Driving to new frontiers

Can AC drives develop any further? Yes, predicts Guy Kennett of Mitsubishi Electric.

Ever-more intelligence is being built into drives.

Twenty years ago, when drives were a new technology, commissioning typically took two or three days.

The cost of this in terms of man-hours and also possibly delayed production could be huge, but in the early to mid 1990s auto-tuning reduced commissioning time to a matter of hours.

Currently it takes about 10 minutes to get a drive up and running, fully tuned to its motor, and this will continue to be reduced significantly; the function will eventually become one of simply fitting a drive.

Critically this will change the culture surrounding drives engineering, and they will find themselves in a host of new fields of application.

One massive developing area is in building services.

Over the last 10 years the drives have been installed in the more sophisticated new buildings and this trend will be amplified massively by the new Part L of Building Regulations, which addresses energy efficiency and recommends drives on even the smallest of pumps, fans or blowers.

Drives' increasing intelligence also opens to possibility of local process control.

The effect is that drives will adopt some PLC functionality, and indeed several manufacturers already offer such things.

Cynics may argue that automation companies won't want to go down this line because it will undermine their PLC sales, while drives-only companies will find it attractive but impossible to source the most up-to-date PLC technologies: in fact the development will be user-driven.

In most cases it will make very little technical difference whether one uses separate PLC or an intelligent drive, the decision will be made by personal preference and custom and practise.

Intelligent drives offer advantages where the installation is remote or inaccessible, where space is limited, where local technical capabilities are very low, or where technical capabilities are expensive to implement.

Within a few years many drives will have IEC61131 programming capabilities, just like a PLC.

However they will tend to have their intelligence capped at being equal to micro and small PLCs: drives could theoretically be fitted with the capabilities of a large PLC or PAC (programmable automation controller) but this would be unattractive to users who would consider the resultant architecture to be restrictive when it came to later systems reconfiguration.

In recent years the size, performance and reliability of IGBTs, the backbone of a drive's switching capabilities, have advanced significantly.

However further reduction in size is limited due to the constraints of current directives.

However new technologies may appear which will allow device reduction without impacting switching performance and long term reliability.

However by combining the control and power electronics, drives can "map" their motors in real time and thus constantly reoptimise.

This is of particular significance because energy saving is fast becoming the number one reason for installing drives.

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