Slow work

Engineers at Nottingham University aim to design a drive that overcomes sensorless designs' inability to operate at zero or low speeds.

With industrial partners

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, they hope to develop drives for a variety of applications.

Controlling AC motors that can change speed and torque quickly is essential for advanced industrial applications, from machine tools to large drives such as those in paper mills.

However, they require a lot of instrumentation, such as position sensors mounted on the drive shaft, which affect the reliability of the system, as there are numerous things that can go wrong. The signal from the motor to the control can be distorted by electromagnetic interference and, in a factory setting, it is easy for a cable to be broken.

The group is trying to control the motor without measuring position or torque.

'Our "box of tricks" that does all the intelligent stuff is a power converter, which takes mains frequency fixed-voltage supply and converts it into a variable frequency voltage supply,' said project leader Mark Sumner. 'Three power cables connect it to the motor, with no feedback signals from the motor.'