Design And Realization Of Soft Switching Chopper Constant Current Transmitter

China is rich in mineral resources, and many reserves proven are among thehighest in the world. With the rapid economic development of our country, therequirement for mineral resources is growing day by day, but with the continuousincrease of mining intensity, many shallow ground resources have been depleted. Inorder to meet the needs of the national economic growth, people turn their attention tothe exploration and exploitation of deep mineral resources. The birth and developmentof magnetotelluric sounding technique, which have been widely used, make up for theshortcomings of traditional deep exploration of mineral resources.Frequency domain magnetotelluric relies upon electrical source emitting device,can realize the geophysical exploration of underground resources. Compared with thenatural source magnetotelluric method, frequency domain electromagnetic soundingmethods use artificial emission source, to get the stronger suppression effect on thesurrounding environment noise detection. Therefore, the design and fabrication of theexcellent performance of the electrical source emitting device is extremely important.The frequency domain electromagnetic sounding instrument abroad started early,and have high level with advanced performance index. After decades of developmentand continuous change, they have formed a series of standard commercial instrument.Although the domestic electromagnetic detection equipment developed relatively late,afterdecades ofdevelopment, thedomesticinstrument hasbegunto takeshape. Inorderto ensure the accuracy of measurement results, electrical source transmitters need tochange the load current according to the set value by the controller and the earth load.Usually the improvement of transmitter frequency can speed up the system response ofcontrol loop, reduce the adjusting time, so as to enhance the current control accuracy.However, with increased frequency of the device, the negative impact is bringing theincrease of switching loss. The bigger heat sinks are needed. And with the lower powerdensity, field application is restricted. In order to solve the contradiction betweenaccuracy and low power density, this paper proposes to use soft switching choppertopology structure as the main electrical source emitting device. Consider about themainstream of the soft switching chopper technologysuch as: quasi resonant converter,zero switching PWM converter, passive soft switching PWM converter. Consideredfrom engineering practicability, including logic control degree of difficulty, restrictionof the power level, work stability, the passive lossless chopper structure is finallychosen as a topology structure of electricity source transmitter. At the same time, this paper analyzes the running status of the converter underdifferent load. The converter that enters the state of hard switching is analyzed. By thesetting of ratio of the resonant capacitor and the charging capacitor, and taking intoaccount the relationship between the resonant cycle and switching cycle, the electricalsource current emission system with the characteristics of soft switch chopper isdesigned. Study on the similarities and differences between the operation states ofconverter under different load conditions. Especially that heavy load converter into thepart of the soft switching state is analyzed, and the passive soft switching converter aregiven for engineering design. The control circuit of the transmitting system has giventhe detailed design of PWM control circuit, the duty ratio of output range0~100%; toensure the stable operation of the machine, setting temperature, over-voltage and over-current protection circuit; the open-loop Bode diagram using frequencydomain, settingreasonable crossover frequency and high, middle,low-frequency gain slope PWMdesign flow link. According to the requirement of current high power transmitter outputindicators, the design process of the air gap inductor is expounded. According to thelength of air gap inductance is designed one more time. The measured maximumtransmitting voltage1000V, the emission current20A, maximum20kW power. Theexperiment shows that the voltage and current waveform of main switch and resonantcapacitor is in soft switching condition, and the efficiency can reach above95%.