Research On Control Of Grid-connected Of Photovoltaic System With Storage Based On Virtual Synchronous Generator

In order to cope with the energy crisis and environmental pressure,photovoltaic(PV)power generation technology has attracted more and more attention.The PV power supply is connected to the power grid through grid-connected inverter.Its response speed is fast and it lacks rotational inertia.Moreover,its frequency voltage is supported by the power grid.As the grid-connected capacity of photovoltaic power sources continues to increase,the power grid is more susceptible to power fluctuations,posing a threat to the safe operation of power systems.As a kind of inverter control strategy,Virtual Synchronous Generator(VSG)can make the output of the inverter approximate the operating characteristics of the synchronous generator,which will promote the large-scale access of the PV power to the grid.Firstly,this paper adopts the structure of two-stage grid-connected PV power generation system.The maximum power point tracking is realized by the front-stage dc booster converter,and the PQ control strategy is realized by the back-stage grid-connected inverter.It is verified by simulation that the system adopts two-stage structure to incorporate the maximum output power of the PV power supply into the power grid and realize power decoupling control.Secondly,the energy storage device adopts lead-acid battery,and the bus voltage on the dc side is regulated by the double-closed-loop voltage stabilizing control strategy.The energy storage inverter adopts VSG control strategy to realize active-frequency and reactive-voltage regulation.The power loop is modeled mathematically and the virtual inertia and damping parameters are designed and analyzed.Power outer loop uses PR regulator to track sinusoidal command current;A grid-connected simulation model of the energy storage system based on VSG is built.The simulation verifies the rationality of the selection of inertia and damping parameters,and verifies the effectiveness of the VSG control strategy by comparing with the traditional control method.Finally,PV power generation system and energy storage system independentlyintegrated into the grid structure,and the simulation model of power complementary the PV system with storage is built.The simulation model of PV grid-connected system with storage is established.By switching different loads on the output side,the simulation results show that the PV system with storage adopts the VSG control strategy can realize the output tracking the power command while the energy storage system introduces the inertia and damping into the power control loop,which can participate in the frequency modulation and voltage regulation on the grid side.The output of the PV system with storage can be approximated by simulating the primary frequency modulation and primary voltage regulation characteristics of the synchronous generator,which is beneficial to large-scale access to the grid.