Capacitor-voltage-balancing control for isolated medium-voltage AC-DC modular matrix converter

This paper presents a capacitor-voltage-balancing control scheme for an isolated medium-voltage AC-DC converter using level-shifted pulse width modulation (PWM) control of a modular matrix converter (MMxC). The proposed isolated AC-DC converter is composed of the primary MMxC with level-shifted PWMcontrol, high-frequency transformer, and secondary H-bridge circuits. The high-frequency transformer of the proposed circuit can be downsized because the level-shifted PWM control scheme makes the rated frequency of the high-frequency transformer equal to the switching-frequency. The proposed capacitor-voltage-balancing control can compensate for the capacitor voltage imbalance of the MMxC using the positive-sequence and negative-sequence circulating-currents with a power supply frequency and high-frequency voltage. In the proposed control system, the three feedback control systems with DC control variables can be developed to compensate for the capacitor voltage imbalance. The effectiveness of the proposed capacitor-voltage-balancing control scheme and the control systems is verified by experiments using a 200 V, 5-kW laboratory prototype.