A Low-Cost Single-Stage PV Inverter

This paper presents a low-cost single-stage PV inverter which integrates a front-end buck-boost converter and an output unfolding dc-ac inverter. It utilize only one main active switch (IGBT, MOSFET etc.) to regulate the output current and performs maximum power point tracking (MPPT) at the PV side. The buck-boost converter is operated in discontinuous current mode (DCM), which allows low cost, reliable, and efficient thyristor to be used in the inverter under natural commutation. An auxiliary circuit is also implemented to provide zero-voltage-switching (ZVS) condition for the main switch. As a result, the switching loss in the converter is minimized and high efficiency can be obtained. Moreover, the current source nature of the converter eliminates the intermediate dc bus capacitor and significantly reduces the need for output filtering inductors, leading to high power density. The concept is validated by test results, however false triggering was observed in experiment. The issue is described and analyzed in details, showing that the state-of-the-art thyristor technology has intrinsic limitation for reliable high frequency operation.