The control system design of a DC to 10 kHz bandwidth 45 kVA current sourced power amplifier suitable for geophysical exploration application is presented. A five-level modulation scheme has been implemented using a modified bridge topology with only four switches. This scheme gives an order-of-magnitude improvement in switching ripple and control performance over two-level modulation. Using this system, a 50 kHz switch frequency allows a 20 kHz, -3 dB bandwidth to be easily achieved. Simulation and tenth scale model test results are presented. The current output waveform reproduction is of high quality over the rated DC to 10 kHz frequency range. The total harmonic distortion is 0.3% at 1 kHz.
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