KR102306880B1 - High efficiency isolated pfc converter - Google Patents

Abstract

It relates to a high-efficiency insulated PFC converter, comprising: a transformer; an inductor unit including a first inductor and a second inductor connected in series to the primary side of the transformer; a switch unit for controlling an output voltage by switching according to an input signal, and a DC-link including a first diode and a second diode connected to the secondary side of the transformer, wherein the main switch includes an inductor unit and an input capacitor is connected to, and the negative switch is connected to the inductor and the clamp capacitor.

Description

High efficiency isolated PFC converter {HIGH EFFICIENCY ISOLATED PFC CONVERTER}

A high efficiency isolated PFC converter is provided.

An AC-DC converter that converts a general AC voltage into a DC voltage has a structure in which a diode bridge, a boost PFC (Power Factor Correction) converter, and a dc-dc converter are combined. Here, the boost PFC converter provides high performance in terms of power factor control, but increases the switching loss for a hard switching operation, thereby reducing power conversion efficiency and acting as a constraint on power density improvement. In addition, the boost PFC converter generates high electromagnetic interference (EMI) noise due to the hard switching operation in a state in which it is directly connected to the input AC system.

And the dc-dc converter uses the same topology as the LLC (Inductor-Inductor-Capacitor) resonant converter to improve the overall efficiency of the system and provide electrical isolation between the input and the load. Accordingly, the LLC resonant converter provides soft switching and can improve power conversion efficiency and power density while minimizing switching loss.

However, a resonant converter such as an LLC resonant converter has a wide output range and has low efficiency in a system requiring high output voltage control performance because the operating point varies depending on the size of the load and it is difficult to control at a light load.

In order to solve these problems, recently, a three-stage AC-DC converter as shown in FIG. 1 has been studied.

1, the 3-stage AC-DC converter consists of a dc-dc stage of an isolated dc-dc converter and a non-isolated dc-dc converter.

Here, the isolated dc-dc converter is designed with high efficiency and electrical insulation as a priority like the existing dc-dc converter. And the non-isolated converter borrows a converter in which the control input value and the output voltage have a linear relationship like the Buck converter. This separation of functions of the DC-DC converter stage enables design optimization for each power conversion stage, and the output control performance is improved, but there is a situation in which the efficiency is lowered due to the hard switching operation of the PFC converter. Additionally, the power conversion efficiency and power density are reduced.

As a related prior document, Korean Patent No. 1,022,772 discloses "power conversion device for fuel cell".

Korean Patent 1,022,772

One embodiment of the present invention is to provide a high-efficiency isolated PFC converter that provides improved output control performance and improved power conversion efficiency.

In addition to the above problems, the embodiment according to the present invention may be used to achieve other problems not specifically mentioned.

A high-efficiency insulated PFC converter according to an embodiment of the present invention relates to a transformer, an inductor unit including a first inductor and a second inductor connected in series to the primary side of the transformer, and a main connected to both ends of the inductor unit, respectively It includes a switch and a sub-switch, and a switch unit for controlling an output voltage by switching according to an input signal, and a DC-link unit including a first diode and a second diode connected to the secondary side of the transformer, The main switch is connected to the inductor unit and the input capacitor, and the secondary switch is connected to the inductor unit and the clamp capacitor.

According to an embodiment of the present invention, it provides high efficiency power conversion even when operating at a high switching frequency by minimizing the switching loss and eliminating the loss due to the diode reverse recovery time problem.

According to an embodiment of the present invention, as the PFC converter stage provides high-efficiency power conversion and electrical insulation performance considered when designing the existing DC-DC converter stage, the DC-DC converter stage has a linear relationship between the control input and the output voltage. The circuit can be applied to provide high efficiency and at the same time improve the output control performance, so it can be effectively applied to applications with a large output voltage range.

1 is a view showing a conventional three-stage AC-DC converter having an additional power conversion stage.
2 is a view showing a system of a two-stage AC-DC converter according to an embodiment of the present invention.
3 is a circuit diagram illustrating a PFC converter according to an embodiment of the present invention.
4 is a circuit diagram illustrating an equivalent circuit according to a mode of a PFC converter according to an embodiment of the present invention.
5 is a view showing a main operating wavelength for operation analysis in the first condition according to an embodiment of the present invention.
6 is a diagram illustrating main waveforms for operation analysis under a second condition according to an embodiment of the present invention.
7 is a diagram illustrating a control algorithm of an isolated PFC converter according to an embodiment of the present invention.
8 is a graph showing experimental results for input current regulation performance according to an embodiment of the present invention.
9 is a graph showing experimental results for the operation of a switch according to an embodiment of the present invention.
10 is a graph illustrating power conversion efficiency according to load conditions according to an embodiment of the present invention.

With reference to the accompanying drawings, the embodiments of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention pertains can easily implement them. The present invention may be embodied in many different forms and is not limited to the embodiments described herein. In order to clearly explain the present invention in the drawings, parts irrelevant to the description are omitted, and the same reference numerals are used for the same or similar components throughout the specification. In addition, in the case of a well-known known technology, a detailed description thereof will be omitted.

Throughout the specification, when a part "includes" a certain element, it means that other elements may be further included, rather than excluding other elements, unless otherwise stated.

In the specification, a duty ratio means a ratio of a conduction section to one cycle in a semiconductor switching device that performs a periodic switching operation.

2 is a diagram showing a system of a two-stage AC-DC converter according to an embodiment of the present invention, and FIG. 3 is a circuit diagram showing a PFC converter according to an embodiment of the present invention.

In general, in a two-stage AC-DC converter, the PFC region performs input current control to obtain low high-frequency distortion, and an isolated dc-dc converter performs output regulation and galvanic isolation in the dc-dc converter region. carry out

On the other hand, as shown in FIG. 2 , in the two-stage AC-DC converter proposed in the present invention, electrical insulation is performed in the PFC region.

Accordingly, the two-stage AC-DC converter is a soft-switching-based isolated PFC converter and a non-isolated dc-dc converter in which the control input-to-output voltage has a linear relationship. dc converter).

Here, the non-isolated dc-dc converter may be referred to as a non-isolated buck converter.

As shown in FIG. 3, the isolated PFC converter is composed of a full-bridge diode rectifier and an isolated resonance dc-dc converter.

The isolated PFC converter includes a transformer, an inductor part, a switch part, and a DC-link part.

The transformer T is connected to the primary side and the secondary side to transform the supplied voltage to apply a current.

Here, the magnetizing inductance Lm is connected in parallel to the primary side of the transformer T and the leakage inductance L _lk is connected in series to the secondary side.

And the inductor part (L ₁ , L _{2 , L) includes a first inductor ( L 1} ) and a second inductor ( L ₂ ) connected in series to the primary side of the transformer.

The first inductor L ₁ and the second inductor L ₂ are input inductors.

And the switch unit (S ₁ , S ₂ , S _1a , S _2a , S) includes a main switch (S ₁ , S ₂ ) and a sub switch (S _1a , S _2a ) respectively connected to both ends of the inductor unit, and the input Controls the output voltage by switching according to the signal

In this case, the main switch includes a first switch (S ₁ ) and a second switch (S ₂ ), and the sub switch includes a third switch (S _1a ) and a fourth switch (S _2a ).

In detail, the first switch S _{1 is} connected to the first inductor L ₁ and the input capacitor C _i , and the second switch S ₂ is the second inductor L ₂ and the input capacitor C _i ) is associated with

And the third switch S _{1a is} connected to the first inductor L ₁ and the clamp capacitor C _C , and the fourth switch S _{2a is} connected to the second inductor L ₂ and the clamp capacitor C _C . Connected.

The main switches (S ₁ , S ₂ ) have the same duty ratio (D), and the PWM signal is generated with a 180 degree phase difference. This improves the effective switching frequency and reduces input current ripple, such as in interleaved converters.

And the main switches (S ₁ , S ₂ ) and the sub switches (S _1a , S _2a ) are complementary to each other. In detail, the first switch S ₁ and the third switch S _1a operate complementarily, and the second switch S ₂ and the fourth switch S _2a operate complementarily.

On the other hand, all switches include each body diode, and before the gate signal involved in the turn-on/turn-off operation of the switch is transmitted, current flows through the body diode to the switch. The switch is turned on with zero voltage.

Through this, the switching loss is minimized since it is connected at zero voltage in the soft-switching operation.

The DC-link unit includes a first diode and a second diode connected to the secondary side of the transformer T, and is connected to the dc-dc transformer.

Here, the first diode D1 and the second diode D2 have a leakage inductance (L _lk ) and a zero current switching (ZCS) turn through a resonance circuit consisting of capacitors (C _r1 ) and (C _{r2 )} achieve off.

This mitigates the losses due to the reverse recovery time problem of diodes D1 and D2.

On the other hand, the isolated PFC converter includes a control algorithm as shown in FIG. 7 that can _{adjust the input current i i and V dc} of the dc-link by adjusting the pulse-width-modulation (PWM) signal of the switch. .

The invented PFC converter is divided into a first condition (duty ratio <0.5) and a second condition based on a duty ratio of 0.5. It is classified in detail into 6 modes according to the operation of the PFC converter in each condition.

4 is a circuit diagram illustrating an equivalent circuit according to a mode of a PFC converter according to an embodiment of the present invention, and FIG. 5 is a diagram showing main operation waveforms for operation analysis under the first condition according to an embodiment of the present invention. And FIG. 6 is a view showing main waveforms for operation analysis under the second condition according to an embodiment of the present invention.

Figure 4 (a) is mode 1, the first switch (S1) of the insulated PFC converter is started by turning on. Since the current i _p flows through the body diode of the first switch S1, the first switch S1 is turned on in a zero voltage state.

During this mode, the primary voltage v _p of the transformer is a negative voltage having a voltage clamp capacitor and -Vc magnetization current i _m is reduced.

Accordingly, power is transmitted from the input side in mode 1 of the isolated PFC converter to the DC-link side via the transformer T.

In addition, the secondary-side current of the transformer flows through D1, and the leakage current (L _lk ) resonates with the resonant capacitors (C _r1 , C _r2 ).

Such a state relationship is expressed in Equation 1 below.

[Equation 1]

Here, vC _r1 represents a capacitor voltage C _r1 , and vC _r2 represents a capacitor voltage C _r2 , respectively.

At this time, since the capacitor (C _dc ) has a sufficiently large value, V _dc is regarded as a constant value and can be expressed by the following Equation (2)

[Equation 2]

And from Equations 1 and 2, the voltage vC _r1 may be calculated through Equation 3 below.

[Equation 3]

는 각 공진 주파수를 나타낸다. here,

denotes each resonant frequency.

And Figure 4 (b) is mode 2, it starts at the time when the power transfer to the DC-link side of the isolated PFC converter is terminated. The diode current i _d1 becomes zero, and the diode D1 becomes zero current and is turned off. Accordingly, losses due to the inverse recovery problem of D1 are minimized.

And Figure 4 (c) is mode 3, the first switch (S ₁ ) is turned off and the third switch (S _1a ) is turned on and starts. Current i flows to the third _S1a is a body diode of the switch (S _1a), the third switch (S _1a) is turned on at the zero voltage state to eliminate the loss of the third switch.

As described above, the isolated PFC converter performs an operation to minimize the switching loss and the loss with respect to the diode reverse recovery time in mode 1, mode 2, and mode 3. Due to the symmetrical switching operation of the circuit of the insulated PFC converter of FIG. 3, modes 4, 5, and 6 are also performed similarly to the modes 1, 2, and 3, respectively.

Accordingly, the isolated PFC converter may implement six modes based on the first condition and the second condition, but is not limited thereto.

5 is a case in which the value of D, which is the first condition, has a value smaller than 0.5, and shows waveforms according to the mode operation of the insulated PFC converter.

In other words, FIG. 5 shows six operating modes during one switching period in the region according to the first condition as main waveforms during one switching period.

First, mode 1 derives the waveform of section 1a from t0 to t1, mode 1 represents the waveform of section 2a from t1 to t2, and mode 1 represents the waveform of section 3a from t2 to t3.

Accordingly, as a symmetrical operation of the circuit, modes 4,5,6 show symmetrical waveforms with those in modes 1,2,3.

6 is a case in which the value of D, which is the second condition, has a value greater than 0.5, and shows waveforms according to the mode operation of the insulated PFC converter.

Referring to FIG. 6 , unlike FIG. 5 , as in the 3b section (t ₂ to t ₃ ) of mode 3 and the 6b section (t ₅ to t ₆ ), which is a symmetric section, the main switch (first switch and second switch) There is a gap where the gate signals of

In section 3b and this interval, the primary voltage v _p of the transformer is 0, and the current i _m is kept constant as in section 3a and section 6a in mode 3 for the first condition.

Assuming that L ₁ and L ₂ have the same inductance value as L, the relationship between the _{average active clamp capacitor voltage Vc and the input voltage v in} under the voltage-second balance law for L during the switching period is:

[Equation 4]

Average voltage due to the symmetric operation of the switching _cr1 v V v _cr1 and _cr2 of the average voltage V _cr2 is the same. Accordingly, since the average voltage (V _cr1 ) is derived as _{nV c from Equation 3, the relationship between V c} and V _dc is as shown in Equation 5 below.

[Equation 5]

Accordingly, referring to Equation 5, it can be seen that the voltage transfer function of the isolated PFC converter is similar to the function of the boost PFC converter.

7 is a diagram illustrating a control algorithm of an isolated PFC converter according to an embodiment of the present invention.

As shown in FIG. 7 , in the isolated PFC converter, a proportional integral controller is used to adjust the _{output voltage V dc .}

In detail, the isolated PFC converter adjusts the duty ratio D to correct the power factor and adjust the DC-link voltage V _dc . Accordingly, the power quality and link voltage adjustment capability are determined by the control algorithm computing D.

Here, if the duty ratio D and the input current variable i _i are used, the equation for the average voltage of the input inductor L (= L ₁ = L ₂ ) during one switching period Ts is as shown in Equation 6 below.

[Equation 6]

Then, the duty ratio D is calculated as in Equation 7 below based on Equations 4 and 6.

[Equation 7]

Here, V _dc,ref is the desired output voltage of the isolated PFC converter.

And the control variables D _n and d can be calculated using the following Equation (9).

[Equation 8]

D _n can be separated from the original non-linear system in equation (7), which makes the relationship between _{d and i i linear.}

In other words, D _n functions as a feed-forward controller to remove disturbances caused by input voltage and DC-link voltage fluctuations and reduce the burden on the feedback controller to convert the non-linear system expressed by 7 in mathematics into a first-order linear system. contribute to

And, in a single power factor, v _i and i _i are the same as in Equation 9 below.

[Equation 9]

Here, V _i and I _i are the peak values of _vi and i _{i , respectively.} and is the frequency of the input AC voltage v _{ac .}

And with respect to Equation 9, the input current reference i _{i_ref} may be derived as in Equation 10 below.

[Equation 10]

Here, I _i ^* is the size of _{i i_ref .} Since the output voltage V _dc is changed by the difference between the input power and the output power, the voltage controller calculates _{I i} ^* such that the _{output voltage is V dc_ref .}

Hereinafter, the performance confirmed through the experimental results for the insulated PFC converter will be described with reference to FIGS. 8 to 10 .

8 is a graph showing experimental results for input current regulation performance according to an embodiment of the present invention, and FIG. 9 is a graph showing experimental results for operation of a switch according to an embodiment of the present invention. And FIG. 10 is a graph showing power conversion efficiency according to load conditions according to an embodiment of the present invention.

An isolated PFC converter was implemented as a 1kW prototype based on TMS320F28377S (microcontroller), and the performance was tested under the conditions of ac voltage of 220V, 60Hz and dc voltage of 360V.

Table 1 below means the values of the detailed parameters used in the experiment.

Parameters/Symbols Value AC voltage / v _ac 220Vrms AC frequency f _ac 60Hz DC voltage (output voltage) / V _dc 360V Switching frequency / f _s 70kHz Primary winding turns / N _p 24 turns Secondary winding turns / N _s 20 turns Magnetizing inductance / L _m 170μH Leakage inductance / L _lk 0.5 μH Input inductor / L 0.8mH Input capacitor / C _i 1 μF Clamp capacitor / C _c 4.4 μF Resonant capacitors / C _r1 , C _r2 2 μF DC capacitor / C _dc 680 μF

8 shows the experimental results for ac voltage and current, the current (i _ac ) has low harmonic distortion and a perfect sinusoidal shape. In this case, the power factor and total harmonic distortion (THD) are measured to be 0.999 and 2.9%, respectively, As shown in FIG. 8 , it can be confirmed that the soft switching operation is performed by providing the ZVS turn-on.

In addition, as shown in FIG. 9 , since the diode disposed on the secondary side of the transformer is also turned off in the zero current state, the loss due to the reverse recovery problem of the diode is minimized. Accordingly, the isolated PFC converter performs high-efficiency power conversion by minimizing power loss even in high-frequency operation.

Figure 10 shows the power conversion efficiency of the prototype according to various load conditions.

As shown in FIG. 10 , it can be confirmed that the maximum efficiency is measured as 96.7% at 60% load, and the efficiency is measured as and 96.3% at the rated load (100%).

In this way, as all power semiconductor switches (S1. S2, S1a, S2a) and power diodes D1 and D2 are soft-switched, the isolated PFC converter minimizes the switching loss of the switch and the loss due to the diode reverse recovery time problem. It can provide high-efficiency power conversion even when operating at a switching frequency.

In addition, the soft-switching operation of the PFC converter directly connected to the input of the isolated PFC converter effectively removes EMI noise compared to the conventional PFC converter, improving overall system reliability.

In addition, as the invented PFC converter is in charge of high efficiency and electrical isolation, the design burden of the dc-dc converter stage is reduced, and a circuit in which the control input to output voltage has a linear relationship such as a buck converter can be applied, resulting in high power conversion efficiency. It is possible to configure a two-stage AC-DC converter that provides high output control performance while providing

Although the preferred embodiment of the present invention has been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention as defined in the following claims are also provided. is within the scope of the

Claims (6)

Transformers,
an inductor unit including a first inductor and a second inductor connected in series to the primary side of the transformer;
a switch unit including a main switch unit and a sub switch unit respectively connected to both ends of the inductor unit, and controlling an output voltage by switching according to an input signal; and
and a DC-link unit including a first diode and a second diode connected to the secondary side of the transformer,
the main switch is connected to the inductor unit and the input capacitor, and the sub switch is connected to the inductor unit and the clamp capacitor;
An isolated PFC converter that adjusts power factor correction and output voltage by adjusting the duty ratio through a feed-forward controller (Dn) that removes disturbances caused by input voltage and DC-link voltage fluctuations and converts a nonlinear system into a first-order linear system .
In claim 1,
Insulated PFC converter further comprising a magnetizing inductance connected in parallel to the primary side of the transformer, and further comprising a leakage inductance connected in series to the secondary side.
In claim 1,
The main switch unit includes a first switch and a second switch,
the first switch is connected to the first inductor and the input capacitor, and the second switch is connected to the second inductor and the input capacitor;
The sub switch unit includes a third switch and a fourth switch,
The third switch is connected to the first inductor and the clamp capacitor, and the fourth switch is connected to the second inductor and the clamp capacitor.
In claim 3,
The first switch and the second switch have a phase difference of 180 degrees, the first switch and the third switch operate complementary, and the second switch and the fourth switch operate complementarily. PFC converter.
In claim 1,
The DC-link unit,
An insulated PFC converter that drives the first diode and the second diode to operate in zero current switching (ZCS) turn-off through a resonance circuit composed of a voltage double capacitor connected to a leakage inductance.
In claim 1,
An insulated PFC converter comprising an algorithm capable of simultaneously controlling an input current and a DC-link voltage by adjusting a pulse-width-modulation (PWM) signal of the switch unit.

Images