DC / DC converters and charging devices

Abstract

To provide a DC / DC converter of a three-phase LLC system which can cope with higher output and reduce ripples of an output waveform without causing cost increase or complication of control.SOLUTION: In a DC / DC converter 10A of a three-phase LLC system comprising: a primary side switching circuit 11; a secondary side rectifier circuit 12; a transformer circuit 13 in which each transformer part is constituted by two parallel transformers; a primary side resonance circuit 14; and a control unit 15, the transformer circuit 13 forms two transformer groups, each transformer group is formed by making each one transformer of each transformer part as one set, primary side coils are connected by balanced connection, and secondary side coils are connected by the balanced connection.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a three-phase LLC (including three-phase CLLC) DC / DC converter and a charging device. [Background technology]

[0002] In recent years, as the capacity of batteries installed in electric vehicles has increased, the capacity of quick chargers has also increased, with the mainstream currently being around 50 kW to 200 kW. The power supply section of a quick charger consists of multiple power supply units, each of which is required to have an output of around 12.5 kW to 30 kW, and there is also a demand for them to be compact, highly efficient, and low cost.

[0003] A power supply unit may consist of, for example, an AC / DC converter, a DC / DC converter, and an output filter. The AC / DC converter is placed before the DC / DC converter, and the output filter is placed after the DC / DC converter. Furthermore, the DC / DC converter uses a current-resonant DC / DC converter, which can be made smaller, more efficient, and less expensive, despite the complexity of controlling fluctuations in input and output voltages and load fluctuations at the output destination.

[0004] Known current-resonant DC / DC converters include three-phase LLC DC / DC converters (see, for example, Patent Document 1). Although three-phase LLC DC / DC converters have an increased number of components due to their three-phase drive, they are more suited to achieving higher output than single-phase full-bridge converters because the current is distributed across three phases. Furthermore, the ripple in the output waveform is reduced to about one-tenth of that of single-phase full-bridge converters, enabling the components that make up the output filter in the subsequent stage (large components such as electrolytic capacitors, film capacitors, and choke coils) to be smaller, lighter, and less expensive. Furthermore, they are attracting attention because they also improve power conversion efficiency.

[0005] The main circuit of a conventional, typical three-phase LLC DC / DC converter 30A is shown in Figure 9. The main circuit of DC / DC converter 30A is made up of high-frequency isolation transformers (hereinafter simply referred to as transformers) T10 to T30, a primary-side switching circuit including switching elements Q1 to Q6, a secondary-side rectifier circuit including rectifier diodes D1 to D6 and a smoothing capacitor Co, and a primary-side resonant circuit.

[0006] The primary resonant circuit comprises a three-phase LLC resonant circuit consisting of resonant coils L1 to L3, the excitation coils (not shown) of transformers T10 to T30, the primary coils of transformers T10 to T30, and resonant capacitors C1 to C3. The primary coils of transformers T10 to T30 are connected in a Y-connection (star connection), with the other ends of the primary coils connected in a balanced connection with the neutral point at point P. Similarly, the secondary coils of transformers T10 to T30 are connected in a Y-connection, with the other ends of the secondary coils connected in a balanced connection with the neutral point at point S.

[0007] Although DC / DC converter 30A can easily achieve high output because it shares power among three phases, variations in the characteristics of the three components that contribute to resonance (resonant coils L1 to L3, transformers T10 to T30, and resonant capacitors C1 to C3) can cause the resonant currents of each phase to become unbalanced. When the resonant currents become unbalanced, for example, differences in the peak values ​​of the three resonant currents occur, causing problems such as heat generation in certain resonant coils or transformers or increased ripple in the output waveform output from the secondary-side rectifier circuit.

[0008] Increasing the drive frequency of the switching elements Q1 to Q6 is an effective way to reduce the size of the DC / DC converter 30A. However, it is necessary to consider the switching losses of the switching elements Q1 to Q6, the core losses (iron losses) of the transformers T10 to T30 and the resonant coils L1 to L3, and the losses due to the skin effect and proximity effect (copper losses) of the windings. Wide-bandgap semiconductors such as silicon carbide (SiC) and gallium nitride (GaN), which have short switching times and low on-state losses, can be used for the switching elements Q1 to Q6. On the other hand, for magnetic components such as the transformers T10 to T30 and the resonant coils L1 to L3, increasing the drive frequency of the switching elements Q1 to Q6 above approximately 100 kHz increases core loss, resulting in heat generation problems. Furthermore, while it becomes necessary to use expensive Litz wire to address the copper loss of the windings, the benefits of this approach are limited. Therefore, the drive frequency cannot be increased excessively.

[0009] As described above, miniaturization of DC / DC converter 30A is restricted by magnetic components such as transformers T10 to T30 and resonant coils L1 to L3. In particular, when the output of DC / DC converter 30A exceeds 10 kW, if each phase of transformers T10 to T30 is configured with a single transformer as shown in Fig. 9, the volume and weight of the transformers T10 to T30 are larger than those of the other components, which results in a problem of a larger product size and higher costs.

[0010] 10 shows a three-phase LLC DC / DC converter 30B in which each phase is configured with two transformers (T11 and T12, T21 and T22, T31 and T32). By connecting the transformers for each phase in parallel, the current flowing through the transformer can be reduced, making it possible to make the transformer smaller, and in DC / DC converter 30B, the component height can be reduced, making it possible to make the product smaller.

[0011] In DC / DC converter 30B, the primary coils of transformers T11 to T32 are connected in parallel, and the secondary coils are connected in series. By connecting the secondary coils of transformers T11 to T32 in series, the secondary currents of transformers T11 to T32 are made uniform (identical). Therefore, even if there are variations in the characteristics of the components that contribute to resonance (resonance coils L1 to L3, transformers T11 to T32, and resonant capacitors C1 to C3), ripples in the output waveform of DC / DC converter 30B can be reduced. However, compared to the configuration in Figure 9, DC / DC converter 30B has a problem in that the secondary currents of transformers T11 to T32 are doubled, which increases the heat generation of transformers T11 to T32, making it difficult to achieve high output.

[0012] 11 shows a three-phase LLC DC / DC converter 30C in which the primary coils of transformers T11 to T32 are connected in parallel, and the secondary coils are also connected in parallel. Connecting the secondary coils of transformers T11 to T32 in parallel reduces the current on both the primary and secondary sides of transformers T11 to T32, but if there is variation in the characteristics of the components that contribute to resonance, this effect is directly reflected in the output, resulting in the problem of larger ripples in the output waveform.

[0013] Non-Patent Document 1 proposes a method for a three-phase LLC DC / DC converter in which the drive frequency of each phase is the same, but the phase difference between the input voltages of each phase input from the primary-side switching circuit to the LLC resonant circuit is changed from 120° to equalize the resonant current of each phase and reduce ripple in the output waveform. However, this method requires current sensors to detect the resonant current of each phase, which increases the number of components and leads to higher costs, and the need to change the phase difference between the input voltages of each phase depending on the operating state of the DC / DC converter complicates control. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] Specification of Chinese Utility Model No. 212935783

Non-Patent Literature

[0015]

Non-Patent Literature 1

Summary of the Invention

Problems to be Solved by the Invention

[0016] The present invention has been made in view of the above circumstances, and the problem thereof is to provide a three-phase LLC type DC / DC converter and a charging device that can cope with high output, and can reduce the ripple of the output waveform without causing high cost or complexity of control.

Means for Solving the Problems

[0017] In order to solve the above problems, the DC / DC converter according to the first aspect of the present invention includes a first transformer section, a second transformer section, and a third transformer section, each transformer section being a transformer circuit composed of N transformers (N is an integer of 2 or more), a first leg, a second leg, and a third leg connected in parallel, each leg including a set of switching elements connected in series, and a primary side switching circuit provided on the primary side of the transformer circuit, a primary-side resonant circuit including a first resonant unit provided between the first leg and the first transformer unit, a second resonant unit provided between the second leg and the second transformer unit, and a third resonant unit provided between the third leg and the third transformer unit, each resonant unit including a resonant coil and a resonant capacitor; a secondary-side rectifier circuit including a plurality of rectifier elements and provided on the secondary side of the transformer circuit; a control unit that provides a predetermined phase difference between the first leg, the second leg, and the third leg and drives the first leg at a predetermined drive frequency to generate current resonance; A three-phase LLC DC / DC converter comprising: The transformer circuits form N transformer groups, Each of the N transformer groups is formed as a set of one transformer from each of the transformer sections, and is characterized in that the primary coils are connected in a balanced connection and the secondary coils are connected in a balanced connection.

[0018] In the DC / DC converter, the control unit includes a storage unit, The storage unit includes: a first phase difference related to the phase difference; With respect to the phase difference, a second phase difference different from the first phase difference; a first threshold value related to an output value of an output current and / or an output power output from the secondary-side rectifier circuit, The control unit The output value can be compared with the first threshold value, and if the output value is less than the first threshold value, the phase difference is set to the first phase difference, while if the output value is equal to or greater than the first threshold value, the phase difference is set to the second phase difference.

[0019] In order to solve the above problem, a DC / DC converter according to a second aspect of the present invention comprises: a transformer circuit including a first transformer unit, a second transformer unit, and a third transformer unit, each of which is composed of N transformers (N is an integer of 2 or more); a primary-side switching circuit provided on the primary side of the transformer circuit, the primary-side switching circuit including a first leg, a second leg, and a third leg connected in parallel, each leg including a set of switching elements connected in series; a secondary-side switching circuit provided on the secondary side of the transformer circuit, the secondary-side switching circuit including a fourth leg, a fifth leg, and a sixth leg connected in parallel, each leg including a set of switching elements connected in series; a resonant circuit including a first resonant unit provided between the first leg and the fourth leg via the first transformer unit, a second resonant unit provided between the second leg and the fifth leg via the second transformer unit, and a third resonant unit provided between the third leg and the sixth leg via the third transformer unit, each resonant unit including a resonant coil and a resonant capacitor provided on both the primary side and the secondary side of each transformer unit; a control unit that performs forward control to transfer power from the primary side switching circuit to the secondary side switching circuit and reverse control to transfer power from the secondary side switching circuit to the primary side switching circuit; A three-phase CLLC DC / DC converter comprising: The control unit In the forward control, a predetermined phase difference is provided between the first leg, the second leg, and the third leg, and the first leg, the second leg, and the third leg are driven at a predetermined drive frequency to generate current resonance; In the reverse direction control, a predetermined phase difference is provided between the fourth leg, the fifth leg, and the sixth leg, and the fourth leg, the fifth leg, and the sixth leg are driven at a predetermined drive frequency to generate current resonance; The transformer circuits form N transformer groups, Each of the N transformer groups is formed as a set of one transformer from each of the transformer sections, and is characterized in that the primary coils are connected in a balanced connection and the secondary coils are connected in a balanced connection.

[0020] In the DC / DC converter, the control unit includes a storage unit, The storage unit includes: a first phase difference related to the phase difference during the forward control; With regard to the phase difference during the forward control, a second phase difference different from the first phase difference; a first threshold value related to a first output value of an output current and / or an output power output from the secondary-side switching circuit during the forward control; a third phase difference related to the phase difference during the reverse direction control; With regard to the phase difference during the reverse direction control, a fourth phase difference different from the third phase difference; a second threshold value related to a second output value of the output current and / or the output power output from the primary side switching circuit during the reverse direction control, The control unit During the forward direction control, the first output value is compared with the first threshold value, and if the first output value is less than the first threshold value, the phase difference is set to the first phase difference, whereas if the first output value is equal to or greater than the first threshold value, the phase difference is set to the second phase difference; During the reverse direction control, the second output value is compared with the second threshold value, and if the second output value is less than the second threshold value, the phase difference is set to the third phase difference, whereas if the second output value is equal to or greater than the second threshold value, the phase difference is set to the fourth phase difference.

[0021] In order to solve the above problem, a charging device according to the present invention includes: any one of the DC / DC converters; an AC / DC converter provided in a stage preceding the DC / DC converter; and an output filter provided in a subsequent stage of the DC / DC converter. [Effects of the Invention]

[0022] The present invention provides a three-phase LLC DC / DC converter and charging device that can handle higher output and reduce ripple in the output waveform without increasing costs or complicating control. [Brief explanation of the drawings]

[0023] [Figure 1] 1A is a block diagram of a charging device according to a first embodiment, FIG. 1B is a circuit diagram of a three-phase LLC DC / DC converter according to a first embodiment, and FIG. 1C is a diagram showing an example of the configuration of a first leg of a primary-side switching circuit. [Figure 2] 10A and 10B are diagrams showing input voltage vectors and output current vectors in a DC / DC converter according to a first embodiment, in which (A) is an input voltage vector with a phase difference of 120°, (B) is an output current vector corresponding to (A), (C) is an input voltage vector with a phase difference changed from 120°, and (D) is an output current vector corresponding to (C). [Figure 3] FIG. 4 is a diagram illustrating an example of a control flow by a control unit of the first embodiment. [Figure 4] FIG. 4 is a diagram illustrating a first modified example of the DC / DC converter of the first embodiment. [Figure 5] FIG. 4 is a diagram illustrating a second modified example of the DC / DC converter of the first embodiment. [Figure 6] FIG. 10 is a diagram illustrating a third modified example of the DC / DC converter of the first embodiment. [Figure 7] FIG. 10 is a diagram illustrating a fourth modified example of the DC / DC converter of the first embodiment. [Figure 8] FIG. 10 is a circuit diagram of a three-phase CLLC DC / DC converter according to a second embodiment. [Figure 9] FIG. 1 is a diagram illustrating a first conventional example of a three-phase LLC DC / DC converter. [Figure 10] FIG. 10 is a diagram illustrating a second conventional example of a three-phase LLC DC / DC converter. [Figure 11] FIG. 10 is a diagram illustrating a third conventional example of a three-phase LLC DC / DC converter. DETAILED DESCRIPTION OF THE INVENTION

[0024] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a three-phase LLC (including three-phase CLLC) DC / DC converter and a charging device according to the present invention will be described with reference to the accompanying drawings.

[0025] [First embodiment] FIG. 1(A) shows a charging device 1A according to a first embodiment of the present invention, and FIG. 1(B) shows a three-phase LLC DC / DC converter 10A according to the first embodiment of the present invention.

[0026] The charging device 1A includes a power supply unit composed of an AC / DC converter 2, a DC / DC converter 10A, and an output filter 3, and a control unit 4 that controls the power supply unit. The charging device 1A is, for example, a rapid charger that charges electrically powered vehicles such as electric vehicles and plug-in hybrid vehicles. Note that while FIG. 1(A) shows only one power supply unit, the charging device 1A may also include multiple power supply units connected in parallel.

[0027] AC / DC converter 2 converts AC power input from AC power supply 5 into DC power while correcting the power factor of the AC power, and outputs the DC power to DC / DC converter 10A. DC / DC converter 10A converts the DC power input from AC / DC converter 2 into desired DC power and supplies it to battery 6 via output filter 3. Battery 6 is, for example, an on-board battery for an electric vehicle. For the sake of explanation, the AC / DC converter 2, DC / DC converter 10A, and output filter 3 will be described separately as three parts, but these three parts are merely classified based on their functions, and they may also be configured as a single integrated circuit board.

[0028] Output filter 3 is a noise filter composed of components such as electrolytic capacitors, film capacitors, and choke coils. Output filter 3 is designed to reduce ripple in the output waveform of DC / DC converter 10A, and if the ripple can be reduced in DC / DC converter 10A, the components of output filter 3 can be made smaller, lighter, and less expensive.

[0029] As shown in FIG. 1(B), the DC / DC converter 10A is a three-phase LLC DC / DC converter including terminals T1 to T4, a primary-side switching circuit 11, a secondary-side rectifier circuit 12, a transformer circuit 13, a primary-side resonant circuit 14, and a control unit 15.

[0030] Terminals T1 and T2 are connected to the DC end of AC / DC converter 2, and terminals T3 and T4 are connected to battery 6 via output filter 3. A DC input voltage V1 is applied to terminals T1 and T2, and a DC output voltage V2 (or a DC current corresponding to the output voltage V2) is output from terminals T3 and T4.

[0031] The primary-side switching circuit 11 includes a first leg, a second leg, and a third leg connected in parallel. The first leg includes a pair of switching elements Q1 and Q2 connected in series, the second leg includes a pair of switching elements Q3 and Q4 connected in series, and the third leg includes a pair of switching elements Q5 and Q6 connected in series. Each pair of switching elements Q1 to Q6 may consist of a single switching element, but it is preferable to configure each pair of switching elements Q1 to Q6 with two or more switching elements connected in parallel for current distribution. For example, as shown in FIG. 1(C), switching element Q1 may consist of two switching elements Q11 and Q12 connected in parallel, and switching element Q2 may consist of two switching elements Q21 and Q22 connected in parallel. The same applies to switching elements Q3 to Q6.

[0032] A diode is connected in parallel in the reverse direction to each current path of the switching elements Q1 to Q6. Furthermore, power semiconductors such as IGBTs (insulated gate bipolar transistors) and MOSFETs (metal-oxide semiconductor field-effect transistors) using SiC (silicon carbide) or GaN (gallium nitride) can be used as the switching elements Q1 to Q6. The anti-parallel diodes of the switching elements Q1 to Q6 may be built-in diodes of the switching elements or individual diodes. Furthermore, partial resonant capacitors may be provided in parallel to each switching element Q1 to Q6, or the parasitic capacitance of each switching element Q1 to Q6 may be utilized.

[0033] The secondary-side rectifier circuit 12 includes a fourth leg, a fifth leg, and a sixth leg connected in parallel, and a smoothing capacitor Co. The fourth leg includes two rectifier diodes D1 and D2 connected in series, the fifth leg includes two rectifier diodes D3 and D4 connected in series, and the sixth leg includes two rectifier diodes D5 and D6 connected in series. The rectifier diodes D1 to D6 correspond to the rectifier elements of the present invention. The smoothing capacitor Co is a capacitor for removing output ripple and is connected between terminals T3 and T4. Note that each rectifier diode may be configured with multiple diodes for current distribution. For example, the rectifier diode D1 may be configured with two diodes connected in parallel, and the rectifier diode D2 may be configured with two diodes connected in parallel. The same applies to the other rectifier diodes D3 to D6.

[0034] The secondary-side rectifier circuit 12 may be any rectifier circuit, and a synchronous rectifier circuit composed of multiple switching elements may be used instead of a three-phase full-bridge rectifier circuit composed of rectifier diodes D1 to D6. The synchronous rectifier circuit has multiple switching elements connected in a three-phase full-bridge configuration, and each switching element is turned on / off by, for example, synchronous rectification control. In this case, each switching element corresponds to a rectifier element of the present invention.

[0035] The transformer circuit 13 includes high-frequency isolation transformers (hereinafter referred to as transformers) T11 to T32. In the transformer circuit 13, the transformers T11 and T12 are connected in parallel to form a first transformer section, the transformers T21 and T22 are connected in parallel to form a second transformer section, and the transformers T31 and T32 are connected in parallel to form a third transformer section. As described above, each transformer section is composed of two parallel transformers, each of which is two transformers connected in parallel, but it may also be composed of three or more parallel transformers, each of which is three or more transformers connected in parallel.

[0036] One end of the primary coil of the transformer T11 is connected to one end of the primary coil of the transformer T12 and is also connected to a connection point X1 between the switching elements Q1 and Q2 via a first resonant section (resonant coil L1 and resonant capacitor C1) of the primary resonant circuit 14. One end of the primary coil of the transformer T21 is connected to one end of the primary coil of the transformer T22 and is also connected to a connection point X2 between the switching elements Q3 and Q4 via a second resonant section (resonant coil L2 and resonant capacitor C2) of the primary resonant circuit 14. One end of the primary coil of the transformer T31 is connected to one end of the primary coil of the transformer T32 and is also connected to a connection point X3 between the switching elements Q5 and Q6 via a third resonant section (resonant coil L3 and resonant capacitor C3) of the primary resonant circuit 14.

[0037] The primary coils of transformers T11, T21, and T31 are connected in a Y (star) configuration (balanced connection), with the other ends of the primary coils connected to the neutral point at point P1. Similarly, the primary coils of transformers T12, T22, and T32 are connected in a Y (balanced connection), with the other ends of the primary coils connected to the neutral point at point P2.

[0038] One end of the secondary coil of transformer T11 is connected to one end of the secondary coil of transformer T12 and to a connection point X4 of rectifier diodes D1 and D2. One end of the secondary coil of transformer T21 is connected to one end of the secondary coil of transformer T22 and to a connection point X5 of rectifier diodes D3 and D4. One end of the secondary coil of transformer T31 is connected to one end of the secondary coil of transformer T32 and to a connection point X6 of rectifier diodes D5 and D6.

[0039] The secondary coils of transformers T11, T21, and T31 are connected in a Y-connection (balanced connection), with the other ends of the secondary coils connected to the neutral point at point S1. Similarly, the secondary coils of transformers T12, T22, and T32 are connected in a Y-connection (balanced connection), with the other ends of the secondary coils connected to the neutral point at point S2.

[0040] That is, in the transformer circuit 13, a first transformer group is formed by a set of the transformers T11, T21, and T31, and a second transformer group is formed by another set of the transformers T12, T22, and T32.

[0041] In this embodiment, the primary and secondary coils are connected in a Y-connection. However, as long as the primary coils are connected in a balanced manner, they may be connected in a Δ-connection (delta connection) or a Δ-Cr connection, and the secondary coils may be connected in a Δ-connection. A Δ-Cr connection is, for example, a connection in which the other ends of the primary coils of transformers T11, T21, and T31 are connected together, a resonant capacitor C1 is interposed between the other end of the primary coil of transformer T11 and the other end of the primary coil of transformer T21, a resonant capacitor C2 is interposed between the other end of the primary coil of transformer T21 and the other end of the primary coil of transformer T31, and a resonant capacitor C3 is interposed between the other end of the primary coil of transformer T31 and the other end of the primary coil of transformer T11. The primary coils of transformers T12, T22, and T32 are connected in a similar manner.

[0042] The primary-side resonant circuit 14 includes a first resonant unit, a second resonant unit, and a third resonant unit, and together with the transformer circuit 13, forms a three-phase LLC resonant circuit. Specifically, the resonant coil L1, the excitation coils and primary coils of the transformers T11 and T12, and the resonant capacitor C1 form the first LLC resonant circuit. The resonant coil L2, the excitation coils and primary coils of the transformers T21 and T22, and the resonant capacitor C2 form the second LLC resonant circuit. The resonant coil L3, the excitation coils and primary coils of the transformers T31 and T32, and the resonant capacitor C3 form the third LLC resonant circuit.

[0043] The excitation coils of the transformers T11 to T32 are included in the transformers T11 to T32 and are not shown in the figure. Also, the resonance coils L1 to L3 are separate components from the transformers T11 to T32, but they may be formed only by the leakage flux of the transformers T11 to T32, or by the leakage flux of the transformers T11 to T32 and separate coils.

[0044] The control unit 15 includes drive circuits for the switching elements Q1 to Q6 for turning the switching elements Q1 to Q6 on and off, a control circuit (including a detection circuit) for sending control signals to the drive circuits, and a storage unit that stores the characteristics of the resonant components described below. The control unit 15 may be configured with an analog circuit, a combination of logic circuits, a digital circuit such as a microcontroller or DSP, or a circuit that combines analog and digital circuits. In the case of an analog circuit, the storage unit may be a specified voltage / current circuit that configures a threshold value, and in the case of a digital circuit, the storage unit may be configured with a memory within the processing unit or a non-volatile memory provided separately from the processing unit.

[0045] The control unit 15, for example, periodically (or constantly) detects the output voltage V2 and the output current output from terminals T3 and T4 using a detector not shown, and changes the drive frequency of the switching elements Q1 to Q6 so that the current value of the output current (hereinafter referred to as the output current value) matches a predetermined target current value.

[0046] Specifically, the control unit 15 alternately turns on and off the switching elements Q1 and Q2 constituting the first leg with a phase difference of 180° with a predetermined dead time, alternately turns on and off the switching elements Q3 and Q4 constituting the second leg with a phase difference of 180° with a predetermined dead time, and alternately turns on and off the switching elements Q5 and Q6 constituting the third leg with a phase difference of 180° with a predetermined dead time. The on-duty of the switching elements Q1, Q3, and Q5 is set to, for example, 50%.

[0047] Furthermore, the control unit 15 drives the switching elements Q1 to Q6 by providing a constant phase difference between the first leg, the second leg, and the third leg (interleaved driving). For example, the control unit 15 sets the phase difference between the first leg and the second leg to 120°, the phase difference between the second leg and the third leg to 120°, and the phase difference between the third leg and the first leg to 120°. In this case, the phase difference between the on-timings of the switching elements Q1, Q3, and Q5 is 120°, and the phase difference between the off-timings is also 120°. Similarly, the phase difference between the on-timings of the switching elements Q2, Q4, and Q6 is 120°, and the phase difference between the off-timings is also 120°.

[0048] Furthermore, control unit 15 sets the drive frequencies of switching elements Q1 to Q6 to the same drive frequency and simultaneously changes the same drive frequencies by the same amount to match the output current value with a predetermined target current value (frequency modulation control). For example, when the current gain (= output current / input current input to terminals T1 and T2) of DC / DC converter 10A is to be reduced below 1, control unit 15 drives switching elements Q1 to Q6 at a drive frequency higher than a first resonant frequency determined by resonant coils L1 to L3 and resonant capacitors C1 to C3. On the other hand, when the current gain is to be increased above 1, control unit 15 drives switching elements Q1 to Q6 at a drive frequency lower than the first resonant frequency and higher than a second resonant frequency determined by resonant coils L1 to L3, excitation coils of transformers T11 to T32, and resonant capacitors C1 to C3.

[0049] By the above control, a first resonant current generated by current resonance of the first LLC resonant circuit flows through the transformers T11 and T12 to the secondary-side rectifier circuit 12, a second resonant current generated by current resonance of the second LLC resonant circuit flows through the transformers T21 and T22 to the secondary-side rectifier circuit 12, and a third resonant current generated by current resonance of the third LLC resonant circuit flows through the transformers T31 and T32 to the secondary-side rectifier circuit 12. The output of the secondary-side rectifier circuit 12 is an output obtained by combining three-phase currents, namely the first resonant current, the second resonant current, and the third resonant current.

[0050] The DC / DC converter 10A is a three-phase LLC type that is driven with a fixed phase difference between the first, second, and third legs, and is therefore able to reduce ripple in the output waveform compared to a single-phase full-bridge type. Furthermore, in the DC / DC converter 10A, transformers T11, T21, and T31 form a first transformer group, and transformers T12, T22, and T32 form another group to form a second transformer group, with the other ends of the primary coils and secondary coils of each transformer group each connected to the neutral point by a Y connection (balanced connection).

[0051] Therefore, in the DC / DC converter 10A, even if there is variation in the characteristics of components that contribute to resonance (hereinafter referred to as resonant components), such as the resonant coils L1 to L3, the resonant capacitors C1 to C3, and the primary and secondary coils of the transformers T11 to T32, it is possible to alleviate the unbalanced state of the first resonant current, the second resonant current, and the third resonant current, and reduce the ripple in the output waveform of the DC / DC converter 10A.

[0052] Table 1 shows example values ​​for the DC / DC converter 10A when there is no variation in the characteristics of the resonant coils L1 to L3, the excitation coils of the transformers T11 to T32, the primary coils, and the secondary coils, and Table 2 shows example values ​​for the case when there is variation in the above characteristics.

[0053] [Table 1]

[0054] [Table 2]

[0055] In Tables 1 and 2, L, Lm1, Lm2, Lp1, Lp2, Ls1, and Ls2 of the first LLC resonant circuit are the inductances of the resonant coil L1, the excitation coil of the transformer T11, the excitation coil of the transformer T12, the primary coil of the transformer T11, the primary coil of the transformer T12, the secondary coil of the transformer T11, and the secondary coil of the transformer T12, respectively. L, Lm1, Lm2, Lp1, Lp2, Ls1, and Ls2 of the second LLC resonant circuit are the inductances of the resonant coil L2, the excitation coil of the transformer T21, the excitation coil of the transformer T22, the primary coil of the transformer T21, the primary coil of the transformer T22, the secondary coil of the transformer T21, and the secondary coil of the transformer T22, respectively. Similarly, L, Lm1, Lm2, Lp1, Lp2, Ls1, and Ls2 of the third LLC resonant circuit are the inductances of the resonant coil L3, the excitation coil of the transformer T31, the excitation coil of the transformer T32, the primary coil of the transformer T31, the primary coil of the transformer T32, the secondary coil of the transformer T31, and the secondary coil of the transformer T32, respectively. The capacitance (electrostatic capacity) of each of the resonant capacitors C1 to C3 is 264 nF.

[0056] Table 2 shows an example where the characteristic variations of the resonant components are set taking into account general manufacturing control variations. Specifically, the characteristic (inductance) variations of the resonant coils L1 to L3 and the primary and secondary coils of the transformers T11 to T32 are set to about 7%, and the characteristic variation of the excitation coils of the transformers T11 to T32 is set to about 20%. The characteristic (capacitance) of the resonant capacitors C1 to C3 generally varies by about 5%, but this is not taken into account here and is assumed to be zero.

[0057] Table 3 shows simulation results of the first resonant current, second resonant current, and third resonant current and their average values ​​when the configurations of the transformers T11 to T32 (connection modes of the primary and secondary coils) are changed in the case where there is variation in the characteristics of Table 2. In the simulation, the drive frequency of the switching elements Q1 to Q6 is set to a value near a frequency higher than the second resonant frequency determined by the resonant coils L1 to L3, the excitation coils and primary coils of the transformers T11 to T32, and the resonant capacitors C1 to C3.

[0058] [Table 3]

[0059] In Table 3, A is the configuration of the transformer circuit 13 of this embodiment. B is a configuration in which six primary coils are connected together in a Y-connection as shown in FIG. 11, and three secondary coils are connected together in a Y-connection as in the transformer circuit 13. C is a configuration in which only the primary coils are connected together in a Y-connection as in the transformer circuit 13, and six secondary coils are connected together in a Y-connection. D is the configuration of the conventional transformer circuit of FIG. 11, in which six primary coils and six secondary coils are both connected together in a Y-connection.

[0060] In Table 3, the ratios of the first resonant current, the second resonant current, and the third resonant current are the ratios of the minimum value to the maximum value of the current after rectification by the secondary-side rectifier circuit 12 (before passing through the smoothing capacitor Co). For example, the ratio of the first resonant current = (minimum value of the first resonant current / maximum value of the first resonant current) × 100 [%]. The average value is the average value of the ratios of the first resonant current, the second resonant current, and the third resonant current.

[0061] The results in Table 3 show that the conventional configuration D (FIG. 11) has the largest difference between the minimum and maximum values ​​of the output current, that the difference between the minimum and maximum values ​​of the output current gradually decreases in the order of configuration C and configuration B, and that configuration A, which is the configuration of transformer circuit 13 of this embodiment, has the smallest difference between the minimum and maximum values ​​of the output current. That is, it can be seen that the DC / DC converter 10A of this embodiment, thanks to the configuration of transformer circuit 13, can alleviate the unbalanced state of the first resonant current, the second resonant current, and the third resonant current and reduce ripple in the output waveform without requiring special control to alleviate the current imbalance of each phase.

[0062] The impact of imbalance in resonant current due to variations in the characteristics of resonant components varies depending on the output current or output power, and is known to be most problematic when the output current or output power is at its maximum. For example, if a large resonant current flows through the primary-side resonant circuit 14 or the transformer circuit 13 and the resonant current of a specific phase becomes larger than expected, abnormal heat generation occurs in the resonant coils L1 to L3 and the transformers T11 to T32, causing a sudden change in characteristics such as inductance. As a result, the resonant current increases even further, and in the worst case, the components that make up the DC / DC converter 10A may be damaged.

[0063] Countermeasures for the above problem will be explained using Fig. 2. Fig. 2 is a diagram showing input voltage vectors and output current vectors when there is variation in the characteristics of resonant components.

[0064] Figure 2(A) shows input voltage vectors v1, v2, and v3 at connection points X1, X2, and X3 when the first, second, and third legs are driven with a phase difference of 120°. The input voltage vectors v1, v2, and v3 are equal in magnitude, and the phase difference θ11 between input voltage vector v1 and input voltage vector v2, the phase difference θ21 between input voltage vector v2 and input voltage vector v3, and the phase difference θ31 between input voltage vector v3 and input voltage vector v1 are all 120°.

[0065] Figure 2(B) shows the output current vectors i1, i2, and i3 corresponding to the resonant currents after rectification by the secondary-side rectifier circuit 12 (before passing through the smoothing capacitor Co) in the case of Figure 2(A). Due to variations in the characteristics of the resonant components, the output current vectors i1 and i3 increase while the output current vector i2 decreases, resulting in an unbalanced state among the output current vectors i1, i2, and i3. The phase differences φ11, φ21, and φ31 between the output current vectors i1, i2, and i3 are shifted from 120°.

[0066] The characteristics of resonant components can be easily measured on a component-by-component basis. The characteristics of coils and transformers are often known in advance through testing. Furthermore, the characteristics of capacitors vary less than those of coils and transformers, and there is a consistent tendency for variations between production lots, making them easy to measure. Meanwhile, it is known that if there is an imbalance in the output current of a three-phase LLC system, the output current can be balanced by shifting the phase of each phase from 120° (see Non-Patent Document 1). Therefore, using simulation or a real circuit (an actual DC / DC converter), the phase difference between the first, second, and third legs can be gradually changed from 120° while the output current or output power is maximized. This allows the phase difference at which the output current vectors i1, i2, and i3 are balanced to be determined.

[0067] Figure 2(C) shows the input voltage vectors v1, v2, and v3 at connection points X1, X2, and X3, where the output current vectors i1, i2, and i3 are in equilibrium. In Figure 2(C), the phase difference θ12 is wider than 120° by α, while the phase difference θ32 is narrower than 120° by β. The phase difference θ22 is θ22 = 120° - α + β, where α and β are angles greater than 0° and less than 120°.

[0068] Figure 2(D) shows the output current vectors i1, i2, and i3 corresponding to the resonant currents after being rectified by the secondary-side rectifier circuit 12 (before passing through the smoothing capacitor Co) in the case of Figure 2(C). Compared to Figure 2(B), the output current vectors i1 and i3 are smaller, and the output current vector i2 is larger, so that the output current vectors i1, i2, and i3 are in a balanced state. In addition, the phase differences φ12, φ22, and φ32 of the output current vectors i1, i2, and i3 are all 120°.

[0069] Next, a method of controlling the switching elements Q1 to Q6 by the control unit 15 will be described with reference to the control flow in Fig. 3. It is assumed that the control unit 15 stores in advance the first phase difference, the second phase difference, and the first threshold values ​​(current threshold value and power threshold value).

[0070] The first phase difference is the phase difference between the first leg, the second leg, and the third leg in the low-medium output range (the low-medium output current range and the low-medium output power range) where the influence of the imbalance in the resonant current due to the variation in the characteristics of the resonant components is relatively small. In this embodiment, the first phase difference is the phase difference (θ11, θ21, θ31) between the input voltage vectors v1, v2, and v3 shown in Figure 2(A), where θ11 = θ21 = θ31 = 120°.

[0071] The second phase difference is the phase difference between the first leg, the second leg, and the third leg in a high output region (high output current region or high output power region) where the influence of imbalance in the resonant current due to variations in the characteristics of the resonant components is relatively large. In this embodiment, the second phase difference is defined as the phase difference (θ12, θ22, θ32) between the input voltage vectors v1, v2, and v3 shown in Figure 2(C), where θ12 = 120° + α, θ22 = 120° - α + β, and θ32 = 120° - β.

[0072] The current threshold is a threshold used by control unit 15 to determine whether the current is in the low-medium output current region or the high output current region. The power threshold is a threshold used by control unit 15 to determine whether the current is in the low-medium output power region or the high output power region. The current threshold and power threshold can be set as appropriate, and for example, the rated output value of DC / DC converter 10A may be set as the threshold.

[0073] After starting control, control unit 15 sets the phase differences among the first, second, and third legs to a first phase difference (θ11, θ21, θ31) (S1). Control unit 15 turns on and off switching elements Q1 to Q6 at the same drive frequency so that the phase differences among the first, second, and third legs become the first phase difference (θ11, θ21, θ31), and controls the drive frequency of switching elements Q1 to Q6 so that the output current value matches a predetermined target current value.

[0074] The phase difference between the on / off timings of switching elements Q1, Q3, and Q5 is 120°, and the phase difference between the on / off timings of switching elements Q2, Q4, and Q6 is also 120°. Switching elements Q1 and Q2 alternate on and off with a phase difference of 180°, with a dead time provided, and switching elements Q3, Q4 and switching elements Q5, Q6 also alternate on and off with a phase difference of 180°, with a dead time provided. The on-duty of switching elements Q1, Q3, and Q5 is set to, for example, 50%.

[0075] The control unit 15, which has started driving the switching elements Q1 to Q6, acquires the output current value and the voltage value of the output voltage V2 from a detector not shown, and calculates and acquires the power value of the output power (hereinafter referred to as the output power value) output from terminals T3 and T4 (S2).

[0076] Next, the control unit 15 compares the output current value acquired in step S2 with a current threshold value pre-stored in the storage unit (S3). If the output current value is equal to or greater than the current threshold value (YES in S3), the control unit 15 sets the phase differences between the first leg, second leg, and third leg to second phase differences (θ12, θ22, θ32) (S4).

[0077] The control unit 15 sets the phase difference to the second phase difference (θ12, θ22, θ32), and controls the drive frequency of the switching elements Q1 to Q6 so that the phase difference between the first leg and the second leg is θ12 = 120° + α, the phase difference between the second leg and the third leg is θ22 = 120° - α + β, and the phase difference between the third leg and the first leg is θ32 = 120° - β, and turns the switching elements Q1 to Q6 on and off at the same drive frequency so that the output current value matches a predetermined target current value.

[0078] In the comparison of step S3, if the output current value is less than the current threshold (NO in S3), the control unit 15 compares the output power value acquired in step S2 with the power threshold pre-stored in the storage unit (S5). If the output power value is equal to or greater than the power threshold (YES in S5), the control unit 15 sets the phase differences between the first leg, second leg, and third leg to second phase differences (θ12, θ22, θ32) (S4). On the other hand, if the output power value is less than the power threshold (NO in S5), the control unit 15 sets the phase differences between the first leg, second leg, and third leg to first phase differences (θ11, θ21, θ31) (S6).

[0079] Next, the control unit 15 determines whether or not to continue the control (S7). The control unit 15 makes the determination in step S7 based on a processing end instruction from a higher-level system (for example, the control unit 4 shown in FIG. 1(A)). If the control unit 15 has not received a processing end instruction, it determines to continue the control (YES in S7) and proceeds to the processing of step S2, but if the control unit 15 has received a processing end instruction, it determines not to continue the control (NO in S7) and ends the control.

[0080] As described above, the control unit 15 sets the phase difference between each leg to the first phase difference (θ11, θ21, θ31) in the low and medium output range, and sets the phase difference between each leg to the second phase difference (θ12, θ22, θ32) in the high output range. The second phase difference (θ12, θ22, θ32) is a phase difference that alleviates the unbalanced state of the output current vector corresponding to each resonant current even if there is variation in the characteristics of the resonant components.

[0081] Therefore, even in the high-output range where the impact of imbalance in the resonant current due to variations in the characteristics of the resonant components is relatively large, the DC / DC converter 10A can mitigate the imbalance in the resonant current and reduce ripple in the output waveform. Furthermore, compared to the method of Non-Patent Document 1 (a method in which the phase difference between the input voltages of each phase is changed according to the operating state of the DC / DC converter while detecting the resonant current of each phase), the number of components can be reduced and the control complexity can be avoided. This also compares favorably with a method in which the resonant current or load current of each phase is detected and the drive frequency of each phase is adjusted individually without changing the phase of each phase to mitigate the imbalance in the resonant current.

[0082] That is, the DC / DC converter 10A can accommodate higher output by connecting the transformers T11 to T32 in parallel, and can reduce ripple in the output waveform by mitigating the imbalance in the resonant current caused by variations in the characteristics of the resonant components, without increasing costs or complicating control.

[0083] In this embodiment, the first phase differences (θ11, θ21, θ31) are set to θ11=θ21=θ31=120°, but they may be set to angles other than 120°. For example, similar to the second phase difference, by using a simulation or an actual circuit and gradually changing the phase differences between the first, second, and third legs from 120° while the output current and output power are in the low-medium output range, the phase differences at which the output current vectors corresponding to the respective resonant currents are in a balanced state may be found, and the found phase differences may be used as the first phase differences.

[0084] In this embodiment, the control unit 15 stores two phase differences for two regions, a first phase difference in the low-to-medium output region and a second phase difference in the high output region, and performs control. However, the control unit 15 may store three or more phase differences for three or more regions. For example, the control unit 15 may store a first first phase difference (first phase difference A) in the low output region, a second first phase difference (first phase difference B) in the medium output region, and a second phase difference in the high output region, and perform control. Alternatively, the control unit 15 may store a first phase difference in the low-to-medium output region, a first second phase difference (second phase difference A) in the high output current region, and a second second phase difference (second phase difference B) in the high output power region, and perform control.

[0085] In addition, the control unit 15 may perform only one of the processes of comparing the output current values ​​(S3 in FIG. 3) or comparing the output power values ​​(S5 in FIG. 3) depending on the type of battery 6 and the purpose of control, and set the phase difference between each leg.

[0086] [First Modification of the First Embodiment] A three-phase LLC DC / DC converter 10B according to the first modification is shown in Fig. 4. The DC / DC converter 10B has the same configuration as the DC / DC converter 10A according to the first embodiment, except for a primary-side resonant circuit 14B.

[0087] In the primary side resonant circuit 14B, the resonant coil of the first resonant section is composed of a resonant coil L11 connected to the primary side coil of the transformer T11 and a resonant coil L12 connected to the primary side coil of the transformer T12, the resonant coil of the second resonant section is composed of a resonant coil L21 connected to the primary side coil of the transformer T21 and a resonant coil L22 connected to the primary side coil of the transformer T22, and the resonant coil of the third resonant section is composed of a resonant coil L31 connected to the primary side coil of the transformer T31 and a resonant coil L32 connected to the primary side coil of the transformer T32.

[0088] According to the above configuration, the resonant current flowing through each of the resonant coils L11 to L32 can be reduced compared to the first embodiment, which makes it possible to reduce the size, weight, and cost of the resonant coils L11 to L32. Furthermore, the amount of heat generated by the resonant coils L11 to L32 can also be reduced.

[0089] In the primary-side resonant circuit 14B, the resonant coils and the resonant capacitors may be interchanged. That is, the resonant capacitor of the first resonant section may be configured with a resonant capacitor C11 connected to the primary coil of the transformer T11 and a resonant capacitor C12 connected to the primary coil of the transformer T12, the resonant capacitor of the second resonant section may be configured with a resonant capacitor C21 connected to the primary coil of the transformer T21 and a resonant capacitor C22 connected to the primary coil of the transformer T22, the resonant capacitor of the third resonant section may be configured with a resonant capacitor C31 connected to the primary coil of the transformer T31 and a resonant capacitor C32 connected to the primary coil of the transformer T32, and the resonant coils L11 to L32 may be configured with the resonant coils L1 to L3 as in the first embodiment.

[0090] [Second Modification of the First Embodiment] 5 shows a three-phase LLC DC / DC converter 10C according to the second modification. The DC / DC converter 10C has the same configuration as the DC / DC converter 10B according to the first modification, except for a primary-side resonant circuit 14C.

[0091] The primary side resonant circuit 14C is the primary side resonant circuit 14B of the first modified example, except that the resonant capacitors of the first resonant section are composed of a resonant capacitor C11 connected to the resonant coil L11 and a resonant capacitor C12 connected to the resonant coil L12, the resonant capacitors of the second resonant section are composed of a resonant capacitor C21 connected to the resonant coil L21 and a resonant capacitor C22 connected to the resonant coil L22, and the resonant capacitors of the third resonant section are composed of a resonant capacitor C31 connected to the resonant coil L31 and a resonant capacitor C32 connected to the resonant coil L32.

[0092] According to the above configuration, the resonant current flowing through each of the resonant coils L11 to L32 and each of the resonant capacitors C11 to C32 can be reduced compared to the first embodiment, thereby making it possible to reduce the size, weight, and cost of the resonant coils L11 to L32 and the resonant capacitors C11 to C32. Furthermore, the amount of heat generated by the resonant coils L11 to L32 and the resonant capacitors C11 to C32 can also be reduced.

[0093] [Third Modification of the First Embodiment] A three-phase LLC DC / DC converter 10D according to the third modification is shown in Fig. 6. The DC / DC converter 10D has the same configuration as the DC / DC converter 10C according to the second modification, except for a primary-side resonant circuit 14D.

[0094] The primary resonant circuit 14D is obtained by moving the positions of the resonant capacitors C11 to C32 to the other end side of the primary coils of the transformers T11 to T32 in the primary resonant circuit 14C of the second modification. The resonant capacitors C11, C21, and C31 are interposed between the other end of the primary coils of the transformers T11, T21, and T31, respectively, and point P1, and the resonant capacitors C12, C22, and C32 are interposed between the other end of the primary coils of the transformers T12, T22, and T32, respectively, and point P2.

[0095] In the first resonance unit, the positions of the resonance coils L11 and L12 and the resonance capacitors C11 and C12 can be changed arbitrarily between the connection point X1 of the switching elements Q1 and Q2 and the points P1 and P2, as long as the equivalent circuit of the first resonance unit remains the same. The same applies to the second and third resonance units.

[0096] Furthermore, in the primary-side resonant circuit 14D, the resonant coils L11 to L32 and the resonant capacitors C11 to C32 may be divided and arranged as long as the equivalent circuits of the resonant parts are the same. For example, the resonant capacitor C11 may be divided into two and arranged on one end side and the other end side of the primary-side coil of the resonant coil L11.

[0097] [Fourth Modification of the First Embodiment] A three-phase LLC DC / DC converter 10E according to a fourth modification is shown in Fig. 7. The DC / DC converter 10E has the same configuration as the DC / DC converter 10A of the first embodiment, except for a secondary-side rectifier circuit 12E.

[0098] The secondary-side rectifier circuit 12E includes three full-bridge rectifier circuits (rectifier diodes D11 to D62) corresponding to the respective transformer sections of the transformer circuit 13. The full-bridge rectifier circuit corresponding to the first transformer section is composed of rectifier diodes D11 to D22, with one end of the secondary coil of the transformer T11 connected to a junction X41 of the rectifier diodes D11 and D21, and one end of the secondary coil of the transformer T12 connected to a junction X42 of the rectifier diodes D12 and D22. The full-bridge rectifier circuit corresponding to the second transformer section is composed of rectifier diodes D31 to D42, with one end of the secondary coil of the transformer T21 connected to a junction X51 of the rectifier diodes D31 and D41, and one end of the secondary coil of the transformer T22 connected to a junction X52 of the rectifier diodes D32 and D42. The full-bridge rectifier circuit corresponding to the third transformer section is composed of rectifier diodes D51 to D62, with one end of the secondary coil of the transformer T31 connected to the junction X61 of the rectifier diodes D51 and D61, and one end of the secondary coil of the transformer T32 connected to the junction X62 of the rectifier diodes D52 and D62.

[0099] According to the above configuration, the load current due to the resonance current flowing through each of the rectifier diodes D11 to D62 can be reduced compared to the first embodiment, which makes it possible to reduce the size, weight, and cost of the rectifier diodes D11 to D62. Furthermore, the amount of heat generated by the rectifier diodes D11 to D62 can also be reduced.

[0100] [Second embodiment] 8 shows a three-phase bidirectional CLLC DC / DC converter 20 according to a second embodiment of the present invention. The DC / DC converter 20 includes terminals T1 to T4, a primary-side switching circuit 21, a secondary-side switching circuit 22, a transformer circuit 23, a primary-side resonant circuit 24 and a secondary-side resonant circuit 24' which correspond to the "resonant circuit" of the present invention, and a control unit 25, and performs bidirectional power transmission.

[0101] The primary side switching circuit 21 has the same configuration as the primary side switching circuit 11 of the first embodiment, except that it includes a smoothing capacitor Co1 connected between the terminals T1 and T2.

[0102] The secondary-side switching circuit 22 includes a fourth leg, a fifth leg, and a sixth leg connected in parallel, and a smoothing capacitor Co2 connected between terminals T3 and T4. The fourth leg includes a pair of switching elements Q7 and Q8 connected in series, the fifth leg includes a pair of switching elements Q9 and Q10 connected in series, and the sixth leg includes a pair of switching elements Q11 and Q12 connected in series. A diode is connected in parallel in the reverse direction to each current path of the switching elements Q7 to Q12. In other words, the secondary-side switching circuit 22 has the same circuit configuration as the primary-side switching circuit 21.

[0103] The transformer circuit 23 has the same configuration as the transformer circuit 13 of the first embodiment, and the primary side resonant circuit 24 has the same configuration as the primary side resonant circuit 14 of the first embodiment.

[0104] The secondary side resonant circuit 24' has the same configuration as the primary side resonant circuit 24, and includes a first resonant section consisting of a resonant coil L4 and a resonant capacitor C4, a second resonant section consisting of a resonant coil L5 and a resonant capacitor C5, and a third resonant section consisting of a resonant coil L6 and a resonant capacitor C6.

[0105] One end of the secondary coils of the transformers T11 and T12 is connected to the connection point X4 of the switching elements Q7 and Q8 via a first resonance section (resonance coil L4 and resonance capacitor C4). One end of the secondary coils of the transformers T21 and T22 is connected to the connection point X5 of the switching elements Q9 and Q10 via a second resonance section (resonance coil L5 and resonance capacitor C5). One end of the secondary coils of the transformers T31 and T32 is connected to the connection point X6 of the switching elements Q11 and Q12 via a third resonance section (resonance coil L6 and resonant capacitor C6).

[0106] The primary-side resonant circuit 24 and the secondary-side resonant circuit 24', together with the transformer circuit 23, form a three-phase bidirectional CLLC resonant circuit. Specifically, the resonant capacitor C1, the resonant coil L1, the transformers T11 and T12 (excitation coil, primary coil, and secondary coil), the resonant coil L4, and the resonant capacitor C4 form a first CLLC resonant circuit. The resonant capacitor C2, the resonant coil L2, the transformers T21 and T22 (excitation coil, primary coil, and secondary coil), the resonant coil L5, and the resonant capacitor C5 form a second CLLC resonant circuit. The resonant capacitor C3, the resonant coil L3, the transformers T31 and T32 (excitation coil, primary coil, and secondary coil), the resonant coil L6, and the resonant capacitor C6 form a third CLLC resonant circuit.

[0107] The excitation coils of the transformers T11 to T32 are included in the transformers T11 to T32 and are not shown in the figure. Also, the resonance coils L4 to L6 are separate components from the transformers T11 to T32, but they may be formed only by the leakage flux of the transformers T11 to T32, or by the leakage flux of the transformers T11 to T32 and separate coils.

[0108] The control unit 25 includes drive circuits for the switching elements Q1 to Q12 for turning the switching elements Q1 to Q12 on and off, a control circuit (including a detection circuit) for sending control signals to the drive circuits, and a storage unit that stores the characteristics of the resonant components. Each drive circuit, control circuit, and storage unit has the same configuration as in the first embodiment.

[0109] If the control unit 25 defines the control that transfers power from the terminals T1 and T2 side to the terminals T3 and T4 side as forward control, then the control unit 25 performs this forward control and reverse control that transfers power from the terminals T3 and T4 side to the terminals T1 and T2 side.

[0110] During forward control, the control unit 25 performs the same control as in the first embodiment for the switching elements Q1 to Q6, and performs diode bridge rectification control for keeping the switching elements Q7 to Q12 always off, or performs synchronous rectification control for turning the switching elements Q7 to Q12 on and off in synchronization with the first to third resonant currents. Reverse control will be described below.

[0111] The control of switching elements Q7 to Q12 during reverse control is the same as the control of switching elements Q1 to Q6 during forward control. The control of switching elements Q1 to Q6 during reverse control is the same as the control of switching elements Q7 to Q12 during forward control, and is diode bridge rectification control or synchronous rectification control as described above.

[0112] During reverse direction control, control unit 25 detects output voltage V1 and the output current output from terminals T1 and T2 with a detector (not shown), and changes the drive frequencies of switching elements Q7 to Q12 so that the output current value matches a predetermined target current value. The drive frequencies of switching elements Q7 to Q12 are all the same.

[0113] Specifically, the controller 25 alternately turns on and off the switching elements Q7 and Q8 constituting the fourth leg with a phase difference of 180° and provides a predetermined dead time, alternately turns on and off the switching elements Q9 and Q10 constituting the fifth leg with a phase difference of 180° and provides a predetermined dead time, and alternately turns on and off the switching elements Q11 and Q12 constituting the sixth leg with a phase difference of 180° and provides a predetermined dead time. The on-duty of the switching elements Q7, Q9, and Q11 is set to, for example, 50%.

[0114] Furthermore, the control unit 25 drives the switching elements Q7 to Q12 while providing a constant phase difference between the fourth, fifth, and sixth legs. For example, the control unit 25 sets the phase difference between the fourth and fifth legs to 120°, the phase difference between the fifth and sixth legs to 120°, and the phase difference between the sixth and fourth legs to 120°. In this case, the phase difference between the on-timings of the switching elements Q7, Q9, and Q11 is 120°, and the phase difference between the off-timings of the switching elements Q7, Q9, and Q11 is also 120°. Similarly, the phase difference between the on-timings of the switching elements Q8, Q10, and Q12 is also 120°, and the phase difference between the off-timings of the switching elements Q8, Q10, and Q12 is also 120°.

[0115] By the above control, a first resonant current generated by current resonance of the first CLLC resonant circuit, a second resonant current generated by current resonance of the second CLLC resonant circuit, and a third resonant current generated by current resonance of the third CLLC resonant circuit flow through the primary-side switching circuit 21. The output of the primary-side switching circuit 21 is an output in which three-phase currents, namely the first resonant current, the second resonant current, and the third resonant current, are combined.

[0116] The resonant capacitor and resonant coil on the secondary side of the transformer can be equivalently converted to the primary side of the transformer, and the resonant capacitor and resonant coil on the primary side of the transformer can be equivalently converted to the secondary side of the transformer. Therefore, the equivalent circuits of the secondary-side resonant circuit 24' and the primary-side resonant circuit 24 in this embodiment are the same as the equivalent circuit of the primary-side resonant circuit 14 in the first embodiment, and the impact of imbalance in the resonant current due to variations in the characteristics of the resonant components is common to this embodiment and the first embodiment. As a result, the results in Table 3 for the first embodiment also apply to this embodiment, and it can be seen that the configuration of the transformer circuit 23 in this embodiment can alleviate imbalances in the first, second, and third resonant currents and reduce ripple in the output waveform.

[0117] Furthermore, during reverse direction control, the control unit 25 executes a control flow similar to the control flow of Fig. 3. The control unit 25 stores in advance a third phase difference, a fourth phase difference, and a second threshold value (current threshold value and power threshold value) in addition to the first phase difference, the second phase difference, and the first threshold value.

[0118] The third phase difference is the phase difference between the fourth leg, the fifth leg, and the sixth leg in a low-medium output range (low-medium output current range and low-medium output power range) where the impact of imbalance in the resonant current due to variations in the characteristics of the resonant components is relatively small. In this embodiment, the third phase difference is defined as the phase difference (θ41, θ51, θ61) between the input voltage vectors v4, v5, and v6 at the connection points X4, X5, and X6 when the fourth leg, the fifth leg, and the sixth leg are driven with a phase difference of 120°, where θ41 = θ51 = θ61 = 120°.

[0119] The fourth phase difference is the phase difference between the fourth leg, the fifth leg, and the sixth leg in a high-output region (high output current region or high output power region) where the impact of imbalance in the resonant current due to variations in the characteristics of the resonant components is relatively large. In this embodiment, the fourth phase difference is the phase difference (θ42, θ52, θ62) between the input voltage vectors v4, v5, and v6 that alleviates the imbalance in the output current vectors corresponding to each resonant current even if there are variations in the characteristics of the resonant components, and is set to θ42 = 120° + α, θ52 = 120° - α + β, and θ62 = 120° - β. α and β are angles greater than 0° and smaller than 120°.

[0120] The current threshold is a threshold used by control unit 25 to determine whether the current is in the low-medium output current region or the high output current region. The power threshold is a threshold used by control unit 25 to determine whether the current is in the low-medium output power region or the high output power region. The current threshold and power threshold can be set as appropriate, and for example, the rated output value during reverse direction control of DC / DC converter 20 may be set as the threshold.

[0121] During reverse direction control, control unit 25 sets the phase difference between each leg to the third phase difference (θ41, θ51, θ61) in the low and medium power range, and sets the phase difference between each leg to the fourth phase difference (θ42, θ52, θ62) in the high power range. Therefore, even in the high power range where the impact of imbalance in resonant current due to variations in the characteristics of resonant components is relatively large, DC / DC converter 20 can mitigate the imbalance in resonant current and reduce ripple in the output waveform without measuring the current imbalance in each phase and performing complex control to mitigate it.

[0122] That is, the DC / DC converter 20 can accommodate higher output by paralleling the transformers T11 to T32, and can alleviate the imbalance in the resonant current caused by variations in the characteristics of the resonant components, thereby reducing ripple in the output waveform, without increasing costs or complicating control.

[0123] In this embodiment, the third phase difference (θ41, θ51, θ61) is set to θ41 = θ51 = θ61 = 120°, but it may be set to an angle other than 120°. For example, similar to the fourth phase difference, by using a simulation or an actual circuit and gradually changing the phase difference between the fourth leg, fifth leg, and sixth leg from 120° while the output current or output power is within the low to medium output range, the phase difference at which the output current vectors corresponding to the respective resonant currents are in a balanced state may be found, and the found phase difference may be set as the third phase difference.

[0124] In this embodiment, the control unit 25 stores two phase differences for two regions, the third phase difference in the low-medium output region and the fourth phase difference in the high output region, and performs reverse direction control. However, the control unit 25 may store three or more phase differences for three or more regions. For example, the control unit 25 may store a first third phase difference (third phase difference A) for the low output region, a second third phase difference (third phase difference B) for the medium output region, and a fourth phase difference for the high output region, and perform control. Alternatively, the control unit 25 may store a first phase difference for the low-medium output region, a first fourth phase difference (fourth phase difference A) for the high output current region, and a second fourth phase difference (fourth phase difference B) for the high output power region, and perform control.

[0125] In addition, the control unit 25 may perform only one of the processes of comparing output current values ​​(corresponding to S3 in Figure 3) or comparing output power values ​​(corresponding to S5 in Figure 3) depending on the type of battery 6 and the control purpose, and set the phase difference between each leg.

[0126] Although the embodiments of the three-phase LLC DC / DC converter and charging device according to the present invention have been described above, the present invention is not limited to the above embodiments.

[0127] A DC / DC converter according to the present invention includes a transformer circuit including a first transformer unit, a second transformer unit, and a third transformer unit, each of which is configured with N transformers (N is an integer of 2 or more), a first leg, a second leg, and a third leg connected in parallel, each of which includes a set of switching elements connected in series, a primary-side switching circuit provided on the primary side of the transformer circuit, a first resonant unit provided between the first leg and the first transformer unit, a second resonant unit provided between the second leg and the second transformer unit, and a third resonant unit provided between the third leg and the third transformer unit, each of which includes a resonant coil and A three-phase LLC DC / DC converter comprising: a primary-side resonant circuit including a resonant capacitor; a secondary-side rectifier circuit including a plurality of rectifier elements and provided on the secondary side of the transformer circuit; and a control unit that sets a predetermined phase difference between the first leg, second leg, and third leg and drives them at a predetermined drive frequency to generate current resonance, wherein the transformer circuit forms N transformer groups, each of which is formed with one transformer from each transformer unit as a group, and the configuration can be changed as appropriate as long as the primary-side coil is connected in a balanced connection and the secondary-side coil is connected in a balanced connection.

[0128] For example, the configurations of the first to third modified examples of the first embodiment can be applied to the primary side resonant circuit 24 and the secondary side resonant circuit 24' of the second embodiment. [Explanation of symbols]

[0129] 1A charging device 2 AC / DC converters 3 Output Filter 4. Control Unit 5 AC power supply 6 Battery 10A~10E DC / DC converter 11 Primary side switching circuit 12, 12E Primary side rectifier circuit 13 Transformer Circuit 14, 14B~14D Primary side resonant circuit 15 Control Unit 20 DC / DC converters 21 Primary side switching circuit 22 Secondary side switching circuit 23 Transformer Circuit 24 Primary side resonant circuit 24' Secondary side resonant circuit 25 Control Unit

Claims

1. a transformer circuit including a first transformer unit, a second transformer unit, and a third transformer unit, each of which is configured with N transformers (N is an integer of 2 or more); a primary-side switching circuit provided on a primary side of the transformer circuit, the primary-side switching circuit including a first leg, a second leg, and a third leg connected in parallel, each leg including a set of switching elements connected in series; a primary-side resonant circuit including a first resonant unit provided between the first leg and the first transformer unit, a second resonant unit provided between the second leg and the second transformer unit, and a third resonant unit provided between the third leg and the third transformer unit, each resonant unit including a resonant coil and a resonant capacitor; a secondary-side rectifier circuit including a plurality of rectifier elements and provided on the secondary side of the transformer circuit; a control unit that provides a predetermined phase difference between the first leg, the second leg, and the third leg and drives the first leg at a predetermined drive frequency to generate current resonance; A three-phase LLC DC / DC converter comprising: The transformer circuit forms N transformer groups, Each of the N transformer groups is formed as a set of one transformer from each of the transformer units, and the primary coils are connected in a balanced connection, and the secondary coils are connected in a balanced connection. A DC / DC converter characterized by:

2. the control unit includes a storage unit, The storage unit includes: a first phase difference related to the phase difference; With respect to the phase difference, a second phase difference different from the first phase difference; a first current threshold value related to an output value of an output current output from the secondary side rectifier circuit; a first power threshold value related to an output value of the output power output from the secondary-side rectifier circuit, The control unit comparing an output value of the output current with the first current threshold and comparing an output value of the output power with the first power threshold; When the output value of the output current is less than the first current threshold and the output value of the output power is less than the first power threshold, the phase difference is set to the first phase difference; When the output value of the output current is equal to or greater than the first current threshold or when the output value of the output power is equal to or greater than the first power threshold, the phase difference is set to the second phase difference.

2. The DC / DC converter according to claim 1.

3. a transformer circuit including a first transformer unit, a second transformer unit, and a third transformer unit, each of which is configured with N transformers (N is an integer of 2 or more); a primary-side switching circuit provided on a primary side of the transformer circuit, the primary-side switching circuit including a first leg, a second leg, and a third leg connected in parallel, each leg including a set of switching elements connected in series; a secondary-side switching circuit provided on a secondary side of the transformer circuit, the secondary-side switching circuit including a fourth leg, a fifth leg, and a sixth leg connected in parallel, each leg including a set of switching elements connected in series; a resonant circuit including a first resonant unit provided between the first leg and the fourth leg via the first transformer unit, a second resonant unit provided between the second leg and the fifth leg via the second transformer unit, and a third resonant unit provided between the third leg and the sixth leg via the third transformer unit, each resonant unit including a resonant coil and a resonant capacitor provided on both the primary side and the secondary side of each transformer unit; a control unit that performs forward control to transfer power from the primary side switching circuit to the secondary side switching circuit and reverse control to transfer power from the secondary side switching circuit to the primary side switching circuit; A three-phase CLLC DC / DC converter comprising: The control unit In the forward control, a predetermined phase difference is provided between the first leg, the second leg, and the third leg, and the first leg, the second leg, and the third leg are driven at a predetermined drive frequency to generate current resonance; In the reverse control, a predetermined phase difference is provided between the fourth leg, the fifth leg, and the sixth leg, and the fourth leg, the fifth leg, and the sixth leg are driven at a predetermined drive frequency to generate current resonance; The transformer circuit forms N transformer groups, Each of the N transformer groups is formed as a set of one transformer from each of the transformer units, and the primary coils are connected in a balanced connection, and the secondary coils are connected in a balanced connection. A DC / DC converter characterized by:

4. the control unit includes a storage unit, The storage unit includes: a first phase difference related to the phase difference during the forward control; With regard to the phase difference during the forward control, a second phase difference different from the first phase difference; a first current threshold value related to a first output value of an output current output from the secondary-side switching circuit during the forward control, and a first power threshold value related to a first output value of an output power output from the secondary-side switching circuit; a third phase difference related to the phase difference during the reverse direction control; With regard to the phase difference during the reverse direction control, a fourth phase difference different from the third phase difference; a second current threshold value related to a second output value of an output current output from the primary side switching circuit and a second power threshold value related to a second output value of an output power output from the primary side switching circuit during the reverse direction control are stored; The control unit During the forward control, comparing a first output value of the output current with the first current threshold and comparing a first output value of the output power with the first power threshold; When the first output value of the output current is less than the first current threshold and the first output value of the output power is less than the first power threshold, the phase difference is set to the first phase difference; When the first output value of the output current is equal to or greater than the first current threshold or the first output value of the output power is equal to or greater than the first power threshold, the phase difference is set to the second phase difference; During the reverse direction control, comparing a second output value of the output current with the second current threshold and comparing a second output value of the output power with the second power threshold; When the second output value of the output current is less than the second current threshold and the second output value of the output power is less than the second power threshold, the phase difference is set to the third phase difference; When the second output value of the output current is equal to or greater than the second current threshold or when the second output value of the output power is equal to or greater than the second power threshold, the phase difference is set to the fourth phase difference.

4. The DC / DC converter according to claim 3.

5. A DC / DC converter according to any one of claims 1 to 4; an AC / DC converter provided in a stage preceding the DC / DC converter; an output filter provided in a subsequent stage of the DC / DC converter; A charging device characterized by:

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