Double Clamping Current Inverter With Adjustable Turn-off Time for Bucking Coil Helicopter Transient Electromagnetic Surveying

As a core component of the bucking coil helicopter transient electromagnetic (TEM) system, the current pulse inverter should agree two crucial aspects, high power and fast turn-OFF. In this article, based on the design and modeling of transmitting coil and bucking coil, a novel current inverter topology based on the double constant voltage clamping technology, which differs from the traditional single clamping technology is firstly proposed and analyzed. By using double clamping technology, both the current pulse's rising edge and falling edge are improved effectively. What's more, the turn-OFF time of the current inverter is adjustable, which is of great difference from the conventional clamping technology with nonadjustable turn-OFF time. The ground and field experiments are implemented to test the performance of the current inverter. The results of the ground test of the performance comparison with worldwide VTEM transmitter verify that it successfully converts the standard 28 V dc source from helicopter power to bipolar approximately trapezoid pulses with a peak current of 300 A and a much faster turn-OFF time than the VTEM transmitter. The results of field exploration further demonstrate that it achieves a high quality of primary field compensation and effectively improve the detection capability of the helicopter TEM surveying system.