Microprocessor based motor control system with phase difference detection

A control circuit for a motor having a main winding and an auxiliary winding, said control circuit comprising:

• a plurality of solid state switches for selectively connecting a line voltage to the main winding and the auxiliary winding;
• a microprocessor coupled to said plurality of solid state switches, said microprocessor controlling said plurality of solid state switches to selectively energize the main winding and the auxiliary winding, said microprocessor including first instructions that enable said microprocessor to determine the phase difference between the line voltage and the voltage between the main winding and the auxiliary winding by detecting zero crossings of the line voltage and zero crossings of the voltage between the main winding and the auxiliary winding, said microprocessor including second instructions that enable said microprocessor to de-energize the motor when said phase difference indicates a motor fault condition.

An apparatus comprising:

• a motor having a main winding and an auxiliary winding;
• connecting means for selectively connecting a line voltage to said main winding and said auxiliary winding;
• microprocessor means coupled to said connecting means, said microprocessor means controlling said connecting means to activate said connecting means to selectively energize said main winding and said auxiliary winding, said microprocessor means including means for determining a phase difference between the line voltage and the voltage between said main winding and said auxiliary winding by detecting zero crossings of the line voltage and zero crossings of the voltage between said main winding and said auxiliary winding, said microprocessor means including means for de-energizing said motor when said phase difference indicates a motor fault condition.

An apparatus comprising:

• a motor having a main winding and an auxiliary winding;
• a plurality of solid state switches for selectively connecting a line voltage to said main winding and said auxiliary winding;
• a microprocessor coupled to said motor and said plurality of solid state switches, said microprocessor controlling said plurality of solid state switches to activate said plurality of solid state switches to selectively energize said main winding and said auxiliary winding, said microprocessor including first instructions that enable said microprocessor to determine a phase difference between the line voltage and the voltage between said main winding and said auxiliary winding by detecting zero crossings of the line voltage and zero crossings of the voltage between said main winding and said auxiliary winding, said microprocessor including second instructions that enable said microprocessor de-energize said motor when said phase difference is less than a predetermined limit.