| Aiming at the problems of the photovoltaic virtual synchronous generator(VSG)technology that has poor grid-connected real-time control effect,poor suppression of power fluctuations,and easy oscillation of DC voltage measurement in the dynamic process,a photovoltaic system optimization based on VSG is proposed.Control Strategy.The main research contents are as follows:1.The basic principles and operating characteristics of photovoltaic power generation systems and virtual synchronous generators are analyzed,and the mathematical models of each component system are established.In order to improve the power generation efficiency of the photovoltaic system,this paper introduces the maximum power tracking method(Maximum Power Point Tracking,MPPT),and simulates and analyzes the island operation of the photovoltaic power generation system based on the MPPT conductance incremental method technology.Photovoltaic island operation system that realizes maximum power tracking.2.The stability of photovoltaic power generation system based on VSG technology is studied.Including the impedance of the inverter to the parallel high-voltage grid,the Influence of the number of distributed power sources in parallel in photovoltaic power generation system on the damping ratio of photovoltaic power generation system,and the influence on the first two operating modes of grid-connected and off-grid.It provides a theoretical basis for the following grid-connected control strategies.3.Propose a control strategy of grid-connected inverter based on droop control.Aiming at the problem of poor real-time control effect of photovoltaic VSG in grid-connected system,a control strategy based on droop control is proposed,which includes two control algorithms of active-frequency and reactive-voltage.The active-frequency control algorithm simulates the damping characteristics and mechanical inertia of traditional synchronous generators,while the reactive-voltage control algorithm simulates the voltage regulation characteristics of traditional synchronous generators.4.Propose an optimized control strategy for photovoltaic system based on VSG.Aiming at the problem that the droop control strategy has a poor effect of suppressing power fluctuations and the DC voltage measurement is prone to oscillation in the dynamic process,a virtual inertial control algorithm is added on the basis of the original algorithm.Among them,the DC virtual inertia algorithm absorbs the power generated by the DC bus voltage change when the DC microgrid grid is disturbed by introducing a "virtual capacitor" on the DC side.Then the small-signal modeling of the photovoltaic power generation system,after the stability analysis of the system parameters,it is known that as the virtual capacitance of the system increases,the oscillation of the output active power and frequency of the VSG is suppressed,which affects the dynamic response of the system slowing shrieking.Therefore,the DC side output voltage will not oscillate during the dynamic process,and the system remains stable.Verify the effectiveness of the algorithm.5.Experimental verification and conclusion.Use MATLAB to build a photovoltaic VSG simulation model to simulate and verify the grid-connected control strategy proposed in this paper.The simulation results show that the simulation of the built photovoltaic VSG system during grid-connected operation shows that the built system meets the basic requirements for grid-connected stable operation.And by comparing the active and reactive power curves of the photovoltaic VSG system with or without virtual inertia control,and the DC bus voltage curve with or without virtual inertia control,it can be known that after the virtual inertia control is added to the system,the overshoot of the DC voltage is 39.% Is less than the previous 42%,and the time to enter the transient state is 5.5s faster than the previous 5.9s,and has good anti-interference characteristics.And the overshoot of active power is12.4% less than 13.8% without virtual inertia control;the time for the system reactive power to trend to 0 is shortened from the original 9.6s to 8.2s,and the power generation efficiency of the system is also improved.Meet the expected requirements of the grid-connected optimization control strategy. |
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