vulnerable and critical hot spots in the power system.

This paper develops a systematic comparison of two nonlinear models of induction machines in magnetic saturation using stator and rotor currents as state variables. One of the models accounts for dynamic cross-saturation effects, whereas the other neglects them. Analytic derivations yield an explicit description of the difference between the models showing that differences can only be observed through transient responses in the saturated region. To refine the comparison, and exclude conditions in the linear magnetic region, the dynamics of self-excited induction generators around stable operating points is analyzed. Unexpected and interesting features of the models are revealed through their linearization in the reference frame aligned with the stator voltage vector, followed by computation of the transfer functions from perturbations to state deviations. The analysis predicts a slower exponential convergence of the simplified model compared to the full model, despite very close responses in the initial period. The comparison is validated via thorough experiments and simulations. This paper provides experimental evidence of the higher accuracy of the full model for transients deep into the saturated region. For realistic operating conditions, the difference is found to be rather small, and often comparable to the steady-state error caused by inaccuracies in the parameters.

Spontaneous self-excitation in induction generators is a fascinating phenomenon triggered by the instability of a zero equilibrium state. Prediction of this condition for various values of free parameters requires many computations of the eigenvalues of a 6 × 6 matrix over a large space. The technical note uses a novel approach to stability using a transformation of the state-space system and an extension of the Hurwitz test to polynomials with complex coefficients. The analytic formulas that are obtained give the values of the minimum load resistance, the range of capacitor values, and the range of speeds for which spontaneous self-excitation appears. The technical note concludes with an illustration of the results on an example.

© 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. A large class of three-phase electrical power systems possess symmetry conditions that make it possible to describe their behavior using single-input single-output transfer functions with complex coefficients. In such cases, an extended root locus method can be used to design control laws, even though the actual systems are multi-input multi-output. In this paper, the symmetric conditions for a large class of power systems are analyzed. Then, the root locus method is revisited for systems with complex coeffcients and used for the analysis and control design of power systems. To demonstrate the benefits of the approach, this paper includes two examples: 1) a doubly fed induction machine and 2) a three-phase LCL inverter.

International audience; In this paper, a new carrier-based pulse-width modulation (PWM) technique for a voltage source inverter (VSI) is presented. The new modulation law is obtained using a particular configuration of a control allocation technique based on a per-switching-state formulation of the 4-leg 2-level inverter. The resulting modulation law is equivalent to the injection of the opposite of the median reference voltage as a zero-sequence voltage. This particular solution produces a smooth transition from a continuous modulation mode at low modulation depth to a dis-continuous modulation mode at high modulation depth. This hybrid solution makes it possible to focus on the THD for low output voltages and reduce losses for higher voltages.

This paper investigates the control of power generation using two-phase squirrel-cage induction machines, where the load is connected to one stator winding and the load voltage is controlled through the other winding. The concept can be applied to three-phase machines as well. A state-space model of the machine is used to identify suitable operating regions. Then, two types of control algorithms are proposed: The first type regulates the frequency and the magnitude of the generated voltage and is suitable for stand-alone operation. The second type also regulates the phase of the voltages, enabling grid synchronization. Experimental results are presented for each of the control algorithms. The closed-loop systems are found able to track the desired reference and to reject disturbances caused by significant changes in load and speed.

The paper presents a new procedure to identify at the same time the electrical parameters of a permanent magnet stepper motor (PMSM) and the initial offset of an incremental encoder. The model considers effects due to the permanent magnet and to variable reluctance, and the resulting theory is applicable to cases where both or only one of these terms is present. The standard DQ model of PMSM's assumes that the permanent magnet is lined up with a winding when the position is zero. When an incremental encoder is used, an initialization procedure is required to zero the initial offset. In contrast, this paper computes a transformed model that accounts for the initial offset. then develops a least-squares identification algorithm that estimates the machine's electrical parameters together with the offset angle. Experiments show that the estimation procedure and a closed-control method using the estimated offset perform similarly compared to when the offset is reset to zero using an initilization procedure.

The paper proposes an algorithm for the rejection of periodic disturbances of unknown frequency. The frequencies of the components of the disturbance are estimated using an orthogonal signals generator based on second-order generalized integrators. A novel feature of the algorithm is that internal signals of the frequency estimator are combined linearly to produce the control signal, resulting in a very simple algorithm. For a sinusoidal disturbance, the entire scheme is governed by a single adaptive parameter. It is shown that, within the assumptions of an averaging analysis, the adaptive system is globally stable and completely rejects the disturbance, even in the presence of plant uncertainty. Bounds on the uncertainty can be computed a priori based on bounds on the disturbance frequency. Simulations demonstrate the properties of the algorithm in a variety of conditions.

In self-excited induction machines, a power generating mode of operation can often be attained only by precharging at least one of the capacitors connected to the windings. The paper shows how a carefully derived state-space model with nonlinear magnetic characteristics enables the assessment of all possible operating regimes including their stability properties. In particular, the analysis reveals the possible existence of an unstable operating regime, which creates a barrier that must be overcome through precharged capacitors. In such case, the analytical results of the paper yield a simple formula that predicts the voltage needed to trigger self-excitation. Close to the boundary, voltages can be generated for extended periods of time before growing to a stable operating regime, or collapsing to zero. Experimental results validate the results of the paper on the transient properties of self-excited induction generators.

This paper is concerned with the rejection of sinusoidal disturbances of unknown frequency acting at the output of unknown plants. Disturbance rejection is based on an adaptive harmonic steady-state (ADHSS) algorithm combined with a magnitude/phase locked-loop (MPLL) frequency estimator. The harmonic steady-state method assumes that the plant can be approximated by its steady-state frequency response. For high-order plants such as those encountered in active noise and vibration control (ANVC), this assumption greatly reduces the number of parameters and enables online estimation of the plant response using simple algorithms. The paper shows that when the MPLL is integrated with the ADHSS algorithm, the two components work together in such a way that the control input does not prevent frequency tracking by the MPLL, and so that the order of the ADHSS can be reduced. Thus, the addition of the MPLL allows disturbances of unknown frequency to be considered without significantly increasing the complexity of the original ADHSS. After analyzing the reduced-order ADHSS in the ideal case, the equations describing the complete system are considered. The theory of averaging is used to gain insight into the steady-state behavior of the algorithm. It is found that the system has a two-dimensional equilibrium surface such that the disturbance is cancelled exactly. A subset of the surface is proved to be locally stable. Extensive active noise control experiments demonstrate the performance of the algorithm, even when disturbance and plant parameters are changing.

Next-generation aircraft with a large number of actuators will require advanced control allocation methods to compute the actuator commands needed to follow desired trajectories while respecting system constraints. Previously, algorithms were proposed to minimize the l 1 or l 2 norms of the tracking error and of the actuator deflections. This paper discusses the alternative choice of the l ∞ norm, or the sup norm. Minimization of the control effort translates into the minimization of the maximum actuator deflection (min―max optimization). This paper shows how the problem can be solved effectively by converting it into a linear program and solving it using a simplex algorithm. Properties of the algorithm are also investigated through examples. In particular, the min―max criterion results in a type of load balancing, where the load is the desired command and the algorithm balances this load among various actuators. The solution using the l ∞ norm also results in better robustness to failures and lower sensitivity to nonlinearities in illustrative examples. This paper also discusses the extension of the results to a normalized l ∞ norm, where the norm of the actuator deflections are scaled by the actuator limits. Minimization of the control effort then translates into the minimization of the maximum actuator deflection as a percentage of its range of motion.

An approach is described for estimating the pump’s variables based only on measuring the motor’s electrical variables. The method is based on extended Kalman filter estimation of the pump’s shaft power and velocity and on-line calculation of the head and flow rate using steady-state pump curves. The application of the method for the head and flow-rate stabilization systems is demonstrated in simulations.

Robots are often run with permanent magnet synchronous motors (PMSM) with a high ratio gearbox. Both parts can produce parasitic oscillations (ripples), which let the robot shake at tool center point. The gearbox ripple problem is more complicated to be solved with control theory because only motor side sensors should be used. Due to the internal model principle gearbox side information is necessary to solve the problem. The first algorithm uses an observer to get gearbox side information where the second algorithm uses a gearbox side rate sensor. The algorithms are tested with a nonlinear SISO problem and with a nonlinear MIMO system. In both cases the ripples are canceled with an adaptive controller which estimates the phase and magnitude of the ripple. This adaptive controller is designed separately and is added to the existing basis controller. The algorithms are tested in simulation and on a testbed, which is an industrial application.

The rejection of periodic disturbances is a problem frequently encountered in control engineering, and in active noise and vibration control in particular. The paper presents a new adaptive algorithm for situations where the plant is unknown and may be time-varying. The approach consists in obtaining online estimates of the plant frequency response and of the disturbance parameters. The estimates are used to continuously update control parameters and cancel or minimize the effect of the disturbance. The dynamic behavior of the algorithm is analyzed using averaging theory. Averaging theory is used to approximate the nonlinear time-varying closed-loop system by a nonlinear time-invariant system. It is shown that the four-dimensional averaged system has a two-dimensional equilibrium surface, which can be divided into stable and unstable subsets. Trajectories generally converge to a stable point of the equilibrium surface, implying that the disturbance is asymptotically canceled even if the true parameters of the system are not exactly determined. Simulations, as well as extensive experiments on an active noise control testbed, illustrate the results of the analysis and demonstrate the ability of the algorithm to recover from abrupt system changes or track slowly-varying parameters. Extensions of the algorithm to systems with multiple inputs/outputs and disturbances consisting of multiple frequency components are provided.

A discrete-time adaptive algorithm is proposed to reject periodic disturbances in the case where the frequencies are unknown and a reference sensor is not available. The stability of the algorithm is analyzed using averaging theory, and the design of the parameters is based on the linearized averaged system. While the algorithm is first designed for rejecting periodic disturbances with one sinusoidal component, it is also extended to deal with cases where the disturbance has multiple sinusoidal components. A frequency separation method is proposed to prevent the frequency estimates from converging to the same value. The effectiveness of the adaptive scheme is validated in simulations and in experiments on an active noise control testbed.

A method is proposed to estimate the rotor time constant TR of an induction motor without measurements of the rotor speed/position. The method consists of solving for the roots of a polynomial equation in TR whose coefficients depend only on the stator currents, stator voltages, and their derivatives. Experimental results are presented

Indirect field-oriented control of an induction machine requires knowledge of the rotor time constant to estimate the rotor flux linkages. Here, an online method is presented for estimating the rotor time constant and the stator resistance, both of which vary during operation of the machine due to ohmic heating. The method uses measurements of the stator voltages, stator currents, and their derivatives (first derivative of the voltages and both the first and second derivatives of the currents). The problem is formulated as finding those parameter values that best fit (in a least-squares sense) the model of the induction motor to the measured output data of the motor. This method guarantees that the parameter values are found in a finite number of steps. Experimental results of an online implementation are presented

The complexity and strong nonlinearity of the model of a self-excited induction generator hinder the systematic design of a voltage regulation system. Using a special reference frame aligned with the stator voltage vector, the paper succeeds in developing a control-oriented linearized model that relates small deviations of the capacitance, load admittance, and angular velocity, to corresponding deviations of the voltage amplitude. Transfer functions are also computed based on the linear model. A stability analysis predicts rapidly decaying oscillatory transients combined with a primary component with slower exponential decay. Simulated transient responses of the full and linearized models demonstrate the validity of the approximation and are in good agreement with experiments.\ud

Three pole-placement controllers are designed for the doubly-fed induction generator (DFIG) in a stator voltage-oriented frame. The pole placement technique is used to compute the parameters of the feedback controller to regulate the active and reactive powers through the rotor side voltage. The main contribution of this paper is representing the DFIG model in the complex domain to reduce the order of the system, yielding simple expressions for the controller gains. Simulations in MATLAB/SIMULINK are used to assess the effectiveness of the proposed controllers.

The deployment of renewable energies requires power electronic converters to produce sinusoidal voltages of appropriate magnitude and frequency. In the case of isolated microgrids, unbalanced loads can result in off-nominal voltages on the loads. A solution to this problem consists in replacing the conventional three-leg converter by a four-leg converter with neutral wire. Four-leg converters have not been studied as extensively as three-leg converters, and existing approaches to control them are based on geometric properties that become difficult to extend to converters with a higher number of levels/switches. The objective of the paper is to show that an approach developed in the context of flight control can be applied to this problem with great advantages. Specifically, control allocation methods are shown to be applicable to a four-leg two-level three-phase inverter. The method offers a single generic control scheme regardless on the number of switches. In addition, the approach may offer the incorporation of interesting converter properties, such as the minimization of switching (or conduction) losses, or the reconfiguration of the inverter in the event of a fault detected on a switch, if redundancies allow it.

This note considers a differential-algebraic approach to estimating the speed of an induction motor from the measured terminal voltages and currents. In particular, it is shown that the induction motor speed /spl omega/ satisfies both a second- and a third-order polynomial equation whose coefficients depend on the stator voltages, stator currents, and their derivatives. It is shown that as long as the stator electrical frequency is nonzero, the speed is uniquely determined by these polynomials. The speed so determined is then used to stabilize a dynamic (Luenberger type) observer to obtain a smoother speed estimate. With full knowledge of the machine parameters and filtering of the sensor noise, simulations indicate that this estimator has the potential to provide low speed (including zero speed) control of an induction motor under full rated load.