MCT8317A datasheet(44/161 Pages) TI1

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Phase

BEMF

}

NEG

}

POS

Phase

Voltage

Phase

BEMF

Phase

Voltage

(a)

(b)

Figure 8-30. Positive and Negative Lead Angle Definition

8.3.10.4 Closed loop accelerate

To prevent sudden changes in the torque applied to the motor which could result in acoustic noise, the

MCT8317A device provides the option of limiting the maximum rate at which the speed command can change.

The closed loop acceleration rate parameter sets the maximum rate at which the speed command changes

(shown in Figure 8-31). In the MCT8317A, closed loop acceleration rate is configured through CL_ACC.

Speed command

input

Speed command

after closed loop

accelerate buffer

Closed loop

accelerate settings

Figure 8-31. Closed loop accelerate

8.3.11 Speed Loop

MCT8317A has a speed loop which can be used to maintain constant speed under varying operating conditions.

Speed loop is enabled by setting CLOSED_LOOP_MODE to 01b. Kp and Ki coefficients are configured through

SPD_POWER_KP and SPD_POWER_KI. The output of speed loop (SPEED_PI_OUT) is used to generate the

DUTY_OUT (see Figure 8-8). The PI controller output upper (VMAX) and lower bound (VMIN) saturation limits are

configured through SPD_POWER_V_MAX and SPD_POWER_V_MIN respectively. When output of the speed

loop saturates, the integrator is disabled to prevent integral wind-up. The speed loop PI controller is as in Figure

8-32.

SPEED_REF is derived from duty command input and maximum motor speed (MAX_SPEED) configured by

user (see Equation 3). In speed loop mode, minimum SPEED_REF is set by MIN_DUTY * MAX_SPEED.

SPEED_REF = DUTY CMD * MAX_SPEED

(3)

MCT8317A

SLLSFQ2 – JANUARY 2023

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