Stability analysis and admittance reshaping for PQ inverters with different power control methods

Abstract

PQ inverters possess the advantage of flexible control of power injection. However, the system stability of PQ inverters is affected by different power control methods. Thus, this paper delves into the system stability of PQ inverters with different power control methods under weak grid. Firstly, there are two kinds of PQ inverters with power control, namely the power control loop (PCL) inverter and the reference current calculation (RCC) inverter. Analysis results show that compared with the PCL method, the inverter using the RCC method can eliminate the control loop, but it will reduce the stability under weak grid. Next, the paper explores the influence of inverter system parameters on the stability margin of PQ inverters, providing detailed guidance for the parameter design of PQ inverters. In addition, in order to improve the system stability of inverters controlled by RCC under weak grid, an admittance shaping strategy is proposed through adding an additional current feedback path. This strategy can increase the amplitude of the inverter output admittance in the mid to high frequency range, thereby significantly improving the stability of the inverter system under weak grid. By adopting this strategy, the stability of grid connected inverters controlled by RCC under weak grid can be comparable to that of those controlled by PCL. Additionally, this strategy is easy to implement and has minimal impact on the transient response of the system. Finally, experimental tests have verified the correctness of the theoretical analysis in the paper.

Keywords

• PQ inverters
• Power control
• Stability analysis
• Admittance modeling
• Admittance reshaping
• Weak grid