Drives and Controls Magazine

Power selector switch makes drive systems more versatile

12 November, 2010

Control Techniques has developed a device for multi-way switching of drive control cables via contactors which, it says, could cut capital costs, make operation more flexible, add redundancy at a low cost, and improve efficiency.

The SPM power selector module (shown above) is designed to be used with CT’s modular Unidrive SPM AC drives and allows automatic re-routing of connections between the control and power stages in parallel drive systems. It also provides automatic control of contactors.

The switch was developed originally for the crane industry, with the aim of eliminating the need for separate hoist drives. CT says it can also make process equipment and test rigs more versatile, allowing operation over a wide power range, and providing continuous operation in the event of a fault, thus giving system redundancy for critical operations.

In the simple example shown below, if one bank of drives fails, the control system takes it out of the circuit automatically using the selector modules. The principle can be extended to large motors with two parallel banks of power modules. In normal operation, either bank of drives (or both) can be used.

When applied to a gantry crane with dual long-travel motors and a main hoist, the module allows just two drives to be used instead of three – by switching the drives between travel and hoist duty – thus delivering significant savings. Similarly, the power range can be expanded using up to 10 modules, again eliminating the need for a separate hoist drive.

For test rigs need operating over wide torque and power ranges, the SPM power modules can be switched out of circuit as the output power demand is reduced and, conversely, re-connected as power demand rises. Matching the drives to the motors makes the test rig more versatile, improves feedback accuracy, and cuts losses, according to CT. One master can work with a string of modules which are switched in and out as required. This also offers the option of
adding more modules at a later date to increase the power.