AC Adjustable Speed Drives

Trends in AC Adjustable Speed Drives Increased intelligence Communication options Open programming structure Microdrives Call them what you may, variable-frequency drive, variable-speed drive, adjustable-speed drive, but ac drives compel manufacturers to put money where their mouths are and get things moving.


Trends in AC Adjustable Speed Drives

  • Increased intelligence

  • Communication options

  • Open programming structure

  • Microdrives

Call them what you may, variable-frequency drive, variable-speed drive, adjustable-speed drive, but ac drives compel manufacturers to put money where their mouths are and get things moving.

New generation products focus on making improvements that users and OEMs continue to demand. Some enhanced capabilities that drive manufacturers incorporate into their products include increased drive intelligence, communication options, and open programming structure.

Capable yet simple

Peter Fischbach, product manager, ac drives, Bosch Rexroth Corp., Electrical Drives & Controls Division (Hoffman Estates, Ill.) says, 'AC drives changed from a simple speed actuator to a decentralized field level machine/process control unit. Most of today's drives offer a flexible and open control/hardware structure with modular fieldbus options, which allow the industry to choose the drive suitable for their application and budget.'

Cahners Research and Control Engineering initiated research among 1,500 readers to examine trends and user issues concerning ac adjustable-speed drives; 279 completed the survey for a 19% response rate.

According to the survey, applications for ac adjustable-speed drives vary widely, from pumps and fans, materials handling equipment, packaging machines, to wire and cable machinery. This variation requires greater demands on drive capabilities and increased innovation.

Scott Whitsitt, global inverter development liaison for Mitsubishi Electric Automation Inc. (Vernon Hills, Ill.) says, 'Perhaps the most striking change is how simple [the operation of ]drives has become.' He considers these once 'highly engineering-intensive' drives to be very common in the industrial world today.

Mr. Whitsitt adds, 'Another important change to ac drives is the amazing increase in performance. The line between ac drives and other motion-control products have been significantly blurred. The choice of using ac drives in applications previously reserved for dc controls and other motion controllers offers enormous benefit to users.'

Charles Forsgard, national drive sales manager, Square D Company (Palatine, Ill.) says, 'Over the past several years, drive networking has advanced from one-way communication using dry contacts and proportional signals to two-way communication helping users troubleshoot problems or tune the drive.'

'The next and most exciting step in this evolution involves the web-enabled Ethernet that will lead to fundamental changes in drive communications,' adds Mr. Forsgard. says.

Respondents were asked what features were most desired in ac drives.

Sixty-three percent responded simple controls/setups; 45% said convenient operator interface; programmability was mentioned 45% of the time and pricing 37%. EMI/RFI protection, ability to copy/download parameters, and communication interface were mentioned 29%, 28%, and 26% of the time, respectively.

Increasing intelligence

According to Mr. Whitsitt, some important demands have not changed: Make it smaller, less expensive, and smarter.

He says, 'Major opportunities exist today in making drives smarter. Perhaps the single biggest opportunity for users and OEMs is the ability to customize drive functions for specific applications quickly and cost-effectively.

While this includes customization by the manufacturer, the real benefit to both customer and manufacturer will come from permitting customers to define and implement their own customizations.'

Mark Borski, product manager, Cutler-Hammer (Milwaukee, Wis.) adds, 'Intelligent drive applications seem to be going in two directions. The first relies on increasing intelligence of the drive through custom applications or custom drive programming. This shifts the intelligence in the application (PLC functions) to the drive.

The second philosophy decreases the drive's application intelligence by adding communication to the drive, which relies on external intelligence, such as PLCs, to control the drive over a network.'

When asked what type of ac drives users prefer, respondents answered Volts/Hertz control 89%, sensorless vector control 41% and field-oriented vector control (closed loop) 33%.

Mr. Borski says, 'Currently, the most influential trend in the drives market is towards using vector/torque control algorithms. As customers demand better control and vector/torque control becomes cost effective for the manufacturer, almost all drives will incorporate that type of technology.'

Respondents also use line conditioning (82%), and microdrives (39%). Standalone drives were used by 89% of respondents, while networked was used by only 32%. While networked systems received a distant second rating, the future seems bright for this feature.

Influential trends

According to the ac drive survey, the most popular communication protocol is DeviceNet with 49% usage; followed by Profibus 29%; AS-Interface, 11%; Interbus 8%; DH+ 5%; Remote I/O 3%, and SERCOS 2%. Another protocol emerging, like in other industries, is Ethernet.

Mr. Whitsitt states, 'Ethernet is clearly the buzz in the industry, but there are still many kinks to be worked out. Perhaps the most critical question is what protocol will we send across the Ethernet backbone.

DeviceNet, Profibus, CC-Link, and nearly every other open network protocol is being decked out for use on Ethernet. The familiar industrial control protocols will continue to dominate even Ethernet due to proven performance and the investment users have already made.'

Bosch Rexroth's Mr. Fischbach comments that another trend to influence drives in the future is flux vector control and its encoderless version. He states that the version will become the standard in future ac drive lines.

Mr. Fischbach says, 'With the pressure on the machine manufacturers and end-users to reduce cost while increasing production/output, end-users expect more and more functionality and flexibility from drive manufacturers.'

Mr. Fischbach sees drive manufacturers staying one step ahead to comply.

AC adjustable-speed drives products

For more information on ac adjustable- speed drives products, circle the following numbers, or visit freeinfo . For a wider listing of manufacturers, go to Control Engineering Buyer's Guide at .

Configured drives meet low-hp applications

Mequon, Wis . -PowerFlex 70 Configured ac drives feature an IP20 (NEMA1) modular construction intended for indoor use. Ideal for global OEMs and end-users with special installation needs, PowerFlex 70 Configured drive's active thermal manager recognizes excessive overloads and makes adjustments to minimize drive overheating, which reduces downtime. PowerFlex 70 handles varying loads common in material handling applications, such as packaging and bottling lines. The drive's sensorless vector control handles constant-torque applications, including mixers, extruders, and centrifuges that require rated torque from zero to full speed.

Rockwell Automation

Circle 374

Variable or constant torque control

Houston, Tex. -Tosvert 130-MV is the latest addition to Toshiba's family of ac adjustable speed drives. It controls variable torque or constant torque motor applications. While the primary application is for single machines, Tosvert 130-MV is said to contain some of the same features as medium-voltage drives for coordinated system applications. It also meets U.S. codes and standards for power quality with respect to the utility system and the connected ac motor.


Circle 376

Provides safety in corrosive environment

Uxbridge, Mass .-Suited for the food and beverage, pharmaceutical, powder and bulk solids, and chemical processing industries, MC Series drives with NEMA 4X, stainless steel enclosure provide protection from water, oil, and corrosive contaminants. Available from fractional to 20 hp, MC Series drives can be configured for either constant- or variable-torque applications. Programming is done through an eight-button keypad fitted with large, finger-size buttons in a front-panel mounting. Features include four preset speeds; two skip speeds with adjustable bandwidth; PID setpoint control for temperature, pressure, and flow; and either Modbus or Metasys serial communication protocol.

AC Technology Corp.

Circle 378

Connectivity within network

Chambersburg, Pa. -WF2 sensorless vector drive offers built-in connectivity with Modbus. This permits communication with industrial automation equipment such as PLCs and PCs. WF2 drives supply a minimum of 150% torque at 0.5 Hz, providing operation in low-speed, high-torque conveying, mixing, moving, filling, and rotating applications. End-users can configure the new-range WF2 as a V/Hz control for use with fans and pumps. The higher-horsepower WF2s are larger and available in protected chassis enclosures, as well as NEMA standards 1 and 12.

TB Wood's Inc.

Circle 379

Add versatility to AFDs

Chicago, Ill. -Pacesetter NEMA 4 Series ac variable-frequency drives allow machinery builders to economically add the versatility of adjustable speed, dynamic braking, and comprehensive motor protection to their products in wet or dusty environments. Two models of inverters cover 115 or 230 V ac 50/60 Hz inputs with 1/4 and 1/2 hp outputs, respectively. The speed of three-phase motors can be controlled by adjusting output frequency up to 120 Hz with either a built-in potentiometer or an external analog signal. Features such as adjustable ramp times, min./max. speed limits, dynamic braking, diagnostic LEDs, adjustable current limit, and a fault-output signal are included.

Bodine Electric Co.

Circle 380

AFD with NEMA 4X housing

Coral Springs, Fla. -KBAC-24D adjustable frequency drive offers speed control in a NEMA-4X/IP-65 washdown and watertight-enclosure. Designed to operate 208-230 V three-phrase ac induction motors through 3.6 A rms, KBAC-24D provides load regulation over a wide-speed range. Tailoring to specific applications is accomplished by selectable jumpers and trimpot adjustments, which eliminate the computer-like programming required on other drives. Optional accessories include a forward-stop-reverse switch, auto/manual switch, signal isolator/run relay and a multi-speed board.

KB Electronics Inc.

Circle 383

3-phase drive for induction motors

Hoffman Estates, Ill .-Refudrive 500 Series is a universal, three-phase drive system for a variety of synchronous and induction motor types. 500 Series contains modular software and hardware said to be tailored to handle virtually any drive task. In addition to a fully programmable terminal strip and flexible technology modules, the user has fieldbus choices of Profibus, Interbus, and CANbus. Users can specify their 500 Series system from the following configurations: high-performance flux vector, sensorless vector, VFD controlled frequency converters, and inverters for dc input in the range from 2 to 500 hp. Power supplies and regenerative units are also available.

Bosch Rexroth Corp.

Circle 385

Micro drive for industrial, HVAC

New Berlin, Wis .-Designed as a modular unit for both wall mount and IEC motor-mount installations, ACS 160 is a NEMA 4 (IP65), micro drive used for industrial and HVAC applications that require reliable, efficient motor operation in hazardous and/or washdown environments. The drive covers a 1/2-3 hp range, at 380-500 V ac input (three-phase). Three optional drive packages, fieldbus, dynamic braking resistor, and control panel are available separately for integral mounting to the drive. ABB expects the drive to be available for NEMA motors in the near future. Adapters will be available to retrofit the drive onto existing ABB motors.

ABB Automation Inc.

Circle 375

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