High-efficiency linear power amplifier for active magnetic bearings

A modified class-G linear amplifier has been developed to improve the overall efficiency of a transconductance amplifier loaded with the high inductance and low resistance typical of the magnetic bearing coils. A simple theoretical characterization has been used to provide some diagrams to optimize the power efficiency as a function of a nonconstant load such as that due to a rotor unbalance. Experimental results are reported that show a more than satisfactory agreement with the expected results and the developed theory.