Research On Control Strategy Of Inverter In Distributed Generation System

Energy is of the utmost importance in social and economic development.In order to achieve sustainable development,the development of smart grid distributed energy control technology has become urgent with each passing day.Among them,the control strategy of the three-phase inverter has become the center of attention.The control strategy of traditional three-phase inverters is mostly based on integer-order theory without taking the fractional-order characteristics of inductors and capacitors into account.As a consequence,the system output presents obvious waveform distortion and often has poor dynamic performance.This thesis fully considers the complicated characteristics of the three-phase inverter's nonlinearity,fast time-varying,strong coupling and high harmonic content caused by the dead zone of the system switch,drawing on the advantages of conventional control strategies,fusing the fractional-order PID control algorithm to improve,and designing two combined double closed-loop control strategies are used to test the control effect of the algorithm through theory and simulation experiments.The foremost contents of this thesis are shown as follows :(1)The mathematical models of the typical three-phase PWM voltage inverter and the three-phase four-wire inverter under the island operation mode in distributed generation system are established.(2)Aiming at the three-phase PWM voltage inverter model in the distributed generation system,a double closed-loop control strategy is designed.Merging the fractional-order PID control algorithm with the model predictive control algorithm,an ameliorated model predictive control with fractional-order characteristics is proposed,which is utilized to the voltage outer loop to realize the control of the load voltage;Discrete time sliding mode control algorithm is applicable to the current inner loop to control the inverter current.In terms of parameter selection,for the purpose of solving the fly in the ointment of low accuracy and efficiency caused by manual debugging based on experience,the differential evolution algorithm with individual optimal memory ability is used to keep the fractional PID parameters at a relative optimum,which makes the algorithm have more intelligence.Through simulation experiments,the improved algorithm compared with the primary model predictive control algorithm,the inverter's dynamic response performance and steady-state performance are more excellent,indicating that the control strategy ameliorates the control quality of the system to a certain extent.(3)On account of the three-phase four-wire distributed generation inverter model in island operation mode,a double closed-loop control strategy is designed.Compound the fractional-order PI control algorithm with the predictive function control algorithm to constitute a fractional-order PI predictive function control algorithm for the voltage outer loop;The fractional order PID control algorithm is used to improve the design of discrete time sliding mode approach law,which is used for the current inner loop.The sliding mode disturbance observer with equal compensation can brought into operation to observe the system so as to beneficially restrain the chattering issue of the sliding mode and disturbance of the system.The simulation results manifest that the control strategy can be availably to the performance of the system.