Simpler variable-torque applications continue to be the most common use for ac adjustable-speed drives, yet manufacturers are adding increasingly sophisticated capabilities and high-level functions to these products. Does this represent a supplier-side overkill or lack of user awareness of the latest ac drive capabilities? Likely it's a bit of both, plus other factors.

An online survey of Control Engineering readers about their views and preferences for adjustable-speed drives (ASDs) indicated pumps, fans, and blowers as the primary applications by nearly half (49%) of respondents. Assembly lines and material handling equipment were the next largest usage sectors at 41% and 31% respectively. The survey, conducted by Reed Research Group during April 2002, is based on 262 respondents involved in the specification, recommendation, and purchase of ASDs. Among these, 57% do so for in-plant requirements, 28% for OEM (resale) requirements, and 15% for both in-plant and OEM needs.

Open-loop (V/Hz) control of ac drives remains the overwhelming choice for 91% of respondents, with sensorless vector control (44%) and closed-loop vector control (42%) running neck and neck. All three categories have shown increasing response over prior surveys

Survey participants identified certain product selection criteria as important to their needs in ac drives. The top three general features they rated as 'very important' were simple controls/setup (65% of those surveyed), convenient operator interface (56%), and pricing (48%). Respondents also rated performance features (see diagram).

Adjustable-speed drives are still largely applied as standalone units, with 96% of survey respondents indicating such usage. However, networked drives are also on the rise as reported by 56% of respondents in this survey. Among those applying networked drives, 59% use RS-232/422/485 as their communication protocol. DeviceNet came in a strong second, with 56% of respondents indicating its use. Modbus (29%) and Profibus (26%) lead a second tier of communication buses. (See more survey results at www.controleng.com.)

Many of the newer products available suggest a different scenario for ac drives' capabilities and potential applications. For one, more manufacturers are including closed-loop control and high-level features-along with V/Hz control in the same drive. They're pushing these drives toward more demanding applications.

According to Rockwell Automation (Mequon, WI) product manager Corey Morton, a single worldwide drive product reduces inventory, helping manufacturers reduce costs in response to pressures of a flat economy. For example, newly introduced PowerFlex 700S drive includes a built-in position regulator for precise machine position feedback, and an embedded control option, allowing full programming and control at the drive level. 'The [PowerFlex] drive family incorporates features common across product platforms-including network communications, operator interfaces, and programming, which allows users to efficiently manage automation investments and increase system performance,' says Mr. Morton.

Craig Nelson, product manager for Applied AC & DC Drives at Siemens Energy & Automation (Alpharetta, GA), notes that ac drives are easily adaptable to various motor technologies besides the induction type, for example, synchronous, switched-reluctance, etc. 'Since ac vector is now firmly developed, most advances have been made on the motion control (servo) side,' he explains. With servo technology coming down in price and gaining acceptance, it's helping to narrow the gap between open- and closed-loop controls.

'Small and extremely user friendly,' is how ABB Drives & Power Products Group (New Berlin, WI) refers to its ACS 800 family of low-voltage drives making its debut worldwide in September 2002. Among advanced built-in features is an Intelligent Start-up Assistant, '[Which] means, literally, that commissioning and tuning of a high-performance drive could not be easier,' says Mark Kenyon, product manager for ACS 800. As for size, ABB's new drive series is up to 50% smaller than its equivalent predecessor in the ACS 600 range.

'Flexible field programmability to provide advanced motor control and protection' is part of Baldor Electric Co.'s (Fort Smith, AR) latest ac drive technology, according to Roddy Yates, product manager. However, Baldor offers three separate product series for V/Hz, sensorless vector, and closed-loop vector control. Says Mr. Yates, 'Using intuitive functional block programming, the basic control can be modified or reconfigured to provide advanced motor control functionality.' Software-enabled features include ability to reconfigure analog and digital I/O points via simple point-and-click commands to suit numerous applications.

Survey results cited here represent a single snapshot of ac drive users' views. Nevertheless, manufacturers must continually assess such needs. Likewise, users need to know that adjustable-speed drives have progressed far beyond traditional applications.

To request information on these products, visit www.controleng.com/freeinfo. For more manufacturers, visit Control Engineering's Buyers Guide at www.controleng.com/buyersguide.

Malcolm Broderick, Reed Reasearch also contributed

Comments? E-mail fbartos@reedbusiness.com

Fort Smith, AR -New complementary product lines cover the three most popular types of induction motor control. Series 35 provides V/Hz control for motors in the 1/3-10 hp range; Series 37 includes sensorless vector control from 1/3 through 150 hp; and Series 38 vector control adds closed-loop control through 500 hp, using a motor-mounted encoder. Each series is available in 230 V or 400/460 V designs, with 50/60 Hz input for global use. Microsoft Windows-based software does the configuration. For added value, optional expansion boards allow interfacing to PLCs via DeviceNet, Profibus-DP, and Modbus. www.baldor.com Baldor Electric Co.

New Berlin, WI -More performance and PLC-like functions allow ACS 800 Series ac drives to perform a wide range of applications, yet offer 50% smaller size than the equivalent predecessor (ACS 600). Designed in a 'bookshelf' style for all sizes, ACS 800 comes with initial ratings of 1.5-600 hp and supply voltages of 230-690 V. Even the largest 600-hp drive has a slim 13.78-in. width. ACS 800 features include Direct Torque Control for rapid response to motor load changes; an integral brake chopper and chokes all inside the drive; easier commissioning via an 'Intelligent Start-up Assistant;' and NEMA 1 or 12 enclosures without the need for derating. www.abb.com/motors & drives. ABB Drives & Power Products