Modelling and simulation of matrix converter under distorted input voltage conditions

Abstract

Matrix converter is an energy conversion device which directly connects a three-phase voltage source to a three-phase load without dc-link components. Therefore, the output of the matrix converter is directly affected by the disturbance or imbalance in the input voltages. Many researchers have made an effort to overcome this problem in recent years. In this paper, the behaviors of the matrix converter controlled with the optimum-amplitude Venturini method are investigated and a novel compensation technique based on fuzzy logic controller is proposed to eliminate the undesirable influences of the input voltage under the distorted input voltage conditions. The proposed technique is based on closed loop control of the three-phase output current to enhance the output performance of the matrix converter. The mathematical model of the proposed system is developed. The simulation of the development model is performed in Matlab&Simulink. Some results demonstrating validity of the proposed compensation technique are presented.

Introduction

Matrix converter (MC) is a single-stage converter, which directly connects between one phase of the input and one phase of the output without the need for intermediate energy storage components. This topology of ac-ac converter was first proposed by Gyugyi and Pelly [6] to obtain an unlimited output frequency. In 1980, a generalized high-frequency switching strategy had been proposed by Venturini [20] and, this single-stage converter was named as “matrix converter”. After the optimum-amplitude method had been proposed by Venturini and Alesina [1], the matrix converter received an increased amount of interest [17].

Traditionally, ac voltages and currents having the variable-amplitude and/or the variable-frequency are indirectly obtained by using rectifier – dc link – inverter system. Indirect power conversion is performed by converting ac to dc, and then converting dc back to ac. The MC converting directly from ac to ac has been intensely studied as an alternative to conventional indirect power converter systems in recent years due to its following outstanding advantages [2], [7], [11], [19].

• Sinusoidal input and output currents.

• Possible with unity displacement factor for any load.

• Four-quadrant operation.

• Regeneration capability.

• Furthermore, a compact design due to the lack of dc-link equipments for energy storage.

These attractive properties have prompted researchers to undertake studies on matrix converter [10]. However, the load side of the MC is directly affected by the distorted and/or unbalanced input voltages due to the lack of dc intermediate circuit in the MC. The distorted and/or non-sinusoidal input voltages may cause undesirable harmonics on output current of the MC. The working performance of the load has deteriorated, when it is exposed to the harmonic and non-sinusoidal currents. If unfavorable effects of the distorted input voltages are eliminated in the MC, the popularity of the MC can increase more. Until now, only a few studies have been presented to reduce the influences of the distorted or unbalanced input voltages [3], [4], [5], [8], [9], [12], [13], [15], [16].

In [5], the performance evaluation of space-vector-modulated matrix converters under input and output unbalanced conditions has been discussed and two input modulation methods have been proposed. The first method is based on keeping the input current vector in phase with the input voltage vector. The second method is used to reduce the harmonic content of the input by modulating dynamically the input current displacement angle. In [13] and [16], a feed-forward compensation method has been presented to obtain balanced sinusoidal output currents under input voltage unbalance. This method is based on measuring the instantaneous values of input voltages. In [12], a strategy for the MC has been proposed to reduce the input harmonics under input voltage unbalance, which is founded on the detection of the reference angle for the input current vector. In [3], two input current modulation strategies have been presented for the MC controlled with the space-vector modulation technique under unbalanced input voltage conditions. The first strategy modulates instant by instant the input current vector in phase with the line-to-neutral voltage vector. The other strategy modulates the input current vector dynamically around the direction of line-to-neutral voltage. In [15], feed-forward and PI based compensation techniques have been presented to improve the output performance of the MC under abnormal conditions. In [8], control strategies eliminating the effect of symmetric supply voltage harmonics have been presented in a space-vector modulated three-phase indirect matrix converter. In [4], a method based on optimal use of zero vectors has been presented for minimizing output current distortion in matrix converter. The optimization of the switching pattern is established upon the graphical analysis of the loci described by the ripple of the current vector in the α–β reference frame.

In this paper, a novel compensation technique based on fuzzy logic controller (FLC) is proposed to eliminate the detrimental effects of the distorted input voltages for matrix converter controlled with Venturini modulation method. Since this technique improving the output performance of the MC performs closed loop control of the output current, three-phase output currents of the MC must be measured by using current sensors. The proposed method not only reduces the output harmonic contents but also ensures over-current protection and control for the load current [9]. Some numerical and simulation results are presented to prove the effectiveness of the proposed compensation technique.