| The flexible DC distribution system can effectively reduce the converter link,improve the acceptance capacity and energy utilization of distributed power supply,and realize the independent decoupling control of the active and reactive power of the converter station,which is more suitable for the development of modern distribution system.However,due to the lack of rotating equipment inside,its inertia is small,and it is relatively isolated from the inertia of the AC system,it is easy to produce low-frequency oscillation phenomenon.At present,the oscillation mechanism is not clear.This paper studies this problem,and the main work is summarized as follows:(1)Introduced the flexible DC power distribution system topology structure and the basic control strategy,this paper expounds the flexible multiple time scale dynamic problems in DC power distribution system,based on features of the network structure and control link it boils down to DC voltage control scale and the exchange current control scale,made clear the connotation of the dynamic scale,and focus on the flexible DC voltage control scale dynamic problems in distribution system,clear the challenge for the present research institute.(2)In view of the present study adopts flexible DC power distribution system low frequency oscillation,electromagnetic transient model for modeling complex,easy generation dimension disaster,using electromechanical transient model is too simple,not accurate simulation problem,put forward the flexible DC power distribution system under DC voltage time scales of physical equivalent circuit model,provides the control parameters of the physical significance of the intuitive explanation,and based on the sensitivity analysis in the physical equivalent circuit model,a reduced order model is proposed on the basis of equivalent with flexible DC power distribution system model based on PSCAD set up detailed simulation comparison,The results show that the equivalent reduced order model is consistent with the detailed model on the time scale of post-perturbation oscillation,which indicates its applicability to the study of low-frequency oscillation problems.Finally a reduced order model using equivalent dynamic process,derived the flexible DC power distribution systems in the low frequency oscillation frequency analysis form,to obtain the analytical relationship between the oscillation frequency and the key parameters,using the method of resolution to depict the network parameters,the influence of controlling parameters on the system oscillation frequency,through PSCAD build flexible DC power distribution system for time domain simulation,the correctness of the result shows that the theoretical analysis.(3)In order to reduce the harm of low-frequency oscillation in the current flexible DC distribution system,this paper uses a physical equivalent model to analyze in detail the role of each component in the low-frequency oscillation process and its physical participation process,and proposes a voltage outer loop control method based on band-pass filter compensation.It provides a new idea for the control optimization design of the system,and the simulation of the flexible DC power distribution system built by PSCAD verifies the effect of the optimization scheme.The simulation results show that the use of band-pass filter compensation can significantly reduce the fluctuation range of the system’s low-frequency oscillation.It can effectively reduce the harm of low frequency oscillation in the flexible DC power distribution system. |
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