Improvement of output voltage control performance for low-speed operation of matrix converter

The matrix converter (MxC) is an ac-to-ac conversion device that can generate variable frequency and variable voltage output. The nine bidirectional switches of an MxC allow pulse-width modulation (PWM) control of input currents and output voltages. PWM switches need 'switch commutations' from one switch to another. During these switch commutations, however, unwanted voltage error occurs like a dead time effect in a voltage source inverter (VSI). When PWM pulse-widths are narrower than the time for completing a commutation sequence, voltage error rapidly increases. In the low-speed range, PWM pulses become narrower and voltage distortions become larger due to incomplete commutations. Moreover, these errors are critical in the low-speed operation because the system is sensitive to the smallest voltage error. In this paper, a new PWM strategy is proposed for improving voltage control performance in the low-speed range. Based on the input and output voltage information, PWM pulse-widths are controlled to avoid incomplete commutation. The feasibility of the proposed method is proved through simulation and experimental results. Index Terms--AC machine, inverter, matrix converter (MxC), pulse-width modulation (PWM) control.