AC Motor Controllers and Drives
Regenerative AC Drive eliminates harmonic distortion.
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Press Release Summary:
ACS DriveIT Low Voltage 800-17 regenerative, 4-quadrant motor drive can run at full power in 80% brownout conditions. It regulates power factor to near unity, regardless of speed or load or AC line conditions. Direct Torque Control removes low-range frequencies up to 1 kHz and compensates for voltage variations, while LCL filtering handles medium and high frequencies. Available from 75-1,250 hp, drive comes in standard cabinet or as modules.
Original Press Release:
New Ultra-Compact Regenerative Drive from ABB Eliminates Harmonic Distortion
(Four-quadrant drive helps keep the power supply clean; runs at full power through 80 percent brownout conditions)
NEW BERLIN, Wis., July, 2003 . . . Extremely efficient utilization of electricity (i.e., regenerative braking and power factor), dramatic levels of harmonic mitigation, and the ability to run at full power in 80 percent brownout conditions are benefits of features built into ABB's new, ACS DriveIT Low Voltage 800-17 regenerative, four-quadrant motor drive. The ultra-compact drives -- up to 80% smaller than alternative units -- range from 75 - 1,250 horsepower (custom units are built up to 4,000 Hp). And a complementary regenerative drive, the ACS 611, is built for 20 - 75 Hp applications.
"These drives are superior in their ability to compensate for power irregularities, fully utilize power produced from a motor during any downloading, braking or generating modes, and are dramatically better than DC-powered drives in mitigating harmonics levels," said John Tisdale, sales manager for the new ACS 800 drive line, ABB Automation Technologies, Drives and Motors.
Regenerative four-quadrant AC drive delivers customer benefits in a range of applications. Typical uses include test benches for motors and transmissions, oil pumps, heavy-duty cranes handling freight containers, centrifuges in food production and process industries, rolling mills, sheet-metal presses, cable-car controls, ski lifts, pump control at water treatment plants, and HVAC chiller control for office buildings.
Power Factor at Unity
Quantum leaps in AC technology have resulted in extremely competitive drives built with IGBT (Integrated Gate Bipolar Transistor) switches that utilize/regenerate energy efficiently. How AC drives utilize electricity - measured as power factor - DC drives cannot approach. The new regenerative drives regulate power factor to near unity, regardless of speed or load or AC line conditions. AC drives keep voltage and amperage levels in virtually perfect sinusoidal sync, which eliminates the need for a large, costly power factor correction capacitor banks. (Power companies, in fact, often penalize users for low power factor.)
Harmonic Mitigation Built Into ACS 800-17
Harmonics are currents produced by any non-linear load (such as UPS systems, computers, electronic lighting, and variable speed drives) and are multiples of 60 Hz. Because harmonics can increase as more devices are added to a common transformer, management of the resulting harmonic distortion is growing in demand and importance, according to ABB. Harmonic distortion can result in mis-operation of sensitive electronic equipment and generators. Harmonics are more of a concern today due to two factors: the extensive use of harmonic-generating equipment; and more of the equipment installed in stand-alone machines and processing lines being sensitive to harmonics.
Reducing harmonics enables industrial users to avoid both potential harm to their own equipment and the penalties set by power companies for introducing harmonics into the supply grid. The drive's elimination of harmonics is achieved through ABB's Direct Torque Control (DTC(TM)), removing low-range frequencies up to 1 kHz, and LCL filtering, handling medium and high frequencies. This enables it to exceed the demands of relevant standards - such as IEEE 519 1992 and the EA G5/4 Engineering Recommendations - for current and voltage distortion.
In a traditional drive, an uncontrolled diode bridge is used in the line input, producing a distorted waveform. In the ABB drive, the line voltage is actively switched, with the switching modulated to deliver a sinusoidal line current. DTC - primarily developed to ensure smooth, accurate motor torque across the speed range - also acts on the line current. It compensates voltage variations, even fast dips, to keep an even waveform. Any switching voltage ripple, deriving from the IGBT power semiconductor devices, is reduced by LCL filtering; this enhances the drive's operation in weak networks.
A further DTC benefit is the absence of the need for a fixed switching frequency, which eliminates the risk of eventual resonance in the power line; such resonance can cause tripping, which can harm other equipment within the network. In addition, there is less switching stress, because switching takes place only when necessary.
Ride-through Capability in Brownouts
The IGBT-based switch construction of a regenerative AC drive's front end, combined with ABB's unique LCL filter, enables motors to run at full power at full motor voltage, in 80 percent "brownout" conditions! This ride-through ability means that, even when there's a dramatic short-term reduction in voltage from the utility grid, the drive sustains full power to the motor and lift, so that operation is not interrupted.
"In our experience, these drives excel in such conditions," noted Tisdale. "In installations alongside DC drives, the latter are tripping out, while the AC drives keep loads turning. In an application such as ski lifts, this ensures safety, full operability - and profitability to owners."
Exact Motor Sizing Saves Money, Too
Regenerative drive end users, in addition to gaining the above benefits, also can achieve cost savings through the elimination of any need for motor over-sizing. In other drives, which do not have the ABB regenerative unit's ability to compensate for network fluctuations, the rectifiers, semiconductors and the cabling all contribute to voltage drop. "This means that the maximum motor voltage might be significantly below the line voltage," said Jari Tukia, product manager for the unit. To compensate for this and deliver full torque, the motor is typically over-sized. "With the ABB regenerative drive, the output voltage can be boosted to the nominal value or higher, even with a low line voltage. This allows the use of motors up to 10 percent smaller that with 6-, 12- or 18-pulse rectifier drives," Tukia said.
The regenerative four-quadrant AC drive is easy to install; it is offered in either a standard cabinet, or as modules. Commissioning is equally simple, with ABB's new "Start-up Assistant" feature giving effective menu-driven help for parameter-setting, for fast plug-and-play operation.
Everything required in an AC drive can be mounted inside the cabinet -- chokes, I/O extensions, fieldbuses and pulse encoder modules, delivering further space savings. No space is needed for additional enclosures or cabinets, while the reduced cabling requirement further lowers costs.
ABB Inc., Automation Technologies, Drives and Motors, is the world's largest manufacturer of electric motors and drives. In the USA, an integrated channel of sales representatives, distributors, and system integrators allow ABB, New Berlin, Wisconsin, to supply a complete line of energy-efficient electric drives, motors and engineered drive systems to a wide range of industrial and commercial customers. Products manufactured include AC variable speed drives for electric motors from 1/8th through 135,000 HP, large AC machines and drives, medium-voltage drives, power electronics and rectifier systems, AC & DC motors, and application-specific drive system solutions to meet diverse customer needs (http://www.abb-drives.com).
ABB (www.abb.com) is a leader in power and automation technologies that enable utility and industry customers to improve performance while lowering environmental impact. The ABB Group of companies operates in around 100 countries and employs about 135,000 people. The company's U.S. operations employ about 11,000 in manufacturing and other facilities in 40 states.
