Research On Additional Damping Control Strategy Of Photovoltaic And Energy Storage Grid-connected System With Hybrid Energy Storag

At present,the increasing installed capacity and the number of put into operation have led to the rapid increase in the permeability and power generation ratio of photovoltaic power plants.Photovoltaic power generation has the characteristics of intermittence and randomness,and the photovoltaic power station will replace the traditional synchronous generator to connect to the power grid,which will inevitably affect the stability and security of the system.Therefore,this paper first analyzes the influence of grid-connected photovoltaic power plants on the oscillation characteristics of power system through small signal model,and then puts forward a damping control strategy for suppressing the low-frequency oscillation of photovoltaic power plants with hybrid energy storage.The specific research contents are as follows:(1)The PV power generation model is built on PSCAD,and the output characteristics of the PV array are analyzed by simulation with different light intensities and different PV cell temperatures.According to the PV plant control system,the mathematical model of grid-connected inverter,the mathematical model of PV array,the mathematical model of DC filter capacitor and the model of PV plant connected to infinite grid are established.Taking into account the volatility of PV output,energy storage devices are added to maintain the DC bus voltage stability,and the dynamic mathematical models of batteries and super capacitors are established to analyze their working characteristics.(2)The PV plant is connected to the infinite grid as the research object,and its small signal model is established,and the eigenvalues,eigenvectors and participation factors of the system state matrix are calculated by the eigenvalue analysis method,and the eigenvalue trajectories when the controller parameters are changed are plotted.The analysis results show that the grid-connected PV plant will affect the oscillation mode and oscillation damping of the system,and the oscillation mode is closely related to the PI controller parameters and DC bus voltage.(3)The synchronous generator power-angle oscillation characteristics and the damping injection principle of the PV plant are analyzed for a PV plant with hybrid energy storage connected to a single infinity system.The analysis results show that the system is prone to low-frequency oscillations because the excitation characteristics of the automatic voltage regulator weaken the synchronous generator’s own ability to regulate the electromagnetic power,while the synchronous generator electromagnetic power can be regulated by changing the active power output of the PV plant,which in turn improves the system oscillation damping.The analysis results also point out the phase relationship between the electromagnetic power,the PV plant output and the system angular frequency.Based on the above analysis,an additional damping controller is designed,and the inverter active additional damping control and hybrid storage dynamic power compensation control based on the additional damping controller are proposed.The simulation results show that the proposed low-frequency oscillation suppression strategy of PV plant with hybrid energy storage can better accomplish low-frequency oscillation suppression when the PV plant adopts no damping control,half-wave damping control,full-wave damping control without energy storage and full-wave damping control with hybrid energy storage.