AN1857 Freescale Semiconductor / Motorola, AN1857 Datasheet - Page 39

• Manufacturer Part Number: AN1857
• Description: A 3-Phase ac Induction Motor Control System Based on the MC68HC908MR32
• Manufacturer: Freescale Semiconductor / Motorola

Phase A
Phase B
Phase C
AN1857
MOTOROLA
The process can be described by following these points:
The process is accessed regularly in the rate given by the set PWM
frequency and the selected PWM interrupt prescaler (register PCTL2).
This process has to be repeated often enough compared to the wave
frequency to generate the correct wave shape. Therefore, for a 16-kHz
PWM frequency, it is called every fourth PWM pulse and thus the PWM
registers are updated at a 4-kHz rate (250 s).
1. Wave pointer for phase A is updated by the TableIncrement.
2. Based on the wave pointer, the required wave quadrant is
3. The quadrant pointer is calculated from the wave pointer with
4. The table value to be determined by the quadrant pointer is
5. The table value is added to (or subtracted from) the 50 percent
6. The result is loaded to the PVAL1 register; PVAL2 register is
1. The phase B wave pointer is calculated as phase A wave pointer
2. See corresponding points of the phase A calculation steps 2
3. The result is loaded to the PVAL3 register; PVAL4 register is
1. The phase B wave pointer is calculated as phase A wave pointer
2. See corresponding points of the phase A calculation steps 2
3. The result is loaded to the PVAL5 register; PVAL6 register is
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selected.
respect to the related quadrant.
fetched from the wave table.
modulus with respect to the related quadrant.
loaded automatically because of complementary PWM mode
selected during the PWM module initialization.
+1/3 of the wave period (1/3 of 0xffff equals 0x5555), which is
equivalent to 120 degrees.
through 5.
loaded automatically because of complementary PWM mode.
+2/3 of the wave period (1/3 of 0xffff equals 0xaaaa), which is
equivalent to 240 degrees.
through 5.
loaded automatically because of complementary PWM mode.
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39