Research On Parameter Configuration And Identification On Active Power Loop Of Synchronverter

Since the essence of the synchronverter is to apply the virtual synchronous generator(VSG)control strategy to the grid-connected inverter,the power angle characteristic of the synchronverter is nonlinear,just like the synchronous generator.This makes the average synchronous power coefficient(SPC)not constant.Since the active loop of the synchronverter is equivalent to a second-order system model,in the active loop parameter design,if the SPC reference value is unreasonably selected,the actual dynamic performance will not match the design expectations when the active loop parameters are determined.It will reduce the phase margin,affect power quality,and even lose stability.In actual operation,many parameters such as sampling and filtering will also affect the actual dynamic performance of the synchronverter.Through parameter identification,the implicit connection between actual results and design expectations can be further found to provide a reference for parameter design.Meanwhile,considering the confidentiality of the manufacturer or the inability of the operator to directly access the detailed data of the synchronverter,parameter identification is a necessary means to analyze the parameters.However,in the online identification method,if the application scope of the linearization model is not considered,the identification accuracy will be affected by the nonlinearity of the power angle characteristic,making the identification result meaningless.In response to the above problems,the main work of this article is as follows:(1)The analysis of synchronverter control and its power angle characteristics nonlinearity.The the operation principle and mathematical model of synchronverter are introduced,and the control strategies of active loop and reactive loop of the synchronverter are analyzed in detail.The relationship between the back-EMF phasor of synchronverter and the terminal voltage phasor is established by the grid-connected equivalent topology,and the cause of the nonlinear power angle characteristics is deduced.The traversing method is proposed to get the SPC.A simulation model of the grid-connected operation mode of the synchronverter is established.Simulation experiments are used to verify the nonlinearity of the power Angle characteristics and the correctness of the active power traversing method,which lays a certain prerequisite for the following chapters.(2)Parameters design method in active power control of synchronverter.Taking the grid-connected operation of synchronverter as an example,the mathematic model of SPC and stability margin is established according to the open-loop transfer function of active loop,then the optional domain of inertia and damping factor is determined,meanwhile the impact of the SPC variation on the selected range is analyzed.According to the closed loop transfer function of the active control loop,the impact of SPC on the operating performance is explained.Finally,a design method of active control parameters is proposed.Simulation experiments are carried out to verify that the proposed active control parameter design method can meet the requirements of relative stability and greatly reduces the error of actual operation and design,at the same time avoids the uncertainty of system parameters during synchronverter operation(3)Parameters indentification method in active power control of synchronverter.Aiming at the off-line identification method,the principal theory of load rejection method is explained in detail.Aiming at the online identification method,the direct method and the power method are introduced respectively.The three linearization models are introduced in detail,meanwhile,based on the the average model and process model,the variation field of the active power is obtained in the step response test.The effectiveness of these parameter identification methods is verified by simulation experiments.At the same time,it also verifies the necessity of considering the scope of application of the linearized model in the power method.