Motorola M68HC08 Reference Manual page 81

5.3.6 Process Commutation Time Calculation, Corrective Calculation 1, Corrective
Calculation 2
5.3.7 Process Desired Speed Setting
5.3.8 Processs Speed Control
DRM028 — Rev 0
MOTOROLA
Freescale Semiconductor, Inc.
These processes provide calculations of commutation time intervals
(periods) (Per_ZCros, Per_ZCrosFlt), from captured time (T_Cmt
T_ZCros, T_ZCros0), and sets Timer 2 with variable T2. These
calculations are described in
Calculation and 3.3.1.3 Running — Commutation Time
The desired speed, held in register Speed_Desired, is calculated from
the following formula:
Speed_Desired = Sp_Input*Coef_Speed_Inp/255 +
Speed_Min_U8
The general principle of the speed PI control loop is illustrated in
Figure 5-3.
REFERENCE
SPEED
SPEED
(Speed_Desired)
ERROR
-
Figure 5-3. Closed Loop Control System
The speed closed loop control is characterized by the feedback of the
actual motor speed.
The actual motor speed is calculated from zero crossing period:
Actual motor speed = 256*Per_Speed_MAX_Range/Per_ZCrosFlt_T2
Software Design
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3.3.1.5 Starting — Commutation Time
PWM
DUTY CYCLE
(OutReg_U8)
PI
CONTROLLER
(256*Per_Speed_MAX_Range/Per_ZCrosFlt_T2)
Software Design
Data Flow
,
Calculation.
CONTROLLED
SYSTEM
ACTUAL MOTOR
SPEED
Designer Reference Manual
81