KR20210048869A - Llc resonant converter - Google Patents

Abstract

According to an embodiment, an LLC resonant converter comprises: an inverter including a first switch and a second switch for varying a frequency; an impedance unit connected in series with the inverter and including a first impedance including an inductor and a capacitor; and a transformer connected in series with the capacitor to convert and output power output through the inverter. The impedance unit can include a second impedance that allows the entire impedance of the impedance unit to increase faster than the impedance of the inverter according as the frequency increases.

Description

LLC resonant converter {LLC RESONANT CONVERTER}

The present invention relates to an LLC resonant converter, and more specifically, to a technique in which a maximum frequency can be lowered while maintaining power efficiency by arranging capacitors in parallel in an inductor.

In general, laptop adapters that operate in a wide input power range (110VAC/220VAC), power supplies for home appliances, and new renewable energy power generation systems such as fuel cells and solar power, have a wide input voltage range to obtain a stable high output voltage. A /DC converter is required.

As such, DC/DC converters applied to various power supplies need to satisfy high efficiency characteristics, high integration, high reliability, and low manufacturing cost. A high switching frequency is required to satisfy these requirements, but as the switching frequency increases, the losses of switching elements related to turn-on and turn-off increase. DC converters can have low efficiency characteristics.

In addition, the isolated DC/DC converter requires a high turn-ratio between the primary and secondary sides of the transformer in order to boost the low input voltage to a high output voltage, thereby increasing the leakage inductance of the transformer. As a result, the switching element may be destroyed or operated with low efficiency as a surge voltage or the like occurs during switching.

Accordingly, in recent years, LLC resonant converters having high efficiency characteristics through a zero voltage switching (ZVS) operation of the main switching element, which can solve this problem, have been widely used.

The LLC resonant converter has high efficiency characteristics in all load ranges through the ZVS operation of the primary switching element and the zero current switching (ZCS) operation of the secondary rectifier diode. Since the configuration is possible and the leakage inductance and magnetizing inductance can be easily manufactured according to the design of the transformer, the circuit can be easily constructed.

However, in the case of the LLC resonant converter according to the prior art, the power output through the transformer was adjusted by changing the frequency. There was a problem to be done.

Accordingly, in one embodiment, the LLC resonant converter is an invention devised to solve the above-described problem. By arranging a separate capacitor in parallel between the inverter and the transformer, the LLC resonant type converter can more efficiently control the amount of power output. This is to provide a converter.

The LLC resonant converter according to an embodiment includes an inverter including a first switch and a second switch for varying a frequency, and an impedance unit connected in series with the inverter and including a first impedance including an inductor and a capacitor. And a transformer connected in series with the capacitor to convert and output power output through the inverter, and the impedance unit has a second impedance that increases the total impedance of the impedance unit faster than the impedance of the inverter as the frequency increases. Can include.

The second impedance may be connected in parallel with the first impedance.

The second impedance may be connected in parallel with the inductor.

The inductor may be connected to the first switch and the second switch, and the capacitor may be connected to the transformer.

The second impedance may include a second capacitor.

The impedance of the second capacitor may have a value smaller than the impedance of the first capacitor.

The impedance unit may be connected in series with a contact point between the first switch and the second switch.

The second impedance may be such that a ratio (Vin/Vout) of the output voltage Vin of the inverter and the output voltage Vout of the transformer decreases faster than when only the first impedance exists as the frequency increases. .

The LLC resonant converter according to an embodiment may prevent excessive current (shoot through) from flowing through a field effect transistor (MOSFET) by lowering a maximum frequency for power regulation.

In addition, by lowering the maximum frequency, the zero voltage switch (ZVS) can be maintained, thereby increasing power efficiency, and an increase in power waste due to charging and discharging of the capacitors of the MOSFET and the diode can be prevented.

In addition, since the frequency change is small, the power loss generated in the core of the transformer is small, and thus the range of the variable amount of power can be increased.

1 is a circuit diagram showing components of an LLC resonant converter according to a conventional embodiment.
2 is a graph showing a ratio of an input voltage and an output voltage according to a change in frequency according to a conventional embodiment.
3 is a circuit diagram showing components of an LLC resonant converter according to an embodiment.
4 is a graph illustrating a ratio of an input voltage and an output voltage according to a change in frequency, according to an exemplary embodiment.

The embodiments described in the present specification and the configurations shown in the drawings are preferred examples of the disclosed invention, and there may be various modifications that can replace the embodiments and drawings of the present specification at the time of filing of the present application.

In addition, terms used in the present specification are used to describe embodiments, and are not intended to limit and/or limit the disclosed invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

In the present specification, terms such as "comprise", "include" or "have" are intended to designate the presence of features, numbers, steps, actions, components, parts, or a combination thereof described in the specification. Or the presence or addition of other features or numbers, steps, actions, components, parts, or combinations thereof, or a combination thereof, and includes ordinal numbers such as "first" and "second" used herein. The terms described above may be used to describe various components, but the components are not limited by the terms.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art may easily implement the present invention. In the drawings, parts not related to the description are omitted in order to clearly describe the present invention.

1 is a circuit diagram showing components of an LLC resonant converter according to a conventional embodiment, and FIG. 2 is a graph showing a ratio of an input voltage and an output voltage according to a change in frequency according to a conventional embodiment.

Referring to FIG. 1, in the case of an LLC resonant inverter according to the prior art, a resonance inductor and a capacitor are connected in series to a half bridge inverter, and an output voltage is converted through a transformer.

In addition, in the case of such a configuration, a method of varying the frequency of the switch of the inverter is used to adjust the voltage output through the transformer. In this case, the rate of change of Vout/Vin according to the frequency change is changed as shown in FIG. .

That is, inductive current must flow for the zero volt switch (ZVS), and the range of the actual operating frequency is operated in the right part of the resonant frequency (about 250khz in Fig. 2), and if you want to lower the power output through the transformer. Increasing the switching frequency lowers the voltage gain (Vout/Vin), so the output power may decrease.

However, as shown in FIG. 2, in order to reduce the power output through the transformer to a level of 40% from the maximum output, the frequency must be 470 kHz, and furthermore, in order to reach a level of 10% of the maximum output, the frequency must be increased to 1400 kHz (graph range). Deviated from) There was a problem with severe frequency change.

That is, according to the prior art, in order to lower the maximum output, the frequency must be increased relatively much. However, if the frequency is increased a lot in the LLC resonant circuit, the MOSFET may be damaged.

For example, in FIG. 1, when the first switch Q1 is turned on and the second switch Q2 is turned off, when the first switch is turned off, a current flows through the diode of the second switch.

That is, while the second switch is turned on again and is turned off again, current flows through the diode of the first switch, and even at the moment the first switch is turned on. Since a current flows through the diode of the second switch Q2, there is a problem in that an excessive current flows through the first switch Q1 and the second switch Q2. 2 There is a problem that the switch Q2 is damaged.

In addition, as the frequency is excessively increased, efficiency deteriorates and heat generation increases, so that damage to the MOSFET may occur, and a core loss may occur in the transformer.

Therefore, according to the prior art, since the frequency is changed so that such a problem does not occur, the frequency that can be changed is limited, and thus the amount of power that can be controlled is limited.

However, in one embodiment, the LLC resonant converter 100 is an invention designed to solve the above-described problem, and by arranging a separate capacitor in parallel between the inverter and the transformer, the LLC resonant converter 100 can more efficiently control the amount of power output. It is to provide a resonant converter. It will be described in detail through the drawings below.

3 is a circuit diagram showing components of an LLC resonant converter according to an embodiment, and FIG. 4 is a graph showing a ratio of an input voltage and an output voltage according to a change in frequency, according to an embodiment.

Referring to FIG. 3, in the case of the LLC resonant converter 100 according to an embodiment, an impedance unit Z in a half bridge type inverter including a first switch Q1 and a second switch Q2. Are connected in series, and specifically, the impedance unit Z includes a first impedance Z1 including a resonance inductor Ls and a first capacitor Cr, and a second impedance Z2 including a capacitor Cp. ) Can be included. In addition, since the impedance unit Z is connected to the transformer T in series, the output voltage is converted through the transformer T. In addition, the impedance of the second capacitor Cp may be configured to have a value smaller than the impedance of the first capacitor Cr.

The reason why the output power decreases as the frequency increases in the LLC resonant converter according to the prior art is that the impedance of the resonator including the inductor and the capacitor increases as the frequency increases.

However, as shown in FIG. 3, when the second impedance Z2 is specifically connected to the second capacitor Cp in parallel with the inductor Ls, the total impedance increases faster as the frequency changes than in the prior art, and output There is an effect that can lower the power output faster by lowering the voltage.

Specifically, according to the prior art, as the frequency increases, the impedance of the resonance part including the inductor and the capacitor can be defined as j*w*Ls +1/(j*w*Cr), and the frequency increases. As it increases, the total impedance increases. In addition, when the configuration as in the present invention is taken, the total impedance can be defined as in Equation (1) below, and if Equation (1) is summarized, the total impedance can be summarized as in Equation (2).

Equation (1)-

Equation (2)-

That is, the total impedance of the present invention increases faster than the impedance according to the prior art as the frequency increases due to the presence of the (1-w2*Ls*Cp) component in the denominator, the ratio of the voltage output through the transformer (T) is It can be seen that it decreases rapidly as shown in FIG. 4.

That is, the resonant frequency (250khz) is almost unchanged, but in the case of adjusting the output to 40%, in the case of the prior art, 470khz had to be increased. In the case of adjusting to 10%, in the case of the prior art, 1400khz had to be increased, but in the case of the resonator according to an embodiment, the output can be adjusted only by increasing it up to 400khz, so there is an advantage in that the output can be more easily adjusted.

Therefore, since the range of the variable frequency controlled to adjust the output is narrower than that of the prior art, excessive current (shoot through) can be prevented from flowing through the field effect transistor (MOSFET), and the maximum frequency for power conversion is reduced to zero voltage. Since the switch ZVS can be maintained, power efficiency can be increased, and there is an effect of preventing an increase in power waste due to charging and discharging of the capacitors of the MOSFET and the diode.

In addition, in the case of FIG. 3, the second impedance Z2 is limited to the second capacitor Cp, but the description is not limited thereto, and any component capable of reducing the total impedance may be included therein.

That is, the second impedance (Z2) is configured such that as the frequency increases, the ratio (Vout/Vin) of the output voltage (Vin) of the inverter and the output voltage (Vout) of the transformer (Vout/Vin) decreases faster than when only the first impedance is present. Can be.

In the case of the LLC resonant converter according to the prior art, the power output through the transformer was adjusted by changing the frequency.However, the rate of change of the strategy versus the frequency change is not large. There was a problem.

However, the LLC resonant converter according to an embodiment can prevent excessive current (shoot through) from flowing through the field effect transistor (MOSFET) by lowering the maximum frequency for power regulation, and by lowering the maximum frequency for power conversion. Since the zero voltage switch ZVS can be maintained, power efficiency can be increased, and an increase in power waste due to charging and discharging of the capacitors of the MOSFET and the diode can be prevented.

In addition, since the frequency change is small, the power loss generated in the core of the transformer is small, and thus the range of the variable amount of power can be increased.

Although the embodiments have been described with reference to limited embodiments and drawings, various modifications and variations can be made from the above description to those of ordinary skill in the art. For example, the described techniques are performed in a different order from the described method, and/or components such as systems, structures, devices, circuits, etc. described are combined or combined in a form different from the described method, or other components Alternatively, even if substituted or substituted by an equivalent, an appropriate result can be achieved. Therefore, other embodiments and claims and equivalents fall within the scope of the claims to be described later.

Q1: Switch #1:
Q2: 2nd switch
Ls: inductor
Cr: first capacitor
Cs: second capacitor
T: transformer
Z1: first impedance
Z2: second impedance
Z: impedance part

Claims (8)

An inverter including a first switch and a second switch for varying a frequency;
An impedance unit connected in series with the inverter and including a first impedance including an inductor and a capacitor; And
A transformer connected in series with the capacitor to convert and output power output through the inverter; and
The impedance unit,
LLC resonant converter comprising a; second impedance for increasing the total impedance of the impedance portion faster than the impedance of the inverter as the frequency increases. The method of claim 1,
The second impedance is,
LLC resonant converter connected in parallel with the first impedance. The method of claim 2,
The second impedance is,
LLC resonant converter connected in parallel with the inductor The method of claim 1,
The inductor is connected to the first switch and the second switch,
The capacitor is an LLC resonant converter connected to the transformer The method of claim 1,
The second impedance is,
LLC resonant converter including second capacitor The method of claim 5,
The LLC resonant converter having an impedance of the second capacitor less than that of the first capacitor. The method of claim 1,
The impedance unit,
LLC resonant converter connected in series with a contact point between the first switch and the second switch. The method of claim 1,
The second impedance is,
As the frequency increases, the ratio (Vout/Vin) of the output voltage (Vin) of the inverter and the output voltage (Vout) of the transformer decreases faster than when only the first impulder exists.

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