Research On Method And Key Technology For Measuring Hysteresis Loops Of Permanent Magnet Materials Based On Pulsed Field

Permanent magnet materials are widely used in new energy vehicles,wind power generation,intelligent robots and other fields.The performance of electrical equipments are closely related to the magnetic properties of permanent magnetic materials.For the accuracy of simulation and design,it is particularly important to measure the magnetic properties of permanent magnetic materials accurately.With the continuous progress of materials science,permanent magnetic materials with ultra-high coercivity continue to come out.For this type of permanent magnet material,if a traditional permanent magnet measuring device is used,the pole head of the electromagnet becomes saturate,causing a large error in the measurement result or measurement failure.Although a vibrating sample magnetometer equipped with a superconducting magnetization device can be used for measurement,the device is technically complex,and the cost of purchase and maintenance is high.At this time,the pulsed field magnetometer is born as needed,with low cost and high measuring magnetization field,which has good application prospects.The pulsed field magnetometer is based on the pulsed field open-circuit measurement method.During the measurement,eddy current is induced in the sample.The magnetic effect of the eddy current affects the accuracy of the measurement.For solving the problem,a time difference method was proposed.This method is based on the principle that the eddy current is proportional to the magnetic field change rate.The sample is measured by two pulsed fields with different pulse widths but the same positive and negative peak fields.The eddy current effect is obtained by calculating the difference between the measurement result and the time.A model of the sample affected by various magnetic fields was constructed,and a complete mathematical derivation of the time difference method was given.According to the requirements of the method,a pulsed field generator with a short pulse width of 8 ms,a long pulse width of 16 ms,and a positive peak magnetic field of 13 T was designed.A multi-physical coupling model of circuit,magnetic field,thermal field and mechanical field in the discharge process was established.The device adopted a dual-coil pulsed magnet system.Compared with foreign four-coil system,magnets were reduced by 50%,and semiconductor control devices were reduced by 75%.It had good structural performance and thermal performance.A design scheme of the coaxial magnetic polarization pick-up coil for measuring samples with a diameter of less than 10 mm was proposed.The calibration methods of pulsed field magnetometer measurement system were analyzed and compared.The pick-up coils are calibrated by methods which are simple and easy to realize.The analog-to-digital conversion process and data processing process of the measurement signal are discussed and analyzed.The design of pulsed field magnetometer measurement system was completed.The fabrication of the dual-coil pulsed magnet and the magnetic polarization pick-up coil was completed.The experimental prototype of the pulsed field magnetometer is built.A variety of samples with different aspect ratios and different materials were measured under the plused field.The measurement results were corrected for eddy current effect and demagnetization effect.Experiments have verified the effectiveness of the time difference method in the correction of the eddy current effect.The measurement results of the Nd Fe B sample are compared with those of the National Insititute od Metrology,China.The measurement error of the main magnetic properties including remanence and coercivity is within 2%.