AN1946 Datasheet, PDF (1/35 Pages) STMicroelectronics – SENSORLESS BLDC MOTOR CONTROL AND BEMF SAMPLING METHODS WITH ST7MC

AN1946
APPLICATION NOTE
SENSORLESS BLDC MOTOR CONTROL
AND BEMF SAMPLING METHODS WITH ST7MC
1 INTRODUCTION
Permanent Magnet Brushless DC Motors are replacing brush motors in numerous applica-
tions as they offer significant energy efficiency improvements, lower acoustic noise and better
reliability to name a few advantages. To be driven and controlled properly, 3-phase Perma-
nent Magnet Brushless motors require a 3 half bridge "inverter" topology to deliver a 6-step or
sine wave signal. They also require the electronic commutation of motor phases to respect the
synchronization between statoric flux and the permanent magnet of the rotor.
Generally, a BLDC motor drive uses one or more sensors giving positional information to keep
synchronization. Such implementation results in a higher drive cost due to sensor wiring and
implementation in the motor. Moreover, sensors cannot be used in applications where the
rotor is in closed housing and the number of electrical entries must be kept to a minimum such
as in a compressor, or in applications where the motor is immersed in a liquid such as some
pumps.
Therefore, for cost and technical reasons, the BLDC sensorless drive is an essential capability
of a brushless motor controller. The ST7MC allows various implementations of sensorless
BLDC control with the lowest possible system cost while maintaining the highest performance.
This paper describes in detail these topologies, their advantages and drawbacks, as well as
their practical implementation. Most of the examples in this paper make use of the ST7MC-
KIT/BLDC Starter kit which allows easy implementation of most topologies described.
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Rev. 2
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