Melexis Nv

Melexis Technologies Nv

Detlef Klose

Thomas Freitag

Christian Paintz

Enrico Reinhardt

In a three phase BLDC motor the rotor position is monitored by detecting the zero crossing points of the induced back EMF signals BEMF_U, BEMF_V, BEMF_W in the phase windings U, V, W. As they are illustrated, the back EMF signals are substantially sinusoidal but they may in other situations be substantially trapezoidal. The three back EMF signals are 120&#xb0; out of phase with each other. In order to accurately monitor the back EMF in a phase winding, the driving waveform for each phase U, V, W includes an undriven period P close to the expected zero crossing point. The period P can be a preset part of the driving waveform or can be an interruption of the normal driving waveform in response to suitable interrupt signals. In order to determine the zero crossing points of each back EMF signal, two (or more) samples of the back EMF are taken during the undriven period P and used to interpolate the back EMF signal to determine the zero crossing point.

Relating to driving brushless DC (BLDC) motors

In order to determine the orientation of the rotor of a brushless DC motor, a sequence of current pulses may be applied to the stator phases U, V, W by the respective drivers HS, LS, HS, LS, HS, LS. The current generated in the stator phases U, V, W in turn generates a current in a shunt resistor. The current in this shunt resistoris monitored by use of a current voltage converterand a comparatorto determine when it exceeds a predetermined threshold. The rise time until the threshold current is exceeded is recorded in capture unit. A processor unitthen calculates a scalar parameter SU, SV, SW for each respective stator phase U, V, W from the recorded rise times associated with each pulse. The orientation of the magnetic axis of the rotor can then be determined by consideration of the scalar parameters SU, SV, SW of each stator phase U, V, W, as the respective rise times of each pulse are determined by the inductive properties of the respective stator phases U, V, W, which in turn are dependent upon the orientation of the rotor.

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Erfurt, Germany

Detlef Klose