| The optical storage DC microgrid effectively solves the "intermittent and volatility" problems of distributed photovoltaic power generation.The overall performance of the system depends on the control performance of DC-DC converter and grid-connected inverter.Therefore,effective control of the DC converter and grid-connected inverter in the optical storage microgrid to ensure the efficient and stable operation of the whole system,it has important theoretical research and application value.In response to the above requirements,the thesis proposes a hybrid energy storage unit control strategy combined with virtual direct current generator(VDG)technology to control the DC-DC converter and improve the stability of the DC bus voltage operation;and a virtual synchronous generator(VSG)is adopted,VSG technology realizes effective control of grid-connected converters,to improves the reliability of grid-connected inverter operation.Through the coordination of the above two control strategies,the anti-interference performance and self-stability ability of the system are effectively improved.The work of this paper is as follows:(1)Structure design and modeling of optical storage microgrid system.Firstly,the structure of the optical storage microgrid system is designed,and mathematical models of photovoltaic cells,DC converters and grid-connected inverters are established.In order to improve the output power of PV power generation unit,Incremental Conductance(INC)algorithm based on integrator is proposed to realize MPPT control of PV power generation unit,which solves the problems of“shock and misjudgment" existing in the traditional algorithm to realize MPPT control and improves the working stability of PV power generation unit.(2)Research on control strategy of hybrid energy storage unit.In order to improve the anti-interference performance of the DC bus voltage of the optical storage microgrid and give full play to the working characteristics of different energy storage batteries,a hybrid energy storage control strategy based on VDG was proposed,and the VDG technology was combined with the energy storage frequency division control strategy to effectively improve the voltage stability of the DC bus,on the basis of giving full play to the advantages of different energy storage batteries and improving the service life of the energy storage unit.(3)Research on the control strategy of the grid-connected converter.In order to improve the self-stabilizing performance of grid-connected inverter in parallel and off-grid mode,the electromagnetic balance equation of synchronous generator and Quasi Proportional Resonance(QPR)controller were combined with the VSG control strategy to simplify the control loop design of VSG and the improved control strategy effectively improves the working stability of grid-connected inverter.(4)Verification of control strategy for optical storage microgrid based on virtual motor technology.The effectiveness of the control strategy designed in this paper is verified by the MATLAB simulation experiment tool and the experimental prototype platform.The experimental results show that:under the designed optical storage microgrid system control strategy,the DC bus voltage fluctuation of the optical storage microgrid is within ±2.3%,the THD of the grid-connected AC current is maintained within 3.5%,and as the output power increases larger,the THD value will be smaller,and the stability of the optical storage microgrid system will be improved. |
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