Combination Motors and Drives Move to Make their Mark
E lectric motors and their control electronics were not created as equals. So it's not a coincidence that until recently they operated in separate locations, connected by often lengthy and costly wiring for power, control, and communication. Electronic controls generally reside in safer, cooler, and more centralized enclosures, while motors face more severe conditions of temperature, humidity, vibration, dust, washdown cleaning, and more, found in the industrial world.
In the last decade, however, the two technologies converged and time became 'right' to unify a range of motors and drives. This integrated approach promised convenience and several benefits, including lower 'system cost' (see main article). Numerous manufacturers have brought a selection of motor/drive products into the market (see table of representative products).
Several motor topologies have been integrated with controls. This article (and the Dec. 2000 CE article ) focuses on the ac induction motor and variable-frequency drive combination, running under open-loop control. (Servo motor based and other closed-loop packages will be covered in a separate article later in 2001.)
This emerging class of products goes under a variety of names, which does not help raise the relatively low level of awareness by potential users. Names such as 'smart motor,' variable-speed motor-a European term offering pros and cons-motor with built-in drive, integral motor/drive, integrated drive motor are all out there. Probably the clearest term in use is integrated motor drive (IMD) that's actually a registered product name of TB Wood's Inc.
IMDs have not realized the full potential envisioned for them five or more years ago. This includes growth in market share and expansion of the power range. Led by Europe, things may be now be changing for market size. A positive sign for integrated motor-drive manufacturers is the growing trend toward distributed control architectures within the entire business enterprise. IMD technology can share in this move.
Heating effects are the greatest enemy of IMDs. Both the motor and power-switching electronics in the controls produce heat. As a result, thermal management of these integrated packages has been honed to a fine edge to combat the problem. Optimized design of mechanical/structural components, heat sinks, cooling, and the layout of elements contribute to the solution. It has enabled development of numerous competing products up to a certain size.
Most suppliers make IMDs up to 7.5-kW (10-hp) rating, or will range up to that size shortly (products table). Very large sized IMDs are the exception. While not a final size, the 7.5 kW output represents a practical plateau above which heating effects build up significantly. Commercializing larger sizes units will require more complex designs and impact product costs.
The speed at which the motor runs affects thermal management. At significant speeds, a motor-shaft-driven fan provides substantial cooling, but becomes inadequate at low speeds. This condition is exacerbated by ongoing improvements in one area of IMD performance-widening of the speed range. Today, typical speed range is 10:1, but a few manufacturers offer 50:1 via more sophisticated controls. Extending the speed range is not a routine exercise, because more cooling is needed to offset the more severe heat generation-when the motor operates at 30 rpm (or below) for some periods. This usually means adding a separate constant-speed blower.
Location of drive electronics relative to the motor brings up a spatial design trade-off that also relates to heating. Most IMDs place the control unit atop the motor (or atn, www.abb.com/motors&drives) and TB Wood's Inc. (Chambersburg, Pa.) prefer axial placement of the electronics for this reason, and also to improve cooling air flow from the axial fan. These designs hold overall height and mounting dimensions identical to that of a standard motor and giveup something on overall unit length. It's largely a matter of design philosophy.
Vibrations and electromagnetic interference (EMI) are some other environmental considerations for integrated motor-drives. Careful design and testing can ruggedize the electronics substantially, while special rotor balancing limits initial motor vibrations. Monitoring may be used to prevent vibrations worsening with motor usage over time. Siemens (Erlangen, Germany) mentions the special design of its CombiMaster electronics package to handle vibration and shock that can reach up to 5 g. As for EMI effects, much less wiring between the integrated motor and drive inherently reduces this concern. Still, most European IMD suppliers include EMI filters in their units. For example, CombiMaster comes with Class A and B EMI filters.
Cost and market issues
Cost considerations for IMDs aren't simple either. Depending on size, a typical motor/drive package carries a premium on initial cost compared to an individual motor and drive. A rugged housing, thermal management, close-coupled wiring, and the special environmental design just mentioned all add to cost. Typical premiums today are in the 15-20% range. But for a total installed system, cost of the integrated design is said to be lower.
Siemens claims lower overall cost when factors such as wiring between individual components, a control panel for the drive, panel air conditioning, and maintenance are considered. 'Component cost is greater, but from a project view, savings of 20-30% are possible in the integrated approach,' says Kevin Vickery, drive product specialist at Siemens Energy & Automation (Batavia, Ill, www.sea.siemens.com).
Rockwell Automation AC Drives Business (Mequon, Wis., www.rockwellautomation.com) cites total installed cost reduction up to 40% with the integrated approach, for similar reasons. However, total ownership cost can be hard to sell to potential users who may have 'initial cost mindset' and also hesitate about new technology.
Adding more sophisticated controls to an IMD brings further cost considerations. For example, if flux vector control is added, the cost of a feedback device (encoder) must be included in any increase of controls pricing, states Roddy Yates, product manager at Baldor Electric Co. (Fort Smith, Ark.).
Recent market studies project cautious growth for IMDs in North America and faster expansion in Europe (see main CE article ). Motion Tech Trends' (MTT, Inglewood, Calif.) Integrated Motor Drive Survey (1Q2000) indicates only 2,600 IMD unit sales in North America in 1999, climbing to about 12,000 units by 2005. MTT projects a more rapid rise of unit sales for the longer term. These numbers, and the corresponding dollar values given in the main article's 'Market views' sidebar, apply to IMDs of 1 hp and larger.
European Market for Variable-Speed Motors , a late-1999 analysis by Frost & Sullivan (London, www.frost.com) puts IMD unit sales at 39,700 in Europe for 1999, growing to 219,400 units in 2006. These figures are in line with greater IMD revenues of the European markets, of which Germany and Italy are the largest (see main article.).
Both surveys indicate that pricing of IMDs is crucial for market expansion. In other words, initial cost of IMDs also must become more competitive with a separate motor and drive solution.
A growing number of companies supply IMD products, with a representative sampling given in the following table. All except two of the companies sell IMDs in North America as noted below. Here is a brief rundown on suppliers not mentioned previously in this Online Extra or the main CE article .
Bonfiglioli Riduttori (Milan, Italy) is a notable, longstanding manufacturer of gear reducers and gear motors. It forms one of four divisions within the Bonfiglioli Group. Localized Motion System (LMS) integrates the company's ac induction motors with electronic drives made by Siemens. LMS Series is available locally through BNA Bonfiglioli North America Inc. (Concord, Ont. Canada, www.bnagear.com).
Another Italian motor manufacturer, Carpanelli Motori Elettrici (Bologna, www.carpanelli.it), makes custom motors with 60% of its production going to special applications. It now includes an IMD offering, called the MII Series. The company does not currently market to North America.
Franklin Electric (Bluffton, Ind., www.fele.com) adds its Integrated Motor Drive System (IMDS) to available products. IMDS Series comes only with single-phase input, and offers 2-pole and 4-pole motor versions.
Combidrive is the integrated motor-drive unit from KEB Antriebstechnik (Karl E. Brinkmann GmbH, Barntrup, Germany, www.kebco.com), available through U.S. subsidiary Kebco, located in St. Paul, Minn.
Leroy-Somer (Angoulême, France, www.leroy-somer.com), a division of Emerson Electric Co. (St. Louis, Mo.), supplies the Varmeca line of integrated motor and drive packages. Ratings for Varmeca have been extended to 7.5 kW.
Mannessmann Dematic (Wetter, Germany, Cleveland, O., www.dematic-us.com) features integral gear motors in its Indrive product targeted for demanding start/stop applications.
Variable Speed Motor SPE100 from Spang Power Electronics (Mentor, O., www.spangpower.com) is a reborn product. This single-phase input IMD was previously marketed by Rockwell Automation, using a Reliance Electric motor combined with an electronics package supplied by Spang. All technology rights are now owned by Spang.
WEG Electric (Jaraguá do Sul, Brazil; Suwanee, Ga, www.wegelectric.com) is the giant Brazilian manufacturer of electric motors and drives. Its MotorDrive (MDW-01) combination product is marketed in Europe and South America, but not currently offered in the U.S.
Top & radial
Besides some general concern about reliability of control electronics working right next to the motor, users naturally want to compare a new solution with an existing one that may feel more 'comfortable.'
James Taylor, project engineer at Dynamic Engineering (Sturgis, Mich.) voices concerns about combination motors and drives. As a consulting engineer for mainly process industry clients, his reasons for not specifying IMDs are that most:
Users rely on a standard drive manufacturer and product, training, and spare parts;
Users' motors are fed from MCC rooms (motor control centers) where the variable-frequency drives are located. VFDs on the motors would require running an additional conduit for control wiring from an I/O panel to the motor, and
Controls are PLC- or DCS-based, making it easy to put some I/O points in the MCC, so there is no control wiring to install.
However, Mr. Taylor sees IMDs more appropriately focused on commercial and HVAC applications.
As a general reply to Mr. Taylor, these integrated motor/drive products are spreading out from their initial stand-alone applications. A growing number of manufacturers supply the technology (see products table). Many of the motors can be supplied as standard models in ratings through 10 hp (7.5 kW) and spares are readily available. However, communication capability is the answer to take full advantage of IMDs. Remote control, communication, and networking features are here or coming shortly to more of this product sector. There is no inherent incompatibility with higher-level, PLC- or DCS-based control systems.
More specifically, Siemens Energy & Automation agrees that a power connection has to be provided, plus a protective device-as with a standard installation. However, serial communication and bus networks incorporated into IMDs simplify control wiring. 'Twisted-pair wiring carries the command signals; also several motor/drive units can be daisy-chained into a network,' says Kevin Vickery, drive product specialist at Siemens E&A. CombiMaster, Siemens' product, offers several ways to network and communicate. 'An appropriate network interface module is needed at the drive,' he adds.
For example, in a bottling line, low-power (24 V) signal could energize a contactor to feed multiple IMDs in a network. Serial commands or other digital signals would then regulate individual motor/drive units in the network. Manual shut off of each unit would also be needed.
Rick Kirkpatrick, director of marketing for Electronic Products at TB Wood's Inc., also mentions the benefit networking multiple IMDs. The power disconnect, fusing, or circuit breaker is still needed, but communication networks reduce the extent of control wiring. Circuit protection can be housed in a small panel or enclosure.
Michael G. Tesar, P.E., development engineer at MEGTEC Systems (U.S. location at DePere, Wis.), mentions 'good economical and performance results' in using IMDs on pumps and for fan control. A manufacturer of equipment for printing, web coating, packaging, and other industrial/environmental markets, MEGTEC has tested many different types of motor/drive units. Mr. Tesar calls T.B. Wood's IMD offering 'a good value and the performance standout at this point.' Integrated Motor Drive from T.B. Wood's includes dc injection braking to slow the motor and load. He explains that most of MEGTEC applications are for pressure control, where the ability to slow more quickly greatly improves the overall loop performance.
As an international company, MEGTEC looks for CE marked products. Mr. Tesar notes difficulty of obtaining CE-approved units from some of vendors. This refers to some U.S.-made products. 'TB Wood's product does not come with CE rating at present and there is no connectivity to a fieldbus network at this time, both are real issues with us,' he says. [DeviceNet communication will be available as an option in January 2001, according to T.B. Wood's (see main article ).]
Mr. Tesar remains keen on the IMD product. 'These drives are compact and very effective in eliminating the `electrics' in a control cabinet,' he adds. 'We will continue to use them in the future and wish they were made [in larger sizes], up to 60 hp.'
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