Research On Control Strategy Of Microgrid Under Off-grid And Grid-connected Operation

With the increasing scarcity of fossil fuels and increasingly prominent environmental problems,microgrids have emerged to reduce the consumption of non-renewable energy.Today’s important renewable energy power generation in my country includes wind and solar power.The operation mode of microgrid is divided into off-grid and grid-connected.Off-grid microgrid solves the problem of power supply in remote areas,while grid-connected microgrid adds security to energy supply.In this paper,the control strategies of microgrid in two different operating states of off-grid and grid-connected are studied.Improve the stability and efficiency of renewable energy power generation when the microgrid is operating off-grid;reduce the impact of the unbalanced voltage at the coupling point on the current quality of the grid and complete the load compensation when the microgrid is connected to the grid.(1)Aiming at the instability of the off-grid operation of the microgrid,a joint control strategy of the wind and solar storage system is proposed,and the working mode conversion controller is used to control the power tracking of the wind and solar power generation system and the charging and discharging of the energy storage system.(2)In view of the low utilization rate of renewable energy power generation,the maximum power tracking control(Maximum Power Point Tracking,MPPT)is proposed in the wind and solar power generation system using fuzzy logic controller(FLC)and perturbation observation method(Perturb and Observe Method,P&O)combined control algorithm;Load Power Tracking Control(LPTC)adopts an iterative calculation method based on power balance gradient voltage.The energy storage system adopts a control strategy based on the state of charge and discharge(Sate of Charge,SOC)and high-power instantaneous charge and discharge.(3)Aiming at the disturbance and unbalance of the voltage at the coupling point of single-stage three-phase photovoltaic grid-connected,a control strategy based on generating a reference signal is proposed.The control strategy first outputs the reference current and then the reference voltage.The reference current output control uses a combination of Extended Kalman Filter(EKF)and harmonic current detection algorithm(Fryze-Buchholz-Dpenbrock,FBD),where EKF is used to output the positive sequence component of the coupling point voltage.Finally,the deadbeat current controller outputs a reference voltage signal to control the inverter to complete the control of the entire grid-connected system.Finally,a simulation model was built to verify the superiority of the proposed MPPT algorithm during off-grid operation,and under the conditions of sudden changes in wind speed,light intensity,and random changes in load,the wind and solar storage system can quickly respond,and the output power of the three subsystems is dynamic.Balance;verify the feasibility of the EKF algorithm during grid-connected operation,and observe the power quality of the grid under the two conditions of voltage balance and unbalance at the coupling point and complete the compensation of the load.