Bimodal Transformerless Inverter With Three Switches

The semi-Z-source inverter (SZSI) 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 photovoltaic output voltages and the grid voltage amplitude). This article proposed an improved inverter based on the SZSI. It inherits the advantage of less leakage current and owns another merit of lower switch voltage stress. Besides, the operation principle of the proposed inverter is bimodal and only two switches operate at high frequency in each mode. First, 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.