Control Strategy Of Grid-connected PV Power System Based On Virtual Synchronous Generator

Photovoltaic (PV) power generation has some advantages, such as simple, not consuming fuel, no noise and pollution. The grid-connected PV power generation is becoming one of the most prospective new energy source, with rapid development and increasing grid-connected capacity. However, the PV power generation is greatly influenced by the environment condition, the PV power fluctuates seriously while the radiation changes fast and may result in some problems for the grid planning, operation and dispatching. Meanwhile, the voltage and frequency variation in the grid can also affect the power generation of PV, which undoubtedly restricts the development of large-scale PV power generation. To solve this problem, a control strategy of grid-connected PV power system based on Virtual Synchronous Generator(VSG) is proposed in this thesis, with which the output power of PV power generation is smoothed and the system can behave like a synchronous generator, adjusting its output power due to the voltage and frequency variation to stabilize the electricity grid.Firstly, the structure of grid-connected PV power generation is described, including BOOST converter and DC/AC inverter. Then the control strategies are described, including the Maximum Power Point Tracking (MPPT) control and the vector control of the inverter. The simulation work is presented at last.Secondly, the structure of the grid-connected PV power system based on VSG and the realization of the VSG control theory is described in detail, the explanation of the VSG modeling is given. Then, through in-depth analysis of the relationship between frequency and active power balance, voltage level and reactive power balance, the principles and design of the speed regulator and excitation controller are introduced.Thirdly, the model of this system is built using MATLAB/SIMULINK. The simulation results show the droop characteristics of VSG; the role of inertia is showed in simulation comparing droop control and control based on VSG. The simulation of the parallel operation of VSG is studied, including smoothing power of the PV generation and functioning as a synchronous generator to the grid.Finally, the hardware and software of battery storage are designed, and the hardware test platform is built. The experimental results demonstrate the output characteristics of the VSG and the role of inertia to the system response. The results verify the Correctness and feasibility of the control strategy.