AN1931D Freescale Semiconductor / Motorola, AN1931D Datasheet - Page 20

• Manufacturer Part Number: AN1931D
• Description: 3-Phase PM Synchronous Motor Vector Control
• Manufacturer: Freescale Semiconductor / Motorola

System Concept
4.3.1.1 Position Sensing
4.3.1.2 Speed Sensing
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The position and speed sensing algorithm uses all of the timers in module A and an additional timer as
a time base. Timers A0 and A1 are used for position sensing. Timer A0 permits connection of three
input signals to the quadrature timer A1, even if timer A1 has only two inputs (primary and
secondary), accomplished by using timer A0 as a quadrature decoder only. It is set to count in the
quadrature mode, count to zero, and then reinitialize. This timer setting is used to decode quadrature
signals only. Timer A1 is connected to timer A0 in cascade mode. In this mode, the information about
counting up/down is connected internally to timer A1; thus, the secondary input of timer A1 is free to
be used for the index pulse. The counter A1 is set to count to +/- ((4*number of pulses per revolution)
- 1) and reinitialize after compare. The value of the timer A1 corresponds to the rotor position.
The position of the index pulse is sensed to avoid the loss of some pulses under the influence of noise
during extended motor operation, which can result in incorrect rotor position sensing. If some pulses
are lost, a different position of the index pulse is detected, and a position sensing error is signaled. If a
check of the index pulse is not required, timer A1 can be removed and timer A0 set as the position
counter A1. The resulting value of timer A1 is scaled to range <-1; 1), which corresponds to <- ; ).
There are two common ways to measure speed. The first method measures the time between two
following edges of quadrature encoder, and the second method measures a position difference (a
number of pulses) per constant period. The first method is used at low speed. At the moment when the
measured period is very short, the speed calculation algorithm switches to the second method.
Figure 4-3. Quad Timer Module A Configuration
Freescale Semiconductor, Inc.
3-Phase PM Synchronous Motor Vector Control
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