Electricity: motive power systems – Limitation of motor load – current – torque or force
Reexamination Certificate
2000-11-21
2002-07-16
Ro, Bentsu (Department: 2858)
Electricity: motive power systems
Limitation of motor load, current, torque or force
C318S254100
Reexamination Certificate
active
06420844
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a BLDC (Brushless Direct Current) motor, in particular to a method for detecting position of the BLDC motor which is capable of detecting position of a rotor of the BLDC motor when a phase voltage outputted from the BLDC motor is “0”.
2. Description of the Prior Art
FIG. 1
is a block diagram illustrating a construction of an apparatus for detecting position of a BLDC (Brushless Direct Current) motor according to the conventional technology. As depicted in
FIG. 1
, the apparatus comprises a position detecting pulse generation unit
11
outputting a position detecting pulse by being inputted a phase voltage generated when the BLDC motor operates and comparing it with a reference potential set in advance, a micro computer
12
controlling the BLDC motor in accordance with a position signal after recognizing an output of the position detecting pulse generation unit
11
as the position signal, its operation will now be described in detail with reference to FIG.
2
.
FIGS. 2A through 2C
are wave form diagrams illustrating wave forms of the each output signal in FIG.
1
.
First, the BLDC motor controlled by a PWM (Pulse Width Modulation) signal generates a back electromotive force while operating. Herein, the phase voltage is equal to the back electromotive force of the BLDC motor
10
when the PWM signal applied to the BLDC motor
10
is in the ON state, the phase voltage is “0” when the PWM signal is in the OFF state and the phase voltage is generated as three phases and are separately inputted to the position detecting pulse generation unit
11
. The position detecting pulse generation unit
11
outputs the position detecting pulse by using the inputted three phases (Ref. FIG.
2
A).
The position detecting pulse generation unit
11
outputs the position detecting pulse to the micro computer
12
which is a “high potential” when the phase voltage is bigger than a reference potential Vf, or is a “low potential” when the phase voltage is smaller than the reference potential Vf.
After that, the micro computer
12
detects a time point when the position detecting pulse is became the “high potential” initially by an interrupt signal, determines the time point as a position detecting time point of the BLDC motor
10
, and operates the BLDC motor by controlling a driving unit (not shown) in accordance with the position detecting time point.
However, as depicted in
FIG. 2C
, in the apparatus for detecting position of the BLDC motor according to the conventional technology, when the phase voltage outputted from the motor is “0”, the position detecting pulse generation unit
11
can not detecting the time point when the back electromotive force is bigger than the reference potential, accordingly a position detecting error &Dgr;t occurs.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a method for detecting position of a BLDC (Brushless Direct Current) motor which is capable of detecting accurately a crossing time point of a back electromotive force and a reference potential by using a phase voltage outputted from the BLDC motor regardless of ON/OFF operation of a PWM (Pulse Width Modulation) signal inputted to the BLDC motor.
In order to achieve the object, the method of the present invention comprises a storing step storing the phase voltage outputted from the motor as a previous phase voltage with a detecting time detecting it when the phase voltage outputted from the motor is smaller than a reference potential set in advance, and a determining step determining a position detecting time point by using the stored detecting time after storing the phase voltage outputted from the motor as the present voltage when the phase voltage outputted from the motor is bigger than the reference potential set in advance.
REFERENCES:
patent: 5057753 (1991-10-01), Leuthold et al.
patent: 5635810 (1997-06-01), Goel
patent: 5783917 (1998-07-01), Takekawa
patent: 5886485 (1999-03-01), Jang
patent: 5929577 (1999-07-01), Neidorff et al.
LG Electronics Inc.
Ostrolenk Faber Gerb & Soffen, LLP
Ro Bentsu
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