Abstract:
A method for determining supply requirements for a motor control system includes determining a performance profile for each of a plurality of drive units. A power supply parameter for each drive unit is generated based on the performance profiles. The power supply parameters for the drive units are combined to generate a rating parameter for the motor control system. In some embodiments, instructions for implementing the method may be encoded on a program storage device or programmed into a processing device for execution.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     Not applicable.  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not applicable  
       BACKGROUND OF THE INVENTION  
       [0003]     The present invention relates generally to motion control systems, and, more particularly, to a method and apparatus for sizing a power processing device serving multiple drive units.  
         [0004]     Motion control systems such as those employed in industrial environments typically require power from one or more power sources, in the form of primary and/or auxiliary power. Not uncommonly, different types or levels of power (e.g., DC or AC power), or powers having multiple different characteristics (e.g., different voltage levels, current levels, etc.) are required.  
         [0005]     Typically, the power that is provided to the motion control systems is received from one or more power lines (e.g., a utility grid) and then converted into the desired forms of power. However, in certain embodiments, power can be received from power sources other than power lines, such as local power generation sources (e.g., local generators or batteries).  
         [0006]     To provide the required forms of primary, control, and/or auxiliary power to the motion control systems based upon the received power, many different front-end circuit components are often required. These front-end circuit components not only can provide power conversion, but also can serve other purposes as well, for example, circuit protection to protect against power spikes. For example, the National Electric Code requires that branch circuit protection be provided in connection with the delivery of power to motor controllers/motor drivers.  
         [0007]     Among the many different circuit components that can be utilized in any given system are power conversion components, switching components, such as contactors, protective components, such as circuit breakers and fuses, filtering components, and even additional power sources. Power processing circuitry may be implemented on an “ad hoc” basis when motion control systems are installed or specialized power processing devices may be implemented.  
         [0008]     One factor that influences the complexity and cost of a power processing circuit or device is the current required to supply the served drive units. Some drive units may serve only a single axis machine, while other drive units may serve multiples axes. Typically, the power processing device is sized based on the maximum current ratings for the served drive units. The number of drive units that a particular power processing device can serve is thus limited by the sum of the maximum current ratings.  
         [0009]     In actual operation, the current requirements for a given drive unit are typically much less than the rated current. Using rated current to size the power processing device reduces the number of drive units that be served by each power processing device, thereby increasing the number or rating of the installed power processing device, which increases the cost and complexity of the motor control system. Therefore, there is a need for a technique to size power processing devices serving one or more drive units that incorporates the actual demand requirements of the drive units.  
         [0010]     This section of this document is intended to introduce various aspects of art that may be related to various aspects of the present invention described and/or claimed below. This section provides background information to facilitate a better understanding of the various aspects of the present invention. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art. The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.  
       BRIEF SUMMARY OF THE INVENTION  
       [0011]     The present inventors have recognized that a technique for sizing a power processing device serving one or more drive units can incorporate the actual demand requirements of the drive units. Accurate sizing of the power processing device reduces system cost by allowing a lower rated, less expensive, power processing device to be used, or by allowing a higher number of drive units to be served by a given power processing device.  
         [0012]     One aspect of the present invention is seen in a method for determining supply requirements for a motor control system. The method includes determining a performance profile for each of a plurality of drive units. A power supply parameter for each drive unit is generated based on the performance profiles. The power supply parameters for the drive units are combined to generate a rating parameter for the motor control system.  
         [0013]     Another aspect of the present invention is seen in a program storage device encoded with instructions that, when executed by a processing device, implement the method.  
         [0014]     Yet another aspect of the present invention is seen in a processing device programmed with instructions that, when executed, perform the method.  
         [0015]     These and other objects, advantages and aspects of the invention will become apparent from the following description. In the description, reference is made to the accompanying drawings which form a part hereof, and in which there is shown a preferred embodiment of the invention. Such embodiment does not necessarily represent the full scope of the invention and reference is made, therefore, to the claims herein for interpreting the scope of the invention.  
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0016]     The invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and:  
         [0017]      FIG. 1  is a simplified block diagram of a motor control system in accordance with one embodiment of the present invention;  
         [0018]      FIG. 2  is a simplified block diagram of a sizing tool for determining current rating requirements for a power processing device in the motor control system of  FIG. 1 ; and  
         [0019]      FIGS. 3A and 3B  illustrate exemplary current profiles for drive units in the system of  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]     One or more specific embodiments of the present invention will be described below. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.  
         [0021]     Referring now to the drawings wherein like reference numbers correspond to similar components throughout the several views and, specifically, referring to  FIG. 1 , the present invention shall be described in the context of a motor control system  100 . The motor control system  100  includes a power supply  110 , a power processing device  120 , and one or more drive units  130 . The power supply  110  typically provides an AC voltage received from a utility grid. The power processing device  120  performs various functions, such as power conversion, switching, protection, filtering, etc. The power processing device  120  may serve one or more drive units  130 . A commercially available power processing device  120  capable of performing the described power conditioning and protection functions is a line interface module (LIM) offered by Rockwell Automation, Inc. of Milwaukee, Wisc. Exemplary line interface modules include models 2094-AL09, 2094-AL75S, 2094-BL02, 2094-BL75S, and 2094-XL75S-Cx. Different models have different voltage and/or current ratings. An exemplary line interface module is also described in U.S. patent application Ser. No. ______, entitled “Line Interface Module,” in the names of Edward J. Arguello, Jr., Michael J. Nelson, Nathaniel D. Herman, and Randall R. Holterman, filed on Sep. 30, 2004, with docket number 110003.00115/04AB223, and incorporated herein by reference in its entirety.  
         [0022]     The drive units  130  generate voltage for powering motors  140  and their associated loads  150  (i.e., referred to as an axis). A particular drive unit  130  may serve multiple axes or a single axis. The construction and operation of drive units  130  for performing this function are well known to those of ordinary skill in the art. Exemplary drive units  130  are drives in the Kinetix 6000 drive family offered commercially by Rockwell Automation, Inc. In general, the drive units  130  produce positive and negative voltage pulses in specific sequences to generate AC voltages having controllable amplitudes and frequencies for the associated motors  140 .  
         [0023]     Turning now to  FIG. 2 , a simplified block diagram of a sizing tool  200  for determining current rating requirements for the power processing device  120  in the motor control system  100  of  FIG. 1  is provided. The sizing tool  200  is implemented by software executing on a general-purpose or specialized processing device  210 . The sizing tool  200  evaluates motion simulation data files  220  for each of the drive units  130  served by the power processing device  120 .  
         [0024]     A motion analyzer engine  230 , executing on the processing device  210  or a different processing device, may be used to generate the motion simulation data files  220 . Motion analyzers and sizing tools are known to those of ordinary skill in the art. An exemplary motion analysis tool suitable for generating the motion simulation data files  220  is Motion Analyzer, Version 4.1, offered by Rockwell Automation, Inc. The motion analyzer engine  230  uses information regarding a single drive unit  130  and its associated motor/load axes to determine operating characteristics (e.g., torque, power requirements, suitability, etc.) for the drive unit  130 . One parameter determined by the motion analyzer engine  230  is the peak and continuous power requirements of the drive unit  130 . The motion analyzer engine  230  evaluates the specified operating requirements for each axis (e.g., duty cycle, acceleration, torque, etc.) and information regarding the specific amplifiers, motors, and loads that make up each axis to determine the suitability of the selected hardware and/or to recommend hardware that meets the requirements.  
         [0025]     In general, the sizing tool  200  uses data in the motion simulation data files  220  for each drive unit  130  served by the power processing device  120  to determine current profiles for each of the drive units  130 . The sizing tool  200  combines the current profiles to generate current rating requirements for the drive unit  130 .  
         [0026]     One component of a motion simulation data file  220  is a power profile for the drive unit  130 . Each axis typically has associated peak and continuous power requirements. In some cases, one or more of the axes may be synchronized. For example, if one axis typically starts a known period of time after another axis, the peak power for the axes will not occur at the same time. The motion analyzer engine  230  accounts for this synchronization and the total peak power is less than the sum of the two peak power values. In the case, where the axes are not synchronized (i.e., random with respect to each other), the motion analyzer engine  230  may use a worst-case approach where all non-synchronized axes achieve peak power requirements at the same time.  
         [0027]     The sizing tool  200  extracts the peak and continuous power requirements for each drive unit  130  from the motion simulation data files  220  and converts the power profiles to current profiles. The sizing tool  200  may convert the power values to current values using the nominal line voltage provided to the drive units  130 . Alternatively, the sizing tool  200  may consider a range of line voltages (e.g., a nominal voltage with ±tolerances, or a user-specified voltage range).  
         [0028]     After computing the current requirements for the drive units  130 , the sizing tool  200  may sum the individual current requirements to generate a total continuous and/or peak current requirement that the power processing device  120  must support. In combining the individual current components for the drive units  130 , the sizing tool  200  may consider synchronization information regarding the drive units  130 . A user may specify. synchronization parameters for the various drive units  130 . The synchronization between drive units  130  is distinct from the synchronization between multiple axes served by a single drive unit  130  described above, but has similar effect. For example, if one drive unit  130  is expected to operate in a known timing relationship with respect to a different drive unit  130 , an offset parameter may be specified. If no synchronization exists, random operation may be presumed, and all drive units  130  may be active simultaneously for determining the current requirements of the power processing device  120 .  
         [0029]      FIGS. 3A and 3B  illustrate exemplary current profiles  300 ,  310  for two drive units  130 . The current profiles are simplified for illustrative purposes and not intended to mirror actual current profiles. An actual profile would comprises sinusoidal waveforms of varying amplitude. As seen in  FIG. 3A , current typically peaks when a motor is activated, as indicated by the region  302 , and then reduces until a steady state current (i.e., corresponding to a steady state velocity) is achieved, as indicated by the region  304 . When a motor is deactivated, a negative current region  306  occurs as regenerative power created by the motor during a regenerative braking operation is fed back to the bus.  
         [0030]     Based on the system design, the user may know that the motor served by the drive unit  130  having the current profile  310  may start at a later time than the motor served by the drive units  130  having the current profile  300 . In the example of  FIGS. 3A and 3B , the current profile  310  is offset from the current profile  300  by about one second. Hence, the peak currents generated during the startup cycle of the drive units  130  do not align. Accordingly, the peak current determined by the sizing tool  200  is less than the peak that would have occurred had no synchronization been specified. In such a case, the sizing tool  200  would have assumed that the drive units  130  experienced their peak current demands at the same time.  
         [0031]     The current profile for the power processing device  120  generated by the sizing tool  200  may have numerous uses. For example, the sizing tool  200  may verify that the proposed application is suitable for the selected power processing device  120 . If the current requirements are exceeded, the sizing tool  200  may access an equipment database  240  that lists power processing devices and their associated ratings to recommend an alternative power processing device  120 . In another embodiment, the user may not specify any particular hardware for the power processing device  120 . The sizing tool  200  may determine the current requirements for the specified drive units  130  and then determine one or more power processing device  120  that may be used. If one power processing device  120  is not sufficient, the sizing tool  200  may divide the drive units  130  into distinct groups, each served by a different power processing device  120  and then iterate to determine current ratings and appropriately sized power processing devices  120  for each group.  
         [0032]     The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.