A newsletter for alumni, students, and friends of the Mechanical Engineering Department at the University of Wisconsin-Madison
Professor Robert D. Lorenz, who has a joint appointment in both Mechanical and Electrical Engineering, has been traveling all over the world to explain the background and applications for his newly patented, self-sensing motor design and control techniques. The Wisconsin Alumni Research Foundation (WARF) was awarded three patents last fall for Lorenz's method of making the motor itself the sensor rather than the current method of attaching external sensors.
"People have been working on this problem for years," he explained, "because of the problems with cables and connectors of external sensors, their extra cost, and lack of reliability and the sheer weight of the cabling and packaging. People are excited by this new technology, beyond my expectations." Lorenz said that it was his background in multiple disciplines that was the key to solving the sensor problem, disciplines such as electromagnetics, estimation theory, image processing, and control theory. "And we do it without degrading the properties of the motor.
His technique extracts information from the motor itself by superimposing a polyphase carrier signal on the power leads to provide a rotating excitation vector that continuously examines the electromagnetic pattern of the rotor and tracks it using inexpensive image processing and closed loop tracking techniques. Tracking images makes the system inherently very insensitive to parameters, Lorenz said. The advanced closed loop tracking techniques assure that the position, velocity, and acceleration signals are produced with high bandwidth and zero lag. Both these aspects add considerably to the value of this integrated technology.
Prof. Lorenz examines his self-sensing motor prototype with Mike Degner, PhD student.
Because this new technology reduces costs and improves reliability, quite a few large companies are already doing development work based on the patents. These include the 63 Wisconsin Electric Machines and Power Electronics Consortium (WEMPEC) companies that support Lorenz's work; Ford, General Motors, Kodak, Samsung, and Goldstar have been particularly active in their advanced product research. "Automotive and aerospace applications are superb fits," said Lorenz. "Those applications demand high reliability and low weight. There's also great potential for use in heavy vehicles where hybrid electric technologies make very good sense. Lockheed-Martin is working on using it in hybrid electric trucks and buses. Ford has been working on prototypes for power steering."
Lorenz is enthused about his invention. "Hands down, this is the most exciting topic to come along in years. It has tremendous growth potential for areas like robots, office automation, and industrial automation. My biggest problem is publishing information in enough places to explain all the dimensions." With the help of six of his graduate students and three visiting researchers, Lorenz is attempting to solve that problem.
Professor Lorenz's other current research projects (involving fourteen
other graduate students) include "Cross-Coupled Control of Multi-Axis
Machine Drives"; "Structured Neural Net Estimator Design"; "Integrated
Control of IC-Engine, Alternator and Inverter Systems"; "Sensorless
Control of Scanning Tunneling Microscopes at the Atomic Level";
"Battery State Estimation for Electric Vehicles"; "High Bandwidth
Disturbance Torque Estimation Methodologies"; and "Rotating Vector
Control of Switched Reluctance Motors."
ME Newsletter is a periodic publication of the University of
Wisconsin-Madison, Department of Mechanical Engineering. Correspondence should be sent to the address below.
Editor: Gail Gawenda
Designer: Lynda Litzkow
NOVEMBER 1997 Contents