Analysis and Countermeasures of Harmonic Instability in a Practical HVDC System With Fixed Series Compensation and STATCOM

In a practical +/- 500 kV/3000 MW line commutated converter-based high-voltage DC (LCC-HVDC) transmission system, a sustained 5.5/105.5 Hz harmonic is observed in the inverter station bus voltage, which results in a power limit because of AC filter resistance harmonic overload protection action. To study this phenomenon and find a solution, a real-time digital and physical closed-loop simulation platform based on RTDS is established and the harmonic instability phenomenon is reproduced. Then, the harmonic instability phenomenon mechanism and impact factors are analyzed based on real-time simulation results. The simulation results show that series resonance and core saturation are the main reasons for the observed harmonic. Unstable harmonic interactions between AC and DC networks result in sustained harmonics. A temporary countermeasure of bypassing the series capacitor is proposed and verified by the field test. To solve the problem thoroughly, a supplementary harmonic damping controller (SHDC) based on a static synchronous compensator (STATCOM) is designed and verified by simulation tests