Forced Oscillation Analysis of Voltage-Oriented Vector Control-Based PV Inverter Connected to Weak Power Grids

Synchronous reference frame-based vector control (SRF-VC) is widely adopted by single stage photovoltaic (PV) inverter to transfer powers into power grids. However, the overshoot effect and power coupling in SRF-VC, i.e., real and reactive powers coupling (RRPC), may cause oscillation amplification and forced oscillation issues when interharmonics of real power reference (P_ref) occur, which is induced by Maximum Power Point Tracking (MPPT) control. In this paper, a frequency domain analytical model is proposed to analyze the effect of overshoot and RRPC on forced oscillation when there is an oscillation source of P_ref induced by MPPT. Firstly, interharmonics of P_ref induced by MPPT is introduced, which can be the oscillation source of forced oscillation. Then, the power coupling mechanisms of SRF-VC are analyzed by visual phasor diagram, which is induced by slow dynamics of PLL in weak grids. Next, the frequency domain model considering RRPC channels are derived to analytically analyze its oscillation amplification characteristics when P_ref at sub/super-synchronous resonance frequency occur. Furthermore, forced oscillation magnitudes influenced by different control parameters are investigated by bode diagram of the proposed frequency domain model. Finally, the influences of overshoot and RRPC on forced oscillation are validated by the simulations and control-hardware-in-loop tests.