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Individual DC Voltage Balancing Method at Zero Current Mode for Cascaded H-bridge Based Static Synchronous Compensator
Zezhou Yang*, Jianjun Sun, Shangsheng Li**, Zhiqiang Liao* and Xiaoming Zha*
Abstract Individual DC voltage balance problem is an inherent issue for cascaded H-bridge (CHB) based converter. When the CHB-based static synchronous compensator (STATCOM) is operating at zero current mode, the software-based individual DC voltage balancing control techniques may not work because of the infinitesimal output current. However, the different power losses of each cell would lead to the individual DC voltages unbalance. The uneven power losses on the local supplied cell-controllers (including the control circuit and drive circuit) would especially cause the divergence of individual DC voltages, due to their characteristic as constant power loads. To solve this problem, this paper proposes an adaptive voltage balancing module which is designed in the cell-controller board with small size and low cost circuits. It is controlled to make the power loss of the cell a constant resistance load, thus the DC voltages are balanced in zero current mode. Field test in a 10kV STATCOM confirms the performance of the proposed method.
Keyword Static Synchronous Compensator (STATCOM), FACTS, High voltage power converters, Multilevel converter, Voltage Source Converter (VSC), DC voltage control
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