Displacement-Sensorless Control Using Electromagnets : Vibration Control by Current and Magnetic Flux Feedback

Abstract

This paper describes vibration control using electromagnets without displacement sensors. An electromagnet for vibration control has two natural feedback loops. One feedback loop is from the gap length to the magnetic flux ; the amount of the magnetic flux depends on the gap length. The other is from the magnetic flux to the coil voltage ; the back electromotive force is derived from the time derivative of the magnetic flux. Through these two feedback loops, information on the gap length pours into the magnetic flux and the coil current ; therefore, the gap length can be detected from these two state variables of the electromagnet without a displacement sensor (self-sensing). The displacement, being the fluctuation of this gap length, can be estimated by subtraction of the coil current from the magnetic flux. The vibration control using this estimated displacement consists of the negative feedback of the magnetic flux and the positive feedback of the coil current. The PD feedback of the estimated displacement can produce a damping effect and positive stiffness.