Processing Magazine

When to consider a multi-drive versus a single drive

October 16, 2006

Drives offer an array of benefits to integrators, OEMs, panel builders and end users who are optimizing energy usage through precise control of motors. Since drives are available both in multi-drive and single drive configurations, it is useful to define the difference and profile the benefits that the next generation of multi-drives now provides to users.

A single ABB industrial drive

Adjustable Speed Drives are used in any application in which there is mechanical equipment powered by motors; the drives provide extremely precise electrical motor control, so that motor speeds can be ramped up and down, and maintained, at speeds required; doing so utilizes only the energy required, rather than having a motor run at constant (fixed) speed and utilizing an excess of energy. Since motors consume a majority of the energy produced, the control of motors, based on demands of loads, increases in importance, as energy supplies become ever more strained. Additionally, end users of motors can realize 25 to 70 percent energy savings via use of motor controllers. (Despite these benefits, the majority of motors continue to be operated without drives.)

Single ABB industrial drives are highly flexible AC drives that can be customized to meet the precise needs of a single-motor application. These units convert AC power to DC, and then invert the DC back to an AC output to a motor. These drives cover a wide, full range of powers and voltages. Single industrial drives also feature a wide range of built-in options as standard equipment. They can be installed for most applications right out of the box; and they also can be ordered and manufactured as a customized unit for a particular application.

What is an ABB multi-drive?

A multi-drive is built from industrial drive modules that are connected to a common DC bus bar. The common bus bar is used to supply the drive modules with DC power, and each module then inverts the DC to AC and powers an individual motor. The DC power is derived from a single supply unit (rectifier) that is built into the front end of the same multidrive configuration. This construction simplifies the total installation and results in many benefits: savings in cabling; reduced line currents and simpler braking arrangements; energy distribution over the common DC bus bar, which can be used for motor-to-motor braking without the need for a braking chopper or a regenerative supply unit; reduced component counts; increased reliability; and space savings; and there is no need for a separate Motor Control Center (MCC).

Where can multi-drives be used?

In general terms, the ABB multi-drives can be used whenever several drives/motors form part of a single or integrated mechanical process. The common supply of the multi-drive enables the implementation of overall safety and control functions, and permits the close coordination of individual drive motors. For example, a paper machine has many motors that must be individually controlled as a complete system. The ABB multi-drives offer fast communication of torque and speed signals between the drives, to control the tension in the paper web. Multi-drives also can be used where the shafts of the individual drive motors are not tightly coupled; for example, in processes where each drive module can be programmed with a speed profile so that the overall use of energy is minimized. These two examples merely demonstrate the range of applications where ABB multidrives offer substantial benefits over other types of drive constructions.

ABB multi-drive promises

Modular configuration of multidrives provides control of multiple motors across a 1 – 7,000 HP power range, from 380 - 600 (690) VAC. A single rectifier unit can be combined with a host of inverter units that are connected in parallel, to provide output current required by any given application. Additional major benefits include:

• Encoder-less Motor Operation

• Superior dynamic-response performance of ABB''s patented Direct Torque Control (DTC) motor control algorithm. Many applications can be run without encoder feedback.

• Flexibility. Only four types of diode rectifiers are used to invert AC three-phase input power to the common DC bus bar across the entire ACS800 power range (200 ? 4600 HP). Inverter modules (drives) are available in seven sizes (R2i ? R8i frame sizes) and cover the 1 – 7,000 HP range; single R8i units, or R8i units in parallel, supply the motors.

• Compact Design. Improvements in technology and power components have reduced the total footprint of these multi-drives by up to 50 percent, compared to the generation of multidrives preceding the ACS800 line! This frees up significant wall-, panel- and floor-space.

• Wide Range of Options. I/O extensions, field buses and a pulse encoder module all fit inside the inverters.

• Adaptive Programming. This program extends the freely programmable I/O and extensive parameter selections built into the multi-drives and accessed via the Start-up assistant. The Adaptive Programming accesses extensive parameter selections for complete flexibility in precise control of all individual motors; like a mini PLC built in.

• Reduced Installation Costs. Since the modular configuration utilizes a common DC bus, the cabling input power required is a single three-phase AC connection. Further, the cabling is wired to the rectifier module through a unique plug-in connector, which then powers the entire common DC line-up. And the plug-in connectors for the inverters (132 kW and up) are wired to the motor terminals. Both the rectifiers and the inverters are rolled in on their wheels and seated into the connectors.

• Redundancy. Common spare parts and the ability to keep running at reduced load, if module is disabled.