Reduction of DC-bus voltage ripples and capacitors for single-phase PWM-controlled rectifiers

The problem of voltage/current ripples is a primary concern for DC systems, e.g. those with fuel cells and batteries. It could seriously deteriorate the system performance on both the source side and the load side. In this paper, a single-phase PWM-controlled rectifier is taken as an example to analyse the ripple energy that causes the voltage ripples on the DC bus. Moreover, a ripple-current compensator is proposed to absorb/inject ripple energy from/to the DC bus so that the voltage ripples are reduced actively. The compensator is a boost/buck converter with an auxiliary capacitor having a voltage higher than the DC-bus voltage. A repetitive controller is then proposed to compensate the ripple energy on the DC bus instantaneously, with a fixed switching frequency. Simulation results are presented to demonstrate that the proposed strategy is able to reduce the voltage ripples on the DC bus considerably. As a result, the DC-bus capacitor can be reduced significantly in order to achieve the same level of voltage ripples.