Grid-Connected Boost-Half-Bridge Photovoltaic Microinverter System Using Repetitive Current Control and Maximum Power Point Tracking

This paper presents a novel grid-connected boost-half-bridge photovoltaic (PV) microinverter system and its control implementations. In order to achieve low cost, easy control, high efficiency, and high reliability, a boost-half-bridge dc-dc converter using minimal devices is introduced to interface the low-voltage PV module. A full-bridge pulsewidth-modulated inverter is cascaded and injects synchronized sinusoidal current to the grid. Moreover, a plug-in repetitive current controller based on a fourth-order linear-phase IIR filter is proposed to regulate the grid current. High power factor and very low total harmonic distortions are guaranteed under both heavy load and light load conditions. Dynamic stiffness is achieved when load or solar irradiance is changing rapidly. In addition, the dynamic behavior of the boost-half-bridge dc-dc converter is analyzed; a customized maximum power point tracking (MPPT) method, which generates a ramp-changed PV voltage reference is developed accordingly. Variable step size is adopted such that fast tracking speed and high MPPT efficiency are both obtained. A 210 W 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.