Novel three-phase phase-locked loop design for microgrid inverter based on harmonic detection technology

As a key component in distributed generation systems, the inverter synchronization unit (Phase-Locked Loop, PLL) is critical for stable control system output. Under grid unbalanced conditions, the traditional Synchronous Reference Frame PLL(SRF-PLL) fails to lock phase accurately. Existing improved schemes integrating filters into PLLs suppress unbalanced interference but reduce bandwidth, degrade dynamic response (prolonging phase-locking time), and face challenging filter parameter tuning under diverse conditions. Additionally, frequency, as the derivative of phase angle, is significantly affected by phase changes. To address these issues, this paper introduces the Triple Fundamental Frequency concept for three-phase systems, proposing a novel orthogonal signal generation method and a corresponding Triple Fundamental Frequency PLL architecture, enabling stable frequency output. To further improve the performance of the phase - locked loop, a harmonic quantization method is integrated to quantify and offset harmonic impacts on the PLL by subtracting quantified data from dynamic outputs. Leveraging triple frequency advantages, this method markedly enhances system dynamic response. Simulation experiments verify the superiority of the proposed harmonic quantization triple fundamental frequency PLL in dynamic response.