AN1911 Freescale Semiconductor / Motorola, AN1911 Datasheet - Page 15

• Manufacturer Part Number: AN1911
• Description: 3-Phase AC Motor Control with V/Hz Speed Open Loop Using DSP56F80X
• Manufacturer: Freescale Semiconductor / Motorola

Freescale Semiconductor, Inc.
Software Design
6.1.5 PWM Generation
Process Description
This process generates a system of three phase sinewaves with addition of third harmonic component
o
shifted 120
to each other using mcgen3PhWaveSine3rdHIntp function from the Motor Control
function library.
The function is based on a fixed wave table describing the first quadrant of sine wave stored in Data
memory of the DSP. Due to symmetry of the sine function, data in other quadrants are calculated using
the data of first quadrant. This saves data memory space. In figure
Figure 6-4
there is an explanation
o
of sinewave generation for phase A (for simplicity). Phase B and C are shifted 120
with respect to
Phase A.
$FWXDO3KDVH Q
3KDVH,QFUHPHQW
$FWXDO3KDVH Q
'XW\&\FOH3KDVH$

R
R
Figure 6-4. Sinewave Generation
Each time the waveform generation function is called, ActualPhase from previous step is updated by
PhaseIncrement, and according calculated phase the value of sine is fetched from the sine table (using
function tfr16SinPIxLUT from DSP functional library). Then it’s multiplied by the Amplitude and
passed to the PWM. For explaining the 3 phase waveform generation with 3rh harmonic addition see
the following formulas:
Indirect Power Factor Correction Using DSP56F80X
15
For More Information On This Product,
Go to: www.freescale.com