Study On Resonance Suppression And Phase Lock Method For Photovoltaic Grid-connected Inverter With LCL Filter

In recent years, countries have increased the development and utilization of solar,wind, geothermal, tidal and other new energy. However，direct current emitted bydistributed generation can not be directly supplied to the grid and AC load, grid interfacedevice must be used before connecting to the grid. Usually the current controlled voltagesource type inverter is popular with photovoltaic (PV) grid-connected system. The LCLfilter is widely used in grid-connected inverter, but its structure determines that it willproduce resonance peak，which will make THD of the grid-connected current rise，even itcan not meet the grid conditions. Therefore, measures must be taken to suppress theresonance to ensure the quality of grid current. Besides, we also need to ensure that thegrid current and grid voltage with the same frequency and phase, it is very important tostudy the synchronization phase-locked technology. How to realize the resonancesuppression and synchronization phase-locked technology on photovoltaic grid-connectedinverter has become the research focus of this thesis.This thesis analyzes the mathematic model of photovoltaic cell, and establishes astrong commonality of PV cell simulation model. And then studies its properties and P&Omethod based on simulations. LCL type photovoltaic grid inverter model is also built andthe parameters of the LCL filter is designed in detail, these lay the foundations for thestudy of photovoltaic grid-connected inverter running.In this paper，the basic principles of SVPWM algorithm and PQ control method ongrid-connected operation are introduced, their respective models for simulation areestablished, which provide control methods for parallel operation and the simulationresults prove the correctness of these two control models.In view of the resonance problem produced by LCL filter, this thesis analyzes thecapacitor branch series resistance of the passive damping method and capacitive currentfeedback active damping method. The simulation results show the two damping methodsboth have a measurable effect on resonance suppression from grid current waveformquality and harmonic spectrum. Active/passive damping dual mode control method is adopted when the inverter power changes, verifying the switching process throughsimulation, achieving smooth transition and grid current THD conforms to the gridconditions, which verifies that the scheme is valid.The structure and working principle of SSRF SPLL are analyzed，the simulationresults suggest SSRF SPLL phase locking in poor performance under grid voltageamplitude unbalance and single-phase grounding fault. And then establish the decouplingmodel according to the the DDSRF SPLL thoughts. The simulation results show that thisstructure can suppress the power grid voltage amplitude unbalance and single-phasegrounding fault disturbance. Through theoretical analysis, when PI control algorithm isadopted, the phase difference between grid-connected current and grid voltage is producedinevitably. A novel phase compensation method is purposed in this thesis, it solves thephase difference problem and ensures unit power factor grid-connected, this schememodel is established, the simulation result proves the validity of the phase compensationmethod.