RSBJEUM0001-0101 Rev. 1.01
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2.5 Calculation of PWM Duty Cycle
Figure 3.1.4
Relationship between PWM Duty Cycle and Rotation Speed Command
PWM duty cycle depends on counting values of TAi. The actual rotation speed is proportion to
PWM duty cycle, the bigger is PWM duty cycle, the faster is the actual rotation speed. In the
course of approaching rotation speed command, the carrier wave cycle pulses can be acquired
by target rotation speed every time. Every result is saved a 1dimension array including 12 data
units. Then 12 elements are added to calculate average value, a current carrier wave pulses
between zero-crossings can be gotten.
According to formula 3.3.1, the current actual rotation speed will be gotten. Consequently, the
PWM duty cycle is changed according to the conditions given below.
Condition
Amount of change
Target rotation speed > Actual rotation speed
+
∆
duty
Target rotation speed > Actual rotation speed
-
∆
duty
TB2
TAi
Sawtooth Wave
modulation
Output
Slow
Fast
