Study of three-phase converter with repetitive control

Since DC-link electrolytic capacitor mainly decides the lifetime of AC/DC/AC converter, it is significant to reduce its size or even cancel it. For the topology in which the rectifier part adopts diodes and the inverter part adopts controlled switches, the working modes of inverter under SPWM are analyzed. Three-phase output voltages are divided into six intervals and the relationship between power factor of load and energy feedback of each interval is deduced on the basis of SPWM characteristics and three-phase load currents waveform. The charge-discharge process of the capacitor in one cycle is analyzed and the method of calculating its smallest capacitance is given. As the DC outputs of rectifier is fluctuant when the DC-link capacitor is cancelled or reduced, the inverter can not apply standard SPWM. The way to remove the lower harmonics caused by DC ripple from output voltage is analyzed and it shows that, fine output voltage waveform can be obtained by applying repetitive control method. Matlab simulation verifies its validity and effectiveness.