Electricity: motive power systems – Induction motor systems – Primary circuit control
Reexamination Certificate
2001-01-18
2003-02-25
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Induction motor systems
Primary circuit control
C318S132000, C318S254100, C318S434000, C318S700000, C318S701000, C318S721000, C318S722000, C318S599000, C318S800000, C318S811000
Reexamination Certificate
active
06525506
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a current restriction circuit of an inverter refrigerator, in particular to a current limit circuit of an inverter refrigerator which is capable of driving a compressor of a refrigerator stably by making current set in advance flow when excess current flows due to an outside factor by adjusting a PWM duty cycle of a pulse width modulation controlling a power element.
2. Description of the Prior Art
In general, an inverter refrigerator is a refrigerator which is capable of optimizing a cooling air discharge and power consumption quantity by improving defects of an ON-OFF type refrigerator turning on/off a compressor with a certain time interval.
The inverter refrigerator comprises a SMPS (Switching Mode Power Supply), switching elements connected to a brushless DC motor (hereinafter, it is referred to a BLDC motor), a gate drive for controlling the switching elements, a position/speed detector for detecting a position and speed of a rotator of the BLDC motor, and a momentary excess current protection circuit.
FIG. 1
is a construction profile illustrating an excess current protection channel of the conventional inverter refrigerator, it comprises a rectification unit
10
for outputting a rectified and smoothed DC power source by rectifying and smoothing a common AC power source inputted from outside, a SMPS
11
for being inputted the DC power rectified and smoothed from the rectification unit
10
and providing the power to each circuit unit inside of an apparatus, an inverter unit
13
for being inputted the DC power provided from the SMPS
11
in accordance with a certain control signal, converting it into three phase power, and outputting it, an excess current detecting unit
12
for detecting excess current generation due to load change from the SMPS
11
, a BLDC motor
16
driven by the 3 phase AC power of the inverter unit
13
, a position/speed detector
17
for detecting the position and speed of the rotator of the BLDC motor
16
, a microcomputer
15
for controlling a pulse width modulation signal by comparing position/speed of the rotator outputted from a detecting signal of the position/speed detector
17
with a requested phase angle and phase difference, and generating a pulse width modulation signal by being inputted an excess current detecting signal from the excess current detecting unit
12
, and a gate driving unit
14
for controlling ON/OFF of the inverter unit
13
in accordance with the pulse width modulation signal outputted from the microcomputer
15
.
The operation of the excess current protecting circuit of the conventional inverter refrigerator will now be described.
First, when the common AC power source inputted from outside is inputted to the rectification unit
10
, the rectification unit
10
outputs the rectified and smoothed DC power source to the SMPS
11
. The SMPS
11
inputted the DC power source provides a power to the each circuit unit as a transformer having different winding ratio each other.
The inverter unit
13
inputted the DC power outputted from the SMPS
11
outputs three phase power to the BLDC motor
16
by being ON/OFF in accordance with a control signal outputted from the gate driving unit
14
.
When the BLDC motor operates, the position/speed detector
17
detects the speed and position of the motor rotator, and applies it to the microcomputer
15
.
The microcomputer
15
judges the position and speed of the rotator by using the position and speed detecting signal of the BLDC motor rotator outputted from the position/speed detector
17
, compares the detected position and speed with the requested phase angle and phase difference, and applies a PWM (Pulse Width Modulation) signal according to it to the gate driving unit
14
.
Herein, the SMPS
11
is constructed with a plurality of windings having different winding ratio each other, accordingly a short circuit occurs frequently due to mutual contact of the windings, and excess current is generated by the load change due to it. Herein, the excess current detecting unit
12
detects the excess current due to the load change of the SMPS
11
, and applies the excess current detecting signal in accordance with it to the microcomputer
15
.
And, the microcomputer
15
outputs a control signal for turning off all switching elements of the inverter
13
to the gate driving unit
14
in order to protect damage of the compressor due to the excess current. It will now be described in more detail with reference to accompanying drawings.
FIGS. 2
a
~
2
c
are waveform diagrams illustrating the operation of the conventional inverter refrigerator excess current protection circuit in the excess current generation. For example, as depicted in
FIGS. 2
a
and
2
b,
when higher than
9
A arm short DC peak voltage is generated, the microcomputer
15
outputs the pulse width modulation signal to the gate driving unit. And, as depicted in
FIG. 2
c,
the gate driving unit
14
protects the compressor by outputting the control signal to the inverter unit
13
in order to make the BLDC motor
16
turn off for 2 seconds ~7 minutes.
However, in the conventional technology, when the excess current is generated, because the compressor is OFF for a certain time (2~7 seconds), mobility of the compressor lowers. In addition, in order to prevent turning off of the compressor during the operation and reduce mobility defect, the DC peak voltage is set as a voltage level corresponding to a high current of the arm short type, for example
9
A, accordingly the efficiency lowers due to damage of the power elements or demagnetization of the motor of the compressor.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a current limit circuit of an inverter refrigerator which is capable of making limit current set in advance flow into a motor of a compressor when excess current is generated by adjusting a PWM duty cycle of a pulse width modulation controlling the operation of current elements.
In order to achieve the above-mentioned objects, the current limit circuit of the inverter refrigerator in accordance with the present invention comprises a power unit
102
for providing DC power source to a BLDC motor
16
by being inputted an AC power source, a current detecting unit
101
for detecting current flowed into the BLDC motor
16
, a control unit
200
for outputting a current limit control signal by being inputted a current detecting signal outputted from the current detecting unit
101
and comparing the present detecting current level corresponding to the current detecting signal with the current limit level set in advance, and a gate driving unit
14
for controlling the operation of the power unit
102
in accordance with the current limit signal outputted from the control unit
200
.
In order to achieve the above-mentioned objects, the present invention comprises a setting process for setting a current limit level flowed into the motor, a comparing process for comparing the set current limit level with the present detecting current level, and a control process for controlling the current limit level so as to be flowed into the motor when the detecting current level is higher than the set current limit level.
REFERENCES:
patent: 4879502 (1989-11-01), Endo et al.
patent: 5353604 (1994-10-01), Oguni et al.
patent: 5483141 (1996-01-01), Uesugi
patent: 6244061 (2001-06-01), Takagi et al.
LG Electronics Inc.
Nappi Robert E.
Ostrolenk Faber Gerb & Soffen, LLP
Smith Tyrone W
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