High speed motor control

• US 20070296368A1
• Filed: 02/05/2007
• Published: 12/27/2007
• Est. Priority Date: 02/03/2006
• Status: Active Grant

• Current Assignee: BAE Systems Land & Armaments Incorporated (BAE Systems Plc)
• Original Assignee: BAE Systems Land & Armaments Incorporated (BAE Systems Plc)
• Inventors: Walters, Keith, Stocker, Stephen, Badzinski, David, Shoemaker, Jeffrey, Woodland, Lane
• Granted Patent: US 7,459,872 B2
• Time in Patent Office: Days
• US Class Current: 318/609
• CPC Class Codes: G05B 11/42 for obtaining a characteristic which is both proportional and time-dependent, e.g. P. I., P. I. D.
• CPC Class Codes: G05B 21/02 electric

Abstract

The present invention relates to an apparatus and method for generating digital electrical signals which are representative of the angular position and rotational velocity of a rotatable shaft or similar movable mechanical component in a servomechanism. In particular, the present invention utilizes oversampling techniques to create an accurate, flexible and responsive method for determining shaft position on a high speed motor. The present invention also includes methods for overcoming deadtime losses and velocity lag.

Claims

1. A method for calculating a position of a motor by the analog output signals of a resolver with at least two stator windings arranged in a perpendicular alignment to each other on a stator and at least one rotor winding arranged on a rotor which can turn in relation to the stator, the method comprising the following steps:

applying a sinusoidal excitation signal to the rotor winding;

deriving a sinusoidal and a cosine resolver signal depending on the angular position of the stator in relation to the rotor form the stator windings;

converting the sinusoidal and cosine resolver signals into a sine and cosine digital signal, wherein converting utilizes any two analog to digital conversion inputs capable of simultaneously sampling the sine and cosine resolver signals at least 8 times per cycle;

filtering the sine and cosine digital signals through a FIR bandpass filter for bandwidth limiting;

decimating the oversampled, filtered sine and cosine digital signal down to the baseband, said decimation by a factor K so as to create a decimated sine and cosine signal;

rectifying the decimated sine and cosine signals;

normalizing the decimated sine and cosine signals;

correcting the quadrature of the decimating sine and cosine signals;

computing an arctangent output signal to derive an angular value for the relative angular position between the rotor and the stator;

converting the arctangent output signal to a position signal, said converting including adding a velocity feed-forward factor to remove lag due to the FIR filter and a velocity lag factor to remove residual velocity lag due to system components, the converting including the steps of;

smoothing the arctangent output signal by inputting into a first integrator,

adding the velocity feed forward factor,

differentiating the arctangent output signal by a discrete IIR filter to produce an interpolated velocity signal;

integrating the interpolated velocity signal by a second integrator to produce an interpolated positions signal;

adding the velocity lag compensation factor to the interpolated position signal to produce a motor position; and

inputting a theta position for incorporation into a torque command to the motor.

2. The method of claim 1 wherein the signal processing procedure is performed by a signal processor.

3. The method of claim 2 wherein the signal processor is designed to run on a double-precision floating point processor.

4. The method of claim 1 wherein the steps related to providing a motor torque command include:

positioning a current sensor along each leg of a three phase system;

measuring the real on and off time of the switch;

calculating the deadtime between a switch command and the actual on and off time; and

operating the switch without having to incorporate a margin of error delay time.

5. An apparatus for measuring the angular position of a shaft of a motor comprising:

a resolver having a rotor, the resolver having a first output representative of the sine of the rotor angle and a second output representative of the cosine of the rotor angle;

a software based resolver-to-digital converter having a first input operably connected to the first output representative of the sine of the rotor angle and a second input operably connected to the second output representative of the cosine of the rotor angle;

said software-based resolver-to-digital converter including a processor for converting the sine of the resolver rotor angle and the cosine of the resolver rotor angle to produce a shaft velocity and a shaft angle, said processor including a routine for decimating a resolver signal by a factor K, correcting for velocity lag and incorporating a velocity feed-forward term.