A novel helicopter-borne time-domain airborne electromagnetic transmitting system was proposed.The PWM modulation technology was used to realize the ascending segment and the flat segment of the trapezoidal wave transmitter system under control,which could improve the control precision of the output current,and solve the problems of large trailing currents during the ascending and tum-offtime.A method combining hardware and software was used to eliminate over-shot of the current falling-edge.Parallel technology and soft switching technology were considered to realize static and dynamic flow of powerful devices.Double closed-loop control technology was proposed to improve the stability of transmitter current waveform and the quality of primary field.CHTEM-Ⅰ system was applied to geophysical surveys.The result indicates that the transmitted magnetic moment of CHTEM-Ⅰ system is about 254 469 A·m2,the ascending time of the proposed circuits is lower than 2.2 ms,tum-offtime is lower than 1.2 ms,and the peak transmitter current is up to 500 A.The system has bigger transmitted magnetic moment,higher noise-signal ratio and better ability to reflect the geological information in deep layers.%提出一种直升机时间域航空电磁发射系统,采用PWM调制技术实现梯形波发射波形的上升沿及平顶段电流可控,提高输出电流的控制精度,解决上升沿、下降沿拖尾的问题,并利用软硬件相结合的方法消除下降沿过冲;研究大功率器件的并联技术和软关断技术,实现大功率器件的动、静态均流;设计双闭环稳压电源,提高发射电流波形的稳定性,改善一次场质量;将CHTEM-Ⅰ系统应用于野外测试.研究结果表明:CHTEM-Ⅰ系统的发射磁矩达254 469 A·m2,发射电流上升时间小于2.2 ms,峰值为500 A,下降沿关断时间小于1 ms,具有发射磁矩大、信噪比高、波形稳定性好、反应深层地质信息能力强的特点.
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