Research On CT Power Supply Based On PWM Rectifier

With the rapid development of my country’s economy and the concept of smart grid,real-time monitoring of transmission lines has become an important factor for restricting the development of the power industry.Current transformer(CT)is widely used in power supply for monitoring equipment.In fact,the current fluctuation of the transmission line is very large,and the application of current transformer induction power is limited,mainly in two aspects:(1)When the current of the transmission line is small,the power acquisition device cannot provide sufficient power for the monitoring equipment,or even stops the power supply,forming a power supply dead zone;(2)When the current of the transmission line is large,the current transformer is saturated,and the output voltage of the secondary side is too high and the equipment is damaged.Based on these two issues,this article carries out the following analysis and research:1.Paper analyzed the principle of current transformer taking power,establishes the circuit model of the power taking device according to the principle,obtain the relational expression of the current transformer size,material,secondary side load and output power,analyze the iron core when there is an air gap,the size of the air gap affects the output power of the secondary side of the current transformer.2.Aiming at the problem of insufficient electric power when the transmission line current is small,paper proposed a parallel matching capacitor on the secondary side of the current transformer.Under the premise of the parameters such as the excitation inductance and hysteresis loss of the current transformer,paper uses the resonance principle to determine the matching the parameters of the capacitance enable the secondary side of the current transformer to output the maximum power possible when the primary current is small.Combined with the lithium battery and the charge and discharge module,the dead zone caused by the too small primary current is eliminated.3.Aiming at the problem that the output voltage of the secondary side of the current transformer is too high when the current of the transmission line is large,it is proposed to integrate the IGBT into the bridge arm of the rectifier circuit to form a semi-active rectifier circuit,and control the gate of the IGBT through the PWM wave to realize the input For voltage modulation,considering the influence of load changes,the relationship between the output voltage and the duty cycle of the PWM wave is deduced,and paper analyzed the working process of the circuit under this control mode in detail.And paper also analyzed the working process of the traditional passive rectifier circuit.4.Paper analyzed the back-stage circuit of the power-taking device,and introduced the operation mechanism and control method of the impact protection module,the relay control module DC-DC module,and the battery charging and discharging module.5.Paper build a simulation model of the CT power supply based on PWM rectification with the Matlab/Simulink,simulated the steady-state output voltage of the power-taking device and the transient output voltage when the transmission line current and the equivalent load impedance change.Analyzed the output characteristics of the power-taking device through the output waveform diagram under various conditions.The simulation results show that the CT power taking device using PWM control semi-active rectifier circuit can maintain a stable output of 5V when the transmission line current fluctuates within 50~1000A and when the load changes,which can meet the power supply requirements of monitoring equipment.Verify the correctness of the theoretical analysis.