Abstract:
A hybrid backplane uses multiple, parallel serial communication channels to provide flexibility and robustness in a motor drive control requiring high-speed data communication for the real-time control of motor waveforms.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   Not Applicable. 
   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not Applicable. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to motor drives providing synthesized power waveforms to electric motors to control the operation of the motors, and in particular to an improved, modular interconnection system for such motor drives. 
   Industrial controllers use specialized computers and other electronic circuitry to control industrial processes and machines. The elements of an industrial controller must be easily reconfigured so that the industrial controller may be easily adapted to a variety of applications. For this reason, the elements of an industrial controller are normally modular, allowing different modules to be selected and assembled within a rack that provides for an interconnection between the modules. This approach allows a wide variety of different hardware configurations to be created rapidly. 
   Motor drives differ from a standard industrial controller in that extremely high communication rates are required among the different drive controls, for example, to precisely synchronize inverter/rectifier control in real time. Gating signals to rectifiers or inverters requires low latency. For this reason, the modules of a motor drive are normally interconnected with dedicated parallel communication channels between the various drive modules. Parallel communication channels communicate the bits of multi-bit data simultaneously with each bit assigned to a different conductor. Single bits of data, for example gating signals, may be assigned to a unique conductor so that multiple single bits are also transmitted in parallel. In this way, extremely high speeds of data transfer or low latency may be reached. These parallel communication channels may be implemented on a backplane, typically a printed circuit having multiple parallel conductors joining multiple connectors that may attach to the modules. As with an industrial controller, the modules may be assembled together within a rack abutting the backplane. 
   In an alternative to the backplane configuration, dedicated parallel communication channels may be implemented by the use of pairs of electrical connectors joined by ribbon cables or the like providing for the parallel conductors. The use of separate parallel channels can increase data speeds and reduce latency. 
   A drawback to such parallel bus structures is that they are relatively inflexible. In the backplane system, when additional single bit data must be transmitted, new conductors must be added to the backplane. This may require a fundamental redesign of the circuit boards of the system or may be impractical for reasons of costs or equipment size limitations. In the harness system, even though new wires may be added to the harness, the connector sizes must change requiring a change of the module circuit boards. Making and changing the connections between modules in the harness system is difficult, requiring the physical routing of wires between particular boards. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention combines the benefits of the physical backplane, allowing simple interconnection of modules, with the features of a high-speed serial network minimizing the number of conductors needed to transmit information. This is done by assembling a backplane not out of multiple parallel conductors but rather out of multiple parallel serial communication channels. 
   In the resulting “serial backplane” modules may be: easily assembled (through a conventional rack and connector system), flexibly reconfigured (via the addressing system of the serial protocol), resistant to single channel failures (by the use of multiple independent serial channels), and/or upgraded to control more gate signals without cost or space penalties (because of the natural conductor savings in serial data transmission). 
   Specifically then, the present invention provides a motor drive system controlling power semiconductor devices to provide controlled power to an electric motor. The motor drive system includes a rack having a housing with a backplane, the housing providing slots holding modules removably held within the rack so that releasable electrical connectors on a rear face of the modules abut mating electrical connector on the backplane. The motor drive system also uses a set of modules including at least one drive control module receiving command signals to provide gating signals for the control of the power semiconductor devices and at least two gate modules receiving gating signals and providing semiconductor drive signals to the power semiconductor devices. Significantly, the backplane provides a set of separate, serial communication channels communicating between the modules, each serial communication channel independently transferring multi-bit data words as sequential single bits. 
   It is thus a feature of one embodiment of the invention to effectively combine a backplane structure with a serial communication protocol to satisfy the unique requirements of a motor drive system. 
   The power semiconductors may be components of rectifiers or inverters. 
   It is thus another feature of one embodiment of the invention to provide a system that accommodates the flexible routing of gating signals used for semiconductor control of input and output power. 
   The separate serial communication channels may include at least one serial communication channel communicating with multiple modules to direct data to specific modules according to at least one address contained in the transmitted data. 
   It is thus a feature of one embodiment of the invention to provide a system that may flexibly route data among modules according to software configurations without rewiring. 
   The separate communication channels may also include at least one serial communication channel dedicated to one pair of modules. 
   It is thus another feature of one embodiment of the invention to provide a serial communication system that is resistant to single channel losses. 
   The serial communication channel may be full-duplex and provide a transfer rate in excess of two gigabits per second. 
   It is thus a feature of one embodiment of the invention to exploit high-speed data communication protocols to permit serial communication channels to stand in place of a high-speed parallel bus structure. 
   The set of modules may further include at least one communication module receiving command signals from a programmable logic controller and at least two drive control modules. The serial communication channels may provide a full mesh interconnection among the communication module and the drive control modules. 
   It is thus a feature of one embodiment of the invention to provide an interconnect system that may offer the robustness of full mesh interconnect that is resistant to communication failures and that is not easily available in a parallel backplane structure. 
   The set of modules further may include a data drive recorder recording data describing operation of the motor drive system. 
   It is thus a feature of one embodiment of the invention to provide ample data capacity for full recording of the operation of the motor drive system in real time. 
   Separate dedicated communication channels may communicate among the control modules and a shared communication channel may communicate among the control modules and the gate modules. 
   It is thus a feature of one embodiment of the invention to provide a backplane structure that flexibly accommodates different types of anticipated communication—those with high data rate and those that require lower data rates but reduced latency. 
   The modules further include input/output modules accepting feedback signals from outside the rack. 
   It is thus a feature of one embodiment of the invention to provide a system that may accommodate all communications normally required in a motor control system. 
   The serial communication channels use low voltage differential signaling. 
   It is thus a feature of one embodiment of the invention to provide an electrical technique that allows a high-speed serial communication protocol to be implemented in a backplane structure. 
   The control modules may include a computer executing stored software allowing the control modules to receive commands to change the gate modules to which they are connected by changing the addressing on a serial communication network. 
   It is thus another feature of one embodiment of the invention to allow software “re-wiring” of the motor control system. 
   Similarly the software may allow the control modules to assume the function of a failed control module. 
   It is thus a feature of one embodiment of the invention to provide a motor control system that may be robust against individual component failures. 
   These particular features and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a simplified perspective view of a motor control system communicating with a rectifier and an inverter to control a motor; 
       FIG. 2  is a front elevational view of the motor controller of  FIG. 1  showing the individual modules that may be installed in the motor controller rack; 
       FIG. 3  is a schematic representation of a prior art modular interconnect system using a connector system to implement separate parallel communication channels; 
       FIG. 4  is a figure similar to that of  FIG. 3  showing a modular interconnect system of the present invention using a serial backplane; 
       FIG. 5  is a simplified representation of the serial backplane structure of the present invention showing the assembly of the backplane out of multiple serial communication channels; 
       FIG. 6  is a perspective view of a portion of the backplane of  FIGS. 4 and 5  showing the connector system used to connect the modules to the backplane; 
       FIG. 7  is a data flow diagram showing the communication among the modules in a first configuration using the backplane of the present invention; and 
       FIG. 8  is a figure similar to that of  FIG. 7  showing a reconfiguration of modules using the backplane of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to  FIG. 1 , a motor controller  10  may be assembled within a cabinet  12  limiting access to the motor controller  10 . The cabinet  12  may have a back panel  14  supporting a motor drive rack  16 , a rectifier  18 , and an inverter  20  which together form the principle components of the motor controller  10 . 
   Within the cabinet  12 , the drive rack  16  may receive DC power  22  and the rectifier  18  may receive a source of three-phase power  24  which is converted to DC power  26  and provided to the inverter  20 . The inverter  20  may in turn provide for synthesized power waveforms  28  which are transmitted out of the cabinet  12  and connected to the windings of the motor  30 . 
   Referring now to  FIGS. 1 and 2 , the motor drive rack  16  may hold a set of modules  32  including a DC-to-DC converter module  36  converting the DC power  22  to convenient voltages for powering the other modules  32 . The set of modules  32  may also include one or more drive control modules  38  which, in response to programming and commands, generate gate trigger signals for triggering semiconductor devices in the rectifier  18  or inverter  20  transmitted to one or more gate driver modules  40 . The gate driver modules  40  may communicate via gate signal leads  42  (typically fiber optic leads) to the power semiconductors in the rectifier  18  and inverter  20 . 
   The modules  32  may also include a drive data recorder module  49  serving to perform data logging and to provide for common memory that may be shared by the other modules  32 . In addition, the modules  32  may include a communication module  50  having a communication line  51  to communicate with an industrial control system, for example, a programmable logical control programmed to provide commands to the motor controllers  10 . 
   The modules  32  may also include I/O modules  44 , for example, digital or analog I/O modules receiving one or more feedback signals  46  from the motor  30 , for example from an encoder  47 , or the like. The I/O modules  44  may also receive monitoring voltages from the inverter  20  and the rectifier  18 , for example, those indicating line current, line voltage, DC link current, motor voltage, and motor current, as is understood in the art. 
   Referring now to  FIG. 3 , in the prior art, the individual modules  32  were connected by parallel bus harnesses  52  in the form of ribbon cables terminated in multi-pin connectors attached to the circuit boards of the individual modules  32 . The drive control modules  38  (and the communication module  50  and a drive data recorder module  49 ) are each connected to one parallel bus harness  52  communicating with a dual port ram  54  to provide for high-speed asynchronous communication between each other. The drive control modules  38  communicate with gate driver modules  40  and with I/O modules  44  through separate parallel bus harnesses  52 . 
   Referring now to  FIGS. 4 and 5 , the present invention provides for a backplane  60  comprised of parallel conductors not forming one or more parallel channels, but rather forming multiple serial channels  62 . As is understood in the art, a serial channel is one in which the bits of multi-bit logical data words are transmitted over a single or pair of conductors as sequential single bits. 
   In a preferred embodiment each serial channel  62  may be of one of two types: dedicated serial channels  64  communicating between only two modules  32 , and shared communication channels  66  communicating among multiple modules  32  and distinguishing among communicating modules  32  using normal addressing techniques known in the art of serial communication in which addressing is contained in header fields or the like. 
   Referring also to  FIG. 6 , each of the serial channels  62  is implemented by means of parallel conductors  68  on a printed circuit board  70  or the like that span multiple electrical connectors  72  attached to the board  70  and arrayed along a line of the conductors  68 . The board  70  and the connectors  72  together provide a physical backplane  74 . 
   Each dedicated serial channel  64  may, for example, employ two conductors  76  providing a first transmission path in one direction, and two conductors  78  providing a transmission path in the opposite direction to provide full-duplex operation. In a preferred embodiment, the dedicated serial channel  64  may operate at variable speeds from 600 megabits per second to 3.125 gigabits per second. A low voltage differential signaling (LVDS) technique may be used with a programmable threshold level of 800 mV to 1600 mV. The particular protocol may be any of a number of serial protocols such as Fiber Channel, Gbit Ethernet, XAUI, Infiniband, Aurora, or other custom protocols. 
   The shared communication channels  66  may use any of a number of conventional shared protocols, for example SPI or I2C or proprietary protocols. Multiple shared communication channels  66  may be used (not shown), for example, one dedicated to analog I/O and the other dedicated to digital I/O. 
   As shown in  FIG. 5  each of the dedicated serial channels  64  will have electrical connection  71  with only one connector  72  so as to provide for a communication between only two modules  32 . The topology of the connection is such as to provide for a separate dedicated serial channel  64  between each pair of the drive control modules  38 , communication module  50  and drive data recorder module  49  as indicated in  FIG. 4  to provide a full mesh interconnect. A full mesh interconnect allows any of the module  32  listed above to connect directly to each other in the interconnect and thus prevents a failure of one module  32  or dedicated serial channel  64  from disrupting communication among all modules  32 . This provides some resistance against hardware failure. A failure of one dedicated serial channel  64  does not isolate any individual module  32  which may communicate with the modules  32  joined by the failed communication module  32  using another module  32  as a bridge. 
   The full duplex operation allows extremely high-speed data transfer between drive control modules  38  as may be needed, for example, for synchronization of motors  30 . 
   The shared communication channels  66  provides connections  71  to each of the connectors  69  on the rear of each the modules  32 . While the dedicated serial channel  64  only connects between the drive control modules  38 , communication module  50 , and the drive data recorder module  49 , the shared communication channels  66  connects among either the I/O or gate driver modules  32 . 
   In practice, gating signals are communicated over separate shared communication channels  66  split between the Inverter and Rectifier Modules. I/O signals are communicated over a separate shared communication channels allowing software reconfiguration of the connections between the drive control modules  38 , communication module  50  and drive data recorder module  49  and various of the I/O modules  44  by changing the address of the serial message which is receivable by all modules  32 . 
   In this regard, and referring now to  FIG. 7 , in the event of a failure of drive control modules  38 ′, drive control modules  38  may reconfigure the parameters of their stored communication program  80  to simply assume the functions of the drive control module  38 ′ and communicate with gate driver modules  40 ′ previously being provided with gating signals from failed drive control modules  38 ′, and to communicate with the communication module  50  on behalf of the failed drive control module  38 ′. 
   Referring to  FIG. 8 , the flexibility engendered by the present serial backplane system further allows, for example, a given drive control module  38   a  to control multiple gate modules  40   a  and  40   b  in parallel which in turn control two rectifiers  18   a  and  18   b  in parallel for increased power capacity. Similarly second drive control modules  38   b  may communicate with gate modules  40   c  and  40   d  controlling inverters  28   a  and  20   b  in parallel. In the prior art system, described with respect to  FIG. 3 , a manual reconfiguration of parallel bus harnesses  52  would have to be implemented, whereas in the present invention, this reconfiguration can be done by a modification of stored programs  80  in the drive control modules  38 . 
   The present invention has been described in terms of the preferred embodiment, and it is recognized that equivalents, alternatives, and modifications, aside from those expressly stated, are possible and within the scope of the appending claims.