Common-Mode Ripple Current Estimator for Parallel Three-Phase Inverters

A common-mode circulating-current controller of the parallel-inverter-system with discontinuous PWM technique that can control the follower-inverter to follow the three-phase modulation waveforms of the master-inverter and reject disturbances by means of hysteresis-control method. In this paper, an analysis method of the common-mode ripple voltage is proposed and consequently a common-mode ripple current estimator is developed based on the proposed analysis method. The proposed estimator guides the circulating-current controller to minimize its hysteresis-width setting and therefore minimize the common-mode circulating-current. The experimental results are presented in this paper to validate the theoretical analysis of the common-mode ripple voltage.