Research On The Stability Mechanism And Distributed Control Strategy Of Multi-source Heterogeneous AC Microgrid

With the gradual expansion of distributed power sources such as photovoltaics and energy storage,it is important to study the control strategy for inverter parallel systems in isolated AC microgrids.The multi-intelligent body consistency algorithm can use the information interaction between neighboring intelligences to achieve consistent node state convergence,but due to the communication network topology,communication delay and other issues will have an impact on the convergence characteristics of the algorithm.Therefore,thesis will conduct an in-depth study on the stability mechanism and distributed control strategy of AC microgrid in terms of theoretical analysis and simulation verification,as follows:(1)The research is carried out for the control strategies of distributed power sources including photovoltaic power generation and energy storage systems.Firstly,the equivalent model of photovoltaic cells is analyzed,the impact of different maximum power tracking algorithms on the dynamic performance of the system is compared and analyzed,and the maximum power tracking control strategy based on particle swarm optimization algorithm is proposed by combining it with particle swarm optimization algorithm.Secondly,the equivalent model and control strategy of the energy storage system are analyzed.Finally,a distributed power simulation model based on MATLAB/Simulink is built to further verify the dynamic performance and effectiveness of the proposed control strategy.(2)The study is carried out for the hierarchical control strategy of the voltage-source inverter system.First,a voltage and current closed-loop controller based on dq decoupling is designed,and the control parameters are selected according to the Byrd diagram analysis.For the system with unbalanced load,the positive and negative sequence separation control method is introduced to realize the stable operation of the system.Secondly,an equivalent droop control strategy based on secondary control is proposed for the parallel system with two inverters,and the stability of the parallel system with two voltage source inverters is analyzed by the steady-state analysis method and the eigenvalue analysis method.Finally,a voltage source inverter system model is built based on the PLECS simulation platform to further verify the effectiveness of the proposed control strategy.(3)The study is conducted to investigate the problem of power unevenly distributed in a multi-inverter parallel system due to the inconsistency of line impedance and other factors.Firstly,the dynamic convergence mechanism of the consistency algorithm is analyzed,and an algorithm model is built to verify its convergence characteristics.Further,a consistent distributed secondary control strategy considering voltage and frequency recovery is proposed to achieve the accurate equalization of output power while regulating the system output voltage and frequency.Secondly,the proposed control strategy is analyzed using steady-state analysis and small-signal analysis.Finally,a parallel inverter system simulation model based on PLECS simulation software is built to verify the proposed control strategy.(4)The effects of non-ideal conditions such as delay links on the stability of the inverter parallel system are investigated.Firstly,the dynamic convergence mechanism of the consistency algorithm with delay link is analyzed,and a simulation model of the consistency algorithm is built to verify the convergence conditions.Secondly,a delaycompensated consistent distributed secondary control strategy is proposed to realize the accurate distribution of system output power under non-ideal conditions.Finally,a simulation model of a six-inverter parallel system based on PLECS simulation software is built to verify the proposed control strategy.