Abstract:
An electronic load module system for testing voltage sources, such as power supplies, batteries, and fuel cells, is characterized by its ability to combine multiple load modules into a single virtual load for use with a first voltage source while simultaneously allowing other load modules in the same system to independently provide a load to an additional voltage source. The load modules may be combined in various configurations without altering the internal physical structure of the system. The system includes a first load module connected with the terminals of the voltage source and an associated control module connected with the first load module to supply a drive signal to the load module. The load system also includes a second load module. The second load module may be connected with the terminals of the voltage source in parallel with the first load module, or the second load module may be connected with the terminals of a second voltage source. A second control module is connected with the second load module to supply a drive signal to the second load module. The multiple load modules and control modules may be mounted in a single chassis.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    A load module is an electronically activated system that creates an electrical current load on a voltage source by using the current control capacity of a field effect transistor or fixed resistive, capacitive or inductive elements switched across the voltage source. Such a load module is often used in the testing of voltage sources, such as power supplies, batteries, and fuel cells. A load module is advantageous as it can simulate numerous types of electrical characteristics on the voltage source being tested. A load module may comprise multiple elements connected in parallel and sharing current equally. 
         [0002]    A transistorized load module system simulates the current drawn by a device on an electronic power source by using the current control capacity of a field effect transistor (FET). A field effect transistor is an elemental electrical device where the current through the device is controlled by the voltage applied to a specific terminal. An FET-based load module may generally consist of a set of FETs mounted in parallel and controlled by adjusting the gate voltage to produce the desired current flow through the system. 
         [0003]    The present invention relates to a virtual parallel load module system in which a plurality of loads can be automatically or selectively connected across a voltage source to control the current supplied to the source. 
       BRIEF DESCRIPTION OF THE PRIOR ART 
       [0004]    Load banks are well known in the patented prior art as evidenced by the Fong U.S. Pat. No. 7,683,553 which discloses a current control circuit in which matching drive currents through a plurality of parallel loads are set. A regulated voltage is provided to one terminal of a capacitor and to one terminal of each load and provides a source of current for the loads. The Tanner U.S. Pat. No. 7,479,713 discloses a fixed output linear voltage regulator used to drive a plurality of loads connected in parallel to control power dissipation. The Locker et al US patent application publication No. 2005/0134248 discloses a load bank having an infinitely variable load and a programming and control unit which is used to control the current flow through a power resistor. The Zhao et al US patent application publication No. 2012/0249094 discloses a load module, which may include a number of sub-sea loads and a number of modular stacked power converters. 
         [0005]    In addition, electronic load systems utilizing FETs are known in the prior art. For example, U.S. Pat. Nos. 6,324,042 and 6,697,245, both to Andrews, disclose an electronic load for the testing of electrochemical energy conversion devices. These patents disclose a device in which analog and digital feedback may be provided to adjust the control signal to the FETs to ensure that each remains within its individual safe operating area. 
         [0006]    While the prior devices operate satisfactorily, they lack versatility in that they are not capable of effectively combining multiple load modules into a single virtual load. In addition, the prior art devices are not capable of combining some of the load modules into a single virtual load for use with a first voltage source while simultaneously allowing other load modules in the same system to independently provide a load to an additional voltage source. The present invention was developed in order to overcome these and other drawbacks of the prior art by providing a load module system in which load modules may be combined in various configurations without altering the internal physical structure of the system. 
       SUMMARY OF THE INVENTION 
       [0007]    Accordingly, it is a primary object of the invention to provide a load system for creating a current to be applied to the terminals of a voltage source. The system includes a first load module connected with the terminals of the voltage source and an associated control module connected with the first load module to supply a drive signal to the load module. In embodiments of the invention, the load module may include a field effect transistor. The load system also includes a second load module. The second load module may be connected with the terminals of the voltage source in parallel with the first load module, or the second load module may be connected with the terminals of a second voltage source. A second control module is connected with the second load module to supply a drive signal to the second load module. The multiple load modules and control modules may be mounted in a single chassis. 
         [0008]    Components of the load module system are connected with a communication network for communicating information regarding characteristics of the setup of the load system to the control modules. The communication network may be a wired or wireless network. In addition, the system may include a processor unit communicating with the control modules via the communications network in order to configure the control modules. The processor unit may be a computer programmed with an interface and setup instructions stored in nonvolatile memory. The system may also include a manual controller connected with the communications network to manually configure the control modules. 
         [0009]    The system may also include a database connected with a computer or directly connected with the communications system. The database can be used to store information regarding characteristics of the control modules. In embodiments of the invention, the processor unit sends control information to the control modules based at least in part upon the information stored in said database. 
         [0010]    A further embodiment of the invention includes a method for configuring a load module system for creating a current to be applied to the terminals of a voltage source. In accordance with the method, a first load module is connected with the terminals of said voltage source. A first value associated with a characteristic of the first module is stored in a non-volatile memory. An additional load module is connected with the terminals of said voltage source in parallel with the first load module, and an additional value associated with a characteristic of the additional module is stored in a non-volatile memory. A user interface is utilized to input a setup configuration indicating that the first load module is connected in parallel with the second load module. A combined value related to the first and additional values is then entered into and stored in non-volatile memory. 
         [0011]    The method may further include the step of inputting a desired current draw for the load system into the user interface. The output of each individual load module may then be determined by counting the number of load modules connected in parallel to the terminals of the voltage source and dividing the desired total current draw by the number of load modules. In an embodiment of the invention, the stored values may be binary integers, which may be stored in a database. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0012]    Other objects and advantages of the invention will become apparent from a study of the following specification, when viewed in the light of the accompanying drawing, in which: 
           [0013]      FIG. 1  is a schematic representation of a field effect transistor used as a load device for a voltage source; 
           [0014]      FIG. 2  is a block diagram of a transistorized electronic load system for a voltage source; 
           [0015]      FIG. 3  is a block diagram of a plurality of load modules connected with a single communications bus; 
           [0016]      FIG. 4  is a block diagram of a plurality of load modules connected with a single communications bus with multiple load modules connected with a single voltage source; 
           [0017]      FIG. 5  is a block diagram of a plurality of load modules connected with a single communications bus with each load module connected with a single voltage source 
           [0018]      FIG. 6  is a block diagram of a plurality of load modules connected with a single communications bus with multiple load modules connected with a single voltage source; 
           [0019]      FIG. 7  is a block diagram of a further embodiment of a plurality of load modules connected with a single communications bus with multiple load modules connected with a single voltage source; and 
           [0020]      FIG. 8  is a flow diagram illustrating a method for controlling a load module system in accordance with embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]      FIG. 1  shows load systems according to the prior art. In  FIG. 1  there is shown a field effect transistor (FET)  2  connected across the terminals  4 ,  5  of a voltage source  6 . The transistor is an electric device where the current through the device is controlled by the voltage applied to a specific terminal. In  FIG. 1 , the load current through two terminals of the transistor  2  is proportional to the voltage applied to the gate terminal. A current  12  passes between a source terminal  4  and a drain terminal  5 . This current  12  may be referred to as the drain current (I drain ). The current  12  is proportional to a voltage applied to gate terminal  10 . This voltage may be referred to as the gate voltage (V gate ). Accordingly, the FET can be modeled by the following simple equation: 
         [0000]        I   drain =Constant* V   gate   [Eq. 1]
 
         [0022]    In embodiments of the invention, the gate terminal  10  is connected with an electronic FET controller  8 . The controller  8  includes a digital to analog converter that provides the gate voltage (V gate ) to the gate terminal  10 . In this manner, the current  12  across the source  4  and drain  5  terminals can be controlled. The digital to analog converter is connected with a processor that controls the output of the digital to analog converter. 
         [0023]    Referring to  FIG. 2 , the load system according to an embodiment of the invention will be described. The load system is used to generate a controlled current across the terminals  104 ,  105  of a voltage source  106 . A load bank  118  is connected in parallel with the source terminals  104 ,  105 . As will be developed below, the load bank includes a plurality of current control devices or loads that are selectively connected with the source terminals. The loads are of the field effect transistor type as shown in  FIG. 1 . A controller  120  is connected with the load bank for selecting at least one load for connection with the source terminals. The controller is in the form of an analog transistor module. A communication network  122  is connected with the loads for communicating status and command information between the loads. The communication network is either a wired or wireless network. 
         [0024]    As further illustrated in  FIG. 2 , a control voltage (V drive )  136  is applied to the load bank  118 . The control voltage is created by a digital to analog voltage converter (DAC) that forms part of the control module  120 . The control module  120 , and its included DAC, are connected through a communications bus  122  to a computer network interface  132 , which is in turn connected with a system microprocessor. In this manner the system microprocessor sends a binary digital pattern (V binary ) to the control module  120 , which then generates the appropriate V gate  signal ( FIG. 1 ) for each FET device  2  of the load bank  118 . V gate  can be expressed by the following equation: 
         [0000]        V   gate =Constant* V   binary   [Eq. 2]
 
         [0025]    Combining Eq. 1 with Eq. 2, it can be seen that the current across an FET  2  is proportional to the binary digital pattern: 
         [0000]        I   drain =Constant* V   binary   [Eq. 3]
 
         [0026]    As discussed above, the user may control the applied load current  112  using a processor connected with a computer network interface  132 . Alternatively, the user may control the current  112  through the use of a manual control interface  134  that is also connected with the communication network  122 , or which may be connected directly to the control module  118 . 
         [0027]    As illustrated in  FIG. 3 , multiple load modules  218   a,    218   b  to  218   n  are used in the same load bank system. These load modules are each connected by source terminals  204   a,    204   b  to  204   n  to a separate voltage source  206   a,    206   b  to  206   n.  Each load module  218   a,    218   b,    218   n  is also connected with a separate control module  220   a,    220   b  to  220   n . These control modules are used to independently apply a control voltage  236   a,    236   b  to  236   n  to load modules  218 . Multiple control modules  220  are connected with an internal communication bus  222 . This communication bus  222 , in turn, connects multiple control modules  220  to a single computer network interface  232  or to a single manual control interface  234 . In this manner, multiple load modules  218  can be installed in a single chassis to provide the ability to test multiple power systems simultaneously with a single device using a single processor unit  240  to the network interface  232 . The processor unit  240  comprises a purpose built microprocessor control device or a general computer having appropriate programming instructions stored in a non-volatile memory. 
         [0028]    Referring to  FIG. 4 , in a system using multiple load modules, it is desirable to control multiple load modules simultaneously so that these connected modules operate and respond as a single unit. For example, a voltage source  206   a  is connected in parallel to two load modules  218   a,    218   b.  In this embodiment, the source terminal  204   a  of the first load module  218   a  is connected in parallel with the source terminal  204   b  of a second load module  218   b  Likewise, the drain terminal  205   a  of the first load module  218   a  is connected in parallel with the drain terminal  205   b  of a second load module  218   b.  With the load modules  218   a,    218   b  and their associated control modules  220   a,    220   b  connected in this manner, the processor unit  240  or manual control interface  234  may be setup through the network interface  232  and communication bus  222  to treat the parallel load modules  218   a,    218   b  as a single virtual load module  219 . Additional load modules  218   n  may be used simultaneously to provide a load for additional voltage sources  206   n.    
         [0029]    Connecting multiple individual modules together as shown in  FIG. 4  requires a high degree of electrical interaction between the units. However, this connection must be performed in a manner that does not require alteration of the internal physical connections between the various components in the system chassis. It is also desirable that the various modules are connected in any possible combination of two or more modules leading to many potential permutations. 
         [0030]    As illustrated in  FIG. 5 , embodiments of the present invention address control of the various potential combinations using a database of the load modules present in the system. The database  242  is connected in a known manner to the processor unit  240 . Alternatively, the database is also connected directly to the communications bus  222 . As discussed below, the database is configured to store information regarding load modules in non-volatile memory. 
         [0031]      FIG. 5  shows an exemplary system including four load modules  218   a,    218   b ,  218   c,    218   d  and four corresponding control modules  220   a,    220   b,    220   c,    220   d.  However, it should be understood that the present invention contemplates a system comprising more than the four load modules shown. The database  242  contains system and operational information regarding the individual modules  218  including specific variables to describe how the modules are physically linked to each other in the system. A database element LINK DATA is a binary value used to associate the connections between the individual modules with the desired setup. 
         [0032]    The example of  FIG. 5  shows the status of a system in which each of the load modules  218   a,    218   b,    218   c,    218   d  is respectively connected with a separate voltage source  206   a,    206   b,    206   c,    206   d.  The LINK DATA element in the database is set for each load module according to the specified setup. In this exemplary setup, the LINK DATA binary value of  0001  is associated with the control module  220   a  connected with a first load module  218   a  for control of a first voltage source  206   a.  In a like manner, the LINK DATA value of 0010 is associated with the control module  220   b  while LINK DATA value 0100 is associated with control module  220   c  and LINK DATA value 1000 is associated control module  220   d.    
         [0033]      FIG. 6  illustrates an example in which two load modules  218   a,    218   b  are connected in parallel to one voltage source  206   a.  The remaining load modules are each connected with a separate voltage source: load module  218   c  with voltage source  206   c  and load module  218   d  with voltage source  206   d.  To coordinate this setup, the LINK DATA values associated with the control modules  220   a,    220   b  and with the two linked load modules  218   a,    218   b  are changed in the database  242 . In this example, LINK DATA value 0011 is associated with both control modules. This value 0011 results from an additive combination of the LINK DATA values associated with the unlinked control modules, 0001 associated with the first module  220   a  and 0010 associated with the second module  220  as shown in  FIG. 5 . This allows the system to treat the combined load modules as a single virtual load module  219 . The LINK DATA value associated with the remaining, independent control modules remains the same: 0100 associated with control module  220   c  and 1000 associated with control module  220   d.    
         [0034]      FIG. 7  illustrates a further example in which three load modules  218   a,    218   b ,  218   d  are connected in parallel to one voltage source  206   a.  The remaining load module  218   c  is connected with a separate voltage source  206   c.  To coordinate this setup, the LINK DATA values associated with the three combined control modules  220   a,    220   b ,  220   d  are changed in the database  242 . In this example, LINK DATA value 1011 is associated with all three control modules. The value 1011 results from an additive combination of the LINK DATA values associated with the unlinked control modules, 0001 associated with the first module  220   a:  0010 associated with the second module  220   b  and 1000 associated with the third module  220   d.  This allows the system to treat the combined load modules as a single virtual load module  221 . The LINK DATA value associated with the remaining, independent control module remains the same: 0100 associated with control module  220   c.    
         [0035]    Operation of embodiments of the present invention may include the following steps. During startup or at anytime thereafter the system operator designates which modules are to operate as linked units by executing a LINK command either via a programming interface associated with the processor unit  240  or the manual user interface  234 . The format of this command is as follows:
       LINK &lt;module number&gt;,&lt;link data&gt;.
 
The module number is the internal system address of the load module (typically 1 through 8), and the link data (LINK DATA value), while interpreted by the system in binary notation, may be provided by the user in decimal notation.
       
 
         [0037]    In a first example, as illustrated by  FIG. 6 , where load modules  218   a  and  218   b  are linked, the user would execute the command: LINK 1, 3. This command would cause the system to load the database entries for the first two modules  218   a,    218   b  with the binary value 0011, which is three in decimal notation and the additive sum of the individual LINK DATA values: 0001 for module  218   a  and 0010 for module  218   b.    
         [0038]    In a second example as illustrated by  FIG. 7 , where load modules  218   a,    218   b  and  218   d  are linked, the user would execute the command: LINK 1, 11. This command would cause the system to load the database entries for modules  218   a,    218   b  and  218   d  with the binary pattern 1011, which is eleven in decimal notation and the additive sum of the individual LINK DATA values: 0001 for module  218   a,  0010 for module  218   b  and 1000 for module  218   d.    
         [0039]      FIG. 8  is a flow diagram of the control process of the example illustrated in  FIG. 6 . In a first step  302 , the user executes a LINK command to combine modules  218   a  and  218   b.  The first module  218   a  is then selected for command operation, step  304 . Next, the first module  218   a  and the linked module  218   b  are commanded to draw 10 Amps, step  306 . In step  308 , the system then retrieves the LINK DATA value for the combined modules from the database  242 . In this example, the LINK DATA value would be 0011. The system then counts the number of “1s” in the binary value; in this example there are two, step  310 . This number, two in this example, is saved as a variable “CNT.” The total desired output, 10 Amps, is then divided by the value of the variable CNT, step  312 . This gives the desired output for each individual module combined together to form the virtual module  219 . This individual module output is saved as a variable “X”, which in this case would equal 5 Amps (ten divided by two). 
         [0040]    The system then goes through a series of decision steps in order to determine the output to use for each of the combined load modules. In the first decision step  314 , the system determines whether the LINK DATA value has a “1” in the binary digit associated with the first load module  218   a.  In this example, the LINK DATA value is 0011, and there is, therefor, a “1” in the corresponding digit. Accordingly, the control module  220   a  for load module  218   a  is programmed to carry a load of 5 Amps in step  315 . Proceeding to step  316 , the same analysis is undertaken. Again, the LINK DATA value is 0011, and there is, therefor, a “1” in the binary digit corresponding to load module  218   b.  The control module  220   b  for load module  218   b  is programmed to carry a load of 5 Amps in step  317 . 
         [0041]    Moving to the following step  318 , the same analysis is performed. In this example, the binary digit corresponding to load module  218   c  does not include a “1.” Accordingly, the control module  220   c  corresponding to load module  218   c  is not programmed to carry a load Likewise, following the analysis performed in step  320 , the control module  220   d  corresponding to load module  218   d  is not programmed to carry a load. 
         [0042]    While the preferred forms and embodiments of the invention have been illustrated and described, it will be apparent to those of ordinary skill in the art that various changes and modifications may be made without deviating from the inventive concepts set forth above.