Distributed Control Strategy Based on a Consensus Algorithm for the Inter-cell and Inter-cluster Voltage Balancing of a Cascaded H-Bridge Based STATCOM

Cascaded H-bridge converters are widely used in the implementation of medium voltage static synchronous compensators (STATCOMs). This is because of the advantages of relatively high-power density and the improved utilisation of low-voltage semiconductor devices. Major concerns with this topology are (i) to ensure a proper balance of the individual DC capacitor voltage in its cells, and (ii) the balancing of the average DC voltage between its clusters. In the research literature, these issues are typically addressed by using centralised control approaches, meaning that both an extensive processing capability and multiple digital outputs and communication channels for the switching signals are required, increasing system complexity. In contrast to this trend, in this paper, a distributed control scheme based on a consensus algorithm is proposed to deal with these issues in a three-phase STATCOM based on a cascaded H-bridge converter. The main advantages of the proposed control scheme are: (i) it does not require a centralised controller, since the cells work autonomously in a cooperative fashion to achieve voltage regulation, distributing the control effort among the cells, and (ii) it increases the fault tolerance of the converter and thus, the reliability of the system by adequately considering its redundancy. Extensive simulation work is provided to validate this proposal, and the characteristics described above.