Modeling And Simulation Of Primary And Secondary Frequency Regulation Of Microgrid Based On Energy Storage Battery

In recent years,distributed power sources have achieved rapid development with the advantages of small investment,clean and environmental protection,reliable power supply and flexible power generation.As a small power grid that coordinates the contradiction between distributed power supply and large power grid,the microgrid has also developed rapidly.The converter control in the microgrid mostly focuses on frequency and voltage recovery,power sharing,and circulation suppression.It is an urgent problem to be solved for frequency problems.Different from the traditional power grid,when the micro-grid is running in off-grid mode,due to its own characteristics,when the active power shortage occurs in the system,the frequency of the micro-grid will fluctuate drastically,affecting the power supply reliability and power quality of the system.The energy storage unit acts as a buffer between the power supply and the load in the microgrid,and can utilize the energy storage to maintain the frequency stability of the microgrid.In this paper,the energy storage inverter is controlled by virtual synchronous machine.The control method has strong anti-load disturbance ability,which can increase the inertia of the system.At the same time,the related theory of the traditional synchronous machine can be introduced to realize the friendly access of the power supply.Therefore,this paper firstly models the energy storage virtual synchronous machine.The bottom layer control is designed as a voltage-current inner loop based on quasi-proportional resonance(PR)control.Compared with the bottom layer control,it is proportional to differential(PI)control voltage and current.The ring energy storage virtual synchronous machine does not require complex coordinate transformation,no cross-coupling term,and has a low harmonic distortion rate when accessing the nonlinear load.Secondly,the power sharing problem of multi-storage virtual synchronous machine is studied,and the virtual exciter is improved.The energy storage virtual synchronous machine whose output reactive power is only related to the no-power droop coefficient is designed,and the parallel energy storage of the two machines is designed.The virtual synchronous machine performs small signal analysis and analyzes the influence of key parameters such as damping and moment of inertia on stability.Finally,based on the above analysis,taking into account the state of charge(SOC)of each energy storage system,a virtual energy storage virtual synchronous machine based on dynamic correction coefficient correction is proposed.Through theoretical analysis,it is proved that in the case of isolated network operation,no matter whether the active load in the system increases or decreases,the parallel multi-storage virtual synchronous machine can coordinate control according to SOC in real time in the process of participating in the secondary regulation of the micro-grid frequency.The output power of each energy storage virtual synchronous machine makes the SOC between different energy storage systems tend to be consistent.The simulation was verified on the Matlab2017/Simulink platform.