Method of controlling operation of synchronous motor and motor control apparatus for the same

A method of controlling operation of a synchronous motor, said synchronous motor making polyphase alternating currents flow through polyphase windings and rotating a rotor by an interaction of a magnetic field formed by said windings with a magnetic field formed by a permanent magnet, said method comprising the steps of:

• determining whether or not said rotor rotates at a revolving speed of not less than a predetermined level, prior to a start of operation of said synchronous motor;
• detecting an electrical angle of said rotor according to a first detection process in case that said rotor rotates at the revolving speed of not less than the predetermined level, and regulating the polyphase currents flowing through said polyphase windings based on the detected electrical angle, said first detection process having a practical accuracy when the revolving speed of said rotor is not less than the predetermined level;
• and
• detecting the electrical angle of said rotor according to a second detection process in case that said rotor rotates at the revolving speed of less than the predetermined level, and regulating the polyphase currents flowing through said polyphase windings based on the detected electrical angle, said second detection process having a practical accuracy when the revolving speed of said rotor is less than the predetermined level.

A motor control apparatus that controls operation of a synchronous motor, said synchronous motor making polyphase alternating currents flow through polyphase windings and rotating a rotor by an interaction of a magnetic field formed by said windings with a magnetic field formed by a permanent magnet, said motor control apparatus comprising:

• a first electrical angle detection unit that detects an electrical angle of said rotor according to a first detection process, said first detection process having a practical accuracy when a revolving speed of said rotor is not less than a predetermined level;
• a second electrical angle detection unit that detects the electrical angle of said rotor according to a second detection process, said second detection process having a practical accuracy when the revolving speed of said rotor is less than the predetermined level;
• a revolving speed computation unit that calculates the revolving speed of said rotor at least based on a variation in electrical angle detected by said first electrical angle detection unit;
• a switching unit that activates said first electrical angle detection unit to detect the electrical angle of said rotor immediately after a start of operation of said synchronous motor, and activates said revolving speed computation unit to calculate the revolving speed of said rotor based on the electrical angle detected by said first electrical angle detection unit, when the revolving speed calculated by said revolving speed computation unit being less than the predetermined level, said switching unit activating said second electrical angle detection unit to detect the electrical angle of said rotor;
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• a control unit that regulates the polyphase currents flowing through said polyphase windings based on the electrical angle detected by either one of said first electrical angle detection unit and said second electrical angle detection unit.

A motor control apparatus that controls operation of a synchronous motor, said synchronous motor making polyphase alternating currents flow through polyphase windings and rotating a rotor by an interaction of a magnetic field formed by said windings with a magnetic field formed by a permanent magnet, said motor control apparatus comprising:

• a revolving speed determination unit that determines whether or not said rotor rotates at a revolving speed of not less than a predetermined level, prior to a start of operation of said synchronous motor;
• a first control unit that detects an electrical angle of said rotor according to a first detection process in case that said rotor rotates at the revolving speed of not less than the predetermined level, and regulates the polyphase currents flowing through said polyphase windings based on the detected electrical angle, said first detection process having a practical accuracy when the revolving speed of said rotor is not less than the predetermined level;
• and
• a second control unit that detects the electrical angle of said rotor according to a second detection process in case that said rotor rotates at the revolving speed of less than the predetermined level, and regulates the polyphase currents flowing through said polyphase windings based on the detected electrical angle, said second detection process having a practical accuracy when the revolving speed of said rotor is less than the predetermined level.