The Design And Research Of DC Current Comparator Based On Magnetic Modulator

Large direct current have wide applications in various industries such asIndustrial production,HVDC transmission,, high-speed rail,scientificexperiments.With more and more application field of direct current and DC powerconsumption is showing an increasing trend.At present, China has implemented anew power plant system,which gradually form a market-oriented pricingmechanism.In order to saving energy and keeping the fairness of the electricitymarket,the accurate measurement of DC currents appears imminent.First,this article introduced the principle of the DC current comparator basedon magnetic modulator,discussed the advantages of double loop magneticmodulator,then given the overall design of the DC current comparator based onmagnetic modulator. Second, this article designed a small magnetic modulation typeDC current comparator to verify the feasibility of the magnetic modulation theory.Hardware circuit mainly includes the ac excitation circuit, transformer, magneticring, power supply, bandpass filter, phase locked frequency multiplier, bias circuit,multiplier, low-pass filter, PI control, power amplifier, etc. Third, in this paper, themeasurement results are analyzed, and the measured results include the open-loop,closed-loop characteristics and the analysis when the actual DC current containharmonics. Finally, the magnetic shielding is designed for dc current comparator,with magnetic circuit method, theoretical analysis was carried out on the shieldingeffectiveness and then using ANSYS to simulate the shieldingeffectiveness.Comparison of theoretical analysis with ANSYS simulation,thesimulation can be proved effective.As can be seen from the experiment and simulation,the accuracy of the smallmagnetic modulation type DC current comparator designed in this article is superiorto5×10-3A,and is not affected by the degree of saturation. The fewer the numberof turns, the smaller the load, the higher the load power factor, the harmonic effecton the comparator is smaller. Using high magnetic permeability material, increasingthe thickness of the magnetic shield can increase the magnetic shieldingeffectiveness, while increasing the inner diameter of magnetic shielding body willdecrease it.