| In the construction of smart grid,AC current monitoring has become one of the most important contents of various power equipment status assessments,fault location and postmaintenance.At present,the non-contact current measurement technology based on the magnetic field detection is widely used in power systems,which can be roughly divided into several types including electromagnetic induction current sensors,Hall current sensors and giant magnetoresistance current sensors,but most of them require a stable external power supply.However,the AC current sensor based on the magnetoelectric laminate is equivalent to a passive two-terminal element in the circuit,so it can work independently without power supply.The classic magnetoelectric current sensors can be divided into a laminated open-loop structure and a core-through closed-loop structure.The laminated open-loop structure mainly includes a single-end clamped cantilever beam and a free-end beam at both ends.When the free beam at both ends is used,it works in the non-resonant mode and has low sensitivity.On the contrary,the single-end clamped cantilever works in the resonant state and has higher sensitivity,but it can be disturbed by the external environment vibration and stray magnetic field easily.Though the core-through closed-loop structure can effectively increase the curent detection sensitivity,most of them cannot realize the operable function.At the same time,the giant magnetostrictive material Terfenol-D is mostly used as the sensitive element,which has low magnetic permeability,large hysteresis,and tougher requirements for DC bias magnetic field,not conducive to practical use.In view of this,this thesis proposes two closed-loop current sensors based on Fe Si B/PZT/Fe Si B magnetoelectric composite for power frequency weak current detection which named split-core closed-contact closed-loop current sensor and split-core tooth-shaped closed-loop current sensor,respetively,and analyzes their performances through theoretical and experimental comparisons.The main conclusions are as follows:1.Based on Comsol Multiphysics software,the simulation and optimization of the magnetic core structure of the current sensor is carried out.The magnetic field convergence effect and magnetic field shielding effect of the split-core closed-loop magnetic core are verified,and the material and size of the magnetic core are determined.The influence of the contact patterns between the magnetic core and the magnetoelectric composite and the open joint shapes of the split-core magnetic core on the magnetic field distribution of the magnetostrictive material are analyzed.According to the simulation results,the above structures can significantly improve the sensing performance of the sensitive element,and can also effectively reduce the measurement errors caused by the wire offset and the air gap of magnetic core open joint.2.Two current sensor performance test systems were built with the signal generator(1)and high current generator(2)as excitation sources,respectively,and the effects of the contact patterns between the magnetic core and the composite(closed contact mode and non-closed contact mode)on the sensor performance are compared and analyzed through experiments.Then a closed-contact closed-loop current sensor based on the Fe Si B/PZT-82/Fe Si B(FPF)magnetoelectric composite is proposed.The results demonstrate that: in system 1,the sensitivity of the power frequency(50 Hz)current in 0～5.5 A is 17.444 m V/A,which is about35 times higher than that of the coreless FPF composite,and 1.2 times higher than that of the non-closed-contact closed-loop current sensor;In system 2,the sensitivity of the power frequency current in 0～20 A is 12.176 m V/A,which is about twice higher than that of the nonclosed-contact closed-loop current sensor.It is worthy noting that when there is an air gap in the magnetic core open joint,the sensor will also effectively improve the sensitivity and linearity of current detection.3.Based on the closed-contact closed-loop current sensor,the influence of the split-core magnetic core open-joint shapes(plane shape and tooth shape)on the performance of the current sensor under different magnetoelectric composites is comparatively studied,and a split-core tooth-shaped closed-loop current sensor is proposed.The results demonstrate that in the range of the power frequency current of 0～5.5 A,compared with the plane-shaped closedloop current sensor,the sensitivity of the tooth-shaped closed-loop current sensor based on Fe Si B/PZT-82/Fe Si B magnetoelectric composite is 28.801 m V/A,which is 1.65 times higher than that of the plane-shaped closed-loop current sensor;the linearity and hysteresis errors are±0.79% and ±1.1%,respectively.The sensitivity of the tooth-shaped closed-loop current sensor based on Fe Si B/PZT-fiber/Fe Si B magnetoelectric composite is 1.238 m V/A,which has been improved by about 3 times;the linearity and hysteresis errors are ±0.88% and ±1.33%,respectively. |
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