Research On Phase Locking And Control Strategy Of Photovoltaic Inverter

Photovoltaic power generation,as a renewable new energy power generation method,has achieved rapid growth in the past few years with its advantages such as safety,reliability,energy conservation,environmental protection,and sustainability.As the basic interface of the grid-connected photovoltaic power generation system,the inverter converts the direct current generated by photovoltaic panels into alternating current synchronized with the power grid.It plays a key role in the entire photovoltaic power generation system.Based on a single-phase LC inverter,this paper focuses on the grid voltage lock-in technology and independent/grid-connected dual-mode steady-state control schemes involved in the grid-connected control of single-phase inverters.The main content of this article is summarized as follows:(1)Aiming at the voltage parameter sags and DC components in a single-phase power grid,an adaptive dimensionality reduction observer is designed to estimate the voltage frequency,phase angle,and amplitude information based on the adaptive observer theory.Compared with the existing grid-side voltage as a simple signal,this method treats the single-phase voltage signal as a parameterized system about unknown frequencies and DC amplitudes,and then uses an observer to estimate the parameters of the dynamic system.This method does not depend on the PLL and overcomes the shortcomings of the commonly used SOGI-PLL in terms of DC component and frequency adaptation.(2)Aiming at the single-phase LC grid-connected inverter studied in this paper,a current tracking control method based on state feedback output regulator is proposed.Firstly,a simplified mathematical model of a single-phase grid-connected inverter is established using the state space averaging method,and the required control algorithm is obtained by combining the theory of the output regulator.The mathematical derivation and the Bode diagram of the transfer function prove that the proposed method can achieve zero steady-state error tracking for sinusoidal signals.(3)In the independent working mode,the inverter control method adopts the voltage outer loop current inner loop control structure.A quasi-proportional resonance controller is selected as the regulator of the voltage loop,and the current loop uses the proposed state feedback output regulator as the control.method.Simulation and experiments verify that the inverter control method can track a given sinusoidal signal without static error,and independently supply power for local conventional loads;In grid-connected mode,the proposed adaptive dimensionality reduction observer is used to phase-lock the grid voltage to obtain the sinusoidal signal required for grid-connection.The output regulator is then used to control the filter inductance of the single-phase LC grid-connected inverter.To achieve grid-connected operation of the inverter.Simulation and experiments verify the control effect of the proposed inverter in the independent/grid-connected two operating modes.(4)Finally,the software and hardware of the single-phase grid-connected inverter experimental platform are designed,the method of selecting the system power circuit device parameters is given,and the design principles of the sampling circuit and the driving circuit are analyzed.The method of sampling and detecting voltage and current signals based on sigma-delta filter is briefly explained.The software part uses a modular programming method to build the system’s main program and interrupt subroutine.The experimental platform was used to verify and debug the above control algorithm under low voltage conditions.