A novel control strategy based on notch filter for four-leg STATCOM

The STATCOM based on four-leg voltage source converter can compensates the negative sequence currents and neutral currents of unbalanced loads. When the STATCOM is compensating the unbalanced loads, the DC side capacitor of the STATCOM is used to absorb and release the unbalanced power. In this case, the DC side voltage of the STATCOM will contain second harmonic wave. In traditional STATCOM control system, one of the control targets is DC side voltage stabilization. The second harmonic wave in DC side voltage will be compensated and it will counteract the unbalanced power absorbing and releasing. It will result in the unbalanced load compensation failure. In this paper, a novel control strategy based on notch filter for four-leg STATCOM is presented. The notch filter smooth the DC side voltage and the control system used the result as the input of voltage control loop. The control loop stabilize the DC sequence of the DC side voltage instead of the real time DC side voltage. With the novel control strategy, the control system can compensate the unbalanced load and stabilize the DC side voltage in the same time. Results of Simulation analysis and prototype experiment show that: with the novel control strategy, the unbalanced load current can be compensated more effectively and the third harmonic currents of the power supply is reduced. The Simulation and experimental results demonstrate that the proposed control strategy based on notch filter for the four-leg STATCOM is effective.