Self-sensing magnetic suspension using an H-bridge type hysteresis amplifier operating in two quadrants

A self-sensing magnetic suspension system with an H-bridge hysteresis amplifier is developed. Since the H-bridge drive circuit consists of a pair of transistors and a pair of diodes, the amplifier operates in two quadrants; the output current has one polarity while the polarity of the voltage applied to the coil is reversed alternatively. The switching characteristics of the amplifier are studied both analytically and experimentally. The measurement results show that the switching frequency is proportional to the air gap between the electromagnet and the suspended object, and insensitive to the value of current command. A digital control system is developed in which the displacement of the suspended object is estimated based on the period time measurement of the switching signal. Self-sensing suspension is achieved with the developed hysteresis amplifiers and the digital control system.