StatCom/BESS using a diode-clamped multilevel inverter

This dissertation, consisting of five papers, presents the results of research on the incorporation of battery energy storage system into a diode-clamped multilevel inverter based Static Synchronous Compensator (StatCom). The main contribution of the work with this dissertation is the practical application of multilevel inverter in StatCom/BESS and the development of the battery reduced structure for the StatCom/BESS.; The first paper introduces the StatCom/BESS based on a five-level diode-clamped inverter. According to the comparison in device rating, harmonics and losses, the multilevel inverter is proved to have advantages over the traditional six-pulse inverter in the high voltage applications. In the second paper, decoupled current PI control is proposed for the StatComBESS. Its behavior under a pre-defined reference step change in a one-bus system is examined. Compared with the linearization PI control, current PI control is superior in terms of response speed and robustness. The third paper compares the diode-clamped topology with the cascaded topology in structure, battery number, voltage and compensated power rating within the same system. The diode-clamped topology requires fewer batteries than the cascaded topology. A more attractive feature of the diode-clamped topology is the feasibility of battery reduction. The fourth paper is focused on the oscillation damping control of the StatCom and StatCom/BESS in a single-machine infinite-bus system. With the active power injection, StatCom/BESS improves the transmission capability and the system dynamic and transient stability. In the fifth paper, StatCom/BESS with reduced battery structure is introduced for the power damping application. The five-level inverter based StatCom/2 BESS is compared with the StatCom/4 BESS and StatCom in the dynamic control performance. Both the analytical results and the simulation results show that with the reduced battery set, StatCom/BESS can still improve the system transient stability and offer effective damping control.