Control stability of inverters with series-compensated transmission lines: analysis and improvement

Abstract

With the rapid development of renewable energy, large amount of power need to be transmitted to loads centers and series-capacitor compensation (SCC) plays an important role in the renewable power transmission. However, it has been pointed out that SCC interacts with inverters and threatens system stability. This research investigates the influence of SCC on inverters control and proposes the strategies for enhancing system stability based on the instability mechanism. The impact of SCC on inverter current control and synchronization control is firstly analyzed. The current control model is established by system transfer function and the synchronization control model focusing on transient stability is established based on the traditional synchronous reference frame phase-locked loop (SRF-PLL). The bode and nonlinear analysis methods are respectively utilized in stability analysis of the current and synchronization control. It is found that SCC has little effect on inverter current control but affects synchronization control seriously. SCC reduces the stability range of synchronization control and causes system instability when there is a large frequency disturbance. In order to improve system stability, two approaches of optimizing the PI controller and designing a bandpass filter (BPF) inside PLL are then proposed. Finally, the simulations and experiments are presented to verify the correctness of theories.