AN1931D Freescale Semiconductor / Motorola, AN1931D Datasheet - Page 22

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

System Concept
4.3.1.2.1 Minimum and Maximum Speed Calculation
Note:
22
The minimum speed is calculated with the following equation:
where:
In the application, the quadrature encoder has 1024 pulses per revolution and a calculation period of
900 s was chosen on the basis of a motor mechanical constant. Thus,
minimum speed as 16.3 rpm.
The maximum speed can be expressed as:
where:
Substitution in
maximum speed of 263672rpm. As demonstrated, the algorithm can measure speed across a wide
range. Because such high speed is not practical, the maximum speed can be reduced to a required
range by the constant k in
where:
In this application, the maximum measurable speed is limited to 6000rpm.
N
T
N
T
k
N
T
To ensure an accurate speed calculation, you must choose the input clock of timer A2 so that
the calculation period of speed processing (in this case, 900 s) is represented in timer A2 as a
value lower than 0x7FFFH (900.10
calc
clkT2
clkT2
min
max
max
(EQ 4-2.)
Freescale Semiconductor, Inc.
3-Phase PM Synchronous Motor Vector Control
(EQ
for N and T
For More Information On This Product,
4-1.). The constant k can be calculated as:
k
=
max
Go to: www.freescale.com
min
Minimum obtainable speed [rpm]
Number of pulses per revolution [1/rev]
Period of speed measurement (calculation period) [s]
Maximum obtainable speed [rpm]
Number of pulses per revolution [1/rev]
Period of input clock to timer A2 [s]
Scaling constant in
Maximum of the speed range [rpm]
Number of pulses per revolution [1/rev]
Period of input clock to timer A2 [s]
clkT2
---------------------------------- -
4NT
=
=
--------------------- -
4NT
(timer A2 input clock = system clock 36 MHz/2) yields a
clkT2 max
-6
------------------ -
4NT
60
/T
60
clkT2
60
clkT2
calc
<=0x7FFFH).
(EQ 4-1.)
(EQ 4-1.)
calculates the
MOTOROLA
(EQ 4-1.)
(EQ 4-2.)
(EQ 4-3.)