3-Phase BLDC Motor Sensorless Control Using MC56F8013

Motor Related ParametersCommutationPer_CmtPresetT_ZCros0 T_Cmt0Zero CrossSignalNo ZeroCross detected andcommutation performedaccording to Per_CmtPresetPer_ZCrosPer_ZCros0Inside SetCalculationPer_ZCros0Per_ZCrosFlt = ( Per_ZCros + PerZCros0 ) / 2Inside PresetCalculationif ( Per_ZCrosFlt * COEF_RUN_CMT_PRECOMP_FRAC * 2 ^ COEF_RUN_CMT_PRECOMP_LSHFT) < Max_PerCmtPer_CmtPresetelsePer_CmtPreset= Per_ZCrosFlt * COEF_RUN_CMT_PRECOMP_FRAC * 2 ^ COEF_RUN_CMT_PRECOMP_LSHFT= Max_PerCmtIn the next incoming commutation (CmtTimeOut)Next cmt time= T_Cmt0 + Per_CmtPresetFigure 7-5. Using COEF_RUN_CMT_PRECOMPWith the help of this shift operation, it is possible to make the commutation period value greater thanFRAC16(1.0).7.5.3.4 COEF_RUN_CMT_PRECOMP_LSHFTCoefficient for calculating the commutation preset period.This coefficient is used with COEF_RUN_CMT_PRECOMP_FRAC to buildCOEF_RUN_CMT_PRECOMP. See 7.5.3.3 COEF_RUN_CMT_PRECOMP_FRAC.7.5.3.5 COEF_RUN_HLFCMTCoefficient for calculating the commutation period after zero crossing is detected, as described inFigure 7-6.3-Phase BLDC Motor Sensorless Control using MC56F8013, Rev. 0Freescale Semiconductor 83