Research And Application Of Small Signal Modeling Method For AC/DC Hybrid System Considering Voltage Variation

In recent years,LCC-HVDC technology has developed rapidly in China,and has become an effective means to solve long-distance and large-capacity transmission.At the same time,it also puts forward higher requirements for the stable operation of AC-DC hybrid system.Most studies on small signal stability analysis of AC/DC hybrid system with LCC-HVDC focus on the influence of DC control system on the stability,and the generator is equivalent to a voltage source,which makes the analysis result unable to fully reveal the AC/DC hybrid system stability mechanism.And the accuracy of small signal model used in studies needs to be improved.In order to accurately analyze the small signal stability of AC/DC hybrid system and improve the system stability,a small signal modeling method for AC/DC hybrid system considering the influence of voltage variation is proposed and applied in this thesis.Firstly,the small signal modeling method for AC/DC hybrid system is studied.In this thesis,the AC/DC hybrid system is divided into AC and DC subsystems,the node injected power and the voltage amplitude and angle is chosen as the connection variable of the AC/DC system,which simplifies the modeling process and enhances the universality of the model.Furthermore,in view of the influence of the dynamic process of the converter bus voltage on the small signal model,a small signal model considering the voltage variation is presented.A new state equation is introduced into the model,the angle relationship inside the inverted side converter station and the expression of trigger angle is corrected.The model is validated by PSCAD electromagnetic transient simulation and compared with the traditional small signal model.The results show that the small signal model considering the influence of voltage variation established by this method has high accuracy and high small interference stability analysis accuracy.Finally,the small signal stability of AC/DC hybrid system is analyzed by using the small signal model considering voltage variation established in this thesis.The influence of parameters on the system stability is studied.The PSCAD electromagnetic transient simulation results show that due to the addition of generators,new eigenvalues that may cross the virtual axis will be added to the AC/DC system,and new instability modes will appear in the system.In order to ensure stability of the system,the stability domain of the control parameters is calculated with the minimum damping ratio as the index.The correctness of the stability domain is verified by simulation,which can provide guidance for improving the operation stability of the system.