Motion Control & Drives

Keeping up with AC drive technology

April 2002 Motion Control & Drives

The market for industrial drives has run much the same path as other automation devices of today. Once considered a simple motor control device, advanced technologies have spread to drives, creating devices that are smarter and more integral to the automation system. Users have come a long way to understanding the benefits of applying variable speed technology to motor control applications, and likewise have developed their own ideas for device improvements.

The Rockwell Automation Drives Business took stock of these ideas through a series of customer focus groups designed to gauge expectations of future drive features and user benefits. The results pointed to several common themes centred on making drives easier to operate and monitor. These themes enhanced the development of a new family of AC drives, called the Allen-Bradley PowerFlex family of drives. The technology advancements are as follows:

Improving information access

Today's drive users demand increased information access, precise control and simpler application integration - in a package that is easy to start up and operate. Beyond that, to successfully integrate drives into the plant, users must identify whether drives communication options are open or proprietary.

Feedback from the focus group was that, an X brand drive with a custom interface that communicates only with that manufacturer's proprietary network is no longer a cost-effective choice. Users and OEMs expressed the need for a standard interface to enable various motor control products to connect to multiple communication options. The consensus was that drives should have open, flexible communications that will meet both present and future needs.

Allen-Bradley drives have addressed this need in several ways. For example, PowerFlex drives incorporate motor control and logic capabilities that provide motor performance and flexible communications within the control process, enabling users to more simply manage information throughout their organisations. These drives will also offer optional embedded communications to help system integrators, OEMs and end users assemble highly integrated applications that link drives into the manufacturing process. PowerFlex drives link to a wide variety of networks including ControlNet, DeviceNet, and remote I/O and serial while maintaining a strong standalone capability as well.

Supporting enhanced reliability

Another common user demand was the need for increased reliability and reduction of downtime. If production stops, resuming the process as quickly as possible - without adversely affecting other processes - is critical. Reduced downtime for users requires two things from a drive; high quality and reliability, and 'trip free' operation. At the newly expanded Rockwell Automation Drives Business headquarters, drives undergo rigorous testing to ensure quality and productivity. Testing measures include extensive qualification tests, the exclusive Rockwell Automation Highly Accelerated Life Testing (HALT), printed circuit board verification, finished drive audits and safety reviews.

These tests, along with improvements in the manufacturing process, have helped to ensure superior quality and reliability for users. Smaller power modules and patented reflected wave reduction software to eliminate damaging peak voltages caused by PWM pulse reflection, along with advanced firmware, structured coding and extensive drive and motor protection, make PowerFlex drives nearly 'trip-free'.

Commonality across components

Getting the most from AC drives requires not only considering individual drive performance, but also how multiple drives work together. One of the major concerns heard from users was that drives should incorporate commonality across platforms - from networks and hardware, to communications and operator interface programming - in order to simplify use and decrease application start-up time for operators. For example, the plant environment at General Motors Grand Blanc in Michigan, USA, adopted new process technology to control motors on a stamping press and welding press. The commonality among the programming and operating terminals of current Allen-Bradley drives allows the operators to more easily understand the controls technology and access the same parameters from various applications throughout the plant. PowerFlex drives build upon that core and incorporate an advanced operator interface that expands ease of use, increases operator understanding and makes multiple drive integration easy.

Drives users also requested simpler and faster start-up methods. PowerFlex drives are setting a new standard for these capabilities through their 'S.M.A.R.T. Start' feature, a user-requested start-up utility installed in each drive. This feature provides the user with fast and easy setup of core parameters, to get the drive 'on line' more quickly and efficiently. In facilities running multiple drives in multiple applications, this commonality makes start-up and maintenance faster and easier for operators.

World-class packaging and performance

Drive performance requirements vary just as much as the operators who run them. Regardless of location, users want to open the box and have immediate implementation - without the hassle of programming the drive to meet certain standards or requirements.

For example, PowerFlex drives are designed with a compact form factor and meet world power ratings, packaging requirements and noise standards - straight out-of-the-box. These drives can also display programming and operator interface text in multiple languages.

The most recent advances in AC drive technology focus on size and performance improvements of the power switching devices known as isolated gated bipolar transistors, or IGBTs. Ideal for lower-level signal control, variable speed drives use IGBTs to provide faster, more accurate operations, clear electrical signals to the motor, and to enable quiet operations. Research into IGBTs helped reduce the form factor of PowerFlex drives while adding more functionality. The latest IGBTs will have faster switching speeds and lower conduction losses.

Seeing the future of AC drives

Demand is high for advanced AC drives. Technology innovations, as well as the increased demand for more efficient products, have resulted in supplier re-evaluations and enhancements of existing products. Focused on both user expectations and ingredients for success and productivity, Rockwell Automation continues to include these advances into its newest drives.

Jeff Sandison, Rockwell Automation

011 654 9700


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