| Due to the limitations of existing insulation design theory,the erosion of unfavorable natural environment,the long-term effect of working voltage,the short-term impact of overvoltage,the imbalance of dielectric insulation performance,etc.Can the insulation of high-voltage electrical equipment meet the design requirements on site and be safe Reliable operation requires strict insulation test verification.For the 10 kV equipment with the largest number of operations,the general equipment operation site does not have the test conditions,and the long test period and high cost of the test for disassembly and transportation to the test station limit the effective implementation of the insulation prevention test for such equipment.Based on understanding the national standard of power frequency withstand voltage test,this paper proposes a portable power frequency withstand voltage test system based on PIC18F4520 microcontroller control and dual power supply.The power supply is AC220 V /50 Hz or DC12 V,that is,when the AC220 V / 50 Hz power supply is used,the power supply is used;when the AC220 V / 50 Hz power supply is not used,the DC12 V power supply is used.Its main work is as follows:(1)Taking PIC18F4520 as the measurement,control and protection center,the structure design of the portable power frequency test system is carried out.Including power supply voltage and current measurement,test voltage and current measurement;including test start and stop control,power supply conversion control,step-up and step-down control and withstand voltage time control;protection links include battery over-and under-voltage protection,thermal protection,including during the test overcurrent protection,etc;Using DC-DC high-frequency boost technology and PWM technology to achieve the conversion of DC12 V to AC220 V / 50 Hz.The rear end of the voltage regulator is connected with a hybrid active filter to complete the filtering of the output voltage.(2)In this thesis,the circuit design and parameter calculation of the portable power frequency test system measurement,control,display system,power circuit,filter and other hardware circuits are carried out.The measurement circuit mainly relies on the voltage and current transformer sampling loop signal,and the voltage signal that can be accepted by the single chip microcomputer is measured through the measurement circuit for measurement.The voltage regulation control mainly relies on the single chip microcomputer CCP module and themotor drive signal amplification circuit to realize the voltage regulation work.In the power circuit,the DC-DC high-frequency boost circuit uses the SG3525 pulse width modulation chip to achieve high-frequency PWM output.The post-stage DC-AC power frequency inverter uses a single-chip microcomputer to complete the SPWM wave output,and the output voltage is fed back through the PI algorithm.The hybrid active filter combines the mathematical model and calculates the specific parameters of each component.(3)The PIC18F4520 chip is used as the control center for measurement,display,control,protection and other subsystems in the test system,and MPLAB IDE is used as the design platform.The system software part was designed in process and written in C language,and the digital control of the portable power frequency test system was completed.(4)Modeling and simulating the designed hardware circuit,and debugging its inverter power system function,input DC12 V,output 220V/50 Hz power frequency single-phase AC voltage.The debugging results are as follows: the output voltage range is 5V220 ?;Debug the filter parameters so that the total harmonic content of the output voltage waveform is less than 0.3%. |
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