Microchip Technology dsPICDEM MCLV-2 Manual de usuario descargar pdf (Pagina 48)

BEMF Capturing

Comparison BEMF and Vbus/2

Creating a virtual Neutral-Point and Compare with BEMF

The drawbacks of this method are:

•This method assumes that the motor

windings parameters are identical.

•The sensed BEMF signals have

positive and negative phase shifts.

•Motor-rated voltage is less than the

VDC voltage most of the time;

therefore, the zero crossing event not

always occurs at VDC/2.

Comparing the BEMF Voltage to the Motor Neutral Point. The

zero crossing sensing method described before can be

improved by having a variable threshold voltage point used to

detect the zero crossing events.

This variable voltage is in fact the motor neutral point. Often,

the motor manufacturers do not wire the motor neutral point.

However, it can be generated by using a resistor network.

Three networks are connected in parallel with the motor

windings and connected together to generate a virtual neutral

point. This is done on the MCLV-2 Board !

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Microchip Technology dsPICDEM MCLV-2 Manual de usuario Pagina 48