Research On Saturation Compensation Of Current Transformer Based On FPGA

The relay protection device plays an important role in the power system,and its accurate action ensures the stability of the power system.When a fault occurs in power system,a primary side current often contain a large number of decaying DC component,this will cause the saturation of the current transformer and secondary side current waveform distortion.The secondary side of the current transformer due to the inability to get the primary side current accurate information that will lead to the secondary side device will generate error action.In view of the related problems of the core saturation of the current transformer,a saturated current correction method based on electromagnetic formula method is proposed in this dissertation,which corrects the secondary side saturation distortion current,improves the measurement accuracy of current transformer,and reduces the malfunction of relay protection device.The specific contents are as follows.1.This dissertation analyzes the digital model of current transformer and classifies it according to its function.The factors that affect the saturation of the core of the current transformer are studied,and it is explain that the influence of the current transformer on the power system when the saturation fault occurs.2.When the current transformer is saturated,the secondary side current is divided into unsaturated period,saturated transition period and saturation period.Meanwhile,according to the singularity of the secondary side current in the saturation transition period,a saturation recognition algorithm is proposed.The new method sets the start-up unit and decision unit,which ensures the stability and accuracy of the saturation recognition,has a smaller amount of computation.3.A saturation compensation method based on the electromagnetic formula method is proposed.Based on the saturation test results,the current value of saturation transition area is estimated by the secondary side current data of unsaturated time.According to the function relation of hysteresis current,secondary side current and magnetic flux,we set up the overdetermined linear equations of magnetic flux estimation,and realize the secondary side current distortion compensation in saturated time.The electromagnetic formula method is applied to calculate the difference of the magnetic flux between two adjacent points,which effectively avoids the influence of remanence on saturation.At the same time,it has smaller computation amount,higher compensation accuracy and better applicability and stability.4.We design a hardware system based on Field Programmable Gate Array(FPGA),and Quartus ? software is used to design the software platform.The saturation compensation algorithm is embedded in the soft core of FPGA to achieve the secondary side distortion current compensation.The stability and reliability of the designed system are verified by many experiments.