JP3714233B2 - Bidirectional DC-DC converter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a DC-DC converter that converts a DC input from a DC power source or the like into an arbitrary DC output via a transformer, and in particular, both the primary side and the secondary side of the transformer are input. Alternatively, the present invention relates to a bidirectional DC-DC converter that can be an output.
[0002]
[Prior art]
An example of a DC-DC converter capable of converting a DC input into a DC output and bi-directionally is shown in FIG.
The DC-DC converter 10 includes an insulation type transformer 2 connected in reverse polarity, and includes a N-channel MOS transistor in series with the primary winding 21 and operates as a normally open switch. SW31 is connected. A diode D31 is connected to the switch SW31 in antiparallel. The primary winding 21 and the switch SW31 connected in series are connected to the positive terminal P. ₁ And negative terminal N ₁ And the positive terminal P in parallel with the primary winding 21 and the switch SW31 connected in series. ₁ And negative terminal N ₁ A smoothing capacitor C1 is connected between them.
[0003]
Similarly, a switch SW41, which is an N-channel MOS transistor and operates as a normally open switch, is connected in series with the secondary winding 22, and a diode D41 is connected in reverse parallel to the switch SW41. The secondary winding 22 and the switch SW41 connected in series are connected to the positive terminal P. ₂ And negative terminal N ₂ And the positive terminal P in parallel with the secondary winding 22 and the switch SW41 connected in series. ₂ And negative terminal N ₂ A smoothing capacitor C2 is connected between them.
[0004]
8 and 9 show waveforms of each part of the DC-DC converter 10. FIG. 8 shows the positive side terminal P. ₁ And negative terminal N ₁ Side is input side, positive side terminal P ₂ And negative terminal N ₂ 9 is a waveform diagram when the output side is the output side, and FIG. ₂ And negative terminal N ₂ Side is input side, positive side terminal P ₁ And negative terminal N ₁ The waveform diagram when the side is the output side is shown.
(A) shows the voltage Vg input to the gate terminal of the switch SW31. ₃₁ Alternatively, the voltage Vg input to the gate terminal of the switch SW41 ₄₁ (B) shows the voltage V between the drain and source of the switch SW31. ₃₁ And the current I flowing through the switch SW31 and the diode D31 ₃₁ Where the drain current of the switch SW31 is positive and the current flowing through the diode D31 is negative. (C) is the voltage V between the drain and source of the switch SW41. ₄₁ And the current I flowing through the switch SW41 and the diode D41. ₄₁ Where the drain current of the switch SW41 is positive and the current flowing through the diode D41 is negative.
[0005]
(D) is the voltage V across the primary winding 21 of the transformer 2. _{twenty one} , (E) is the voltage V across the secondary winding 22 of the transformer 2. _{twenty two} , (F) is the voltage V across the smoothing capacitors C1 and C2. _C1 And V _C2 Represents.
In FIG. 7, a DC power source (not shown) is connected to the positive terminal P. ₁ And negative terminal N ₁ To supply DC power, and as shown in FIG. _{twenty one} When the switch SW31 is controlled to be in the ON state (FIG. 8A), the switch SW31 becomes conductive, and the positive terminal P is connected to the primary winding 21. ₁ And negative terminal N ₁ An input voltage is applied between them (FIG. 8D). As a result, an exciting current flows through the primary winding 21, and the current I flowing through the switch SW31. ₃₁ Increases linearly (FIG. 8B) and stores energy in the transformer 2.
[0006]
At this time, since the transformer 2 has a reverse polarity, the voltage V across the secondary winding 22 _{twenty two} Has a reverse polarity (FIG. 8E), and a reverse voltage is applied to the diode D41, so that no current flows through the diode D41 (FIG. 8C).
Further, since the switch SW31 is in a conductive state, the voltage V at both ends thereof is set. ₃₁ Becomes substantially zero (FIG. 8B), and the voltage V across the switch SW41 ₄₁ Is the voltage V across the smoothing capacitor C2. _C2 (FIG. 8C).
[0007]
From this state, time t _{twenty two} When the switch SW31 is switched to the OFF state (FIG. 8A), a back electromotive force is generated in the transformer 2 (FIGS. 8D and 8E), so that the diode D41 becomes conductive and the diode D41, A current flows through the path of the secondary winding 22 and the capacitor C2, and the energy stored in the transformer 2 is discharged by the secondary winding 22, and the smoothing capacitor C2 and the positive terminal P ₂ To be supplied. Further, the current I flowing through the diode D41 ₄₁ Changes linearly (FIG. 8C).
[0008]
And time t _{twenty three} When the switch SW31 is turned on, the above time t _{twenty one} In this case, when the switch SW31 is turned on before the energy stored in the transformer 2 can be fully discharged to the secondary side, as shown in FIG. Furthermore, the residual energy is a current I flowing through the switch SW31. ₃₁ Is superimposed as a direct current component. Subsequently, time t _{twenty four} Thus, the switch SW31 is turned off, and the voltage V across the smoothing capacitor C2 is _C2 By controlling the switch SW31 to be on / off so as to be constant, the same operation as described above is repeated, and the positive terminal P ₂ And negative terminal N ₂ Is supplied with DC power.
[0009]
Conversely, in FIG. 7, a DC power source (not shown) is connected to the positive terminal P. ₂ And negative terminal N ₂ 9 to supply DC power, as shown in FIG. ₂₆ When the switch SW41 is controlled to be in the ON state (FIG. 9A), the secondary winding 22 is connected to the positive terminal P. ₂ And negative terminal N ₂ Since an input voltage to the switch SW41 is applied (FIG. 9E), the current I flowing through the switch SW41 ₄₁ Increases linearly (FIG. 9C). At this time, since the transformer 2 has a reverse polarity, the voltage V across the primary winding 21 _{twenty one} Becomes reverse polarity (FIG. 9 (d)), a reverse voltage is applied to the diode D31, and the current I flows through the diode D31. ₃₁ Does not flow (FIG. 9B).
[0010]
Further, since the switch SW41 is in a conductive state, the voltage V at both ends thereof is set. ₄₁ Becomes substantially zero (FIG. 9C).
From this state, time t ₂₇ When the switch SW41 is switched to the OFF state (FIG. 9A), a back electromotive force is generated in the transformer 2 (FIGS. 9D and 9E), so that the diode D31 becomes conductive and the diode D31, A current flows through the path of the primary winding 21 and the smoothing capacitor C1, and the energy stored in the transformer 2 is released by the primary winding 21, and the smoothing capacitor C1 and the positive terminal P ₁ Current I flowing through the diode D31 ₃₁ Changes linearly (FIG. 9B).
[0011]
Then, after the energy stored in the transformer 2 has been released to the primary side (FIG. 9B), the time t ₂₈ When the switch SW41 is turned on, the time t ₂₆ The switch SW41 is repeatedly turned on / off so that the voltage across the smoothing capacitor C1 is constant, whereby the same operation as described above is repeated, and the positive terminal P ₁ And negative terminal N ₁ Is supplied with DC power.
[0012]
[Problems to be solved by the invention]
However, as shown in FIG. 8B and FIG. 9C, the current I flowing through the switch SW31 or SW41. ₃₁ , I ₄₁ 8 changes linearly, so that time t in FIG. _{twenty two} Or time t _{twenty four} 9 when the switch SW31 is turned off or at time t in FIG. ₂₇ Or time t ₂₉ Therefore, when the switch SW41 is switched off, there is a problem that the cutoff current increases and the switching loss is large.
[0013]
In addition, during the period when the switches SW31 and SW41 are controlled to be off, a voltage about twice the input voltage is applied between the drain and source of the switches SW31 and SW41 in some cases. Necessary. Such an element having a high withstand voltage has a large on-resistance and an increase in conduction loss. Such increase in conduction loss leads to heat generation of the semiconductor switch element, and power conversion efficiency is lowered.
[0014]
Therefore, the present invention has been made paying attention to the above-mentioned conventional unsolved problems, and is capable of reducing the cut-off current and heat generation of the semiconductor switching element and improving the power conversion efficiency. The object is to provide a DC converter.
[0015]
[Means for Solving the Problems]
In order to achieve the above object, a bidirectional DC-DC converter according to claim 1 of the present invention includes a transformer having a primary winding and a secondary winding connected to the same polarity as the primary winding, and the primary winding. A first switching means connected in series with the line; a capacitor connected in series with the secondary winding; and a second switching connected across the secondary winding and the capacitor connected in series. And a third switching means connected in series with the second switching means, both ends of the primary winding and the first switching means, and the second switching means and the third switching means. DC power is input to either one of the two ends, and DC power is extracted from the other.
[0016]
In the first aspect of the invention, when DC power is input to the primary winding side, for example, the first and third switching means are made conductive, the capacitor and the transformer inductance are resonated, and charge is stored in the capacitor. At the same time, by supplying power, the current flowing through the first switching means is changed into a sine wave. Next, the first and third switching means are cut off and the second switching means is turned on to discharge the capacitor charge. At this time, since the current flowing through the first switching means changes in a sine wave shape, the cutoff current at the time of interruption can be reduced by shutting off the first switching means at an appropriate timing.
[0017]
On the other hand, when DC power is input to the secondary winding, for example, the first and third switching means are turned on to resonate the capacitor and the transformer inductance to store charges in the capacitor and to supply power. As a result, the current flowing through the third switching means is changed into a sine wave. Next, the first and third switching means are cut off and the second switching means is turned on to discharge the capacitor charge. At this time, since the current flowing through the third switching means changes in a sine wave shape, it is possible to reduce the interruption current at the time of interruption by interrupting the third switching means at an appropriate timing.
[0018]
According to a second aspect of the present invention, there is provided a bidirectional DC-DC converter including a transformer having a primary winding and a secondary winding connected to the same polarity as the primary winding, and a first connected in series with the primary winding. Switching means, second switching means connected to both ends of the primary winding and the first switching means, a capacitor connected in series with the secondary winding, and the secondary winding and the capacitor And a third switching means connected to both ends and a fourth switching means connected in series with the third switching means, and a preset midway extraction point of the primary winding and the first switching means DC power is input to one of either the end opposite to the primary winding side and both ends of the third switching means and the fourth switching means, and DC power is supplied from the other. Take out It is characterized in that that is a cormorant.
[0019]
In the invention according to claim 2, when DC power is input to the primary winding side, for example, the first and fourth switching means are made conductive, the capacitor and the transformer inductance are resonated, and the capacitor is charged. By storing and supplying power, the current flowing through the first switching means is changed into a sine wave. Next, the first and fourth switching means are cut off, and the second and third switching means are made conductive to discharge the capacitor charge, and the current flowing through the second switching means is changed into a sine wave shape. Let At this time, since the current flowing through each switching means changes in a sine wave shape, it is possible to reduce the cutoff current at the time of interruption by shutting off each switching means at an appropriate timing.
[0020]
On the other hand, when DC power is input to the secondary winding, for example, the first and fourth switching means are turned on to resonate the capacitor and the transformer inductance to store electric charge in the capacitor and supply power. As a result, the current flowing through the fourth switching means is changed into a sine wave. Next, by cutting off the first and fourth switching means and turning on the second and third switching means, the charge of the capacitor is discharged and the current flowing through the third switching means is changed into a sine wave. . At this time, since the current flowing through each switching means changes in a sine wave shape, it is possible to reduce the cutoff current at the time of interruption by shutting off each switching means at an appropriate timing.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described.
FIG. 1 is a circuit diagram of a DC-DC converter 10 according to a first embodiment of the present invention. As shown in FIG. 1, the DC-DC converter 10 includes an insulated transformer 2 connected so that the primary side and the secondary side have the same polarity, and the primary winding 21 of the transformer 2 is configured. Is connected in series with a switch SW31 made of an N-channel MOS transistor and operating as a normally open switch. A diode D31 is connected to the switch SW31 in antiparallel. The primary winding 21 and the switch SW31 connected in series are connected to the positive terminal P. ₁ And negative terminal N ₁ Furthermore, in parallel with the primary winding 21 and the switch SW31 connected in series, the positive terminal P ₁ And negative terminal N ₁ A smoothing capacitor C1 is connected between them.
[0022]
On the other hand, positive side terminal P ₂ And negative terminal N ₂ A switch SW42 that operates as a normally open switch and a switch SW41 connected in series are connected between the switches, which are N-channel MOS transistors. Further, the positive terminal P ₂ And negative terminal N ₂ A smoothing capacitor C2 is connected between them.
Diodes D41 and D42 are connected in antiparallel to the switches SW41 and SW42, respectively. Between the drain and source of the switch SW42, the secondary winding 22 of the transformer 2 and the capacitor C3 connected in series are connected.
[0023]
Next, the operation of the first embodiment will be described.
2 and 3 show the waveforms of the respective parts of the DC-DC converter 10, and FIG. ₁ And negative terminal N ₁ Side is input side, positive side terminal P ₂ And negative terminal N ₂ 3 shows the waveform when the output side is the output side, and FIG. ₂ And negative terminal N ₂ Side is input side, positive side terminal P ₁ And negative terminal N ₁ It shows a waveform when the side is the output side.
[0024]
2 and 3, (a) shows the voltage Vg input to the gate terminal of the switch SW31. ₃₁ The voltage Vg input to the gate terminal of the switch SW41 ₄₁ And the voltage Vg input to the gate terminal of the switch SW42. ₄₂ Represents. (B) is the voltage V between the drain and source of the switch SW31. ₃₁ And the current I flowing through the switch SW31 and the diode D31 ₃₁ Where the drain current of the switch SW31 is positive and the current flowing through the diode D31 is negative. (C) is the drain-source voltage V of the switches SW41 and SW42. ₄₁ , V ₄₂ And the current I flowing through the switch SW41 and the diode D41. ₄₁ And the current I flowing through the switch SW42 and the diode D42. ₄₂ Where the drain current of the switches SW41 and SW42 is positive and the current flowing through the diodes D41 and D42 is negative. The solid line corresponds to the switch SW41 or the diode D41, and the broken line corresponds to the switch SW42 or the diode D42.
[0025]
(D) is the voltage V across the primary winding 21 of the transformer 2. _{twenty one} , (E) is the voltage V across the secondary winding 22 of the transformer 2. _{twenty two} , (F) is the voltage V across the capacitor C3. _C3 , (G) is the voltage V across the smoothing capacitors C1 and C2. _C1 , V _C2 Represents.
In FIG. 1, a DC power source (not shown) is connected to the positive terminal P. ₁ And negative terminal N ₁ To supply DC power, and as shown in FIG. ₁ When the switches SW31 and SW41 are turned on and the switch SW42 is turned off (FIG. 2A), the switch SW31 becomes conductive and the primary winding 21 is connected to the positive terminal P. ₁ And negative terminal N ₁ An input voltage is applied between them (FIG. 2 (d)). As a result, a primary current flows through the primary winding 21 to transmit energy to the secondary winding 22. Since the transformer 2 has the same polarity, a current flows through the path of the diode 41, the capacitor C3, the secondary winding 22, and the smoothing capacitor C2, and the current I flowing through the diode D41 due to the inductance of the transformer 2 and the resonance of the capacitor 3 ₄₁ (FIG. 2 (c)) increases or decreases in a sine wave shape, and accordingly, the current I flowing through the switch SW31. ₃₁ Also increases or decreases in a sine wave shape (FIG. 2B).
[0026]
The energy of the secondary winding 22 is the positive terminal P ₂ Is supplied to a load (not shown) via the capacitor and charges are stored in the capacitor C3. Accordingly, the voltage V across the capacitor C3 is stored. _C3 When (FIG. 2 (f)) decreases in a sine wave shape, the voltage V across the secondary winding 22 _{twenty two} On the contrary, (FIG. 2 (e)) increases in a sine wave shape.
At this time, since the switch SW31 and the switch SW41 are in a conductive state, the voltage V across the both ends thereof. ₃₁ And V ₄₁ Becomes substantially zero (FIG. 2 (c)), and the voltage V across the secondary winding 22 is connected across the switch SW42. _{twenty two} And voltage V across capacitor C3 _C3 Is applied (FIG. 2 (c)) and becomes a substantially constant value, which becomes the output voltage.
[0027]
From this state, time t ₂ When the switches SW31 and SW41 are turned off and the switch SW42 is turned on (FIG. 2A), current flows in the path of the capacitor C3, the diode D42, and the secondary winding 22 due to the charge stored in the capacitor C3. , The current I flowing through the diode D42 ₄₂ (FIG. 2C) decreases in a sine wave shape.
Along with this, the voltage V across the capacitor C3 _C3 (FIG. 2 (f)) increases in a sine wave shape, and the voltage V across the secondary winding 22 _{twenty two} (FIG. 2 (e)) has a reverse polarity and increases in a sine wave shape. Further, as the current flowing through the diode D42 and the secondary winding 22 decreases in a sine wave shape, the voltage V across the primary winding 21 is reduced. _{twenty one} (FIG. 2 (d)) is a voltage that increases in the form of a sine wave of reverse polarity. Further, the voltage V across the switch SW31 ₃₁ (FIG. 2 (b)) shows the voltage V across the primary winding 21. _{twenty one} Is opposite in polarity and increases sinusoidally.
[0028]
At this time, since the switch SW42 is in a conductive state, the voltage V at both ends thereof is set. ₄₂ Becomes substantially zero, and the voltage V across the switch SW41 ₄₁ Is the voltage V across the smoothing capacitor C2. _C2 (FIG. 2 (c)).
And time t _Three Then, again, the switches SW31 and SW41 are turned on and the switch SW42 is turned off, and the smoothing capacitor C ₂ By sequentially switching the switches SW31 to SW42 in the same manner as described above, the same operation as described above is repeatedly performed so that the voltage between both ends of the positive terminal P is constant. ₂ And negative terminal N ₂ Is supplied with DC power.
[0029]
Conversely, in FIG. 1, a DC power source (not shown) is connected to the positive terminal P. ₂ And negative terminal N ₂ To supply DC power, and as shown in FIG. ₆ When the switches SW31 and SW41 are turned on and the switch SW42 is turned off (FIG. 3A), the secondary winding 22 has a positive terminal P. ₂ And N ₂ Between the input voltage and the voltage V of the capacitor C3 _C3 The difference voltage is applied. As a result, the inductance of the transformer 2 and the capacitor C3 resonate, current flows through the path of the secondary winding 22, the capacitor C3, and the switch SW41, and electric charge is stored in the capacitor C3, and the current I flowing through the switch SW41. ₄₁ Increases or decreases sinusoidally (FIG. 3C). Further, a current flows through the path of the diode D31, the primary winding 21, and the smoothing capacitor C1, and the positive terminal P ₁ The current I flowing through the diode D31 is supplied to a load (not shown) via ₃₁ Increases and decreases sinusoidally (FIG. 3 (b)), and charges are stored in the capacitor C3. _C3 When (f) in FIG. 3 increases in a sine wave shape, the voltage V across the secondary winding 22 _{twenty two} Conversely, (FIG. 3E) decreases in a sine wave shape. Further, the voltage V across the primary winding 21 _{twenty one} (FIG. 3D) shows the voltage V across the capacitor C1. _C1 Becomes the output voltage.
[0030]
At this time, since the switch SW31 and the switch SW41 are in the conductive state, the voltage V ₃₁ And V ₄₁ Becomes substantially zero, and an input voltage is applied to both ends of the switch SW42 (FIGS. 3B and 3C).
From this state, time t ₇ When the switches SW31 and SW41 are turned off and the switch SW42 is turned on (FIG. 3A), a current flows through the diode D42 and charges are stored in the capacitor C3. Current I ₄₂ (FIG. 3 (c)) increases sinusoidally and the voltage V across the capacitor C3 _C3 Decreases sinusoidally (FIG. 3F). Voltage V across the secondary winding 22 _{twenty two} (FIG. 3 (e)) has a reverse polarity and the voltage V across the capacitor C3. _C3 As it decreases, it increases conversely.
[0031]
Further, the current I flowing through the switch SW42 and the secondary winding 22 ₄₂ As the voltage increases in a sine wave shape, the voltage V across the primary winding 21 _{twenty one} (FIG. 3 (d)) has a reverse polarity and decreases in a sinusoidal manner, and the voltage V across the switch SW31. ₃₁ (FIG. 3 (b)) shows the voltage V across the primary winding 21. _{twenty one} Is opposite in polarity and decreases to a sine wave.
At this time, since the switch SW42 is in a conductive state, the voltage V at both ends thereof is set. ₄₂ Becomes substantially zero, and the voltage V across the switch SW41 ₄₁ Is equivalent to the input voltage (FIG. 3C).
[0032]
And time t ₈ Then, the switches SW31 and SW41 are turned on again and the switch SW42 is turned off, and the switches SW31 to SW42 are sequentially switched in the same manner as described above so that the voltage across the smoothing capacitor C1 is constant. The same operation as above is repeated, and the positive terminal P ₁ And negative terminal N ₁ Is supplied with DC power.
Here, as shown in FIGS. 2 and 3, the current flowing through the switches SW31 and SW41 is a sinusoidal current. Therefore, it can be seen that the cut-off current when the switch SW31 or SW41 is cut off can be reduced as compared with the conventional case shown in FIG. Further, the voltage applied to the switches SW41 and SW42 is substantially equal to the input voltage or the output voltage.
[0033]
Therefore, in the past, a voltage about twice the input voltage was applied, but the applied voltage can be greatly reduced. Therefore, the cut-off current of the switch can be reduced, the switching loss can be reduced, and an element having a low withstand voltage can be applied, so that the heat generation of the switch can be reduced and the power conversion efficiency can be improved.
The first embodiment corresponds to claim 1, the switch SW31 and the diode D31 correspond to the first switching means, the switch SW42 and the diode D42 correspond to the second switching means, the switch SW41 and the diode D41 corresponds to the third switching means.
[0034]
Next, a second embodiment of the present invention will be described.
The second embodiment is the same as the DC-DC converter 10 in the first embodiment shown in FIG. 1 except that the configuration of the primary side of the transformer 2 is different. Therefore, the same reference numerals are given to the same parts, and detailed description thereof is omitted.
In the second embodiment, as shown in FIG. 4, a primary winding 21 r is further wound around the primary winding 21. That is, one end of the primary winding 21r is connected to the primary winding 21 and the positive terminal P. ₁ The other end of the primary winding 21r is connected to the source side of the switch SW31 via a switch SW32 made of an N-channel MOS transistor and operating as a normally open switch. A diode D32 is connected to the switch SW32 in antiparallel. The number of turns of the primary winding 21 and the primary winding 21r is set to be equal.
[0035]
Next, the operation of the second embodiment will be described.
5 and 6 show the waveforms of the respective parts of the DC-DC converter 10, and FIG. ₁ And negative terminal N ₁ Side is input side, positive side terminal P ₂ And negative terminal N ₂ The waveform when the output side is the output side, FIG. ₂ And negative terminal N ₂ Side is input side, positive side terminal P ₁ And negative terminal N ₁ It shows a waveform when the side is the output side.
[0036]
(A) is the voltage Vg input to the gate terminal of the switch SW31. ₃₁ The voltage Vg input to the gate terminal of the switch SW32 ₃₂ The voltage Vg input to the gate terminal of the switch SW41 ₄₁ And the voltage Vg input to the gate terminal of the switch SW42. ₄₂ Represents. (B) is the voltage V between the drain and source of the switches SW31 and SW32. ₃₁ , V ₃₂ And the current I flowing through the switch SW31 and the diode D31 ₃₁ And the current I flowing through the switch SW32 and the diode D32. ₃₂ Where the drain currents of the switches SW31 and SW32 are positive and the currents flowing through the diodes D31 and D32 are negative. The solid line corresponds to the switch SW31 or the diode D31, and the broken line corresponds to the switch SW32 or the diode D32. (C) is the drain-source voltage V of the switches SW41 and SW42. ₄₁ , V ₄₂ And the current I flowing through the switch SW41 or the diode D41 ₄₁ And the current I flowing through the switch SW42 or the diode D42. ₄₂ Where the drain currents of the switches SW41 and SW42 are positive and the currents flowing through the diodes D41 and D42 are negative. The solid line corresponds to the switch SW41 or the diode D41, and the broken line corresponds to the switch SW42 or the diode D42.
[0037]
(D) is the voltage V across the primary winding 21 of the transformer 2. _{twenty one} , (E) is the voltage V across the secondary winding 22 of the transformer 2. _{twenty two} , (F) is the voltage V across the capacitor C3. _C3 , (G) is the voltage V across the smoothing capacitors C1 and C2. _C1 , V _C2 Represents.
In FIG. 4, a DC power source (not shown) is connected to the positive terminal P. ₁ And negative terminal N ₁ To supply DC power, and as shown in FIG. ₁₁ When the switches SW31 and SW41 are turned on and the switches SW32 and SW42 are turned off (FIG. 5A), the positive terminal P is connected to the primary winding 21. ₁ And negative terminal N ₁ An input voltage is applied between them (FIG. 5D), and a primary current flows through the primary winding 21 to transmit energy to the secondary winding 22. Since the transformer 2 has the same polarity, a current flows through a path for charging the smoothing capacitor C2 through the path of the diode 41, the capacitor C3, the secondary winding 22, and the smoothing capacitor C2, and the positive terminal P ₂ Through which a current I flowing through the diode D41 is generated by the inductance of the transformer 2 and the resonance of the capacitor C3. ₄₁ Increases and decreases in a sine wave shape (FIG. 5C), and accordingly, the current I flowing through the primary winding 21 and the switch SW31. ₃₁ (FIG. 5B) also increases or decreases in a sine wave shape.
[0038]
The secondary winding 22 has a positive terminal P. ₂ In addition, energy is supplied to a load (not shown) via and the electric charge is stored in the capacitor C3. Along with this, the voltage V across the capacitor C3 _C3 When (f) in FIG. 5 decreases to a sine wave, the voltage V across the secondary winding 22 _{twenty two} Conversely, (FIG. 5 (e)) increases in a sine wave shape.
At this time, since the switch SW31 and the switch SW41 are in a conductive state, the voltage V across the both ends thereof. ₃₁ And V ₄₁ Becomes substantially zero, and the voltage V across the switch SW32 ₃₂ Is the sum of the input voltage and the primary winding 21r, and the voltage V across the switch SW42. ₄₂ Is the voltage V across the secondary winding 22 _{twenty two} And voltage V across capacitor C3 _C3 Is applied, and becomes a substantially constant value, which becomes the output voltage.
[0039]
From this state, time t ₁₂ When the switches SW31 and SW41 are turned off and the switches SW32 and SW42 are turned on (FIG. 5 (a)), the current stored in the capacitor C3, the diode D42, and the secondary winding 22 is caused by the electric charge stored in the capacitor C3. Current flows through the diode D42. ₄₂ Increases and decreases sinusoidally (FIG. 5C).
Along with this, the voltage V across the capacitor C3 _C3 (FIG. 5 (f)) increases sinusoidally and the voltage V across the secondary winding 22 _{twenty two} (FIG. 5E) has a reverse polarity and increases in a sine wave shape. Further, the current I flowing through the diode D42 and the secondary winding 22 ₄₂ Increases and decreases in a sine wave, current flows through the path of the primary winding 21r, the switch SW32, and the smoothing capacitor C1, and the current I flowing through the switch SW32 ₃₂ Increases and decreases sinusoidally (FIG. 5B).
[0040]
At this time, since the switches SW32 and SW42 are in a conductive state, the voltage V at both ends thereof. ₃₂ , V ₄₂ Becomes substantially zero, and the voltage V across the switch SW31 ₃₁ Is the sum of the input voltage and the primary winding 21, and the voltage across the switch SW41 is the voltage V across the smoothing capacitor C2. _C2 (FIGS. 5B and 5C). Further, since the voltage across the primary winding 21r has a reverse polarity and is clamped to the input voltage, the voltage V across the secondary winding 21 _{twenty one} Is equivalent to the reverse polarity of the input voltage (FIG. 5D).
[0041]
And time t ₁₃ Then, the switches SW31 and SW41 are turned on again, the switches SW32 and SW42 are turned off, and the voltage V across the smoothing capacitor C2 is controlled. _C2 In the same manner as described above, by sequentially switching the switches SW31 to SW42, the same operation as described above is repeatedly performed, and the positive terminal P ₂ And negative terminal N ₂ Is supplied with DC power.
On the contrary, in FIG. 4, a DC power source (not shown) is connected to the positive terminal P. ₂ And negative terminal N ₂ To supply DC power, and as shown in FIG. ₁₆ When the switches SW31 and SW41 are turned on and the switches SW32 and SW42 are turned off (FIG. 6A), the secondary winding 22 has a positive terminal P. ₂ And negative terminal N ₂ Between the input voltage and the voltage V of the capacitor C3 _C3 The difference voltage is applied. As a result, the inductance of the transformer 2 and the capacitor C3 resonate, a current flows through the path of the secondary winding 22, the capacitor C3, and the switch SW41, and charges are stored in the capacitor C3. At this time, the current I flowing through the secondary winding 22 and the switch SW41 ₄₁ Increases and decreases sinusoidally (FIG. 6 (c)), and accordingly, the current I flowing through the path of the diode D31, the primary winding 21, and the smoothing capacitor C1. ₃₁ Is also increased or decreased in a sine wave form (FIG. 6B), and the voltage V across the primary winding 21 _{twenty one} Is the voltage V across the smoothing capacitor C1. _C1 This becomes the output voltage (FIG. 6D). At this time, the current I ₃₁ Is the positive terminal P ₁ The energy is supplied to a load (not shown) via.
[0042]
A charge is stored in the capacitor C3, and the voltage V _C3 Increases sinusoidally (FIG. 6 (f)), the voltage V across the secondary winding 22 _{twenty two} Conversely decreases sinusoidally (FIG. 6E).
At this time, since the switch SW31 and the switch SW41 are in the conductive state, the voltage V ₃₁ And V ₄₁ Becomes substantially zero, and the voltage V across the switch SW32 ₃₂ Is the voltage V across the smoothing capacitor C1. _C1 Thus, the input voltage is applied to both ends of the switch SW42 (FIGS. 6B and 6C).
[0043]
From this state, time t ₁₇ When the switches SW31 and SW41 are turned off and the switches SW32 and SW42 are turned on (FIG. 6 (a)), the electric charge stored in the capacitor C3 causes the capacitor C3, the secondary winding 22, and the switch SW42 to pass through. Current flows and current I flows through the switch SW42. ₄₂ Increases or decreases sinusoidally (FIG. 6 (c)), and accordingly, the voltage V across the capacitor C3. _C3 (FIG. 6F) decreases in a sine wave shape. Also, the voltage V across the secondary winding 22 _{twenty two} (FIG. 6 (e)) has the opposite polarity, and the charge V of the capacitor C3 _C3 As it decreases, it increases in a sine wave shape.
[0044]
Further, the current I flowing through the capacitor C3 and the secondary winding 22 ₄₂ Is changed into a sine wave shape, the current I flowing through the path of the diode D32, the primary winding 21r, and the capacitor C1. ₃₂ (FIG. 6B) increases or decreases in a sine wave shape. At this time, the voltage V across the primary winding 21 _{twenty one} (FIG. 6D) has a reverse polarity, and the voltage V across the switch SW31. ₃₁ (FIG. 6B) shows the voltage V across the primary winding 21. _{twenty one} And reverse voltage. At this time, the current I ₃₂ Is the positive terminal P ₁ The energy is supplied to a load (not shown) via.
[0045]
At this time, since the switches SW32 and SW42 are in a conductive state, the voltage V at both ends thereof. ₃₂ , V ₄₂ Becomes substantially zero, and the voltage V across the switch SW41 ₄₁ Is equivalent to the input voltage (FIGS. 6B and 6C).
And time t ₁₈ Then, again, the switches SW31 and SW41 are turned on and the switches SW32 and SW42 are turned off, and the smoothing capacitor C ₁ By sequentially switching the switches SW31 to SW42 in the same manner as described above, the same operation as described above is repeatedly performed so that the voltage at both ends of the positive terminal P is constant. ₁ And negative terminal N ₁ Is supplied with DC power.
[0046]
Here, as shown in FIGS. 5 and 6, the current flowing through the switches SW31 and SW41 is a current that increases and decreases in a sine wave shape. Therefore, by switching the switches SW31 and SW41 in consideration of the amount of current flowing through the switches SW31 and SW41, the cut-off current can be reduced in this case as in the first embodiment. In addition, since the voltage applied to the switches SW41 and SW42 is almost equal to the input voltage or the output voltage, the switching loss can be reduced and the heat generation of the switch can be reduced and the power conversion efficiency can be reduced. Can be improved.
[0047]
Furthermore, in the second embodiment, energy can be supplied to the load in almost the entire switching cycle, and the utilization factor of the transformer can be improved.
In each of the embodiments described above, the case where a MOS transistor is used as the switching means has been described. However, the present invention is not limited to this, and can be applied to other semiconductor switching elements, and the same effects as the above can be obtained. Can do.
The second embodiment corresponds to claim 2, the switch SW31 and the diode D31 correspond to the first switching means, the switch SW32 and the diode D32 correspond to the second switching means, the switch SW42 and the diode D42 corresponds to the third switching means, and the switch SW41 and the diode D41 correspond to the fourth switching means.
[0048]
【The invention's effect】
As described above, according to the bidirectional DC-DC converter according to the present invention, since the current flowing through the switching means is changed into a sine wave, the cutoff current of the switching means can be reduced, and Since the voltage applied to the switching means can be reduced, the switching loss can be reduced, the heat generation of the switching means can be reduced, and the power conversion efficiency can be improved.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing an example of a DC-DC converter according to a first embodiment of the present invention.
FIG. 2 is a waveform diagram for explaining the operation of the first embodiment;
FIG. 3 is a waveform diagram for explaining the operation of the first embodiment;
FIG. 4 is a circuit diagram showing an example of a DC-DC converter according to a second embodiment of the present invention.
FIG. 5 is a waveform diagram for explaining the operation of the second embodiment;
FIG. 6 is a waveform diagram for explaining the operation of the second embodiment;
FIG. 7 is a circuit diagram showing an example of a conventional DC-DC converter.
FIG. 8 is a waveform diagram for explaining a conventional operation.
FIG. 9 is a waveform diagram for explaining a conventional operation.
[Explanation of symbols]
2 transformers
10 DC-DC converter
21, 21a, 21b Primary winding
22 Secondary winding
SW31, SW32, SW41, SW42 switch
D31, D32, D41, D42 Diode
C1, C2 smoothing capacitor
C3 capacitor

Claims (2)

A transformer having a primary winding and a secondary winding connected to the same polarity as the primary winding;
First switching means connected in series with the primary winding;
A capacitor connected in series with the secondary winding;
A second switching means connected to both ends of the secondary winding and the capacitor connected in series, and a third switching means connected in series with the second switching means;
DC power is input to one of the both ends of the primary winding and the first switching means, and both ends of the second switching means and the third switching means, and DC power is extracted from the other. A bidirectional DC-DC converter characterized by comprising: A transformer having a primary winding and a secondary winding connected to the same polarity as the primary winding;
First switching means connected in series with the primary winding;
Second switching means connected to both ends of the primary winding and the first switching means;
A capacitor connected in series with the secondary winding;
Third switching means connected to both ends of the secondary winding and the capacitor, and fourth switching means connected in series with the third switching means,
Between the preset midway extraction point of the primary winding and the end of the first switching means opposite to the primary winding side, and both ends of the third switching means and the fourth switching means A bidirectional DC-DC converter characterized in that DC power is input to one of the two and DC power is extracted from the other.

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