A Study on High Power Density in Two-Stage Single-Phase Photovoltaic Systems Utilizing a HERIC Inverter

The Highly Efficient and Reliable Inverter Concept(HERIC) inverter is a transformerless topology with high power conversion efficiency and power density in photovoltaic(PV) system. The HERIC inverter reduces leakage current by electrically decoupling the DC and AC sides during the freewheeling period. The modulation scheme applied to the HERIC inverter affects its operating range, loss characteristics, and DC-link current characteristics. In this paper, modulation schemes for the HERIC inverter are reviewed in terms of leakage current characteristics and operating modes. The conduction and switching losses characteristics of the modulation schemes are then analyzed. Based on this analysis, an appropriate modulation scheme is determined with respect to high efficiency operation. In addition, the DC-link capacitor current characteristics are investigated to reduce the thermal stress imposed on the capacitor. Based on this analysis, a ripple current reduction method is proposed for a two-stage single-phase photovoltaic (PV) system to improve system reliability and power density. Consequently, this study contributes to achieving high power density operation in two-stage single-phase PV systems. The validity of the analytical results and the proposed method is verified through experiments.