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A Bipolar Half-Sine Current Inverter for Airship-Borne Electromagnetic (AEM) Surveying

A topology of a bipolar half-sine current inverter for geophysical airship-borne transient electromagnetic (EM) surveying is developed. In detail, the RLC series resonance inverter with novelty is designed and analyzed. The key parameters of the output current with very small overshoots and high current amplitude are calculated and simulated, respectively. The results of calculation and simulation agree well with each other. The circuit design and principle analysis of the converter are described clearly. The main reason we choose series resonance current inverter rather than the more common parallel one is that a low-voltage source, such as a standard 28-V dc voltage of the usual aircraft power source, could realize high peak current output through a transient series resonance process efficiently. The proposed current inverter is successfully implemented to the airship-mounted geophysical surveying systems. It achieves a substantial improvement of performance and provides an alternative for the traditional fixed-wing EM systems or helicopter EM systems with much lower cost and higher efficiency. Besides, the experimental results for explorations demonstrate that the measured magnetic field of three axes also agrees well with application requirements of airship-borne EM system.