Cascaded H-Bridge Low Capacitance Static Compensator With Modular Switched Capacitors

In this article, the effect of large double frequency capacitor voltage ripple (CVR) on harmonic performance, efficiency, and capacitor lifetime in the cascaded H-bridge low capacitance static reactive power compensator (StatCom) (LC-StatCom) is analytically determined. With insight provided by the analysis, an LC-StatCom with modular switched capacitors is proposed that provides a degree of freedom to control the CVR magnitude. The premise of the operation is to keep redundant capacitor modules in standby mode when operating with lower currents. In addition, it is shown that by distributing losses between additional dc-side switches and the main H-bridge switches, the proposed concept provides opportunities for choosing an optimal hybrid combination of semiconductor technologies. The proposed concept is evaluated using a simulated 8.5 MVA StatCom and feasibility of the proposed system is confirmed by experiments on a seven-level 0.8 kVA single-phase LC-StatCom prototype.