Research On Event-triggered Control For Power Sharing In AC Microgrids

In order to promote the utilization of renewable energy,distributed power generation technology has developed rapidly in recent years.The unified management of distributed generation through the microgrid can overcome the impact of distributed generation on the grid and improve the reliability of power supply.However,in the islanded microgrid,due to the mismatched line impedance,there is a circulating current between inverters that adopt droop control,and the reactive power can not be shared accuratly.Moreover,when the microgrid has unbalanced and nonlinear loads,the traditional droop control does not consider the problem of unbalanced and harmonic power sharing.In addition,the secondary control of the traditional microgrid adopts the communication method of periodic sampling,which will cause a waste of communication "resources".This dissertation takes the islanded microgrid as research object,and focuses on the problem of power sharing and distributed secondary control communication,the following researches are carried out:A inverter model is established and introduced the design structure of primary control in detail;the principle of realizing the reactive,unbalanced and harmonic power sharing by regulating the virtual impedance at the fundamental positive(negative)sequence and harmonic frequencies is analyzed.The reasons for the generation of circulating current are discussed,and a scheme is proposed to effectively suppress the circulating current.In terms of many wasted communication resources caused by the periodic sampling control in the existing islanded microgrid,a event-triggered control strategy is proposed.Compared with traditional periodic sampling control strategy,the proposed control strategy is based on aperiodic sampling,which can reduce the communication cost of secondary control.The stability of the proposed controller is proved by the Lyapunov theory;the minimum interval of event triggering time is analyzed,and the Zeno phenomenon is ruled out.The simulation results verify that the proposed control strategy can greatly reduce the number of communication between inverters.In terms of inaccurate output power sharing and the generation of circulating current between inverters when the microgrid adopts traditional droop control,a power control strategy based on adaptive virtual impedance regulation is proposed.The control method is that each distributed generation uses the event-triggered algorithm to obtain the power sharing error,which can be adapted by the ProportionalIntegral controller and a virtual impedance correction item is generated,this value is used to adaptively regulate the components of the virtual impedance at the fundamental positive(negative)sequence and harmonic frequencies to achieve accurate sharing of reactive,unbalanced and harmonic power,and eliminate the circulating current between inverters.An islanded microgrid simulation model is established in MATLAB/Simulink to verify the proposed control strategy,and a microgrid test system is built in the laboratory to further verify the effectiveness of the proposed control method.