Research On Cooperative Operation Of Multiple PV And Energy Storage Units Based On Flexible Virtual Inertial Control

The virtual synchronous generator(VSG)technology can effectively solve the problem of inertia reduction brought about by the grid connection of distributed energy.Therefore,when the PV and energy storage units are connected to the grid,the use of VSG control can improve the power quality of the system.The virtual inertia is a key parameter that affects the control effect of the VSG.According to the operating performance of the VSG unit,the value of the virtual inertia can be flexibly adjusted to improve the operating effect of the VSG control.In the scenario of multiple PV and energy storage units working together.The operating performance of each unit in cooperative operation is different,so when there is a power disturbance,the inertial support capability that each unit can provide is also different.In order to reasonably allocate the virtual inertia of each PV and energy storage unit according to the operating performance of each PV and energy storage unit to better realize the inertial support of the PV and energy storage unit to the system,this thesis conducts a detailed study on the control strategy of the coordinated operation of multiple PV and energy storage units.The main work content is as follows:(1)Based on the analysis of VSG control principles,the focus is on the basic principles of flexible virtual synchronous generator(FVSG)control and multi-constraint flexible virtual inertia(M-FVI)control that were studied in the early stage of this research group.The virtual inertia can be flexibly adjusted in consideration of the frequency change rate and the important constraints affecting the stable operation of the system,which can maintain the stable operation of the optical storage unit and improve the inertial support capability of the PV and energy storage units to the system.Existing researches on flexible control of virtual inertia are mostly carried out in systems with single VSG units.Based on this,this thesis conducts research on cooperative operation between multiple PV and energy storage units to realize the collaboration control strategy of multiple PV and energy storage units in the system based on VSG.(2)This thesis proposes a control strategy for coordinated operation of multiple PV and energy storage units containing hybrid energy storage devices.Combining the working characteristics of each energy storage device,a control strategy for coordinated operation is formulated: In high-frequency disturbances,supercapacitors with faster response speed are preferred to provide inertial support.When the energy of the supercapacitors is insufficient,the supercapacitors and batteries Work together to smooth out high-frequency disturbances and maintain frequency quality.In the case of low-frequency disturbances,according to the difference between the battery SOC and the rated capacity of the converter station in each unit,fuzzy control is used to realize the reasonable distribution of virtual inertia between the units.This thesis also uses the method of root locus analysis to reveal the influence mechanism of the main parameter changes in the cooperative control strategy on the stability of the system,which provides a theoretical basis for the selection of control parameters in the system.Finally,a corresponding experiment was carried out in the hardware-in-the-loop experiment platform to verify the effectiveness of the proposed control strategy.(3)This thesis proposes a multi-VSG units cooperative control strategy based on the TOPSIS algorithm,and further studies the cooperative control between multi-VSG units under multi-index comprehensive evaluation.The state of charge of the energy storage device,the adjustable power margin of the converter,the adjustable power of the charge and discharge of the energy storage device,and the adjustable power per unit time of the system are selected as the evaluation indicators for collaborative control.The TOPSIS algorithm accurately evaluates the inertial support capability of each VSG unit based on the actual operating performance of each VSG unit.When a power disturbance occurs,a VSG unit with good safety performance is selected to provide greater inertial support.And through the hardware-in-the-loop experiment platform,an AC system with multiple VSG units was built to verify the effectiveness of the proposed control strategy.