Sensorless motor braking system

Abstract

An electric motor control system includes a power inverter and control circuitry configured to control the power inverter either according to a target voltage in a voltage-based control mode or according to a target current in a current-based control mode. A controller is operable to switch operation of the control circuitry between the voltage-based control mode and the current-based control mode. The controller may be configured to operate the control circuitry in the current-based control mode at lower motor operating speeds where stator current margin is of greater significance, and to operate the control circuitry in the voltage-based control mode at higher motor operating speeds where stator voltage margin is of greater significance.

1 . A motor control braking system comprising:
 motor control circuitry;   a first braking mechanism configured to generate a target voltage for maximizing motor losses;   a second braking mechanism configured to generate a target flux producing current for maximizing motor losses; and   a controller for switching operation of the motor control braking system between generating the target voltage and the target flux producing current.   
     
     
         2 . The motor control braking system of  claim 1 , wherein the first braking mechanism is configured to augment a maximum voltage value of a first control signal generated by the motor control circuitry. 
     
     
         3 . The motor control braking system of  claim 2 , wherein the first braking mechanism includes a difference component for receiving a first signal containing motor reference speed information from the motor control circuitry, for receiving a second signal containing actual motor speed information from the motor control circuitry, and for generating a third signal containing information indicating a difference between the reference speed and the actual speed, the first braking mechanism further including an integrating component for integrating the third signal and communicating an integrated signal to the motor control circuitry. 
     
     
         4 . The motor control braking system of  claim 3 , further comprising a first braking switch, the controller being configured to actuate the first braking switch for selectively engaging the first braking mechanism. 
     
     
         5 . The motor control braking system of  claim 1 , wherein the second braking mechanism is configured to augment a flux producing current component of a second control signal generated by the motor control circuitry. 
     
     
         6 . The motor control braking system of  claim 5 , wherein the second braking mechanism includes: a difference component for receiving a first signal containing motor reference speed information, for receiving a second signal containing actual motor speed information, and for generating a third signal containing information indicating a difference between the reference speed and the actual speed, and an integrating component for integrating the third signal and communicating an integrated signal to the motor control circuitry. 
     
     
         7 . The motor control braking system of  claim 6 , further comprising a second braking switch, the controller being configured to actuate the second braking switch for selectively engaging the second braking mechanism. 
     
     
         8 . The motor control braking system of  claim 1 , wherein the control circuitry includes: a DC bus for delivering power to a power inverter at a forward operating power level, and a capacitor coupled with the DC bus and operable to receive and store electrical energy generated that exceeds the forward operating power level. 
     
     
         9 . The motor control braking system of  claim 8 , further comprising a voltage regulator for limiting an amount of induced voltage during braking by regulating a motor slip frequency. 
     
     
         10 . The motor control braking system of  claim 1 , further comprising a current limiter component for imposing a maximum stator current. 
     
     
         11 . A method of braking a motor, the method comprising:
 generating a target voltage for maximizing voltage losses;   generating a target flux producing current for maximizing motor losses; and   switching between generating the target voltage and generating the target flux producing current.   
     
     
         12 . The method of  claim 11 , further comprising augmenting a maximum voltage value of a first control signal generated by motor control circuitry. 
     
     
         13 . The method of  claim 12 , further comprising receiving a first signal containing motor reference speed information from motor control circuitry, receiving a second signal containing actual motor speed information from the motor control circuitry, generating a third signal containing information indicating a difference between the reference speed and the actual speed, and integrating the third signal and communicating an integrated signal to the motor control circuitry. 
     
     
         14 . The method of  claim 13 , further comprising actuating a first braking switch for selectively engaging a first braking mechanism. 
     
     
         15 . The method of  claim 12 , further comprising augmenting a flux producing current component of a second control signal generated by the motor control circuitry. 
     
     
         16 . The method of  claim 15 , further comprising receiving a first signal containing motor reference speed information, receiving a second signal containing actual motor speed information, generating a third signal containing information indicating a difference between the reference speed and the actual speed, and integrating the third signal and communicating an integrated signal to the motor control circuitry. 
     
     
         17 . The method of  claim 16 , further comprising actuating a second braking switch for selectively engaging a second braking mechanism. 
     
     
         18 . The method of  claim 1 , further comprising delivering power to a power inverter at a forward operating power level, and receiving and storing electrical energy generated that exceeds the forward operating power level. 
     
     
         19 . The method of  claim 18 , further comprising regulating a motor slip frequency to limit an amount of induced voltage during braking. 
     
     
         20 . A method of braking a motor, the method comprising:
 actuating a first braking switch for selectively engaging a first braking mechanism;   augmenting a maximum voltage value of a first control signal generated by motor control circuitry;   generating a target voltage according to the augmented maximum voltage value for maximizing voltage losses;   actuating a second braking switch for selectively engaging a second braking mechanism;   augmenting a flux producing current component of a second control signal generated by the motor control circuitry;   generating a target flux producing current according to the augmented flux producing current component for maximizing motor losses; and   switching between generating the target voltage and generating the target flux producing current.