KR101490096B1 - Bidirectional DC-DC converter - Google Patents

Abstract

The present invention relates to a bidirectional DC-DC converter including each inductor operated in a boost mode and a buck mode and converting the boost mode and the buck mode without reducing the efficiency of a power. The present invention includes: a first power unit which applies a power to a lower part; an inductor unit which applies the power of the first power unit and a second power unit to the lower part and is installed in parallel to have a different setting value depending on the buck mode and the boost mode; a switch unit which is installed in serial to switch the power applied from the inductor unit or the second power unit; and the second power unit which is connected to both ends of the switch unit and applies the charged power to the switch unit in the buck mode.

Description

Bidirectional DC-DC converter < RTI ID = 0.0 >

The present invention relates to a bidirectional DC-DC converter, and more particularly, to a bidirectional DC-DC converter having respective inductors operated in a boosting mode and a step-down mode so that the boosting mode and the step- will be.

Generally, the DC-DC converter is used in a state in which charge / discharge means is connected to both the input side and the output side, and the prior art is disclosed in Japanese Patent Application Laid-Open No. 2001-128369.

The DC-DC converter in this publication has two switching elements (a MOS transistor having a body diode) connected to a reactor, one MOS transistor is turned off, and the other The MOS transistor is turned on and off to convert DC power. By changing the MOS transistor to be turned off and the MOS transistor to be turned on and off, bidirectional charging processing is enabled.

The device of this publication has the advantage that bidirectional charging can be performed. However, since one MOS transistor is always turned off, a forward current flows through the body diode, and the diode loss there is large . Therefore, it is difficult to use this device in a power supply circuit or the like where a diode loss is a problem.

On the other hand, there is a DC-DC converter of synchronous rectification type in which two MOS transistors are inverted with respect to each other as a non-isolated DC-DC converter that reduces diode loss and achieves high efficiency.

In order to prevent a current from flowing to a MOS transistor that is turned on at the start of operation, the non-breakdown DC-DC converter has a soft start that shortens the on-duty time initially, Control is generally performed.

However, in the case of the synchronous rectification control type DC-DC converter, if the power source is connected to the output side thereof, the on-duty time of the other MOS transistor becomes long during the soft start control and there is a contradiction that the current flows there . When a current flows through a MOS transistor, the transistor itself may be destroyed.

A related prior art is disclosed in U.S. Patent Publication No. 20030042880.

The present invention provides a bidirectional DC-DC converter having respective inductors operated in a boost mode and a step-down mode, and capable of converting the step-up mode and the step-down mode without reducing the efficiency of the power source.

The technical objects to be achieved by the present invention are not limited to the above-mentioned technical problems.

According to an aspect of the present invention, there is provided a bi-directional DC-DC converter including: a first power source for applying power to a lower portion; a second power source for applying power to the first power source and the second power source, A switch unit connected in series to switch a power source to be supplied from the inductor unit or the second power source unit, and a switch unit connected to both ends of the switch unit, And a second power source for applying the charged power to the switch unit in a buck mode.

Specifically, the inductor unit includes a first inductor connected between the first power supply unit and the switch unit and configured to apply power to the first power supply unit in the buck mode, and a second inductor connected in parallel with the first inductor, And a second inductor for applying power from the first power supply unit to the second power supply unit through the switch unit.

Wherein the switch unit is composed of a first switch and a second switch and is connected in series to both ends of the second power unit, the power source connected between the first switch and the second switch connected in series to the inductor unit, And the power supplied from the second power supply unit can be applied to the lower side through switching.

Wherein the first power source unit applies power to the lower power source in the buck mode and charges the power source in the boost mode and the second power source unit is a buck mode The power source may be charged, and in the boost mode, the power source may be downwardly applied.

As described above, according to the present invention, two inductors having separate inductances are selected and operated as switches. One of the two inductors has an inductance value optimized for a buck mode and the other has a boost mode mode, and the inductor designed with the inductance value optimized for each mode is selected and operated by the selection switch, so that the buck mode and the boost mode conversion are performed without reducing the power efficiency. There is a possible advantage.

1 is a circuit diagram showing a configuration of a bi-directional DC-DC converter according to an embodiment of the present invention.
2A is a diagram illustrating a mode for charging the first inductor in the step-down mode of the bidirectional DC-DC converter according to the present invention.
FIG. 2B is a diagram illustrating a mode of discharging the first inductor in the step-down mode of the bidirectional DC-DC converter according to the present invention.
3A is a diagram illustrating a mode for charging a second inductor in the step-up mode of the bidirectional DC-DC converter according to the present invention.
3B is a diagram illustrating a mode of discharging the second inductor in the boost mode of the bidirectional DC-DC converter according to the present invention.
FIG. 4A is a view showing a step-down mode waveform in which the bidirectional DC-DC converter according to the present invention operates at 125 w.
4B is a diagram showing a waveform of a boost mode in which the bidirectional DC-DC converter according to the present invention operates at 500 watt level
FIG. 5A is a diagram illustrating a step-down mode waveform in which the bidirectional DC-DC converter according to the present invention operates at 125 w.
5B is a view showing a boost mode waveform in which the bidirectional DC-DC converter according to the present invention operates at 500 watt level.
FIG. 6A is a diagram showing a waveform of a step-down mode of the bidirectional DC-DC converter according to the present invention.
6B is an operation waveform showing a boosting mode of the bi-directional DC-DC converter according to the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same components are denoted by the same reference symbols whenever possible. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

FIG. 1 is a diagram illustrating a bidirectional DC-DC converter according to an embodiment of the present invention. Referring to FIG. 1, a bidirectional DC- An inductor unit 30 configured to be in parallel with a set value according to a boost mode and a switch unit 30 connected in series to switch a power source applied from the inductor unit 30 or the second power source unit 20, And a second power supply unit 20 connected to both ends of the switch unit 40 and applying the charged power to the switch unit 40 in a buck mode.

As shown in FIGS. 2A and 2B, when the first power source unit 10 is in the buck mode, the first power source unit 10 applies power to the lower power source, The power supplied through the inductor unit 30 is charged.

The inductor unit 30 is connected to the lower part of the first power unit 10 so that the power supplied from the first power unit 10 is applied downward or the power supplied through the switch unit 40 is supplied to the first power unit 10 ).

The inductor unit 30 is connected in parallel to the first inductor L1 and the second inductor L2 and is connected between the first power unit 10 and the switch unit 40. [

The first inductor L1 is set to match the buck mode and the power applied through the switch unit 40 is applied to the first power unit 10 in the buck mode.

The second inductor L2 is set to be in a boost mode and the power applied from the first power supply unit 10 is applied to the switch unit 40 in a boost mode.

The switch unit 40 is connected in series with the first switch Q1 and the second switch Q2.

The inductor unit 30 is connected to the series connection of the first switch Q1 and the second switch Q2, and the second power supply unit 20 is connected to both ends of the inductor unit.

The first and second switches are operated according to a buck mode and a boost mode. The switch unit 40 is operated to charge and discharge the inductor unit 30 according to each mode.

The second power supply unit 20 connected to both ends of the switch unit 40 charges the power applied in the buck mode and applies the power to the lower power in the boost mode.

Such a configuration will be described below with reference to an embodiment.

2 shows circuit operation in a buck mode. In this buck mode, the second switch Q2 always operates in the off state. 2A is a mode for charging the first inductor L1. When the first switch Q1 is turned on, the power source of the second power source unit 20 is charged at both ends of the first power source unit 10 And forms a voltage by flowing to the output terminal (Vout) to be formed.

2B is a section in which the power stored in the first inductor L1 flows into the output stage Vout. When the first switch Q1 is turned off, the charged first inductor L1 changes its polarity to discharge the first inductor L1, Is applied to the first output terminal (Vout) through the internal body diode of the second switch (Q2). Thus, the energy applied to the output terminal Vout forms a voltage. This output voltage is formed by the input / output relation as shown in the following Equation 1, and the same relation as that of the step-down converter circuit is established.

Equation 1

3 shows the circuit operation in the boost mode. In the boost mode, the first switch Q1 is always off. 3A is a mode for charging the second inductor L2. When the second switch Q2 is turned on, the power of the first power source unit 10 is charged to form a voltage in the second inductor L2.

3B is a section where power stored in the second inductor L2 flows into the output terminal Vout formed at both ends of the second power supply unit 20. When the second switch Q2 is turned off, the charged second inductor L2 has a polarity And the voltage of the first power source unit 10 and the voltage of the second inductor L2 are added and applied to the output terminal Vout through the internal body diode of the first switch Q1. The applied power source forms a voltage.

As shown in Equation 2 below, the input-output relation is the same as that of the boosting converter circuit.

Equation 2

In order to compare the performance of the proposed bidirectional DC-DC converter, the buck mode was designed to have an optimized inductance value of 548uH at 125W and the boost mode at 500W at 180uH. Simulation and experiment were performed. The proposed bidirectional DC-DC converter operates by selecting the first or second inductor (L2) suitable for each mode by the switch unit (40). And operates as a first inductor L1 in the buck mode and as the second inductor L2 in the boost mode. The experimental conditions except the input / output relation and the inductance value of each mode are designed to be the same. Other variables used in the experiments are listed in Table 1.

Parameter Value Input Voltage ( V _dc ) S: simulation
_{(V dc _ buck, V dc} _ boost) E: experimental S: 141 V, 70.5 V
E: 124 V, 55 V Output Voltage ( V _out ) S: simulation
_{(V out _ buck, V out} _ boost) E: experimental S: 70.5 V, 140 V
E: 62 V, 55 V Switching Frequency ( f _s ) 20 kHz Output Capacitor ( C ) 470 μF Inductor ( L1 )
(Operation Buck mode) 548 μH Inductor ( L2 )
(Operation Boost mode) 180 μH Load Resistance ( R _L )
(R _{L _ buck} / _boost R _{L _)} 40Ω Duty ratio 50% (0.5)

4 is a simulation waveform of each operation mode operated by the first inductor L1 optimized for the buck mode. FIG. 4A is a buck mode waveform operating at 125 w and FIG. 4B is a boost mode waveform operating at 500 watts.

Indicates the inductor current, the voltage between the switch source and the drain, the duty ratio, the output voltage, and the output current from the top. When operating with an inductor with a 548uH inductance value, the buck mode and boost mode currents in the inductor are continuous and the characteristics of the converter are common. Here, in the boost mode operation, the inductance is designed to be large so that the current ripple is reduced, and the inductor loss is increased.

5 is a simulation waveform of each mode operated by the second inductor L2 optimized for the boost mode. FIG. 5A shows a buck mode waveform operating at 125 w, and FIG. 5B is a boost mode waveform operating at 500 w. Indicates the inductor current, the voltage between the switch source and the drain, the duty ratio, the output voltage, and the output current from the top. When operating with an inductor with an inductance value of 180uH, the inductor current in the buck mode is discontinuous and the current in the boost mode inductor appears continuously. Therefore, it can be seen that the single inductor is not designed based on the boost mode in the CCM mode design of the conventional bidirectional converter.

6 shows experimental results when the inductance value of the proposed bidirectional DC-DC converter is 180 占.. FIG. 6A is a buck mode, and FIG. 6B is a boost mode operation waveform. From the beginning, the output voltage V _O Or the input voltage V _IN and the inductor current I _L. 6A does not have a general step-down converter characteristic. It operates in discontinuous mode because the inductance value is less than the optimized value. The discontinuous mode operation increases the peak current of the inductor.

However, Fig. 6B has a general boost converter characteristic. Therefore, it can be seen from the experiment that the optimized inductance values are designed differently in each mode. Therefore, the bidirectional converter proposed uses two optimized inductors, which can reduce the losses in the non-optimized inductors, thus improving the efficiency.

mode
&
Induc
Tance In
put
volt
[V] In
put current
[A] In
put power
[W] Out
put volt
[V] Out
put current
[A] Out
put power
[W] Efficiency
[%] buck
&
548uH 123.5 0.968 119.55 64.3 1.63 104.8 87.8 Buck
&
180uH 122.3 0.911 111.42 63.5 1.64 104.14 93.6 boost
&
548uH 54.2 6.99 379 122.5 2.709 331.85 87.6 boost
&
180uH 54.7 6.12 335 112.2 2.745 307.98 91.9

As shown in Table 2, when the inductance is 180 μH, it is 5.8% higher than when the inductance is 548 μH. It can be seen that the efficiency is increased because of the discontinuous mode operation. However, when operating in boost mode, the efficiency was found to be 4.3% greater at 180μH than when the inductance was 548μH. It can be seen that the efficiency is improved by using the optimized inductor.

Table 2 shows the input voltage, input current, input power, output voltage, output current, output power, and output power when the inductance is 548 μH and 180 μH in the buck mode and the boost mode, Respectively.

One of the inductors has an inductance value optimized for a buck mode and the other has an inductance value for a boost mode. And the inductor designed with the inductance value optimized for each mode by the selection switch is selected and operated so that the buck mode and the boost mode can be converted without reducing the power supply efficiency .

10: first power supply unit 20: second power supply unit
30: inductor part L1: first inductor
L2: second inductor
40: switch unit Q1: first switch
Q2:
Vout: Output stage

Claims (4)

A first power source for applying power to a lower portion of the first power source; An inductor unit configured to apply power to the first power source unit and the second power source unit in a downward direction and configured in parallel so that set values according to a buck mode and a boost mode are different; A switch unit connected in series to switch a power source applied from the inductor unit or the second power source unit; And a second power source connected to both ends of the switch unit to apply the charged power to the switch unit in a buck mode, the bidirectional DC-DC converter comprising:
The inductor unit includes:
A first inductor connected between the first power supply unit and the switch unit and applying power to the first power supply unit in the buck mode; And a second inductor connected in parallel with the first inductor to apply a power from the first power source to the second power source through the switch unit.
delete The method according to claim 1,
Wherein the switch unit is composed of a first switch and a second switch and is connected in series to both ends of the second power unit, the power source connected between the first switch and the second switch connected in series to the inductor unit, DC converter according to claim 1, wherein the second power supply unit applies power to the second power supply unit through the switching unit.
The method according to claim 1,
Wherein the first power source unit applies power to the lower power source in the buck mode and charges the power source in the boost mode and the second power source unit is a buck mode DC converter according to claim 1 or 2, wherein the power source is charged in the boost mode and the power is applied in the boost mode in the boost mode.

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