DC ripple current reduction on multilevel, multiport, single-phase DC/AC converter for renewable energy applications

This paper presents a new approach for DC-link 120 Hz ripple power cancellation in single-phase DC/AC converter for renewable energy applications. The converter utilizes the superior features of the switched capacitor circuit and the gallium nitride devices to achieve high efficiency and power density. The system has two-port, the first acts as a pure capacitor and can achieve continuous variable ac capacitor 0 ~ C_ac to absorb the 120 Hz dc ripple power whereas the second port is designed to be the output. A small size DC-link capacitor can be achieved through adjusting the phase angle between the two-ac port voltages of the converter to cancel the second-order frequency. The theoretical analysis confirms that the 2ω component can be entirely eliminated from the system and a 2 kW prototype is built to verify the circuit analysis. Comparing to the conventional H-bridge converter, the ac capacitance can be reduced by 80 times.