An improvement of neutral-point balancing algorithm of STATCOM

Utilizing User-Defined (UD) modeling function of Electromagnetic Transient Simulator for DC and AC Power System (ETSDAC) in Advanced Digital Power System Simulator (ADPSS), this paper establishes an STATic synchronous COMpensator (STATCOM) model based on three-level inverter, whose function is the same as the STATCOM model in Electro-Magnetic Transients Program (EMTP). Neutral-point balancing algorithm used in this STATCOM model is using two-level modulation scheme for some phase when unbalance exits. After pointing out disadvantages of this algorithm, namely: problems caused by switch devices in series, this paper proposes a new neutral-point balancing algorithm, three-level voltage deviation between two capacitors hysteresis-band control algorithm. The neutral-point will be balanced by PWM control according to the state of voltage deviation between two capacitors and the direction of neutral-point current. Using this algorithm, an STATCOM model in ADPSS is established and simulated. The simulation results indicate the improvement of neutral-point balancing algorithm of STATCOM is feasible and effective.