A Capacitance-Minimized, Doubly Grounded Transformer less Photovoltaic Inverter With Inherent Active-Power Decoupling

Two major challenges in the transformerless photovoltaic (PV) inverters are the presence of common-mode leakage currents, and as in most single-phase converters the need for reliable and compact double-line-frequency power decoupling. In the proposed doubly grounded inverter topology with innovative active-power-decoupling approach, both of these issues are simultaneously addressed. The topology allows the PV negative terminal to be directly connected to the neutral, thereby eliminating the capacitive-coupled common-mode ground currents. The decoupling capacitance requirement is minimized by a dynamically variable dc-link with large voltage swing, allowing an all-film-capacitor implementation. Furthermore, the use of wide bandgap devices enables the converter operation at higher switching frequency, resulting in smaller magnetic components. The topology uses only four switches and potentially enables a high power density solution. The operating principles, design and optimization, and control methods are explained in detail, and compared with other transformer-less, active-decoupling topologies. A 3 kVA, 100/75 kHz single-phase hardware prototype at 400 V dc nominal input and 240 V ac output with a wide range of power factor has been developed using SiC MOSFETs with only 45 mu F/1100 V dc-link capacitance. Extensive experimental results from the prototype are presented to validate the concept, design, and superior performance of the proposed topology.