| Electromagnetic detection is one of the important means of geophysical exploration, and it is widely used in oil and gas resources exploration, mineral exploration, archaeological research, modern city construction, safety prediction of tunnel and mine and hydrological exploration etc. However, our country is still dependent on imported high-performance electromagnetic detection equipment at present, it has important academic significance and practical value to design and develop electromagnetic detection system with independent intellectual property rights of China. Based on the background of electromagnetic detection technology, and according to the requirements of the electromagnetic transmit waveform, the timedomain and frequency-domain electromagnetic detection transmitter system have been researched and designed in this thesis, and mainly completed the following work:(1) In this thesis, the development and status of electromagnetic detection technology and instrument are studied, comparison is made for the advantages and disadvantages of domestic and foreign electromagnetic transmitter, and the necessity of transmit waveform improvement under an optimized power supply system is pointed out.(2) Combined with the advantages of the existing electromagnetic detection transmitter power supply system, the time-domain electromagnetic transmitter which takes a generator as power supply is designed. The parameters of the uncontrolled rectifier which LC filter are optimized, and the power factor of 0.9 is achieved. The modeling and design of control system is completed, the comparison of open-loop and closed-loop system shows that the closed-loop system has good steady-state performance and dynamic performance, and the transmit voltage is tunable with a wide range of 0V to 1000 V.(3) According to the demand of fast turn-off transmit waveform in the time-domain electromagnetic detection, the transmitting circuit with clamping voltage at droppingedge is designed. In the MATLAB/Simulink model which contains the part of the power supply system, the improvement of transmit waveform quality is verified, the turn-off time is only 80?s with a transmit current of 20 A.(4) According to the demand of transmit waveform and a wide frequency range in frequency-domain electromagnetic detection, based on fast turn-off transmitting circuit, the transmitting circuit able to improve the rising-edge is designed. In the MATLAB/Simulink model which contains the part of the power supply system, a common full bridge transmitting circuit is compared with the transmitting circuit proposed in this thesis. The results show that the proposed transmitting circuit ensures a stable transmit current under the power supply fluctuation, and the amplitude of the transmit current is more than three times of the common full bridge circuit at the frequency of 30 kHz, the total commutation time is only 11.1?s which broaden the frequency range of transmit waveform.(5) According to the demand of circuit power loss and thermal analysis, PLECS is applied in the modeling of time-domain electromagnetic detection transmitter, the power devices were detailed modeled in order to calculate the losses and power efficiency, and the contribution of loss reduction of phase-shifted control is verified. The thermal circuit is analyzed, and maximum thermal resistance of heat sink is obtained, this provides the thermal simulation basis in building a prototype model and shortens the developing and testing process. |
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