PWM Voltage Source Inverter Research Articles

Phase voltage estimation of a PWM VSI and its application to vector-controlled induction machine parameter estimation

For high-performance vector control of an induction machine, rotor resistance estimation is required. The commonly used state-space class of estimators requires voltage transducers as instantaneous phase voltages are used in the estimation algorithm. A phase voltage estimator is developed for a pulsewidth modulation voltage-source inverter. The voltage estimates are used in a rotor resistance estimator and practical results show that the usual phase-voltage transducers are unnecessary.

Multilevel selective harmonic elimination PWM technique in series-connected voltage inverters

Selective harmonic elimination pulsewidth modulation (SHEPWM) method is systematically applied for the first time to multilevel series-connected voltage-source PWM inverters. The method is implemented based on optimization techniques. The optimization starting point is obtained using a phase-shift harmonic suppression approach. Another less computationally demanding harmonic suppression technique, called a mirror surplus harmonic method, is proposed for double-cell (five-level) inverters. Theoretical results of both methods are verified by experiments and simulations for a double-cell inverter. Simulation results for a five-cell (11-level) inverter are also presented for the multilevel SHEPWM method.

Series active power filter compensates current harmonics and voltage unbalance simultaneously

An active power filter connected in series to the power distribution system is presented and analysed. The series active power filter is implemented with a three-phase PWM voltage-source inverter and operates with a resonant LC passive filter connected in parallel to the power lines. The proposed scheme is able to simultaneously compensate current harmonics, the fundamental negative and zero sequence voltage components generated by the voltage source unbalance, and also eliminates the zero sequence current harmonic components that circulate through the neutral conductor. The active power filter is discussed in terms of the principles of operation under steady-state and transient conditions. The design and implementation of the power and control circuits are reported. Key predicted results are verified experimentally on a 5 kVA prototype model.

Power devices for medium voltage PWM converters

The accelerated pace of change in semiconductor power devices, has been remarkable, and the number of power devices described in the literature is staggering and can be bewildering to both power device specialists and power electronics equipment designers. The high-voltage insulated gate bipolar transistor and the integrated gate commutated thyristor are identified as best suited for medium-voltage pulsewidth modulated voltage source inverter stack design. These devices are examined from the viewpoint of power electronics applications.

Cascade sliding mode control of a field oriented induction machine drive

This study deals with the application of sliding mode control theory to induction machine fed by a PWM voltage source inverter in which the system operates in the field oriented control. Thus, after determining the decoupled model of the machine, a set of simple surfaces have been applied to a cascade structure and the associated control laws have been synthesized. Furthermore, in order to reduce chattering phenomenon, smooth control functions with appropriate threshold have been chosen. Simulation study is conducted to show the effectiveness of the proposed method and then validated by an experimental prototype.

Rotor time constant updating scheme for a rotor flux-oriented induction motor drive

This paper presents a simple online rotor time constant identification scheme of an indirect field-oriented induction motor for the purpose of improving the performance and robustness of the drive. The proposed technique neither requires any special test signal nor any complex computations. This scheme is based on a special switching technique of the current-regulated pulsewidth modulation (CRPWM) voltage-source inverter (VSI), which allows measuring the induced voltage across the stator phase. The rotor time constant is then identified directly from this measured voltage. This proposed technique provides six windows within one electric cycle to update the rotor time constant, which should be sufficient for all practical purposes. Simulated results followed by experiments are presented to validate the effectiveness of the proposed technique.

A fault protection scheme for series active power filters

A protection scheme for series active power filters is presented and analyzed in this paper. The proposed scheme protects series active power filters when short-circuit faults occur in the power distribution system. The principal protection element is a varistor, which is connected in parallel to the secondary of each current transformer. The current transformers used to connect in series the active power filter present a low-magnetic saturation characteristic increasing current ratio error when high currents circulate through the primary winding, thus generating lower secondary currents. In this way, the power dissipated by the varistors is significantly reduced. After a few cycles of short-circuit currents flowing through the varistor, the gating signals applied to the active power filter switches are removed and the pulsewidth-modulation (PWM) voltage-source inverter (VSI) is short circuited through a couple of antiparallel thyristors.

On-line dead-time compensation technique for open-loop PWM-VSI drives

A new on-line dead-time compensation technique for low-cost open-loop pulsewidth modulation voltage-source inverter (PWM-VSI) drives is presented. Because of the growing numbers of open-loop drives operating in the low-speed region, the synthesis of accurate output voltages has become an important issue where low-cost implementation plays an important role. The so-called average dead-time compensation techniques rely on two basic parameters to compensate for this effect: the magnitude of the volt seconds lost during each PWM cycle and the direction of the current. In a low-cost implementation, it is impractical to attempt an on-line measurement of the volt-seconds error introduced in each cycle-instead an off-line measurement is favored. On the other hand, the detection of the current direction must be done on line. This becomes increasingly difficult at lower frequencies and around the zero crossings, leading to erroneous compensation and voltage distortion. This paper presents a simple and cost-effective solution to this problem by using an instantaneous back calculation of the phase angle of the current. Given the closed-loop characteristic of the back calculation, the zero crossing of the current is accurately obtained, thus allowing for a better dead-time compensation. Experimental results validating the proposed method are presented.

Study on resonant fly-back converter for DC distribution system

This paper describes a resonant fly-back converter with thyristor switches, which can be used for the DC distribution with a PWM voltage-source inverter. The proposed converter operates to change high-voltage DC into low-voltage DC with isolation and large converting ratio. The converter has a main thyristor switch and an LC resonant circuit with an auxiliary thyristor switch for commutation in the primary side of the gap transformer. The operation of the proposed converter was verified through computer simulations with EMTP and experiments with a hardware scaled-model. The proposed converter could be implemented with commercially available components and proven technologies for supplying electricity to the rural or remote customer.

Dynamic overmodulation characteristics of triangle intersection PWM methods

In this paper, the dynamic overmodulation characteristics of current-regulated carrier-based high-performance pulsewidth modulation (PWM) voltage-source inverter drives are investigated. Dynamic and steady-state overmodulation operating modes are clearly distinguished, and the requirements for obtaining high performance in each mode are shown to be significantly different. Dynamic overmodulation characteristics of the modern triangle intersection PWM methods are modeled and shown to be unique for each method. The study reveals space-vector PWM (SVPWM) exhibits a minimum voltage magnitude error characteristic. It also indicates all the advanced triangle intersection PWM methods, including SVPWM, have limited dynamic overmodulation performance. To enhance the performance, an algorithm with superior performance is adapted from the direct digital PWM approach. Detailed induction motor drive simulations and experimental results illustrate the characteristics of modern triangle intersection PWM methods and the performance gained with the new dynamic overmodulation algorithm.

Sensorless full-digital PMSM drive with EKF estimation of speed and rotor position

This paper concerns the realization of a sensorless permanent magnet (PM) synchronous motor drive. Position and angular speed of the rotor are obtained through an extended Kalman filter. The estimation algorithm does not require either the knowledge of the mechanical parameters or the initial rotor position, overcoming two of the main drawbacks of other estimation techniques. The drive also incorporates a digital d-q current control, which can be easily tuned with locked rotor. The experimental setup includes a PM synchronous motor, a pulsewidth modulation voltage-source inverter, and floating-point digital-signal-processor-based control system.

Use of an LC filter to achieve a motor-friendly performance of the PWM voltage source inverter

By putting an LC filter between a PWM voltage source inverter and induction motor, standard industrial motors can also be utilized for adjustable speed drive applications. In this paper, the application of an LC filter to medium voltage motors fed by inverters with switching frequencies below 1000 Hz is described. For different filter topologies, rules for the electrical design are discussed as well as solutions for the stability problem. Also discussed are solutions against common mode voltage stress on the motor terminals. An example shows the implication of the filter on the minimum inverter power which has to be installed to feed a given motor.

Spectrum Analysis for EMI Produced by Voltage-Source PWM Inverters

Spectrum Analysis for EMI Produced by Voltage-Source PWM Inverters

New protection issues of a matrix converter: design considerations for adjustable-speed drives

Induction motors are traditionally controlled by standard pulsewidth modulation voltage-source inverters. An alternative is the matrix converter, which consists of nine bidirectional switches. This converter has benefits compared to a standard inverter, like sinusoidal input current and bidirectional power flow. The main disadvantage is the lack of a bidirectional switch, because such a switch may be done by two transistors and two diodes. An important topic is protection of the matrix converter, and this paper proposes two new protection circuits for matrix converters with a reduced number of components. The number of protection diodes is reduced by six. Design expressions of the protection circuit are calculated and validated by simulation. The standard protection circuit and the new circuits are demonstrated by simulation to have the same performance. Experimental results on an 8 kVA matrix converter show the design expressions are correct. It is concluded that it is possible to reduce the necessary power components in a matrix converter.

ROBUST CURRENT CONTROL METHOD OF VOLTAGE SOURCE PWM INVERTER

ABSTRACT In recent years, the voltage source PWM (Pulse Width Modulated) inverter is used for power supply in the field of motor control. Current tracking control of inverter is very important because current control ability affects control performance of plants. In this paper, the robust current control method of voltage source PWM inverter is presented; current is controlled to be exactly equal to the reference current under variations of load parameters and operating conditions. The influence of parameter variations is restrained by feedback gain based on Lyapunov's direct method. The feedback gain is calculated on-line to ensure system's stability with various disturbances.

Analysis of negative spikes on DC-link current in voltage-source PWM inverters

The occurrence of negative spikes on the DC-link current in voltage-source PWM inverters is newly formulated, analysed and verified. Based on the introduction of a new vector, namely the dead time vector, the occurrence of these negative current spikes can be mathematically modelled, and hence can be identified at the instant of dead time intervals, in which two phases change their switching states simultaneously and satisfy a unique condition. The theoretical results are verified by comparing with both device-oriented PSpice simulation and experimental measurement. Since the proposed analysis is so general, it can readily be applied to other PWM inverters with various switching schemes.

Reactive power compensation and load balancing in electric power distribution systems

This article presents a new method for reactive power compensation and load balancing in a four-wire, three-phase distribution system. An IGBT-based PWM voltage source inverter with a dc bus capacitor is used as a compensator. The hysteresis-based carrierless PWM current control is employed to derive switching signals to the devices of the compensator. A detailed dynamic model of the complete scheme is developed to study the steady-state and transient behaviour of the proposed compensator. Simulated results for the cases of single-phase, two-phase and three-phase lagging power-factor loads are presented and discussed in detail to demonstrate the reactive power compensation and load balancing capabilities of the compensator.

Carrier-based PWM-VSI overmodulation strategies: analysis, comparison, and design

In this paper, the overmodulation region voltage-gain characteristics and waveform quality of carrier-based pulsewidth-modulated (PWM) methods are investigated. Through detailed analytical study, voltage-gain characteristics are extracted independent of carrier frequency. The influence of blanking time and minimum pulsewidth (MPW) control on the inverter gain characteristics are studied and shown to be significant. A comparative evaluation of the modulator characteristics reveals the advantageous high-modulation-range characteristics of discontinuous PWM methods and, in particular, the superior overmodulation performance of a discontinuous PWM method. The modulation methods under consideration are tested on a PWM voltage-source inverter (VSI)-fed induction motor drive in the laboratory, and the theoretical results are verified by experiments. Also, a gain linearization technique is presented and experimentally verified. The results of this study are useful in the design, performance prediction and development of high-performance overmodulation strategies for PWM-VSI drives.

Study and simulation of a cycloconverter-active filter device with a unity power factor

This paper presents a new approach to suppress disturbances drawn between a direct high power phase-controlled converter and the supply network. The first stage is based on the suppression of the average reactive power owing to ZCS/ZVS mixed mode inside the converter. The second stage allows to suppress harmonic currents and reactive power fluctuations by means of a PWM voltage source inverter. The DC side of this inverter is connected at the input of the principal converter in order to clamp the overvoltages caused by the ZVS mode on the impedant network.

Active cancellation of the common-mode voltage produced by a voltage-source PWM inverter

This paper proposes an “active common-mode noise canceler” that is capable of eliminating the common-mode voltage produced by a voltage source PWM (pulsewidth modulated) inverter. It generates a compensating voltage which has the same amplitude as, but the opposite phase to, the common-mode voltage produced by the PWM inverter. The compensating voltage is superimposed on the inverter output by a common-mode transformer. As a result, the common-mode voltage applied to the load is canceled completely. The design method of the active common-mode noise canceler is also presented in detail. A prototype has been constructed and tested to verify the effectiveness for an induction motor drive system of 3.7 kW using an IGBT (insulated gate bipolar transistor) inverter. Some experimental results show that the proposed active common-mode noise canceler makes a significant contribution to eliminating the common-mode current or the ground current, and it prevents an electric shock from being received by anyone handling it. © 1998 Scripta Technica, Electr Eng Jpn, 124(3): 64–72, 1998