ABB’s Automation Products Division is the world’s largest manufacturer of electric motors and drives. One of ABB’s innovations is its direct torque control or DTC which is an optimized AC drive control principle where inverter switching directly controls the flux and torque of the electric motor. In DTC the optimal switching is determined for every control cycle at 25 micro-second intervals. Other control methods typically use a modulator or similar to create a switching pattern based on signals from motor control. These modulators cause unnecessary delays which do not occur with DTC.
When an electric motor is rotating over a wide speed range, a drive equipped with DTC has several in-built safety functions like over speed limits in torque control mode, torque limits, safe and smooth flying start and totally controlled emergency stops.
â€œThe measured motor current and voltage are inputs to an adaptive motor model which produces an exact actual value of flux and torque every 25 microseconds. Two-level comparators compare the actual values of flux and torque to the reference values. Depending on the outputs from the two-level controllers, the optimum pulse selector directly determines the optimum inverter switch positions. The inverter switch positions again determine the motor voltage and current, which in turn influence the motor torque and flux and the control loop is closed,â€ says ABB.
A couple of years ago, a high-speed electrical car was powered by ABB motors and drives. Called the ABB e=motion car, it had the company’s DTC drive which helped for fast acceleration as it provides good control of motor torque with full motor torque available even at zero speed. â€œAlthough a geared vehicle can achieve 100 mph in a few seconds, its rate of acceleration falls away much more quickly compared to our system; this one will continue to accelerate even past the 300 mph mark, provided sufficient battery power is available,â€ said Frank Griffith, one of the ABB UK team who helped to develop the car’s power system.
Currently, ABB is making a big push into the market for machinery drives which overlaps servo drives. The market is estimated to be worth nearly USD 3 billion annually. The company has recently launched a new product dedicated to this market. It is based on AC drive technology incorporated with DTC control and can replace servo drives in many applications. With this product the company is focusing on industries such as materials handling, packaging, textiles, plastics etc.
ABB’s DTC technology continues to give the company an edge in numerous markets since the know-how saves energy and can be used to control machinery as well as auxiliary applications. According to the company, DTC technology helps companies to run their processes without interruptions as DTC prevents nuisance trips and DTC is also robust against supply network fluctuations and interruptions.
Automotive Industries spoke to Pekka Tiitinen, vice president and head of ABB’s global LV drives business
AI: Please tell us about how your DTC advanced motor control platform enables a faster development cycle and therefore faster time-to-market.
To answer this question let met first highlight the importance of DTC. With DTC the limits of AC motor control has been reached. These limits are now determined by the motor parameters themselves. To get faster control out of a complete variable speed drive (that is a motor plus frequency converter) one must design motors with smaller rotor time constants and small inertias. But the DTC control in the frequency converter is no limiting factor.
That DTC is no longer a limiting factor has two major implications for product development. Firstly, we have shifted the focus in R&D from motor control schemes to other aspects of the drive system, including cooling, mechanical design, user interfaces, etc. Secondly, from the point of view of application engineering, the fact that the inner control loops are so fast makes the design of the out control loops a little easier.
AI: What are the advantages of DTC-based products and what kind of flexibility does it allow across a range of applications?
I already mentioned the importance of having a very fast inner torque control loop. Another advantage of DTC is the high starting torque at very low speeds, including zero speed. Further, we have developed the DTC control over the years and have created solutions not only for asynchronous motors, but also for synchronous motors, including permanent magnet motors.
AI: What are some of the innovations in ABB’s advanced test and measurement solutions?
I would like to highlight the new test bench application solution. The intelligence built into the drive to improves response times, increases the number of control options and enables smooth transition from speed control to torque control and vice versa. Those features are appreciated by our test bench customers.
AI: What are ABB Drive’s automotive OEM capabilities?
Starting with from our position as technology leader in the drives market we have steadily increased our market share and are now the market leader. This means that we have more resources available to help our customers. It also means that we have been able to build up our expertise and know-how of many applications. We make this expertise available to our OEM customers through dedicated OEM teams. Further, we now have four AC drives factories around the globe where we make identical products on identical product lines to the same quality standards. This factory base, together with the qualified personnel in all the sales offices, means that we can also effectively serve OEM customers who are exporting their equipment.
AI: What are ABB Drive’s future objectives?
We continue to invest in the development of drives. As I mentioned the focus has shifted from developing control methods to other aspects of the design of drives. Drives are becoming smaller, smarter and easier to use. As the result the market where our drives can be used continues to expand. Also many of the innovations that are put to our new machinery drives are being incorporated in our higher power drives. That means good news to our customers in the business of advanced test systems for the automotive industry.