DC drive bucks AC trend

10 November 2008

Control Techniques, an Emerson company, released a new DC drive, bucking the overwhelming trend towards development and investment in AC technology. The Mentor MP is designed to provide the same control platform as the company’s AC drive and is RoHS compliant.

Richard Smith, product manager of Mentor MP, said: ‘Our extensive market research shows that DC drives are here to stay.’

Control Techniques claims retaining an existing DC motor and upgrading the drive makes good environmental and investment sense to an upgrade project. The company went on to suggest it provides the opportunity to enhance the overall system performance and reliability whilst minimising problematic re-engineering and installation work.

Mentor MP offers three option module slots and an inbuilt field controller.

Smith said: ‘The simulation and modelling technology used to develop Mentor MP today simply wasn’t available a few years ago.’

Galvanic isolation between power and control is a standard feature in AC drives and, in the case of power-side failure, protects the control circuits and customer connected equipment. Other DC drives feature a form of isolation that relies on only impedance only isolation, which Control Techniques says has limitations. Mentor MP technology achieves Galvanic Isolation.

Each Mentor MP has three universal option module slots offering users unrivalled flexibility to choose from any combination of the 18 option modules available. These economically priced option modules are common across Control Techniques’ AC, DC and Servo drive ranges and include functionality extensions such as additional feedback options and expanded I/O and onboard programmable control.

The range of optional fieldbus connectivity includes Profibus-DP, Interbus-S, DeviceNet, CANopen and various Ethernet protocols such as Modbus TCP/IP, Ethernet/IP and EtherCAT.

Communications gateway solutions can also be implemented within the drive by installing two or three fieldbus option modules.

A new external field controller option, the FXMP25, provides field forcing for high dynamic applications; such as very fast reversing (e.g. typical machine tool spindle applications) while a new feature allows reverse jogging control with two-quadrant drives for lower-cost systems that do not require fast reversal. In addition, Mentor MP has a field controller mode that allows itself to act as a field control for larger DC motors, where the field current can be greater than the capacity of the FXMP25.

Mentor MP uses Control Technique’s software tools, developed to support the programming and drive configuration of their AC drive ranges. For example CT Soft, used for drive configuration, includes a configuration wizard allowing existing Mentor users to transfer drive settings from an existing Mentor II drive to the Mentor MP.

Mentor MP is designed to retrofit simply for Mentor II users. It has the same mechanical footprint, main fixing centres and power connections are located in the same place.

SyPTLite, used already by AC drive users, can be used for simple IEC language ladder programming onboard the drive.

Mentor MP offers the capability to link multiple AC, DC and Servo drives together with extensive I/O, controlling PCs and Operator Interfaces using CTNet to create a truly distributed control system. Each drive can house a programmable option module called SM Applications which is programmed using SyPTPro, an IEC61131-3 style programming tool with function block, ladder logic, and structured text language capability. This on-board configuration can often eliminate a stand alone controller and so reduce system cost. Further option modules can be used to connect with I/O, fieldbus or Ethernet protocols for control and monitoring.

SM Applications modules can also be loaded with existing, proven, application-specific software such as crane control, winder/rewinder, flying shear and other commonly used automation functions.

John Murphy, VP of strategic planning, said: ‘Despite the common perception that DC is in terminal decline, our research suggests that the global DC drives market is still growing albeit more slowly than the AC market. In fact with the credit crisis we expect continued growth over the next couple of years as engineers decide to retain perfectly good plant such as DC motor based process lines. Recently Control Techniques' market share in DC has been steadily increasing and reached 13 per cent in 2007. We have a target of 18 per cent market share by 2012 which seems eminently achievable.’

‘But perhaps our biggest market advantage comes from our global network of Drive Centres, which are able to retain, develop and share their many years of experience in DC drive automation systems.’

The Mentor MP covers output current ranges from 25A to 1850A with a single module approach – and 7,400A when paralleled. It is available in 12 and 24-pulse configurations providing low harmonics. Optional keypads are offered as high-brightness LED or multi-language LCD with plain text versions and a range of 18 plug-in option modules including SM-EtherCAT, SM-Register and SM-Applications can provide extra control, functionality and communication. Whilst Smartcard technology provides parameter, PLC and motion program storage in addition to drive parameter ‘cloning’.

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