| The Virtual Synchronous Generator(VSG),as the key equipment of distributed power conversion,can increase the inertia and damping of the system and improve the frequency stability of the power grid.VSG system with good transient performance of power and frequency under different disturbance can better reflect its support for inertia and damping of power grid.However,the simulation of the external characteristics of the traditional synchronous motor introduces transient oscillation into the output response of the VSG,which reduces the transient performance and is not conducive to the safe operation of the converter.In addition,the transient performance requirements of VSG are not consistent under different disturbances.The trade-off between different transient properties is often contradictory.Based on this,this paper mainly studies the transient characteristic optimization technology for the active power and frequency of virtual synchronous generation,(reflects the flexibility of VSG control?)The main research work is as follows:The mathematical model of an ideal synchronous generator is established,and the principle and realization process of VSG are described by comparing the rotor motion characteristics,stator current equation and voltage and frequency regulation control.The VSG system for LCL type three-phase grid-connected inverter is designed and its power frequency small signal model is established.Aiming at the transient oscillation problem of VSG,a VSG transient performance optimization strategy based on advance compensation is studied.Under the condition that the steady-state damping of the system remains unchanged,the equivalent damping of the virtual synchronous machine at a specific frequency can be increased,and the transient oscillation can be effectively suppressed.Aiming at the multi-objective optimization of transient response characteristics of VSG under different perturbations,a virtual inertia adaptive control scheme based on genetic algorithm was proposed.Firstly,the transient response process of VSG under different disturbances is analyzed in detail.In order to solve the problem of adaptive inertia control that the adaptive law can not accurately constrain the transient response performance,genetic optimization algorithm is used to obtain the virtual inertia change trajectory under different perturbations,which conforms to the transient performance constraints.On this basis,the adaptive control function of virtual inertia is summarized and applied to VSG control,which can effectively eliminate transient oscillation in the response process,constrain the frequency change rate and range of VSG,and increase the time freedom in response regulation of VSG output power.Finally built a VSG experiment platform based on parallel synchronous generator,completed the VSG operation and its transient response characteristics of experimental research,this paper is verified by comparison research based on the modified VSG lead compensation control strategy,and the adaptive law is based on the genetic algorithm offline virtual inertia control on transient response performance of VSG is effective and feasible. |
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