Zero Leakage Current Single-Phase Quasi-Single-Stage Transformerless PV Inverter With Unipolar SPWM

Power inverters for distributed photovoltaic (PV) power generation systems usually need to fulfill several requirements, e.g., the safety, the voltage boost capability, and the reduced volume and the cost. An improved transformerless single-phase quasi-single-stage common-mode PV inverter with four switches and an improved unipolar modulation strategy are proposed in this article. The inverter features double-grounded to solve potential safety issues caused by the leakage current. In addition, its voltage boosting is accomplished by a quasi- single-stage conversion structure so that PV system efficiency can be improved. Meanwhile, it benefits continuous input current so is suitable for PV application. In this article, the operation principle of the proposed inverter, the improved modulation strategy, and two grid-tied control strategies are introduced. The voltage and current stresses of the components are analyzed, and parameter design guideline is further given. Both the off-grid and grid-tied experiments were conducted to verify the theoretical analysis.