Mr. Bauer, Danfoss has a substantial portion of the development of the electrical drives technology with the static frequency converters. How did it all start?
Bauer: Since its invention in1889, the main disadvantage of synchronous AC motors is its controllability. Because of the relationship between the rotor speed and the frequency of the AC supply, the rotor speed is fixed. At a conference in 1966 Danfoss engineers looked for an engineering design solution to this problem. Since at that time there were limited means of achieving variable speed. Then, in 1968, came the break-through with the static frequency converter manufactured in series. Even if only 14 devices were produced the first year, this was the starting signal. It took another few years before the technology had its break-through for the mass-market and the devices had to become smaller and economically more viable.
You talk about the fact that the break-through needed some time. Which factors were decisive for final success?
Bauer: On the basis that from 1968, the first devices were oil cooled, one of the most important steps was air cooling, which provided for substantially smaller units. Afterwards the introduction of digital technologies in the late 80’s gave the next step in the development. The first industry-specific frequency converters showed up in the early 90’s. At the same time the introduction of bus technologies provided for an increasing spread. In the meantime the drives have become modular in construction and include ever more functions and more intelligence. This made the drives suitable for use in a wider range of applications.
Where does static frequency converter technology have its main influence on drive technology?
Bauer: Static frequency converters have a large influence on modern drives technology. Not least, it was this economical, robust and maintenance-free regulation that made AC asynchronous motors the standard in many applications. Also, electronic motor control made for lower prices, increased process optimization and better utilization of production lines for improved product quality. Ever smaller electronics helped to build more compact plants. Integrated intelligence provides greater flexibility and offers a host of new functions in the area of safety and control. At the moment, modern frequency converters are among the most effective means for saving energy – a response to the demands raised in the discussion about climatic change and global warming. Only efficiency across the whole application spectrum will lower energy consumption quickly and effectively.
How do you see the trends for future developments for the drive systems?
Bauer: In Danfoss we see four large areas which, above all, will drive innovations and further development. Firstly it is the need for efficient use of energy. Increasing energy prices lead to a greater attention to the life cycle costs of the overall systems, as well as the efficiency of the assigned drive solution. In addition the intensified employment of these devices in itself creates a potential problem: The disturbance in the form of harmonic wave loads on the supply system endangers the network. In this area all manufacturers must make appropriate counter measures available. Within the range of drive functionality we see a further integration of control and safety functions in the coming years leading to more intelligent drives. The „Safe Stop" is only at the beginning of over the evolution of increasingly safe frequency converters. The market is opening slowly and demanding further control solutions. The increasing use of direct drives, of permanent magnet motors and of high torque motors will mark the immediate future. Demand will emerge for concepts that can control standard synchronous motors exactly in the same way as these motor types. Only in this way can costs for training, maintenance know-how and spare part stocks can be kept at a profitable level.
What’s in your opinion essential in the search for a frequency converter platform?Bauer: Users should consider not only the initial purchase cost, but the entire life cycle costs. Because the initial costs are only approximately 10%; the largest part of the life-time costs includes commissioning, maintenance and particularly the absorbed energy costs. Even if 10 to 30 % energy can be saved with effective speed regulation, as much as 60% can be obtained by optimization of the whole system. An important criterion in the selection of suitable frequency converters is the question of the EMC performance. Until recently users of electronic equipment were safe respecting limit values, employing line reactors, sufficiently dimensioned intermediate circuits and EMC filters. These measures are expensive and require additional space in the cabinets or the plant and additional wiring costs. A truly modular build concept for all the drives in a system, with a consistent control concept for all power ratings, offers the best and safest overall drives system solution.