Patent Application
20100123425
The present invention relates generally to the field of power electronic devices, and particularly to a electric motor drives and their coordinated operation.
Electric motors and motor drives are ubiquitous throughout industrial, commercial, material handling, process and manufacturing settings, to mention only a few. In many applications, motors may simply be started and allowed to run at a relatively constant speed. However, many processes motors must be operated at different speeds and even in different types of control regimes, such as to control a rate of advancement of a product, a rate of production, torque applied to a load, and so forth. Motor drives are used in such applications, and allow for a range of control options, from simple speed control to much more sophisticated control of a controlled parameter, such as torque, pressure, flow rates from pumps and fans, and so forth.
A typical motor drive employed with a single or three phase induction motor utilizes power from the power grid, and performs power conversion to produce output power with desired current, voltage and frequency characteristics. The output power can be manipulated by the drive control circuitry to implement the type of control sought. For example, based upon feedback from the application driven by the motor and from the motor itself, complex processes may be controlled automatically by the motor drive, typically based upon preprogramming by operators.
Some applications require some degree of coordination in the operation of motors. For example, in an integrated or complex processing or manufacturing operation, two or more motors will need to turn at the same or nearly the same speed, or must power loads in a shared manner. In printing and similar continuous product applications, particularly, a high degree of synchronized control may be very useful for product quality and production efficiency. Such applications are sometimes referred to as multi-axis, due to the need to control multiple rotating machines in a harmonized manner. However, with conventional motor drives, such synchronized operation is either unavailable, substantially limited in accuracy, or costly.
There is a need for new approaches to motor drive and motor synchronization that can address such applications. In particular, there is a need for cost effective motor drives that can provide a high degree of coordinated control when linked to one another.
The present invention provides a novel approach to motor control designed to address such needs. The invention may be employed in a wide range of applications, but is particularly well suited to demanding situations in which motors are to be controlled in a precisely coordinated manner. In accordance with certain aspects of the invention, a motor drive comprises a control circuit that is separately supported with respect to certain functional circuits. The functional circuits are coupled to the control circuit via respective dedicated serial interfaces. An interrupt scheme implemented by the control circuit ensures that data is collected from all functional circuits in a deterministic and synchronous manner. Multiple interrupts with different periodicity may be used for collecting data used by the control circuit for different purposes.
The control circuit clock is synchronized with that of other drives in an overall system. Synchronization of the clocks, in turn, assures that the interrupts of all such synchronized drives are generated in a coordinated fashion. Data collected from the functional circuits, then, is assured of being collected at the same time, and may be utilized by the same drive or by other drives for synchronized operation.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
Beginning now with
As described further below, the motor drive is adapted to receive three-phase power from a power source, such as the electrical grid and to convert the fixed frequency input power to controlled frequency output power. The motor drive 100 may manage both application of electrical power to the loads, typically including various machines or motors. The drive may also collect data from the loads, or from various sensors associated with the load or the machine system of which the load is part. Such data may be used in monitoring and control functions, and may include parameters such as current, voltage, speed, rotational velocity, temperatures, pressures, and so forth. The motor drive 100 may be associated with a variety of components or devices (not shown) used in the operation and control of the loads. Exemplary devices contained within the motor drive 100 are motor starters, overload relays, circuit breakers, and solid-state motor control devices, such as variable frequency drives, programmable logic controllers, and so forth. As discussed further below, the motor drive 100 may include expandable functionality through the addition of option boards installed in a backplane inside the motor drive 100. Additionally, the motor drive 100 may be used in conjunction with other motor drives, such that a plurality of motor drives may be used to control one or more processes. As also discussed below, functions within the drive are synchronized, and the drive (and its internal functions) may be synchronized with other drives in an overall machine system.
The control circuitry 202 and driver circuitry 204 may include a control circuit board and various optional function circuits, referred to herein as “option boards”, in accordance with an embodiment of the present invention, as discussed further below. The driver circuitry 204 signals the switches of the power electronic switching circuitry 206 to rapidly close and open, resulting in a three phase waveform output across the output terminals 218, 220, and 222. The driver circuitry 204 is controlled by the control circuitry 202, which may operate autonomously, or which may respond to command inputs from the remote control monitor 208 through a network. Similarly, operation of the driver circuitry may be coordinated, via the control circuitry, with that of other drives. Many different control schemes and functions may be implemented by the control circuitry, and programs for such operation may be stored on the control board, such as for closed loop speed control, closed loop torque control, among many others.
An inverter 244 is coupled to the DC bus and generates a three phase output waveform at a desired frequency for driving a motor 216 connected to the output terminals 218, 220, and 222. In the illustrated embodiment, within the inverter 244, for each phase, two insulated gate bipolar transistors (IGBT's) 246 are coupled in series, collector to emitter, between the high side 238 and low side 236 of the DC bus. Three of these transistor pairs are then coupled in parallel to the DC bus, for a total of six transistors 246. Each of the output terminals 218, 220, and 222 is coupled to one of the outputs between one of the pairs of transistors 246. The driver circuitry 204 signals the transistors 246 to rapidly close and open, resulting in a three phase waveform output across output terminals 218, 220, and 222. The driver circuitry 204 is controlled by the control circuitry 202.
In some embodiments, multiple motor drives and motors may be used to control a process. For example, as illustrated in
As discussed above, in some embodiments a motor drive may add functionality, connections, or both through the addition of option boards installed in the motor drive. The option boards may be in communication with other motor drives, motors, sensors, or other devices. As discussed above with respect to
To facilitate addition of the option cards, a motor drive may include a “pod” 400 having a chassis 402 as shown in
The pod chassis 402 may include a one or more backplanes 408, which generally support and provide the physical interconnect between the control board 404 and various option boards. The backplanes 408 may include a printed circuit board having any number of slots, plugs, connectors, or other interface structures. The backplane 408 provides for distribution of power and data signals, and enables the option cards to be interfaced with a network. For example, as shown in
The pod chassis 402 may also include additional features to increase reliability and performance. The chassis 402 may include one or more fans 412 and one or vents 414 on any portion of the chassis 402 to allow for airflow and heat dissipation.
For example, beginning with
Finally,
As described above, in some embodiments the pod 400 may have two (or more) backplanes, as indicated by a dashed regions 612 and 614. In the illustrated embodiment, because each backplane 612 and 614 may include three interface slots, which in one embodiment may be PCI-E style connector slots, three dedicated serial buses are provided on each backplane. In addition to communication with the control board 602, the option boards 604 may communicate with each other via a network 616. By using the network 616, the option boards 604 may communicate with each other without first routing the communication through the control board 602. In other embodiments, the option boards 604 may route communication to other options boards on the same backplane or an adjacent backplane via the control board 602.
As described above, in a presently contemplated embodiment, each channel of the dual channel full duplex serial interfaces 606 may transmit a specific signal. In this embodiment, the signal processing may be implemented by means of an FPGA on the control board 602. In other embodiments the signal processing may be implemented in software and may use a processor on the control board 602.
To ensure synchronization, regardless of the clock timing of each option board, each signal 700 and 702 may have a data acquisition interval and a transfer interval. For example, the Control Event signal may include a data acquisition window 704 and a transfer interval 706. In one embodiment, the data acquisition window 704 for the Control Event signal may about 6 μs, and the transfer interval may be about 128 μs to about 256 μs. At the end of the data acquisition window, a processor on the control board is interrupted, e.g., via an IRQ, to ensure no wasted idle or wait time is consumed by the CPU. By providing a data acquisition window 704, the control board is ensured of receiving all data from the option boards in the pod. Thus, in a presently contemplated embodiment, the rising edge 708 of the Control Event signal, the option boards may shift their register to the control board within the 6 μs window. The clock rate of the option boards may be set at the appropriate level to ensure this data is transferred in the data acquisition window. The clock rate may be standardized at 32 MHz, although other rates may be employed. Advantageously, this ensures that all registers (signals) from the options boards will be synchronized. That is, no matter when each option board acquired its data, all options board must report to the control board by the end of the data acquisition window. In one embodiment, the Control Event signal may be referred to as a “Control Event Primary” signal and may be used for control task (commutation) data acquisition from the option cards, such as for such data as torque references, encoder feedback, etc. Further, to facilitate communication with the serial interface, the option boards may include a shift register interface having a 32-bit length, and the transfer rate may controlled by a clock on the option board.
Similarly, in a presently contemplated embodiment, the System Event signal 702 may include a data acquisition interval 710 and a transfer interval 712. In such an embodiment, the data acquisition window 710 for the System Event signal 702 may be about 20 μs and the transfer interval may be about 1-2 ms to about 256 μs. In some embodiments, the System Event signal 702 may provide for both a primary and secondary message sent on the data acquisition interval and transfer interval respectively. In such an embodiment, the secondary message must be completed prior to the end of transfer interval. In one embodiment, the primary message may be referred to as a “System Event Primary” and have a 64 byte storage limit, and the secondary message may be referred to as “Secondary Event Continuous” and have a 512 byte storage limit.
It should be noted that the particular speed, data acquisition interval length, interrupt spacing, and so forth used in the drive may be different from that set forth in the present discussion. For example, the timing of the deterministic interrupt scheme is set based upon such factors as the amount of data to be transferred from the option boards (or from the control circuit to the option boards), and the duration of the data acquisition interval desired, as compared to the duration of the processing window needed. That is, the processing circuitry of the control board will collect and process the data received, and perform the control functions for operation of the motor coupled to the drive, and will need some time to perform such functions. The data acquisition window may be set to a duration that is a function of the anticipated processing time, such as 10%. Such considerations may result in design choices within the ambit of those skilled in the art.
It will be appreciated that the use of dedicated serial interfaces for each functional circuit (option board), and the interrupt scheme for transfer and collection of data from all such circuits provides a deterministic, synchronous interrupt structure that permits very fast data transfer rates. The serial interfaces essentially function as bit shift registers for the transfer of data without the need for traffic control between the circuits. Similarly, it should be noted that while the rate of transfer of data from the functional circuits may be set, such as at 32 MHz, this rate is actually configurable. Thus, where less data is to be delivered in the available time, a slower data transfer rate from the functional circuit may be set (e.g., as low as 2 MHz), while for more demanding data transfer, even higher rates may be set (e.g., 64 MHz). Moreover, the rates of data transfer from the different option boards, even within a single drive, need not be the same. Different rates may be set for different option boards, while still maintaining synchronization in operation by virtue of the dedicated serial interfaces and deterministic interrupt scheme. Similarly, different data transfer rates may be used for different channels for each board, and these rates may be changed over time. In certain applications the use of different data transfer rates may aid in reducing harmonic distortion or interference between the interfaces and channels.
The System Event Primary may be used for a “login” function on the serial interface such that each option card may use this signal to log on to the control board and establish communication. The System Event Primary may be used for system task data acquisition, such as analog I/O, digital I/O, feedback, communications, etc. Additionally, in one embodiment the System Event Continuous signal may provide additional communication such as transfer of large data blocks.
To facilitate communication and interfacing of a control board with the option boards, the control board and/or option boards may use profiles to assist with the “log on” of the option boards.
In one embodiment, the HMI on a motor drive may provide a user interface for accessing, managing, and configuring the option boards installed in a pod of the motor drive. As mentioned above, the user interface may be provided on a processor and a memory of the control board. In many applications, however, the initial configuration of the drive will be performed by coupling the drive to a workstation, which may include a conventional programmed computer (e.g., personal computer). Screen views provided by software on the workstation, or served by the drive to the workstation facilitate in selecting parameter settings, units of measure, parameter names, and so forth. The profile for each option board, moreover, greatly facilitates this process, and each profile may already preconfigure certain of the settings for the option board, or may reduce the set of options presented to the installer or system integrator to those available or appropriate to that option board and selected system setup. The profiles may thus be part of an automatic device configuration scheme, streamlining setup of the drives by reducing the information presented to the installer and guiding the installer though the setup. It is presently contemplated that such individual profiles may be stored on the option boards (i.e., each option board including its respective profile), and fed to the control board, or a library of profiles may be stored on the control board, and an appropriate profile used for configuration of a specific option board if it is recognized as present in the drive by the control board. Such profiles may also be downloaded to the drive from a library, such as via the network connection provided to the drive, or upon initial installation. Certain of these options may allow for expansion of the number and types of functional circuits available over time.
It should be noted that in another presently contemplated implementation, the profile data (defining functions of the functional circuits, parameters they provide or need for operation, rates of transfer of data, etc.) may be provided (e.g., uploaded) directly from the functional circuits to the control circuit without reference to a database or library or profiles. This approach essentially relies on storage of the profile data in the functional circuitry and loading or transfer of the data to the control circuit. However, this approach may prove more generic insomuch as additional functional circuits may be developed over time, and these may “self-configure” the control circuitry which would need no prior information or data relating to the profile or to the functional circuit.
By selecting a node 908, e.g., a control board 908, or an option board 912, a user may display the parameters associated with that control board or option board. For example, the right hand pane 904 a list of parameters is displayed, such as the speed parameters 914. The right hand pane 904 may display information about each item listed, including a node column 916, a slot column 918, and a parameter number 920, with each column displaying the node, slot and parameter respectively of each item. To configure a node, a user may select a parameter, as illustrated by the selected parameter 922 (Speed Ref A Set, e.g., a speed reference).
As shown in
The interrupt scheme described above permits synchronization of all functions within the motor drive, including the acquisition of data from all functional circuits supported on the option boards. That is, because all data is received serially from all of the option board functional circuits and in response to the Command and System interrupts, all of the data is assured of being received by the control circuitry at the same time. Once received, the data can be acted upon by the processing capabilities of the control circuitry in the interim between interrupts. For data that directly affects motor control, sometimes referred to as communication data, the data acquisition is particularly fast, with little time between the interrupts. For other data, the intervals may be more widely spaced in time.
The same interrupt scheme, and close synchronization of data acquisition can also allow for very accurate synchronization between drives linked to one another via a network. For example,
Drive 1004 is similarly configured. It includes a control circuit 1014 and a series of functional circuits 1016 that communicate with the control circuit 1014 via dedicated serial interfaces, with data transfer again being coordinated via interrupts as described above. The control circuit 1018 similarly produces control signals that are applied to drive circuit 1018 for driving motor 1020.
In system 1000, the operation of motors 1012 and 1020 is coordinated and synchronized, such as for “multi-axis” control. Such coordinated control is extremely useful in many applications, such as integrated machines in which motors handle product in continuous processes. Examples may include printing applications, paper making applications, product handling applications, and so forth, to mention only a few.
To permit such high degree of synchronization, a synchronization counter 1022, or similar device, is included in each drive, and synchronizes the clock of the control circuit for that drive with that of other drives interconnected in the system. In a presently contemplated embodiment, the drives are interconnected via a network connection 1024, which utilizes an Ethernet communications protocol, although other protocols may be used. The coordination of the synchronization counters is performed in accordance with IEEE 1588 standards.
It has been found that the use of such clock synchronization between drives, in conjunction with the use of dedicated serial interfaces for functional circuits, and the interrupt scheme for transfer and collection of data from the functional circuits permits an unprecedented degree of coordination and synchronization of the drives. That is, in the overall system, all functional circuits (e.g., input/output circuits, communications circuits, encoders, parameter estimation/calculation circuits, etc.) of all drives can be precisely coordinated insomuch as the interrupts for transfer and collection of data from all such circuits occurs at the same time, as coordinated by synchronization of the clocks of all drives. Such coordination allows the drives to be used in applications and with a degree of precision that was heretofore unavailable in similar production equipment.
It should also be noted that, as mentioned above, the use of dedicated serial data interfaces for the functional circuits, and the interrupt structure described above also permits sending and receiving synchronized messages between the control circuitry and the functional circuits. That is, during an interrupt, a rising edge is used to start a message transfer between the control and functional circuits. This may be referred to as the primary message transfer. In addition to this message transfer, however, a secondary message transfer may be implemented between the control and functional circuits. This may occur when the interrupt ends (returns to a low state, i.e., a falling edge is detected). In a presently contemplated implementation, this secondary transfer occurs after the initial 6 μs or 20 μs timing interval (or any other interrupt interval employed) until the next periodic interrupt. This secondary message transfer allows for further utilization of the serial transfer bandwidth.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
