| With the expansion of the scale of energy development,electric energy transmission and electric power construction in our country,and the steady progress of the 13 th Five-Year Plan and the energy strategy of West-East Power Transmission Project in China,line commutated converter high voltage direct current(HVDC)technology has been developed in an all-round and rapid way,and more HVDC transmission projects have been operated.HVDC has been a key factor affecting the operational safety and stability of the grid.Meanwhile,it plays an irreplaceable role in the operation and maintenance of the power grid.Compared with AC transmission,HVDC transmission has the technical advantage of rapid regulation of control system,and can finally improve the operation characteristics of the whole power grid.The control system is an important part of HVDC system,which is the basis of ensuring the stable operation of the whole system.The value of controller parameters directly affects the operation characteristics of the system and the ability to resist disturbance.At present,in practical engineering,the parameters of constant current,constant voltage and constant extinction angle proportional plus integral(PI)controller are often adjusted by off-line electromagnetic transient simulation and dynamic performance test of control and protection system.This method is essentially a trial and error method,which lacks theoretical basis and stability and stability margin under different working conditions.In view of this situation,this paper studies the controller parameter setting method of HVDC system.Firstly,this paper introduces the operation principle and control strategy of HVDC system,establishes the linear state space model of HVDC system at stable operation point,i.e.small disturbance model.After verifying the correctness of small disturbance model,the state space model is transformed into the system linear transfer function model with controller parameter variables,and uses the transfer function model to analyzes the coupling strength of the two sides of the control system.Due to the weak coupling strength,the two sides of the control system can be studied separately.Then,according to the first Lyapunov method,the controller parameter range that meets the requirements of stable operation of the system is calculated,and the correctness of the results is verified.The time-domain performance of the system is calculated by using the state space model of the system,and the relationship between the control parameters and the time-domain performance is expressed in the two-dimensional plane.The preliminary setting range of the proportional plus integral controller is obtained by analyzing the two-dimensional image.In order to analyze the problems in the range setting of the system control parameters and the influence of the controller parameters on the frequency domain performance of the system further,this paper uses the frequency expression suitable for the stability margin of the non-minimum phase system to obtain the value boundary expression of the controller parameters.After analyzing the boundary expression of the controller parameters and the image on the two-dimensional plane,it is found that the relationship between the parameter value of the PI controller and the system stability margin is given,and the setting range of the parameters of the PI controller is obtained.At the same time,the frequency-domain performance and the time-domain performance of the system running under the same control parameter are corresponding to each other,and the time-frequency-domain performance correspondence of the system without considering the change of the control parameter of the opposite system is obtained,which provides some help for the adjustment of controller parameters in practical work.Finally,the research contents are summarized,and the future research about the influence of different Phase-Locked Loop(PLL)and PLL parameters on HVDC system stability used by the transfer function model is prospected. |
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