Common-Mode Voltage Characteristics of Matrix Converter According to PWM Method

Abstract

The matrix converter (MxC) is an ac-to-ac conversion device that can generate variable magnitude variable frequency output voltage. Nine bi-directional switches of MxC allow PWM control of output voltages and input currents. PWM switching needs “switch commutations” from one switch to another. During the switch commutations, however, unwanted voltage error occurs similar to the dead time effects in Voltage Source Inverter (VSI). When PWM pulse width is narrower than the time required for the commutation, voltage error increases rapidly. This voltage distortion is critical in the low speed operation as system becomes sensitive to even a small voltage error. In this paper, a new PWM strategy is proposed for improving voltage control performance in the low voltage region. Based on the input and output voltage information, PWM pulse-widths are controlled to avoid incomplete commutations. The feasibility of the proposed method is proved by simulation and experimental results. In addition, common mode voltage characteristics of MxC are discussed. Common-mode voltage and dv/dt cause motor bearing and ground leakage currents through the parasitic capacitances. Leakage current creates noise problems that can interfere with other equipment. Common-mode voltage characteristics of MxC are presented and discussed using two PWM methods. Simulated and experimental results are presented. Common-mode voltage of two-level VSI and MxC are also compared.