A Decentralized Master-Slave Method for Three-Phase Cascaded H-Bridge System

For the cascaded H-bridge system, the existing decentralized methods are mainly focused on single-phase systems. Designing a decentralized method for the three-phase cascaded H-bridge system is more challenging, particularly, for achieving phase-to-phase frequency synchronization and three-phase voltage balance without real-time communication among each distributed generation (DG). To achieve this, this article proposes a decentralized master-slave method for three-phase cascaded H-bridge systems, where no communication is required for each local control unit of DGs. The overall control is divided into two parts. One part is for the master DG to realize phase synchronization among phases A, B, and C, which is designed by modifying the power factor angle through droop control. The other part is for slave DGs to achieve frequency synchronization of the modules in each phase, which adopts the power factor angle droop control. Small signal stability analysis based on fast and slow time scale separation is carried out for the proposed method. Last, the control-hardware-in-loop tests and experimental results prove the effectiveness of the proposed method.