Driving forward: the world of electrical variable speed drives is as broad and diverse in range and application as the technologies it embraces. Mark Venables explains.

A DISCUSSION on the future path of electrical variable speed drives used to be a straightforward matter. The direction for advancement was governed by the customer demand for lower cost and smaller products, and both the control and power domains were limited by advances in silicon. Today that discussion is far more complex, involving the perhaps surprising question: 'What is a drive?'

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A simple enough question you may think. But attempts at an answer quickly reveal that the world of electrical variable speed drives is as broad and diverse in range and application as the technologies it embraces.

Indeed, the application of electrical variable speed drives is so widespread--from lathes and machining centres, automotive alternators to computer disk drives and printers--that their very presence is often overlooked. But the fact is that any product with moving parts probably has a drive involved somewhere.

In terms of technology, the principles of motor control adopted in the various applications are well established, and invariably depend upon control of voltage or current and, in many AC drives, frequency.

Worldwide the demand for AC variable speed drives is growing significantly, while sales of DC drives is roughly flat. Manufacturers are keeping pace with the demand by expansion of their own and their suppliers' manufacturing capacity. Most of this additional capacity is being added in Asia, but there is also growth in Europe and South America.

'While there is a temptation to consider variable speed drives a commodity and the associated technology to be mature, I take a very different view,' said Geraint Evans of Control Techniques. 'Many manufacturers do offer seemingly very similar products and, in that respect, drives may appear as commodity products. But there are many differentiating features and functions associated with different manufacturers.

'These differences can be very significant when considering specific applications or systems designs. These typically include interfaces to other equipment--including Fieldbuses and Ethernet on-board programability of advanced functions--many of which until recently required a motion controller or PLC until recent drive releases.'

Last year ABB launched its ventilation-specific drive, prompting many within the industry to proclaim the end of the generic models as drives evolve towards function-specific types.

'Industry-specific products are not a new phenomenon,' said Evans. 'Control Techniques, for instance, has variations of AC drive specially set up for the heating and ventilation and lift markets which have grown in significance as the quest for ease of set-up and operation gathers pace.

'A specific product allows only those features and functions relevant to that application to be retained and displayed. Industry-specific products are rarely driven by cost.'

Evans said that this sector will certainly grow, but the demise of the generic product is unlikely. He pointed out that the issue is volume related--to justify a specific product and ensure global support.

The variable speed drives industry has for many years accepted that varying the speed of most loads saves a significant amount of energy. This saving will continue to stimulate sales of drives because efficiency is heavily driven by monitoring and control, and drives play a crucial and growing role in optimising almost all manufacturing processes.

It is a sobering thought for drive designers and manufacturers that customers are rarely fundamentally interested in the finer points of a drive control system. Indeed, most consider a drive as little more than a means to an end--no more than a solution to their problem. The drive has historically been a component in a solution, but increasingly the capability of a drive allows complex, complete solutions without other external control elements.

In the majority of cases, drives are part of a system. As such it is necessary for the parts of the system to communicate with one another, transmitting commands and/or data.

This communication can take many forms, from traditional analogue signals through to wireless communication systems. The drives industry has been working hard to produce lower cost, higher performance drives, with good flexible and dynamic interfaces to other industrial products such as PLCs and human machine interfaces (HMIs). Other suppliers have taken a more holistic view of customer needs, moving from a component supply situation to a solution provider.

The capability, flexibility and power is available today in products, and many customers are implementing simple yet considerably elegant high-performance systems. It is clear that the future is firmly in their hands--perhaps more so now that at any time in the past 30 years.

But this flexibility has been shown to offer systems designers and customers significant advantages in performance, cost and reliability with no single approach to an application solution. So at the end of the day the applications engineer is in the best position to decide on the structure of the solution.

Now drives manufacturers are giving him the power to make the best choice.

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