Study On Control Strategy Of Cascaded H-Bridge STATCOM Considering Unbalanced Conditions

With the improvement of the industrialization degree of the country,the demand for electricity is increasing,and the load of power distribution is increasing,the voltage of the power grid is very easy to fluctuate and the power quality is damaged.The power quality of power grid has attracted more and more attention.In order to improve the power quality of the power grid,reactive power compensation devices must be used in the operation of the power grid.At present,STATCOM,as the most promising reactive power compensation device,can realize real-time compensation for reactive power.It is applicable in many occasions and easy to realize.Therefore,in this paper,star-structured cascaded H-bridge STATCOM is selected as the object to study the control strategy of inter-phase and inter-phase voltage sharing in case of power grid fault unbalance.This article begins by presenting the context of the various reactive compensation schemes and presents their development and application.The current state of research and the topology of STATCOM are analyzed in detail.At the same time,the regulation strategy and operation of the stellar h-bridge STATCOM studied in this article are detailed,which is helpful for the following study of the phase-to-phase and intra-phase voltage equalization control strategy of STATCOM.Then,for the imbalance phenomenon caused by the phase-to-phase voltage of star-connected H-bridge STATCOM when the power grid is out of balance due to fault,the traditional control strategy to equalize the phase-to-phase voltage of STATCOM by injecting zero-sequence voltage is analyzed first.In order to eliminate a large number of trigonometric functions and nonlinear operations in the traditional phase-to-phase voltage equalizing control strategy and improve the response speed,this paper improves the traditional zero-sequence voltage equalizing control strategy,The mathematical expression of active power is converted from abc coordinate system to dq coordinate system through Parker transformation,and an improved feedforward control strategy of zero-sequence voltage injection phase-to-phase voltage sharing control is proposed.Simulink simulation software is used to verify the above two-phase voltage sharing control strategy,and compare and analyze the simulation results.The results show that the phase-to-phase voltage sharing control strategy of improved feedforward control zero sequence voltage injection proposed in this paper improves the response speed and stability,and can effectively realize phase-to-phase voltage sharing.Finally,in view of the voltage imbalance in STATCOM phase,this paper first analyzes the traditional STATCOM phase voltage sharing control principle,and then,for the control failure and system oscillation caused by the current mutation in the traditional STATCOM phase voltage sharing control strategy,based on the original active vector superposition strategy,while adjusting the duty cycle to eliminate the traditional STATCOM phase voltage sharing control,Control failure and system vibration caused by sudden change of current.Through simulation analysis,the effectiveness of the improved STATCOM phase voltage sharing control strategy is proved.