Virtual Synchronous Generator Control Of Photovoltaic Power Station And Oscillation Suppression Strategy

Due to the outstanding advantages of clean and efficient photovoltaic power generation,it has been widely used.A large number of photovoltaic grid-connection makes inverters and other low-inertia power electronic devices participate in the power grid regulation and control,resulting in a yearly decrease in the proportion of the capacity of synchronous generators in the power system.Synchronous generator is always in the dominant position of power system because of its special inertia and damping,but now the system has been missing inertia and damping for a long time,which will greatly reduce the stability margin of the system,and even cause serious power grid accidents.Virtual Synchronous Generator(VSG)technology solves the problem of inertia and damping loss in power system by simulating the external characteristics of Synchronous Generator,which has become a hot inverter control strategy in microgrid.The basic structure of large photovoltaic power station and output characteristics of photovoltaic array are analyzed,and the photovoltaic power station and its grid-connected control system are modeled.In view of the weak grid characteristics of large photovoltaic power stations,a weak power grid model coupled with the grid impedance and the Point of Common Coupling(PCC)was established to simulate and analyze the system resonance phenomenon caused by the weak power grid.An active conductance resonance suppression method is adopted to make the higher harmonics pass through the filter capacitor and the lower harmonics pass through the conductance.This method solves the resonant problem caused by multiple inverters in parallel in the weak grid environment,and suppresses the harmonic current output,which plays a great role in improving the power quality.Based on the analysis of the disadvantages of inertia loss in large-scale photovoltaic power station,an inverter control strategy called virtual synchronous generator is designed,and the VSG system is simulated.For the grid power oscillation problems caused by the virtual synchronous generator algorithm,the correlation between the parameters of the virtual synchronous generator and the oscillation state is deeply analyzed,and a virtual synchronous generator oscillation suppression strategy with adaptive inertia and damping coefficient is proposed,which enables the control parameters to be adjusted online during the system operation to realize power oscillation suppression and shorten the transient time of the system.The dynamic characteristics of photovoltaic power supply exhibited serious nonlinearity.The operation interval of photovoltaic is divided into stable and unstable regions by taking the Maximum Power Point(MPP)as the boundary.When the photovoltaic power supply is used as the source of the virtual synchronous generator,the stability of the system will be reduced owing to its structure.If the output of the photovoltaic power supply cannot meet the power demand of the system,the parallel energy storage capacitor of the DC terminal cannot restore the stability of the system in the face of the continuous drop of the supporting voltage,it will lead to the working point sliding into the unstable region,and then cause more serious power oscillation.The grid-connected system of Photovoltaic Virtual Synchronous Generator(PV-VSG)is modeled,and the stability of the Photovoltaic Virtual Synchronous Generator is analyzed.An improved power oscillation suppression strategy of virtual synchronous machine considering the characteristics of photovoltaic source side is proposed.The strategy solves the power oscillation problem of Photovoltaic virtual synchronous generator,and the effectiveness of the proposed control strategy is verified by simulation.In order to verify the control strategy,a photovoltaic cell simulator was designed to realize the "all-weather operation" of the photovoltaic power supply.The experimental platform of photovoltaic virtual synchronous generator based on Lab VIEW as the upper computer and DSP as the lower computer is built.The experimental platform realizes data acquisition through the data acquisition card,realizes the communication function with the serial port,besides that,enables the system to have the function of online observation and real-time parameter adjustment.The experimental results fully verify the feasibility of the virtual synchronous generator control strategy and the practicability of the experimental platform.