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Regenerative DC motor control for heavy industry applications

18 May 2016

Sprint Electric presents its extended range of digital DC drives up to 2250 Amps, ideal for controlling DC motors used in heavy industry applications.

PLX drives are able to regenerate energy back to the mains supply under braking without the need for expensive, complex intermediate storage, resistive dumping or additional power bridges. Available in current ratings up to 2250 Amps at supply voltages up to 690 VAC, the motor controllers are compact, powerful, flexible, and easy to program thanks to the drive.web control technology. 

DC drives of the PLX range are available as two quadrant or regenerative four quadrant types. The four quadrant model uses two thyristor bridges to enable it to motor and brake in both directions of rotation. This allows it to reverse the torque to slow the load very gently or almost instantaneously, regenerating energy at the same time. Unlike an AC drive, it is able to generate full torque at zero speed, enabling the load to be held stationary in complete safety without the need for mechanical brakes, an especially useful feature for winders and hoists. This ability means DC is also ideal for applications such as mixers, extruders and rollers that require high starting torques and accurate control at low or zero speed, as well as for paper machines, wire drawing and machining. 

All models ranging from 650 to 2250 Amps (980KW/1320 HP) are offered with two AC busbar position options, either top entry or bottom entry. The two options make it easier to use the existing cabling in retrofit installations, or give the choice of wiring options for new design. The PLX range is available as high voltage (690V AC) or standard voltage (480V AC) models. A 690V AC supply allows the use of 750V DC armature motors. Compared to the standard voltage this provides an increase in shaft power, up to 1500KW/2000 HP for the 2250A model, that is 50 percent more power delivered without an increased cable size.

Thanks to the control technology drive.web, the drives can be controlled over the Ethernet without the need for a PLC or supervisory computer. The control system includes graphical configuration tools that provide diagnostics and configurability of all drives on the network, either locally or remotely via the Internet. The graphical tools allow the full configuration of the drives, provide service diagnostics, full documentation and an operator interface for local control. Software functions and fieldbus communications options include Profibus, DeviceNet, CC-Link, EtherNet/IP, Modbus and CANopen.

Many applications with electric drives require frequent accelerating and braking. When accelerating or lifting loads, electrical energy is converted into kinetic or potential energy and much of this can be recovered when braking or lowering the load. Often this recovered energy is converted to heat using a brake resistor without any economic benefit. But in some applications it is worth passing on this braking energy for another use. Lenze's new r700 takes power recovery to new levels of economic efficiency, practicality and, most importantly, simplicity. Launched at Hanover Fair, the regenerative module is available in two versions with 24 and 48kW peak power. Its special feature is the separation of supply and recovery paths, permitting an economic system design. Due to its efficiency of 98 percent and elimination of external filters, the Smart Energy Recovery quickly pays for itself and impresses with a compact design. Retrofitting existing machinery is a simple task.  

In the past regenerative units for power recovery often failed to make economic sense. They were difficult to install, too complicated to set up and the investment cost far outweighed any power savings. The new Lenze r700 Smart Recovery Unit makes power recovery feasible, even in applications hitherto deemed unprofitable. By decoupling the power supply and recovery lines, the recovery unit is made simple. This is illustrated by the facts that no EMC filters are required for connection to the mains, and no programming is needed to set up the system. The Smart Recovery Unit is simply connected to the DC bus of the drive or drives. Power is only returned to the mains when there is too much energy in the DC bus. 

Typical implementation areas include storage and retrieval units, also other lifting and handling equipment in which a relatively high amount of energy is accumulated as the load is lowered. In such cases the power supply to the drives is dimensioned as normal whilst the recovery unit can be dimensioned only on the surplus braking energy which can be accurately calculated with Lenze Drive Designer software. This leads to compact and economic selections. Depending on the quantity of power recovered, the system pays for itself in around a year.

The new Lenze r700 Smart Recovery Unit breaks new ground for saving energy with dynamic drives. Setting up the system is easy with no EMC filters, no programming and compact dimensions. Energy is returned to the mains reducing electricity bills instead of being lost as heat from braking resistors.


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