Variable Speed Compressor Startup Control

Abstract

A drive controller for a motor of a compressor includes a drive circuit that applies voltages to windings of the motor. The drive controller includes a speed control module that controls the drive circuit to rotate the motor at a requested speed. The drive controller includes a speed determination module that generates the requested speed. The drive controller includes a locked rotor protection module that identifies a locked rotor condition and, in response to identifying the locked rotor condition, instructs the speed determination module to power down the motor. The locked rotor protection module acquires an estimated speed of the motor upon expiration of a predetermined time interval that begins upon startup of the motor. The locked rotor protection module identifies the locked rotor condition in response to the estimated speed being lower than a threshold speed. The threshold speed is based on the requested speed.

What is claimed is: 
     
         1 . A drive controller for a motor of a compressor, the drive controller comprising:
 a drive circuit that applies voltages to windings of the motor;   a speed control module that controls the drive circuit to rotate the motor at a requested speed;   a speed determination module that generates the requested speed; and   a locked rotor protection module that identifies a locked rotor condition and, in response to identifying the locked rotor condition, instructs the speed determination module to power down the motor, wherein:   the locked rotor protection module acquires an estimated speed of the motor upon expiration of a predetermined time interval that begins upon startup of the motor,   the locked rotor protection module identifies the locked rotor condition in response to the estimated speed being lower than a threshold speed, and   the threshold speed is based on the requested speed.   
     
     
         2 . The drive controller of  claim 1  wherein the threshold speed is a predetermined percentage of the requested speed. 
     
     
         3 . The drive controller of  claim 2  wherein the predetermined percentage is 20 percent. 
     
     
         4 . The drive controller of  claim 1  wherein the threshold speed and the predetermined time interval are programmed so that presence of liquid refrigerant in the compressor upon startup of the motor is not identified as the locked rotor condition. 
     
     
         5 . The drive controller of  claim 1  wherein the locked rotor protection module initiates heating of the compressor in response to identifying the locked rotor condition. 
     
     
         6 . The drive controller of  claim 1  wherein the locked rotor protection module increments a counter in response to identifying the locked rotor condition. 
     
     
         7 . The drive controller of  claim 6  wherein the locked rotor protection module permits the motor to be automatically restarted after a predetermined delay following identification of the locked rotor condition. 
     
     
         8 . The drive controller of  claim 7  wherein the locked rotor protection module, in response to the counter reaching a predetermined threshold, prevents the motor from being automatically restarted. 
     
     
         9 . The drive controller of  claim 6  wherein the locked rotor protection module clears the counter in response to the estimated speed being greater than the threshold speed. 
     
     
         10 . The drive controller of  claim 1  further comprising:
 a startup module that starts the motor by (i) causing the speed determination module to ramp the requested speed from zero up to a predetermined dwell speed and (ii) causing the speed determination module to maintain the requested speed at the predetermined dwell speed for a predetermined dwell time period, 
 wherein the locked rotor protection module acquires the estimated speed of the motor upon the earlier of (i) expiration of the predetermined time interval or (ii) a beginning of the predetermined dwell time period. 
 
     
     
         11 . The drive controller of  claim 10  wherein the predetermined time interval is 12 seconds, the predetermined dwell speed is 3600 rpm, the predetermined dwell time period is 120 seconds, the speed determination module ramps the requested speed from zero up to the predetermined dwell speed at 1000 rpm per second, and the threshold speed is 20 percent of the requested speed. 
     
     
         12 . A method of operating a drive controller for a motor of a compressor, the method comprising:
 applying voltages to windings of the motor;   controlling the voltages to rotate the motor at a requested speed;   acquiring an estimated speed of the motor upon expiration of a predetermined time interval that begins upon startup of the motor;   selectively identifying a locked rotor condition in response to the estimated speed being lower than a threshold speed, wherein the threshold speed is based on the requested speed; and   in response to identifying the locked rotor condition, powering down the motor.   
     
     
         13 . The method of  claim 12  wherein the threshold speed is a predetermined percentage of the requested speed. 
     
     
         14 . The method of  claim 13  wherein the predetermined percentage is 20 percent. 
     
     
         15 . The method of  claim 12  wherein the threshold speed and the predetermined time interval are programmed so that presence of liquid refrigerant in the compressor upon startup of the motor is not identified as the locked rotor condition. 
     
     
         16 . The method of  claim 12  further comprising initiating heating of the compressor in response to identifying the locked rotor condition. 
     
     
         17 . The method of  claim 12  further comprising incrementing a counter in response to identifying the locked rotor condition. 
     
     
         18 . The method of  claim 17  further comprising automatically restarting the motor after a predetermined delay following identification of the locked rotor condition. 
     
     
         19 . The method of  claim 18  further comprising, in response to the counter reaching a predetermined threshold, preventing automatic restarting of the motor. 
     
     
         20 . The method of  claim 17  further comprising clearing the counter in response to the estimated speed being greater than the threshold speed. 
     
     
         21 . The method of  claim 12  further comprising:
 starting the motor by (i) ramping the requested speed from zero up to a predetermined dwell speed and (ii) maintaining the requested speed at the predetermined dwell speed for a predetermined dwell time period, wherein the acquiring includes acquiring the estimated speed of the motor upon the earlier of (i) expiration of the predetermined time interval or (ii) a beginning of the predetermined dwell time period. 
 
     
     
         22 . The method of  claim 21  wherein the predetermined time interval is 12 seconds, the predetermined dwell speed is 3600 rpm, the predetermined dwell time period is 120 seconds, the ramping the requested speed from zero up to the predetermined dwell speed is performed at 1000 rpm per second, and the threshold speed is 20 percent of the requested speed.