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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.

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.

© 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.

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...

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.

© 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.

A nonlinear least-squares method is presented for the identification of the induction motor parameters. A major difficulty with the induction motor is that the rotor state variables are not available measurements so that the system identification model cannot be made linear in the parameters without overparametrizing the model. Previous work in the literature has avoided this issue by making simplifying assumptions such as a "slowly varying speed." Here, no such simplifying assumptions are made. The problem is formulated as a nonlinear least-squares identification problem and uses elimination theory (resultants) to compute the parameter vector that minimizes the residual error. The only requirement is that the system must be sufficiently excited. The method is suitable for online operation to continuously update the parameter values. Experimental results are presented.

The paper reviews available methods for the rejection of periodic disturbances. Such disturbances are often encountered in active noise and vibration control, due to rotating machinery. The emphasis of the paper is on feedback control problems where reference sensors are not available. The case where the frequency of the disturbance is known is considered first. Two sets of algorithms are discussed: one based on the internal model principle of feedback control theory, and the second based on adaptive feedforward cancellation. An interesting observation is that algorithms originating from both approaches can be shown to be equivalent under certain conditions. When the frequency of the disturbance is unknown, an intuitive approach consists in combining a method for the rejection of disturbances of known frequency with a frequency estimator. Alternatively, one may seek to develop a stable adaptation mechanism so that the disturbance is cancelled asymptotically. While algorithms can be designed to adapt to plant and disturbance parameters, the most successful approaches use some limited plant information to adapt the magnitude, frequency, and phase parameters of the control signal. Applications are discussed throughout the paper. Copyright © 2004 John Wiley & Sons, Ltd.

The paper proposes a reconfigurable flight-control system for the tracking of altitude, heading, sideslip, and velocity commands. The control law can serve for the command of unmanned air vehicles or as an autopilot for piloted aircraft. The inner core of the algorithm consists of a reconfigurable control system providing tracking of pitch-, roll-, and yaw-rate commands. It is based on a model reference control law and a stabilized recursive least-squares algorithm. The outer loop is based on a linear design, with compensation for the nonlinear couplings arising from flight dynamics. Some parameters of the outer loop are identified in real time in order to adapt to varying flight conditions. The algorithm is evaluated using a nonlinear F-16 simulation model. The results demonstrate the consistent performance of the algorithm through various flight conditions, as well as its turn coordination capabilities, its reconfiguration after a floating left elevator failure, its ability to move across the power curve, and its tolerance to measurement noise and turbulence.

The direct allocation method is considered for the control allocation problem. The original method assumed that every three columns of the controls effectiveness matrix were linearly independent. Here, the condition is relaxed, so that systems with coplanar controls can be considered. For fast online execution, an approach using spherical coordinates is also presented, and results of the implementation demonstrate improved performance over a sequential search. Linearized state-space models of a C-17 aircraft and of a tailless aircraft are used in the evaluation. Oincreasethe reliability ofaircraft,cone gurations with a large numberofactuatorsandcontrolsurfacesareadvantageous.Recone gurable control laws may be used to exploit all of the available control power despite failures and damages. 1;2 Control allocation is the problem of distributing the control requirements among multiple actuators to satisfy the desired objectives while accounting for the limited range of the actuators. Although solutions exist for the control allocation problem, an issue of current interest is that of the feasibilityoftheirimplementationonexistingcomputersforaircraft with a large number of actuators. 3 The direct allocation approach 4i6 is based on the concept of the attainable moment set (AMS), which is the set of all of the moment vectors that are achievable within the control constraints. The methodofdirectallocation allowsoneto achieve100%oftheAMS, whereas some other approaches such as daisy chaining, pseudoinverse,and generalized inversesolutionshavebeen shown to achieve

The paper presents a detailed analysis of self-excited induction generators with resistive-inductive loads. A nonlinear dynamic model is derived that enables a unified analysis of both the steady-state and transient characteristics of the machine. Steady-state operating modes are first determined, and self-excitation boundaries are derived. Computations are straightforward and do not require iterations. The dynamic model is also used to compute the eigenvalues of the linearized system around an operating mode. Experimental data show good agreement with computational results using the dynamic model. It is found that the addition of inductance generally, but not necessarily, enlarges the set of conditions where self-excitation is possible, and increases the stability of the operating modes.

International audience; The paper presents a new sensorless parameter identification method for permanent magnet stepper motors. Current sensors are assumed available, but mechanical sensors are not. Data is obtained with open-loop commands at multiple speeds. A new frame is proposed that presents advantages similar to the d-q frame, but without the need for a position sensor. The method exploits derived linear parameterizations and least-squares algorithms. In some cases, overparameterization is resolved using elimination theory. The parameters identified using the new procedure are found to be very close to those obtained with sensors. The approach is potentially applicable to other types of synchronous motors.

In this note a globally stable methodology is proposed to estimate the frequency, phase, and amplitude of a sinusoidal signal affected by additive structured and bounded unstructured disturbances. The structured disturbances belong to the class of time-polynomial signals incorporating both bias and drift phenomena. Stability and robustness results are given by resorting to Input-to-State stability arguments. Simulation comparative results show the effectiveness of the proposed technique.

The paper proposes a discrete-time algorithm for the rejection of sinusoidal disturbances of unknown frequency. The algorithm is adapted from an existing continuous-time algorithm and the overall nonlinear system is analyzed using a linear approximation. The paper shows that the noise rejection properties may be predicted using an in-phase/quadrature decomposition of the noise similar to the one encountered in the theory of phase-locked loops. Estimates are obtained for the standard deviations of the plant output and of the adaptive parameters. Simulations validate the predictions of the analysis, despite the nonlinear nature of the adaptive system and the high level of noise applied.

This paper proposes an active noise control algorithm for periodic disturbances of unknown frequency. The algorithm is appropriate for the feedback case in which a single error microphone is used. The previously-proposed algorithm (Bodson et al. (1997)) for the rejection of sinusoidal noise sources is extended for the cancellation of multiple harmonics. Unlike many other approaches, the estimates of the frequencies of the separate harmonics are tied together within the algorithm to account for the integer multiplicative relations between them. The dynamic behavior of the closed-loop system is analyzed using an approximation that is shown, in simulations, to provide an accurate representation of the system's behavior. Experimental results on an active noise control testbed demonstrate the success of the method in a practical environment.

Generalizes the authors' work on high-performance control of induction motors to machines that exhibit significant magnetic saturation. The controller design is based on the standard d-q model of the induction motor which has been modified to account for the saturation of the iron in the main (magnetic) path of the machine. An input-output linearization controller is used to provide independent (decoupled) control of the speed and flux. With this controller, the flux reference becomes an extra degree of freedom for the designer to help achieve performance objectives. Taking into account saturation along with the voltage and current constraints, the flux reference is chosen to achieve the optimal torque (maximum for acceleration and minimum for deceleration) at any given speed. Experimental results are given to demonstrate the input-output controller's effectiveness in providing the tracking of a given position and speed trajectory while simultaneously tracking the optimal flux reference. The set of experiments are fast point-to-point motion control moves with an inertial load comparing the input-output controller based on the saturated magnetics model with that based on the linear magnetics model.

This paper considers a method proposed by Chaplin and Smith for the cancellation of repetitive vibrations. Direct implementation of the concepts of the patent is not straightforward because of the lack of precise information regarding certain components, and because of the absence of guidelines for the design of a system with satisfactory stability and performance properties. This paper proposes a specific algorithm based on the concepts of the patent, and provides an approximate analysis which is found useful to obtain a closed-loop system with predictable dynamic characteristics. Simulations demonstrate the validity of the approximation and the success of the design. A tendency of the algorithm for convergence toward undesirable operating states is identified, and an improved version is derived. The algorithm is also compared to another algorithm proposed-for the same purposes.

The results are discussed of a series of e ight tests in which a computationally efe cient real-time parameter identie cation and control recone guration algorithm was evaluated. A modie ed sequential least-squares technique was used for identie cation. Signie cant challenges were encountered because of the poor information content of the signals used for identie cation and because of requirements for autonomy, reliability, and fast adaptation. A requirement for real-time operation in e ight-control computers with limited computational throughput imposed additional constraintson the recone gurable controllerand the parameterestimation algorithm. The identie cation algorithm is presented with solutions that were developed to address problems posed by the specie c application. Typical parameter identie cation results from the e ight tests are shown. The e ight tests culminated in a successful landing of an F-16 with a simulated missing elevon.

SUMMARY The di⁄erential-geometric techniques of nonlinear control developed over the last 20 years or so include static and dynamic feedback linearization, input—output linearization, nonlinear state observers and disturbance decoupling. The theory has now reached a level of maturity where control practicioners are making e⁄ective use of the techniques for electric motors. Indeed, DC and AC motors have well-defined nonlinear mathematical models which often satisfy the structural conditions required of the di⁄erential-geometric theory. In this paper, the application of various di⁄erential-geometric methods of nonlinear control is shown by way of examples including DC motors (series, shunt and separately excited), induction motors, synchronous motors and DC—DC converters. A number of contributions are surveyed which show the benefits of the methods for the design of global control laws by systematic means. ( 1998 John Wiley & Sons, Ltd.

Limits on the motion and on the rate of motion of the actuators driving the control surfaces of aircrafts significantly affect the performance of flight control systems. After a failure, the constraints become even more restrictive, because of the loss of control power and because of the increase in cross-couplin gs between the axes. In the paper, model reference adaptive control algorithms are considered for flight control reconfiguration and four methods are proposed to handle the problems arising due to actuator saturation. The methods are based on a scaling of the control inputs, a relaxation of the control requirements, a scaling of the reference inputs, and a least-squares approximation of the commanded accelerations. Simulations demonstrate the effectiveness of the methods for the control of a twin-engine fighter aircraft. It is found that even the simplest method considerably improves the responses compared to those obtained without modification. Further, despite the widely different concepts and complexity levels of the four methods of command limiting, the performance is found to be similar in most cases.

The paper presents an algorithm for the tuning of two input shaping methods. These methods are designed to prevent the excitation of oscillatory modes in resonant systems. The first input shaping method produces a control signal that is the linear combination of delayed versions of the reference input. The resulting control system is linear time-invariant but infinite-dimensional. Its transfer function has an infinite number of complex zeros, with some of them placed exactly at the locations of the resonant modes of the plant. In contrast, the second input shaping method is based on a pole/zero cancellation of the resonant modes using a finite-dimensional controller. For both input shaping methods, tuning is useful to optimize performance and an algorithm is developed for the automatic adjustment of the controller parameters. Experimental results are presented for a system in which a motor is used to control the position of a flexible arm. The step response of the plant is poorly damped, but is much improved with input shaping. The control performance is found to be comparable for both methods, and the tuning method is found to be simple and effective.

This paper discusses the problem of maximizing the torque of permanent magnet synchronous motors in the presence of voltage and current constraints. Formulas are given that are suitable to operation with voltage and current source inverters and to real-time computation. Generally, the available torque is limited by current constraints at low speeds and by voltage constraints at high speeds, and there is often an intermediate range of speeds where both the voltage and the current constraints are active. The paper specifies how optimal operation can be achieved in all three ranges, and at what speeds the optimal operation transitions from one mode to another. An example is discussed to illustrate the contributions of the paper and experimental results demonstrate the usefulness of the formulas in a high-performance robotic application.

Two algorithms are presented for the rejection of sinusoidal disturbances with unknown frequency. The first is an indirect algorithm where the frequency of the disturbance is estimated, and the estimate is used in another adaptive algorithm that adjusts the magnitude and phase of the input needed to cancel the effect of the disturbance. A direct algorithm that uses the concept of a phase-locked loop is also presented in which frequency estimation and disturbance cancellation are performed simultaneously. Approximate analyses are presented for both schemes and the results are found useful for the selection of the design parameters. Simulations are given which demonstrate the validity of the analytical results and the ability of the algorithms to reject sinusoidal disturbances with unknown frequency. The indirect algorithm is found to have a larger capture region for the parameter estimates, whereas the direct algorithm has superior convergence properties locally about the optimum parameter estimates