Hongwu She

A Research on Space Vector Modulation Strategy for Matrix Converter Under Abnormal Input-Voltage Conditions

The matrix converter is a single-stage ac-ac power conversion device without dc-link energy storage elements. Any disturbance in the input voltages will be immediately reflected to the output voltages. In this paper, a modified space vector modulation strategy for matrix converter has been presented under the abnormal input-voltage conditions, in terms of unbalance, nonsinusoid, and surge (sudden rising or sudden dropping). By using the instantaneous magnitude and phase of input-voltage vector to calculate the voltage modulation index and input-current phase angle, this modified modulation strategy can eliminate the influence of the abnormal input voltages on output side without an additional control circuit, and three-phase sinusoidal symmetrical voltages or currents can be obtained under normal and abnormal input-voltage conditions. The performance of the input currents is analyzed when the matrix converter uses different modulation strategies. Some numerical simulations are presented to confirm the analytical results. Tests are carried out on a 5.5-kW matrix converter prototype. Experimental results verify the validity of the proposed strategy.

Implementation of Voltage-Based Commutation in Space-Vector-Modulated Matrix Converter

A novel voltage-based commutation (VBC) strategy without explicit input-voltage measurement is proposed in this paper. By properly selecting the width of the critical intervals, the two-step uncritical commutation and four-step critical commutation approaches are utilized to realize safe VBC. The general switching patterns of space-vector modulation (SVM) are analyzed, and the four-step critical commutations are avoided by using four selected SVM switching patterns; thus, all the commutations in the matrix converter can be achieved by two-step VBC. In order to prevent the commutation processes from being interrupted, the triple-zero-vector switching pattern and the single-zero-vector switching pattern are utilized by selecting an appropriate commutation time and the output-voltage/current distortion is minimized. Prototype experiments have been carried out to show the validity of the control strategies.

Damped input filter design of matrix converter

This paper deals with the input filter design of matrix converter. Regard the matrix converter as a buck type PWM rectifier in the input side, the transfer function of input current using LC input filter is deduced. The parameter selection approach for the capacitor and inductor is presented. It has been verified that when LC circuit is adopted in the input filter, the input current will oscillate near the LC resonant frequency in both steady state and start-up process for the very low damping factor, and then the input current waveforms will be distorted. An improved input filter topology to increase the damping factor is then presented, and the damping resistance parameter selection method of the input filter is presented based on frequency response approach. To avoid the current spike at the start-up process, a start-up circuit is then proposed. The improved input filter has been tested on a 5.5kW matrix converter prototype and good performances are achieved.

Nonlinear Compensation Method for Output Performance Improvement of Matrix Converter

A nonlinear compensation method for matrix converter is proposed to compensate the voltage error between the reference voltage and actual output voltage. The output voltage error caused by voltage-based commutation process is analyzed, and the parasitic capacitor effect of the matrix converter on a forced commutation process is investigated. It is found that the parasitic capacitor effect could reduce the total output voltage error caused by the commutation process, and it makes the output voltage error relate to not only the direction of the load current but also the magnitude of the load current. The voltage error caused by the voltage-based commutation process is obtained considering the switching pattern, and then, the general function of the total voltage error is obtained considering the on-state voltage drop of the switching devices. The effectiveness of the compensation method has been verified by passive R -L load experiments and induction motor vector control experiments.

Space vector modulated matrix converter under abnormal input voltage conditions

An improved space vector modulation (SVM) approach for matrix converter (MC) operation in unbalanced and non-sinusoidal input voltage condition was presented. The concept of modulation vector was introduced, and the relationship of output voltage and input voltage of MC by space vector denotation was deduced. Using the modulation vector approach, an improved SVM approach was proposed to improve the output performance of MC in abnormal input voltage conditions. The novel approach was based on dynamic control of the output voltage modulation vector respect to the instantaneous input voltage vector. By this method, the unbalanced and non-sinusoidal input voltages could be automatically compensated without any extra calculation so the output voltage could keep balanced and sinusoidal in expected value. The validity of the improved SVM approach was verified by simulation and experiments.

Implementation of two-step voltage commutation matrix converter

This paper describes an implemention and testing of a 5kW matrix converter based on two-step voltage commutation. The primary objective of this research effort is to develop the practical applications of voltage commutation strategy in matrix converter. A prototype converter has been built using eighteen 60-A 1000-V discrete insulated gate bipolar transistors (IGBTs) based on the controller DSP in combination with FPGA. An improved commutation strategy is used for guaranteeing safe control of bidirectional switches at zero crossing of the input line voltage without additional explicit input voltage sign measurement circuits. The prototype converter and the commutation strategy have been tested under various operating conditions.

Research on two-step voltage-controlled commutation strategies for Matrix Converter

Reliable current commutation between switches in matrix converters is more difficult to achieve than in conventional voltage-source inverters since there are no natural freewheeling paths. Based on analyzing the causes of input phase voltage short circuit in the critical situation, an improved method for two-step voltage commutation strategy is proposed in this paper. By using the critical intervals, defining new commutation steady states (P, M, N) and new commutation intermediate states (PM, MN, NP), selecting special zero vectors and changing sequence of vectors, the short circuit phenomenon in the critical intervals can be avoided. The method has little influence on input currents and output voltages. Experimental results of a 5kW matrix converter prototype verify the validity and feasibility of the safe commutation method. The power equipment need not precise circuit to detect the polarity of input line voltage and the control circuit is easy to realize.

Vector control of induction motor based on output voltage compensation of matrix converter

This paper deals with the performance improvement of the matrix converter induction motor drive system. Rotor-flux-oriented vector control strategy is adopted in the drive system, and a novel current loop control scheme is proposed to realize decoupled control of the magnetizing current and the torque current with a unique controller. The output voltage error caused by voltage-based two-step commutation process and the switching device on-state voltage drop are analyzed in detail, and then a compensation method is proposed to eliminate the output voltage error. Using the compensation method, the command output voltage can be used as actual one in motor drive applications, and the measurement errors in the output acquiring circuit are avoided. Simulation and experimental results are presented to illustrate the validity of the proposed methods.

Research on matrix converter control strategy under abnormal input voltages

Due to lack of dc-link energy storage elements in the matrix converter, any disturbance in the input voltages will be immediately reflected to the output voltages. In order to guarantee safe and stable operation of matrix converters under abnormal input voltage conditions, the paper proposes an improved method to real-time calculate voltage modulation ratio using the space vector magnitude of output and input voltages. The input current performance of matrix converters is analyzed using this strategy and a method to eliminate the harmonic components of the input current under unbalanced input voltage conditions is presented. Some numerical simulations are presented to confirm the analytical results. Tests are carried out on a 5kW matrix converter prototype. Experimental results verify the proposed strategy in the paper works very well without an additional control circuit. Just need to adjust the calculation of space vector modulation ratio that the matrix converter can output three-phase sinusoidal symmetrical voltage under normal and abnormal input voltage conditions.