Research on High-frequency Resonance Mechanism and Active Harmonic Suppression Strategy of Power Systems with Power Electronics

Only one of the three Guangxi-side transmission lines of Luxi back-to-back asynchronous interconnection HVDC project between Yunnan Power Grid and the main grid of China Southern Power Grid is at work because of early faults in April 2017. And then there are harmonic components with a frequency of 1270 Hz appearing in the Guangxi-side bus voltage and output current. Affected by this harmonic component, the VSC-HVDC converter transformer tap changer of Luxi back-to-back asynchronous interconnection HVDC project is out of order because of frequent operation and therefore the VSC-HVDC unit is shut down. Firstly, this paper introduces the Luxi back-to-back asynchronous interconnection HVDC high-frequency resonance event and explains the resonance mechanism between MMC-based (Modular Multilevel Converter) VSC-HVDC and AC system. Secondly the harmonic impedance of MMC is calculated and the impedance analysis method is proposed to improve the control structure of MMC. Finally, through the PSCAD/EMTDC simulation, the phenomenon of resonance events is reproduced. Based on this the validity of the proposed method is proved and the harmonic current components are completely suppressed.