Sensorless Magnetic Levitation Control by Measuring the PWM Carrier Frequency Component

Active magnetic levitation control has been gradually used for clean room carrier or highspeed magnetic bearings. Usually it requires a displacement sensor causing some trouble of noncollocated sensor and actuator arrangement, and a good sensor is expensive. A sensorless active magnetic control has been reported, but not so successful. This paper introduces a simple sensorless active levitation control. The magnet is driven by a constant voltage pulse width modulated (PWM) signal. The PWM carrier frequency component of the measured current is the function of the magnetic inductance, which is the function of the gap displacement. This signal is put into a detecting circuit to produce the control signal. A simple test apparatus is made to clarify its capability. The results are showing high possibility of this sensorless levitation control.