Magnetic bearing having PID controller and discontinuous controller

Magnetic bearings support a rotating body without direct contact and will be used widely for various purpose due to its significant feature e.g. low noise, maintenance-free and use in various surrounding. However, unlike conventional bearings, magnetic bearings have electric power loss. Direct current flows in the exciting coil to levitate a rotor. The use of series dropper-type amplifiers to control this current generate great losses. To reduce these losses, the authors adopted pulse width modulation (PWM) type amplifiers instead of series dropper type. To decrease losses further, the switching frequency of the control voltage of the exciting coil must be decreased. In this paper, the authors describe a combined PID-discontinuous controller that reduces the above losses of the magnetic bearing. The theoretical analyses are confirmed by experiments