Multi-drive systems explained
Integrators, OEMs, panel builders, and end users who are interested in optimizing energy use through the precise control of motors need to consider multi-drive systems. Since drives are available in multiple- and single-drive configurations, it is useful to define the difference and highlight the benefits that the next generation of multi-drives can provide.
A multi-drive is built from industrial drive modules connected to a common dc bus bar. Key units of ABB's ACS800 multi-drive system, supply and inverter sides, are shown.
Adjustable speed drives can be used in any application where mechanical equipment is powered by motors. The drives provide extremely precise electrical motor control so motor speeds can be ramped up and down, and maintained, at required speeds. Doing so uses only the energy required, rather than using an excess of energy while a motor runs at constant (fixed) speed.
Since motors consume a majority of all energy produced, the control of motors, based on load demands, increases in importance as energy supplies become ever more strained. In addition, end users of motors can realize 25% to 70% energy savings by using motor controllers.
Single drives are highly flexible ac drives that can be customized to meet the 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 full range of powers and voltages, can include built-in options as standard equipment, and can be installed for most applications right out of the box.
A single rectifier
A multi-drive, on the other hand, 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 multi-drive 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. There is also no need for a separate motor control center (MCC).
In general terms, multi-drives can be used whenever several drives and 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, such as in a paper machine.
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.
Source: ABB, Automation Products, Low Voltage Drives, supplies a variety of energy-efficient electric drives, motors, and engineered drive products, including the new ACS800 multi-drive system. For more, visit www.abb.us/drives .