Design Of Unbalanced Three-phase Compensation Device On Column

With the development of national economy,the single phase load in the distribution network is increasing,and the power consumption is also becoming more and more common,it is very easy to make distribution transformer work on three-phase asymmetry.It will produce a large number of negative sequence and zero sequence current,and it is the main reason of unbalanced three-phase current on the column.The compensation of negative sequence and zero sequence current on the column can reduce the pollution caused by the unbalanced three-phase network,reduce the power loss and improve the quality of power supply.This paper describes the current situation and development trend of unbalanced three phase,and the passive compensation device and active compensation device are compared in this paper.Through the research and analysis of various compensation devices,the performance characteristics of the compensation device are expounded systematically.According to the design requirements and the compensation effect,the compensation device with the best compensation effect is selected as the unbalanced compensator,which can compensate the phase power supply in the three-phase four wire system.In this article,by studying the current situation and development trend of unbalanced three phase,according to the characteristics of three-phase four wire system,an improved three-phase id-iq detection method is proposed.In this method,the instantaneous current of each phase is processed by zero sequence current,the zero sequence current and the instantaneous current without zero sequence current are obtained.Then,we carry out the alpha-beta transform and p-q coordinate transformation for the three-phase current without the zero sequence current,vector synthesis in p-q coordinates,the instantaneous negative sequence current in the system is obtained.The negative sequence current of each phase of the system is obtained by rotating vector,the negative sequence current of each phase is added to the zero sequence current of the system to obtain the current to be compensated in each phase of the system.This method realizes the instantaneouscompensation of negative sequence and zero sequence current in unbalanced system,avoids the influence of the integral link delay,and improves the real-time compensation and compensation accuracy.The simulation results show that the proposed algorithm is able to compensate the negative and zero sequence current in unbalanced three phase,after compensation,the unbalance of power supply current is improved effectively.The unbalance compensation control system is also analyzed in this article.By comparing the PWM voltage control strategy,the PWM direct current control strategy and the indirect current control strategy,PWM direct current control is chosen as the control strategy.According to the compensation current,the control system sets the hysteresis width,adjust the precision of system unbalance compensation,control each IGBT conduction,compensating the unbalanced current of the system to improve the stability of the system.Through the simulation of the control system and the whole system,the effectiveness of the proposed compensation scheme is verified by Simulink.Finally,the hardware circuit of the system is designed,and the IGBT,capacitance and inductance parameters are calculated and selected.