Analysis and Suppression Strategy of Synchronous Frequency Resonance for Grid-Connected Converters With Power-Synchronous Control Method

The power-synchronization control (PSC) method of grid-connected converters, which is based on the active power orientation, is a promising solution for high-penetration renewable power generation systems. Unfortunately, synchronous frequency resonance (SFR) is inevitably found in PSC-controlled converters, especially when connected to inductive networks, which seriously damages the stability of the system. The relatively small equivalent resistance of the inductive network is regarded as the main cause of SFR, and a virtual resistor (VR) is usually employed to dampen this kind of oscillation. However, another important reason for SFR is the nonminimum phase effect of the loop gains, which is discussed in this article. Considering the dynamics of the grid equivalent inductance, the small-signal model of PSC-controlled converter is established. By this, the mechanism of SFR and the nonminimum phase effect are revealed. Furthermore, a conjugate poles elimination control method based on auxiliary branches introduced into the power control loops is proposed to suppress SFR, which can also broaden the control bandwidth compared with the VR method. Finally, the theoretical analysis is verified by simulations and hardware-in-loop experimental results.