Self-adaptive Secondary Frequency Control Strategy Based On Equivalent Model Identification Of Microgrid

For isolated island microgrid systems,the static and dynamic performance of frequency is an important guarantee for the reliable and stable operation of the system.the frequency quality of the system is usually maintained by combining the primary frequency modulation control based on the bottom inverter and the secondary frequency modulation control based on the central controller(MGCC).A droop control strategy of a microgrid inverter is equivalent to a primary frequency modulation link in a power system and belongs to a differential regulation.In order to achieve frequency non-differential regulation,the output power of multiple frequency modulation units in the system can be changed by centralized secondary frequency control based on PI regulator.In order to improve the adaptability of the second frequency modulation controller,the parameters of the second frequency modulation controller are modified adaptively.Two typical network control strategies in isolated island microgrid are compared and analyzed firstly: droop control and virtual synchronous generator(VSG)control.VSG control is a special droop control.After that,the off-line identification process of single microgrid inverter model is studied,and the overall frame of inverter model identification is put forward,and detailed analysis is carried out from the angles of excitation mode,data sampling,model identification structure and off-line model identification algorithm,respectively.The correctness of off-line model identification of inverter is verified in MATLAB/Simulink simulation environment.Based on the theory that the equivalent damping and inertia of the traditional power system synchronous unit network have superposition characteristics,the feasibility of the equivalent of multiple networked inverters as a single VSG model is proved theoretically.Lastly,aiming at the problem of poor adaptability of PI control based secondary frequency modulation to microgrid system model,combined with multi-inverter and MGCC secondary frequency modulation,the detailed mathematical model of the system is established,and the poles of the system are optimized according to the principle of optimal system pole allocation in automatic control principle.The simulation results show that the proposed strategy has good adaptability under different operating conditions of microgrid.