Modeling and Triple-Loop Control of ZVS Grid-Connected DC/AC Converters for Three-Phase Balanced Microinverter Application

This paper presents modeling and triple-loop control for a high-efficiency three-phase balanced inverter for using in grid-connected two-stage microinverter applications. An average signal model based on a synchronous rotation frame for a three-phase four-wire inverter has been developed. The inner current loop consists of a variable frequency bidirectional current mode (VFBCM) controller which regulates output filter inductor current thereby achieving ZVS, improved system response, and reduced grid current THD. Active damping of the LCL output filter using filter inductor current feedback is discussed along with small signal modeling of the proposed control method. Since the dc-link capacitor plays a critical role in two-stage microinverter applications, a dc-link controller is implemented outside of the two current control loops to keep the bus voltage constant. Finally, based on a two-stage 400-W prototype, simulation and experimental results are presented to verify the validity of the theoretical analysis, the effectiveness and feasibility of the proposed VFBCM control strategy.