Abstract:
A method for determining power semiconductor operating temperatures uses a database of measured temperatures. Each temperature is associated with operating conditions and determined by laboratory testing in an environment indicative of operation of the power semiconductors actual operations.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application No. 60/958,206 which was filed on Jul. 3, 2007. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This application is directed towards a method of predicting the junction temperature of a power semiconductor. 
         [0003]    In the field of power semiconductors it is known that the temperature of the junction has a large impact on the operation of the device relying on the semiconductor, as well as impacting the lifespan of the semiconductor. Exceeding a temperature threshold can cause the junction to rapidly deteriorate and break. Also known in the art is the fact that, due to varied operating conditions, the temperature of the junction is not merely a function of the quantity of electrical power being passed through it. 
         [0004]    When using a semiconductor junction in an application which has a widely varied and harsh operating environment (such as a hybrid or electric vehicle), the operating temperature can be greatly affected by the environment. Because the operating temperature has an impact on the life and functionality of a semiconductor junction, it is desirable to provide substantially accurate information regarding the temperature of the semiconductor. Since it is not desirable to include a temperature sensor on each semiconductor junction, it is desirable to develop a method of predicting the temperature of the semiconductor junction. 
         [0005]    Known temperature prediction algorithms attempt to account for the operating conditions of the device. In order to predict a temperature, current methods utilize complex and detailed computer simulations which attempt to take the operating conditions into consideration. The output of these simulations is then used to create a database of predicted temperatures which can be utilized by a controller to predict the actual temperature. These simulations are time intensive, and can often result in predictions that differ significantly from the actual running temperatures. 
         [0006]    It is therefore desirable to develop a quicker and more accurate method of determining temperature predictions and creating a prediction database. 
       SUMMARY OF THE INVENTION 
       [0007]    Disclosed is a method for predicting the operating temperature of a semiconductor junction where the operating conditions are checked against a database of expected temperatures and an appropriate temperature is selected and where the database of predicted temperatures is constructed based on test conditions that are substantially similar to real world operating conditions. 
         [0008]    These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a block diagram of an example test setup for performing the described method. 
           [0010]      FIG. 2  is a schematic illustration of an example semiconductor junction. 
           [0011]      FIG. 3  is a flow chart for a method of creating a prediction database of an embodiment. 
           [0012]      FIG. 4  is a schematic illustration of an example hybrid vehicle including a controller utilizing gathered temperature data. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0013]    In order to facilitate faster and more accurate predictions of the operating temperature of a semiconductor junction, it is necessary to develop a new apparatus and method for determining the predictions. 
         [0014]    A disclosed example method (illustrated in  FIG. 1 ) involves attaching the test semiconductor junction apparatus  50  to a dynamometer  102  in a test bench  104  and recording the temperatures of the semiconductor junction apparatus  50  with the dynamometer  102  producing a torque/speed cycle that would normally be experienced by a semiconductor junction  20  (see  FIG. 2 ) in its intended application. While the dynamometer  102  is operating, the system  100  records the operating temperature of the semiconductor junction apparatus  50 . The torque/speed of the dynamometer  102  can be controlled and recorded contemporaneously with the recorded temperature and associated with that temperature. Alternatively, the torque/speed of the dynamometer for each temperature can be determined after the test cycle, based on the torque/speed cycle profile, and achieve the same results. 
         [0015]    After the temperature information and the torque/speed cycle information (or other operating information) has been recorded both sets of information are compiled in a database in the data acquisition unit  110  where each temperature record is associated with at least a specific torque/speed. This can be done by using a timestamp during the initial recordation process, or any other known method of association. Once the temperature data and the torque/speed data (or any other operating conditions desired) are associated with each other it becomes possible to predict the temperature of the semiconductor junction during actual operation by determining the operating conditions and performing a database lookup. This method of determining predictions is significantly more accurate, than the known method of estimating operating conditions, inputting the estimates into a computer algorithm and running a simulation to determine predicted temperatures. Additionally the creation of the predicted temperature database is faster using the above described method than using the computer simulations known in the art. 
         [0016]    In order to create above described apparatus it is necessary to develop a sensor system capable of measuring the operating temperature of a semiconductor junction while it was actually operating.  FIG. 2  illustrates an apparatus according to an embodiment of the invention where such a measurement is capable. In this embodiment the semiconductor junction  20  has an input  30  and an output  40  which may be connected in a manner as it would be connected in an operating consumer application. The semiconductor junction  20  also has a temperature sensor  10  attached directly to the semiconductor junction. The current of the temperature sensor output is directly proportional to the temperature of the semiconductor junction  20 . The temperature sensor  10  output then sends a variable current signal  60  indicating the temperature to a data acquisition unit  110 . 
         [0017]    The temperature sensor  10  can be attached to the semiconductor junction  20  by placing a unit of thermally conductive and electrically isolative epoxy on the semiconductor junction  20  surface and then placing the temperature sensor on the unit of epoxy. This is then left to dry and once dried, the temperature sensor  10  is affixed to the semiconductor junction  20 . Alternatively any other known method of thermally connecting the temperature sensor  10  to the semiconductor junction  20  could be used. 
         [0018]    Referring again to  FIG. 1 , the test bench  104  contains a dynamometer  102 , and the apparatus  50 , which comprises a temperature sensor  10  and a semiconductor junction  20 . The test bench  104  (and consequently the dynamometer  102 ) is connected to a high voltage DC power supply  106 . The DC power supply  106  provides electrical power to the test bench  104  and enables the dynamometer  102  to replicate the torque/speed profile of actual operating conditions of the semiconductor junction  20 . The temperature sensor  10  is mounted on the semiconductor junction  20 , and then connected through signal wires  60 A,  60 B to an amplifier  108 . The temperature sensor  10  outputs a current signal which is dependent on its temperature, and is sent to the amplifier  108  where it is conditioned to be in a form readable by a data acquisition unit  110 . The amplifier  108  additionally is connected to two low voltage independent power sources  112 ,  114 . These power sources  112 ,  114  facilitate the amplification and conditioning performed in the amplifier  108 . Once the current signal has been conditioned to be in a format that can be read by the data acquisition unit  110 , it is sent to the data acquisition unit  110 . The data acquisition unit  110  records the temperature data in a database for constructing the predicted temperature database. 
         [0019]    The test bench  104  of this embodiment can be constructed in any manner which would accurately reflect the conditions of an actual consumer unit, such as an electric or hybrid vehicle ( FIG. 4 ) for example. This allows the temperature data recorded by the temperature sensor  10  to be more accurate than a predictive algorithm, as it avoids the problem of attempting to assign a quantifiable value to each potential variable found in the system. The example of  FIG. 3  utilizes a dynamometer  102  in the test bench  104 , however, it is anticipated that other equipment or additional equipment could be used in the test bench  104  as necessary to simulate the actual operating conditions. 
         [0020]    Electromagnetic noise emanating from nearby components can disrupt temperature measurement. The electromagnetic noise typical occurs in the form of high frequency voltage fluctuations, and can result in inaccurate measurements in any system relying on voltage signals. The example temperature sensor  10  is a silicon based temperature transducer which produces a current proportional to the temperature transducer&#39;s absolute temperature. Because, the output of the temperature sensor  10  is current based, the output avoids data corruption due to noise caused by voltage fluctuations. In this example an Analog Devices AD950 temperature sensor is used. However, it is known that any sensor capable of avoiding noise and accurately detecting the temperature of a semiconductor junction could be used and still meet the requirements of this disclosure. 
         [0021]      FIG. 3  is a flow chart showing an example method for creating a database of predicted temperatures and their associated operating conditions. The method includes the step of establishing test conditions (Step  1 ). Step  1  includes designing a test system  100  with similar operating conditions to an actual implementation, and then constructing the test system  100  in a testing facility. The example the test conditions simulate conditions encountered during the operation of an electric vehicle. Therefore, the resulting predicted temperatures are based on actual operating temperatures of a test system  100  that is substantially similar to a semiconductor junction as it would be implemented in an electric vehicle or other consumer application. 
         [0022]    Temperature data is recorded as indicated at step  2  and involves running the test system and recording the temperature data from the temperature sensor  10 . In this step the semiconductor junction  20  is installed in the test system  100  along with the temperature sensor  10 . The output from the temperature sensor  10  is recorded in a computer or some other form of memory as the test is run. The recorded temperature data is utilized to create a list of semiconductor junction temperatures related to different operational parameters. 
         [0023]    Operating conditions are recorded as indicated at Step  3  simultaneously with the recording temperature data. Information about the specific operating conditions can include (but is not limited to) information about the torque/speed cycle, the ambient air temperature, or any other information indicative of system operating conditions. The test may be designed such that temperature data is taken at predetermined operating conditions. Therefore temperature data is recorded for each of the predetermined operating conditions. 
         [0024]    Once Steps  2  and  3  have been performed, a database is created utilizing the temperature and operating condition data as indicated at Step  4 . In Step  4 , recorded data from steps  2  and  3  is merged into one database. The result of merging the temperature and operating conditions data is a data set that contains a temperature associated with each data point in the set of recorded operating conditions. The association between temperature and operating conditions can be done in any number of ways. One example method includes associating the first temperature to the first operating condition set (determined in step  3 ). Another example method includes recording a time stamp along with each recordation in steps  2  and  3  and then associating data sets having identical time stamps with each other. As appreciated, other methods of association known in the art are within the contemplation of this invention. It is also within the contemplation of this method that the procedure of Step  4  may be performed as data is being recorded, thereby reducing the time required for the creation of the prediction database. 
         [0025]    After data is compiled in a single database, the database is stored as indicated at step  5 . The created database is stored in a data acquisition unit&#39;s memory  116  for subsequent transfer to the consumer unit  210 . In the consumer unit  210 , the temperature prediction database  206  can be stored in controller memory  204 , or any other accessible memory unit within the consumer unit  210 . Once the database  206  is fully installed the final consumer unit  210  can predict the temperature of the semiconductor junction  50  by determining the operating conditions of the semiconductor junction  50 , looking up those operating conditions in the database  206 , and then reading an associated temperature. The associated temperature is then the predicted temperature, and the controller  202  can respond accordingly. 
         [0026]      FIG. 4  illustrates an embodiment of a consumer unit  210  where the database  206  is stored in a controller&#39;s  202  memory  204 . The controller is connected to a hybrid motor  200  which contains at least one power semiconductor. During the construction or installation of the controller  202 , the database  206  is transferred from the data acquisition unit&#39;s  110  memory to the controller&#39;s  202  memory  304 . In the embodiment of  FIG. 4  the consumer unit  210  is a hybrid car, although it is anticipated that any application utilizing power semiconductor junctions could employ this technique as well. 
         [0027]    Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.