Notch filter constraints analysis and SPLL design under unbalanced voltage conditions

When the network voltage is unbalanced, reactive component under synchronous rotating coordinate system will contain twice frequency AC component, which influences phase-locked precision. In order to accurately lock phase, notch filter is added to the Soft Phase-locked Loop(SPLL). This paper focuses on the research of the PLL system containing notch filter. Based on the consideration of stability and rapidity, not only the regulator paramenter design but also the contraints of notch filter quatity factor(Q-factor) is analyzed. The two different approximate treatments, low frequency band reduced-order approximate treatment(LFBROAT) and high frequency band reduced-order approximate treatment(HFBROAT), is adopted to analyze the notch filter, it is obtained that HFBROAT can guarantee the stability of the system finally. Through the modeling of SPLL containing notch filter, not only the regulator paramenter design mothod but also the contraints of notch filter Q-factor is obtained, thereby it is ensured that the system has good dynamic and static performance.Through modeling of SPLL contained notch filter, the regulator parameter design method and the constraints of notch filter Q-factor are obtained, and thereby ensure that the system has good dynamic and static performance. The results of simulation and experimental verify the feasibility and correctness of the theoretical analysis and design.