AC Adjustable-Speed Drives

This `online extra' article provides added information to that contained in `AC Drives Meet and Exceed User Demands,' appearing in the September 2002 issue of CE.

By Frank Bartos, executive editor September 17, 2002

This article is an expanded version of the click here

Adjustable-speed control of ac induction motors (and other types of motors) continues to grow in industrial applications and the building automation sector, due to dramatic savings in energy usage. Simplified configuration and start-up procedures also help promote these newer ac drives. The latest models build in increasingly sophisticated capabilities and high-level functions-such as field programmability, open/closed-loop control in one drive, and compact “bookshelf” designs.

An online survey, conducted by Reed Research Group during April 2002, asked readers of Control Engineering about their views and preferences for adjustable-speed drives (ASDs). The survey was 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.

Survey highlights are discussed in the main article with additional details presented here. Survey participants identified certain selection criteria as important for their ac drives. The top four performance features they rated as “very important” were tripless operation (38% of those surveyed), torque control (32%), distance between motor and drive (30%), and dynamic braking (25%).

Adjustable-speed drives are still largely applied as standalone units (96% of respondents so indicating), but networked drives are also on the rise. [Multiple responses allow percentages greater than 100%.] Over half of respondents (56%) say they use networked drives, compared to 32% in the previous survey (June 2001 Product Focus) and about 30% two years ago. A breakdown of various communication protocols in use among those applying networked drives is shown in the ”Networked Drives” diagram.

Power range, purchasing patterns

All size ranges of ASDs are widely used among those surveyed. The 1-5 hp range remains the most common, where 77% of respondents indicate usage, while 35% do so in sizes greater than 50 hp.

Nearly one in four surveyed (24%) report that their ac drive purchases will grow over the coming year, while only 3% foresee a decline in purchases. A large majority (73%) says their need for ac drives will remain about the same. Average increase in purchases is expected to be 26%. As for dollar figures, 37% of respondents purchased ac drives worth $30,000 or more over the past year. Average spending per respondent was $81,200.

”Off-the-shelf” drives dominate over customized drives in the buying patterns of respondents (86% vs. 14% on average). These purchasing figures change only slightly from five years ago, to today, to five years from now.

New products = more value and performance

More manufacturers are including closed-loop control and high-level features-along with open loop, V/Hz control in the same drive, pushing the newer drives toward more demanding applications.

Craig Nelson, product manager for Applied AC & DC Drives at Siemens Energy & Automation (Alpharetta, GA), refers to ac drives’ adaptability to other motor technologies, such as synchronous and switched-reluctance as diversification. He says, ”Diversification of products and application know-how are the ways to continue growth in these economic times.”

Also citing the recent flat economy, Rockwell Automation Mequon, WI) product manager Corey Morton stresses the need for manufacturers to ”aggressively lower costs.” He considers ac drives’ valuable features to be the ones that ”allow manufactures to reduce training, installation, and maintenance costs, while maintaining high levels of performance and reliability.”

User convenience is on the rise in drive products. For example, an interactive commissioning tool built into ACS 800 drive family just introduced by ABB Inc. Automation Technology Products Div . (New Berlin, WI) handles the start up process from the moment power is turned on, explains Mark Kenyon, product manager for ACS 800. “Guided commissioning” in the Start-up Assistant asks users for motor nominal values, I/O configuration, accel/decel rates, and other application-specific parameters. The Assistant also detects the presence of, and offers guidance for, such option modules as I/O extensions or fieldbus modules. Another tool, Adaptive Programming, expands user programming to include all common mathematical and logical functions, switches, comparators, filters, and timers. It provides a set of 15 blocks through which users can perform any operation among a predefined set of 20 functions. ”It’s like having PLC functions inside your drive,” says Mr. Kenyon.

The view from Baldor Electric Co . (Fort Smith, AR) is that adjustable-speed drives are definitely here to stay. ”Over the years, our product line has evolved from the basic inverter to control frequency (speed), to the latest in vector-drive technology, which allows for enhanced speed, torque, and positioning performance with or without a feedback device,” says Randy Breaux, Baldor’s vp of marketing.

AC drive products

The following product listings are in addition to those in the main article in CE’s September 2002 issue. For more manufacturers, visit Control Engineering’s Buyers Guide at .

3 types of control in one drive

Salem, VA – Versatile AV-300i drive serves high-end standard applications, as well as sophisticated process control, yet is reportedly cost-effective for less complex control, such as water pumps. Choice of V/Hz, sensorless vector, or flux vector operation is software selectable. When set for vector control, users can regulate speed or torque current-and transition easily between either-with features such as outer-loop PID, encoder follower, speed droop, inertia compensation, and speed draw. Rated for 3/4-800 hp, AV-300i drive supports 230, 400, and 460 V ac input. Access to the internal dc bus from the terminal board allows connection to the common bus dc feeds, or ability to add external high-current dynamic braking. AV-300I works with the same controls and software tools as other GE drives for the ease of users. The standard software configuration tool features trending, startup wizards, parameter archiving, and online services. The drive connects to several communication protocols, including Profibus, DeviceNet, and Genius. It is also UL-, cUL-, and CE-labeled.

GE Industrial Systems

Advanced flux-vector drive

Houston, TX – With or without an encoder feedback, G7 Series PWM adjustable-speed drives offer flux-vector technology to handle the most demanding industrial conditions, says the manufacturer. G7 drive is rated up to 350 hp at 460V, 60 hp at 230V, and 300 hp at 600V. Torque control plus speed regulation are available. Closed-loop speed regulation is 0.01% from 0.02 to 120 Hz (up to 0.1% from 0.6 to 80 Hz, in open loop,). Its torque regulation capability is

Toshiba International Corp

`Microdrive’ pushes performance, price, compact size

Chambersburg, PA – A new member of the E-trAC family of ac drives, EF1, continues the focus on high flexibility and high performance ac drives at competitive prices, according to the manufacturer. EF1’s ”micro” enclosure (NEMA 1/IP31) derives its very compact size and reduced parts count from use of the latest chip and wire bonding technology. EF1 drive is designated a ”world-class” product with models rated for 115 V, 200/230 V (single and three phase), and 380/460 V ac supplies. The drive is available in either hp or kW ratings up to 5 hp (4 kW). Higher ratings are due for release in the coming months. Some models integrate an EMC filter in the enclosure for applications where RFI noise is an issue. This integration simplifies EMC installations, eliminating the need for extra bolt-on components and saving valuable panel space.

TB Wood’s Inc .

Process-specific ac drives

Pittsburgh, PA – HV9000 Series Adjustable Frequency Drives come with functions specifically designed for HVAC and related applications, such as pump and fluid control. These drives also provide connectivity to industry-specific communications options. Networking possibilities include Johnson Controls’ Metasys N2, Siemens Building Technologies’ Apogee FLN, LonWorks, and Modbus RTU control systems.

HV9000 Series is available from 1 to 1,000 hp at 208, 230, 480, and 575 V ac supply voltages. Preset software options reduce set-up time and ease programming. HVDrive configuration software helps to control and monitor the drive, while serving as a tool to save parameter sets, print parameter lists, and view/print trending reports.


Low-cost, `open-loop vector’ drive

Eden Prairie, MN – Commander SE Digital AC Drive, the company’s lowest cost variable-frequency drive (VFD), is positioned at the opposite end of its Unidrive-which offers open- or closed-loop vector, servo, and regenerative control. Commander SE (the designation standing for “simple” and “easy” to use) is intended for pumps, conveyors, mixers, fans, ovens, and related applications. SE drive has a size range of 1/3-50 hp, 1- or 3-phase, at 230 or 460 V ac supply voltage, and comes with a NEMA 1 (IP21) enclosure. Among notable standard features are “advanced drive configuration” for optimal control/flexibility, dual analog channel inputs with PID control, programmable analog output, and ability to drive dual motors. Communication choices are RS-485 with Modbus RTU protocol (standard), complemented by Profibus-DP, DeviceNet, and Interbus-S plug-in modules. SESoft-a Microsoft Windows-based configuration tool-and QuicKey cloning module complete a Commander SE package.

Emerson Control Techniques

VFD offers flexibility, wide power range

Hoffman Estates, IL – Rexroth 500 Series Variable Frequency Drive (VFD) functions include speed and torque control in a package characterized by modular construction of hardware and software. This new VFD series offers output ratings from 2 to 850 hp, along with programmable I/O points. Its SERCOS interface expands connectivity options besides previoius Profibus, Interbus, and CANopen choices. Several features help to simplify startup and operation, among which are automatic motor optimization, “guided commissioning” via the control panel, and REFUwin software tool. Freely configurable function blocks, including PID controllers, math blocks, digital gates, timers, and application-specific blocks help reduce cost and control complexity of operating the drive.

Bosch Rexroth, Electric Drives and Controls Div .

`Commercial ac inverter’ offers communication choices

Schaumburg, Ill. – Intended for HVAC and variable-torque applications, newly released 3G3PV commercial ”ac inverter” (adjustable-speed drive) features two software-selectable communication buses important to this application sector-Metasys, from Johnson Controls, and Apogee, from Siemens. Other networking choices available are DeviceNet (via an option card) and RS-422/485 serial communication. The 3G3PV inverter carries ratings of 0.75-125 hp (0.56-94 kW) at 230 V ac input; and 0.75-500 hp (0.56-375 kW) at 460 V ac. The drive is UL-, cUL- and CE-compliant. Other practical features are part of 3G3PV drive: A removable terminal strip allows wiring connections to be left intact in case of drive replacement (or size change). Means to replace the cooling fans is simplified-with operating time of these key components displayed or recorded. High-slip braking is included without the need for a dynamic braking resistor. A built-in dc reactor (for units 22 kW and larger) helps filter line disturbances and harmonics. An industrial version of 3G3PV drive will follow later.

Omron Electronics LLC