SLLU335A August 2021 – January 2022 MCF8316A
This fault gets triggered when the estimated BEMF voltage drops below the programmed Abnormal BEMF threshold % [ABNNORMAL_BEMF_THR] of the programmed or MPET estimated BEMF constant Ke [MOTOR_BEMF_CONST] which is programmed as 40% (default value). For example, if the estimated /measured Ke is 5 mV/Hz and programmed Abnormal BEMF threshold is 40%, this fault gets triggered when the estimated Ke drops below 2 mV/Hz. This fault can also get triggered when the programmed Ke is inaccurate.
Step 1: Estimated BEMF voltage drops when the motor speed drops. Motor speed can drop due to load dynamics (sudden change in load). For applications with load dynamics, we expect speed to drop and recover back. Because the speed drops, the BEMF voltage will also drop and can trigger this fault. For such applications, it is recommended to set the Abnormal BEMF threshold to 10% to avoid triggering this fault.
Step 2: This fault can get triggered if the programmed Ke is inaccurate. Follow steps recommended in Section 3.6.2 to obtain accurate Ke.