Patent Publication Number: US-2013235494-A1

Title: Integrated Bypass Apparatus, System, and/or Method for Variable-Frequency Drives

Description:
RELATED APPLICATIONS 
     This application is a nonprovisional of, and claims the benefit of priority from, U.S. Provisional Patent Application No. 61/531,612, filed Sep. 6, 2011, which is hereby incorporated by reference in its entirety 
    
    
     COPYRIGHT NOTICE 
     ©2012 Cerus Industrial Corporation. A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. 37 CFR §1.71(d), (e). 
     TECHNICAL FIELD 
     The present application is directed to the field of variable-frequency drives for motors that drive equipment such as fans, pumps, and the like, and, in particular, to the field of bypass assemblies and bypass circuits for such variable-frequency drives. 
     BACKGROUND 
     The phrases adjustable-speed, variable-speed, or variable-frequency drive (“VFD”) refer to equipment assemblies that provide a means for driving and adjusting the operating speed of a mechanical load, such as a motor. The motor can be used to drive fans, belts, pumps, or other electromechanical devices. For example, VFDs are very common in heating, ventilation, and air conditioning (HVAC) applications. While variable-frequency drives can be broadly described as including the electric motor, a speed controller or power converter, and/or auxiliary devices and/or equipment, it is also common to use the term VFD to refer to just the corresponding controller. 
     Because VFDs are electronic devices and coupled to moving components, they are prone to fail, which can be particularly concerning if the VFD is installed in a critical environment and/or applications. In such critical applications, it is known to use a traditional bypass assembly as a solution to provide system redundancy in case of VFD failure. Existing bypass assemblies are added to a VFD installation with an additional enclosure. However, the resulting combined installation is expensive, complicated, bulky, and frequently impractical in many applications and/or installation sites. 
     In the event the VFD fails, an installed bypass assembly is used to switch the controlled motor to a full-run condition. However, because typical bypass runs the motor at full-speed once it is engaged, additional problems can result. As but one example, in an HVAC application, full-speed motor operation can result in over/under pressurization of the building and ductwork, which can be damaged as a result. 
     Furthermore, many present “green-building” initiatives and building and/or industrial energy management applications attempt to measure total power consumption by electrical equipment such as VFDs. However, traditional bypass assemblies do not measure power consumption, and installations employing separately added power metering equipment are additionally bulky and cumbersome. Furthermore, such power metering typically measures power output, which is not a true representation of power consumption for the system. 
     SUMMARY 
     Subject matter consistent with the present application can comprise a bypass assembly integrated with a variable-frequency and provisioned in a single unitary enclosure. One advantage of such an integrated bypass is substantially reduced size, cost, and/or complexity in the combined VFD/bypass assembly, compared to traditional installations. 
     An additional advantage can include the ability to manage airflow with a bypass assembly to ensure sufficient airflow is maintained substantially without running the motor full time. Such improved bypass assemblies can reduce energy consumption, protect duct work from over-pressurization, and improve comfort for building occupants. 
     A further advantage of integrated bypass assemblies, as disclosed herein, is pre-configured support for integrated metering functionality, suitable for accurate measurement of power consumption in both VFD and bypass modes of operation. 
     Additional aspects and advantages of this invention will be apparent from the following detailed description of preferred embodiments, which proceeds with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates one embodiment of a system configuration consistent with the present subject matter. 
         FIG. 2  illustrates a process flow diagram representing one operating methodology embodiment consistent with the present subject matter. 
     
    
    
     DETAILED DESCRIPTION 
     For purposes of illustrating concepts consistent with the present subject matter, the following description is presented to facilitate discussion. Embodiments disclosed herein are presented for illustrative purposes, and not by way of limitation. Those skilled in the relevant art will readily appreciate that additional, fewer, or alternative components to the various elements described below could be employed without departing from the scope or content of the claimed subject matter. 
     In the field of variable-speed motor controls, one or more embodiments of bypass circuits and/or corresponding embodiments of bypass electronics can be integrated advantageously with a variable-frequency drive (“VFD”) circuit and/or corresponding electronics. Such an integrated bypass can be disposed within a single unitary enclosure housing the VFD. In the case of an inverter fault, over temperature fault, or other error in the variable-frequency drive, motor operation can be automatically transferred to the bypass to help ensure air delivery, maintain drive life, and for other benefits. Some additional advantages of the integrated bypass can include reduced size, cost, and/or complexity in the combined VFD/bypass assembly, the ability to manage airflow in bypass without full-time running a fan motor, and integrated power metering functionality. 
     To further illustrate, at least in part, one or more concepts of the present subject matter,  FIG. 1  is presented as one embodiment of a system configuration representing one illustrative embodiment of bypass circuitry and/or corresponding electronic components integrated with a variable-frequency drive. With particular reference to  FIG. 1 , various components typical of a variable-frequency drive are illustrated. For example,  FIG. 1  illustrates a motor  100  operating on three-phase, three line power via conductors  102 . Variable-frequency drive power  104  is regulated/controlled by a microprocessor-based variable-frequency drive control board  106 . 
     Those skilled in the art will appreciate that the previously mentioned variable-frequency drive components can, in one embodiment, be configured and/or provisioned within a single, unitary housing representing a starter apparatus for motor  100 . Additionally, a true disconnect  108  can be included, such that the resulting starter would be suitable for classification as a combination starter. Disconnect  108  can substantially allow line power in conductors  102  to be cut off from the rest of variable-frequency drive system. A variable-frequency drive employing control board  106 , and operating to provide starter functionality, can provide for control and protection of motor  100  through additional components including a variable-frequency drive contactor  110  and an overload relay and/or overload protection circuit, which can include current detection circuitry and/or components, such as the current transformers  112  illustrated in  FIG. 1 . In addition to the variable-frequency drive control board  106  controlling operation of motor  100  through varied application of variable fervency drive power  104 , which may additionally include optional filtering  114 , microcontroller-based control board  106 , operating as a starter embodiment, can protect motor  100  from unsafe thermal operating conditions via the overload current transformers (CTs)  112 . If the overload current transformers  112  detect unsafe levels of current the conducting lines  102 , the overload relay circuitry integrated with the control board  106  can signal the contacts of the VFD contactor  110  to separate (e.g., by de-energizing a normally energized contactor coil, etc.), in order to cut off motor  100  from the VFD power  104  supplied through the conductor lines  102 . 
     Continuing further with  FIG. 1 , it will be appreciated that additional input/output and user interface components can be employed for a variable-frequency drive control board  106  based, at least in part, on the specific implementation or environment in which the variable-frequency drive control board  106  is intended to be employed. Those skilled in the art will appreciate that many of the input/output components illustrated in  FIG. 1  provide functionality typical to standard variable-frequency drive controllers and/or motor starters providing variable-frequency motor control. For example, control board  106  in  FIG. 1  represents several additional inputs, including the illustrated for digital inputs  116  and the signal inputs  118 ,  120 ,  122 . Additionally, outputs such as the digital outputs  124  and two relay outputs  126  can also be provided as part of the control board  106  interface components. Control board  106  can also include a 24 VDC 100 mA output signal  128  and a CM output  130  as indicated in  FIG. 1 . For building automation and/or remote control and monitoring functionality, RS-485 I/O and/or additional communications interfaces  132  can also be provided for (e.g., Modbus, BACnet, APOGEE PLN(P1), etc.), to name but a few. 
     The VFD control board embodiment  106 , illustrated in  FIG. 1 , also illustrates several potential user interface inputs/outputs that could be employed to facilitate installation, operation, maintenance, or other interactive purposes for a user. By way of example, and not by way of limitation, user interface components of variable-frequency drive control board  106 , as illustrated in  FIG. 1 , include Hand-Off-Auto selector buttons  144 , a touch screen LCD display  142 , a jumper/selector switch  148 , as well as indicator pilot lights  146 . Of course those skilled in the relevant art will appreciate that additional, fewer, or alternative user interface components could be employed without departing from the scope of the present subject matter. For example, while the pilot light indicators  146  are illustrated as presenting a run indication and a fault indication for the motor, additional information, such as a power indicator could also be included. Control board  106  also includes an Ethernet port  140  which can be provided, at least in part to substantially aid and communications. For example Ethernet port  140  can be used with an attached laptop and/or other mobile computing device. It also could be used with appropriate communications technologies and/or networking components to generate HTML to a web browser for fast setup, cloning of units, or remote monitoring purposes, to name but a few examples. 
     It should also be appreciated with reference to  FIG. 1  that operating power  150  for control board  106  can be obtained, as but one example, directly or indirectly from line power supplied through conductors  102 . As operating power  150  in the embodiment illustrated in  FIG. 1  is at 24 VAC, and the line power through conductors  102  for a three-phase motor  100  is typically well in excess of that amount (e.g., 480 VAC, etc.), a control power transformer  152  can be employed to step down the line power from conductors  102  to a suitable range for providing control power input  150 . 
     The VFD control board  106  embodiment of  FIG. 1  is also illustrated as being configured to produce a contactor coil control signal  134  for controlling the VFD contactor  110  as previously mentioned. In one embodiment control signal  134  is represented as a 24 VAC control signal sufficient to energize, de-energized, and/or otherwise modulate the coil for VFD contactor  110 . Similarly, control board  106  can produce a bypass contactor control signal  136  for purposes of controlling a bypass contactor  138  as described in more detail below. Such bypass contactor control signal  136  could also be represented as a 24 VAC signal, as but one example. Those skilled in the art will appreciate that additional and/or alternative signals and/or control methodology could also be used to control one or more contactors to achieve the desired and/or intended functionality. 
     As  FIG. 1  illustrates, if control board  106  indicates a bypass condition is present, power to motor  100  through the conductors  102  can be disconnected via separating contacts of the VFD contactor  110  and power through conductors  102  can be supplied to motor  100  through the circuit path passing through bypass contactor  138 . It should be appreciated that, with the configuration illustrated in  FIG. 1 , regardless of whether motor  100  is operated via VFD contactor  110  or bypass contactor  138 , the overload current transformers  112  monitor current supplied to motor  100  via conductors  102 . 
     It should be appreciated that, as illustrated in  FIG. 1 , embodiments of bypass circuitry and/or bypass components can be strategically integrated with more substantially typical variable-frequency drive circuits and/or components and enclosed in a single unitary enclosure in order to provide the desired functionality with substantially reduced size, cost, and installation complexity. This presents a substantial advantage, in that integrated bypass drives, consistent with the present subject matter, present compact, lightweight, and consolidated electronic assemblies, thus substantially allowing them to fit into smaller locations and/or installation sites. 
     In addition to the cost, size, and simplified maintenance/installation advantages of integrating bypass functionality with a variable-frequency drive, as previously indicated, it should be appreciated that integrating control circuits and electronic component as illustrated in  FIG. 1 , can also afford substantial benefits for present embodiments for purposes of control methodologies, energy management, improved equipment life, and power metering. A few illustrative advantages of integrated bypass apparatuses, systems, and/or methods as disclosed herein are described in detail below. However, the following described advantages are presented for illustrative purposes, and not by way of limitation. 
     One aspect of the novel functionality is related to how a bypass contactor (such as contactor  138  in  FIG. 1 ) is operated in bypass mode, at least in part, to substantially overcome problems typically experienced with traditional bypass assemblies. Additionally, present integrated bypass embodiments can substantially incorporate intelligent management features into the bypass by modulating the bypass contactor within predetermined and/or configurable time intervals, or in response to maintaining a desired pressure (for example, in a PID implementation). Whether it is tied to a pressure sensor with a PID loop, or to a time clock, present bypasses can be operated to achieve specific desired functionality and characteristics. As but one example, in a time interval embodiment, a control board operating in bypass mode can modulate a bypass contactor to run the motor at set intervals (e.g., 10 minutes with the motor on, followed by 10 minutes with the motor off, etc.) as but one example presented for illustration and not intended for purposes of limiting the present subject matter. As such, a substantially average amount (e.g., typical, etc.) of air volume can be delivered to a building during the course of the bypass operation. 
     Additionally, and/or alternatively, a bypass contactor can be controlled and/or modulated, at least in part, in response to, or in an attempt to maintain, a desired pressure at one or more locations monitored throughout a building (e.g, PID implementation, etc.). For example, a bypass embodiment can control and/or operate the contactor modulation to substantially approximately maintain a desired set point pressure, at least in part, in response to one or more inputs measured by one or more pressure sensors and supplied via an input to a control board operating the bypass. Additionally, present embodiments can include one or more additional controls for advantageously enabling, at least in part, functionality for controlling and/or modulating air duct dampers in order to restrict and/or otherwise manage airflow during bypass operation. A control board, such as control board  106  in  FIG. 1 , could provide suitable output control signals via one or more appropriately selected signal and/or control output elements (e.g., outputs  124  or  126 ,  128 ,  130 , etc. from control board  106  in  FIG. 1 ). Of course, if desired, suitable control outputs could be provided to modulate and/or control a supply damper to maintain a desired pressures in either bypass or direct variable-frequency-drive mode operation. 
     As another example of a control methodology consistent with present bypass embodiments, the VFD controller can initiate a signal and/or command controlling the bypass circuitry as to a desired number of rotations per minute (RPR) intended for the controlled motor. In response, the bypass circuitry can then cycle (e.g., like with a PID loop) the contactor at one or more appropriate intervals in order to, at least in part, try and keep the motor rotations within the intended range measured against a known time clock. Of course, this only represents one possible example of various possible contactor modulation methodologies implementable by an integrated bypass embodiment consistent with the present subject matter. 
     An additional and/or alternative advantage of present integrated VFD bypass embodiments is exhibited in the field of power measurement and/or metering. Preset integrated bypass embodiments substantially enable power measurement in both the VFD and bypass modes, which also substantially can allow for sub-metering when in bypass mode. Metering and/or data handling can be conducted to a predetermined level and/or standard, such as, for example, 1% ANSI grade metering with comprehensive utility-grade data built right into the drive, as but one example. 
     With affording the ability to meter the bypass and/or the VFD, present embodiments, such as the integrated VFD bypass circuit embodiment illustrated in  FIG. 1 , can substantially offer significant value over traditional VFD installations employing non-integrated, add-on bypass configurations. The present embodiments can also facilitate sub-metering of the bypass specifically, which can provide valuable information for energy management considerations or building automation optimization or other considerations. With traditional bypasses, someone who wanted to monitor power at the point of the bypass would be required to buy and install a separate and expensive power meter. Present embodiments, on the other hand, substantially enable power metering as an integrated function, regardless of whether the power is going through the VFD drive or the bypass unit. 
     This functionality is enabled, in large part, by the placement, configuration, and/or consolidated/combined measurement duties of circuit power measuring elements such as illustrated in  FIG. 1 . For example, with specific reference to  FIG. 1 , placement and configuration of the overload CT&#39;s  112  and voltage sampled through control power transformer  152  additionally and cooperatively can be used to meter power to the whole circuit, not just at the output. This is regardless of the specific circuit path motor power follows (e.g., voltage and current can be sensed and metered regardless of whether the VFD circuit or the bypass circuit are operating the motor  100 ). 
     With standard, commercially available VFD drive technology, a kilowatt-hour power value can be reported for the drive, but it is calculated as a value indicating output power. Such reported values are not representative of the total power consumption for the drive circuit(s). 
     Conversely, present integrated VFD bypass embodiments can offer the aforementioned functionality as a built-in, integrated feature. Power metering functionality can be accomplished either as a true power measurement using voltage and current measurements enabled by the integrated circuitry, or as an i 2 t power representation from current measured by the current sensors/CTs employed for purposes of offering overload protection for the VFD and/or bypass circuits. The same circuit components used to provide overload protection can also substantially enable advantageous power metering. This integrated power-metering functionality provides significant advantages over traditional bypass implementations known in the art. It is also worth noting that enabling true power measurement, in addition to just current measurement, can facilitate improved detection of equipment failures such as belt loss, and can facilitate rapid and appropriate alerting of automation systems in the event of the detected error. 
     Power monitoring is an important part of new legislative efforts, green building initiatives, and other market and/or industry trends, and present embodiments help make power monitoring simple and convenient with combined-purpose circuit elements offering integrated and multi-faceted functionality. This is a significant improvement over power metering conducted on the output of a drive, or having a drive calculate power output, neither of which accurately represent actual power consumed by the electronic drive equipment. Because most existing bypasses or drives are packaged as having two separate control boards, one for the VFD and one for the bypass, it would be counterintuitive for present equipment manufacturers to redesign their drives and/or control boards in a way that would provide the advantageous power metering functionality enabled by embodiments consistent with the present subject matter. 
     Another novel feature of presently described integrated bypass VFDs is the ability to switch to bypass mode when the VFD is running at or substantially at full speed. This can allow the VFD to turn off while the load (e.g., motor, etc.) is connected directly to the line current. This functionality can be employed, at least in part, to reduce energy consumption, extend VFD life, and reduce harmonics from the VFD system in the building, as well as for other desired reasons. 
     In certain conditions, VFDs operate under full- or near-full load for extended periods. The control board of present integrated VFD bypass embodiments can detect such operation of the VFD. If temperature in the VFD elements or the conductors increases to an unsafe level, or if the VFD is run at full load extensively, the controller can selectively engage the bypass. This methodology can be used, at least in part, to extend VFD equipment life. Typical bypass assemblies do not offer this important functionality and thus are not as reliable or energy efficient. 
     Additional functionality, such as the ability to support a fireman&#39;s override mode to initiate the purging of smoke from a building, can also be enabled consistent with the present embodiments. Similarly, sleep and wake up functions can be enabled to increase energy savings by deactivating the drive during low-demand times. Pre-heater functionality, can be included with present embodiments to protect the motor and inverters from damage when installed in damp locations and/or environments. 
       FIG. 2  illustrates one example of a high-level operating methodology embodiment consistent with one or more aspects of the present subject matter as disclosed above. With specific reference to  FIG. 2 , at step  200  the control board and/or integrated electronic elements can monitor circuit current and/or voltage. At decision  202  it can be determined whether a bypass condition exists and/or a bypass of the VFD is otherwise desired. If decision  202  indicates that no bypass is desired  204 , the circuit controller can preferably close VFD contactor and open bypass contactor at step  206  (or ensure they are closed and opened, respectively). The motor can then be operated through the VFD circuit at step  208 , at which point the process can return to step  200 . Alternatively, if it is determined at decision  202  that a bypass of the VFD is desired  210 , then the bypass contactor can be controlled closed and the VFD contactor can be opened at step  212 , the motor can then be operated through the bypass circuit at step  214  and the process can return to step  200 . 
     It will be obvious to those having skill in the art that many changes may be made to the details of the above-described embodiments without departing from the underlying principles of the invention. The scope of the present invention should, therefore, be determined only with reference to the claimed subject matter.