An inverter for generating harmonic rich current waveforms for aircraft mounted electromagnetic surveying systems

An inverter topology that has been developed for geophysical surveying applications makes it possible achieve very fast current reversal in magnetic field coils. The inverter also makes it possible to generate waveforms that contain a variable high frequency spectrum superimposed on a high amplitude low frequency fundamental. A feature, which is attractive from an implementation point of view is a low voltage source such as a battery can be combined with high voltage transistors to meet high dynamic requirements. Two variations of the topology are discussed namely a clamped and unclamped version. The proposed inverter was successfully implemented in two aircraft mounted geophysical surveying systems achieving substantial performance improvement over the older systems. A 40 kW system was constructed for a fixed wing aircraft and a smaller, battery operated system was implemented on a helicopter.