Modeling and control of a full-bridge modular multilevel STATCOM

Due to its unique topology, the Modular Multilevel STATCOM has many advantages but requires a sophisticated controller and puts higher requirements on simulation tools. To simulate the STATCOM in real-time is preferable because it enables hardware-in-the-loop test of the system in various scenarios including extreme fault conditions, which cannot be tested on a real STATCOM. This paper presents a model of full-bridge sub-module which enables fast offline and real-time simulation of the STATCOM. A control scheme with a new submodule capacitor voltage balancing method is also proposed in this paper. The model and the controller are investigated for different operating conditions. Implemented in a real-time simulator, the model can be simulated in real time at a time step of 20 μs, 131 times faster than its reference model. As demonstrated by the results, the proposed control scheme is effective and robust.