Novel Active Ripple Filtering Schemes Used In Little Box Inverter

Abstract:
Single-phase, full-bridge inverters inherently draw ripple current at twice the output frequency from its input DC bus. This introduces significant ripple on its DC bus voltage, and in the input DC source current. These are normally filtered out by placing a bulk capacitor in the DC bus, which affects the power density. Two novel schemes and control methods are presented, which help reduce the input ripple current considerably, while using a comparatively low-valued DC bus capacitor. These also help improve the power density and reliability of the inverter by reducing the size of the DC bus capacitor. Comparative analysis of the proposed schemes versus legacy schemes is presented. The proposed methods are verified by simulation and experimentation. The results show a significant reduction in peak-to peak ripple at the input. The concept was used and tested in the Little Box Challenge 2kW inverter prototype. Experimental results are given to verify the effectiveness of the proposed active filters and control methods.