SLLU336A May   2021  – January 2022 MCT8316A

 

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4.3.4 Faster startup timing

Startup time is the time taken for the motor to reach closed loop from zero speed. For applications that require quick startup time, we recommend choosing either Initial Position Detection (IPD) or Align as the startup method.

Option 1: Initial Position Detection (IPD)

Step 1: Select IPD [MTR_STARTUP] as the motor startup method.

Step 2: Increase IPD current threshold [IPD_CURR_THR] to rated current of the motor. Use equation 4 to choose the correct IPD_CURR_THR.

Step 3: Increase IPD clock value [IPD_CLK_FREQ] to higher frequency up to a value where the device does not trigger IPD frequency fault. Check section 3.4.4 (Step 3) for more details.

Step 4: Select IPD repeating times [IPD_REPEAT] to 1 time.

Step 5: Configure IPD release mode [IPD_RLS_MODE] to Tri state.

Step 6: Select Open loop current limit [OL_ILIMIT] to be the same as cycle by cycle current limit [ILIMIT].

If the device triggers cycle by cycle current limit [CBC_ILIMIT], it is recommended to increase [ILIMIT] upto the stall current of the motor. Configuring this to a value higher than motor stall current might overheat or damage the motor.

Step 7: Increase Open loop acceleration coefficient A1 [OL_ACC_A1] and Open loop acceleration coefficient A2 [OL_ACC_A2].

Note:

A1 and A2 can be increased until open loop current reaches Lock detection current threshold [LOCK_ILIMIT]. Open loop current can be measured using oscilloscope.

Increasing Open loop acceleration coefficient A1 [OL_ACC_A1] and Open loop acceleration coefficient A2 [OL_ACC_A2] might trigger LOCK_LIMIT or CBC_ILIMIT. If this happens, reduce A1 and A2 until LOCK_LIMIT no longer triggers.

Step 8: For ultra-fast startup time (less than 100 ms) it is recommended to follow below steps.

  • Disable auto-handoff [AUTO_HANDOFF].

  • Configure Open loop handoff cycles [OL_HANDOFF_CYCLES] to 3.

  • Configure INTEG_ZC_METHOD to Integration.

  • Enable Dynamic degauss [DYN_DEGAUSS_EN]

  • Configure open to closed loop handoff threshold [OPN_CL_HANDOFF_THR] to a value lesser than or equal to 20 Hz.

For startup times above 100ms, it is recommended to follow below steps.

  • Enable auto-handoff [AUTO_HANDOFF].

  • Configure Open loop handoff cycles [OL_HANDOFF_CYCLES] to 6.

  • Enable Dynamic degauss [DYN_DEGAUSS_EN]

Note:

If Abnormal speed fault [ABN_SPEED] gets triggered, it is recommended to decrease open loop acceleration constants [OL_ACC_A1] and [OL_ACC_A2] and also retune IPD by increasing the IPD current threshold [IPD_CURR_THR] and IPD repeat times [IPD_REPEAT].

Step 9: Increase Closed loop acceleration rate [CL_ACC]

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: Align

Step 1: Select align as the motor startup method in [MTR_STARTUP].

Step 2: Configure align time [ALIGN_TIME] to 5 ms.

Step 3: Follow Step 6 to Step 9 in Option 1.

Figure 4-2 shows FG, phase current and motor electrical speed waveform. Motor takes 50 ms to reach target speed from zero speed.

Figure 4-2 Phase current, FG and motor speed - Faster startup time.

Note:

If Abnormal speed fault [ABN_SPEED] or Loss of sync [LOSS_OF_SYNC] fault gets triggered, it is recommended to follow below debug steps.

  1. Select Double align as the motor startup method in [MTR_STARTUP].

  2. Increase align time [ALIGN_TIME].

  3. Configure align current threshold [ALIGN_CURR_THR] to 50% of cycle by cycle current limit [ILIMIT].

  4. Configure First cycle frequency select [FIRST_CYCLE_FREQ_SEL] to 0.