Design Of Low Distortion Alternating Current Source For Insulation Test

In view of the serious loss caused by insulation accident of high voltage motor,higher standards and requirements are put forward for AC power supply for motor AC partial discharge test.A digital AC power supply based on single-phase full bridge differential symmetry principle is designed.Firstly,the overall structure of AC power supply is constructed,the topology of inverter circuit and the characteristics of SPWM modulation mode are studied.The existing problems,especially the DC component,are analyzed.A single-phase full bridge differential symmetrical inverter circuit is proposed,which can effectively offset the DC component.If appropriate control algorithm is adopted,the harmonic can be reduced.Secondly,according to the hardware design goal,the power devices and control chips are selected,and the control circuit board,interface conversion circuit board,drive circuit board and output filter are designed.The control chip adopts RT1052 cross-border processor;the power device adopts high-speed IGBT module;the auxiliary power supply of driving circuit board is isolated by transformer,and the driving chip is isolated by optocoupler;the SPWM signal adopts differential output to improve the anti-interference performance.On the premise of meeting the design requirements,it has high cost performance.Then,the CPU and SDK software structure of MCUXpresso IDE is studied.On this basis,the system software is designed in detail,including project creation,SDK configuration and SPWM program.Using MCUXpresso IDE software does not need to write the underlying cumbersome program,as long as you need to configure parameters and call related functions,which reduces the complexity of using the software.Finally,the experiment and analysis of the AC power system are carried out.First,the frequency response of IGBT is measured,and then the waveform output ability of single-phase full bridge differential symmetrical inverter circuit is tested.The experimental results show that the single-phase full bridge differential symmetrical inverter can effectively suppress the DC component,the total harmonic distortion of the output voltage is low,the waveform is pure,and the voltage amplitude and frequency meet the requirements.The experimental results are basically in accordance with the design requirements.