Grid-connected boost-half-bridge photovoltaic micro inverter system using repetitive current control and maximum power point tracking

Abstract

This paper presents a novel boost-half-bridge micro inverter and its control implementations for single-phase grid-connected photovoltaic systems. The proposed topology consists of a transformer isolated boost-half-bridge DC-DC converter and a full-bridge pulse-width-modulated inverter. The boost-half-bridge converter integrates the conventional boost converter and the half-bridge converter by using only two active devices. The promising features such as circuit simplicity, low cost, high efficiency and high reliability are obtained. Moreover, a high performance plug-in repetitive controller is proposed to regulate the grid current. High power factor (> 0.99) and very low total harmonic distortions (0.9% ∼ 2.87%) are guaranteed under both heavy and light load conditions. Dynamic stiffness is also achieved under load step change conditions. In addition, a variable step size MPPT method is adopted such that fast tracking speed and high MPPT efficiency are both guaranteed. A 210W prototype was fabricated and tested. Simulation and experimental results are provided to verify the validity and performance of the circuit operations, current control and MPPT algorithm.