Magnetic bearing control apparatus and vacuum pump

A vacuum pump being mounted with a magnetic bearing control apparatus including:

• an electromagnet which supports a control object in a state floating in the air;
• an inductive element connected in series to a coil of the electromagnet;
• a switching amplifier which supplies a current to the electromagnet;
• voltage extracting means which extracts a voltage applied to the inductive element at timings occurring repeatedly with a prescribed period;
• sample-holding means which holds a voltage extracted at a timing which is one of the timings until a next timing for extracting, and sample-holding means acquires the voltage applied to the inductive element based on a signal having been synchronized over control cycles of the switching amplifier;
• current change rate obtaining means which obtains, based on a voltage held by the sample-holding means, a signal proportional to a time derivative of a current flowing through the coil of the electromagnet;
• and
• displacement estimating means which estimates, based on a signal obtained by the current change rate obtaining means, a displacement between the control object and the electromagnet,
• a current supplied to the electromagnet being controlled based on a displacement estimated by the displacement estimating means,
• wherein the voltage extracting means extracts the voltages applied to the inductive element at prescribed timings in each of a current increase period in which the current increases and a current decrease period in which the current decreases,
• wherein an adding means adds up two extracted voltages,
• wherein a current flowing through the electromagnet is estimated based on a value obtained by addition by the adding means, and
• wherein the control object is a rotor shaft, and
• the vacuum pump includes the electromagnet in plurality for floatingly supporting the rotor shaft in a radial direction and/or an axial direction.