Development Of Fast Response Direct Current Current Transformer Based On Multi Sensor Fusion

The flat-top pulsed magnetic field is the important development direction for pulsed magnetic field with its high stability and high strength.The realization of high stability FTPMF is essential for further research and development of major scientific experimental systems.To achieve high stability FTPMF,it is necessary to measure pulsed current with ppm-level accuracy and the magnetic modulated Direct Current Current Transformer(DCCT),the highest accuracy current sensor in existence,is the optimal choice.However,when faced with a wide range change of measured currents in a short time,the DCCT can easily enter a false balance state where the core is saturated and DCCT cannot operate.How to solve the false balance of the DCCT without affecting the high measurement accuracy of the DCCT is the focus of this paper.Firstly,the change process of magnetic potential,magnetic field strength and induced voltage in the core of the magnetic modulator when facing currents of different amplitude ranges is analyzed from the detection principle of the DCCT.The relationship between the generation of false balance and the linear range of the magnetic modulator is also analyzed,and the essential cause of false balance is that the maximum value of the unbalanced current(the difference between the ampere-turns ratio of the primary and secondary currents)exceeds the linear range of the magnetic modulator is obtained.Which leads to the solution of false balance in this paper: reducing the maximum value of unbalance current.By analyzing the response curve of the DCCT in the dynamic process,it is concluded that the method to reduce the unbalance current maximum is to enhance the dynamic response of the DCCT.A feedforward system with Hall sensor and DCCT fusion is proposed,and the principle of which is analyzed in detail.The principle of false balance recovery under the new scheme is analyzed and explained,and the feasibility of the DCCT false balance self-recovery under the fusion scheme is verified by simulation.The transfer function model of fusion system is constructed under reasonable assumptions,and it is theoretically demonstrated that the new scheme can ensure the high accuracy characteristics of DCCT steady-state measurements while solving the DCCT false balance.In terms of the implementation of the new scheme,the structural design of the Hall sensor is analyzed and the scheme with the minimum Hall sensor measurement error is determined through simulation.The overall structure of the fusion system is designed,and the scheme selection,design and fabrication of the fusion system sensors and circuits are carried out,and finally a prototype DCCT system based on multi-sensor fusion with 30 k A range is completed.In order to test the performance of the prototype,an experimental platform based on the fusion system and the primary current power supply system is built,and the self-recovery test of false balance and the DCCT dynamic performance improvement test are conducted.The experimental results show that the new system proposed in this paper can prevent the occurrence of false balance in dynamic processes and can realize the self-recovery from false balance,which greatly enhances the dynamic response performance of the existing DCCT.The measurement accuracy of the fusion system is calibrated at the National High Voltage Metrology Station,and the test results show that the accuracy of the prototype is better than 10 ppm over 10% of the measurement range.Thus the feasibility and superiority of the proposed DCCT based on multi-sensor fusion are proved.Finally,all the works have done in the paper is summarized and the further research in the future is prospected.