Electricity: motive power systems – Switched reluctance motor commutation control
Reexamination Certificate
2001-07-19
2002-12-17
Dang, Khanh (Department: 2837)
Electricity: motive power systems
Switched reluctance motor commutation control
C318S132000, C318S434000, C318S432000, C068S012160
Reexamination Certificate
active
06495980
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and method for sensing a laundry amount in a washing machine, and more particularly, to an apparatus and method for sensing a laundry amount in a washing machine which is capable of improving the degree of sensing of the laundry amount to heighten an efficiency of a washing machine by controlling a current and detecting a speed to reduce an error of sensing the amount of the laundry caused due to an inconstant common AC power supply especially in an inverter washing machine using a brushless DC (BLDC) motor.
2. Description of the Background Art
Recently, in view of improving a cleaning degree and reducing noise and energy consumption, washing machines mostly adopt an inverter which is able to control the speed of a motor therein. The operations of such a conventional washing machine will now be described with reference to the accompanying drawings.
FIG. 1
is a schematic circuit diagram showing the construction of a general BLDC motor driving apparatus in the conventional art.
As shown in the drawing, the BLDC motor driving apparatus includes a rectifier
10
receiving a common AC power supply voltage and rectifying it to a DC voltage, an inverter
20
receiving the DC voltage from the rectifier
10
through a smoothing capacitor C
1
and converting it to a three-phase AC voltage according to gate drive signals from a gate driving unit
60
to be described, a BLDC motor
30
driven by the three-phase AC voltage from the inverter
20
, a rotor position detector
40
detecting the position of a rotor of the BLDC motor
30
, a microcomputer
50
receiving a position detect signal from the rotor position detector
40
and outputting a control signal according to the position detect signal, and the gate driving unit
60
receiving the control signal from the microcomputer
50
and outputting the gate drive signals to the inverter
20
in response to the control signal.
The operation of the BLDC motor driving apparatus constructed as described above will now be explained.
First, the rectifier
10
rectifies a common AC power supply voltage and outputs the DC voltage. The outputted DC voltage is smoothed by the smoothing capacitor and applied to the inverter
20
.
Upon receipt of the DC voltage, the inverter
20
converts it to a three-phase AC voltage and drives the BLDC motor
30
with the three-phase AC voltage according to the gate drive signal from the gate driving unit
60
.
At this time, the rotor position detector
40
detects the position of the rotor of the BLDC motor
30
by using a position sensor and applies it to the microcomputer
50
.
Upon receipt of the position detect signal from the rotor position detector
40
, the microcomputer
50
applies the control signal generated according to the position detect signal, according to which the gate driving unit
60
receives the control signal and applies the gate drive signals to the inverter
20
in response to the control signal.
Thereafter, the operations as described above are repeatedly performed to control driving of the BLDC motor
30
.
In order to effectively control a washing/rinsing stroke, an inverter washing machine adopting the BLDC motor which performs the above operations should accurately detect the weight of the laundry, that is, the amount of the laundry.
There are two methods for sensing the amount of the laundry; one is to sense the amount of the laundry in such a manner that the motor is accelerated to a predetermined speed for a certain time period and then the power supply is cut off, during which the deceleration time period, that is, corresponding to the inertia according to the amount of the laundry; and the other is to sense the amount of the laundry by measuring the time taken to accelerate the motor to a certain speed.
Generally, the conventional system in which a pulsator receives a rotational force from a motor via a clutch and a gear or changes a direction adopts the method for sensing the amount of the laundry by measuring the inertia according to the amount of the laundry.
Meanwhile, in the case of a direct drive washing system in which a pulsator or a washing tub is driven by being directly connected with a motor, the time taken to accelerate the motor to a certain speed is measured to sense the amount of the laundry.
As shown in
FIGS. 2A through 2E
, the motor is initially positioned at a reference point and then the strength of a voltage applied to the motor is regularly increased. This is possible by controlling an inverter switch of the inverter
20
at an appropriate duty ratio as shown in FIG.
2
A.
With reference to
FIG. 2B
which shows the amplitude of a voltage applied to the motor, when the duty ratio is increased, the interval where the inverter is switched on is extended. Thus, it is noted that an average value of the voltage applied to the motor becomes gradually higher as time goes by.
With reference to
FIG. 2A
, if the amount of the laundry is greater than a reference amount of the laundry, since the motor must develop more torque to reach a certain reference speed or a reference position, a longer time is taken compared to a reference time.
Conversely, if the amount of the laundry is less than the reference amount, the motor needs less energy, and thus, it reaches the reference speed or the reference position within a shorter time than the reference time.
That is, as described above, the amount of the laundry can be detected by computing a time during which the motor or the washing tub reaches a certain speed or a certain position after a certain voltage is applied to the motor.
In this method for sensing the amount of the laundry, factors affecting the accuracy of the sensed amount of the laundry include mechanical factors such as the deflection of a bearing housing, the vibration or imbalance or shaking of a washing tub and the deflection of a damper, motor factors such as the inductance and a rotor position sensing Hall-effect sensor, the factor of a voltage detector, the factor of a voltage variation and the factor of a control circuit vibration due to temperature, etc.
Among those factors, the most influential factor is the voltage detecting error caused due to a variation of the source voltage.
That is, in the case that the amount of the laundry is sensed by the time necessary for reaching a certain reference speed or a certain reference position, a certain source voltage is to be applied regardless of the amount of the laundry or the circumstances. If a certain source voltage is not applied according to the circumstances, the computed value of the amount of the laundry will exhibit a large error from an actual value.
FIGS. 3A through 3E
are signal waveforms exhibiting an error in detecting the amount of the laundry in the case that a certain source voltage is not applied to the motor.
As shown in
FIGS. 3B and 3D
, in the case that, for the same laundry amount, if the source voltage is higher than the reference voltage, if the source voltage applied to the motor in a certain duty ratio is increased, more voltage than the reference voltage would be applied to the motor, so that the motor can reach the reference speed or the reference position earlier than the reference time.
That is, as the motor reaches the reference speed or position earlier than the reference time to by as much as &Dgr;t
1
, a laundry amount sensing error is generated corresponding to the time &Dgr;t
1
. Conversely, in the case that the source voltage is lower than the reference voltage, the motor reaches the reference speed later by as much as &Dgr;t
2
, so that it is detected that there is a greater laundry amount than the actual laundry amount corresponding to the time &Dgr;t
2
.
FIG. 3D
shows an AC power source voltage variation and a corresponding variation of a voltage of a DC link terminal in an inverter. The DC link voltage directly affects an average AC voltage applied to the motor through the inverter.
In an effort to solve the laundry amount sensing error caused due to the variation
Cho Kwan Yuhl
Kim Hak Woon
Dang Khanh
LG Electronics Inc.
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