Study On Detection Method Of Power Synchronization Signal Under Complex Operating Conditions

In the 21 st century,the problem of energy shortage and environmental pollution is becoming more and more serious.How to make better use of distributed energy generation and integrate it into the power grid has attracted more and more attention.Distributed Power Generation System realizes the organic connection with the distribution network through the inverter,and the premise of grid-connection is to ensure that the current output by the inverter and the distribution network voltage are in the same frequency and phase.Especially in the non ideal condition,it is very important to inject positive sequence fundamental current into the distribution network to support the grid and realize effective grid connection.Whether the inverter can accurately obtain the positive sequence signal of the voltage fundamental wave of the distribution network has a great impact on the output control of the grid connected inverter,so it is necessary to find an efficient and feasible synchronous signal detection method to quickly and accurately extract the synchronous information of the grid.In order to ensure the safe and reliable integration of the inverter into the distribution network,this paper studies the detection method of synchronous signal under the unbalanced power grid,including DC component and multiple harmonics.Firstly,the existing classical synchronous signal detection methods are analyzed theoretically,and then a phase-locking method(MVF-ANF-PLL)based on multivariable filter(MVF)and adaptive notch(ANF)is proposed to deal with the unbalanced and multiple harmonics of the power grid.This proposed PLL scheme eliminates the harmonic components existing in the distorted grid through MVF in the static coordinate system,and employs the two orthogonal outputs of ANF to cancel out the double frequency oscillations in d-q axes components of grid voltage caused by negative sequence component.In this way,the influence of grid voltage distortion and imbalance on the extraction of synchronization signals are eliminated.Simulation and experiments have verified the rationality of the method.Then aiming at the problem of DC bias in power grid,the improved dual adaptive notch filter PLL(IDANF-PLL)which can eliminate DC bias and suppress voltage imbalance in power grid is obtained by improving ANF,and the IDANF and MVF are added to the SRF-PLL,and a phase-locking method IDANF-MVF-PLL based on an improved dual adaptive notch and multivariable filter is proposed.The accurate acquisition of grid voltage synchronization information is realized,and it is verified by simulation and experiment.Finally,according to the characteristics of the empirical mode decomposition(EEMD)and the maximum correlation coefficient method,a new non phase-locked loop synchronous signal detection method based on EEMD is proposed.In this method,EEMD is used to decompose the input voltage signal into finite intrinsic mode functions(IMF),and then the maximum correlation coefficient method is used to extract the positive sequence fundamental frequency of the grid voltage,which does not need the harmonic filtering module or the positive and negative sequence separation,simplifying the phase-locked structure.Theoretical and experimental results show that the proposed method can accurately collect the voltage synchronization information of the grid under complex conditions such as three-phase voltage imbalance,sudden change in phase or frequency,harmonic and DC components.