Seamless Switching Control Strategy Of Micro-grid Between Grid-connected And Islanded

Since the energy crisis and global warming is becoming increasingly serious, the development of renewable energy and power generation technology is one of effective measures. In order to improve the benefit and value of the distributed generation system, micro-grid composed by distributed generation unit accessed to network is an effective way. The seamless switching control strategy of micro-grid is an important control method to ensure safe and stable operation. In this paper, the research object is micro-grid inverter, and the research on the smooth switching control of grid connected inverter based on energy storage system is mainly studied.The mathematical model of grid connected inverter between grid-connected and islanded operation mode is built up, PQ control and droop control strategies are studied based on the transfer function of grid connected inverter, and two closed-loop regulator parameters are designed, the simulation model of grid-connected inverter is built by the simulation software, PQ control and droop control are verified by the simulation model.The mathematical model and the charge-discharge characteristics of super capacitor and battery storage device is researched, the basic principle of bidirectional DC/DC converters is analyzed, the mathematical model of the DC/DC converter is established, constant voltage control and constant power control strategy are given, the simulation model of energy storage converter is built by the simulation software, constant voltage control and constant power control strategy are verified by the simulation model.The basic principle of the traditional seamless switching control is studied,difference between grid voltage and output voltage of grid connected inverter are analyzed and simulated with different voltage amplitude, frequency and phase. Aiming at the shortage of the traditional seamless switching control strategy, the hybrid energy storage is proposed. The energy management and coordination control method of hybrid energy storage system are given,decoupled double synchronous phase-locked loop(DDSPLL), improved droopanticipating synchronization control and anti-saturation proportional integrator is given to overcome the shortage of the traditional synchronous phase-locked loop(SPLL), anticipating synchronization control and PI regulator, and the simulation analysis is carried out for DDSPLL and SPLL. Finally, the microgrid simulation model based on hybrid energy storage system is built by Matlab/Simulink simulation software, and the simulation verification is carried out on the traditional seamless switching control and the improved seamless switching control strategy.