Research On Power Grid Stability Control Strategy Based On Virtual Synchronous Generator

With the development and utilization of clean energy such as solar energy and wind energy,the development of distributed power has reached an unprecedented level.Distributed power depends on a three-phase grid-connected inverter connected to the AC bus and can be connected to a large power grid to cooperate with the inverter.The control strategy of the device,the distributed power supply can continue to contribute.However,although the inverter as a power electronic device has a good regulation effect,it cannot provide a certain inertial support for the power grid like a traditional synchronous generator,and it is difficult to maintain a stable operation of the power grid.Virtual synchronous generator(Virtual Synchronous Generator,VSG)technology is a control technology for three-phase inverters,through the corresponding virtual synchronous control strategy to achieve the synchronous generator of distributed power,increase the damping and inertia of distributed power to better adapt to load fluctuations.In this paper,the microgrid system composed of distributed photovoltaic and distributed wind power as the power source is taken as the research object.Based on the traditional three-phase inverter control method,a virtual synchronous generator control strategy is added,and the corresponding dynamic power characteristics of the photovoltaic power source are introduced.The source-side control of the distributed photovoltaic virtual synchronous generator has a certain reserve capacity,combined with the load shedding control strategy,the distributed wind power generation has a certain primary frequency modulation capability.The virtual synchronous generator control is to adjust the rotor motion and operating characteristics of the virtual synchronous generator through the adjustment of the three-phase grid-connected inverter,when the system is greatly disturbed,it will also appear as a transient process like a synchronous generator.Without certain control,the virtual rotor angle of the virtual synchronous generator may continue to increase and lose the stability of synchronous operation.The thesis mainly does the following work: First,according to the operation principle of the synchronous machine,I designed more stable virtual rotor control,virtual governor control,virtual exciter control,and overall control structure.Then the power point conversion control with backup capacity of the inverter photovoltaic source is analyzed in combination with the dynamic characteristics of the photovoltaic power source.Finally,the feasibility of the control strategy is verified under specific working conditions through simulation software.Secondly,based on the current vector control method of the rotor side converter of the doubly-fed wind generator,the virtual synchronous generator control strategy is added to complete the distributed wind generator virtual synchronization control,and combined with the load shedding control strategy,the system has a certain reserve Capacity and one-time frequency modulation capability,and then perform simulation analysis under different working conditions.Finally,study the transient stability of the system after the distributed photovoltaic power supply virtual synchronous generator and distributed wind power generation virtual synchronous generator run in parallel,and establish a distributed power supply virtual synchronous generator system structure under the corresponding pre-synchronous control strategy.Based on the extended equal area method,the virtual power angle dynamic characteristic equation of the two-machine system is obtained.The current equalization link in the inverter control is used to determine the system stability by the extended equal area method and the corresponding control method is proposed to improve the system stability.The corresponding control strategy is verified in Simulink simulation software.