MCT8317A datasheet(45/161 Pages) TI1

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SPEED_REF

SPEED_MEAS

OUT

SPEED_PI_OUT

VMAX

VMIN

Switch Close

If VMIN<OUT <VMAX

DUTY CMD

MAX_SPEED

Figure 8-32. Speed Loop

8.3.12 Input Power Regulation

MCT8317A provides an option of regulating the (input) power instead of motor speed - this input power

regulation can be done in two modes, namely, closed loop power control and power limit control. Input power

regulation (instead of motor speed) mode is selected by setting CLOSED_LOOP_MODE to 10b. This should

be accompanied by setting CONST_POWER_MODE to 01b for closed loop power control or to 10b for power

limit control. In either of the power regulation modes, the maximum power that MCT8317A can draw from the

DC input supply is set by MAX_POWER - the power reference (POWER_REF in Figure 8-33) varies as function

of the duty command input (DUTY_CMD) and MAX_POWER as given by Equation 4. The hysteresis band for

the power reference is set by CONST_POWER_LIMIT_HYST. In both the power regulation modes, the minimum

power reference is set by MIN_DUTY x MAX_POWER.

POWER_REF = DUTY_CMD x MAX_POWER

(4)

In both the power regulation modes, MCT8317A uses the same PI controller parameters as in the speed loop

mode. Kp and Ki coefficients are configured through SPD_POWER_KP and SPD_POWER_KI. 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. The key difference between closed loop power control and power

limit control is in the when the PI controller decides the DUTY_OUT (see Figure 8-8) applied to FETs.

In closed loop power control, DUTY_OUT is always equal to POWER_PI_OUT from the PI controller

output in Figure 8-33. However, in power limit control, the PI controller decides the DUTY_OUT only if

POWER_MEAS > POWER_REF + CONST_POWER_LIMIT_HYST. If POWER_MEAS < POWER_REF +

CONST_POWER_LIMIT_HYST, the PI controller is not used and DUTY_OUT is equal to DUTY_CMD.

Essentially, in closed loop power control, input power is always actively regulated to POWER_REF whereas,

in power limit control, input power is only limited to POWER_REF and not actively regulated to POWER_REF.

When output of the power PI loop saturates, the integrator is disabled to prevent integral wind-up.

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MCT8317A

SLLSFQ2 – JANUARY 2023

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MCT8317A Datasheet(PDF) 45 Page - Texas Instruments