Research On The Control Strategy Of Small Power Photovoltaic Grid-connected Inverter

Renewable green energy has been widely applied and promoted around the world relying on its own advantages.Judging from the development of the energy industry at home and abroad,whether or not Distributed Energy could become an emerging source of high-efficiency and high-quality energy depends on its research on grid-connected inverter control technology.When the inverter connects to the grid,it will be interfered by various factors which affect the normal operation of the grid greatly.Therefore,how to improve the dynamic control performance of the inverter and ensure power quality are particularly important.This thesis firstly establishes the mathematical model of the inverter with LCL filter circuit.The filter performance and parameter selection method of the LCL filter circuit are summarized.Because of existing resonant peak in the LCL filter circuit,which would affect the stability of the control system.Therefore,the thesis compares several damping methods and introduces classic inverter control strategies,including Multiple Proportional Resonant current feedback control method and Deviation Decouple Control method based on Disturbance Observer.Relying on good anti-interference performance and robustness,the Model Predictive Control is more suitable for controlling the grid-connected inverter than other controllers.In this context,this thesis proposes an advanced Model Predictive Control.On the basis of rolling optimization and feedback correction in the traditional Model Predictive Control,the predicted current of k+2 moment is brought into the objective function through the two-step prediction of the controller and the optimal solution sequence is obtained.This strategy could guarantee good dynamic stability when the load parameter and reference command current are changed.When the power system works normally,the grid frequency will deviate from50 Hz,which existing frequency fluctuation of ±0.5Hz.At this time,the traditional Repetitive Controller could not effectively control the grid-connected inverter.Therefore,the thesis optimizes the traditional Repetitive Control based on LCL grid-connected inverter and proposes an improved control method.Firstly,this strategy simplifies the mathematical model of the LCL grid-connected inverter in ??two-phase stationary coordinate system.The auxiliary repeat control branches are connected to the controller considering grid frequency deviation,and the weight coefficient of the auxiliary branches are designed according to the stability condition.The simulation and experiment shows that the improved control method has good control accuracy when existing frequency fluctuation.