In the popular electromagnetic exploration technique, a bipolar artificial pulse current is emitted from an electromagnetic transmitter into the ground to generate a transient secondary electromagnetic field in the surface strata, and the geological structure in obtained by analysing the distribution of the secondary magnetic field. This paper presents a cascaded electromagnetic transmitter to overcome the drawbacks of the existing transmitters. First, the structure and composition of the earth load are analysed when the transmitter is working in the low frequency or high frequency mode, and the relationship between the earth load and the emission frequency is provided directly. Then, based on the small-signal model of phase-shifted full-bridge converter, the influencing factors on the stability of the source converter are analysed and summarized in details when the transmitter worked in the whole frequency range. Moreover, we have derived the possible solutions to ensure the steady-state and dynamic features of the source converter output in the whole frequency range. Two methods are developed through detailed analysis: increase the gain of the voltage-loop transfer function, and increase the output filter inductance of the source converter. Finally, the research findings have been verified by a prototype through an experimental simulation.
electromagnetic exploration, cascade, phase-shifted full-bridge (PSFB), earth load, voltage-loop gain, whole frequency range.
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