KR20200053925A - Power transforming apparatus having noise reduction function, compressor including the same and the method for the same - Google Patents

Abstract

The present invention relates to a power converting device. Particularly, the present invention relates to a power converting device capable of reducing electromagnetic interference (EMI) noise, a compressor including the same, and a controlling method thereof. The power converting device comprises: an inverter including a plurality of switching elements and generating an alternating current (AC) signal for driving a motor; a gate driving unit driving the plurality of switching elements; a variable resistor unit connected between the gate driving unit and the switching element; an output current detection unit detecting output current of the inverter; and a control unit transmitting a control signal to the gate driving unit and transmitting the signal of changing a resistance value to the variable resistor unit to have different modulation resistance values in accordance with the output current detected by the output current detection unit.

Description

Power conversion device, compressor including same, and control method thereof {Power transforming apparatus having noise reduction function, compressor including the same and the method for the same}

The present invention relates to a power conversion device, and more particularly, to a power conversion device capable of reducing electromagnetic interference (EMI) noise, a compressor including the same, and a control method thereof.

Generally, a compressor uses a motor as a driving source. AC power is supplied to the motor from the power converter.

It is generally known that such a power conversion device mainly constitutes a rectification unit, a power factor control unit, and an inverter-type power conversion unit.

First, the commercial voltage of the AC output from the commercial power supply is rectified by the rectifying unit. The voltage rectified by the rectifying unit is supplied to a power conversion unit such as an inverter. At this time, the power converter generates AC power for driving the motor using the voltage output from the rectifier.

In some cases, a DC-DC converter may be provided between the rectifier and the inverter to improve power factor.

Such an inverter converts power using switching elements that switch at a high speed, and electromagnetic interference (EMI) noise may occur in this process.

In addition, as electronic devices gradually evolve to include smart functions, EMI noise due to high-speed switching is gradually deteriorating and standby power is also deteriorating.

In order to reduce the EMI noise, a noise filter core may be used, or a circuit for frequency modulation phase delay may be used.

However, when only the noise filter core is used, such noise reduction performance is deteriorated, and the circuit for frequency modulation phase delay requires a complicated circuit configuration.

In order to reduce this noise, filters with a combination of inductors and capacitors are additionally installed to limit them, and EMC films are used and ground paths are also produced. In addition, inductors may be mounted on the windings in addition to these means.

When this method is applied, the effect of reducing noise is improved, but the overall circuit driving efficiency is lowered, it takes up a large volume, and may be a cause of increase in manufacturing cost.

Accordingly, there is a need for a method capable of increasing the performance of reducing EMI noise without complicated circuit configuration.

The technical problem to be achieved by the present invention is to minimize the at least one of the additional area for additional cost / circuit change / circuit configuration, power conversion device capable of efficiently improving the EMC and EMI characteristics, a compressor including the same and control thereof I want to provide a method.

As a first aspect for achieving the above technical problem, the present invention includes an inverter for generating an AC signal for driving a motor including a plurality of switching elements; A gate driver driving the plurality of switching elements; A variable resistor connected between the gate driver and the switching element; An output current detector for sensing the output current of the inverter; And a control unit transmitting a control signal to the gate driving unit and transmitting a signal varying the resistance value to the variable resistance unit to have a different modulation resistance value according to the output current sensed by the output current detection unit. have.

In addition, the variable resistor unit may be a digital variable resistor whose resistance value is adjusted according to a voltage value transmitted from the controller.

In addition, the modulation resistance value may be increased according to the output current sensed by the output current detector.

In addition, the modulation resistance value may be increased in proportion to the output current sensed by the output current detector.

Further, the control unit may control the variable resistor unit such that the modulation resistance value determined according to the output current sensed by the output current detector changes.

In addition, the control unit may control the variable resistance unit such that the modulation resistance value varies within a predetermined range around the determined modulation resistance value.

As a second aspect for achieving the above technical problem, the present invention can provide a compressor including the power conversion device described above.

As a third aspect for achieving the above technical problem, the present invention includes an inverter for generating an AC signal for driving a motor including a plurality of switching elements, a gate driver for driving the plurality of switching elements, and the gate driver and the A method of controlling a power conversion device including a variable resistor connected between switching elements, the method comprising: sensing an input voltage and an output current of the inverter; Controlling the switching element by transmitting a control signal to the gate driver; And outputting a control voltage to the variable resistor unit to have different modulation resistance values according to the change of the output current.

In addition, in the step of outputting a control voltage to the variable resistor unit, the modulation resistance value may be controlled to increase in proportion to the output current.

In addition, the step of outputting a control voltage to the variable resistor section, determining the control voltage of the variable resistor section according to the output current change; Varying the determined control voltage in a predetermined range; And outputting the variable control voltage.

According to the present invention, by having a substantially aperiodic PWM driving voltage by resistance value modulation, noise can be dispersed, and thus EMC and EMI can be improved.

As described above, according to an embodiment of the present invention, EMC and EMI can be improved by stabilizing a driving signal.

In addition, while improving the EMC and EMI, the overall circuit driving efficiency is not lowered, the volume of the circuit does not increase, and the manufacturing cost does not increase.

1 is a block diagram showing a power conversion apparatus according to an embodiment of the present invention.
2 is a circuit diagram showing a power conversion apparatus according to an embodiment of the present invention.
3 is a block diagram showing a part of a power conversion apparatus according to an embodiment of the present invention.
4 is a graph showing the preceding term according to the input voltage of the variable resistance unit of the power conversion apparatus according to an embodiment of the present invention.
5 is a flowchart illustrating a control method of a power conversion apparatus according to an embodiment of the present invention.
6 is a flow chart showing a specific process for controlling the variable resistor of the power converter according to an embodiment of the present invention.
7 is a signal diagram showing a drive signal of a power conversion apparatus according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

While the invention allows for various modifications and variations, specific embodiments thereof are illustrated and illustrated in the drawings, which will be described in detail below. However, it is not intended to limit the invention to the particular forms disclosed, but rather the invention includes all modifications, equivalents, and substitutes consistent with the spirit of the invention as defined by the claims.

When an element, such as a layer, region, or substrate, is referred to as being “on” another component, it will be understood that it may be directly on another element or intermediate elements may be present therebetween. .

Although the terms first, second, etc. can be used to describe various elements, components, regions, layers and / or regions, these elements, components, regions, layers and / or regions It will be understood that it should not be limited by these terms.

1 is a block diagram showing a power conversion apparatus according to an embodiment of the present invention, Figure 2 is a circuit diagram showing a power conversion apparatus according to an embodiment of the present invention.

1 and 2, the power converter 100 is a rectifier 110 for rectifying the AC power supply 10, the converter rectifying the DC voltage rectified by the rectifying unit 110, the converter 120 to control the power factor 120 ), Converter control unit 130 for controlling converter 120, inverter 140 for outputting three-phase AC current, inverter control unit 150 for controlling inverter 140, and converter 120 and inverter 140 It may include a DC-link capacitor (C).

The inverter 140 outputs a three-phase alternating current, and the output current may be supplied to the motor 200. Here, the motor 200 may be a compressor motor that drives the air conditioner. Hereinafter, it will be described as an example that the motor 200 is a compressor motor driving the air conditioner, and the power converter 100 is a motor driving device driving the compressor motor.

However, the motor 200 is not limited to the compressor motor, and may be used in a variety of application products using alternating frequency variable voltage, for example, an AC motor such as a refrigerator, a washing machine, an electric vehicle, a car, and a vacuum cleaner.

Meanwhile, the motor driving apparatus 100 may further include a DC-link voltage detector (B), an input voltage detector (A), an input current detector (D), and an output current detector (E).

The motor driving apparatus 100 receives AC power from the system, converts power, and supplies the converted power to the motor 200.

The converter 120 converts the input AC power supply 10 to a DC power supply. The converter 120 may use a DC-DC converter that operates as a power factor control (PFC) unit. In addition, the DC-DC converter may use a boost converter. In some cases, the converter 120 may be a concept including the rectifier 110. Hereinafter, the converter 120 will be described as an example using a boost converter.

The rectifying unit 110 receives the single-phase AC power supply 10 and rectifies it, and outputs the rectified power to the converter 120 side. To this end, the rectifying unit 110 may use a full-wave rectifying circuit using a bridge diode.

As such, the converter 120 may perform a power factor improvement operation in the process of boosting and smoothing the voltage rectified by the rectifier 110.

The converter 120 includes an inductor L1 connected to the rectifier 110, a switching element Q1 connected to the inductor L1, a capacitor C connected in parallel with the switching element Q1, and A diode D1 connected between the switching element Q1 and the capacitor C may be included.

The step-up converter 120 is a converter capable of obtaining an output voltage higher than the input voltage. When the switching element Q1 is conducted, the diode D1 is cut off and energy is stored in the inductor L1, and stored in the capacitor C. The discharged electric charge is discharged to generate an output voltage at the output terminal.

In addition, when the switching element Q1 is blocked, the energy stored in the inductor L1 is added when the switching element Q1 conducts, and is transferred to the output terminal.

Here, the switching element Q1 may perform a switching operation by a separate pulse width modulation (PWM) signal. That is, the PWM signal transmitted from the converter control unit 130 is connected to a base (or gate) terminal of the switching element Q1, so that the PWM signal can perform a switching operation.

The switching element Q1 may use a power transistor, for example, an insulated gate bipolar mode transistor (IGBT).

IGBT is a switching device having a structure of a power metal oxide semi-conductor field effect transistor (MOSFET) and a bipolar transistor, and is a device capable of small driving power, high speed switching, high withstand voltage, and high current density.

As such, the converter control unit 130 may control the turn-on timing of the switching element Q1 in the converter 120. Accordingly, the converter control signal Sc for the turn-on timing of the switching element Q1 can be output.

To this end, the converter control unit 130 may receive the input voltage Vs and the input current Is from the input voltage detector A and the input current detector B, respectively.

In some cases, the converter 120 and the converter control unit 130 may be omitted. That is, the output voltage that has passed through the rectifying unit 110 may be charged in the DC-link capacitor C or drive the inverter 140.

In addition, when a direct current power source is used, such as a power conversion device used in a vehicle, the rectifier 110, the converter 120, the DC-link capacitor C and the converter controller 130 may be omitted. Alternatively, the DC-link capacitor C in FIGS. 1 and 2 may correspond to a battery of an automobile.

That is, the AC power for driving the compressor motor 200 in the inverter 140 may be generated using the DC power supplied from the battery of the vehicle. In this case, the power conversion device 100 may be dominated by an inverter 140.

The input voltage detector A may detect the input voltage Vs from the input AC power supply 10. For example, it may be located at the front end of the rectifier 110.

The input voltage detector A may include a resistance element, an OP AMP, and the like for voltage detection. The detected input voltage Vs is a discrete signal in the form of a pulse, and may be applied to the converter control unit 130 to generate the converter control signal Sc.

Next, the input current detection unit D may detect the input current Is from the input AC power supply 10. Specifically, it may be located at the front end of the rectifier 110.

The input current detector D may include a current sensor, a current transformer (CT), and a shunt resistor for current detection. The detected input voltage Is is a discrete signal in the form of a pulse and may be applied to the converter control unit 130 to generate the converter control signal Sc.

The DC voltage detector B detects the pulsating voltage Vdc of the DC-link capacitor C. For detecting the power supply, a resistance element, OP AMP, or the like can be used. The detected voltage (Vdc) of the DC-link capacitor (C), as a discrete signal (discrete signal) in the form of a pulse, can be applied to the inverter control unit 150, DC voltage (Vdc) of the DC-link capacitor (C) ) May generate an inverter control signal (Si).

Meanwhile, unlike the drawings, the detected DC voltage may be applied to the converter control unit 130 and used to generate the converter control signal Sc.

The inverter 140 is provided with a plurality of inverter switching elements (Qa, Qb, Qc, Qa ', Qb', Qc '), and a predetermined frequency of the DC power supply (Vdc) smoothed by the on / off operation of the switching element It can be converted to a three-phase AC power supply, and output to the three-phase motor 200.

Specifically, the inverter 140 is a pair of upper and lower arm switching elements (Qa, Qb, Qc) and lower arm switching elements (Qa ', Qb', Qc ') connected in series with each other, and a total of three pairs of upper and lower arm switching The elements can be connected in parallel to each other.

Similar to the converter 120, the switching elements of the inverter (Qa, Qb, Qc, Qa ', Qb', Qc ') can use a power transistor, for example, an insulated gate bipolar transistor (insulated gate bipolar mode transistor) ; IGBT) can be used.

The inverter controller 150 may output the inverter control signal Si to the inverter 140 in order to control the switching operation of the inverter 140. The inverter control signal Si is a pulse width modulation (PWM) switching control signal, based on an output current (io) flowing through the motor 200 and a DC-link voltage (Vdc) that is both ends of the DC-link capacitor (C). Can be generated and output. At this time, the output current io may be detected from the output current detector E, and the DC-link voltage Vdc may be detected from the DC-link voltage detector B.

The output current detector E can detect the output current io flowing between the inverter 140 and the motor 200. That is, the current flowing through the motor 200 is detected. The output current detector E can detect all of the output currents ia, ib, and ic of each phase, or may detect the output currents of two phases by using three-phase balance.

The output current detector E may be located between the inverter 140 and the motor 200, and a current transformer (CT), a shunt resistor, or the like may be used for current detection.

The inverter control unit 150 specifically includes a driving unit 151 driving a plurality of inverter switching elements Qa, Qb, Qc, Qa ', Qb', Qc ', and a control unit transmitting a driving signal to the driving unit 151 It may include (152).

At this time, a variable resistor 160 (see FIG. 3) may be provided between the driving unit 151 and at least one of the inverter switching elements Qa, Qb, Qc, Qa ', Qb', Qc '. In this case, a gate resistor (not shown) may be located between the driver 151 and other inverter switching elements Qa, Qb, Qc, Qa ', Qb', Qc '.

Alternatively, a variable resistor 160 may be provided between the driving unit 151 and each of the inverter switching elements Qa, Qb, Qc, Qa ', Qb', Qc '.

At this time, the control unit 152 transmits a driving signal (switching control signal) to the gate driver and at the same time, to the variable resistor unit 160 to have a different modulation resistance value according to the output current detected by the output current detector E. Signals with variable resistance values can be transmitted.

Energy for the frequency of the corresponding driving signal is modulated by modulating the driving signal applied to the gate terminal of the switching elements (Qa, Qb, Qc, Qa ', Qb', Qc ') by the variable resistor unit 160 and its control process Can be dispersed and noise can be reduced. That is, electromagnetic interference (EMI) characteristics may be improved.

This configuration and operation will be described in detail below.

3 is a block diagram showing a part of a power conversion apparatus according to an embodiment of the present invention.

Referring to FIG. 3, a variable resistor 160 may be provided between a gate terminal of the switching element Qa and a driving unit 151 for driving the switching element Qa.

At this time, as described above, the control unit 152 may transmit a PWM control signal to the driving unit 151, and the driving unit 151 may transmit a driving signal for driving the switching element Qa in each phase corresponding to the control signal. Can be.

Although the variable resistance unit 160 is connected to one switching element Qa in FIG. 3, other switching elements, for example, other switching elements Qb, Qc, and Qa 'shown in FIG. 2, The variable resistor unit 160 may also be connected to Qb 'and Qc').

In addition, as mentioned above, the variable resistor 160 may be connected to at least one of the other switching elements Qa, Qb, Qc, Qa ', Qb', Qc 'shown in FIG. 2.

The control unit 152 transmits a signal for varying the resistance value to the variable resistance unit 160 to have a different modulation resistance value according to the output current detected by the output current detection unit E (see FIG. 1) independently of the control signal. Can be.

In this case, the variable resistor unit 160 may be a digital variable resistor whose resistance value is adjusted according to a voltage value transmitted from the control unit 152. Accordingly, the variable resistor unit 160 may have a modulation resistance value that varies according to the voltage value received from the control unit 152.

4 is a graph showing a preceding term according to an input voltage of a variable resistor part of a power conversion device according to an embodiment of the present invention.

As described above, the resistance value of the variable resistor unit 160 may change according to a voltage value transmitted from the control unit 152. At this time, the input voltage, for example, when the control unit 152 is implemented as a microcomputer driven by a 5V voltage, may have a value between 0V and 5V, and thus a resistance value between 0Ω and 100Ω. Can be.

In this case, a voltage value of 0 V to 2.5 V may be used, and the resistance value of the variable resistor unit 160 used at this time may be 5 Ω to 50 Ω.

In addition, the modulation resistance value may be increased according to the output current sensed by the output current detector E. That is, the larger the output current sensed by the output current detector E, the larger the modulation resistance value.

In this case, the modulation resistance value may be increased in proportion to the output current sensed by the output current detector E. For example, the control unit 152 may output a voltage value for controlling the variable resistor unit 160 in proportion to the output current detected by the output current detection unit E. That is, the control unit 152 may increase the voltage value output to the variable resistor unit 160 in proportion to the output current detected by the output current detector E.

The control voltage value output from the control unit 152 to the variable resistor unit 160 may be modulated according to the output current sensed by the output current detector E. At this time, the control voltage value may additionally fluctuate in the value determined according to the output current sensed by the output current detector E.

That is, the control unit 152 may control the variable resistor unit 160 such that the modulation resistance value determined according to the output current sensed by the output current detector E fluctuates within a predetermined range.

Specifically, the control unit 152 controls the variable resistance unit 160 such that the modulation resistance value determined according to the output current sensed by the output current detection unit E varies within a predetermined range around the determined modulation resistance value. Can be.

This constant range can be, for example, 10% up and down in the determined modulation resistance value. For example, when the modulation resistance value is determined to be 10 Ω, the control unit 152 may control the variable resistor unit 160 to vary between 9 Ω to 11 Ω, which is a 10% variation from 10 Ω. The variable period may be arbitrary.

The change in resistance value of the variable resistance unit 160 under the control of the control unit 152 is summarized in Table 1 below.

Here, Iout represents the output current sensed by the output current detector E, and Vout represents the output voltage for controlling the variable resistor 160 by the controller 152. In addition, the gate on resister indicates a gate resistance connected to the switching element, that is, an actual resistance value of the variable resistor 160.

As shown, the output voltage for controlling the variable resistor unit 160 in the control unit 152 increases in proportion to the output current detected by the output current detector E, and accordingly, the gate resistance value connected to the switching element It can grow.

In addition, the variable resistance unit 160 may be controlled by the controller 152 so that the gate resistance value fluctuates within a predetermined range (for example, 10% up and down). For example, when the output current sensed by the output current detector E is 10A, the controller 152 may output a voltage value varying within 10% at 0.5V to the variable resistor 160.

5 is a flowchart illustrating a control method of a power conversion apparatus according to an embodiment of the present invention.

Hereinafter, a process of controlling the power conversion device described above will be described in detail with reference to FIGS. 1 to 5. The control process may be performed in the control unit 152.

First, after the motor 200 is initially driven, an operation (S100) of sensing the input voltage Vdc and the output current io of the inverter 140 may be performed. That is, the input voltage Vdc and the output current io input to the inverter 140 through the rectifier 110 and / or the converter 130 may be sensed.

Thereafter, according to an embodiment of the present invention, the PWM control signal may be output from the control unit 152 to the driving unit 151 according to the target driving speed of the corresponding motor 200 (S200).

Then, in the driving unit 151, a driving signal for driving the switching element of the inverter 140 may be output to the switching element.

As described above, the PWM driving signal is output from the driving unit 151 by the PWM control signal to drive the motor 200 at the target speed.

At this time, the resistance value between the switching element and the driving unit 151 may change according to a change in the output current io.

That is, the control unit 152 may control the variable resistor unit 160 such that the resistance value between the switching element and the driving unit 151 is modulated (S300).

The process of controlling the variable resistor unit 160 may include the following process.

That is, the control voltage of the variable resistor 160 may be output so that the resistance value between the switching element and the driver 151 is modulated according to the change of the output current io (S310).

The resistance value of the variable resistor unit 160 may be updated at regular intervals or at regular intervals according to the control voltage (S320).

At this time, as described above, the control voltage value for controlling the variable resistor unit 160 may be modulated according to the output current sensed by the output current detector E. At this time, the control voltage value may additionally fluctuate in the value determined according to the output current sensed by the output current detector E.

That is, according to an embodiment of the present invention, the control unit 152 may control the variable resistor unit 160 such that the modulated resistance value determined according to the output current detected by the output current detector E fluctuates within a predetermined range. have.

Specifically, according to an embodiment of the present invention, the control unit 152 is variable so that the modulation resistance value determined according to the output current detected by the output current detection unit E is variable within a predetermined range around the determined modulation resistance value. The resistor 160 can be controlled.

6 is a flowchart illustrating a specific process of controlling a variable resistor of a power conversion device according to an embodiment of the present invention.

Referring to FIG. 6, a process of controlling the variable resistor unit 160 of the power conversion device 100 by outputting a control voltage to the variable resistor unit 160 may specifically include the following process.

First, the control voltage of the variable resistor unit 160 may be determined according to a change in output current (S311).

Thereafter, the determined control voltage may be varied within a certain range (S312).

Then, the variable control voltage may be output to the variable resistor unit 160 (S313).

By controlling the variable resistor unit 160 through this process, when driving a switching element, electromagnetic interference (EMI) characteristics may be improved.

7 is a signal diagram showing a drive signal of a power conversion apparatus according to an embodiment of the present invention.

Hereinafter, the effect according to an embodiment of the present invention will be described with reference to FIG. 7.

As described above, the inverter 140 or the converter 120 uses a switching element to change power.

The on / off operation of the switching element causes noise, which adversely affects electromagnetic compatibility (EMC).

In order to reduce this noise, filters with a combination of inductors and capacitors are additionally installed to limit them, and EMC films are used and ground paths are also produced. In addition, inductors may be mounted on the windings in addition to these means.

When this method is applied, the effect of reducing noise is improved, but the overall circuit driving efficiency is lowered, it takes up a large volume, and may be a cause of increase in manufacturing cost.

Therefore, as in the present invention, the driving signal can be stabilized by controlling the gate resistance by controlling the variable resistor unit 160 described above with respect to the slope of the rise time in which the amplitude of the signal increases when the switching element is operated.

In FIG. 7, a dotted line represents a drive signal when the magnitude of the drive signal has a fixed resistance value (No modulation), that is, a periodic PWM drive voltage. In this case, it can be seen that noise is concentrated as illustrated, which may adversely affect EMC and EMI.

The dashed line in FIG. 7 represents a drive signal when the magnitude of the drive signal has a modulated resistance value (Modulated), that is, a substantially aperiodic PWM drive voltage by resistance value modulation.

In this case, as shown, it can be seen that noise is dissipated, so that EMC and EMI can be improved.

As described above, according to an embodiment of the present invention, EMC and EMI can be improved by stabilizing a driving signal.

In addition, while improving the EMC and EMI, the overall circuit driving efficiency is not lowered, the volume of the circuit does not increase, and the manufacturing cost does not increase.

On the other hand, the embodiments of the present invention disclosed in the specification and drawings are merely presented as specific examples for ease of understanding, and are not intended to limit the scope of the present invention. It is obvious to those skilled in the art to which the present invention pertains that other modified examples based on the technical idea of the present invention can be implemented in addition to the embodiments disclosed herein.

100: power converter 110: rectifier
120: converter 130: converter control unit
131: converter drive unit 150: inverter control unit
151: driving unit 152: control unit
160: variable resistor

Claims (10)

Inverter for generating an AC signal for driving the motor including a plurality of switching elements;
A gate driver driving the plurality of switching elements;
A variable resistor connected between the gate driver and the switching element;
An output current detector for sensing the output current of the inverter; And
It characterized in that it comprises a control unit for transmitting a control signal to the gate driving unit, and a signal for varying the resistance value to the variable resistance unit to have a different modulation resistance value according to the output current detected by the output current detection unit Power conversion device. The power conversion device of claim 1, wherein the variable resistance unit is a digital variable resistance whose resistance value is adjusted according to a voltage value transmitted from the control unit. The power conversion device of claim 1, wherein the modulation resistance value increases according to an output current sensed by the output current detection unit. The power conversion device of claim 3, wherein the modulation resistance value increases in proportion to the output current sensed by the output current detection unit. The power converter according to claim 1, wherein the control unit controls the variable resistance unit such that the modulation resistance value determined according to the output current sensed by the output current detection unit fluctuates. The power converter according to claim 5, wherein the control unit controls the variable resistance unit such that the modulation resistance value varies within a predetermined range around the determined modulation resistance value. A compressor comprising the power conversion device of any one of claims 1 to 6. A power conversion device including an inverter for generating an AC signal for driving a motor including a plurality of switching elements, a gate driver for driving the plurality of switching elements, and a variable resistor connected between the gate driver and the switching element. In the control method,
Sensing the input voltage and output current of the inverter;
Controlling the switching element by transmitting a control signal to the gate driver;
And outputting a control voltage to the variable resistor unit to have different modulation resistance values according to the change of the output current. The method of claim 8, wherein the step of outputting a control voltage to the variable resistor unit controls the modulation resistance value to increase in proportion to the output current. The method of claim 8, wherein the step of outputting a control voltage to the variable resistor,
Determining a control voltage of the variable resistor unit according to the change in the output current;
Varying the determined control voltage in a predetermined range; And
And outputting the variable control voltage.

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