Method and apparatus for indirectly measuring induction motor slip to establish speed control
AssigneeA.O. Smith Corporation
InventorBrian Thomas Branecky
Life of this patent
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Abstract
A method of establishing motor speed control, the method comprising the acts of generating a desired speed command, indirectly measuring the slip of the motor, and adjusting the speed command in response to the slip to maintain a constant speed.
Claims21
A method of establishing motor speed control of a motor receiving power from an inverter, the method comprising the acts of:
- generating a desired speed command;
- supplying a bus voltage to the inverter;
- controlling the inverter to supply an alternating current (AC) motor voltage and an AC motor current to the motor, the controlling act resulting in a bus current;
- indirectly measuring the slip of the motor based on the bus voltage, bus current, AC motor voltage, and AC motor current;
- and
- adjusting the speed command in response to the slip to maintain a constant speed.
A method of establishing motor speed control of a motor powered by an inverter, the method comprising the acts of:
- generating a desired speed command;
- indirectly measuring the slip of the motor, the act of indirectly measuring the slip including the acts of determining an inverter bus voltage, an inverter bus current, a supplied motor voltage and a supplied motor current, calculating a power factor of the motor using the inverter bus voltage, inverter bus current, supplied motor voltage and supplied motor current, and calculating the slip based on the power factor;
- and
- adjusting the speed command in response to the slip to maintain a constant speed.
A software program, stored in a computer readable medium, for establishing constant motor speed control of a motor powered by an inverter, the software program performing the acts of:
- generating a desired speed command;
- indirectly measuring and calculating the slip of the motor based on a bus voltage and a bus current of the inverter and a voltage and a current supplied to the motor;
- and
- adjusting the speed command in response to the slip to maintain a constant motor speed.
An induction motor comprising:
- a rotor;
- a stator;
- and
- a control circuit for driving the rotor at a predetermined speed relative to the stator, the control circuit including
- an inverter that receives a bus voltage and supplies a voltage and a current to the motor in response to a control signal, the control of the inverter resulting in a bus current;
- an estimating circuit to calculate a motor slip based on the bus voltage, bus current, supplied motor voltage, and supplied motor current;
- and
- a compensating circuit to adjust a motor speed based on the motor slip to allow constant speed control of the motor regardless of changes in motor load.
Dependencies are inferred from the claim text.