The Research On Modeling Based On Multi-Frequency Band Dynamic Phasor For Transmission Line And Transformer

With the development of high voltage direct current(HVDC)transmission in recent years,as well as a large number of wind power and photovoltaic connecting to the grid,our country’s power grid has become the world’s largest and highest voltage level AC/DC hybrid grid.In large scale AC/DC hybrid power grid,the nonlinearity is strong,and the dynamic time constant of each component is very different.How to control and protect the power grid accurately,so that it can operate safely and reliably,has become a big problem.Therefore,we need to learn as much as possible about any situation that may make any influence on the safe and stable operation of large-scale AC/DC hybrid power grid,as well as the impact of the failure of a point or even a certain area on the whole system.Compared with electromechanical transient simulation,electromagnetic transient simulation technology is more suitable for studying the fast transient process in AC/DC hybrid power grid,and can more accurately reflect the real situation in the system.However,due to the detailed component model and small simulation step size,the electromagnetic transient simulation technology will cause a lot of simulation burden in large-scale power grid simulation,resulting in too long simulation time.Therefore,it is necessary to study a more rapid and high accuracy simulation method for large-scale AC/DC hybrid power grid simulation.In this paper,the multi-frequency band dynamic phasor method is used to build a fast simulation mathematical model with higher accuracy.Through the multi-frequency band dynamic phasor method,more harmonics are intercepted and recombined into N frequency bands to shift frequency respectively,and then parallel simulation is carried out with CPU.Compared with the dynamic phasor method,more harmonics can be considered under the same simulation scale to improve the simulation accuracy.In addition,N frequency bands are independent of each other,so the simulation speed can be further improved when parallel simulation is adopted.According to the principle and characteristics of multi-frequency band dynamic phasor method,this paper focuses on the study of transmission line and transformer models based on multi-frequency band dynamic phasor.As the most common component in power system,transmission line plays an important role in both AC system and DC system.There are many electromagnetic transient models for transmission lines,which are mainly divided into centralized parameter lines and distributed parameter lines.Based on the analysis of centralized parameter lines and distributed parameter lines,multi-frequency band dynamic phasor difference mathematical models for single lossless transmission lines,single lossy lines and three phase lossless symmetrical circuits are established in this paper.Then,the validity of the proposed model is verified by an example of a single-phase no-load line.According to different simulation requirements,transformer can establish different mathematical models.The model established in this paper is used in the simulation of large-scale AC/DC hybrid power grid,and the external characteristics of the transformer should be considered more.Therefore,after comprehensively comparing the advantages and disadvantages of the unified equivalent magnetic circuit model,the impedance matrix model and the controlled source model,this paper selects the impedance matrix model to establish the single-phase double-winding transformer model and the single-phase three-winding transformer model based on the multi-frequency band dynamic phasor,and considers the saturation problem of the transformer separately.Finally,an example of no-load single-phase double-winding transformer is used to verify the effectiveness of the multi-frequency band dynamic phasor model.In conclusion,according to the simulation analysis of multi-frequency band dynamic phasor transmission lines and transformers,it can be seen that compared with the traditional fast simulation method,multi-frequency band dynamic phasor method provides a fast and accurate simulation method for large-scale AC/DC hybrid power grid simulation.