Two-switch dual-buck grid-connected inverter

Renewable energy sources, such as solar energy and fuel cells, are desirable due to their pollution-free property. In order to utilize the present infrastructure of the utility grid for power transmission and distribution, grid-connected inverters are required for distributed generation systems and should have high reliability. However, shoot-through problem exists in the conventional bridge-type inverters, which is a major killer to the reliability of the inverters. A dual-buck half-bridge inverter (DBHBI) has been proposed to solve this problem, but the input-voltage utilization rate of the DBHBI is just half that of the full-bridge inverter. In addition, the voltage waveform before the output filter is bipolar, so weight and volume of the output filter is larger than that with unipolar modulation. In order to solve the above mentioned problems, this paper proposes a two-switch dual-buck grid-connected inverter. The freewheeling current flows through the independent diodes instead of the body diodes of the switches, so reverse recovery loss of diodes can be reduced. Half of the power devices operate in high frequency at each half line cycle, and the others switch at grid period and can realize zero-current switching (ZCS), thus the efficiency can be increased. Moreover, uniploar modulation is adopted, therefore, weight and volume of the output filter can be decreased. The input-voltage utilization rate of the proposed inverter is twice that of the DBHBI. Design guidelines and examples for hysteresis-band selection and LCL filter design are reported. The proposed inverter is globally stable with hysteretic current control and could be simplified to a current amplifier. Finally, simulation results verify the theoretical analysis and satisfy IEEE Std. 929-2000.