JP2018014852A - Insulated dc/dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an insulated DC/DC converter capable of achieving energy saving and high efficiency.SOLUTION: An insulated DC/DC converter 10 includes: a primary-side switch circuit 14; and a first resonant coil Land a second resonant coil L. In the insulated DC/DC converter, at a low load current, an inductance value of the second resonant coil Lis higher than that of the first resonant coil Land becomes dominant, while, at a high load current, the inductance value of the first resonant coil is higher than that of the second resonant coil Land becomes dominant. The insulated DC/DC converter is configured such that a rate of change of a combined inductance value becomes larger at the low load current than that at the high load current. The primary-side switch circuit 14 is activated by zero voltage switching both at the low load current and at the high load current.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an insulation type DC / DC converter.

  In recent years, in order to realize a recycling society as a measure against global warming, it is urgently necessary to realize energy saving and high efficiency of power supply equipment. Among them, an insulation type DC / DC converter mounted on an air conditioner, a solar power generation device, a household storage battery, an automobile, or the like is used for various applications as a core of power supply equipment. In particular, the phase shift type full bridge type DC / DC converter has a medium size and high efficiency of several kilos to several tens of kilowatts and can correspond to a wide range of voltages. For this reason, realizing the energy saving and high efficiency of the phase shift type full bridge type DC / DC converter will greatly advance the realization of a recycling society.

FIG. 10 shows a phase shift type full bridge type DC / DC converter 1 described in Non-Patent Document 1. In the phase shift method full-bridge DC / DC converter 1, energy saving, in order to achieve high efficiency, the leakage inductance and / or external resonant coil _{L 1} of the transformer TR _1, switching element _Q 1 to Q ₄ The switching elements Q _{1 to} Q ₄ are preferably turned on / off by zero voltage switching (ZVS) by the action of the parasitic capacitors and / or the external capacitors C _{1 to} C ₄ .

If by the action of an external resonant coil _{L 1} and the external capacitor _C 1 -C ₄ realizing zero-voltage switching, charging and discharging time of the external capacitor _C 1 -C ₄ is from the turn-off time of the switching elements _Q 1 to Q ₄ as becomes longer, thereby determining the capacitance of the external capacitors C ₁ -C _4, the energy stored in the external resonant coil L _1, to complete the charge and discharge of external capacitors C ₁ -C ₄ It needs to be large enough.

However, since the energy stored in the external resonant coil L ₁ is proportional to the square of the load current flowing in the external resonant coil L _1, the low load current, to achieve zero-voltage switching in the energy shortage I can't. In this case, the switching elements Q _{1 to} Q ₄ are turned on / off by hard switching, switching loss increases, and efficiency decreases. On the other hand, increasing the inductance value of the external resonant coil L ₁ in an attempt to avoid this, since the resonance time is too long, can not be ensured ON duty of the switching element Q ₁ to Q _4, the output is reduced Or the loss may increase at a high load current.

  By the way, in Patent Document 1, in a simple inverter device including a variable impedance type resonance coil composed of a saturable reactor and a switching element, resonance amplitude detection means is provided, and the output of the resonance amplitude detection means is constant. It has been proposed to increase the inductance value of the resonant coil when the value is below the value.

  However, the inverter device described in Patent Document 1 is greatly different in configuration from the above-described phase shift type full bridge type DC / DC converter 1. Moreover, the saturable reactor generally has a characteristic that the inductance value changes sharply. For this reason, even if the proposal of Patent Document 1 is adopted in the phase shift type full bridge type DC / DC converter 1, it is difficult to obtain a desired inductance value at both low load current and high load current.

  Patent Document 2 discloses an inductor whose inductance value changes according to the current value based on the knowledge that adjusting the inductance value of the resonance circuit is effective for realizing zero voltage switching in the DC / DC converter. It has been proposed to use a variable inductor having a gap-shaped coil-shaped core having a special curved surface shape.

  However, there is no description about whether or not the inductance value required by the variable inductor can be obtained, and the variable inductor has an increased processing cost, the necessity of cooling measures due to heat generation, and the adjustment of the inductance value is difficult. There is a problem that it cannot be used due to temperature rise. For this reason, it is practically difficult to use the variable inductor of Patent Document 2 in the phase shift type full bridge type DC / DC converter 1.

Japanese Unexamined Patent Publication No. 7-87747 Japanese Patent No. 3682773

Katsuya Hirachi, “Technical Memo No. 201110928 of the Flatland Laboratory, Principle of Soft Switching of Phase-Shift Full Bridge DC / DC Converter”, [online], September 28, 2011, Maizuru National College of Technology, [June 24, 2016 Day search], Internet <URL: http://hirachi.cocolog-nifty.com/kh/files/20110928-1.pdf>

  This invention is made | formed in view of the said situation, The place made into the subject is providing the insulation type DC / DC converter which can implement | achieve energy saving and high efficiency.

In order to solve the above problems, an insulated DC / DC converter according to the present invention provides:
An insulating transformer having a primary winding and a secondary winding;
A primary side circuit including a primary side switch circuit provided on the primary side of the insulating transformer,
A secondary circuit provided on the secondary side of the insulating transformer,
A control circuit for performing phase shift control on the primary side switch circuit;
An isolated DC / DC converter comprising:
The primary side circuit includes a first resonance coil and a second resonance coil provided between the primary side switch circuit and the primary winding,
The first resonance coil, the second resonance coil, and the primary winding are connected in series with each other,
The first resonance coil and the second resonance coil are:
When the load current is low, the inductance value of the second resonance coil becomes higher than the inductance value of the first resonance coil, and when the load current is high, the inductance value of the first resonance coil is the same as that of the second resonance coil. Higher than the inductance value, and
The rate of change of the combined inductance value of the first resonance coil and the second resonance coil is configured to be larger at the low load current than at the high load current,
The control circuit includes:
The primary side switch circuit is operated by zero voltage switching both at the low load current and at the high load current.

  According to this configuration, since the primary side switch circuit is operated with zero voltage switching at both low load current and high load current, the switching loss of the switch elements constituting the primary side switch circuit is reduced, Efficiency can be improved over a wide load current range including both low load current and high load current, which contributes to energy saving. In addition, since the switching loss is reduced, in a power supply device including the insulated DC / DC converter, it is possible to reduce the noise by reducing the size of the heat sink and reducing the capacity of the cooling fan.

In the insulation type DC / DC converter,
The primary side switch circuit is a full bridge circuit,
The first resonance coil has one end connected to a connection point of the first switch element and the second switch element constituting the first leg of the full bridge circuit, and the other end connected to one end of the primary winding,
One end of the second resonance coil is connected to a connection point of the third switch element and the fourth switch element constituting the second leg of the full bridge circuit, and the other end is connected to the other end of the primary winding. Can be configured.

In the insulation type DC / DC converter,
A first rectifying element having an anode connected to the other end of the first resonance coil and a cathode connected to one end of the first leg;
A second rectifying element having an anode connected to the other end of the first leg and a cathode connected to the other end of the first resonance coil;
A third rectifying element having an anode connected to the other end of the second resonance coil and a cathode connected to one end of the second leg;
A fourth rectifying element having an anode connected to the other end of the second leg and a cathode connected to the other end of the second resonance coil,
The secondary side circuit includes a secondary side switch circuit,
The control circuit preferably performs synchronous rectification control on the secondary side switch circuit to perform a reverse power conversion operation for supplying power from the secondary side to the primary side of the insulating transformer.

  According to this configuration, the first resonance coil and the second resonance coil provide impedance between the full bridge circuit and the insulating transformer, and the first to fourth rectifier elements bypass the first to fourth switch elements. To prevent the current from flowing through the first to fourth switch elements during the reverse power conversion operation, so that the parasitic capacitors or the outside of the first to fourth switch elements are switched when the first to fourth switch elements are switched. It is possible to suppress voltage oscillation generated by discharging the charge of the attached resonant capacitor.

In the insulation type DC / DC converter,
The first resonance coil and the second resonance coil may be configured such that at least one of a material, a shape, a size, and a number of turns is different.

  ADVANTAGE OF THE INVENTION According to this invention, the insulation type DC / DC converter which can implement | achieve energy saving and high efficiency can be provided.

1 is a circuit diagram of an isolated DC / DC converter according to a first embodiment of the present invention. It is a figure which shows the ideal inductance characteristic of a resonance coil. It is a figure which shows the inductance characteristic of a 1st resonance coil. It is a figure which shows the inductance characteristic of a 2nd resonance coil. It is a figure which shows the synthetic | combination inductance characteristic and ideal inductance characteristic of a 1st resonance coil and a 2nd resonance coil. It is a figure which shows the relationship between the winding number of a resonance coil, and an inductance characteristic. It is a circuit diagram of the insulation type DC / DC converter which concerns on 2nd Embodiment of this invention. It is a timing chart of the switch element at the time of reverse direction power conversion operation. It is a timing chart of the switch element at the time of forward power conversion operation. It is a circuit diagram of the conventional insulation type DC / DC converter.

  Hereinafter, an embodiment of an insulated DC / DC converter 10 according to the present invention will be described with reference to the accompanying drawings.

[First Embodiment]
FIG. 1 shows an isolated DC / DC converter 10 according to a first embodiment of the present invention. The insulation type DC / DC converter 10 includes a transformer TR ₁₀ (corresponding to the “insulation transformer” of the present invention) having a primary winding and a secondary winding, and a primary side (primary winding side) of the transformer TR _10. ) Provided on the secondary side (secondary winding side) of the transformer TR ₁₀ , and a control circuit 13. Here, in consideration of conversion efficiency and suppression of heat generation, the transformer TR ₁₀ is assumed to use a transformer with a relatively high degree of coupling (leakage of magnetic flux).

The isolated DC / DC converter 10 is a phase shift-synchronous rectification type full-bridge DC / DC converter, and includes a forward power conversion operation for supplying power from the primary side to the secondary side of the transformer TR ₁₀ , and a transformer TR. ₁₀ performs a reverse power conversion operation for supplying power from the secondary side to the primary side.

The primary side circuit 11 includes a smoothing capacitor C ₁₀ , a full bridge circuit 14, a first resonance coil L _11, and a second resonance coil L ₁₂ .

Smoothing capacitor C ₁₀ is connected at one end to the output terminal T ₁₁ of the high potential side and the other end is connected to the low potential side of the input and output terminals T _{11 '.}

Full-bridge circuit 14 includes a first switching element _{Q 11,} and the second switching element _{Q 12,} a third switch element _{Q 13,} and a fourth switching element _{Q 14.} The first switch element _{Q 11} the upper arm of the first leg, the second switching element _{Q 12} lower arm of the first leg, the third switching element _{Q 13} arms on the second leg, the fourth switching element _{Q 14} second Configure the lower arm of 2 legs. The first to fourth switch elements Q _{11 to} Q ₁₄ perform ON / OFF operations by phase shift under the control of the control circuit 13. That is, based on the first switching element _{Q 11} and the second switching element _{Q 12} of the the first switching element _{Q 11} 180 degrees phase-inverted with respect to ON / OFF operation at 50% duty, ON / OFF 50% duty The operating third switch element Q ₁₃ and the fourth switch element Q ₁₄ whose phase is inverted by 180 degrees with respect to the third switch element Q ₁₃ are controlled by a phase shift amount corresponding to the load. As the first to fourth switch elements Q _{11 to} Q ₁₄ , for example, power elements such as IGBT and MOSFET can be used.

Each of the first to fourth switching elements _Q 11 _{to Q 14,} diode _D 11 _{to D 14} are connected in inverse-parallel. As the diode, each of the first to fourth switching elements Q _{11 to} Q ₁₄ and an external diode element different from the parasitic diode can be used. Furthermore, capacitors C _{11 to} C ₁₄ are connected in parallel to the first to fourth switch elements Q _{11 to} Q ₁₄ , respectively. As the capacitors C _{11 to} C ₁₄ , parasitic capacitors of the first to fourth switch elements Q _{11 to} Q ₁₄ , or external resonance capacitors different from the parasitic capacitors can be used.

The first resonance coil L ₁₁ has one end connected to a connection point between the first switch element Q ₁₁ and the second switch element Q ₁₂ and the other end connected to one end of the primary winding of the transformer TR ₁₀ . The second resonance coil L ₁₂ has one end connected to the connection point of the third switch element Q ₁₃ and the fourth switch element Q ₁₄ and the other end connected to the other end of the primary winding of the transformer TR ₁₀ . That is, during the forward power conversion operation, the first resonance coil L ₁₁ , the second resonance coil L _12, and the capacitors C _{11 to} C ₁₄ are partially resonant circuits when the first to fourth switch elements Q _{11 to} Q ₁₄ are switched. And the soft switching operation (zero voltage switching operation) of the first to fourth switch elements Q _{11 to} Q ₁₄ is realized.

Appropriate range of the resonant inductance of the partial resonance circuit, the relationship between the resonance time and the. 1 to ON-duty of the fourth switching element Q ₁₁ to Q _14, determined by the input voltage and current range of isolated DC / DC converters 10 be able to. For example, the minimum value and the maximum value of the resonance inductance can be determined by the following equations.
Minimum value = Resonance capacitance x Input voltage / Minimum resonance operating current Maximum value = Transformer primary voltage x Trans dead time / Transformer primary peak current

In the above formula, the resonant capacitance is the capacitance value of the capacitors C _{11 to} C ₁₄ . The input voltage is a voltage value of a voltage input to the input / output terminals T ₁₁ and T ₁₁ ′ of the isolated DC / DC converter 10. The minimum resonance operating current is a minimum current value required for the first resonance coil L ₁₁ , the second resonance coil L _12, and the capacitors C _{11 to} C ₁₄ to perform partial resonance. Incidentally, on the assumption that the leakage magnetic flux of the transformer _{TR 10} is small, the first resonance coil _{L 11,} although the inductor value of the second resonance coil _{L 12} is dominant, the leakage flux of the transformer _{TR 10} is if it is greater, it is necessary to consider the leakage magnetic flux of the transformer TR _10. Transformer primary voltage is the voltage value of the voltage applied to the primary winding of the transformer TR _10. The dead time is a time during which both switch elements located diagonally in the full bridge circuit 14 are in the OFF state. Transformer primary side peak current is the peak value of the current flowing in the primary winding of the transformer TR _10.

More practically, the ideal inductance characteristic of the resonant inductance can be experimentally determined in a specified current range. Table 1 shows the inductance value and the load current value of the resonance inductance determined experimentally (peak current value flowing through the primary winding of the transformer TR _10), in FIG. 2, the ideal inductance characteristic approximated calculated from Table 1 Show.

  As shown in FIG. 2, the ideal inductance characteristic is such that the rate of change of the inductance value with respect to the load current becomes large at low load current (4 to 11 [A] in the present embodiment), while at high load current ( In the present embodiment, the rate of change is small in 11 to 22 [A]). In general, a core such as a ferrite having a large inductance value at a low load current has a large rate of change of the inductance value with respect to the current, and the core is saturated at a high load current and loses the inductance value. On the other hand, in the case of an iron dust material core that maintains a desired inductance value even at high load currents, the rate of change of the inductance value with respect to the current is small, and it is difficult to obtain a desired inductance value even at low load currents. For this reason, it is not realistic to realize the ideal inductance characteristic with one resonance coil.

Therefore, in the present embodiment, the above-described ideal inductance characteristic is realized by two resonance coils having different characteristics, the first resonance coil L ₁₁ and the second resonance coil L ₁₂ . That is, the inductance value at low load currents are low, the first resonance coil L ₁₁ of iron dust material or the like having a the gradual deterioration of characteristics of the inductance even at a high load current, high inductance values at low load currents, a high load in the combined inductance of the second resonance coil L _12, such as ferrite or amorphous material with reduced large characteristic inductance value when current is realized ideal inductance characteristics described above.

In other words, the inductance value of the second resonance coil L ₁₂ during low load current becomes higher dominant than the inductance value of the first resonance coil L _11, the inductance value of the first resonance coil L ₁₁ is at the time of high load currents It becomes higher dominant than the inductance value of the second resonance coil L _12. Then, the change rate of the combined inductance value of the first resonance coil L ₁₁ and the second resonance coil L ₁₂ is better at low load current is greater than at high load currents.

Table 2 shows the inductance value and the load current value of the first resonance coil L ₁₁ experimentally obtained. FIG. 3 shows the inductance characteristics approximately calculated from Table 2 in accordance with the high load current range of Table 1 (11 to 22 [A] in the present embodiment).

Table 3 shows the inductance value and the load current value of the second resonance coil L ₁₂ experimentally obtained. FIG. 4 shows the inductance characteristics approximately calculated from Table 3 in accordance with the low load current range shown in Table 1 (4 to 11 [A] in the present embodiment).

Table 4, the inductance value of the second resonance coil L ₁₂ calculated from the inductance characteristics of FIG. 4, the inductance value of the first resonance coil L ₁₁ calculated from the inductance characteristics of Figure 3, the first resonance coil L ₁₁ and the showing the combined inductance value of the second resonance coil _{L 12.} FIG. 5 shows the combined inductance characteristics approximately calculated from Table 4 and the ideal inductance characteristics shown in FIG.

From Figure 5, in this embodiment, the first resonance coil L ₁₁ by the combined inductance of the second resonance coil L _12, it can be seen that to achieve the ideal inductance characteristic of the resonant inductance. As a result, in the present embodiment, the soft switching operation (zero voltage switching operation) of the first to fourth switch elements Q _{11 to} Q ₁₄ can be realized both in the low load current and the high load current. , Can contribute to energy saving. Further, since the switching loss is reduced by the soft switching operation, in the power supply device including the insulation type DC / DC converter 10, it is possible to reduce the noise due to the downsizing of the heat sink and the reduction in the capacity of the cooling fan.

In the present embodiment, in order to realize an ideal inductance characteristic by the combined inductance of the first resonance coil L ₁₁ and the second resonance coil L ₁₂ , the first resonance coil L ₁₁ uses an iron dust system as a magnetic core that is not easily saturated. and, the second resonance coil L ₁₂ is using ferritic or amorphous material as easy magnetic core saturation.

Further, by changing the first resonant coil L ₁₁ the number of turns of the second resonance coil L _12, as shown in FIG. 6, it is possible to change the inductance characteristics at low load currents. Specifically, by increasing the number of turns (number of turns C <number of turns B <number of turns A), it is possible to increase the inductance value at the time of low load current.

Referring again to FIG. 1, the secondary circuit 12 includes a fifth switch element _{Q 15} and the sixth switching element consisting of _{Q 16} secondary switch circuit (push-pull circuit) 15, a coil _{L 13} and the smoothing capacitor C ₁₅ LC circuit.

The control circuit 13 is configured by a control IC (integrated circuit) such as a microcomputer or FPGA (field programmable gate array). The control circuit 13 during forward power conversion performs phase shift control for shifting the phase of the PWM signals of the first to fourth switch elements Q _{11 to} Q ₁₄ with respect to the full bridge circuit 14, and the secondary side switch circuit 15. fifth, it performs synchronous rectification control to synchronize the switching operation of the sixth switch element _{Q 15, Q 16} to the switching operation of the first to fourth switching elements _Q 11 _{to Q 14} against.

The control circuit 13 performs phase shift control and synchronous rectification control so that the secondary-side terminal voltage _VOUT is maintained during forward power conversion, but the terminal voltage _VOUT is defined in advance by an external power source or the like. When the voltage rises above the specified voltage, the above control (phase shift control for the full bridge circuit 14 and synchronous rectification control for the secondary side switch circuit 15) is performed and the secondary side is reversed to the primary side. Direction power conversion.

Specifically, the control circuit 13, the OFF time of the second switching element _{Q 12} are slightly longer than the ON time of the first switching element _{Q 11,} a first switching element _{Q 11} and the second switching element _{Q 12} so they contain a dead time together in the OFF state, the first switch element _{Q 11} with inverting the phase of the second switching element _{Q 12,} the OFF time of the third switch element _{Q 13} of the fourth switching element _{Q 14} and slightly longer than the oN time, to include a dead time and the third switching element _{Q 13} and the fourth switching element _{Q 14} is both OFF state, the third switching element _{Q 13} of the fourth switching element _{Q 14} Invert the phase. Further, the control circuit 13, with respect to the first switching element _{Q 11} and the second switch element _{Q 12} phase shifts the phase of the third switching element _{Q 13} and the fourth switch element _{Q 14.} The amount of phase shift during the reverse power conversion operation is minimized because it is controlled to minimize the amount of power conversion in the forward direction.

Further, the control circuit 13, a fifth switch element _{Q 15} only when the first switching element _{Q 11} and the fourth switch element _{Q 14} are both ON state to the OFF state, the second switching element _{Q 12} and the third switching element Q ₁₃ is in the OFF state the sixth switch element _{Q 16} only when both of the oN state.

  The phase shift control during the forward power conversion operation is common to the phase shift control during the reverse power conversion operation, except for the phase shift amount. Since the phase shift amount during the forward power conversion operation is controlled by the forward power conversion amount, it is generally set to a value larger than the phase shift amount during the reverse power conversion operation. On the other hand, the synchronous rectification control during the forward power conversion operation is common to the synchronous rectification control during the reverse power conversion operation.

[Second Embodiment]
FIG. 7 shows an insulated DC / DC converter 20 according to a second embodiment of the present invention. The insulation type DC / DC converter 20 includes a transformer TR ₂₀ (corresponding to the “insulation transformer” of the present invention) having a primary winding and a secondary winding, and a primary side (primary winding side) of the transformer TR _20. ) Provided at the secondary side (secondary winding side) of the transformer TR ₂₀ , and a control circuit 23.

The isolated DC / DC converter 20 is a phase shift-synchronous rectification type full bridge type DC / DC converter, and includes a forward power conversion operation for supplying power from the primary side to the secondary side of the transformer TR ₂₀ , and a transformer TR. ₂₀ performs a reverse power conversion operation for supplying power from the secondary side to the primary side.

Primary circuit 21 includes a smoothing capacitor _{C 20,} a primary full-bridge circuit 24, a first resonance coil _{L 21,} and a second resonance coil _{L 22,} and a first rectifying element _{D A,} second rectifying element It comprises a D _B, a third rectifier element _{D C,} and a fourth rectifier element _{D D.} The primary side circuit 21 is mostly in common with the primary side circuit 11 in the first embodiment except that the primary side circuit 21 includes first to fourth rectifying elements D _{A to} D _D.

The first rectifying element D _A, a diode, an anode connected to the other end of the first resonance coil L _21, a cathode connected to one end of the first leg of the primary full-bridge circuit 24. In other words, the first rectifier element D _A, connected in parallel with the first switching element Q ₂₁ via the first resonance coil L _21, a first resonance coil L ₂₁ and the first switching element Q when switching the reverse power conversion operation A current path that bypasses ₂₁ is formed.

Second rectifying element D _B is a diode, the cathode is connected to the other end of the first resonance coil L _21, anode connected to the other end of the first leg of the primary full-bridge circuit 24. That is, the second rectifying element D _B is connected in parallel to the second switching element Q ₂₂ via the first resonance coil L _21, a first resonance coil L ₂₁ and the second switch element Q when switching the reverse power conversion operation A current path that bypasses ₂₂ is formed.

Third rectifying element D _C is a diode, the anode is connected to the other end of the second resonance coil L _22, a cathode connected to one end of the second leg of the primary full-bridge circuit 24. That is, the third rectifier element D _C is connected in parallel to the third switching element Q ₂₃ through a second resonance coil L _22, a second resonance coil L ₂₂ and the third switch element Q when switching the reverse power conversion operation A current path that bypasses ₂₃ is formed.

Fourth rectifying element D _D is a diode, the cathode is connected to the other end of the second resonance coil L _22, anode connected to the other end of the second leg of the primary full-bridge circuit 24. That is, the fourth rectifier element D _D is connected in parallel to the fourth switching element Q ₂₄ through a second resonance coil L _22, a second resonance coil L ₂₂ and the fourth switch element Q when switching the reverse power conversion operation A current path that bypasses ₂₄ is formed.

The first resonance coil L ₂₁ has one end connected to a connection point between the first switch element Q ₂₁ and the second switch element Q ₂₂ , and the other end connected to one end of the primary winding of the transformer TR ₂₀ . The second resonance coil L ₂₂ has one end connected to the connection point of the third switch element Q ₂₃ and the fourth switch element Q ₂₄ , and the other end connected to the other end of the primary winding of the transformer TR ₂₀ . That is, during the forward power conversion operation, the first resonance coil L ₂₁ , the second resonance coil L ₂₂ , each parasitic capacitor and the external resonance capacitors C _{A to} C _D are connected to the first to fourth switch elements Q _{21 to} Q. _A partial resonance circuit is configured at the time of ₂₄ switching, and a soft switching operation (zero voltage switching operation) of the first to fourth switching elements Q _{21 to} Q ₂₄ is realized.

Furthermore, as in the first embodiment, the inductance value of the second resonance coil L ₂₂ at the time of low load current becomes higher dominant than the inductance value of the first resonance coil L _21, a first resonance at the time of high load currents inductance value of the coil L ₂₁ becomes higher dominant than the inductance value of the second resonance coil L _22. Then, the change rate of the combined inductance value of the first resonance coil L ₂₁ and the second resonance coil L ₂₂ is better at low load current is greater than at high load currents. For this reason, the soft switching operation (zero voltage switching operation) of the first to fourth switch elements Q _{21 to} Q ₂₄ can be realized at both low load current and high load current, which contributes to energy saving. be able to.

The secondary side circuit 22 includes a secondary side full bridge circuit 25 and a secondary side LC circuit including a coil L ₂₃ and a smoothing capacitor C ₂₅ provided in a subsequent stage of the secondary side full bridge circuit 25.

The secondary full bridge circuit 25 includes a fifth switch element Q ₂₅ , a sixth switch element Q ₂₆ , a seventh switch element Q _27, and an eighth switch element Q ₂₈ . The fifth to eighth switch elements Q _{25 to} Q ₂₈ perform a switching operation under the control of the control circuit 23. As the fifth to eighth switch elements Q _{25 to} Q ₂₈ , power elements such as IGBTs and MOSFETs can be used.

Each of the first to eighth switching elements _Q 25 _{to Q 28,} diode are connected in inverse-parallel. As the diodes, parasitic diodes of the fifth to eighth switch elements Q _{25 to} Q ₂₈ or a diode element different from the parasitic diode can be used. Further, each of the fifth to eighth switching elements _Q 25 _{to Q 28,} a capacitor is connected in parallel. As the capacitor, the parasitic capacitors of the fifth to eighth switch elements Q _{25 to} Q ₂₈ or an external resonant capacitor different from the parasitic capacitor can be used.

The control circuit 23 is configured by a control IC (integrated circuit) such as a microcomputer or FPGA (field programmable gate array). The control circuit 23 performs phase shift control for shifting the phase of the PWM signals of the first to fourth switch elements Q _{21 to} Q ₂₄ with respect to the primary side full bridge circuit 24. On the other hand, synchronous rectification control for synchronizing the switching operation of the fifth to eighth switch elements Q _{25 to} Q _{28 with} the switching operation of the primary side full bridge circuit 24 is performed.

FIG. 8 shows a timing chart of the first to eighth switch elements Q _{21 to} Q ₂₈ during the reverse power conversion operation. Incidentally, as shown in FIG. 8, PWM duty of the primary full-bridge circuit 24 (PWM duty of the first switching element _{Q 21} and the third switch element _{Q 23)} is assumed to be set to 50%.

When the voltage between the terminals T ₂₂ and T ₂₂ ′ on the secondary side rises above a specified voltage that is defined in advance by an external power source or the like during the forward power conversion operation, the control circuit 23 controls the phase with respect to the primary side full bridge circuit 24. Shift power is converted from the secondary side to the primary side while performing synchronous rectification control on the secondary full bridge circuit 25.

Specifically, the control circuit 23, the OFF time of the second switching element _{Q 22} are slightly longer than the ON time of the first switching element _{Q 21,} a first switching element _{Q 21} and the second switching element _{Q 22} Invert the phases of the first switch element Q ₂₁ and the second switch element Q ₂₂ so as to include the dead time (time t _{2 to} t _{3 in} FIG. 8) in which both are in the OFF state, and the third switch element Q _23. the OFF time slightly longer than the oN time of the fourth switching element _{Q 24,} the time _t 4 ~ dead time (Fig. 8 in which the third switching element _{Q 23} and the fourth switching element _{Q 24} is both OFF state to include a t _5), reversing a third switch element _{Q 23} of the phase of the fourth switching element _{Q 24.} Further, the control circuit 23, the phase of the first switching element _{Q 21} and the second switch element _{Q 22,} shifts the phase of the third switching element _{Q 23} and the fourth switch element _{Q 24.} The amount of phase shift during the reverse power conversion operation is minimized because it is controlled to minimize the amount of power conversion in the forward direction.

Further, the control circuit 23, a first switching element _{Q 21} and the fourth to sixth switching elements _{Q 26} and the seventh switch element _{Q 27} only when both the ON state switching element _{Q 24} is turned OFF, the second switch element the Q ₂₂ and the third switch element fifth switching element only when _{Q 23} are both oN state _{Q 25} and the eighth switch element _{Q 28} is in the OFF state.

At time _t 2 ~t Isolated in ₅ DC / DC converter 20, since the fifth to eighth switching elements _Q 25 _{to Q 28} is turned ON, 2 without current flows through the secondary winding of the transformer _{TR 20} A current flows through the coil L ₂₃ of the secondary LC circuit, and energy is stored in the coil L ₂₃ .

When the fifth switching element _{Q 25} and the eighth switch element _{Q 28} is turned OFF at time _t 5 ~t _6, current flows through the secondary winding of the transformer _{TR 20,} power is supplied to the primary side. On the primary side, the third switch element Q ₂₃ is turned on and the second switch element Q ₂₂ and the third switch element Q ₂₃ are turned on, but the first resonance coil L ₂₁ and the second resonance coil L ₂₂ are turned on. since act to inhibit the current flowing through the second switching element Q ₂₂ and the third switch element Q _23, current flows through the second rectifier element D _B and the third rectifier element D _C. Therefore, the voltage oscillation parasitic capacitor and an external charge resonant capacitor C _C of the third switch turns ON at the third switching element Q ₂₃ of the element Q ₂₃ is produced by being released is suppressed.

In the insulated DC / DC converter 20 at the time t _{6 to} t ₉ , the fifth to eighth switch elements Q _{25 to} Q ₂₈ are turned on, so that no current flows through the secondary winding of the transformer TR ₂₀ . energy is accumulated in the coil _{L 23.}

When the sixth switch element Q ₂₆ and the seventh switch element Q ₂₇ are turned off at time t _{9 to} t ₁₀ , a current opposite to that at time t ₅ to t ₆ flows through the secondary winding of the transformer TR _20. Electric power is supplied to the primary side. On the primary side, the fourth switch element Q ₂₄ is turned on and the first switch element Q ₂₁ and the fourth switch element Q ₂₄ are turned on, but the first resonance coil L ₂₁ and the second resonance coil L ₂₂ are turned on. since act to inhibit the current flowing through the first switching element Q ₂₁ and the fourth switch element Q _24, current flows through the first rectifier element D _a and a fourth rectifier element D _D. Therefore, the voltage oscillation charge resonant capacitor C _D of the parasitic capacitor and an external fourth switching element turns ON at the fourth switching element Q ₂₄ of Q ₂₄ is produced by being released is suppressed.

FIG. 9 shows a timing chart of the first to eighth switch elements Q _{21 to} Q ₂₈ during the forward power conversion operation. As shown in FIG. 9, the phase shift control during the forward power conversion operation is common to the phase shift control during the reverse power conversion operation except for the phase shift amount. Since the amount of phase shift is controlled by the amount of power conversion in the forward direction, the phase shift amount is larger than that during reverse power conversion operation. On the other hand, the synchronous rectification control during the forward power conversion operation is common to the synchronous rectification control during the reverse power conversion operation.

Eventually, in the present embodiment, the ideal inductance characteristic is realized by the combined inductance of the first resonance coil L ₂₁ and the second resonance coil L ₂₂ , and therefore, the first to the first resonance coil L ₂₁ at both low load current and high load current. The soft switching operation (zero voltage switching operation) of the fourth switch elements Q _{21 to} Q ₂₄ can be realized, which can contribute to energy saving. Further, since the switching loss is reduced by the soft switching operation, in the power supply device including the insulated DC / DC converter 20, it is possible to reduce the noise due to the downsizing of the heat sink and the reduction in the capacity of the cooling fan.

Further, in the present embodiment, the first to fourth rectifying elements D _{A to} D _D form a current path that bypasses the first to fourth switch elements Q _{21 to} Q ₂₄ , and the first power conversion operation is performed during the reverse power conversion operation. by hardly-current flows through the fourth switching element _Q 21 _{to Q 24,} first to fourth parasitic capacitor of the switch element _Q 21 _{to Q} the first to fourth switching elements _Q 21 _{to Q 24} at the time of switching of ₂₄ and / or external charge resonant capacitor C _a -C _D can be suppressed voltage vibration generated by being released. Therefore, according to the insulated DC / DC converter 20, it is possible to efficiently perform power supply from the primary side to the secondary side and power supply from the secondary side to the primary side.

  As mentioned above, although embodiment of the insulation type DC / DC converter concerning the present invention was described, the present invention is not limited to each above-mentioned embodiment.

In the present invention, at least one of the switching pattern in the phase shift control or the switching pattern in the synchronous rectification control can be appropriately changed. For example, in the second embodiment, to perform the phase shift between the rising and falling of the fourth switching element Q ₂₄ edge of the first switching element Q _21, the first switching element Q ₂₁ and the fourth switch element Q ₂₄ is When the switches are simultaneously turned on, the sixth switch element Q ₂₆ and the seventh switch element Q ₂₇ may be turned off to perform synchronous rectification.

The primary side circuit of the present invention has a voltage topology circuit topology, includes a primary side switch circuit, a first resonance coil, and a second resonance coil, and includes a first resonance coil, a second resonance coil, and an insulating transformer 1. If the next windings are connected in series with each other, the configuration can be changed as appropriate. For example, the first resonance coil L ₁₁ of the first embodiment has one end connected to the connection point of the first switch element Q ₁₁ and the second switch element Q ₁₂ and the other end via the second resonance coil L _12. it may be connected to one end of the primary winding of the transformer TR _10.

  In the first resonance coil and the second resonance coil of the present invention, the inductance value of the second resonance coil is dominantly higher than the inductance value of the first resonance coil at the time of low load current, and the first resonance coil at the time of high load current. The inductance value of the coil becomes dominant higher than the inductance value of the second resonance coil, and the rate of change of the combined inductance value of the first resonance coil and the second resonance coil is lower than when the load current is high. As long as the zero voltage switching of the full bridge circuit can be realized at both low load current and high load current, the configuration can be changed as appropriate.

  The secondary side switch circuit included in the secondary side circuit of the present invention can be appropriately changed in configuration as long as the synchronous rectification control is performed by the control circuit of the present invention.

  The insulated DC / DC converter according to the present invention may be a soft switching type such as a partial resonance or resonance type using the first resonance coil and the second resonance coil. For example, instead of the voltage type full bridge + current type push-pull circuit as in the first embodiment or the voltage type full bridge + current type full bridge circuit as in the second embodiment, a voltage type half bridge + current A type push-pull circuit, a voltage type half bridge + current type full bridge circuit, or the like may be employed.

  The insulation transformer part of the present invention may be composed of, for example, a plurality of transformers connected in series or in parallel.

10, 20 Insulation type DC / DC converter 11, 21 Primary side circuit 12, 22 Secondary side circuit 13, 23 Control circuit 14 Full bridge circuit 15 Secondary side switch circuit (push-pull circuit)
24 Primary side full bridge circuit 25 Secondary side full bridge circuit

Claims (4)

An insulating transformer having a primary winding and a secondary winding;
A primary side circuit including a primary side switch circuit provided on the primary side of the insulating transformer,
A secondary circuit provided on the secondary side of the insulating transformer,
A control circuit for performing phase shift control on the primary side switch circuit;
An isolated DC / DC converter comprising:
The primary side circuit includes a first resonance coil and a second resonance coil provided between the primary side switch circuit and the primary winding,
The first resonance coil, the second resonance coil, and the primary winding are connected in series with each other,
The first resonance coil and the second resonance coil are:
When the load current is low, the inductance value of the second resonance coil becomes higher than the inductance value of the first resonance coil, and when the load current is high, the inductance value of the first resonance coil is the same as that of the second resonance coil. Higher than the inductance value, and
The rate of change of the combined inductance value of the first resonance coil and the second resonance coil is configured to be larger at the low load current than at the high load current,
The control circuit includes:
An isolated DC / DC converter, wherein the primary side switch circuit is operated with zero voltage switching both at the low load current and at the high load current. The primary side switch circuit is a full bridge circuit,
The first resonance coil has one end connected to a connection point of the first switch element and the second switch element constituting the first leg of the full bridge circuit, and the other end connected to one end of the primary winding,
One end of the second resonance coil is connected to a connection point of the third switch element and the fourth switch element constituting the second leg of the full bridge circuit, and the other end is connected to the other end of the primary winding. The insulated DC / DC converter according to claim 1, wherein: A first rectifying element having an anode connected to the other end of the first resonance coil and a cathode connected to one end of the first leg;
A second rectifying element having an anode connected to the other end of the first leg and a cathode connected to the other end of the first resonance coil;
A third rectifying element having an anode connected to the other end of the second resonance coil and a cathode connected to one end of the second leg;
A fourth rectifying element having an anode connected to the other end of the second leg and a cathode connected to the other end of the second resonance coil,
The secondary side circuit includes a secondary side switch circuit,
The control circuit performs synchronous rectification control on the secondary side switch circuit, and performs a reverse power conversion operation for supplying power from the secondary side to the primary side of the insulation transformer. The insulated DC / DC converter according to claim 2. The insulated DC / DC converter according to any one of claims 1 to 3, wherein the first resonance coil and the second resonance coil are different in at least one of material, shape, size, and number of turns. .

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