Industrial drives into the future

Industrial drives technology in Australia and New Zealand sits on the threshold of major change as old barriers to progress are broken down by new technologies, spurred on by unstoppable demands of greater workplace safety and efficiency.

We have already glimpsed the future of industrial drives technology as environmental impact has in recent years become a substantial contributing factor to the design, manufacture and application of modern machinery.

For many years now, Australian manufacturers and suppliers have had to ensure their products fall under an audible noise threshold for OH&S reasons. Back in 1999 we saw changes to ensure conformity in electrical and electronic systems regarding EMI (electromagnetic interference) under the 'C-Tick' legislation (AS/NZS 4251.1).

Presently, the focus is on 'Motor MEPS' (minimum energy performance standards), under the standard AS/NZS 1359.5.2004. This was a legislated process with mandated efficiency requirements introduced in 2001 (regarding electric motors sold in Australia and New Zealand) and the market will see further mandated increases in April 2006.

The MEPS process is designed to reduce power greenhouse gas emissions and is under state and territory law. Many of our international trading partners are also introducing legislated efficiency requirements for products so this is the future. From some of the examples above we can see the relationship between environmental impact and machine design already in component form.

The decade ahead

The next 10 years will see even greater change with the advent of broader 'system' efficiencies, through which plant engineers across the spectrum of industry will be looking to make gains on the complete machine or even entire plant operating efficiencies. Any and all gains in efficiency mean fewer greenhouse gas emissions due to better utilisation of power as a resource and this translates into a benefit for all.

Modern machinery and industrial processes will require flexibility and the ability to adjust throughput to cater for peaks and troughs in demand for consumer, resources or industrial production.

In this process, the old distinctions between mechanical and electrical processes will be broken down as the broader field of mechatronics engineering comes to the fore. Leading mechatronics suppliers will increasingly move into the role of 'solutions providers' as opposed to a 'component suppliers'. The resultant systems will be based around a broader spectrum of integrated technologies (electronic inverters, electrical motors and mechanical gearboxes) than was previously the case and they will be much more flexible.

Until now, design engineers have often been tied to motors with fixed speeds or rates of production because the AC induction motor (the workhorse of today's industrial world) is what is referred to as a 'fixed speed prime mover'. This term implies exactly what you get with an AC motor: a 'fixed' speed, 'fixed' power therefore 'fixed' torque. The engineer decides what output torque is required and then is forced to make a binding decision in terms of speed. Of course gearboxes and other mechanical means can be employed to reduce the speed while increasing torque (torque and speed are inversely proportional); however, again the end result is a fixed reduction rate therefore a fixed speed.

Engineers have employed various means to provide a variable output giving the machine a certain degree of flexibility. These include pneumatics, hydraulics or mechanical speed variation, but often these solutions represent a compromise and can be messy, hazardous, inefficient and require high maintenance.

Engineers experienced in the mechanical design and application of machines (conveyors, cranes, pumps, mixers, etc) have been aware for some time of the potential of electronic drives, but are intimidated by older-technology inverters and older VVVF electronic drives.

AC inverters have been available in different forms for many years. In its most basic form, an AC inverter takes a fixed AC sine wave, converts it to DC and stores it in a power stack or 'DC link'. When output voltage/current is required, the inverter rapidly switches the DC signal on and off to produce an approximation of an infinitely variable AC sine wave.

The output switching process is known as pulse width modulation (PWM). The whole process is controlled by a microprocessor so the results are very predictable, stable and, of course, can be adjusted according to user requirements.

The end result is the ability to make your common AC induction motor start and stop, speed up and slow down, all with infinitely variable operating and performance characteristics. The process also has the benefits of being clean and virtually maintenance free once the drive has been programmed and commissioned.

However, until recently the efficient application of inverter technology was shrouded in mystery for many potential users and was relegated to the domain of the electrical department. Unfortunately, the electrical department was frequently not experienced in the mechanical application required, so frequently there were problems with system integration that resulted in lost production and wasted money.

Modern technology and shifts in design philosophy are overcoming these obstacles. Modern vector drives are not only far more powerful than their predecessors but also have much simpler user interfaces and are much cheaper into the bargain. Their flexibility allows the products to do far more than simply change the output speeds in motors. The new-generation products have introduced 'logic' modules and other process control functions to facilitate automation and efficiencies, such as comparators, positioning systems, and precision timers, etc that can simplify the electrical system design, giving further efficiency and commercial gains.

The major advancement of recent times has occurred in the drive processor (CPU) where more computing power is available for dedicated tasks such as flux vector calculations. This has led to the development of the vector drive where both the AC motor's magnetising current and torque producing current are calculated and manipulated, leading to excellent motor performance over a very wide range of speeds with high levels of accuracy at the required speed. These days having an AC motor produce 100%+ rated torque at zero speed is a simple task, whereas a few years ago it was quite tricky. Developments in the CPU have also facilitated the control of 'process' functions (like PLCs with timers, comparators, logic modules etc) to allow the AC inverter to not only control an AC motor but other tasks in the machine as well. When you add the ability of a machine to have variable speed with, for example, a delayed start and a predetermined run time and then add, say, the ability to open and close a valve via a relay output only when the motor has reached 50% of its rated speed, you can see the flexibility modern technology gives you.

What is described here is a very simple task for inverters available today. These advances increase system efficiency, reduce cost and allow improved logistics because we can now do in a single machine what previously required many similar machines.

Using the Bonfiglioli ACT series as an example, we have four data sets or memories that are independently adjustable and remotely switchable. This allows users to have up to four totally different operating characteristics from a single drive. When you combine the multiple data set functionality to the features offered in a single data set (four logic modules, two comparators, two timers, multiple fixed or infinitely variable speed motor speed, multiple starting and stopping methods, etc) you have the basis for huge variations in machine control from a single inverter.

On a broader scale, we are seeing plant lines using fieldbus integration technology in order to have the individual process line talk and communicate its operations to the entire plant using very simple two-wire cables under communication protocols such as RS232, RS485, DeviceNet, CAN and Profibus via drive and communication interfaces on the SPL, ACT and VCB series of Bonfiglioli inverters. This makes entire plant line networks very powerful but extremely easy to install and maintain.

The concept behind fieldbus integration has made the installation, maintenance, operation and production of end users far more efficient, so by investing in a technology, an efficiency dividend is realised offering commercial benefit to both the manufacture and the consumer.

Physically smaller drives

Other advances in technology in areas such as the DC link (think of it as a big rechargeable battery inside the inverter) have kept pace with modern industry requirements, leading to physically smaller and more efficient drives being available.

This advance is very important to achieving system efficiency in order to reduce the environmental impacts of industry (remembering that efficiency gains on electric motors are now written into law, illustrating how serious a business issue this has become).

A past problem has been that when designers achieve variable speeds by using conventional technologies (for arguments sake, pneumatics or mechanically variable speed), they may reduce the efficiency of the system through areas such as air leaks or friction losses. This can lead to a compromise between operating requirements and energy consumption and this can negate the legally required efficiency gains.

If you use an AC inverter with an AC induction motor, however, you can actually see system efficiency improve simply by using the two in conjunction with each other. The drive offers an automatic power factor correction (improving reactive power consumption) and also has other benefits such as 'sleep' or 'standby' modes, meaning the motor only works (thereby consuming energy) when it needs to, as opposed to continuous and sometimes wasteful operation.

To this arrangement we can also interconnect multiple AC inverters/DC links and then 'capture' energy produced by the motors when they are working (rapidly decelerating AC induction motors or induction motors with negative slip will act as a generator). Normally this energy is wasted; however, we can use this energy to feed into the other drives in a process line or even feed the excess energy back into the AC mains.

The gains are illustrated by the tests Bonfiglioli Vectron undertakes for all inverters it manufactures. These are tested under full load, with the power used for testing being generated by the tests themselves, minimising the impact on the environment and showing the potential for industry.

Conclusion

The changes described here, while fairly revolutionary in terms of benefits, will be applied in a rapid but nevertheless more evolutionary manner. Industry will take time to adapt, with drives suppliers needing to expand their services to act as solutions providers rather than component vendors.

Bonfiglioli, for one, is investing heavily in the mechatronics design field under its IS sales channel. IS stands for industrial solutions, so by its very name it is identifiable as a consultancy outlet. It is a simple fact that when proposing a complete solution, you need competence in both mechanical and electrical fields, which is what advanced suppliers will offer.

A translator or facilitator between electrical and mechanical design allows smooth integration. A supplier of mechatronics solutions also needs to be able to draw from its expertise as not only a supplier, but, more importantly, as a manufacturer of electronic, electrical and mechanical products. When you are intimately familiar with your products, you know exactly how all of those products will work when combined together in a package.

Bonfiglioli is working through tools such as the DSC program (drive service centre) to help guide the marketplace through consultation with customers on where they can make system efficiency gains - thereby increasing production, lowering operating costs and meeting the present and future legislated requirements in the local and international markets.