Impedance Modeling and Resonance Suppression Method for Current Source VSG Under Weak Grid Conditions

다국어 초록 (Multilingual Abstract)

A large proportion of renewable energy is integrated into power system, resulting in the gradual electrifi cation of the power system and appearing the characteristics of a weak power grid. Under weak grid, current source virtual synchronous generator (VSG) is prone to resonance. To ensure stable and uninterrupted operation of renewable energy through power electronic devices connected to grid, this paper proposes a composite control method based on grid voltage feedforward (GVF) and q-axis impedance reshaping (QAIR) for current source VSG converter resonance suppression. Firstly, sequence impedance modeling (SIM) and stability analysis are conducted on current source VSG converter. Under weak grid, the negative resistance eff ect caused by phase-locked loop (PLL) in the low frequency range makes system unstable in grid connection.
To eliminate the negative resistance instability caused by PLL, a current source VSG GVF control resonance suppression method is established. SIM of this method and stability analysis are conducted. Secondly, a QAIR resonance suppression method for current source VSG converter is established. SIM of the method is conducted and stability analyzed. On the basis of above two methods, a composite resonance suppression method based on GVF and QAIR is established, and SIM and stability analysis are conducted. Simulation and experimental tests are conducted on the stability of GVF, QAIR, and GVF + QAIR composite resonance suppression current type VSG systems. The test results showed that the method based on GVF + QAIR resonance suppression is more eff ective, compared to GVF/QAIR resonance suppression method. Under weak grid, it has better ability to eliminate negative resistance eff ects and harmonic suppression caused by PLL, further improving grid-connected stability.