Pictures of the Future    Spring 2006

Mighty Motors

Even though today’s electric motors are the product of 170 years of technology development, they still have plenty of potential for improvement. Siemens researchers are finding out how to make electric motors more powerful, economical and flexible. Their objective is to combine individual components into a harmonized drive system.

The electric motor was invented some 170 years ago and has been steadily refined ever since. You might therefore assume that its technological potential would have been exhausted by now—but that’s not the case. In fact, experts look more than a little surprised when asked if major advances are still possible. "Naturally," says Rolf Vollmer, a developer at Automation and Drives (A&D) in Bad Neustadt, Germany, and a Siemens Inventor of the Year in 2005. "Innovators are constantly improving drive technology. For example, we’ve been able to more than double motor torque—without increasing the size of the motor."

"Our range of drive systems is huge," adds Dr. Gerd-Ulrich Spohr, head of the Technology Strategy department at A&D in Nuremberg. "Some of the motors are specialized devices produced in small lots. Others, instead, are poduced by the million each year." The smallest motors are about the size of a pack of cards and are used, for example, to move the examination tables in computer tomographs. The largest are installed in ships or help to transport gas from offshore platforms to land-based facilities. The output of these devices ranges from just a few watts to 100 MW, and generators at power plants can produce over 1,000 MW. Motor speeds range from a few rpm—for instance, in wind turbines (see insert)—to 15,000 rpm in gas compressors. Siemens motors propel track-based trains at speeds of up to 350 km/h (see High Speed Rail and Rail Propulsion Systems), while motors in the Transrapid maglev power it up to 500 km/h. Electric motors also control the precise movements of welding robots and drive the conveyor belts that transport luggage at airports.

The market for electric motors is huge. Sales in Germany alone totaled some 8.5 bill. € in 2005. Particularly innovative segments, such as variable speed synchronous motors, are posting annual growth rates of 10 % worldwide. Although the last fifteen years have been marked by tremendous cost-cutting pressure, especially due to competition from Asia, Siemens has been equal to the challenge.

Today, A&D, which has 60,000 employees, is growing faster than the market, and is the leader in most power classes. The group recently improved its position by acquiring Flender, a German firm that makes gearbox and drive systems, and U.S.-based Robicon, which specializes in converters for large-scale drive systems in the oil, gas, and water industries. A&D’s motors are as varied as their uses (see box); most are standard motors, operate at constant speeds, and run on power from the electric grid. These asynchronous motors are the backbone of the industry and are used to power pumps, conveyor belts and refrigerator compressors. However, even these simple devices, which are relatively inexpensive to produce, can be improved—which is why Siemens has developed motors that can significantly cut electricity costs (see Industrial Motors). "Customers don’t really want a motor; they want motion, power and performance—in other words, torque and speed," says Spohr. With this in mind, A&D developers are not only making motors more powerful, but are also using fewer or more economical materials to produce them.

Smaller units can be used more flexibly—one of the trends experts are observing in machine construction, logistics and large-scale motor development. In the future, drive systems will have to be smaller, consume less energy and provide more power. For example, a robot arm contains six high-tech motors that control the arm’s precise movements when welding a vehicle body.

Holistic Approach. The approach taken by A&D goes beyond the optimization of motors. The group is involved in complete power trains, meaning energy supply, motor, converter, gearbox and brakes. Here it is crucial that all of the components work together smoothly. For example, sensor data from one part of the chain is used to optimize the operation of another part. A&D has assembled teams that examine and improve the interaction of power train components in labs located in Bad Neustadt, Erlangen and Nuremberg. "We are the only company that does this," says Spohr. "And that gives us a major competitive advantage." Siemens experts also simulate motors and entire drive systems on computers (see Applications: Current Events).

"By creating a big modular kit, we can offer customers a drive system solution tailored to their specific needs," says Spohr. "The benefits become clear when a component fails. For instance, suppose you have a machine with a V-belt that’s integrated into a production chain. Even if the belt tears, the motor driving it will continue to run." Other units notice the problem, however, and enable the system to react in a predefined manner. Depending on the safety level, the motor is switched off automatically and a technician is notified, or the unit is partially or completely shut down. "If the individual components don’t understand each other, the disruption could escalate and cause the entire production system to fail," says Spohr.

A&D refers to this modular concept, which involves the transfer of intelligent networking and plug and play systems to the world of industry, as Totally Integrated Automation (TIA). Ideally, such a system can configure itself because it "understands" its own design. Although such continuity across components has its price, customers value it—especially if they’ve ever purchased cheap, separate system components, only to discover that motors don’t work with converters, or that the system can’t be controlled properly.

A&D’s new Flender operation fits the TIA concept perfectly. A company that specializes in mechanical drive technologies, Flender produces gearboxes that support A&D’s claim of being able to provide drive system solutions from a single source. "We began working with modular systems early on," says Georg Boeing, head of Gearbox Development at Flender in Tübingen. Flender is well-known for high-performance gearboxes that operate quietly thanks to optimized gear-tooth arrangement. "We worked closely with Siemens for years before the acquisition," he says. It was therefore easy to install 15,000 Flender gearboxes at Dubai’s new airport to augment drive units for the luggage transport systems, escalators and elevators (see Pictures of the Future, Fall 2005, Airports).

Decentralized Decision Making. Airport luggage transport systems require thousands of motors to work together in a precisely aligned manner. Decentralized drive systems from A&D are perfect for this task, since they control functions exactly where the work is taking place. They are thus more flexible and cheaper to operate. Today, data and power usually flow through a central control unit in a star-shaped circuit. Decentralized and networked architectures consist of smaller, intelligent units consisting of conveyor belts, drives, sensors and logic components. This reduces the amount of cable needed and simplifies maintenance. Ultimately, it also means that the only components in operation are those that are actually needed.

Saving Energy with Converters. "Many people still don’t understand the principle behind variable speed drive systems," says Kaufhold. Nevertheless, the benefits are clear. In fact, by consuming less energy, such systems pay for themselves in two years or less. "Imagine having a motorized pump," says Kaufhold. "The motor’s always on and you regulate water flow with a tap. If you’ve got a converter, it will regulate the flow. As a result, the motor only consumes as much electricity as is needed." Depending on the type of unit, energy savings can total 30 to 50 % (see chart). For instance, in a pump system at LW Baden-Württemberg, one of Germany’s leading water supply companies and a provider of drinking water to three million people, Sinamics "varies flow rates between 50 and 230 l/s as needed," says Kaufhold. Calculations indicate that this will cut the company’s electricity bill by almost 200,000 € a year.

Frequency converters are semiconductor components that are usually installed in switchgear cabinets next to a motor. "A crucial issue here is energy recovery capability," says Dr. Hubert Schierling, who is responsible for predevelopment of standard drives at A&D. "For example, when a motor is braked sharply, the excess energy often ends up in a resistor in the converter, which then heats up." In elevators, around 30 % of the energy is consumed in this way. "However," says Schierling, "we already have converters in our decentralized automation systems that return this energy to the power network. And that puts Siemens in a unique position." Schierling believes that such systems will eventually become standard.

Another important task is to ensure that the converter electronics and the power network are compatible. For example, rapid changes in switching operations should not lead to voltage fluctuations or the creation of alternating fields—both of which can affect electronic systems in other devices. Filters as big as the converters themselves are sometimes installed to prevent this. "Silicon carbide converters will soon solve this problem," says Schierling. "This semiconductor is more temperature resistant than today’s silicon devices. It can also handle higher current densities and much higher switching frequencies." As a result, future filters could be much more compact. SiCED, a joint venture between Siemens and Infineon, has already developed silicon-carbide diodes and transistors in the lab. In five to ten years, it may be possible to mount the converter directly onto the motor, which would simplify cabling and cooling procedures. "And that will provide another boost for decentralized drives," says Schierling.

Because the magnetic field is distributed across several waves, only one-fifth of the magnetic flux is present in the stator. Much less iron is therefore needed to conduct the magnetic field. "In other words, without increasing its size, the motor can generate more than twice the torque," says Vollmer, who holds 43 patents. Because harmonic motors have slightly higher losses, they are not suitable for all applications, but are ideal for those requiring very high torque, such as plastic-injection processes for CDs.

At the end of 2005, A&D presented another innovation: the combination drive. Here, development engineers from Siemens and printing press manufacturer MAN Roland successfully combined a rotary and a linear drive in a single housing. This unique innovation will be used in offset printing presses. Here, the rollers must not only rotate but also move sideways to ensure that the ink is distributed precisely and evenly—and thus guarantee high print quality. Up until now, manufacturers have met this challenge by using an inflexible and fault-prone mechanical system. The combination drive can shift the thick rollers, which are 1.5 m long, weigh several tons and rotate at 1,850 rpm, some 2.5 cm sideways—opening up completely new possibilities for printing processes. The motor has been designed to run for an impressive 50,000 hours. By comparison, after only 5,000 hours of operation, a passenger car will have traveled at least 200,000 km. Prototypes of the combination drive already exist, and it could also be used in other machines and industries.

A&D also plans to further improve performance using superconducting coils. For example, the world’s first fast-rotating generator with high-temperature superconductors will propel ships in the future (see Superconducting Generators). The use of special materials will ensure that even though it is smaller and more economical to operate than conventional generators, it can still generate four megawatts. "As you can see, the electric motor still has a lot of potential that’s just waiting to be exploited," says Spohr.
                                                                                                Norbert Aschenbrenner