PWM斩波与恒压钳位控制瞬变电磁发射系统

A TEM system with PWM chopping and constant voltage clamp control

针对磁性源发射系统中波形质量差,效率低、下降沿关断慢等问题,提出一种PWM斩波和恒压钳位控制方式相结合的控制方法,并通过软件仿真比较采用该方法的发射电路与传统的H桥发射电路的波形质量和关断时间。研究结果表明:该方法通过提高发射线圈电流下降段的馈能电压,加快IGBT关断过程发射线圈电流下降速度,缩短关断时间,丰富发射波形的频率成分,有利于瞬变电磁探测。同时,馈能环节能够回收发射线圈能量,提高整个发射系统的效率。采用PWM斩波控制技术控制发射电流平顶段,平顶段发射电流斜率为0,降低了发射电流上升段和平顶段对接收信号的干扰。发射波形近似理想梯形波,与无钳位的传统发射电路相比,在发射电流为15 A的情况下,下降沿时间由500μs缩短为100μs,对于浅层的探测效果更好。

In order to solve the strong electromagnetic interference,low efficiency and slow turn-off speed of the magnetic source TEM system,a method with PWM chopping and constant voltage clamp control was proposed.This method was compared with the conventional H-bridge transmission circuit using the circuit simulation software.The results show that increasing the feedback voltage can speed up the coil current dropping speed,thus the IGBT turn-off transmitter coil current rate of decline improves greatly,the turn-off time reduces and the frequency component of the transmission waveform signal enriches.It is benefit to the transient electromagnetic detection.Meanwhile,the feedback circuit can recycle the transmit coil energy to improve the efficiency of the transmission system and the emission current flat top section with a PWM chopper control makes flat top section emission current slope 0.This decreases the interference of the emission current top segment and increases segment on the received signal.The emission waveform is almost close to the ideal trapezoidal wave.Compared with the traditional transmission circuit without clamping,the circuit falling edge time is shortened from 500μs to 100μs,which is better for the shallow detection.