Development of Self-Sensing Magnetic Bearings Using Variable-Switching-Frequency Amplifiers

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This research investigated on seIf-sensing magnetic bearings using the switching signals of variable-switching-frequency amplifiers (hysteresis amplifiers) for feedback ccntroL The approach was both theoretical and experimental.First ; hysteresis amplifiers were classified based on the kind of power supply and the quadrants of operation. The dynamics of each amplifier was studied analytically. A test circuit of each type was manufacturect It was experimentally confirmed that the switching frequency of each amplifier was proportional to the gap between the suspended object and the electromagnet It was also shown that the hysteresis amplifier with an H-bridge drive had several advantages as power amplifiers for self-sensing magnetic bearings. They are(1) The speeds of increase and decrease of current are same although a unipoIar power supply is used.(2) The switching frequency in insensitive to the value of current command to the amplifier because the H-bridge reverses the polarity of the voltage applied to the coil alternatively.Second, the control system design of self-sensing magnetic bearings was discussed. Since the signal to be fed back in given in the form of frequency, the control system can be designed in different ways from those of conventional active magnetic bearings with analog type sensors. According to the signal conversions performed in the system, the configurations of control system are classified as1) Control system using frequency-to-voltage converters(2) Control system using phase detectors(3) Control system using countersThe characteristics of each control system were clarified Self-sensing suspension was achieved with these control systems.The results obtained by this research are fundamentaI and useful to promote industrial applications of the self-sensing magnetic bearings with variable- switching-frequency amplifiers. It is planed to develop a small-size magnetic bearing system by taking advantage of self-sensing operation