WARF: P93025US
Method and Apparatus for Transducerless Position and Velocity Estimation in Drives for AC Machines

INVENTORS

•

Patrick Jansen, Robert Lorenz

AC machine drives typically require mechanical shaft transducers to control torque and provide trajectory tracking. Shaft transducers and the associated wiring add significantly to the cost and size of the machine as well as the rate of failure of the overall system. Induction machines, which are generally more rugged and economical than other machine types, are particularly compromised by the addition of transducers. Consequently, it has long been recognized that the elimination of position or velocity transducers would be particularly beneficial in reducing costs and improving performance in motor motion control applications.

However, estimation of rotor position and velocity in the induction machine, which is by far the most common machine type and thus has the most significant commercial potential, is complicated by the smooth symmetric rotor and symmetric induced rotor currents and slip. Accurate position and velocity measurement in induction machines can only be obtained by tracking spatial phenomena within the machine. Limited success has, however, been obtained determining the rotor position in less complex machines (such as synchronous and reluctance machines that have inherent spatially dependent rotor properties that can be easily tracked). UW-Madison researchers have developed a drive system for polyphase AC machines that controls torque and tracks the trajectory in induction, synchronous and reluctance machines while eliminating shaft transducers. The drive system provides power to the stator windings of the machine, which includes a component at the fundamental drive frequency and a superimposed signal component that is at a higher frequency and of much lower power than the drive power. The superimposed signal is preferably a frequency high enough and a power low enough that the signal component does not substantially affect the motion of the rotor. The rotor of the machine has saliencies which affect the response of the stator windings to the signal frequency based on rotor rotational position.

The stator response to signal frequencies are detected and measured to provide a correlation between the signal frequency and the rotor position. The information on rotor position as a function of time and the velocity of the rotor can be utilized in a controller to provide power to the motor to drive it at a desired speed or torque, or to a desired position.

This drive system can be used on machines having inherent rotor saliency, such as some permanent magnet synchronous machines and all synchronous reluctance machines. However, it is particularly advantageous when used with induction machines, by introducing saliencies in the rotor which primarily affect only the relatively high frequency of the additional excitation signal.

• AC machines, including synchronous, reluctance and induction machines
• Vehicle and aerospace actuators, servo drives and pumps and compressors where efficiency and startup torque control are important features

• Eliminates the transducer component in AC machines
• Reduces cost, complexity and size and improves reliability of motor drives
• Existing AC machines can be easily modified to work with this drive system.

For current licensing status, please contact our team at licensing@warf.org or phone 608.262.4924. (Clicking this link will open a contact form in a popup window. If you have problems viewing the form, try disabling your popup blocker software.)