01-11-2012, 05:10 PM
Filtering of Hall-Sensor Signals for Improved Operation of Brushless DC Motors
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INTRODUCTION
BRUSHLESS dc (BLDC) motors are becoming very inexpensive
and popular in various applications. Although
there have been numerous sensorless approaches proposed in
the literature, the Hall-sensor-controlled BLDC motors are preferred
in many applications due to their relative simplicity, low
cost, and reliable operation in wide range of loading conditions
and speeds. The most common operation is achieved using the
120◦ switching logic to control the six-step voltage-source inverter
[1]–[3]. To achieve a balanced operation among the motor
phases, the Hall sensors must be placed exactly 120 electrical degrees
apart. However, in many low-precision motors, the sensor
positioning could be quite inaccurate [4], [5]. Many advanced
controls also rely on Hall-sensor position/speed estimation [4],
in which case their performance will be affected.
EFFICIENT ALGORITHM AND ITS IMPLEMENTATION
The filtering block shown in Fig. 2 accepts the original Hallsensor
signals (input), and provides the switching circuitry with
the modified signals (output). The purpose of filtering is to
remove harmonics from the sequence τ (n). This can be achieved
using averaging filters that have the following form:
CONCLUSION
This letter describes a very efficient and straightforward approach
for implementing the averaging of the Hall-sensor signals
for improving the operation of low-precision BLDC motor
drive systems. Using this approach, any of the filters can be
readily implemented either in the code of existing motor controllers,
or as a dongle in a low-power standalone programmable
integrated circuit.