High efficiency current mode control for three-phase micro-inverters

Three-phase micro-inverters are critical to the success of AC modules in Mega Watt PV farms. A high performance micro-inverter must have high power density, high reliability, and low cost. Boundary Current Mode (BCM), Variable Hysteresis Current Mode (VHCM), and Constant Hysteresis Current Mode (CHCM) are derived from a proposed softswitching current mode control scheme which is based on the general half-bridge three-phase inverter topology. The frequency range and switch losses are compared and discussed. The VHCM has the highest efficiency at over 97.6%, while the CHCM has the narrowest frequency range. A hybrid control platform combining analog and logic units with DSP was designed and built to achieve the high-speed peak current control. A high frequency, high efficiency, and high power density micro-inverter was built for experimentation. The experimental results verify that the proposed control scheme is a promising solution for high performance three-phase micro-inverters.