Note
LOCK_LIMIT fault handling:
Closed loop acceleration rate [CL_ACC] can be increased until closed loop current reaches Lock
detection current threshold [LOCK_ILIMIT]. Closed loop current can be measured using oscilloscope.
Increasing closed loop acceleration rate [CL_ACC] might trigger LOCK_LIMIT. If this happens, reduce
closed loop acceleration rate [CL_ACC] until no longer triggers.
Option 2: Slow first cycle
Step 1: Select Slow first cycle as the motor startup method in [MTR_STARTUP].
Step 2: Select Align or slow first cycle current limit [ALIGN_OR_SLOW_CURRENT_ILIMIT] to be the same as
Current limit for Torque PI loop [ILIMIT].
Step 3: Keep increasing Align or slow first cycle current ramp rate [ALIGN_SLOW_RAMP_RATE] until the open
loop current reaches 100% of the rated current of the motor.
Step 4: Follow Step 5 to Step 9 in Option 1.
4.3.6 Gradual and Smooth Start up Motion
For applications that require slow and gradual startup with lower speed overshoots during handoff, follow the
below recommendations.
Step 1: Decrease Open loop acceleration coefficient A1 [OL_ACC_A1] and Open loop acceleration coefficient
A2 [OL_ACC_A2].
Step 2: Enable Iq ramp down after transition to closed loop [IQ_RAMP_EN]
If there is speed overshoots, it is recommended to decrease ramp rate for reducing difference between
estimated theta and open loop theta [THETA_ERROR_RAMP_RATE].
4.3.7 Improving Speed Regulation
For applications that require better speed regulation, it is recommended to tune Speed loop PI controllers
[SPD_LOOP_KP] and [SPD_LOOP_KI]. Kp coefficient of speed loop [SPD_LOOP_KP] controls the settling time
and speed overshoots. Ki coefficient of Speed loop [SPD_LOOP_KI] controls speed overshoot and ensures
regulation of speed at set value and drives the error to zero. Speed loop PI controller gains can either be
auto-tuned by MCF8316A or tuned manually.
Auto Tuning: MCF8316A auto calculates Speed loop PI controller gains by setting [SPD_LOOP_KP] and
[SPD_LOOP_KI] to zero.
Manual Tuning: Follow below steps to tune Speed loop PI controller gains manually
Step 1: Disable Speed loop [SPEED_LOOP_DIS]
Step 2: Disable closed loop [CLOSED_LOOP_DIS]
Step 3: Issue non-zero speed command to start the motor (refer to Section 3.5, step 1 on how to issue non-zero
speed command). Motor will spin in open loop.
Step 4: Allow the open loop current to settle down and then measure the peak open loop current.
Step 5: Enter 110% of measured peak phase current as the Iq reference when speed loop is disabled
[FORCE_IQ_REF_SPEED_LOOP_DIS]
Step 6: Enable closed loop [CLOSED_LOOP_DIS]. Now the motor will enter closed loop in torque mode.
Stp 7: Adjust the Iq reference [FORCE_IQ_REF_SPEED_LOOP_DIS] such that the motor speed reaches the
maximum speed.
Step 8: Speed loop Kp [SPD_LOOP_KP] is calculated using Equation 6.
www.ti.com Basic Controls
SLLU335A – AUGUST 2021 – REVISED JANUARY 2022
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MCF8316A Tuning Guide 19
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