A 5-Level HERIC Active-Clamped Inverter With Full Reactive Power Capability for Grid-Connected Applications

Distributed generation systems integrated into the modern electrical grid demand novel circuit architectures that can combine high efficiency and high power density together. The transformerless highly efficient and reliable inverter concept (HERIC) topologies are notable due to their mitigated leakage current concerns, constant common-mode voltage, and high efficiency. Nonetheless, the HERIC-based structures feature a maximum of three-level ac output voltage, forcing the conversion system to integrate large output filters to meet the grid codes. This article introduces a novel HERIC active-clamped converter with bidirectional power flow and full reactive power capabilities that can achieve five-level output voltage. This is accomplished by means of a phase-shifted pulsewidth modulation technique that effectively doubles the apparent switching frequency of the inverter and improves the quality of the injected ac power. Consequently, the topology can achieve higher power conversion efficiency, while using the same or a smaller output filter. To verify the feasibility of the proposed converter, a 2.5-kW SiC-based prototype was built and tested in the laboratory under different operation conditions.