Research On Voltage Synchronization Three-Phase Phase-Locked Loop Under Non-ideal Grid Conditions

With the depletion of traditional energy and the increasingly prominent enverionmental problem,the penetration rate of renewable energy to the power grid continues to increase.Renewable energy such as solar energy and wind energy have the characteristics of intermittence,fluctuation,and unpredictability,so it is difficult to generate electrical energy continuously,stably,and efficiently.Distributed generation(DG)is the main way for integrating renewable energy into the power grid,and phase-locked loop(PLL)is one of the key techniques to achieve grid-connected synchronous control.The voltage of non-ideal grid often affected by adverse factors such as frequency step,phase jump,imbalance,harmonic distortion and so on,and the performance of the PLL will directly affect the stability of DG system and output power quality.To this end,the reacher object of this paper is three-phase PLL,aiming to design a new PLL structure that meets non-ideal grid conditions,to achieve a precise and fast estimation of grid voltage frequency and phase.To research and design of new type of PLL,Synchronous Reference Frame PLL(SRF-PLL)is studied comprehensively in this paper,the dynamic and steady-state response characteristics of SRF-PLL is analyzed,the harmonic forms of three-phase input disturbance voltage in the different reference frame are determined,and the mutual limitation between filtering capability and response speed by simulation results are verified For the SRF-PLL can't precisely estimate the frequency and phase under voltage unbalance and harmonic distortion,to achieve accurately detect fimdamental positive sequence component,the separation methods of fundamental positive and negative sequence component under voltage unbalance is studied A crossing decoupling Double Complex Coefficient Filter(DCCF)is incorporated into SRF-PLL in a stationary reference frame that is an effective method to separate and extract the fundamental positive and negative sequence component.However,the complex coefficient filter is a band-pass filter,and its filtering capability is not well.An improved PLL based on crossing decoupling DCCF is suggested in this paper,the Multiple Variable Filter(MVF)with voltage amplitude non-attenuation and zero-phase shift characteristics is introduced in the front of crossing decoupling DCCF structure,and a new PLL structure is designed to enhance the filtering capability of PLL under harmonic distortion.At the same time,the small-signal model of new PLL is derived to design the parameter,and the effectiveness and robustness of new PLL are confirmed by simulation.In order to eliminate the influence voltage dc offset on PLL performance,and realize to the unbalanced voltage,even-order,and odd-order harmonics components high-efficiency filtering.Based on the study of the filtering principle and characteristic of Moving Average Filter(MAF)and Delay Signal Cancelation(DSC),and a design method of hybrid filters for PLL is proposed,in which ??DSC2 and MAF are used as out-loop and in-loop filters of designing PLL respectively.A feed-forward path is designed to compensate phase error caused by ??DSC2 when frequency drifts.The proposed PLL can estimate the frequency and phase of grid voltage fast and accurately while eliminating the disturbance of non-ideal grid To compensate phase delay caused by MAF of the designed PLL,a cascaded phase-lead compensator mothed is suggested,which significantly improves the response speed of the PLL system.In addition,the parameters are systematically optimized design based on the derived small signal model.Finlly,the feasibleness and effectiveness of the designed PLL are confirmed using simulation and numerical results.