Research On Voltage Control And Stability Improvement Strategy Of DC Microgrid

In the context of the global energy crisis,the development of clean and green energy has become a trend.As a small system that can integrate new energy in the region,DC microgrid has become an important development direction of current power system.The research on its voltage control strategy and system stability improvement strategy are also hot research subject at present.In this paper,the voltage control strategy of DC microgrid is studied based on DC electric spring(DCES)technology,and the stability improvement strategy of DC microgrid is studied for the system stability problem caused by constant power load.Firstly,the voltage control strategy of DC microgrid is studied,and a DC microgrid voltage control strategy considering DC electric spring is proposed.The control strategy introduces DCES unit which composes of DCES and partial load to respond to the system voltage fluctuation.By dividing the system operation mode,each unit is reasonably arranged to respond to voltage fluctuations in an orderly manner.The DC bus voltage is used as the communication signal to realize the automatic switching of each operation mode.The specific control strategy of each unit under the control strategy is also given.For DCES unit,a DCES control strategy considering the voltage constraints of non-critical loads is proposed.The current limit is added on the basis of the traditional double-loop control to ensure the power quality of non-critical loads during operation.In the emergency of a large shortage of system power,the voltage constraints of non-critical loads are removed,and the voltage regulation ability of DCES unit is improved for a short time by sacrificing the power quality of non-critical loads.Finally,a simulation model is built to verify the effectiveness of the proposed control strategy.The voltage control strategy proposed in this paper can coordinate the orderly response of each unit to voltage fluctuations and control the DC bus voltage within the allowable range.And the access of the DCES makes part of the load of the DC microgrid respond to the system voltage fluctuations,reducing the amount of abandoned light and load of the system in emergencies.Then,based on the proposed voltage control strategy,the system stability problem caused by constant power load is studied,and a DC microgrid stability control strategy based on virtual DC machine(VDCM)is proposed.Taking the bidirectional DC/DC converter of energy storage as the research object,and based on the principle of a DC machine,the control strategy introduces a VDCM link on the basis of traditional droop control with the inductance current as the feedback quantity to increase the system damping and reduce the influence of constant power load on system stability.By establishing the small signal model of the DC microgrid with the proposed control strategy,the stability of the system is analyzed with the principle of impedance matching.Then the proposed control strategy is compared with the traditional VDCM control strategy.Finally,the simulation model and hardware experimental platform are built to verify the effectiveness of the proposed control strategy.The stability control strategy proposed in this paper makes the converter have the inertia and damping characteristics of a DC machine.This not only improves the stability of the system,but also improves the dynamic response performance to a certain extent.Its control effect is better than that the traditional VDCM control strategy.