Research On Piezoelectric Beam Current Sensor For Three-Phase Four-Wire Conductors

With the rapid development of smart,efficient and clean smart grids,it is necessary to accurately and timely collect relevant important information in order to ensure the safe and efficient operation of the power grids,of which current information is especially important.As current measuring devices,current sensors play an important role in people's lives and in the fields of industry and agriculture,which are widely used in industrial equipment,new energy,automotive electronics,medical equipment and other fields.Most current sensors require external power supply,so high energy consumption can not meet the requirements of the smart grids,and most current sensors can only measure a single wire,which greatly limits its application.In response to these problems,some scholars have proposed a cantilever beam current sensor structure,which can passively measure AC or DC current,thus greatly reducing the power consumption of the sensors.At the same time,the structure is small and the cost is low,which is suitable for the promotion and application of the smart grids.However,for the three-phase four-wire AC current,which is widely used in many fields such as industry and agriculture,there is no effective measurement method.Therefore,based on the current research status at home and abroad,this thesis proposes a piezoelectric cantilever beam current sensor capable of realizing the three-phase four-wire AC current amplitude with star-connected symmetric load measurement,which features low power consumption,small size and simple structure.According to the theory of electromagnetic field,the spatial magnetic field gradient distribution around the three-phase four-wire wires is studied and analyzed.Further theoretically analyze the stress state characteristics of the permanent magnet in the surrounding space.A theoretical model of piezoelectric cantilever beam current sensor is established,analyze its working principle in detail and the sensor output response is derived.Theoretical analysis shows that the output voltage amplitude of the sensor is proportional to the amplitude of the AC current to be measured.Secondly through simulation analysis of influence of structural geometric parameters on the natural frequency and output response of the sensor,the optimal design of the sensor structure is completed and keep the sensor operating frequency away from the first-order natural frequency.The influence of the simple harmonic external load on the output response in different directions is analyzed.It is concluded that in order to ensure the accuracy and stability of the sensor operation,a good measurement position is selected where the effective external load amplitude is large and the external load amplitude is small.Finally,according to the results of simulation analysis,the sensor structure is fabricated and the piezoelectric cantilever beam current sensor for three-phase four-wire AC current measurement system is built.Analyze the selection of the appropriate measurement location and multiple sets of experimental data were measured.Experimental data shows that the sensor output voltage amplitude is linear with the AC current amplitude and the characteristics of the experimental results are consistent with the theoretical simulation analysis,which proves the feasibility of sensor measurement.The piezoelectric cantilever beam current sensor proposed for the three-phase four-wire AC current measurement can realize non-contact passive measurement.In the thesis,the influence of different measurement positions on the sensitivity of the sensor and its causes are studied in detail,and a new measurement method is proposed for the three-phase four-wire AC current in the supply system in the industrial and agricultural fields.