Motorola M68HC08 manual Process Desired Speed Setting, Closed Loop Control System

Semiconductor, Inc.

Freescale Semiconductor, Inc.

Software Design

Data Flow

5.3.6Process Commutation Time Calculation, Corrective Calculation 1, Corrective Calculation 2

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 3.3.1.5 Starting — Commutation Time Calculation and 3.3.1.3 Running — Commutation Time Calculation.

5.3.7 Process Desired Speed Setting

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

5.3.8 Processs Speed Control

The general principle of the speed PI control loop is illustrated in

Figure 5-3.

Freescale

REFERENCE

SPEED

(Speed_Desired)

-

SPEED ERROR

PI

CONTROLLER

PWM

DUTY CYCLE

(OutReg_U8)

CONTROLLED

SYSTEM

ACTUAL MOTOR

SPEED

(256*Per_Speed_MAX_Range/Per_ZCrosFlt_T2)

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

DRM028 — Rev 0		Designer Reference Manual
MOTOROLA	Software Design	81
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