Controller for magnetic bearing system

A controller for a magnetic bearing system of the type having a rotor yoke made of a magnetic material which is rigidly secured to a rotary shaft, a pair of electromagnet stators rigidly secured to a casing with a minute gap provided between the same and said rotor yoke, each stator having a coil for generating magnetomotive force, a displacement sensor for measuring relative displacement between said rotary shaft and said casing, and a combination of a compensation circuit and a power amplifier for controlling the level of magnetic attraction force acting between said rotor yoke and said pair of electromagnet stators on the basis of a signal output from said displacement sensor, said controller comprising:

• said power amplifier including two operational amplifiers which are supplied with a signal output from said compensation circuit and two power transistors for amplifying the respective outputs of said operational amplifiers,
• wherein the signal output from said compensation circuit is input to both the non-inverting input terminal of one of said operational amplifiers and the inverting input terminal of the other operational amplifier, and an exciting coil bias voltage is input to the respective inverting input terminals of the two operational amplifiers in parallel to said input signal.