Power conversion system

Abstract

To provide a power conversion system which mitigates heat concentration to switching elements in a part of a plurality of switching elements.SOLUTION: A power conversion system 100a comprises an insulation transformer 102 and comprises a first bridge circuit 111 and a second bridge circuit 112 on a primary side and a secondary side of the insulation transformer 102. Each of the bridge circuits comprises: an insulation DC / DC converter 110 including one or more switching elements connected in series and consisting of a plurality of legs connected in parallel with each other; and a control device 106a which generates a drive pulse for driving the switching elements of the insulation DC / DC converter 110. The control device 106a periodically performs a timing switching operation for switching ON timing of a drive pulse for one leg and OFF timing of a drive pulse for the other leg in the drive pulses for one bridge circuit.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a power conversion system that uses an isolated DC / DC converter. [Background technology]

[0002] FIG. 11 is a circuit diagram showing an example configuration of a power conversion system 100 that uses an isolated DC / DC converter 110. The isolated DC / DC converter 110 has an isolated transformer 102 whose primary and secondary windings are electrically isolated. A series inductor 104a is connected to the primary winding of the isolated transformer 102. This series inductor 104a is the leakage inductance of the primary winding of the isolated transformer 102 or an external inductance added to this leakage inductance. Note that if only the leakage inductance is used for power transmission, the external inductance is not necessary. A similar series inductor 104b is also connected to the secondary winding of the isolated transformer 102.

[0003] The first bridge circuit 111 is a circuit that supplies a primary AC voltage v1 to a primary winding of the isolation transformer 102. The first bridge circuit 111 is a full bridge circuit in which a leg 131 made up of series-connected switching elements 101a and 101b and a leg 132 made up of series-connected switching elements 101c and 101d are connected in parallel. In this example, each of the switching elements 101a to 101d is made up of a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) and a diode connected in anti-parallel to the MOSFET. A capacitor 103a is connected in parallel to the first bridge circuit 111. A primary DC voltage E1 is applied to the first bridge circuit 111. In this first bridge circuit 111, a primary AC voltage v1 for the isolation transformer 102 is output from between an intermediate node between the switching elements 101a and 101b and an intermediate node between the switching elements 101c and 101d.

[0004] The second bridge circuit 112 is a circuit that supplies a secondary AC voltage v2 to the secondary winding of the isolation transformer 102. Similar to the first bridge circuit 111, the second bridge circuit 112 is a bridge circuit in which a leg 141 made up of series-connected switching elements 101e and 101f and a leg 142 made up of series-connected switching elements 101g and 101h are connected in parallel. A capacitor 103b is connected in parallel to the second bridge circuit 112. A secondary DC voltage E2 is applied to the second bridge circuit 112. In the second bridge circuit 112, the secondary AC voltage v2 for the isolation transformer 102 is output from between an intermediate node between the switching elements 101e and 101f and an intermediate node between the switching elements 101g and 101h.

[0005] The DC voltage detection unit 107a is a circuit that detects a primary side DC voltage E1 applied to the first bridge circuit 111. The DC voltage detection unit 107b is a circuit that detects a secondary side DC voltage E2 applied to the second bridge circuit 112.

[0006] The control device 106 is a device that generates drive pulses Ga to Gd for driving the switching elements 101a to 101d of the first bridge circuit 111, respectively, and drive pulses Ge to Gh for driving the switching elements 101e to 101h of the second bridge circuit 112, respectively.

[0007] The drive circuit unit 105a drives the switching elements 101a to 101d with drive pulses Ga to Gd generated by the control device 106, and the drive circuit unit 105b drives the switching elements 101e to 101h with drive pulses Ge to Gh generated by the control device 106.

[0008] The control device 106 controls the phases of the edges of the drive pulses Ga to Gh for driving the switching elements 101a to 101h based on the primary-side DC voltage E1 detected by the DC voltage detector 107a and the secondary-side DC voltage E2 detected by the DC voltage detector 107b, and controls the power transmission of the isolation DC / DC converter 110.

[0009] Hereinafter, an operation example of the power conversion system 100 will be described with reference to the waveform diagram of FIG. 12. In the power conversion system 100, the first bridge circuit 111 and the second bridge circuit 112 output the primary-side AC voltage v1 and the secondary-side AC voltage v2 having the same period (wavelength). In the following description, the terms phase angle or phase difference are used, which means the relative lengths of various periods expressed with one period (one wavelength) of the primary-side AC voltage v1 and the secondary-side AC voltage v2 being 2π. Also, in the following description, the secondary-side DC voltage E2 and the secondary-side AC voltage v2 mean the voltage values converted to the primary side. That is, when the number of turns of the primary-side winding of the isolation transformer 102 is n1 and the number of turns of the secondary-side winding is n2, the voltage value obtained by multiplying the actual secondary-side DC voltage by the coefficient n1 / n2 (the voltage value converted to the primary side) is the secondary-side DC voltage E2. The same applies to the secondary-side AC voltage v2. Also, in the following description, the low-voltage side and the high-voltage side mean the side where low voltage is generated and the side where high voltage is generated among the primary side and the secondary side of the isolation DC / DC converter 110. For example, if there is a relationship of E1 < E2 between the primary-side DC voltage E1 and the secondary-side DC voltage E2 converted to the primary side, the primary side is the low-voltage side and the secondary side is the high-voltage side, and if there is a relationship of E1 > E2, the primary side is the high-voltage side and the secondary side is the low-voltage side.

[0010] In the operation example of FIG. 12, there is a relationship of E1 < E2 between the primary-side DC voltage E1 and the secondary-side DC voltage E2. Therefore, the primary side is the low-voltage side and the secondary side is the high-voltage side. In this operation example, the control device 106 outputs a primary-side AC voltage v1 of a rectangular wave having an amplitude of ±E1 and a duty ratio of 50% to the first bridge circuit 111, and outputs a secondary-side AC voltage v2 of a rectangular wave having an amplitude of ±E2, a duty ratio of 50%, and a phase angle δ lagging with respect to the primary-side AC voltage v1 to the second bridge circuit 112. Here, the duty ratio may be slightly shifted from 50%. When the phase of the secondary-side AC voltage v2 lags with respect to the primary-side AC voltage v1 in this way, in the isolated DC / DC converter 110, power transmission from the primary side to the secondary side is performed. Hereinafter, the operation of this power transmission will be described.

[0011] In the isolated DC / DC converter 110, the voltage difference between the primary-side AC voltage v1 and the secondary-side AC voltage v2 is applied to an inductance L consisting of the leakage inductance l of the isolation transformer 102 and an external inductance L aux such that L = l + L aux and a current i that satisfies the following equation (1.1) flows through the primary winding of the isolation transformer 104. Also, a current corresponding to this current (the same current as current i when the turns ratio of the primary and secondary windings of the isolation transformer 102 is 1) flows through the secondary winding of the isolation transformer 104. di / dt = (v1(t) - v2(t)) / L ……(1.1)

[0012] In this operation example, during the period of phase angle δ from the rising edge of the primary-side AC voltage v1 and during the period of phase angle δ from the falling edge of the primary-side AC voltage v1, the primary-side AC voltage v1 and the secondary-side AC voltage V2 have opposite polarities. Therefore, during this period, a larger voltage difference than in other periods is applied to the inductance L, and as shown in FIG. 12, the time gradient of the current i becomes larger.

[0013] Therefore, the power P transmitted from the primary side to the secondary side increases depending on the phase difference δ between the primary side AC voltage v1 and the secondary side AC voltage v2. Specifically, if the fundamental wave angular frequency of the primary side AC voltage v1 and the secondary side AC voltage v2 is ω, the transmitted power P from the primary side to the secondary side is given by the following equation (1.2). P =(E1E2 / (ωL))δ(1-(δ / π)) ……(1.2)

[0014] Therefore, the control device 106 controls the phases of the edges of the drive pulses Ga to Gh for driving the switching elements 101a to 101h, thereby controlling the period (phase angle δ) during which the primary-side AC voltage v1 and the secondary-side AC voltage v2 of the isolation transformer 102 have opposite polarities, thereby controlling the transmission power P between the primary side and the secondary side.

[0015] However, in this operation example, if the phase difference δ between the primary AC voltage v1 and the secondary AC voltage v2 is increased in order to increase the transmission power P, there is a problem in that the peak value of the current i flowing through the isolation transformer 104 becomes excessively large. Therefore, Patent Document 1 proposes a technique for reducing the peak value of the current i by pulse-width modulating one of the primary AC voltage v1 and the secondary AC voltage v2.

[0016] FIG. 13 is a waveform diagram showing an example of the operation of the power transmission control disclosed in Patent Document 1. In FIG. 13, / Gb, / Gd, / Gf, and / Gh represent the level-inverted waveforms of the drive pulses Gb, Gd, Gf, and Gh. The same applies to FIG. 14, which will be described later. In the example of operation shown in FIG. 13, the high-voltage side secondary AC voltage v2 maintains a voltage of opposite polarity to the primary AC voltage v1 for a period of phase angle δ from the rising edge of the low-voltage side primary AC voltage v1, then maintains zero voltage for a period of phase angle φ, and then rises to a voltage of the same polarity as the primary AC voltage v1. That is, in Patent Document 1, the pulse width of the high-voltage side secondary AC voltage v2, which is generated with a delay of phase angle δ, is shortened by phase angle φ (to zero voltage).

[0017] In this way, the current i flowing through the isolation transformer 104 changes with a large time gradient during the period of phase angle δ, and then changes with a smaller time gradient during the period of phase angle φ than the previous period, reaching a peak value, thereby preventing the peak value from becoming excessively large.

[0018] 13, the control device 106 controls the period (phase angle δ) during which the AC voltages on the primary and secondary sides of the isolation transformer 102 are opposite in polarity, thereby controlling the transmission power P between the primary and secondary sides. This transmission power P is expressed by the following equation. P =(E1E2 / (ωL))((π-φ)(2δ+φ)-2δ 2 ) / (2π) …(1.3) Hereinafter, for convenience, the control shown in Patent Document 1 will be referred to as continuous current mode phase control. Note that this continuous current mode phase control is also disclosed in Patent Document 2.

[0019] The continuous current mode phase control described above has a problem: reverse power is generated, which is transmitted in the opposite direction to the transmission direction determined by the phase relationship between the primary AC voltage v1 and the secondary AC voltage v2, resulting in reactive power.

[0020] For example, in the operation example of Fig. 13, the phase of the secondary AC voltage v2 lags behind the primary AC voltage v1, and the direction of power transmission is from the primary side to the secondary side. However, in continuous current mode phase control, the polarity of the current i flowing through the isolation transformer 104 is reversed within a period of phase angle δ starting from the rising edge (or falling edge) of the primary AC voltage v1. During this period of phase angle δ, the period after the timing when the polarity of the current i is reversed is reverse power P transmitted from the secondary side to the primary side, which is the reverse direction of the transmission direction determined by the phase relationship between the primary AC voltage v1 and the secondary AC voltage v2. b This reverse power P b is the power P transmitted from the primary side to the secondary side before the polarity reversal of the current i occurs during the period of phase angle δ.f and cancel each other out.

[0021] In this way, in the phase control of the continuous current mode, the reverse power P b This causes a problem of a corresponding drop in transmission efficiency. This problem occurs particularly when the DC voltage difference between the primary and secondary sides is large or when the load is light, and causes an increase in conduction loss (deterioration in power transmission efficiency).

[0022] Non-Patent Document 1 discloses a power transmission control technology different from Patent Documents 1 and 2. Specifically, Non-Patent Document 1 avoids the occurrence of reverse power by generating a period in which both the primary-side AC voltage v1 and the secondary-side AC voltage v2 are zero voltage.

[0023] Fig. 14 is a waveform diagram showing an example of the operation of the power transmission control disclosed in Non-Patent Document 1. In this example, both the primary-side AC voltage v1 and the secondary-side AC voltage v2 simultaneously change from a voltage of a first polarity (positive polarity in this example) to zero voltage, and then both maintain zero voltage for a period of phase angle γ. Thereafter, the low-voltage side primary-side AC voltage v1 changes to a voltage of a second polarity (negative polarity in this example) opposite to the first polarity, and then, with a delay of phase angle φ-δ, the high-voltage side secondary-side AC voltage v2 changes to a voltage of the second polarity. Thereafter, the primary-side AC voltage v1 and the secondary-side AC voltage v2 change from a voltage of the second polarity to a voltage of the first polarity, following waveforms similar to those described above.

[0024] In this operation example, the current i flowing through the isolation transformer 102 increases during a period of phase angle φ-γ when the primary AC voltage v1 is a voltage of the first or second polarity and the secondary AC voltage v2 is zero, and then during a period when both the primary AC voltage v1 and the secondary AC voltage v2 are voltages of the same polarity, the current i flowing through the isolation transformer 102 decreases to zero, and this operation is repeated.

[0025] Then, during the period of phase angle γ after the current i flowing through the isolation transformer 102 decreases and becomes zero, both the primary-side AC voltage v1 and the secondary-side AC voltage v2 become zero voltage, the change in the current i flowing through the isolation transformer 102 stops, and no polarity reversal occurs. As a result, no reverse power occurs.

[0026] In this operational example, power P transmitted from the primary side to the secondary side depends on the peak value of current i flowing through isolation transformer 102. The peak value of current i depends on the length of the period of phase angle φ-γ. Therefore, controller 106 controls the period of phase angle γ during which both the AC voltages on the primary and secondary sides of isolation transformer 102 are zero, and also controls phase angles φ and γ, thereby controlling transmission power P between the primary and secondary sides. This transmission power P is expressed by the following equation: P =(E1E2 / (ωL))(A(1-A)(π-γ) 2 ) / (2π) …(1.4) In this equation (1.4), A is given by the following equation: A = Low-voltage side DC voltage / High-voltage side DC voltage<1 ……(1.5) Hereinafter, for convenience, the control of the transmission power P shown in Non-Patent Document 1 will be referred to as discontinuous current mode phase control. [Prior art documents] [Patent documents]

[0027] [Patent Document 1] Patent No. 6948938

[0028] [Patent Document 2] Patent No. 6171022 [Non-patent literature]

[0029] [Non-Patent Document 1] Kondo, Higaki, and Yamada, "Demonstration of Loss Reduction Effect of Bidirectional Isolated DC / DC Converter for Charging and Discharging Electric Vehicles with Suppressed Reactive Power," IEEJ Transactions on Power Systems, Vol. 137, No., pp. 673-680 (2017) Summary of the Invention [Problem to be solved by the invention]

[0030] In the conventional power conversion system described above, large power consumption is constantly generated in certain switching elements among the switching elements constituting the first bridge circuit and the second bridge circuit. For example, in the operation example shown in Figure 8, when the current i flowing through the primary winding of the isolation transformer 102 reaches its peak value, large power consumption Qg and Qh corresponding to the peak value of current i are periodically and repeatedly generated in the switching elements 101g and 101h. The same is true in the operation example shown in Figure 9. In this way, in conventional power conversion systems, heat concentration occurs in certain switching elements, so a cooling element matching the junction temperature of the switching element where this heat concentration occurs must be provided in the switching element module, which poses a problem of increased size of the cooling element.

[0031] The present invention has been made in consideration of the above-described circumstances, and has an object to provide a power conversion system in which heat concentration on some of a plurality of switching elements is alleviated. [Means for solving the problem]

[0032] According to one aspect of the present invention, there is provided a power conversion system comprising: an isolated DC / DC converter having an isolation transformer, at least one bridge circuit on each of a primary side and a secondary side of the isolation transformer, each bridge circuit including one or more switching elements connected in series, and a plurality of legs connected in parallel with each other; and a control device that generates drive pulses for driving the switching elements of the isolated DC / DC converter, wherein the control device periodically performs a timing swapping operation to swap the on-timing of a drive pulse for one leg of one of the one or more bridge circuits with the off-timing of a drive pulse for another leg.

[0033] In a preferred embodiment, the control device performs the timing interchange operation based on the on-timing or off-timing of the drive pulse that corresponds to the start and end points of a zero voltage period during which the AC voltage applied to the isolation transformer is zero.

[0034] In another preferred aspect, the power conversion system comprises: an isolated DC / DC converter having an isolation transformer and at least one bridge circuit on each of the primary and secondary sides of the isolation transformer, each bridge circuit including one or more switching elements connected in series, and consisting of a plurality of legs connected in parallel with each other; and a control device that generates drive pulses for driving the switching elements of the isolated DC / DC converter, wherein the control device periodically performs a timing interchange operation to invert the polarities of both drive pulses for one leg and another leg of one of the one or more bridge circuits during a period in which the polarities of both drive pulses match.

[0035] In another preferred aspect, the power conversion system may include a DC voltage detection unit that detects DC voltages on both the primary side and the secondary side of the isolated DC / DC converter, and the control device may determine a bridge circuit that is to be a target of the timing interchange operation, based on the DC voltages on the primary side and the secondary side detected by the DC voltage detection unit.

[0036] In another preferred embodiment, the control device may perform discontinuous current mode phase control, in which a period during which both the AC voltages on the primary side and the secondary side of the isolation transformer are zero, by controlling the phase of an edge of the drive pulse, or continuous current mode phase control, in which a period during which the AC voltages on the primary side and the secondary side of the isolation transformer are opposite in polarity, by controlling the phase of an edge of the drive pulse, in accordance with the magnitude of the control variable.

[0037] In this aspect, the control device may control the phase of the edge of the drive pulse so that current values ​​at inflection points before and after a peak point of the current flowing through the isolation transformer match in both the phase control in the discontinuous current mode and the phase control in the continuous current mode. [Effects of the Invention]

[0038] According to the power conversion system of one aspect of the present invention, it is possible to prevent a particular switching element from constantly consuming large amounts of power, and to mitigate heat concentration on the particular switching element. [Brief explanation of the drawings]

[0039] [Figure 1] 1 is a circuit diagram showing a configuration of a power conversion system according to an embodiment of the present invention. [Figure 2] 4 is a waveform diagram showing an example of an operation of discontinuous current mode phase control executed in the power conversion system. FIG. [Figure 3] 4 is a waveform diagram showing an example of the operation of continuous current mode phase control executed in the power conversion system. FIG. [Figure 4] 3 is a waveform diagram showing an example of the overall operation of the power conversion system. FIG. [Figure 5] 3 is a diagram illustrating an example of power transmission characteristics in the power conversion system. FIG. [Figure 6] FIG. 10 is a waveform diagram showing the operation of a modified example of the embodiment. [Figure 7]FIG. 10 is a waveform diagram showing a first operation example of a timing interchange operation in the same embodiment. [Figure 8] FIG. 10 is a waveform diagram showing a second operation example of the timing interchange operation in the same embodiment. [Figure 9] FIG. 10 is a waveform diagram showing a third operation example of the timing interchange operation in the same embodiment. [Figure 10] FIG. 10 is a waveform diagram showing a fourth operation example of the timing interchange operation in the same embodiment. [Figure 11] 1 is a circuit diagram showing a configuration example of a power conversion system. [Figure 12] 3 is a waveform diagram showing basic operating waveforms of the power conversion system. FIG. [Figure 13] 4 is a waveform diagram showing an example of operation of phase control in continuous current mode in the power conversion system. FIG. [Figure 14] 4 is a waveform diagram showing an example of the operation of phase control in discontinuous current mode in the power conversion system. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0040] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a circuit diagram showing the configuration of a power conversion system 100a according to an embodiment of the present invention. In this power conversion system 100a, the control device 106 in the conventional power conversion system (Fig. 11) is replaced with a control device 106a.

[0041] The elements of the power conversion system 100a other than the control device 106a are the same as those of a conventional power conversion system (Fig. 7). That is, the isolated DC / DC converter 110 includes an isolation transformer 102, and a first bridge circuit 111 and a second bridge circuit 112 connected to the primary side and the secondary side of the isolation transformer 102, respectively, and each including one or more switching elements connected in series and a plurality of rectifiers connected in parallel to each other. A DC voltage detector 107a detects a primary-side DC voltage E1 applied to the first bridge circuit 111, and a DC voltage detector 107b detects a secondary-side DC voltage E2 applied to the second bridge circuit 112. The drive circuit unit 105a drives the switching elements 101a to 101d of the first bridge circuit 111 based on drive pulses Ga to Gd generated by the control device 106a, and the drive circuit unit 105b drives the switching elements 101e to 101h of the second bridge circuit 112 based on drive pulses Ge to Gh generated by the control device 106a.

[0042] In this embodiment, the control device 106a generates drive pulses Ga to Gh for driving each of the switching elements of the first bridge circuit 111 and the second bridge circuit 112 based on the primary side DC voltage E1 and the secondary side DC voltage E2 detected by the DC voltage detection units 107a and 107b and the control variable D.

[0043] As described above, continuous current mode phase control can transmit a certain amount of power over a wide voltage range, but it has the problem of reducing power transmission efficiency due to the generation of reverse power. On the other hand, discontinuous current mode phase control can avoid the generation of reverse power, but it has the problem of difficulty in transmitting a certain amount of power over a wide voltage range, including when the voltage difference between the primary and secondary sides is small. Therefore, performing only either continuous current mode phase control or discontinuous current mode phase control makes it difficult to transmit power with high efficiency over a wide voltage range. Therefore, in this embodiment, the control device 106a executes both continuous current mode phase control and discontinuous current mode phase control.

[0044] As described above, in continuous current mode phase control, the phase angle δ of the phase lag between the primary-side AC voltage v1 and the secondary-side AC voltage v2 and the phase angle φ during the period when the high-voltage side AC voltage maintains zero voltage are manipulated. On the other hand, in discontinuous current mode phase control, there is no phase lag (phase angle δ) between the primary-side AC voltage v1 and the secondary-side AC voltage v2, and the phase angle γ during the period when both the low-voltage side and high-voltage side AC voltages maintain zero voltage and the phase angle φ during the period when the high-voltage side AC voltage maintains zero voltage are manipulated. Furthermore, in this case, since one of the phase angles γ and φ depends on the other, only one of the phase angles γ and φ is actually manipulated. Therefore, in this embodiment, a single control variable D is associated with the manipulated object of discontinuous current mode phase control, and the same control variable D is associated with the manipulated object of continuous current mode phase control. This allows discontinuous current mode phase control or continuous current mode phase control to be performed depending on the magnitude of the control variable D.

[0045] Specifically, in this embodiment, the control device 106a controls the transmission of power P between the primary side and secondary side of the isolated DC / DC converter 110 by performing discontinuous current mode phase control, which controls the period during which both the primary side AC voltage v1 and the secondary side AC voltage v2 are zero voltage by controlling the phases of the edges of the drive pulses Ga to Gh, or continuous current mode phase control, which controls the period during which the primary side AC voltage v1 and the secondary side AC voltage v2 are opposite in polarity by controlling the phases of the edges of the drive pulses Ga to Gh, in accordance with the magnitude of the control variable D.

[0046] The control variable D is a control variable determined according to the target transmission power. The larger the control variable D, the larger the transmission power P between the primary side and the secondary side. In a preferred embodiment, the control variable D is provided to the control device 106a from a host device that controls the power conversion system 100a. In another preferred embodiment, the control variable D is determined by the control device 106a based on the operating status and load status of the isolated DC / DC converter 110.

[0047] The control variable D can take a value between 0 and 3π / 2. When the control variable D is greater than or equal to 0 and less than or equal to π, the control device 106a performs phase control in discontinuous current mode. When the control variable D is greater than or equal to π and less than or equal to 3π / 2, the control device 106a performs phase control in continuous current mode. The above is an outline of the phase control in the discontinuous current mode and the continuous current mode, which is the first feature of this embodiment.

[0048] Furthermore, as described above, conventional power conversion systems have a problem in that a specific switching element periodically consumes large amounts of power, causing heat concentration in that switching element. Therefore, the control device 106a performs a timing swap operation to mitigate this heat concentration.

[0049] More specifically, the control device 106a periodically performs a timing interchange operation to interchange the on-timing of the drive pulse for one leg of one of the first bridge circuit 111 and the second bridge circuit 112 with the off-timing of the drive pulse for the other leg. The period in this case may be the switching period of the first bridge circuit 111 and the second bridge circuit 112 or a longer period. In this embodiment, the period is the switching period, and the control device 106a performs the timing interchange operation based on the on-timing or off-timing of the drive pulse that marks the start and end of a zero-voltage period during which the AC voltage applied to the isolation transformer 102 is zero. Here, the on-timing refers to the timing at which the switching element to which the drive pulse is supplied turns on, i.e., the timing of the rising edge of the drive pulse. The off-timing refers to the timing at which the switching element to which the drive pulse is supplied turns off, i.e., the timing of the falling edge of the drive pulse.

[0050] The timing interchange operation in this embodiment can also be explained as follows: That is, the control device 106a periodically performs a timing interchange operation in which the polarities of the drive pulses for one leg of one of the first bridge circuit 111 and the second bridge circuit 112 are inverted with the drive pulse for the other leg during a period in which the polarities of both drive pulses match.

[0051] Then, the control device 106a determines the bridge circuit to be subjected to the timing interchange operation based on the detected DC voltage values ​​on the primary side and secondary side detected by the DC voltage detection units 107a and 107b. The above is an outline of the timing switching operation for mitigating heat concentration, which is the second feature of this embodiment.

[0052] Next, details of the phase control, which is the first feature of this embodiment, will be described. Below, a case where power is transmitted from the primary side to the secondary side of the isolated DC / DC converter 110 will be described. Also, below, a case where the primary side is the low voltage side and the secondary side is the high voltage side will be described.

[0053] FIG. 2 is a waveform diagram showing an example of phase control in discontinuous current mode. In FIG. 2, / Gb, / Gd, / Gf, and / Gh represent level-inverted waveforms of drive pulses Gb, Gd, Gf, and Gh. The same applies to other waveform diagrams (FIG. 3, and FIGS. 6 to 10). In the example of FIG. 2, the control device 106a detects inflection points Q before and after the peak point P1 (P2) of the current i flowing through the isolation transformer 102. 11 and Q 12 (Q 21 and Q 22 The phase of the edge of the drive pulse is controlled so that the current values ​​of the two electrodes match.

[0054] Specifically, the control device 106a controls the phases of the edges of the drive pulses Ga to Gh so that the sum of the time integral of a first differential voltage (E1-0>0 in the example of FIG. 2) during a first period T1 (phase angle φ-γ) during which the first differential voltage occurs between the low-voltage side primary AC voltage v1 and the high-voltage side secondary AC voltage v2, and the time integral of a second differential voltage (E1-E2<0 in the example of FIG. 2) during a second period T2 (phase angle π-φ) during which a second differential voltage of opposite polarity to the first differential voltage occurs between the low-voltage side primary AC voltage v1 and the high-voltage side secondary AC voltage v2 becomes zero. That is, in the example of FIG. 2, the control device 106a controls the phases of the edges of the drive pulses Ga to Gh so that the following equation (2.1) is satisfied. E1(φ-γ)+(E1-E2)(π-φ)=0 ……(2.1) Although the primary side DC voltage E1 and the secondary side DC voltage E2 fluctuate over time in the strict sense, they are regarded as constant voltages in the above equation (2.1) because their time constants are large.

[0055] By such control, the current i of the isolation transformer 102, which is generated by the difference voltage between the primary-side AC voltage v1 and the secondary-side AC voltage v2, becomes zero at the start timing of the third period T3 (period of phase angle γ) when both the primary-side AC voltage v1 and the secondary-side AC voltage v2 become zero voltage, thereby avoiding the generation of reverse power.

[0056] The above has explained the phase control of the edges of the drive pulses Ga to Gh in the period before and after the timing when the positive peak point P1 occurs in the current i, but the phase control of the edges of the drive pulses Ga to Gh in the period before and after the timing when the negative peak point P2 occurs in the current i is also similar.

[0057] One object of this embodiment is to perform phase control of the drive pulses Ga to Gh based on a single control variable D not only in the continuous current mode but also in the discontinuous current mode. For this reason, in this embodiment, in the discontinuous current mode, the phase angle γ is determined based on the control variable D, and the phase angle φ is made to depend on this phase angle γ. Specifically, this is as follows.

[0058] Solving the above equation (2.1) for φ gives the following equation (2.2). φ(γ) =(1-(E1 / E2))π+(E1 / E2)γ =(1-A)π+Aγ ……(2.2) Here, A is as shown in the above formula (1.5).

[0059] Furthermore, the control variable D in the discontinuous current mode is related to the phase angle γ as follows: D=π-γ ……(2.3)

[0060] When a control variable D, where 0≦D≦π, is given, the control device 106a calculates the phase angle γ from the control variable D according to equation (2.3), and calculates the phase angle φ from the phase angle γ according to equation (2.2).

[0061] The discontinuous current mode phase control has been explained above by focusing on the change in the differential voltage between the primary side AC voltage v1 and the secondary side AC voltage v2. However, if we focus on the changes in the primary side AC voltage v1 and the secondary side AC voltage v2 individually, the explanation will be as follows.

[0062] In the discontinuous current mode phase control, the control device 106a sequentially generates a first period T1 during which one of the primary-side AC voltage v1 or the secondary-side AC voltage v2 of the isolation transformer 102 (specifically, the low-voltage side) has a first polarity (positive polarity in the example of FIG. 2) and the other (specifically, the high-voltage side) has zero voltage, a second period T2 during which both the primary-side AC voltage v1 and the secondary-side AC voltage v2 have the first polarity, and a third period T3 during which both the primary-side AC voltage v1 and the secondary-side AC voltage v2 are zero voltage, and reduces the third period T3 according to the magnitude of the control variable D (see equation (2.3) above).

[0063] Furthermore, in the phase control of the discontinuous current mode, the control device 106a controls the phases of the edges of the drive pulses Ga to Gh so that the sum of the time integral of the differential voltage between the primary AC voltage v1 and the secondary AC voltage v2 in the first period T1 and the time integral of the differential voltage between the primary AC voltage v1 and the secondary AC voltage v2 in the second period T2 becomes zero (see equation (2.1) above).

[0064] Next, a specific example of phase control of the edges of the drive pulses in the discontinuous current mode will be described. In the following description, unless otherwise specified, the phase angle refers to the phase of the rising edges of the drive pulses Ga and / Gb in FIG. 2 (phase angle θ 12 = 0) is the reference position (starting point). In other words, the phase angle θ 34 is the phase angle of the rising edge of the drive pulses Gc and / Gd relative to the reference position, and the phase angle θ 56 is the phase angle of the rising edge of the drive pulses Ge and / Gf relative to the reference position, and the phase angle θ 78 is the phase angle of the rising edge of the drive pulses Gg and / Gh relative to the reference position.

[0065] In the operation example of FIG. 2, the falling edge of the primary AC voltage v1 to zero voltage (the beginning of the third period T3) occurs due to the rising edges of the drive pulses Gc and / Gd. The falling edge of the primary AC voltage v1 to zero voltage has a phase angle π-γ. Therefore, the phase angle θ of the rising edges of the drive pulses Gc and / Gd 34 is calculated using the following formula (2.4): θ 34 =π-γ =π-π+D =D ……(2.4)

[0066] The rising edge of the secondary AC voltage v2 to zero voltage (the beginning of the third period T3) is generated by the rising edges of the drive pulses Ge and / Gf. The falling edge of the secondary AC voltage v2 to zero voltage has a phase angle -γ. Therefore, the phase angle θ of the rising edges of the drive pulses Ge and / Gf 56 is calculated using the following formula (2.5): θ 56 =-γ =D-π ……(2.5)

[0067] The falling edge of the secondary AC voltage v2 from zero voltage (the beginning of the second period T2) is generated by the rising edges of the drive pulses Gg and / Gh. The falling edge of the secondary AC voltage v2 from zero voltage is generated by the phase angle θ 56 +π+φ. Therefore, the phase angle θ of the rising edges of the drive pulses Gg and / Gh 78 is calculated using the following formula (2.6): θ 78 =θ56+π+φ =D-π+π+φ =D-π+π+π-AD =π+(1-A)D ……(2.6) The above is the phase control in the discontinuous current mode in this embodiment.

[0068] 3 is a waveform diagram showing an example of phase control in the continuous current mode in this embodiment. In this embodiment, in the continuous current mode as well as in the discontinuous current mode, the inflection points Q before and after the peak point P1 (P2) of the current i flowing through the isolation transformer 102 are 11 and Q 12 (Q 21 and Q 22 The phase of the edge of the drive pulse is controlled so that the current values ​​of the two electrodes match.

[0069] Specifically, the control device 106a controls the phases of the edges of the drive pulses so that the sum of the time integral of a first differential voltage (E1-0>0 in the example of FIG. 3) during a fifth period T5 (phase angle φ) during which the first differential voltage occurs between the primary-side AC voltage v1 and the secondary-side AC voltage v2 of the isolation transformer 102, and the time integral of the second differential voltage during a sixth period T6 (phase angle π-δ-φ) during which a second differential voltage (E1-E2<0 in the example of FIG. 2) of opposite polarity to the first differential voltage occurs between the primary-side AC voltage v1 and the secondary-side AC voltage v2 of the isolation transformer 102, becomes zero. That is, in the example of FIG. 3, the control device 106a controls the phases of the edges of the drive pulses Ga to Gh so that the following equation (3.1) is satisfied. E1φ+(E1-E2)(π-δ-φ)=0 ……(3.1)

[0070] The above has explained the phase control of the edges of the drive pulses in the period before and after the timing when the positive peak point P1 occurs in the current i, but the phase control of the edges of the drive pulses Ga to Gh in the period before and after the timing when the negative peak point P2 occurs in the current i is also similar.

[0071] As already explained, the purpose of this embodiment is to perform phase control of the drive pulses Ga to Gh based on a single control variable D in both the discontinuous current mode and the continuous current mode. For this reason, in this embodiment, in the continuous current mode, the phase angle δ is determined based on the control variable D, and the phase angle φ is made to depend on this phase angle δ. Specifically, this is as follows.

[0072] Solving the above equation (3.1) for φ gives the following equation (3.2). φ(δ) =(1-(E1 / E2))(π-δ) =(1-A)(π-δ) ……(3.2)

[0073] Also, in continuous current mode, the control variable D is related to the phase angle δ by the following equation: D=δ+π ……(3.3)

[0074] In this embodiment, when a control variable D that satisfies π≦D≦3π / 2 is given, the control device 106a calculates the phase angle δ from the control variable D according to equation (3.3), and calculates the phase angle φ from the phase angle δ according to equation (3.2).

[0075] By performing such control, continuity of the change in the waveform of the current i flowing through the isolation transformer 102 is ensured when the mode transitions between the discontinuous current mode and the continuous current mode.

[0076] The continuous current mode phase control has been explained above by focusing on the change in the differential voltage between the primary side AC voltage v1 and the secondary side AC voltage v2. However, if we focus on the changes in the primary side AC voltage v1 and the secondary side AC voltage v2 individually, the explanation will be as follows.

[0077] In the continuous current mode phase control, the control device 106a sequentially generates a fourth period T4 (phase angle δ) during which the primary-side AC voltage v1 and the secondary-side AC voltage v2 of the isolation transformer 102 have opposite polarities, a fifth period T5 (phase angle φ) during which one of the primary-side AC voltage v1 or the secondary-side AC voltage v2 (specifically, the low-voltage side) has a first polarity and the other (specifically, the high-voltage side) has zero voltage, and a sixth period T6 (phase angle π-δ-φ) during which both the primary-side AC voltage v1 and the secondary-side AC voltage v2 have the first polarity, and increases the fourth period T4 according to the magnitude of the control variable D.

[0078] Furthermore, in the phase control of the continuous current mode, the control device 106a controls the phase of the edge of the drive pulse so that the sum of the time integral of the difference voltage between the primary side AC voltage v1 and the secondary side AC voltage v2 in the fifth period T5 and the time integral of the difference voltage between the primary side AC voltage v1 and the secondary side AC voltage v2 in the sixth period T6 becomes zero (see equation (3.1)).

[0079] Next, a specific example of phase control of the edges of the drive pulses Ga to Gh in the continuous current mode will be described. In the operation example of FIG. 3, polarity reversal of the primary AC voltage v1 (at the beginning of the fourth period T4) occurs due to the rising edges of the drive pulses Gc and / Gd. The polarity reversal of the primary AC voltage v1 has a phase angle π. Therefore, the phase angle θ of the rising edges of the drive pulses Gc and / Gd 34 is calculated using the following formula (3.4): θ 34 =π ……(3.4)

[0080] Furthermore, the rise of the secondary AC voltage v2 to zero voltage (at the beginning of the fifth period T5) is caused by the rising edges of the drive pulses Ge and / Gf. The rising edges of the secondary AC voltage v2 to zero voltage have a phase angle δ. Therefore, the phase angle θ of the rising edges of the drive pulses Ge and / Gf 56 is calculated using the following formula (3.5): θ 56 =δ =D-π ……(3.5)

[0081] The falling edge of the secondary AC voltage v2 from zero voltage (the beginning of the sixth period T6) occurs at the rising edges of the drive pulses Gg and / Gh. The falling edge of the secondary AC voltage v2 from zero voltage occurs at a phase angle θ 56 +π+φ. Therefore, the phase angle θ of the rising edges of the drive pulses Gg and / Gh 78 is calculated using the following formula (3.6): θ 78 =θ 56 +π+φ =D-π+π+φ =D+φ =D+(1-A)(2π-D) =AD+2π(1-A) =(D-2π)A ……(3.6) The above is the phase control in the continuous current mode in this embodiment.

[0082] Fig. 4 is a waveform diagram showing an example of the overall operation of the power conversion system 100a. Fig. 5 is a diagram showing an example of the power transmission characteristics in the power conversion system 100a. The operation of this embodiment can be summarized as follows with reference to these figures.

[0083] In this embodiment, when the control variable D is within the range of 0≦D≦π, discontinuous current mode phase control is performed. In this discontinuous current mode, there is no period (phase angle δ) during which the primary-side AC voltage v1 and the secondary-side AC voltage v2 have opposite polarities. Furthermore, in the discontinuous current mode, as the control variable D increases, the period during which both the low-voltage side and high-voltage side AC voltages maintain zero voltage (phase angle γ=π−D) decreases, and the period during which the high-voltage side AC voltage maintains zero voltage (phase angle φ=π−AD) decreases.

[0084] In this discontinuous current mode, no reverse power is generated, and the power P transferred between the primary and secondary sides is given by the following equation: P =((E1E2) / (ωL))A(1-A)D2 / (2π) ……(4.1) In this discontinuous current mode, no reverse power is generated, so power can be transmitted with little loss when the DC voltage difference between the primary and secondary sides is small or when the load is light.

[0085] In this embodiment, when the control variable D is within the range of π≦D≦3π / 2, phase control in continuous current mode is performed. In this continuous current mode, there is no period (phase angle γ) during which both the primary-side AC voltage v1 and the secondary-side AC voltage v2 are zero voltage. In the continuous current mode, as the control variable D increases, the period (phase angle δ=D-π) during which the primary-side AC voltage v1 and the secondary-side AC voltage v2 are opposite in polarity increases, and the period (phase angle φ=(1-A)(2π-D) during which the high-voltage side AC voltage maintains zero voltage decreases.

[0086] In this continuous current mode, power is transmitted during the period when the primary AC voltage v1 and the secondary AC voltage v2 are in opposite polarity, and the power P transmitted between the primary and secondary sides is given by the following equation: P =((E1E2) / (ωL))(a(A)D 2 +b(A)D+c(A)) / (2π) …(4.2) Here, a(A), b(A), and c(A) are as follows: a(A)=-(1+A 2 ) ……(4.3) b(A)=(4A 2 -A+3)π ……(4.4) c(A)=-2(2A 2 -A+1)π 2 …(4.5) In this continuous current mode, a certain level of power can be transmitted over a wide voltage range, and power can be transmitted with high efficiency even under heavy loads.

[0087] As shown in Figure 5, when the control variable D is changed from 0 to 3π / 2, the power P transmitted from the primary side to the secondary side changes continuously. Furthermore, when the control variable D is π, the operating mode of this embodiment is at the boundary between the discontinuous current mode and the continuous current mode. At this boundary, the phase angles δ, φ, and γ calculated assuming the discontinuous current mode coincide with the phase angles δ, φ, and γ calculated assuming the continuous current mode. Therefore, the current waveform of the isolation transformer changes continuously during the transition between the discontinuous current mode and the continuous current mode.

[0088] As described above, according to this embodiment, discontinuous current mode phase control or continuous current mode phase control is performed depending on the magnitude of one control variable D, so that power can be transmitted between the primary side and the secondary side with high efficiency over a wide voltage range.

[0089] Furthermore, according to this embodiment, both discontinuous current mode phase control and continuous current mode phase control are performed using one control variable D, which has the advantage of simplifying the control and making it stable.

[0090] In the above description, Figures 2 and 3 show the relative phase relationship between the primary AC voltage v1 and the secondary AC voltage v2 and an example of the waveforms of the drive pulses Ga to Gh for realizing such a phase relationship. However, the waveforms of the drive pulses Ga to Gh are merely an example, and even if the waveforms of the drive pulses Ga to Gh are changed, the relative phase relationship between the primary AC voltage v1 and the secondary AC voltage v2 can be made the same as in Figures 2 and 3. Therefore, the waveforms of the drive pulses Ga to Gh may be changed as long as the relative phase relationship between the primary AC voltage v1 and the secondary AC voltage v2 can be made as shown in Figures 2 and 3. Figure 6 shows a modified waveform of the drive pulses Ga to Gh in discontinuous current mode. This embodiment also achieves the same effect as above.

[0091] Next, the timing switching operation for mitigating heat concentration, which is the second feature of this embodiment, will be described in detail.

[0092] 7 is a waveform diagram showing a first operation example of the timing interchange operation in this embodiment. In this operation example, the control device 106a performs phase control in continuous current mode. In this first operation example, the primary side DC voltage E1 is smaller than the secondary side DC voltage kE2 converted to the primary side, so the control device 106a targets the second bridge circuit 112 for the timing interchange operation.

[0093] In the first operation example, in the first cycle in which the phase is from 0 to 2π, the switching element 101g of leg 142 turns off at the falling edge of the drive pulse Gg, the current flowing through the isolation transformer 102 reaches a peak value, and a large power consumption Qg corresponding to this peak value is generated in the switching element 101g.

[0094] Also, in the first period, at the falling edge of the drive pulse Gh, the switching element 101h of the leg 142 is turned off, the current flowing through the isolation transformer 102 reaches a peak value, and a large amount of power consumption Qh corresponding to this peak value is generated in the switching element 101h.

[0095] If no measures are taken, the same operation will be repeated in the second period from phase 2π to phase 4π and in each period from the third period onwards, causing heat concentration in switching elements 101g and 101h.

[0096] Therefore, in the first operation example, the control device 106a periodically performs a timing swapping operation to swap the on timing of the drive pulses Ge, Gf, Gg, and Gh for one leg of the second bridge circuit 112 with the off timing of the drive pulses for the other leg.

[0097] Specifically, in the second period from phase 2π to 4π, the control device 106a interchanges the on-timing (rising edge timing) of the drive pulse Ge for leg 141 with the off-timing (falling edge timing) of the drive pulse Gg for leg 142 (first half timing interchange in FIG. 7). Also, in the second period, the control device 106a interchanges the off-timing (falling edge timing) of the drive pulse Ge for leg 141 with the on-timing (rising edge timing) of the drive pulse Gg for leg 142 (second half timing interchange in FIG. 7).

[0098] When such a timing swapping operation is performed, in the second period, the switching element 101f of leg 141 is turned off at the falling edge of the drive pulse Gf, the current flowing through the isolation transformer 102 reaches a peak value, and a large power consumption Qf corresponding to this peak value is generated in the switching element 101f.

[0099] Also, in the second period, at the falling edge of the drive pulse Ge, the switching element 101e of the leg 141 is turned off, the current flowing through the isolation transformer 102 reaches a peak value, and a large amount of power consumption Qe corresponding to this peak value is generated in the switching element 101e.

[0100] In this way, by performing the timing interchange operation, the switching elements that generate large power consumption can be switched from the switching elements 101g and 101h in the first period to the switching elements 101f and 101e in the second period.

[0101] In each of the third and subsequent cycles, the timing switching operation described above is repeated, for example, once every two cycles, thereby reducing the concentration of heat on a specific switching element.

[0102] The above timing interchange operation can be rephrased as follows: That is, the control device 106a periodically performs a timing interchange operation to invert the polarities of the drive pulses for one leg and the drive pulse for the other leg of one bridge circuit (the second bridge circuit 112 in this example) out of the first bridge circuit 111 and the second bridge circuit 112, during a period in which the polarities of both drive pulses match.

[0103] Here, the period when the polarity of the drive pulse for one leg and the polarity of the drive pulse for the other leg match is the zero-voltage period, during which the AC voltage applied to the isolation transformer 102 is zero. Therefore, the edges of the drive pulses that form the start and end points of this zero-voltage period are subject to timing swapping. This is because, within the zero-voltage period, the waveform of the current i flowing through the isolation transformer 102 does not change even if the timing of the edges of the related drive pulses is swapped.

[0104] In the first operation example, in the second cycle from phase 2π to 4π, the period from the rising edge of drive pulse Ge to the falling edge of drive pulse Gg before the timing interchange is a period in which the polarities of both drive pulses match. Therefore, control device 106a inverts the polarities of both drive pulses during this period. Also, in the second cycle, the period from the falling edge of drive pulse Ge to the rising edge of drive pulse Gg before the timing interchange is a period in which the polarities of both drive pulses match. Therefore, control device 106a inverts the polarities of both drive pulses during this period. When this polarity inversion operation is performed, the same results as when the timing interchange operation described above is performed are obtained.

[0105] 8 is a waveform diagram showing a second operation example of the timing interchange operation in this embodiment. In this operation example, the control device 106a performs phase control in discontinuous current mode. In this second operation example, the primary side DC voltage E1 is smaller than the secondary side DC voltage kE2 converted to the primary side, so the control device 106a targets the second bridge circuit 112 for the timing interchange operation.

[0106] In the second operation example, in the first period from 0 to 2π in phase, large power consumption Qg corresponding to the peak value of current i occurs in switching element 101g at the falling edge of drive pulse Gg, as in the first operation example. In the first period, large power consumption Qh corresponding to the peak value of current i occurs in switching element 101h at the falling edge of drive pulse Gh, as in the first operation example.

[0107] Therefore, in the second period from phase 2π to 4π, the control device 106a, like the first operation example, swaps the on-timing (timing of the rising edge) of the drive pulse Ge for leg 141 and the off-timing (timing of the falling edge) of the drive pulse Gg for leg 142 (first half timing swap in FIG. 8). Also, in the second period, the control device 106a, like the first operation example, swaps the off-timing (timing of the falling edge) of the drive pulse Ge for leg 141 and the on-timing (timing of the rising edge) of the drive pulse Gg for leg 142 (second half timing swap in FIG. 8).

[0108] When such a timing interchange operation is performed, in the second period, at the falling edge of the interchanged drive pulse Gf, large power consumption Qf corresponding to the peak value of current i occurs in switching element 101f. Also, in the second period, at the falling edge of the interchanged drive pulse Ge, large power consumption Qe corresponding to the peak value of current i occurs in switching element 101e.

[0109] In this way, by performing the timing interchange operation, the switching elements that generate large power consumption can be switched from the switching elements 101g and 101h (first period) to the switching elements 101e and 101f (second period).

[0110] In each of the third and subsequent cycles, the timing switching operation described above is repeated, for example, once every two cycles, thereby reducing the concentration of heat on a specific switching element.

[0111] 9 is a waveform diagram showing a third operation example of the timing interchange operation in this embodiment. In this operation example, the control device 106a performs phase control in continuous current mode. In this third operation example, the primary side DC voltage E1 is greater than the secondary side DC voltage kE2 converted to the primary side, so the control device 106a targets the first bridge circuit 111 for the timing interchange operation.

[0112] In the third operation example, in the first period from 0 to 2π in phase, large power consumption Qd corresponding to the peak value of current i occurs in switching element 101d at the falling edge of drive pulse Gd. Also in the first period, large power consumption Qc corresponding to the peak value of current i occurs in switching element 101c at the falling edge of drive pulse Gc.

[0113] Therefore, in the second period from phase 2π to 4π, the control device 106a interchanges the on-timing (rising edge timing) of the drive pulse Gc for leg 132 with the off-timing (falling edge timing) of the drive pulse Ga for leg 131 (first half timing interchange in FIG. 9). Also, in the second period, the control device 106a interchanges the off-timing (falling edge timing) of the drive pulse Gc for leg 132 with the on-timing (rising edge timing) of the drive pulse Ga for leg 131 (second half timing interchange in FIG. 9).

[0114] When such a timing interchange operation is performed, in the second period, large power consumption Qa corresponding to the peak value of current i occurs in switching element 101a at the falling edge of drive pulse Ga after the timing interchange. Also, in the second period, large power consumption Qb corresponding to the peak value of current i occurs in switching element 101b at the falling edge of drive pulse Gb after the timing interchange.

[0115] In this way, by performing the timing interchange operation, the switching elements that generate large power consumption can be switched from the switching elements 101d and 101c (first period) to the switching elements 101a and 101b (second period).

[0116] In each of the third and subsequent cycles, the timing switching operation described above is repeated, for example, once every two cycles, thereby reducing the concentration of heat on a specific switching element.

[0117] 10 is a waveform diagram showing a fourth operation example of the timing interchange operation in this embodiment. In this operation example, the control device 106a performs phase control in discontinuous current mode. In this fourth operation example, the primary side DC voltage E1 is greater than the secondary side DC voltage kE2 converted to the primary side, so the control device 106a targets the first bridge circuit 111 for the timing interchange operation.

[0118] In the fourth operation example, in the first period from 0 to 2π in phase, similar to the third operation example, large power consumption Qd corresponding to the peak value of current i occurs in switching element 101d at the falling edge of drive pulse Gd. Also, in the first period, similar to the third operation example, large power consumption Qc corresponding to the peak value of current i occurs in switching element 101c at the falling edge of drive pulse Gc.

[0119] Therefore, in the second period from phase 2π to 4π, the control device 106a performs the same timing interchange operation as in the third operation example.

[0120] When this timing interchange operation is performed, in the second period, similar to the third operation example, large power consumption Qa corresponding to the peak value of current i occurs in switching element 101a at the falling edge of drive pulse Ga after timing interchange. Also, in the second period, similar to the third operation example, large power consumption Qb corresponding to the peak value of current occurs in switching element 101b at the falling edge of drive pulse Gb after timing interchange.

[0121] In this way, by performing the timing interchange operation, as in the third operation example described above, the switching elements that generate large power consumption can be switched from switching elements 101d and 101c (first cycle) to switching elements 101a and 101b (second cycle).

[0122] In each of the third and subsequent cycles, the timing switching operation described above is repeated, for example, once every two cycles, thereby reducing the concentration of heat on a specific switching element.

[0123] As described above, according to this embodiment, heat concentration on a specific switching element is alleviated, and therefore the cooling body provided in the switching element module can be made smaller.

[0124] Although one embodiment of the present invention has been described above, other embodiments of the present invention are also possible. For example, in the above embodiment, the control device 106a performs phase control in discontinuous current mode or phase control in continuous current mode depending on the magnitude of the control variable D, but it is also possible to perform only one of the phase controls. Alternatively, the control device 106a may perform phase control in continuous current mode or a mode other than the continuous current mode. [Explanation of symbols]

[0125] 100, 100a...power conversion system, 106, 106a...control device, 110...isolated DC / DC converter, 102...isolated transformer, 104...series inductor, 111...first bridge circuit, 112...second bridge circuit, 101a to 101h...switching elements, 131, 132, 141, 142...legs, 103a, 103b...capacitors, 105a, 105b...drive circuit section, 107a, 107b...DC voltage detection section.

Claims

1. an isolated DC / DC converter having an isolation transformer, with at least one bridge circuit on each of a primary side and a secondary side of the isolation transformer, each bridge circuit including one or more switching elements connected in series and consisting of a plurality of legs connected in parallel with each other; a control device that generates a drive pulse for driving a switching element of the isolated DC / DC converter, a control device that periodically performs a timing swapping operation to swap an on-timing of a drive pulse for one leg of one bridge circuit among one or more bridge circuits with an off-timing of a drive pulse for another leg.

2. 2. The power conversion system according to claim 1, wherein the control device performs the timing interchange operation based on on-timings or off-timings of the drive pulses that correspond to start and end points of a zero voltage period in which the AC voltage applied to the isolation transformer is zero.

3. an isolated DC / DC converter having an isolation transformer, with at least one bridge circuit on each of a primary side and a secondary side of the isolation transformer, each bridge circuit including one or more switching elements connected in series and consisting of a plurality of legs connected in parallel with each other; a control device that generates a drive pulse for driving a switching element of the isolated DC / DC converter, the control device periodically performs a timing swapping operation to invert the polarities of drive pulses for one leg and another leg of one of the one or more bridge circuits during a period in which the polarities of both drive pulses coincide with each other.

4. a DC voltage detection unit for detecting DC voltages on both the primary side and the secondary side of the isolated DC / DC converter; The power conversion system according to any one of claims 1 to 3, characterized in that the control device determines a bridge circuit to be subjected to the timing interchange operation based on the DC voltages on the primary side and the secondary side detected by the DC voltage detection unit.

5. 5. The power conversion system according to claim 4, wherein the control device performs discontinuous current mode phase control in which a period during which both the AC voltages on the primary side and the secondary side of the isolation transformer are zero voltage by controlling a phase of an edge of the drive pulse, or performs continuous current mode phase control in which a period during which the AC voltages on the primary side and the secondary side of the isolation transformer are opposite in polarity by controlling a phase of an edge of the drive pulse, in accordance with a magnitude of a control variable.

6. 6. The power conversion system according to claim 5, wherein the control device controls the phase of the edge of the drive pulse so that current values ​​at inflection points before and after a peak point of the current flowing through the isolation transformer match in both the phase control in the discontinuous current mode and the phase control in the continuous current mode.

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