Power Decoupling Strategy for Voltage Modulated Direct Power Control of Voltage Source Inverters Connected to Weak Grids

The grid voltage modulated direct power control (GVM-DPC)-based inverter is an attractive solution to regulate the instantaneous real and reactive powers injected into power grids. However, the power coupling in GVM-DPC, i.e., interactions between the real and reactive power loops, may deteriorate its transient performance. In this paper, a power decoupling strategy for GVM-DPC is proposed based on a dynamic feedforward power compensation (DFPC) algorithm. It is proved that the proposed strategy has better decoupling performance than that of the traditional virtual impedance method (VIM). Firstly, power coupling characteristics in GVM-DPC are analyzed, indicating that the ignorance of voltage angle variation at the point of common coupling (PCC) will result in severe power coupling. Then, power coupling magnitudes are derived according to relationships among the real power, reactive power and PCC voltage. Next, the coupling magnitudes are compensated into the power control loop of the GVM-DPC for the better decoupling performance. The transient performance of inverter using DFPC is studied based on the impedance analysis. Also, the relationship between coupling magnitude and grid side impedance is studied, which indicates the limited power decoupling capability of VIM. Finally, the proposed method is validated by the simulations and a hardware-in-loop system.