Abstract:
An electric drive system may include a plurality of heat sensitive components, at least one temperature sensor positioned in or on each of the components and a system controller. The temperature sensors may be interconnected with the system controller to transmit temperature data from their respective heat sensitive components to the system controller. The system controller may be configured to transmit a reduced performance command in the event that a reached-temperature-threshold-limit signal is received from any one or more of the temperature sensors. System shutdown due to over temperature faults may be avoided.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention generally relates to electric drive systems and more particularly to methods and apparatus for providing thermal protection for such systems. 
         [0002]    A high-power electric drive system contains many components that are subject to substantial amounts of heat load. All these components may have their own thermal designs for heat rejection and are usually equipped with temperature sensors for protection from over-temperature. Typical operation of the system is to allow full performance until a component exceeds a safe temperature limit, and then the whole system will shut down. A system controller may restart the system after the component temperature cools down. However, during shutdown, the system is not available for operation. For some applications, this is not a desirable or even acceptable condition. The issue can be more complicated when the components of the system are installed in different environments. 
         [0003]    As can be seen, there is a need for a thermal protection system that may allow a drive system to continue operation during periods when the temperature of one or more of its components approaches a predetermined safe limit. 
       SUMMARY OF THE INVENTION 
       [0004]    In one aspect of the present invention, an electric drive system may comprise: a plurality of heat sensitive components; at least one temperature sensor positioned in or on each of the components; and a system controller, the temperature sensors being interconnected with the system controller to transmit temperature data from their respective heat sensitive components to the system controller, the system controller being configured to transmit a reduced performance command in the event that a reached-temperature-threshold-limit signal is received from any one or more of the temperature sensors. 
         [0005]    In another aspect of the present invention, a system controller for an electric drive system may comprise: a temperature comparator configured to receive inputs from temperature sensors located on or in a plurality of components of the electric drive system; and a command generator interconnected with the temperature comparator and interconnected with a motor controller of the electric drive system to transmit a reduced performance command to the motor controller responsively to receipt of a reached-temperature-threshold-limit signal being received by the temperature comparator. 
         [0006]    In still another aspect of the present invention, a method for operating an electric drive system may comprise the steps of: establishing temperature threshold limits for a plurality of components of the electric drive system, the temperature threshold limit for any particular one of the plurality of components being at a temperature lower than temperature shutdown limit for the particular one of the plurality of components; monitoring temperatures of the plurality of components to detect if the temperature of any particular one of the plurality of components reaches the temperature threshold limit for said particular one of the plurality of components; and initiating a reduction in performance of the electric drive system in the event that the temperature of any particular one of the plurality of components reaches the threshold limit for said particular one of the plurality of components. 
         [0007]    These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is block diagram that schematically illustrates an electric drive system in accordance with an exemplary embodiment of the present invention; 
           [0009]      FIG. 2  is a block diagram that schematically illustrates a system controller in accordance with an exemplary embodiment of the present invention; 
           [0010]      FIG. 3  is a graph illustrating a relationship between temperature of a component of the electric drive system of  FIG. 1  and speed of a motor of the electric drive system of  FIG. 1 ; and 
           [0011]      FIG. 4  is a flow chart of a method for operating the electric drive system of  FIG. 1  in accordance with an exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]    The following detailed description is of the best currently contemplated modes of carrying out exemplary embodiments of the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims. 
         [0013]    Various inventive features are described below that can each be used independently of one another or in combination with other features. 
         [0014]    Broadly, embodiments of the present invention generally provide methods and apparatus that prevent a drive system from shutdown by reducing system performance when the temperature of any component of the drive system rises above a preset threshold value. A preset temperature threshold that is less than a shutdown temperature limit may be determined for each temperature-monitored component within the system. Any component temperature that goes above its threshold limit may trigger a system controller to initiate self-protection mode. In this mode, the controller may limit the appropriate system performance parameters to tame component temperature behavior. While in the self-protection mode of operation, the system may experience some degradation in performance, but a complete system shutdown may be avoided. 
         [0015]    Referring now to  FIG. 1 , there is shown, an exemplary electric drive system  12  such as a drive system that may be employed in an aircraft electric taxi system (ETS). In an ETS, an airplane (not shown) may use an auxiliary power unit (not shown) to power the drive system  12  to taxi in and/or out of a runway. All or part of the airplane engines may be turned off during taxiing to save fuel. The electric drive system  12  may include an autotransformer rectifier unit (ATRU)  14 , a motor controller/inverter  16 , a gearbox  18  and a traction motor  20 . Temperature sensors  14 - 1 ,  16 - 1 ,  18 - 1  and  20 - 1  may be positioned in the ATRU  14 , the motor controller/inverter  16 , the gearbox  18  and the traction motor  20  respectively. The temperature sensors  14 - 1 ,  16 - 1 ,  18 - 1  and  20 - 1  may be configured and interconnected with the system controller  22  to continually transmit temperature data to a system controller  22 . In some embodiments of the system  12 , the motor controller/inverter  16  may perform some or all of the roles of the system controller  22 . 
         [0016]    The temperature sensors  14 - 1 ,  16 - 1 ,  18 - 1  and  20 - 1  may transmit an 
         [0017]    ATRU temperature signal  14 - 2 , a motor controller temperature signal  16 - 2 , a gearbox temperature signal  18 - 2  and a motor temperature signal  20 - 1  respectively. 
         [0018]    It should be noted that while  FIG. 1  symbolically shows only a single temperature sensor in each of the ATRU  14 , the motor controller/inverter  16 , the gearbox  18  and the traction motor  20 , this symbolic representation is made for purposes of simplicity. In reality, multiple temperature sensors may be positioned in one or more of the components of the electric drive system  12 . For example, the motor  20  may be provided with a first temperature sensor near one of its bearing, a second sensor near another one of its bearings and a third sensor near its stator winding. Similarly, the gearbox  18  may be provided with multiple temperature sensors near its bearings and still another sensor adapted to measure lubricant temperature. 
         [0019]    Referring now to  FIG. 2 , an exemplary embodiment of the system controller is shown in block diagram format. The system controller  22  may include a temperature monitor  24 , a memory or reference unit  26 , a processor  28  and a command generator  30 . 
         [0020]    In operation, the system controller  22  may continually receive temperature signals such as the signals  14 - 2 ,  16 - 2 ,  18 - 2  and  20 - 2 . If one or more of the temperature signals presents a temperature above a threshold temperature for a particular component of the electric drive system  12 , then the system controller  22  may act to produce a command for performance reduction of the electric drive system  12 . In this regard, the system controller may be considered to receive a reached-temperature-threshold-limit signal. In an exemplary mode of operation, the temperature monitor  24  may transmit a threshold-exceed signal  24 - 1  to the processor  28 . The processor  28  may interact with the reference unit  26  to determine a type and magnitude of performance reduction that may be needed to reconcile the threshold-exceed signal  24 - 1 . The processor  28  may then interact with the command generator  30  so that the command generator  30  may produce a performance reduction command  30 - 1  to the motor controller  16  of  FIG. 1 . The motor controller  16  may then reduce voltage applied to the motor  20  (see  FIG. 1 ) or reduce current provided to the motor  20 . Voltage reduction may be used to reduce performance under conditions in which speed reduction is desired. Current reduction may be used to reduce performance under conditions in which acceleration reduction is desired. 
         [0021]    In some circumstances, threshold exceeding temperatures may develop in more than one component of the electric drive system  12 . The system controller  22  may be provided with a low-win logic circuit  32  to deal with such a condition. The low-win logic circuit  32  may select which one of multiple reached-temperature-threshold-limit signals may require the greatest amount of performance reduction for achievement of mitigation of high temperature. The selected signal may then be used as the threshold-exceed signal  24 - 1  for transmittal to the processor  28  and ultimately for selection of the performance reduction command  30 - 1 . 
         [0022]    The reference unit  26  may store component-specific functional relationships between types, magnitudes and/or rates of performance reduction and corresponding rates of temperature decrease that may be produced by a particular performance reduction. The reference unit  26  may be programmed to utilize various algorithms such as polynomial functions and look-up tables to store its relevant functional relationships. 
         [0023]    For example, the reference unit  26  may store a functional relationship of rate of performance reduction vs. rate of temperature decrease for a bearing in the motor  20  that is illustrated in a functional relationship shown in  FIG. 3 . In  FIG. 3  a graph line  36  illustrates bearing temperature and a graph line  38  illustrates motor speed. It may be seen that at a time T 0  when bearing temperature  36  exceeds a threshold temperature  40  of 150° C., motor speed  38  may be decreased at a rate of about 1500 revolutions per minute (rpm) in 75 seconds. This rate of change of speed (i.e. performance reduction) may reduce an increase of bearing temperature  36  and ultimately may reduce the bearing temperature  36 . It may also be seen that the motor speed  38  may be maintained at a speed of 8500 rpm until the bearing temperature  36  returns to a level equal to the threshold temperature  40 . In the example of  FIG. 3 , the bearing temperature  36  may never reach a safety shutdown limit temperature  50  and thus shutdown of the electric drive system  12  may be avoided. 
         [0024]    Referring now to  FIG. 4 , a flow chart  400  illustrates a method that may be employed to operate the electric drive system  12  in a manner that may provide thermal protection and avoid shutdown in the event of temperature increases of one or more components of the electric drive system  12 . In a step  402 , temperature threshold limits may be established for a plurality of components of the electric drive system, the temperature threshold limit for any particular one of the plurality of components being at a temperature lower than temperature shutdown limit for the particular one of the plurality of components (e.g. the threshold temperature limit  40  of  FIG. 3  may be established at a temperature level lower than the safety shutdown limit temperature  50  of  FIG. 3 ). In a step  404 , temperatures of a plurality of components may be monitored to detect if the temperature of any particular one of the plurality of components reaches the temperature threshold limit for said particular one of the plurality of components (e.g. the temperature monitor  24  may monitor temperature signals such as the signals  14 - 2 ,  16 - 2 ,  18 - 2  and  20 - 2 ). In a step  406 , determination may be made if one or more threshold temperatures are exceeded. In a step  408 , a reduction in performance of the electric drive system may be initiated in the event that the temperature of any particular one of the plurality of components reaches the threshold limit for said particular one of the plurality of components. In the step  404 , determination may be made that after initiation of performance reduction in step  408 , the temperature threshold may no longer be exceeded. In step  410  normal operation of the electric drive system may be restored. 
         [0025]    It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.