Novel current control method for PWM inverters

A new current control scheme is suggested which is suitable for AC servo drives. The scheme has a simple feedback configuration to determine an optimal stator voltage vector. Minimisation of either current deviations or switching frequency is possible without changing the controller configuration.     

A dynamic decoupling control scheme for high-speed operation ofinduction motors

In a high-speed operation of a vector-controlled induction motor, coupling between d-q current dynamics impairs the characteristics of torque response. The feedforward decoupling scheme does not perform well if an error exists in the motor parameter estimation. We derive a dynamic decoupling condition when the two additional proportional integral current controllers are used. A great advantage of this dynamic decoupling controller is the robustness to the motor parameter estimation errors. Further, we observe that overmodulation methods lead to the violation of the decoupling condition, thereby yielding a poor performance in the high-speed high-power operation. As a method of resolving this problem, we propose a decoupling preserving overmodulation algorithm which also enhances the torque transient response. Through simulation and experimental results, we demonstrate the improved performance of the proposed controller     

A voltage control strategy for current-regulated PWM inverters

Alternative voltage control strategies for current-regulated PWM inverters are analyzed, including previously established feedforward and feedforward/feedback controllers and a newly proposed decoupling feedback control strategy. The steady-state and dynamic characteristics of each of these control methods are illustrated and compared for a selected inverter design. It is shown that the feedforward controller exhibits steady-state error and an undesirable overshoot of the output voltages during startup. The addition of a feedback loop eliminates the steady-state error and reduces the overshoot; however, the natural response is underdamped regardless of the choice of feedback gains. A decoupling feedback control strategy that eliminates the disadvantages of the feedforward and feedforward/feedback controllers is described. Using the decoupling feedback controller, it is possible to eliminate the steady-state error and place the closed-loop poles wherever desired. Moreover, if the closed-loop poles are selected appropriately, it is possible to eliminate the overshoot of the output voltages during startup transients     

Optimal control of three-level PWM inverters

An harmonic loss-minimized optimal PWM strategy for three-level inverters is investigated. The different PWM methods for low-, middle-, and high-speed regions are presented. It is shown that, for three-level inverters, the optimized strategy in all speed regions differs from the optimal PWM strategy of two-level inverters. The developed optimal control ensures a minimum of harmonic losses for a predetermined number of commutations of three-level PWM inverters and for a given value of the fundamental harmonic voltage     

Phase compensation second-order repetitive control for CVCF PWM inverters

Phase compensation for high-order repetitive control (HORC) can improve system transient and steady-state performances. The phase compensator is often designed as the inverse transfer function of a closed-loop system. No other phase compensation methods for HORC have been reported up to now. Hence, in this paper, a simple approximate phase cancellation second-order repetitive control (RC) is proposed. The compensator is a linear combination of two different linear phase lead compensators, which can better fit the inverse of a plant model phase curve compared with the conventional linear phase compensator. Optimisation is introduced to design the parameters of the approximate phase cancellation second-order RC. Analysis and design of the second-order repetitive controlled pulse width modulation inverter system are presented. Simulations and experiments are provided to demonstrate the effectiveness of the optimisation method and verify the advantage of the approximate phase cancellation compensator.     

A new simplified space-vector PWM method for three-level inverters

In this paper, a new simplified space-vector pulse width modulation (SVPWM) method for a three-level inverter is proposed. This method is based on the simplification of the space-vector diagram of a three-level inverter into that of a two-level inverter. If simplified by the proposed method, all the remaining procedures necessary for the three-level SVPWM are done like conventional two-level inverter and the execution time is greatly reduced. The DC-link neutral-point potential control algorithms are implemented more easily. The proposed method can be applied to the multi-level inverters above three-level. The validity of the new SVPWM method is verified by experiment with a 1000 kVA three-level insulated gate bipolar transistor (IGBT) inverter     

A speed estimator for high performance sensorless control ofinduction motors in the field weakening region

The paper proposes a modified version of the model reference adaptive system (MRAS) based speed estimator, whose outputs of the reference and the adjustable model are rotor flux space vectors. The estimator is modified in such a way that the variation in the instantaneous level of the main flux saturation during operation in the field weakening is recognized and properly compensated at all times. The speed estimation scheme is equally applicable to both vector controlled and direct torque controlled induction machines, since it operates in the stationary reference frame and requires measurement of only stator voltages and currents. Verification of the proposed scheme is provided by simulation and by experimentation on an indirect feedforward rotor flux oriented induction machine for speed references of up to twice the base speed     

Adaptive control in series load PWM induction heating inverters

Permanent variations of the electric properties of the load in induction heating equipment make difficult to control the plant. To overcome these disadvantages, the authors propose a new approach based on adaptive control methods. For real plants it is enough to present desired performances or start-up variables for the controller, from which the algorithms tune the controllers by itself. To present the advantages of the proposed controllers, comparisons are made to a PI controller tuned through Ziegler–Nichols method.     

Multicarrier PWM strategies for multilevel inverters

Analytical solutions of pulsewidth-modulation (PWM) strategies for multilevel inverters are used to identify that alternative phase opposition disposition PWM for diode-clamped inverters produces the same harmonic performance as phase-shifted carrier PWM for cascaded inverters, and hybrid PWM for hybrid inverters, when the carrier frequencies are set to achieve the same number of inverter switch transitions over each fundamental cycle. Using this understanding, a PWM method is then developed for cascaded and hybrid inverters to achieve the same harmonic gains as phase disposition PWM achieves for diode-clamped inverters. Theoretical and experimental results are presented in the paper.     

Motion control of rigid robots driven by current-fed induction motors

The problem of controlling a rigid manipulator driven by induction motors operating in the current-command mode to follow a desired trajectory is considered in this paper. Based on a fourth-order reduced model of an induction motor, a current controller is proposed using only measurements of link positions and velocities as well as stator currents of induction motors. The rotor flux is estimated through a closed-loop observer. Provided that the flux observer is properly initialized, this controller is singularity-free and ensures the global exponential tracking to the desired trajectory. Simulations are presented to illustrate the performance of this controller.     

Tuning rules for the PI gains of field-oriented controllers ofinduction motors

The authors have previously shown that field-oriented controllers for induction motors preserve stability under a wide range of variations of the motor and controller parameters. However, as is well known, the transient performance critically depends on the tuning of the gains of the proportional-integral (PI) velocity loop, a task which is rendered difficult because of the high uncertainty on the rotor resistance. The problem we address in this paper is how to develop an offline procedure to choose these gains. The main contribution of our work is a very simple frequency-domain test that, for each setting of the PI gains, evaluates the maximum range of the relative rotor resistance estimate for which global stability is guaranteed. In this way, we provide a quantitative estimate of the performance of the PI controller. The stability result may also be used in a dual manner, fixing now the range of the rotor resistance, and estimating an admissible interval for the PI gains that preserves global stability. Instrumental for our study is the exploitation of an energy dissipation (strict passivity) property of the system     

A passive soft-switching snubber for PWM inverters

This paper presents a regenerative passive snubber circuit for pulse-width modulation (PWM) inverters to achieve soft-switching purposes without significant cost and reliability penalties. This passive soft-switching snubber (PSSS) employs a diode/capacitor snubber circuit for each switching device in an inverter to provide low dv/dt and low switching losses to the device. The PSSS further uses a transformer-based energy regenerative circuit to recover the energy captured in the snubber capacitors. All components in the PSSS circuit are passive, thus leading to reliable and low-cost advantages over those soft-switching schemes relying on additional active switches. The snubber has been incorporated into a 150 kVA PWM inverter. Simulation and experimental results are given to demonstrate the validity and features of the snubber circuit.     

Pulse-based dead-time compensator for PWM voltage inverters

The dead time necessary to prevent the short circuit of the power supply in pulsewidth-modulated (PWM) voltage inverters results in output voltage errors. Although individually small, when accumulated over an operating cycle, the voltage errors are sufficient to distort the applied PWM signal. This paper presents a method to correct for the dead-time errors. The pulse-based dead-time compensator (PBDTC) is less hardware- and software-intensive than other dead-time compensation methods providing a low-cost solution. The pulse-based technique is developed by analyzing the effects of dead time on a pulse-by-pulse basis and correcting each pulse accordingly. The technique is evaluated through simulation and experimental results. Other compensation methods are evaluated, and the results compared with the pulse-based technique. This comparison indicates previous methods can produce magnitude and phase errors in the applied terminal voltage, whereas the proposed method compensates for the dead time without significant magnitude and phase errors in the terminal voltage of PWM voltage source inverters     

Modulation strategy for single phase PWM inverters

A novel pulse width modulation (PWM) strategy that closely approximates the harmonic performance of the off-line harmonic minimised PWM technique for single phase PWM inverters is presented. The proposed on-line PWM technique digitally reproduces the characteristics of hysteresis band modulation for which the switching frequency is directly controlled by adapting the width of the hysteresis band. The software implementation is achieved using the conventional equations for regular-sampled PWM, combined with the pulse-position modulation (PPM) function characteristic of hysteresis band modulation     

Minimum-loss vector PWM strategy for three-phase inverters

A novel vector PWM method for three-phase voltage-controlled inverters is described. The so-called minimum-loss vector PWM (MLVPWM) strategy is characterized by the minimum amount of switching losses incurred in the inverter switches. Comparative analysis proving superiority of the MLVPWM technique over the existing regular-sampling PWM methods, and results of experimental investigation of a prototype modulator are presented     

Adaptive decentralized control of robot manipulators driven by current-fed induction motors

In this paper, an adaptive decentralized control scheme with a rotor-flux observer is proposed for the tracking control of robot manipulators actuated by current-fed induction motors. To cope with all parametric uncertainties in the electromechanical systems, an adaptive law is designed so that all the signals of closed-loop systems are bounded, and the tracking errors in position, velocity and rotor fluxes converge to a residual set.     

Hybrid integrator backstepping control of robotic manipulators driven by brushless DC motors

In this paper, a hybrid integrator backstepping controller is proposed for robotic manipulators actuated with brushless DC motors in the presence of arbitrary uncertain inertia parameters of the manipulator and the electrical parameters of the actuators. The main features are: 1) the design, requiring at most the joint velocities and stator currents feedback; 2) the semiglobal asymptotic stability of the controller being established in the Lyapunov sense; and 3) suitability of the scheme for multijoint robots. Simulation results are included to demonstrate the tracking performance.     

A novel overmodulation technique for space-vector PWM inverters

In this paper, a novel overmodulation technique for space-vector pulsewidth modulation (PWM) inverters is proposed. The overmodulation range is divided into two modes depending on the modulation index (MI). In mode I, the reference angles are derived from the Fourier series expansion of the reference voltage which corresponds to the MI. In mode II, the holding angles are also derived in the same way. The strategy, which is easier to understand graphically, produces a linear relationship between the output voltage and the MI up to six-step operation. The relationship between those angles and the MI can be written in lookup tables or, for real-time implementation, can be piecewise linearized. In addition, harmonic components and total harmonic distortion (THD) of the output voltage are analyzed. When the method is applied to the V/f control of an induction motor, a smooth operation during transition from the linear control range to the six-step mode is demonstrated through experimental results     

Adaptive repetitive control of PWM inverters for very low THDAC-voltage regulation with unknown loads

An adaptive repetitive control scheme is proposed and applied to the control of a pulsewidth-modulated (PWM) inverter used in a high-performance AC power supply. The proposed control scheme can adaptively eliminate periodic distortions caused by unknown periodic load disturbances in an AC power supply. The proposed adaptive repetitive controller consists of a voltage regulator using state feedback control, a repetitive controller with tuning parameters and an adaptive controller with a recursive least-squares estimator (LSE). This adaptive repetitive controller designed for AC voltage regulation has been realized using a single-chip digital signal processor (DSP) TMS320C14 from Texas Instruments. Experimental verification has been carried out on a 2 kVA PWM inverter. Simulation and experimental results show that the DSP-based adaptive repetitive controller can achieve both good dynamic response and low total harmonic distortion (THD) under large-load disturbances and uncertainties     

利用单片机PWM信号进行舵机控制

基于单片机的舵机控制方法具有简单、精度高、成本低、体积小的特点,并可根据不同的舵机数量加以灵活应用.