Research On Optimization Of Control Parameters Of Islanded Microgrid With Time Delay

In today's energy background,the microgrid with new energy as the main power generation unit has gradually become a research hotspot.Whether an islanded microgrid with weak architecture and small overall inertia can withstand the impact of small disturbances all the time is the top priority in the field of microgrid research.The small-signal model is the basis for the optimization of micro-grid control parameters.At present,the small-signal model of the microgrid is constructed by using a simplified transfer function model,which does not consider the time-delay link.However,the time delay problem exists in any power system,and the time delay is also an important factor affecting the stability of small signals in power systems.For the microgrid system,there exist inherent time delays in the inverter power response that is PWM time delay and digital circuit acquisition time delay.Therefore,in this thesis,the linearized small-signal model of the microgrid with time delay is established.The influence of different parameters on the stability of the small-signal system is analyzed by eigenvalues,and PI parameters are optimized.A microgrid isolated network system with two parallel distributed power sources is established using Matrix Laboratory.The system characteristic differences between the microgrid with time delay considered and the microgrid without time delay considered are compared.The rationality of the small-signal model with time-delay link and the superiority of the control parameter optimization method proposed in this thesis are verified.The main research contents are as follows:(1)The linearized small-signal model of each control link of microgrid inverters without considering the influence of time delay is constructed by state space representation,and the linearized small-signal model of island microgrid without considering the influence of time delay is obtained.Through the third-order Pade approximation method,the small-signal model with the time-delay link is obtained,and the small-signal model with the time-delay link is added to the small-signal model of the general micro-grid inverter(without considering the influence of time delay),so the linearized small-signal model of the single inverter with time delay is established.Finally,the linearized small-signal model of the microgrid with time delay is constructed.(2)The small signals stabilities of the microgrid small-signal models established above including the model without considering the influence of the time delay and the model considering the time delay are compared.By comparing the changes of root locus in the cases of varying the droop coefficient,the PI parameter of the voltage and current double loop,the time constant,and the load,it is found that the parameters applicable to the microgrid system without considering the time delay are not applicable to the microgrid system considering the time delay.It further illustrates the influence of the time-delay link on the small signal stability of the microgrid system and the necessity of re-optimizing the control parameters on the microgrid system with time delay.(3)A multi-objective optimization objective function consisting of the damping ratio,the stability margin,and the small signal stability is established.The three objective functions are transformed into single objective function by linear weighting method,and then the particle swarm optimization algorithm is used to optimize the control parameters of the time-delay microgrid.Finally,the accuracy of the linearized small-signal model of the islanded microgrid with the time-delay link and the superiority of the parameter optimization method proposed in this model are verified by simulations.