Coordination control of positive and negative sequence voltages of cascaded H-bridge STATCOM operating under imbalanced grid voltage

摘要

When the grid voltage is imbalance, the current decoupling control strategy in d-q frame designed for the balanced system still let STATCOM output balanced voltage. In this case, the negative sequence component in the grid voltage may cause the device overcurrent. Here, the positive and negative sequence of grid voltage are separated first and that of the STATCOM output voltage is also controlled independently. However, how to determine and coordinate the positive and negative sequence voltage have not been effectively investigated yet. From the perspective of power balance, this paper gets the quantitative relationship between the phase shift angles of the positive and the negative sequence voltages. It also gets the quantitative relationship between the modulation ratios of the positive and the negative sequence voltages, and hence the effective coordination control strategy of positive and negative voltages of cascaded STATCOM operating under imbalanced grid voltage was developed. In addition, the phase of the positive and negative voltages, which is critical for the proposed coordination control strategy, can be obtained by the advanced open-loop phase synchronisation scheme. Finally, its detailed implementation was also provided. Simulation results show that the proposed method is correct and effective.