Electricity: motive power systems – Switched reluctance motor commutation control
Reexamination Certificate
2000-10-06
2002-09-10
Ro, Bentsu (Department: 2837)
Electricity: motive power systems
Switched reluctance motor commutation control
C318S721000
Reexamination Certificate
active
06448725
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a brushless direct current (BLDC) motor, and more particularly to an apparatus for detecting a rotor position in a BLDC motor.
2. Background of the Related Art
A BLDC motor has higher efficiency and is easier to be controlled than other motors. In this respect, the BLDC motor is generally used for variable speed driving of a compressor for refrigerator/air-conditioner and a washing machine.
To drive the BLDC motor, a flux of a stator should be controlled to be electrically orthogonal or have an angle with respect to a flux of a permanent flux from a rotor. To this end, a speed of the motor is controlled in such a manner that a position of a rotor is always detected and switching states of inverter switching elements are adjusted to determine a flux position of a stator in accordance with the detected rotor position. Accordingly, the configuration for detecting the rotor position is essential for the speed control of the BLDC motor.
Furthermore, a driving mode of the BLDC motor is divided into a rectangular current waveform and a sinusoidal current waveform depending on applied phase current.
A related art apparatus for detecting a rotor position of a BLDC motor will be described with reference to the accompanying drawings.
FIG. 1
shows a speed control device of a related art BLDC motor. Referring to
FIG. 1
, the speed control device includes a BLDC motor
1
, a rotor position detector
2
, a speed detector
3
, a subtracter
4
, a speed controller
5
, a voltage controller
6
, and an inverter
7
. The rotor position detector
2
detects a phase of a voltage applied to the inverter
7
, which is output to a BLDC motor, so as to detect the rotor position. The speed detector
3
detects a driving speed of the BLDC motor
1
by a signal detected by the rotor position detector
2
. The subtracter
4
subtracts a speed detecting signal input from the speed detector
3
from a speed command input from a driving controller (not shown) to obtain a speed error. The speed controller
5
outputs a voltage command (voltage size) of the speed error output from the subtracter
4
. The voltage controller
6
determines switching time of the inverter
7
by the signal from the rotor position controller
2
and the voltage command from the speed controller
5
. The inverter
7
outputs direct current as a voltage of a variable frequency to correspond to the switching time determined by the voltage controller
6
. The BLDC motor
1
is driven by the voltage from the inverter
7
.
The operation of the aforementioned related art speed control device of the BLDC motor will be described below.
In a two-phase conducting mode in which current occurs only in a period of 120°, a speed command output from a driving controller (not shown) and a speed detecting signal &ohgr;
&ggr;
detected by the speed detector
3
are subtracted from the subtracter
4
, and the resultant value, i.e., the speed error is output to the speed controller
5
.
The speed detecting signal &ohgr;
&ggr;
from the speed detector
3
is calculated by the output of the rotor position detector
2
. An encoder or a hall sensor is used as the rotor position detector
2
. The rotor position detector
2
the rotor position of the BLDC motor
1
and outputs the detected value to the speed detector
3
and the voltage controller
6
.
Subsequently, the speed controller
5
outputs the voltage signal (voltage command), which corresponds to the speed error output from the subtracter
4
, to the voltage controller
6
.
The voltage controller
6
determines switching state of the inverter
7
in accordance with the voltage signal output from the speed controller
5
to control the speed.
At this time, the encoder or the hall sensor may be used as the rotor position detector
2
. In case of the compressor for refrigerator/air-conditioner, it is difficult to use the sensor due to environmental factors such as temperature and pressure. Accordingly, it is necessary to the rotor position from a voltage or current applied to the motor.
In the driving waveforms, the rectangular current waveform permits the rotor position to be detected from a phase voltage in a region to which voltage or current is not applied. In other words, the rotor position can be detected per electrical angle of 60° by detecting the point where the phase voltage of the open phase to which voltage or current is not applied becomes zero.
However, in the sinusoidal current waveform, voltage or current is always applied to three phases of A, B and C regardless of the rotor position. Accordingly, in the same manner as the rectangular current waveform, the rotor position cannot be detected with the voltage information of the open phase. Thus, the rotor position can be detected by detecting all the voltages or current of the three phases of A, B and C.
As shown in
FIG. 3
, the rotor position detector
2
for detecting the rotor position without using the sensor includes a current detector
51
, a voltage detector
52
, a first position detector
53
, a second position detector
54
, and a third position detector
55
. The current detector
51
detects current of each phase from a predetermined alternating current voltage of each phase output from the inverter
7
. The voltage detector
52
detects a voltage of each phase from a predetermined alternating current voltage of each phase output from the inverter. The first position detector
53
detects the rotor position in accordance with the current of the phase A detected by the current detector
51
and the voltage of the phase A detected by the voltage detector
52
. The second position detector
54
detects the rotor position in accordance with the current of the phase B detected by the current detector
51
and the voltage of the phase B detected by the voltage detector
52
. The third position detector
55
detects the rotor position in accordance with the current of the phase C detected by the current detector
51
and the voltage of the phase CA detected by the voltage detector
52
.
Each of the first to third position detectors
53
,
54
and
55
includes a first integrator
71
for integrating current of a virtual neutral point for each phase output from the current detector
51
, a second integrator
72
for integrating a voltage of a virtual neutral point for each phase output from the voltage detector
52
, a mixer
73
for mixing a signal output from the second integrator
72
, an operation signal of a signal output from the first integrator
71
and a proportional coefficient R, and an operation signal of the current of one phase among the phases and a proportional coefficient L with one another, and a comparator
74
for comparing a signal output from the mixer
73
with a predetermined signal and outputting the resultant value.
The operation of the aforementioned rotor position detector
2
will be described below.
The predetermined alternating current voltage as shown in
FIG. 2
is supplied from the inverter
7
to the respective phases A, B and C of the stator of the BLDC motor. A predetermined power is generated in the BLDC motor
1
in accordance with the predetermined alternating current voltage for each phase output from the inverter
7
.
The rotor position detector
2
detects the rotor position of the BLDC motor
1
in accordance with the predetermined alternating current voltage for each phase output from the inverter
7
and outputs the resultant signal.
In other words, the current detector
51
within the rotor position detector
15
detects current for each phase from the predetermined alternating current voltage for each phase output from the inverter
7
, and the voltage detector
52
detects the voltage for each phase from the predetermined alternating current voltage for each phase output from the inverter
7
.
The first position detector
53
detects the rotor position in accordance with the current for the phase A detected by the current detector
51
and the voltage for the phase A detected by the voltage detec
Cho Kwan Yuhl
Lee Dong Myung
Fleshner & Kim LLP
LG Electronics Inc.
Ro Bentsu
LandOfFree
Apparatus for detecting rotor position in brushless direct... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus for detecting rotor position in brushless direct..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus for detecting rotor position in brushless direct... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2833786