KR101796376B1 - The method and apparatus which bus converter operation with variable switching frequency employing llc converter - Google Patents

Abstract

An apparatus for operating a bus converter using an LLC converter according to an exemplary embodiment of the present invention may include an operation detecting unit for calculating a first voltage and a second voltage to be used for estimating a switching frequency of an LLC converter, A calculation unit for calculating a resultant value filtered by the filter unit and a reference voltage, a switching frequency estimating unit for estimating a switching frequency based on the voltage obtained through the calculating unit, and a switching unit The switching frequency can follow the resonance frequency by performing real-time control with the detected information in the LLC converter even in a wide input / output voltage range through a frequency modulation unit for applying the switching frequency estimated by the frequency estimating unit to the LLC converter .

Description

BACKGROUND OF THE INVENTION Field of the Invention [0001] The present invention relates to a bus converter that operates at a variable frequency using an LLC converter,

The present invention relates to an apparatus and method for operating a bus converter using an LLC converter at a variable frequency, and more particularly, to a system and method for operating a bus converter using an LLC converter, And more particularly, to a device and a driving method for determining a switching frequency.

A resonant converter is a converter that resonates electric energy with a specific resonant frequency and transfers energy to the output side. Of these resonant type converters, the LLC converter improves disadvantages of a wide switching frequency variation problem and a large circulating current of a parallel resonant converter (PRC) in order to control the output voltage of a series resonant converter (SRC) It is widely used in medium capacity class due to efficiency and switching noise reduction effect. In general, the bus converter has a non-isolated converter inserted at the input stage, and an isolated converter operated at fixed frequency with a fixed duty ratio of 50% at the output stage. Half-bridge or full-bridge type is used as the primary side of the output stage, and it is possible to transfer the energy to the secondary side through the transformer by changing the DC voltage to the AC voltage. The output voltage is determined by the turn ratio. Therefore, the converter applicable to the output stage is limited, and LLC resonant converter is one of the most suitable circuit as it has many advantages compared with other converters.

The advantage is that when operating in region-2, the voltage applied to the drain-source at the turn-on time of the primary-side switches in the full load range is made zero to reduce the switching loss There is a possibility that voltage-switching (Zero Voltage Switching) is possible and the switch is turned off in a state close to Zero Current Switching even at the time of turn-off and the switching loss is small . Also, since the secondary side rectifying diode has a small loss at the time of turn-off, it is easy to increase the power density due to the high frequency operation.

However, region-2 has a lower switching frequency than the resonance frequency. In this case, the effective current flowing through the power supply element is larger than that during operation in the region-1 region. Therefore, it is the optimum operation to operate at the point of time when the resonance frequency and the switching frequency, which are the intersections of the area-1 and the area-2, are the same.

In the conventional method, a technology in which the LLC converter operates as a fixed-rate and fixed-frequency bus converter is commercialized (Korean Patent Registration No. 10-1031217). However, in this method, there is a possibility that optimum operation may not be realized unexpectedly due to the tolerance of resonance inducing devices called resonance tanks. The tolerance is expressed not only by a simple process error but also by a temperature change in operation. This has the disadvantage that the output voltage can be controlled at a region where the soft-switching is impossible or at a point where the conduction loss is large because the effective current is large.

Therefore, the bus converter using the LLC converter needs a technology that can maintain the advantages of the conventional converter while at the same time enabling the optimal operation of the tolerance of the resonant tank elements.

As a countermeasure against the above-mentioned problem, the present invention provides a technique for increasing the efficiency of the LLC bus converter by making it possible to perform optimal operation in which the effective current is minimized even in the presence of the tolerance of the resonance tank element for determining the resonance frequency .

In order to accomplish the above object, the present invention can provide an apparatus for operating a bus converter using an LLC converter at a variable frequency.

An apparatus for operating a bus converter using an LLC converter according to an exemplary embodiment of the present invention may include an operation detecting unit for calculating a first voltage and a second voltage to be used for estimating a switching frequency of an LLC converter, A calculation unit for calculating a resultant value filtered by the filter unit and a reference voltage, a switching frequency estimating unit for estimating a switching frequency based on the voltage obtained through the calculating unit, and a switching unit And a frequency modulator for applying the switching frequency estimated by the frequency estimator to the LLC converter.

At this time, the switching frequency is a frequency that makes the effective current of the LLC converter minimum, and a device for operating the bus converter using the LLC converter at a variable frequency can operate the main switch of the LLC converter according to the estimated switching frequency.

An LLC converter according to an embodiment of the present invention includes a resonant tank including a resonant inductor and a resonant capacitor, a plurality of main switches for supplying or blocking an input voltage to the resonant tank, and a primary winding and a secondary winding A main transformer, and a plurality of main switches may include a first switch and a second switch.

The main transformer may be connected to an auxiliary circuit of a third winding for measuring the first voltage and the second voltage.

The auxiliary circuit according to an embodiment of the present invention may include a half-wave rectifying circuit including a diode or a full-wave rectifying circuit including a plurality of diodes, and the first diode or the second diode included in the secondary side of the main transformer A voltage proportional to the difference between both ends of the voltage is transmitted to both ends of the third winding, and the first voltage and the second voltage can be measured based on the voltage of the third winding.

The first voltage of the apparatus for operating the bus converter using the LLC converter in which the auxiliary circuit according to the embodiment of the present invention is not connected is operated at a variable frequency is the voltage of the first diode or the second diode included in the secondary side of the main transformer, The second voltage may be an output voltage measurement of the main transformer, and the switching frequency may be estimated based on the first voltage, the second voltage, and the reference voltage.

Also, the secondary structure of the main transformer may be a double-ended type that can transfer two electrical energy within one cycle.

In another embodiment of the present invention, a method for operating a bus converter using an LLC converter at a variable frequency can be provided.

A method for operating a bus converter using an LLC converter according to an exemplary embodiment of the present invention at a variable frequency includes calculating a first voltage and a second voltage to be used for estimating a switching frequency of an LLC converter, Calculating a filtered result and a reference voltage, estimating a switching frequency based on the voltage obtained through the operation, and modulating the frequency to apply the estimated switching frequency to the LLC converter can do.

The switching frequency is the frequency at which the effective current of the LLC converter is minimized, and the main switch of the LLC converter can be operated according to the estimated switching frequency.

Meanwhile, as an embodiment of the present invention, a computer-readable recording medium on which a program for causing the computer to execute the above-described method may be provided.

By using the LLC converter according to an embodiment of the present invention and using a bus converter operating at a variable frequency, real-time control can be performed with the detected information in the LLC converter even in a wide input / output voltage range so that the switching frequency follows the resonant frequency .

In addition, the present invention has an advantage that the accuracy of the control is improved, the cost and the volume of the device are not increased, and the control algorithm is simple, since the information of the secondary side need not be transmitted to the primary side for the calculation.

In addition, by applying the output voltage information to the optimum motion detector, the same effect can be obtained even in the initial operation and the variable of the output voltage, and data is not required through the trial and error for the optimum operation by performing the real time control .

1 is a block diagram of a bus converter operable at a variable frequency using an LLC converter in accordance with an embodiment of the present invention.
2 shows an exemplary circuit diagram of an LLC converter according to one embodiment of the present invention and a block diagram of an apparatus for operating a bus converter using an LLC converter at a variable frequency.
3 is an exemplary circuit diagram of an auxiliary circuit (b) to which a half-wave rectifying circuit is connected and a full-wave rectifying circuit is connected.
4 is an exemplary circuit diagram of a bus converter operating at a variable frequency using an LLC converter with an auxiliary circuit omitted in accordance with an embodiment of the present invention and a block diagram of an apparatus for operating a bus converter using an LLC converter at a variable frequency .
5 shows the current waveform of the secondary side rectifying diode according to the switching frequency.
FIG. 6A shows the main waveform according to the prior art when the resonance frequency is higher than the switching frequency, and FIG. 6B shows the main waveform when the apparatus according to an embodiment of the present invention is applied.
FIG. 7A shows the main waveform according to the prior art when the resonance frequency is lower than the switching frequency, and FIG. 7B shows the main waveform when the apparatus according to the embodiment of the present invention is applied.
FIG. 8A is a block diagram of a bus converter operating at a variable frequency using an LLC converter according to an embodiment of the present invention. FIG. 8B is a block diagram schematically showing an internal structure of an LLC converter according to an embodiment of the present invention. .
9 is a flowchart illustrating a method of driving a bus converter operating at a variable frequency using an LLC converter 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, which will be readily apparent to those skilled in the art. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

The terms used in this specification will be briefly described and the present invention will be described in detail.

While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. Also, in certain cases, there may be a term selected arbitrarily by the applicant, in which case the meaning thereof will be described in detail in the description of the corresponding invention. Therefore, the term used in the present invention should be defined based on the meaning of the term, not on the name of a simple term, but on the entire contents of the present invention.

When an element is referred to as "including" an element throughout the specification, it is to be understood that the element may include other elements, without departing from the spirit or scope of the present invention. Also, the terms "part," " module, "and the like described in the specification mean units for processing at least one function or operation, which may be implemented in hardware or software or a combination of hardware and software . In addition, when a part is referred to as being "connected" to another part throughout the specification, it includes not only "directly connected" but also "connected with other part in between".

The LLC converter can control the output voltage to be a constant voltage by varying the switching frequency when the input voltage to output voltage ratio and the load current fluctuate. When the load current is low, the switching frequency is higher than that of the resonant tank to reduce the transfer of electric energy. In the opposite case, the switching frequency is lower than the resonant tank frequency.

In the specification, "region-1" means a section in which the switching frequency is higher than resonance frequency, and "region-2" means section in which the switching frequency is lower than resonance frequency.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

1 shows a block diagram of a bus converter operable at a variable frequency using an LLC converter in accordance with an embodiment of the present invention.

The output voltage V _out is controlled at the front end (e.g., input end) of the bus converter to maintain a constant voltage, and the output current can additionally be controlled according to the output side application (e.g., load connection state, etc.). The control module of the converter can internally calculate the output voltage and the signal capable of detecting the difference between the switching frequency and the resonance frequency, thereby outputting the switching frequency that minimizes the effective current at a fixed ratio. The controller according to an embodiment of the present invention may be referred to as an apparatus for operating a bus converter using an LLC converter at a variable frequency.

5 shows the current waveform of the secondary side rectifying diode according to the switching frequency.

5 is a waveform that is generated when the peak value of the current is different because the output current should be the same even when the electric energy is transferred to the output side at different times. When the switching frequency is equal to the resonance frequency of the resonance tank 6100, a dotted line waveform is shown. When the switching frequency is smaller than the resonance frequency, a solid line waveform is shown.

Each current peak value X ₁ and X ₂ can be obtained as follows.

Therefore, since the effective current and the current peak value are proportional, the conduction loss can be increased when it is located in the region-2.

FIG. 2 shows an exemplary circuit diagram of an LLC converter according to an embodiment of the present invention and a block diagram of an apparatus for operating a bus converter using an LLC converter at a variable frequency, and FIG. 8A is a block diagram of an LLC FIG. 8B is a block diagram schematically illustrating an internal configuration of an LLC converter according to an exemplary embodiment of the present invention. Referring to FIG.

Referring to FIGS. 2 and 8A, an apparatus for operating a bus converter using an LLC converter according to an exemplary embodiment of the present invention at a variable frequency includes a first voltage to be used for estimating a switching frequency of the LLC converter 6000, 2, a filter unit 2000 for filtering the result of the operation by the motion detector, an operation unit for calculating the resultant value filtered by the filter unit 2000 and the reference voltage The switching frequency estimating unit 4000 for estimating the switching frequency based on the voltage obtained through the calculating unit 3000 and the switching frequency estimated by the switching frequency estimating unit 4000 to the LLC converter 6000 And a frequency modulating unit 5000 for performing frequency modulation.

8B, the LLC converter 6000 includes a resonance tank 6100 composed of an inductor and a capacitor, a main switch 6200 inserted for connection or disconnection of an input voltage, a main transformer for isolation and boost / And may be configured as a diode of interest.

At this time, the switching frequency is a frequency that makes the effective current of the LLC converter 6000 the minimum, and the apparatus for operating the bus converter using the LLC converter 6000 with the variable frequency is the LLC converter 6000 according to the estimated switching frequency. The main switch 6200 of the main switch 6200 can be operated.

An LLC converter according to an embodiment of the present invention includes a resonance tank 6100 including a resonance inductor and a resonance capacitor, a plurality of main switches 6200 for supplying or blocking an input voltage to the resonance tank 6100, And a main transformer including a winding and a secondary winding, and the plurality of main switches 6200 may include a first switch 6210 and a second switch 6220.

Also, the auxiliary transformer 7000 of the third winding for measuring the first voltage and the second voltage may be connected to the main transformer.

When the main switch M ₁ 6200 is turned on in the LLC converter 6000, the input side current is applied to the primary side coil of the main transformer to form a magnetic field. As a result, the magnetic field is induced in the secondary side coil, and the current induced in the secondary side linearly increases due to the output voltage as the secondary side diode D ₁ is turned on, The electric energy is transmitted to the output side by the turn ratio by the difference between the current I _Lr of the resonance inductor and the current I _Lm of the magnetizing inductance. When the main switch M ₁ 6200 is turned off, the alternate main switch M ₂ 6200 is turned on and the other diode D ₂ is turned on at the secondary side to perform the same operation as the above method .

The voltage at both ends (V _sec1 , V _sec2 ) of the secondary main transformer or the voltage across both ends (V _tr ) of the transformer located at the auxiliary circuit 7000 is fixed at a value proportional to the absolute value of the output voltage during optimum operation, The AC voltage of the square wave can be formed due to the characteristics of the transformer according to the operation of the transformer 6200.

If there is a situation in which the resonance inductance of the resonant inductor and the resonant capacitor reaches 0A under the condition that the main switch M ₁ or M ₂ 6200, 6210 and 6220 is ON, the condition 2 The diode D ₁ or D ₂ on the car side is turned off and the junction capacitance of the diode and the resonance tank 6100 element on the primary side are resonated so that the output voltage of the main transformer is located on the secondary side A difference in the reverse voltage of the diode can be observed, thereby confirming whether or not the optimum operation is achieved.

3 is an exemplary circuit diagram of an auxiliary circuit 7000 in which (a) the auxiliary circuit 7000 connected to the half-wave rectifying circuit 7100 and (b) the full-wave rectifying circuit 7200 are connected.

The auxiliary circuit 7000 according to an embodiment of the present invention may include a half wave rectifying circuit 7100 including a diode or a full wave rectifying circuit 7200 including four diodes, A voltage proportional to the difference between the voltage across the first diode 6310 or the second diode 6320 is delivered to both ends of the third winding and the first voltage and the second voltage The voltage can be measured.

The auxiliary circuit 7000 is supplied with a voltage proportional to the difference between the voltages across the secondary diodes D ₁ and D ₂ (6310 and 6320) on the secondary side at both ends of the auxiliary winding (V _tr ) 7000) The third winding voltage V _tr of the transformer constitutes a rectifying circuit 7100 or 7200 with a diode D _tr or four diodes D _tr1 , D _tr2 , D _tr3 and D _tr4 , So that the output voltage can be indirectly known through the voltage Vpeak of the peak detector circuit 7110 and 7120 using the resistor R _peak and the capacitor C _peak .

4 is an exemplary circuit diagram of a bus converter operating at a variable frequency using an LLC converter in which the auxiliary circuit 7000 is omitted according to an embodiment of the present invention and a device for operating a bus converter using an LLC converter at a variable frequency Fig.

The first voltage of the device for operating the bus converter using the LLC converter 6000, to which the auxiliary circuit 7000 is not connected, according to an embodiment of the present invention is operated at a variable frequency is a first diode included in the secondary side of the main transformer, The second voltage may be a voltage measurement of the main transformer 6310 or the second diode 6320 and the second voltage may be an output voltage measurement of the main transformer and the switching frequency may be estimated based on the first voltage, have.

At this time, the resonance frequency can be tracked by eliminating the resonance time by controlling the switching frequency so that the voltage at both ends of the secondary side diode is kept at twice the output voltage, so that the resonance frequency can be tracked. In the detector (Optimal Operation Detection), a square wave output signal is outputted by using a comparator.

The comparator output is converted into a DC voltage via the filter unit 2000, and the output DC voltage is feedbacked so as to follow V _duty ^* which is half the maximum output voltage of the comparator. This means that the time of the current flowing through the diode D ₁ is controlled to be half the resonance period, and naturally the diode D ₂ also allows the current to flow for the same time. Finally, the frequency modulator 5000 drives the main switch 6200 in a pulse frequency modulation (PFM) manner. When the electric energy is sufficiently transferred to the output side to enter the steady state, the LLC converter 6000 It operates like a bus converter with fixed frequency and fixed rate.

The secondary structure of the main transformer of the bus converter operating at the variable frequency using the LLC converter 6000 according to an embodiment of the present invention may be a double-ended system capable of transferring two electric energy within one cycle (V _signal , V _out, etc.) may be detected and applied in other forms without being limited thereto.

FIG. 6A shows the main waveform according to the prior art when the resonance frequency is higher than the switching frequency, and FIG. 6B shows the main waveform when the apparatus according to an embodiment of the present invention is applied. FIG. 7A shows the main waveform according to the prior art when the resonance frequency is lower than the switching frequency, and FIG. 7B shows the main waveform when the apparatus according to the embodiment of the present invention is applied.

Referring to FIG. 6A, when the resonance frequency is higher than the switching frequency, a soft commutation effect can be obtained since the current flowing through the diode on the secondary side reaches 0A and the diode on the opposite side is conductive. However, in the main switch 6200 during a period in which power transmission is not performed, the conduction loss due to the circulating current increases as much as the amount of magnetizing inductance, and the effective current in the secondary side diode also increases, which may cause conduction loss. Conversely, referring to FIG. 7A, when the resonance frequency is smaller than the switching frequency, the conduction loss due to the circulating current in the main switch 6200 can be minimized, but the switching loss increases due to the large magnitude of current flowing at the time of turn- . In addition, hard commutation may occur in the secondary side diode, which may cause reverse recovery loss of the diode.

According to the bus converter operating at the variable frequency using the LLC converter according to the embodiment of the present invention, the LLC converter 6000 is operated at the same switching frequency as the resonance frequency by performing the real time control even when the tolerance of the device exists The conduction loss and the switching loss can be minimized as shown in the waveforms of FIG. 6 (b) or FIG. 7 (b).

FIG. 9 is a flowchart illustrating a method of driving a bus converter operating at a variable frequency using the LLC converter 6000. Referring to FIG.

In another embodiment of the present invention, a method for operating a bus converter using an LLC converter at a variable frequency can be provided.

A method for operating a bus converter using an LLC converter according to an exemplary embodiment of the present invention at a variable frequency includes a step S1000 of calculating a first voltage and a second voltage to be used for estimating a switching frequency of the LLC converter 6000, A step S2000 of filtering the result of the operation, a step S3000 of calculating a filtered result and a reference voltage, a step S4000 of estimating a switching frequency based on the voltage obtained through the operation S4000, Modulating the frequency to apply the frequency to the LLC converter 6000 (S5000).

The contents of the above-described apparatus can be applied in connection with the method according to an embodiment of the present invention. Therefore, the description of the same contents as those of the above-mentioned apparatus has been omitted in connection with the method.

One embodiment of the present invention may also be embodied in the form of a recording medium including instructions executable by a computer, such as program modules, being executed by a computer. Computer readable media can be any available media that can be accessed by a computer and includes both volatile and nonvolatile media, removable and non-removable media. In addition, the computer-readable medium may include both computer storage media and communication media. Computer storage media includes both volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. Communication media typically includes any information delivery media, including computer readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave, or other transport mechanism.

It will be understood by those skilled in the art that the foregoing description of the present invention is for illustrative purposes only and that those of ordinary skill in the art can readily understand that various changes and modifications may be made without departing from the spirit or essential characteristics of the present invention. will be. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. For example, each component described as a single entity may be distributed and implemented, and components described as being distributed may also be implemented in a combined form.

The scope of the present invention is defined by the appended claims rather than the detailed description and all changes or modifications derived from the meaning and scope of the claims and their equivalents are to be construed as being included within the scope of the present invention do.

1000: motion detection unit
2000:
3000:
4000: Switching frequency estimating unit
5000: frequency modulation section
6000: LLC Converter
6100: resonance tank
6200: Main switch
6210: First switch
6220: Second switch
6310: First diode
6320: Second diode
7000: Auxiliary circuit
7100: Half-wave rectification circuit
7200: Full wave rectification circuit
7110, 7120: peak detector circuit

Claims (11)

An apparatus for operating a bus converter using an LLC converter at a variable frequency,
An operation detecting unit for calculating a first voltage and a second voltage to be used for estimating the switching frequency of the LLC converter;
A filter unit for filtering a result of the operation by the motion detection unit;
A calculation unit for calculating a resultant value filtered by the filter unit and a reference voltage;
A switching frequency estimating unit for estimating the switching frequency based on the voltage obtained through the calculating unit; And
And a frequency modulator for applying the switching frequency estimated by the switching frequency estimator to the LLC converter,
The LLC converter includes a main transformer including a primary winding and a secondary winding,
Wherein the switching frequency is a frequency at which the effective current of the LLC converter is minimized,
Wherein the first voltage is a voltage measurement value of a first diode or a second diode included in a secondary side of the main transformer and the second voltage is an output voltage measurement value of the main transformer,
Wherein the switching frequency is estimated based on the first voltage, the second voltage and the reference voltage, and the main switch of the LLC converter is operated according to the estimated switching frequency. Frequency.
The method according to claim 1,
The LLC converter includes:
A resonance tank including a resonance inductor and a resonance capacitor; And
And a plurality of main switches for supplying or interrupting an input voltage to the resonant tank,
Wherein the plurality of main switches include a first switch and a second switch,
And an auxiliary circuit of a third winding for measuring the first voltage and the second voltage may be connected to the main transformer.
3. The method of claim 2,
Wherein the auxiliary circuit includes a half-wave rectifying circuit including a diode or a full-wave rectifying circuit including a plurality of diodes,
Wherein a voltage proportional to a difference between both terminals of a first diode or a second diode included in a secondary side of the main transformer is transferred to both ends of the third winding, And the second voltage is measured. A device for operating a bus converter using an LLC converter, the variable converter comprising:
delete 3. The method of claim 2,
Wherein the secondary structure of the main transformer is a double-ended type that can transfer two electrical energy within one cycle. The apparatus for operating a bus converter using an LLC converter at a variable frequency.
A method for operating a bus converter using an LLC converter at a variable frequency,
Computing a first voltage and a second voltage to be used for estimation of the switching frequency of the LLC converter;
Filtering the result of the operation;
Calculating the filtered result value and a reference voltage;
Estimating the switching frequency based on the voltage obtained through the operation; And
Modulating the frequency to apply the estimated switching frequency to the LLC converter,
The LLC converter includes a main transformer including a primary winding and a secondary winding,
Wherein the switching frequency is a frequency at which the effective current of the LLC converter is minimized,
Wherein the first voltage is a voltage measurement value of a first diode or a second diode included in a secondary side of the main transformer and the second voltage is an output voltage measurement value of the main transformer,
Wherein the switching frequency is estimated based on the first voltage, the second voltage and the reference voltage, and the main switch of the LLC converter is operated according to the estimated switching frequency. Frequency.
The method according to claim 6,
The LLC converter includes:
A resonance tank including a resonance inductor and a resonance capacitor; And
And a plurality of main switches for supplying or interrupting an input voltage to the resonant tank,
Wherein the plurality of main switches include a first switch and a second switch,
Wherein the main transformer is connected to an auxiliary circuit of a third winding for measuring the first voltage and the second voltage.
8. The method of claim 7,
Wherein the auxiliary circuit includes a half-wave rectifying circuit including a diode or a full-wave rectifying circuit including four diodes,
Wherein a voltage proportional to a difference between both terminals of a first diode or a second diode included in a secondary side of the main transformer is transferred to both ends of the third winding, And the second voltage is measured. A method for operating a bus converter using an LLC converter at a variable frequency.
delete 8. The method of claim 7,
Wherein the secondary structure of the main transformer is a double-ended type in which two electrical energy can be transmitted within one cycle. The method for operating a bus converter using an LLC converter at a variable frequency.
A computer-readable recording medium on which a program for implementing the method of any one of claims 6 to 8 and 10 is recorded.

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