Hybrid communication topology and protocol for distributed-controlled cascade H-bridge multilevel STATCOM

Distributed control scheme is preferred in the application of the multiple modules based system due to its simple structure, low maintenance and high scalability. This paper proposed a hybrid communication topology and protocol to realize the distributed control applied in the cascade H-bridge (CHB) multilevel static synchronous compensator (STATCOM) with master and slave controllers. In the same layer of the three-phase modules, the three slave controllers communicate with the master controller by the fundamental ring loop. In different layers of the three-phase modules, communication loops operate in parallel. In order to avoid the slow real-time response of the traditional ring communication structure which is not adaptive to power electronic facilities, this paper proposed a routing switching protocol. By switching the communication between the modified control data and fault signals, the protocol can achieve both quick control and fault response. Moreover, the synchronization among different modules are also dealt with by the proposed protocol. The topology and protocol are evaluated in the FPGA based control platform and the CHB multilevel STATCOM prototype. The experimental results verified the validity, flexibility and reliability of the proposed topology and protocol.