Modeling And Simulation Of Multi-frequency Bands Dynamic Phasor For MMC

With the emergence of photovoltaic,wind power and other new forms of power generation,China’s energy structure has begun to transform from traditional energy to new energy,and China’s power grid has gradually formed a large grid system with multi-terminal AC-DC hybrid connection.In this process,with the access of a large number of power electronic equipment,the power system is becoming electronized.HVDC transmission has the advantages of long transmission distance and large transmission capacity,and is gradually replacing the development of AC transmission in China’s cross-regional transmission.The three technological changes of HVDC are all related to the development of the core equipment converter,and the modular multilevel converter(MMC)has become a research hotspot because of its advantages such as low distortion,low switching loss and flexible control.However,with the increase of voltage level,the complex topology brings great challenges to the efficiency of simulation.Therefore,it is necessary to take into account the accuracy of the premise of efficient rapid simulation technology.This paper will focus on the study of fast simulation algorithm to improve the simulation efficiency of the MMC converter model.This paper first introduces the principle of the existing frequency reduction algorithm,deduces the application formula of the dynamic phasor model based on the state space method,builds an improved dynamic phasor model on this basis,uses the dynamic phasor to reconstruct the accurate time domain solution,and validates the correctness of the method of reestimating the initial value through the simulation example.Then,based on the existing frequency reduction methods,the multi-frequency bands dynamic phasor method is proposed.The multi-frequency bands dynamic phasor method is used to deduce the process of signal frequency decomposition,recombination and frequency shift step by step,and the principle of large length simulation can be studied.Compared with the traditional dynamic phasor method,the multi-frequency bands dynamic phasor method can give consideration to the calculation speed and accuracy,and is more suitable for the simulation of large-scale power grid.The multi-frequency bands dynamic phasor theory is applied to the MMC,and the multi-frequency bands dynamic phasor model of the MMC is established.The simulation results show that the model can give consideration to the accuracy and speed of the simulation,which improves the simulation efficiency of the MMC.When considering the interaction between the MMC and various parts of the system from the system level,and ignoring the influence of the dynamic characteristics of the MMC itself,only the dynamic characteristics of the steady-state fundamental frequency can be considered to establish the MMC electromechanical transient model.In this paper,under the framework of the traditional MMC electromechanical transient simulation model,the primary system and the control system are unified through phase component modeling.On the one hand,the method based on phase component can simplify the data interface and exchange.On the other hand,the simplification of inner loop control and the introduction of phase shifting in the modeling process of the control system can simplify and reduce the complexity of the MMC electromechanical transient model,improve the efficiency of the MMC electromechanical transient simulation model,and finally verify the effectiveness of the model through simulation.