AN1910 Freescale Semiconductor / Motorola, AN1910 Datasheet - Page 15

• Manufacturer Part Number: AN1910
• Description: 3-Phase AC Motor Control with V/Hz Speed Closed Loop Using the DSP56F80X
• Manufacturer: Freescale Semiconductor / Motorola

$FWXDO3KDVH Q
The function is based on a fix wave table describing the first quadrant of sine wave stored in data
memory of the DSP. Due to symmetry of sine function, data in other quadrants are calculated using the
data of first quadrant. It saves data memory. The sinewave generation for phase A, simplicity, is
explained in
Each time the waveform generation function is called, ActualPhase from previous step is updated by
PhaseIncrement, and according calculated phase the value of sine is fetched from the sine table (using
function tfr16SinPIxLUT from DSP functional library). Then it’s multiplied by amplitude and passed
to the PWM. Explanation of the 3-phase waveform generation with 3rh harmonic addition, see the
following formulas.
Where PWMA, PWMB and PWMC are calculated, dutycycles passed to PWM driver and amplitude
determine the level of phase voltage amplitude.
'XW\&\FOH3KDVH$
3KDVH,QFUHPHQW
PWMA
PWMB
PWMC
Figure
$FWXDO3KDVH Q
=
=
=
------ - Amplitude
------ - Amplitude
------ - Amplitude
3-Phase AC Motor Control with V/Hz Speech Closed Loop
1
1
1
6-4.
3
3
3
Freescale Semiconductor, Inc.
Phases B and C are shifted 120
For More Information On This Product,
Figure 6-4. Sinewave generation
R
Go to: www.freescale.com
sin
sin
sin
+
–
–
1
-- -
6
120
240
sin
0
0

3
+
+
o
1
-- -
6
1
-- -
6
with respect to Phase A
+
sin
sin
0.5
3
3
+
+
0.5
0.5
.
Software Design
(EQ 6-1.)
R
15