Bimodal Transformerless Inverter With Three Switches

The semi-Z-source inverter with least switch count (only two switches) eliminates the leakage current due to the doubly grounded structure. However, the main disadvantage is the high voltage stresses of the switches (the sum of double PV output voltages and the amplitude grid voltage). This paper proposed an improved inverter based on the SZSI. It inherits the advantage of the less leakage current and owns other merit of lower switch voltage stresses. Besides, the operation of the proposed inverter is bimodal and only two switches operate at high frequency in each mode. Firstly, the circuit structure and the operation principle are introduced in detail. Then, the grid current controllers in both modes are designed. Two comparisons are investigated for better clarification of the pros and cons of the proposed inverter. Finally, experimental results, obtained with a 500-W laboratory prototype are presented to validate its performance.