Research on STATCOM DC side capacitor voltage stratified control strategy

The Static Synchronous Compensator (STATCOM) has the advantages of fast response, small footprint, and high compensation accuracy in reactive power compensation and it is widely used in low voltage distribution networks. This paper mainly studies the DC-side capacitor voltage control. For the DC side capacitor voltage control, a layered control strategy is applied in this paper. The first layer control is the overall DC side capacitor voltage control, and the second layer control is the phase-to-phase DC side voltage equalization control. In the overall DC-side voltage control, the second-harmonic pollution caused by the second-harmonic component is suppressed by adding filter links in the feedback channel. This control strategy only exchange the positive sequence active components in the power grid and will not cause pollution to the grid. For the phase-to-phase DC-side voltage equalization control, this paper proposes a voltage equalization control method based on zero-sequence injection voltage. The zero-sequence voltage components is also discussed, which need to be injected when the grid voltage is balanced and unbalanced. The layered control strategy proposed in this paper will not inject negative sequence and harmonic components into the grid and avoid pollution to the grid during the compensation process.