position estimation and therefore the motor commutation and rotation. It is recommended to estimate the motor
parameters before motor startup to minimize the impact caused due to possible parameter variations.
The MCF8316A has Motor parameter extraction tool (MPET) which estimates the motor phase resistance, the
motor phase inductance and the motor Back-EMF constant. Go to “Control Configuration - Motor parameter
extraction tool (MPET)”.
Step 1: Enable Measure motor resistance [MPET_R], Measure motor inductance [MPET_L] and Motor BEMF
constant [MPET_Ke].
Step 2: Enable MPET Start command [MPET_CMD]. Make sure the motor is stationary before enabling MPET
start command.
Step 3: After successful motor parameter extraction, copy the estimated parameters to the respective shadow
registers by enabling MPET write to shadow register flag.
Note
1. If the device triggers MPED_IPD_FAULT, increase the MPET IPD Current threshold till the rated
current of the motor.
2. If the device triggers MPED_IPD_FAULT, decrease MPET Open loop slew rate
[MPET_OPEN_LOOP_SLEW_RATE].
3. If the fault still persists, increase MPET Open loop current reference
[MPET_OPEN_LOOP_CURRENT_REF] and decrease MPET Open loop speed reference
[MPET_OPEN_LOOP_SPEED_REF]
shows the phase current waveform during motor parameter measurement.
current waveform during R, L and Ke measurement. Bottom half of
shows the IPD current waveform
during R and L measurement. R is measured during the rising of phase current and L is measured during the
falling of phase current. After R and L measurement, motor spins in open loop. Once the speed reaches MPET
open loop speed reference [MPET_OPEN_LOOP_SPEED_REF], motor is coasted. BEMF voltage of all three
phases are measured and Ke is calculated.
Figure 4-5. MPET - Phase current
Figure 4-6. IPD current waveform during Rand L
measurement
4.3.2 Initial Speed Detection of the Motor for Reliable Motor Resynchronization
The Initial Speed Detection (ISD) function is used to identify the initial condition of the motor. It is important to
know the initial condition of the motor for reliable resynchronization. Motor resynchronization failures can occur
when the device attempts to start the motor while the motor is coasting or spinning in the direction opposite to
the intended direction of spin. Motors can coast in applications that require frequent motor starts and stops, or if
the motor Is being forced externally or if there is a power interruption. Motors can spin in the direction opposite to
the intended direction of spin if motor phase wires are connected to OUTA, OUTB and OUTC in wrong sequence
or when wrong direction command is issued. Motors with higher inertia coast for a longer period of time. It is
recommended to have ISD enabled in applications that require frequent motor starts and stops and use higher
inertia motors.
Basic Controls
SLLU335A – AUGUST 2021 – REVISED JANUARY 2022
MCF8316A Tuning Guide
15
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