So for reducing current ripple, the methods of reducing voltage of power source and increasing tum-on frequency may are used, but the excessively low power source voltage will affect the response speed of magnetic bearing's electromagnetic force and the excessively high tum-on frequency will make the switching loss to increase, the switch power amplifier efficiency to drop. According to (17), the current ripple of three-level switching power amplifier is irrelevant to the voltage of
power source, is inversely proportional to tum-on frequency and coil inductance.