Detection of loss of cooling air to traction motors

Abstract

A thermal protection apparatus for an AC traction motor including a stator, a rotor, a blower fan and an inverter includes a method and apparatus for predicting the motor temperature assuming that the blower is operational. The method and apparatus also determines an estimated motor temperature by measuring the motor resistance or the rotor slip. The estimated motor temperatures compared to the predicted motor temperature to determine the condition of the motor cooling system.

What is claimed is:  
     
         1 . A method for determining the adequacy of a cooling system associated with a motor, said method comprising: 
 (a) calculating the predicted motor temperature;    (b) estimating the motor temperature;    (c) comparing the predicted motor temperature with the estimated motor temperature; and    (d) producing a signal when the difference between the predicted motor temperature and the estimated motor temperature exceeds a preselected value.    
     
     
         2 . The method of  claim 1  wherein the motor has at least two phase windings, with each phase winding coupled by a first respective combination of a first switch and a first diode to a positive voltage line and a second respective parallel combination of a second switch and a second diode to a negative voltage line, and wherein the step (b) comprises: 
 (b1) supplying voltage to the positive and negative voltage lines; and  
 (b2) switching on and off selected ones of the first and second switches to provide a substantially DC current to the motor;  
 (b3) determining the voltage across a motor winding and a current through said motor winding;  
 (b4) calculating the motor resistance in accordance with the measured current and voltage; and  
 (b5) calculating the estimated motor temperature based on the motor resistance.  
 
     
     
         3 . The method of  claim 2  wherein the step (b2) comprises: 
 switching on the second switch coupled to a first one of the at least two phase windings; and  
 switching on and off the first switch coupled to a second one of the at least two phase windings.  
 
     
     
         4 . The method of  claim 3  wherein after switching on the second switch coupled to the first one of the at least two phase windings and switching on and off the first switch coupled to the second one of the at least two phase windings for a first time period, for a second time period; 
 switching on the second switch coupled to the second one of the at least two phase windings; and  
 switching on and off the first switch coupled to the first one of the at least two phase windings.  
 
     
     
         5 . The method of  claim 1  wherein the step (a) further comprises: 
 (a1) measuring the ambient air temperature of the motor;  
 (a2) measuring the atmospheric air pressure of the motor;  
 (a3) using the measured ambient air temperature and the measured atmospheric air pressure to predict temperatures at a plurality of nodes in the motor.  
 
     
     
         6 . The method of  claim 1  wherein the step (b) further comprises determining the motor resistance and estimating the motor temperature therefrom.  
     
     
         7 . The method of  claim 6  wherein the motor resistance is determined from the motor slip.  
     
     
         8 . The method of  claim 6  wherein the motor resistance is determined from the injection DC current into the motor.  
     
     
         9 . The method of  claim 6  wherein the motor resistance is determined from the injection of AC current into the motor.  
     
     
         10 . The method of  claim 1  wherein the step (b) further comprises: 
 (b1) measuring the motor rotor slip;  
 (b2) calculating the rotor resistance from the rotor slip; and  
 (b3) calculating the rotor temperature from the rotor resistance.  
 
     
     
         11 . An apparatus for determining the adequacy of a cooling system associated with a motor, said method comprising: 
 a processor for providing a predicted motor temperature based on ambient conditions and motor physical parameters;    sensors for measuring predetermined motor operational parameters;    a processor responsive to said sensors for providing an estimated motor temperature;    a comparator for comparing the predicted motor temperature with the estimated motor temperature; and    a signal generator for producing a signal when the difference between the predicted motor temperature and the estimated motor temperature exceeds a preselected value.    
     
     
         12 . The apparatus of  claim 11  wherein the sensors measure the motor current and voltage.  
     
     
         13 . The apparatus of  claim 11  wherein the sensors measure the motor rotor slip.  
     
     
         14 . The apparatus of  claim 11  wherein the estimated motor temperature is an average motor temperature.  
     
     
         15 . The apparatus of  claim 11  wherein the motor comprises a plurality of windings and the sensors measure predetermined operational parameters for one or more of said plurality of windings, and wherein the processor responsive to the sensors provides an estimated temperature for each of the one or more of said plurality of windings and provides an average thereof, representing estimated motor temperature.  
     
     
         16 . An article of manufacture comprising: 
 a computer product comprising a computer-usable medium having a computer-readable code therein for determining the adequacy of a cooling system associated with a motor, said computer-readable code in the article of manufacture comprising:    a computer-readable program code module for calculating a predicted motor temperature;    a computer-readable program code module for receiving motor operational parametric data and for determining an estimated motor temperature;    a computer-readable program code module for comparing the predicted motor temperature with the estimated motor temperature; and    a computer-readable program code module for producing a signal when the difference between the predicted motor temperature and the estimated motor temperature exceeds a predetermined value.