The future of drives
April 1st 2006

It looks as if AC drives technology will keep developing on several fronts for some years yet, predicts Guy Kennett of Mitsubishi Electric.This could have a major impact on how they are used in a wide range of engineering projects

The most important development is that drives will become even more intelligent. Back in the 1980s it typically took two or three days to commission a drive. By the early-mid 1990s technology had advanced and commissioning time was down to a single day. A big breakthrough came with the development of auto-tuning which, at a stroke, reduced commissioning time to an hour or two.

The trend has continued so that it now rarely takes more than 10 minutes to get a drive up and running. In the foreseeable future, commissioning time will reduce to zero; the function will become one of simply fitting a drive. This future saving of 10 minutes will not be significant in terms of cost saving, but it will have a massive effect in changing the culture surrounding drives engineering.

For some applications drives will become commodities, in that they will be completely accessible to users. Where previously users have had to rely on drives experts, soon they will be able to do everything themselves with ease, confidence and (most importantly) guaranteed outcomes.

Process control

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.

In most cases it will make very little technical difference whether one uses a drive-and- 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. Another significant difference is that intelligent drives are likely to use expansion racks rather than have on board I/O. This is to maintain configuration flexibility in the field, and in fact follows a trend that is already evident in PLCs.

However, the question arises: how many machine and mechanical engineers are sufficiently familiar with IEC61131 that they will be able to set drives parameters and or enable process improvement? The final result of this development strand is likely to be that integrated controllers will offer many benefits in terms of ease of installation and assured communications, but for (relatively few) situations where 'best in class' performance is required standalone equipment will win out.

Power electronics While great things can be expected of the control circuits, developments in the power circuits are a little harder to forecast. In recent years the size, performance and reliability of IGBTs, the backbone of a drive's switching capabilities, have all advanced significantly. However they all now appear to be at a final plateau. Any further reduction in size is likely to adversely affect switching performance and may intensify local heating effects, which will in turn impact upon reliability and long term performance.

Therefore to improve switching and waveform manipulation, either better cooling has to be achieved, a fundamental development in power electronic technology used or drives must be redesigned to reduce their reliance on power circuitry.

However by using the control electronics in conjunction with the power electronics, we are already seeing improvements in drives' ability to 'map'the motor with which they are used. Some drives are already able to dynamically map their motors in real time, which leads to instant optimisation of performance and therefore a significant reduction in the voltage vector. The effect of this is a substantial improvement in a drives ability to save energy when compared with a fixed speed drive.

This is of particular significance because energy saving is fast becoming the Number One reason for installing drives. So just as energy efficiency is becoming a key driver for industry, drives are stepping up to the plate ready and able to really address the issues of the day.

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