Research On Secondary Voltage Control Of Islanded Microgrids

In the trend of global energy transformation,more and more new energy has been developed and utilized.Therefore,some researchers put forward the "smart grid" scheme to solve the transformation of power system.In recent years,the proportion of renewable energy generation in traditional energy generation has gradually increased.In order to solve the impact and adverse effects of more and more energy generating units incorporated into the large power grid,the concept of "microgrid" is proposed.Microgrid is a kind of small-scale power grid that can be autonomous,and its operation mode is changeable,which can not only be connected to the grid,but also operate in isolated island.This paper focuses on the secondary voltage control of islanding microgrid.The theory of multi-agent system is applied to the control of microgrid.Among them,we regard the problem of secondary voltage recovery as the problem of distributed coordination and consistency.The advantage of using distributed control strategy is that the communication network is simpler and the single point fault caused by centralized control is avoided.In this paper,firstly,the islanding microgrid model is established,which integrates the distributed power model and the network model composed of multiple micro sources.Secondly,when the load disturbance occurs,the micro grid and the main grid are disconnected and enter the island mode.The primary control ensures the voltage stability,but also causes the voltage deviation.Therefore,we study and design a two-stage voltage control scheme to compensate for this deviation.Here we use the sliding mode variable structure control algorithm to achieve the stability of the system.In view of the chattering phenomenon of sliding mode,we use RBF neural network to approach the functional relationship between sliding hyperplane and exponential approach law of the system,adjust the switching control gain of sliding mode control to eliminate the chattering caused by sliding mode control.Finally,the stability analysis of the control system is given.In addition,considering the external interference and the inaccuracy of the complex system model is an inevitable and urgent problem to be solved,we add the disturbance term to the established islanding microgrid model.As a supplement of power grid,microgrid aims to improve the reliability and quality of power supply.In order to achieve this goal,for micro grid control system,in addition to ensuring the stability of the system,there are also high requirements for control time and transient performance.Therefore,this paper designs a distributed finite time two-stage voltage control scheme.Among them,we choose the nonsingular terminal sliding mode algorithm to restore the voltage to the reference value in the finite time.Finally,an example is simulated in MATLAB to verify the feasibility of the proposed control strategy and analyze the robust performance of the controller.