Induction motors including speed sensing circuits for motor control

An induction motor assembly comprising:

• an induction motor including a stator core having a stator yoke and a plurality of teeth extending from the stator yoke toward a central opening, the central opening extending from a first end of the stator core to a second end of the stator core opposite the first end, the plurality of teeth spaced apart from one another and defining a plurality of slots between the plurality of teeth, the induction motor further including a main winding and an auxiliary winding located within the plurality of slots and wrapped around the plurality of teeth, the main winding coupled with a line terminal to receive power from a power source, and the auxiliary winding coupled with the line terminal to receive power from the power source;
• one or more switches coupled between the line terminal and at least one of the main winding and the auxiliary winding to selectively inhibit supply of power from the power source to the at least one of the main winding and the auxiliary winding;
• a control circuit coupled to control switching operation of the one or more switches, the control circuit configured to:
• obtain a main winding voltage value representative of a voltage across the main winding;
• receive an auxiliary winding voltage value according to a sensed voltage across the auxiliary winding;
• determine at least one of a rotational speed of the induction motor or a load of the induction motor, according to a polynomial equation having specified coefficients, wherein the main winding voltage value and the auxiliary winding voltage value comprise inputs to the polynomial equation;
• and
• control switching operation of the one or more switches according to the determined rotational speed or the determined load, or generate a log of the determined rotational speed or the determined load in memory for monitoring.

A method of controlling an induction motor assembly, the assembly including an induction motor having a stator core including a stator yoke and a plurality of teeth extending from the stator yoke toward a central opening, the central opening extending from a first end of the stator core to a second end of the stator core opposite the first end, the plurality of teeth spaced apart from one another and defining a plurality of slots between the plurality of teeth, the induction motor further including a main winding and an auxiliary winding located within the plurality of slots and wrapped around the plurality of teeth, the assembly including one or more switches coupled between a line terminal of a power source and at least one of the main winding and the auxiliary winding, the method comprising:

• obtaining a main winding voltage value representative of a voltage across the main winding;
• obtaining an auxiliary winding voltage value representative of a voltage across the auxiliary winding;
• calculating a phase difference between the voltage across the main winding and the voltage across the auxiliary winding;
• determining at least one of a rotational speed of the induction motor and a load of the induction motor, according to the calculated phase difference, the main winding voltage value and the auxiliary winding voltage value;
• and
• controlling switching operation of the one or more switches according to the determined rotational speed or the determined load, or generating a log of the determined rotational speed or the determined load in memory for monitoring.