TMS320F240 DSP Solution for Obtaining Resolver Angular Position and Speed(pdf 23)英文.pdf

Application Report
SPRA605 - February 2000
TMS320F240 DSP Solution for Obtaining Resolver
Angular Position and Speed
Martin Staebler DSP Field Application
ABSTRACT
This application report presents a TMS320F240 DSP solution for obtaining the angular
position and speed of a resolver.
A resolver is an absolute mechanical position sensor used, for example, in servo
applications. It is basically a rotating transformer. The sinusoidal input reference is amplitude
modulated with the sine and cosine of the mechanical angle, respectively. These two output
signals have to be decoded to obtain the angular position.
For decoding the resolver output signals, a basic method is introduced. It utilizes
undersampling and an inverse tangent function. To achieve a higher angular resolution an
improved method, which adds oversampling techniques is used. Due to an integral invariant
filter, which is bination of an IIR and FIR filter, the digitized angular position does not
suffer any velocity lag.
Thanks to its peripherals, the Texas Instruments TI TMS320F240 DSP can be ideally used
for decoding the two resolver output signals as well as for generating the input reference
frequency. The hardware interfacing of the resolver to the TMS320F240 is shown and the
software realization of the improved method on the TMS320F240 is documented. All
software routines are patible. The angular resolution achievable with the
TMS320F240 is up to 14 bits, at a CPU loading of 13%.
Thus, the TMS320F240 will eliminate the cost for the external resolver-to-digital conversion
IC, since the algorithm runs in addition to the motor control task.
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2 The Resolver – An Absolute Angle Transducer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3 Obtaining Angular