Method and apparatus for controlling three-phase electric motor
AssigneePower Drive Efficiency Ltd
InventorsIgor Alexander Turevsky, Moshe Haim Naiman, Arthur Naiman
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Abstract
Methods and control apparatus for operating a three-phase electric motor are described, in which the motor windings are switched between Star and Delta connections depending on torque requirements, and in which the motor windings are switched to a braking mode when braking torque is required. The electromagnetic torque of the motor is monitored, and a command to switch from Star to Delta is given when the electromagnetic torque rises to reach or exceed a threshold.
Claims12
A method/a controller for controlling an operation of a three-phase motor driving a load, wherein the motor is operable in both Star and Delta configurations, comprising:
- monitoring an electromagnetic torque produced by the motor;
- monitoring a rotation speed of the motor;
- comparing the electromagnetic torque produced by the motor to a threshold value, and
- switching the motor from Star to Delta or from Delta to Star configuration on a basis of that comparison;
- wherein the electromagnetic torque produced by the motor is monitored by:
- monitoring the rotation speed of the motor;
- monitoring phase currents in the three phases of the motor;
- monitoring derivatives of the phase currents in the three phases of the motor;
- monitoring phase voltages in the three phases of the motor;
- determining an instant at which the phase current and its derivative are both zero in one phase, and the derivative of the phase current is zero in a second phase;
- measuring the values, at that instant, of:
- a. the phase voltage in the one phase;
- b. the phase voltage in the second phase;
- and
- c. the phase current in the second phase,
- determining an electromagnetic power produced by the motor at that instant on the basis of the measured values;
- and
- calculating the electromagnetic torque produced by the motor at that instant on the basis of the determined value for electromagnetic power and the rotation speed.
A controller for controlling an operation of a three-phase motor, comprising:
- a phase current monitor for monitoring the respective phase currents in the three phases of the motor;
- a phase voltage monitor for monitoring the respective phase voltages in the three phases of the motor;
- a plurality of switches comprising a first group of switches operable when closed to connect the three-phase motor in Delta configuration and a second group of switches operable when closed to connect the three phase motor in Star configuration;
- and
- processor circuitry operable to:
- monitor a rotation speed of the motor;
- monitor the phase currents in the three phases of the motor;
- calculate and monitor derivatives of the phase currents in the three phases of the motor;
- monitor the phase voltages in the three phases of the motor;
- determine an instant at which the phase current and its derivative are both zero in one phase, and the derivative of the phase current is zero in a second phase;
- measure values, at that instant, of:
- a. the phase voltage in the one phase;
- b. the phase voltage in the second phase;
- and
- c. the phase current in the second phase,
- determine an electromagnetic power produced by the motor at that instant on a basis of the measured values;
- and
- calculate an electromagnetic torque produced by the motor at that instant on a basis of the determined value for electromagnetic power and the rotation speed;
- compare the electromagnetic torque produced by the motor to a threshold value, and
- control the plurality of switches to switch the motor from Star to Delta or from Delta to Star configuration on the basis of that comparison.
A method of driving a load by a three-phase electric motor supplied from a three-phase supply, wherein the three-phase electric motor may be switched from Star to Delta or from Delta to Star configuration, the method comprising:
- monitoring an electromagnetic torque produced by the motor;
- monitoring a rotation speed of the motor;
- comparing the electromagnetic torque produced by the motor to a threshold value, and
- switching the motor from Star to Delta or from Delta to Star configuration on a basis of that comparison;
- wherein the electromagnetic torque produced by the motor is monitored by:
- monitoring the rotation speed of the motor;
- monitoring phase currents in the three phases of the motor;
- monitoring derivatives of the phase currents in the three phases of the motor;
- monitoring phase voltages in the three phases of the motor;
- determining an instant at which the phase current and its derivative are both zero in one phase, and the derivative of the phase current is zero in a second phase;
- measuring the values, at that instant, of:
- a. the phase voltage in the one phase;
- b. the phase voltage in the second phase;
- and
- c. the phase current in the second phase,
- determining an electromagnetic power produced by the motor at that instant on the basis of the measured values;
- and
- calculating the electromagnetic torque produced by the motor at that instant on the basis of the determined value for electromagnetic power and the rotation speed.
Dependencies are inferred from the claim text.