| With the increase of the utilization rate of new energy and the popularization of distributed power generation,the inverter as an interface for energy exchange between the power grid and the distributed power source,its control strategy has also received more and more attention.In recent years,virtual synchronous generator(Virtual Synchronous Generator,VSG)control is considered to be a very promising inverter control strategy,which can simulate the rotor motion characteristics of synchronous generators,so that power electronic converters have the same generator Similar inertial characteristics.However,when multiple VSGs are operated in parallel,they will face more complicated cooperative control problems and stability problems than traditional parallel inverters.Therefore,this paper studies the parallel connection of independent microgrids composed of multiple distributed power generation units.The specific control content of VSG’s collaborative control strategy is as follows:First,this paper introduces the typical structure of microgrid and distributed power generation unit in detail,establishes a parallel distributed power generation unit model based on droop control,and studies the dynamic response characteristics of the traditional inverter based on droop control.Secondly,based on the mathematical model of the synchronous generator,this paper gives the control structure and principle of the VSG,and analyzes the dynamic characteristics of a single VSG and multiple parallel VSGs respectively,and compares it with the traditional droop control.The results show that VSG control can effectively improve the system inertia and reduce the amplitude of frequency oscillation in transient state.In addition,by choosing the damping coefficient reasonably,VSG control and droop control can have the same droop characteristics.However,when multiple VSGs are operated in parallel,the system will exhibit similar oscillation problems as parallel synchronous generators.In order to compensate the frequency deviation caused by the VSG droop characteristic,and at the same time suppress the power oscillation between the parallel VSGs and achieve a reasonable power distribution,this paper proposes a second frequency modulation control based on the consensus algorithm.This control strategy utilizes a sparse communication network to exchange information between adjacent nodes,which can restore the system’s steady-state frequency to the rated value,realize the proportional distribution of active power between VSGs,avoid transient power oscillations,and retain VSG Inertial characteristics provided.Finally,in the PSCAD / EMTDC simulation software,this paper builds a microgrid simulation platform composed of parallel VSGs to verify the effectiveness of the proposed control strategy under conditions such as sudden load changes,different parameter conditions and communication failures. |
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