Zero-Sequence-Voltage Injection Based on Square-Wave to Balance Cluster Voltages for Star-Connected Cascaded STATCOM
Lu Daorong1, Wei Miaoyu1, Yu Yu1, Zhang Yuming2, Hu Haibing1
1. College of Automation Engineering Nanjing University of Aeronautics and Astronautics Nanjing 211100 China; 2. Zhejiang Huazheng Inspection & Testing Co. Ltd Jinhua 321002 China
Abstract：When star-connected cascaded H-bridge STATCOM compensates for the negative sequence current, the active power among clusters will be unbalanced, which will cause unbalanced cluster voltage. To maintain cluster voltage balance, zero sequence voltage is usually injected to redistribute the three-phase active power. However, the traditional calculation algorithms of the zero-sequence voltage are generally derived from the model based on active power, the equations are complicated and the mathematical mechanism is unclear. In addition, the injection of zero sequence voltage will greatly increase the output voltage of STATCOM, thus limiting the compensation range of the negative sequence current. This paper explores the geometric mechanism between zero sequence voltage and other electrical quantities with the help of voltage phasor diagrams, and proposes a special method for solving zero sequence voltage. To extend the range of the negative sequence current, this paper also studies a zero-sequence voltage injection method in the form of a square wave to improve the DC side voltage utilization of STATCOM. Finally, 10kV/±1Mvar star CHB STATCOM simulation platform and 400V/±7.5kvar experimental testbench verify the proposed control method.
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2022, Vol. 37 
