Bidirectional isolated DC / DC converter

Abstract

This enables the realization of a DC / DC converter that can effectively expand the power conversion range on both the charging and discharging sides, and suppress DC bias phenomena. [Solution] The system has an LLC circuit 23 located between the transformer 20 and the primary circuit 21, and is configured to perform charging and discharging operations. The primary circuit 21 has an intermediate voltage output section located between two primary capacitors C1 and C2 arranged in series, which applies a primary half voltage Vin(LO) to the LLC circuit 23. The controller 17 is configured to change the switching pattern in charging and discharging operations based on switching control information. Before starting the charging operation at startup, voltage balancing control is performed to eliminate the voltage difference between the two primary capacitors C1 and C2.

Description

[Technical Field]

[0001] The disclosed technology relates to a bidirectional isolated DC / DC converter suitable for automotive chargers. [Background technology]

[0002] In recent years, the electrification of automobiles, such as electric vehicles and hybrid vehicles, has been remarkable. These vehicles that run on electricity are equipped with high-output batteries as their power source. In order to charge these batteries, these vehicles are also equipped with on-board chargers (OBCs) that convert AC power, which is the commercial power source, into DC power.

[0003] Most OBCs (Out-of-Body Converters) use an AC / DC converter to convert AC voltage to DC voltage, and a DC / DC converter to convert the DC voltage output from the AC / DC converter to a different voltage. The conversion of voltage magnitude is mainly performed by the DC / DC converter.

[0004] For DC / DC converters, isolated DC / DC converters are generally used, which have a transformer interposed between the input side (primary side) and the output side (secondary side) from the standpoint of electrical safety.

[0005] Furthermore, among isolated DC / DC converters, resonant DC / DC converters are often used from the perspective of improving efficiency. However, resonant DC / DC converters have the disadvantage of a narrow voltage operating range due to the constraints of zero-voltage switching (ZVS).

[0006] Commercial power supplies generally use AC voltages of 100V to 200V. In contrast, vehicle batteries use DC voltages ranging from 48V to over 400V. Therefore, it is desirable for DC / DC converters to be able to handle such a wide range of power conversions, and there is a need to expand the range of power conversions they can handle.

[0007] In addition, it is preferable for the OBC (Onboard Battery Controller) to not only charge the battery but also output power from the battery. Therefore, the DC / DC converter is required to have so-called bidirectional functionality, capable of both charging and discharging.

[0008] Regarding the technology to be disclosed, Patent Document 1 proposes a technique for expanding the power output range in a resonant DC / DC converter.

[0009] Disclosed is an isolated DC / DC converter equipped with a predetermined LLC resonant converter circuit. The on / off operation of a switching element located on the input side of the LLC resonant converter circuit is switched using different modulation schemes. In this way, the magnitude of the voltage output to the LLC resonant circuit side is changed.

[0010] Furthermore, Patent Document 2 discloses a converter equipped with a primary side circuit having the same structure as the circuit targeted by the disclosed technology (Figure 10 in the same specification). However, this converter only supports charging operations and does not support discharging operations. The driving method also differs from the disclosed technology. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Japanese Patent Publication No. 2021-35328 [Patent Document 2] Japanese Patent Publication No. 2017-93179 [Overview of the project] [Problems that the invention aims to solve]

[0012] The technology described in Patent Document 1 assumes a specific LLC resonant converter circuit and controls it using the same basic operation as the asymmetric half-bridge method. Therefore, since only half of the input voltage can be used, it is actually unsuitable for high power applications.

[0013] Furthermore, since the duty ratio is controlled in a fixed state (25%, 50%, 75%) at a predetermined value, the actual control range of the output voltage has to be narrowed. Moreover, since that technology is targeted at the charging operation, it does not support the discharging operation.

[0014] In the converter of Patent Document 2 described above, during the charging operation, a DC bias phenomenon may occur and the switching element may be damaged.

[0015] That is, in the primary circuit thereof, two capacitors (reference numerals 51 and 52) arranged in series are disposed. When the charging operation is started with a voltage difference between these capacitors, a DC bias phenomenon occurs and an overcurrent results, and in the worst case, the switching element is damaged.

[0016] Therefore, this specification discloses a technology that can effectively expand the applicable power conversion range to both the charging side and the discharging side in a DC / DC converter and can also suppress the DC bias phenomenon.

Means for Solving the Problems

[0017] The disclosed technology relates to a DC / DC converter including a converter mechanism including a bidirectional isolated LLC resonant circuit and a controller for controlling the converter mechanism.

[0018] The bidirectional isolated LLC resonant circuit has a transformer having a primary coil and a secondary coil, a primary circuit located on the primary side of the transformer and including a primary input / output terminal pair and six primary switching elements, a secondary circuit located on the secondary side of the transformer and including a secondary input / output terminal pair and four secondary switching elements, and an LLC circuit located between the transformer and the primary circuit.

[0019] The primary circuit includes two primary capacitors arranged in series and electrically connected between the primary input / output terminal pair, and an intermediate voltage output section located between the two primary capacitors that applies a primary half voltage, which is an intermediate voltage of the primary voltage input to the primary input / output terminal pair, to the LLC circuit.

[0020] Furthermore, the bidirectional isolated LLC resonant circuit is configured to perform a charging operation in which a DC voltage is input to the primary input / output terminal pair and output from the secondary input / output terminal pair, and a discharge operation in which a DC voltage is input to the secondary input / output terminal pair and output from the primary input / output terminal pair.

[0021] The controller has switching control information relating to the duty cycle and phase shift set according to the relative magnitudes of the input and output DC voltages, and is configured to change the switching patterns of the primary and secondary switching elements in the charging and discharging operations based on the switching control information, and performs voltage balancing control to eliminate the voltage difference between the two primary capacitors before the start of the charging operation at startup.

[0022] In other words, this DC / DC converter includes a predetermined bidirectional isolated LLC resonant circuit and is configured to perform charging and discharging operations. Its controller has switching control information regarding the duty cycle and phase shift set according to the relative magnitudes of the input and output DC voltages, and based on this switching control information, it changes the switching patterns of the primary and secondary switching elements during charging and discharging operations.

[0023] This DC / DC converter controls charging and discharging operations by combining duty cycle and phase shift according to the relative magnitudes of the input and output DC voltages. This allows for simple, highly efficient, and precise control, effectively expanding the power conversion range on both the charging and discharging sides.

[0024] Furthermore, this DC / DC converter performs voltage balancing control to eliminate the voltage difference between the two primary capacitors before the charging operation begins during startup.

[0025] As mentioned above, if charging is started while there is a voltage difference between these capacitors, a DC bias phenomenon occurs, resulting in overcurrent, and in the worst case, the switching element may be damaged. In contrast, this DC / DC converter can eliminate the voltage difference between the two primary capacitors when starting the charging operation. Therefore, even if a voltage difference remains between the two primary capacitors before startup, the DC bias phenomenon can be suppressed.

[0026] If the DC voltage output during the charging operation is greater than the primary half voltage, the controller may control the duty cycle and switch between the primary voltage and the primary half voltage to operate the LLC circuit.

[0027] This allows the positive and negative waveforms of the voltage applied to the primary side of the transformer to be made equal, thus suppressing the DC bias phenomenon even during charging operation after startup, i.e., in a steady state.

[0028] For example, the above-described bidirectional isolated LLC resonant circuit may be configured as follows: The primary side circuit has a first leg in which two primary side switching elements are arranged in series, a second leg in which two pairs of elements consisting of two primary side switching elements connected in series are arranged in series, a third leg in which two primary side capacitors are arranged, a fourth leg in which one intermediate capacitor is arranged, a fifth leg in which two diodes are arranged in series, a pair of primary side main lines with the primary side input / output terminal pair arranged at one end, and the first, second, and third legs connected in parallel between each other, a pair of bypass lines connected in parallel to the portion between the primary side switching elements included in each of the pair of elements in the second leg, and the fourth and fifth legs connected in parallel between each other, and a connecting line connected to the portion between the two diodes in the fifth leg and the portion between the two primary side capacitors in the third leg.

[0029] The secondary circuit includes a sixth and seventh leg, each having two of the secondary switching elements arranged in series; an eighth leg, each having one secondary capacitor; and a pair of secondary main lines, one end of which has the secondary input / output terminal pair, and the sixth, seventh, and eighth legs connected in parallel between them.

[0030] The LLC circuit further comprises: a primary side upper relay wiring connecting the positive terminal end of the primary coil to the portion between the two pairs of elements in the second leg; a primary side lower relay wiring connecting the negative terminal end of the primary coil to the portion between the two primary switching elements in the first leg; a secondary side upper relay wiring connecting the positive terminal end of the secondary coil to the portion between the two secondary switching elements in the sixth leg; and a secondary side lower relay wiring connecting the negative terminal end of the secondary coil to the portion between the two secondary switching elements in the seventh leg, wherein the LLC circuit has a primary side resonant capacitor and a primary side resonant inductance arranged in series with the primary side upper relay wiring.

[0031] This allows for a relatively simple circuit configuration while effectively expanding the power conversion range on both the charging and discharging sides.

[0032] The bidirectional isolated LLC resonant circuit may further include a secondary LLC circuit located between the transformer and the secondary circuit.

[0033] This would allow for a more effective expansion of the power conversion range that can be handled on both the charging and discharging sides.

[0034] The above-described bidirectional isolated LLC resonant circuit may also be configured as follows: The primary side circuit comprises a first leg and a second leg, each having two primary side switching elements arranged in series; a third leg, each having two primary side capacitors; a pair of primary side main lines, each having a primary side input / output terminal pair at one end, with the first, second, and third legs connected in parallel between them; and a connecting line, each having two primary side switching elements arranged in series with their current-carrying directions facing each other, and connected to the portion between the two primary side switching elements in the second leg and the portion between the two primary side capacitors in the third leg.

[0035] The secondary circuit includes a sixth and seventh leg, each having two of the secondary switching elements arranged in series; an eighth leg, each having one secondary capacitor; and a pair of secondary main lines, one end of which has the secondary input / output terminal pair, and the sixth, seventh, and eighth legs connected in parallel between them.

[0036] The LLC circuit further comprises: a primary side upper relay wiring connecting the positive terminal end of the primary coil to the portion between the two primary side switching elements in the second leg; a primary side lower relay wiring connecting the negative terminal end of the primary coil to the portion between the two primary side switching elements in the first leg; a secondary side upper relay wiring connecting the positive terminal end of the secondary coil to the portion between the two secondary side switching elements in the sixth leg; and a secondary side lower relay wiring connecting the negative terminal end of the secondary coil to the portion between the two secondary side switching elements in the seventh leg, wherein the LLC circuit has a primary side resonant capacitor and a primary side resonant inductance arranged in series with the primary side upper relay wiring.

[0037] This circuit configuration, like the bidirectional isolated LLC resonant circuit described above, allows for a relatively simple circuit configuration while effectively expanding the power conversion range on both the charging and discharging sides.

[0038] In the case of this bidirectional isolated LLC resonant circuit, the bidirectional isolated LLC resonant circuit may further include a secondary LLC circuit located between the transformer and the secondary circuit.

[0039] This would allow for a more effective expansion of the power conversion range on both the charging and discharging sides, similar to the bidirectional isolated LLC resonant circuit described above. [Effects of the Invention]

[0040] The disclosed technology effectively expands the power conversion range on both the charging and discharging sides. In addition, it suppresses DC bias phenomena. Therefore, a high-performance DC / DC converter can be realized. [Brief explanation of the drawing]

[0041] [Figure 1] This is a schematic diagram illustrating an example of the application of the disclosed technology. [Figure 2] This diagram illustrates a bidirectional isolated LLC resonant circuit. [Figure 3] This is a control block diagram of the controller during charging operation. [Figure 4] This is a table summarizing switching control information. [Figure 5] This is the resonance curve of an LLC circuit. [Figure 6A] This is an illustrative diagram of the switching pattern during charging. [Figure 6B] This is an illustrative diagram of the voltage waveform of the transformer voltage VTR. [Figure 7] This table summarizes the settings and details of each operating state at startup. [Figure 8] This is an illustrative diagram of the switching pattern during discharge. [Figure 9] This is an example of the results of effectiveness verification through simulation. [Figure 10A] This is an example of the results of effectiveness verification through simulation. [Figure 10B] This is an example of the results of effectiveness verification through simulation. [Figure 10C] This is an example of the results of effectiveness verification through simulation. [Figure 11] This is another form of a bidirectional isolated LLC resonant circuit. [Figure 12] This is a modified example of a bidirectional isolated LLC resonant circuit. [Modes for carrying out the invention]

[0042] The following describes the disclosed technology. However, the following description is merely illustrative in nature. The components of the circuit are also assigned predetermined symbols together with alphanumeric codes. For convenience, the symbols may be used for explanation or illustration.

[0043] <Overview of DC / DC Converter> FIG. 1 illustrates an example of applying the DC / DC converter according to the disclosed technology to an on-vehicle charger 3 (OBC). The on-vehicle charger 3 is mounted on a vehicle 1 that runs using electric power such as an electric vehicle and a hybrid vehicle, together with a high-output battery 4 for driving and a low-output lead-acid battery 4a for electrical components.

[0044] The upper part of FIG. 1 shows the vehicle 1 being charged and the commercial power supply 2. The commercial power supply 2 outputs a high-voltage alternating voltage such as 100V and 200V. By connecting the commercial power supply 2 and the vehicle 1 with a cable, the battery 4 is charged. At that time, the on-vehicle charger 3 is interposed between the battery 4 and the commercial power supply 2 and converts the alternating voltage into a direct current voltage corresponding to the battery 4.

[0045] As shown in the middle part of FIG. 1, the on-vehicle charger 3 is composed of a DC / DC converter 5, an AC / DC converter 6, etc. The AC / DC converter 6 is a device that converts an alternating input voltage Eac into a direct current output voltage Vin or converts a direct current input voltage Vin into an alternating output voltage Eac.

[0046] The DC / DC converter 5 is a device that inputs a direct current voltage and converts it into direct current voltages of different magnitudes for output. The disclosed technology is applied to this DC / DC converter 5. The DC / DC converter 5 is a so-called bidirectional type that can be input and output from either direction.

[0047] In other words, the DC / DC converter 5 converts the DC voltage Vin converted by the AC / DC converter 6 into a predetermined DC voltage Vout and outputs it to the battery 4 or lead-acid battery 4a (charging operation, described later). The DC / DC converter 5 also converts the DC voltage Vout input from the battery 4 or lead-acid battery 4a into a predetermined DC voltage Vin and outputs it to the AC / DC converter 6 (discharging operation, described later).

[0048] In the case of this DC / DC converter 5, since it is incorporated into the on-board charger 3, its structure and function are configured to be superior to its discharge operation, as will be described later. Therefore, its structure and function will be explained primarily in terms of its charging operation.

[0049] As shown in the lower diagram of Figure 1, the DC / DC converter 5 includes a converter mechanism 16 that includes an output current sensor 10, a primary-side first voltage sensor 11, a primary-side second voltage sensor 12, a secondary-side voltage sensor 13, a bidirectional isolated LLC resonant circuit 15, and a controller 17 that controls the converter mechanism 16.

[0050] The output current sensor 10 is a Hall element type sensor and is installed at predetermined positions on the primary main line 36 and the secondary main line 54, which will be described later. As shown in Figure 2, during charging, the output current sensor 10 directly measures the current (output current Iout) flowing through the secondary input / output terminal 50 and outputs it to the controller 17.

[0051] The primary-side first voltage sensor 11 is installed at a predetermined position on the primary-side main line 36 and directly measures the high voltage (primary-side voltage Vin) acting between the pair of primary-side main lines 36, 36 and outputs it to the controller 17. The primary-side second voltage sensor 12 is installed at a predetermined position between the negative-side primary-side main line 36 and the connecting line 38 and directly measures the low-voltage intermediate voltage (primary-side half voltage Vin(LO)) acting between the primary-side main line 36 and the connecting line 38 and outputs it to the controller 17.

[0052] The primary-side first voltage sensor 11 may be installed at a predetermined position between the positive-side primary main line 36 and the connecting line 38, and may measure the voltage (high-voltage side primary half voltage Vin(HI)) which is a high-voltage intermediate voltage acting between the primary main line 36 and the connecting line 38.

[0053] In the case of this DC / DC converter 5, the primary voltage Vin, the primary half voltage Vin(LO), and the high-voltage primary half voltage Vin(HI) are measured. To do this, it is sufficient to measure any two of the primary voltage Vin, primary half voltage Vin(LO), and high-voltage primary half voltage Vin(HI). By doing so, all three values ​​can be obtained.

[0054] The secondary voltage sensor 13 is installed at a predetermined position on the secondary main line 54 and directly measures the high voltage (secondary voltage Vout) acting between the pair of secondary main lines 54, 54 and outputs it to the controller 17.

[0055] Based on these measured values, the controller 17 outputs a drive voltage to the 10 switching elements S1 to S10 (the first to tenth switching elements S1 to S10) of the bidirectional isolated LLC resonant circuit 15 to control them on and off. In other words, it switches the energized state (on) and the de-energized state (off) of these switching elements S1 to S10 at predetermined timings.

[0056] (Bidirectional isolated LLC resonant circuit) Figure 2 shows a Type I bidirectional isolated LLC resonant circuit 15 (hereinafter also referred to as converter circuit 15) corresponding to the disclosed technology. The converter circuit 15 is generally composed of a transformer 20, a primary circuit 21 located on its primary side, a secondary circuit 22 located on its secondary side, and an LLC circuit 23 located between the transformer 20 and the primary circuit 21.

[0057] The primary circuit 21 has a pair of primary input / output terminals 30 (a primary input / output terminal pair) and six primary switching elements S1 to S6. The secondary circuit 22 has a pair of secondary input / output terminals 50 (a secondary input / output terminal pair) and four secondary switching elements S7 to S10. With this configuration, the DC / DC converter 5 is configured to perform a charging operation in which a DC voltage is input to the primary input / output terminals 30 and output from the secondary input / output terminals 50, and a discharging operation in which a DC voltage is input to the secondary input / output terminals 50 and output from the primary input / output terminals 30.

[0058] The primary switching elements S1-S6 and secondary switching elements S7-S10 consist of known MOSFETs and the like, each having gate, source, and drain terminals. They are turned on by applying a predetermined drive voltage to the gate terminal. Both the primary switching elements S1-S6 and secondary switching elements S7-S10 are arranged so that the direction of current flow when turned on is from the positive terminal to the negative terminal. The primary switching elements S1-S6 and secondary switching elements S7-S10 include a freewheeling diode 24 connected in antiparallel.

[0059] The transformer 20 has a primary coil 20a and a secondary coil 20b. N1 is the number of turns of the primary coil 20a, and N2 is the number of turns of the secondary coil 20b. N1:N2 represents the turns ratio. In the case of the converter circuit 15 in this embodiment, N1:N2 is 1:1. However, the turns ratio can be changed according to the specifications of the operating range of the input and output voltages.

[0060] The primary circuit 21 has a first leg 31, a second leg 32, a third leg 33, a fourth leg 34, a fifth leg 35, a pair of primary main lines 36, 36, a pair of bypass lines 37, 37, and a connecting line 38.

[0061] In the first leg 31, two primary-side switching elements S3 and S4 are arranged in series. In the second leg 32, four primary-side switching elements S5, S1, S2, and S6 are connected in series. For the sake of explanation, these are also assumed to be two pairs of elements 25, each consisting of two primary-side switching elements (S5, S1 and S2, S6) connected in series, arranged in series.

[0062] In the third leg 33, two primary capacitors C1 and C2 are arranged in series. These primary capacitors C1 and C2 have the same capacitance. In the fourth leg 34, one intermediate capacitor C3 is arranged. In the fifth leg 35, two diodes D1 and D2 are arranged in series. These diodes D1 and D2 are arranged so that the direction of current flow is from the negative terminal to the positive terminal.

[0063] The first leg 31, the second leg 32, and the third leg 33 are connected in parallel between a pair of primary main lines 36, 36. A primary input / output terminal 30 is located at one end of these primary main lines 36, 36. The third leg 33, the second leg 32, and the first leg 31 are arranged in order from the side of the primary input / output terminal 30.

[0064] A pair of bypass lines 37, 37 are connected in parallel to the area between the primary-side switching elements (S5, S1 and S2, S6) included in each of the element pairs 25, 25 in the second leg 32. The fourth leg 34 and the fifth leg 35 are connected in parallel between these bypass lines 37, 37. A connecting line 38 is connected to the area between the two diodes D1, D2 in the fifth leg 35 and to the area between the two primary-side capacitors C1, C2 in the third leg 33 (intermediate voltage output area 43).

[0065] The positive terminal end of the primary coil 20a is connected to the portion between the two element pairs 25, 25 in the second leg 32 by the primary upper relay wiring 45. The negative terminal end of the primary coil 20a is connected to the portion between the two primary switching elements S3, S4 in the first leg 31 by the primary lower relay wiring 46.

[0066] In the primary side upper relay wiring 45, the primary side resonant capacitor Cr and the primary side resonant inductance Lr (leakage inductance) are arranged in series from the second leg 32 side. The excitation inductance Lm is connected in parallel with the primary side coil 20a.

[0067] The excitation inductance Lm may be the inductance generated by the main magnetic flux of the transformer 20. The LLC circuit 23 is composed of the primary side resonant inductance Lr, the excitation inductance Lm, and the primary side resonant capacitor Cr. The primary side resonant inductance Lr may also be a parasitic element of the transformer 20.

[0068] The secondary circuit 22 has a sixth leg 51, a seventh leg 52, an eighth leg 53, and a pair of secondary main lines 54, 54.

[0069] In the sixth leg 51, two secondary switching elements S7 and S8 are arranged in series, and in the seventh leg 52, two secondary switching elements S9 and S10 are arranged in series. In the eighth leg 53, one secondary capacitor C4 is located. The sixth leg 51, the seventh leg 52, and the eighth leg 53 are connected in parallel between a pair of secondary main lines 54, 54. A secondary input / output terminal 50 is located at one end of these secondary main lines 54, 54. The eighth leg 53, the seventh leg 52, and the sixth leg 51 are located in order from the side of the secondary input / output terminal 50.

[0070] The positive terminal end of the secondary coil 20b is connected to the area between the two secondary switching elements S7 and S8 in the sixth leg 51 by the secondary upper relay wiring 57. The negative terminal end of the secondary coil 20b is connected to the area between the two secondary switching elements S9 and S10 in the seventh leg 52 by the secondary lower relay wiring 58.

[0071] During charging, the primary voltage Vin is applied to the pair of primary main lines 36, 36. Consequently, the primary voltage Vin is also applied to each of the first leg 31, second leg 32, and third leg 33.

[0072] Furthermore, during charging, a voltage (transformer voltage VTR) acts between the primary side upper relay wiring 45 and the primary side lower relay wiring 46, causing a current (transformer current ITR) to flow through the primary side upper relay wiring 45. As a result, a secondary side voltage Vout is applied to the pair of secondary side main wires 54, 54, causing a current (output current Iout) to flow through the secondary side input / output terminals 50.

[0073] (Control during charging operation by the controller) Next, we will explain the control of the charging operation by the controller 17 (control of the discharging operation will be described later).

[0074] Figure 3 shows a control block diagram of the controller 17 during charging operation. Figure 4 shows a table summarizing the switching control information of the controller 17. Figure 5 shows the resonance curve of the LLC circuit 23. Figure 6A shows an example of the carrier waveform during charging operation and the corresponding switching patterns (switching time chart) of each switching element.

[0075] As shown by the arrows in Figure 5, the LLC circuit 23 typically adjusts the output voltage within an operating frequency range between the lower limit fm and the upper limit fr of the resonant frequency. Therefore, the operating frequency of the LLC circuit 23 in this DC / DC converter 5 can also be set within this range. However, it is preferable to fix the operating frequency of the LLC circuit 23 to the upper limit fr of the resonant frequency or a value near it, as indicated by the circle in Figure 5. This allows for a smaller excitation inductance Lm, thus enabling a smaller transformer 20.

[0076] Therefore, in this controller 17, the operating frequency of the LLC circuit 23 is fixed to the upper limit value fr of the resonant frequency or a value near it, and the output current Iout is controlled according to the required output voltage. The lower limit value fm and the upper limit value fr of the resonant frequency are determined by the performance of the primary side resonant capacitor Cr, primary side resonant inductance Lr, and excitation inductance Lm that constitute the LLC circuit 23.

[0077] Although not shown in the diagram, the controller 17 comprises hardware such as a processor and memory, and software such as control programs and data implemented in the memory. Through the cooperation of these components, the controller 17 has a configuration such as a CC / CP switching unit 17a, a current regulator 17b, a control unit 17c, and a drive circuit 17d, as shown in Figure 3.

[0078] The CC / CP switching unit 17a has a divider 17e and a current limiter 17f. The CC / CP switching unit 17a has a command value for output power (output power command value) Pout * Enter the command value for the output current (output current command value) Iout * This is output to the current regulator 17b.

[0079] In detail, the input output power command value Pout * This is divided by the output voltage Vout in the divider 17e, thereby producing the output current command value Iout. * The output current command value Iout is calculated. * This is passed through the current limiter 17f.

[0080] The current limiter 17f has an upper limit (+Iout.lim) that caps out the current above a predetermined value and a lower limit (-Iout.lim) that caps out the current below a predetermined value. The current limiter 17f controls the output current command value Iout between these upper and lower limits. * Restrict.

[0081] As a result, for example, in charging operation, the output current command value Iout * Until it reaches the upper limit, the output power command value Pout* and a predetermined output current command value Iout corresponding to the output voltage Vout * is output (CP mode). On the other hand, when the output current command value Iout * exceeds the upper limit, the output current command value Iout * outputs the upper limit value (CC mode).

[0082] In addition to the output current command value Iout, the primary-side voltage Vin, the secondary-side voltage Vout, and the output current Iout are input to the current regulator 17b. Then, based on these, the current regulator 17b outputs a first parameter dctl * (corresponding to the command value of the duty ratio) to the control unit 17c. As will be described later, the first parameter dctl * is used for setting the duty ratios of the first, second, fifth, and sixth switching elements S1, S2, S5, and S6 in PWM control. *

[0083] The control unit 17c receives the first parameter dctl * together with a second parameter da * and a phase angle Δφ used for phase shift. The second parameter da * is used for setting the duty ratios of the third, fourth, seventh, and eighth switching elements S3, S4, S7, and S8 in PWM control, as will be described later.

[0084] The control unit 17c has predetermined switching control information regarding the switching of the converter circuit 15.

[0085] Fig. 4(a) is a table summarizing the switching control information during the charging operation, and Fig. 4(b) is a table summarizing the switching control information during the discharging operation. These switching control information is set according to the magnitude relationship of the DC voltages input and output to the converter circuit 15, and includes information regarding PWM control and phase shift.

[0086] ​During charging, the charging voltage range of the converter circuit 15 is divided into three ranges, from the first to the third, according to the relative magnitudes of the primary voltage Vin (input voltage) and the secondary voltage Vout (output voltage), and switching control information is set for each of these ranges (first to third charging switching control information). According to this first to third charging switching control information, the ninth and tenth switching elements S9 and S10 of the secondary circuit 22 are kept off at all charging voltage ranges.

[0087] During discharge operation, the discharge voltage range is divided into two ranges, the first and second, according to the relative magnitudes of the secondary voltage Vout (input voltage) and the primary voltage Vin (output voltage) of the converter circuit 15, and switching control information is set for each of these ranges (first and second discharge switching control information). According to this first and second discharge switching control information, the first, second, fifth, and sixth switching elements S1, S2, S5, and S6 of the primary circuit 21 are kept off at all times within the entire discharge voltage range.

[0088] The first charging voltage range is when the secondary voltage Vout exceeds the primary voltage Vin. According to the first charging switching control information, in the first charging voltage range, a full-bridge control method is used, and PWM control is performed for the switching of switching elements S1 to S8.

[0089] Of these, the third and fourth switching elements S3 and S4 of the primary circuit 21 are the second parameter da * PWM control is performed at =0.5. In the 7th and 8th switching elements S7 and S8 of the secondary circuit 22, a phase shift is performed along with the same PWM control. Specifically, the switching patterns of the 7th and 8th switching elements S7 and S8 are shifted by the phase angle Δφ (see Figure 6A). As a result, ZVS (Zero Voltage Switching) becomes possible even at high voltages.

[0090] The second charging voltage range is when the secondary voltage Vout is less than or equal to the primary voltage Vin and exceeds half of the primary voltage Vin. According to the second charging switching control information, in the second charging voltage range, the control method is the full-bridge method, similar to the first charging switching control information, and PWM control is performed for the switching of switching elements S1 to S6.

[0091] However, since the output voltage is not high, ZVS is possible. Therefore, unlike the first charging switching control information, no phase shift is performed in the secondary circuit 22. The seventh and eighth switching elements S7 and S8 are always turned off.

[0092] The third charging voltage range is when the secondary voltage Vout is less than or equal to half of the primary voltage Vin. According to the third charging switching control information, in the third charging voltage range, a half-bridge control method is used, and PWM control is performed for the switching of switching elements S1 to S6.

[0093] Of these, the third and fourth switching elements S3 and S4 of the primary circuit 21 are the second parameter da * PWM control is performed with a value of =1.0. The seventh and eighth switching elements S7 and S8 are always off.

[0094] Furthermore, in this configuration, switching elements S1, S2, S5, and S6 are duty cycle controlled across the entire charging voltage range. As a result, as will be described later, if switching elements S5 and S6 are always controlled with the same duty cycle, and their on-period Ton is the same for each switching cycle TSW, the positive and negative waveforms of the transformer voltage VTR applied to the transformer 20 will be equal. The bias in the transformer voltage VTR will be eliminated. Therefore, the DC bias phenomenon can be suppressed.

[0095] However, if there is a voltage difference between the two primary capacitors C1 and C2 before the charging operation begins at startup, a DC bias phenomenon may occur due to that voltage difference. Therefore, it is necessary to eliminate the voltage difference between these primary capacitors C1 and C2 before the charging operation begins at startup, and the disclosed technology incorporates measures to achieve this (details will be provided later).

[0096] Based on the first to third charging switching control information, the control unit 17c changes the switching patterns of the primary switching elements S1 to S6 and the secondary switching elements S7 and S8 during the charging operation and outputs a predetermined control signal to the drive circuit 17d.

[0097] As shown in Figure 3, the drive circuit 17d receives the control signal along with the PWM frequency TPWM and the dead time Td. Based on this input information, the drive circuit 17d outputs a drive voltage to the first to tenth switching elements S1 to S10. This activates the converter mechanism 16, and the DC / DC converter 5 performs the required charging operation.

[0098] (Specific example of switching control during charging operation) Figure 6A illustrates the switching patterns of each switching element S1 to S8 during charging (steady state). This corresponds to the state within the first charging voltage range.

[0099] The waveform shown at the top of Figure 6A is a sawtooth wave (carrier) used in PWM control. The period of the sawtooth wave, TSW, is the switching period. Below it, an image of the switching patterns of each switching element S1 to S8 corresponding to that carrier is displayed.

[0100] The third and fourth switching elements S3 and S4 are turned on or off at the base point of the carrier period (phase is 0 degrees or 360 degrees). Thus, the third and fourth switching elements S3 and S4 are controlled by the second parameter da *It is turned off or on based on this, thereby setting predetermined on and off periods.

[0101] The seventh and eighth switching elements S7 and S8 have on and off periods set, similar to the third and fourth switching elements S3 and S4, and their phase is shifted by a phase angle Δφ.

[0102] The duty cycle setting range for the fifth switching element S5, the second switching element S2, the sixth switching element S6, and the first switching element S1 is set to 0 or more and 0.5 or less. That is, the first parameter dctl used to set the duty cycle of these switching elements S5, S2, S6, and S1 is * This is set based on the base point of the carrier period, as well as the midpoint of the carrier period (phase 180 degrees).

[0103] Specifically, the fifth switching element S5 and the second switching element S2 are turned on or off at the base point of the carrier period. Then, the fifth switching element S5 and the second switching element S2 are turned on or off from their base point by the first parameter dctl * The ON period (Ton) and OFF period are set within a range up to [a certain point].

[0104] On the other hand, the sixth switching element S6 and the first switching element S1 are turned on or off at the midpoint of the carrier period. Thus, the sixth switching element S6 and the first switching element S1 are switched on or off from their midpoint along the first parameter dctl * The ON period (Ton) and OFF period are set within a range up to [a certain point].

[0105] As a result, switching elements S5 and S6 are controlled with the same duty cycle, and their on-period Ton is the same for each switching cycle TSW. This equalizes the positive and negative waveforms of the transformer voltage VTR, eliminating the bias in the transformer voltage VTR. Therefore, the DC bias phenomenon can be suppressed. And the first parameter dctl * By changing this setting, the transformer current ITR can be controlled.

[0106] The fifth switching element S5, the second switching element S2, the sixth switching element S6, and the first switching element S1 always operate in a synchronous rectification switching pattern. Therefore, the losses of the switching elements can be reduced.

[0107] Figure 6B(a) illustrates the waveform of the transformer voltage VTR applied to the transformer 20 by the switching pattern shown in Figure 6A. The first parameter dctl * It is controlled within the range of 0 to 0.5, and the second parameter da * It is set to 0.5. As mentioned above, the control method is a full-bridge method. The controller 17 controls the duty cycle and switches between the primary voltage Vin and the primary half voltage (primary half voltage Vin (LO) or high-voltage primary half voltage Vin (HI)) on the LLC circuit 23.

[0108] This allows the on-period Ton to vary within the range from half of the positive and negative primary voltages Vin to the primary voltage Vin, thereby adjusting the waveform of the transformer voltage VTR. Even when the waveform of the transformer voltage VTR is adjusted, the positive and negative waveforms of the transformer voltage VTR remain the same, thus suppressing the DC bias phenomenon. Furthermore, the ZVS conditions are also met within these ranges.

[0109] Figure 6B(b) shows the second parameter da * An example of the transformer voltage VTR waveform when is set to 1.0 is shown. In this case, it corresponds to the state in the third charging voltage range. As described above, the control method is a half-bridge method. The controller 17 applies the primary half voltage (primary half voltage Vin(LO) or high-voltage primary half voltage Vin(HI)) to the LLC circuit 23 while controlling the duty cycle.

[0110] Therefore, the output voltage Vout is in the range of 0 to half of the primary voltage Vin, and the on-period Ton varies within that range, allowing adjustment of the transformer voltage VTR waveform. Even when the transformer voltage VTR waveform is adjusted, the positive and negative waveforms of the transformer voltage VTR remain the same, thus suppressing the DC bias phenomenon.

[0111] (Startup control) Thus, even if the DC bias phenomenon can be suppressed in the steady state of charging operation, as mentioned above, if there is a voltage difference between the two primary capacitors C1 and C2 before the start of charging operation at startup, the DC bias phenomenon may occur due to that voltage difference. Therefore, in order to effectively suppress the DC bias phenomenon, it is necessary to eliminate the voltage difference between these primary capacitors C1 and C2 before the start of charging operation at startup.

[0112] Therefore, the controller 17 performs control (voltage balance control) to eliminate the voltage difference between the two primary capacitors C1 and C2 before the charging operation starts at startup.

[0113] Figure 7 shows a table summarizing the settings and details of each operating state during startup. This DC / DC converter 5 is configured to go through the stages of operating states St0 to St3 during startup.

[0114] Operating state St0 is a preliminary process for the charging operation. Before the charging operation starts, the controller 17 performs the voltage balance control described above. Specifically, the second parameter da * The value is set to 1.0, and a half-bridge control method is adopted. As a result, the output voltage Vout is in the range of 0 to half of the primary voltage Vin. The third switching element S3 is always off, and the fourth switching element S4 is always on.

[0115] Then, the output power command value Pout * Set to 0. This will set the output current command value Iout *The voltage also becomes 0, and no actual charging occurs. Switching still occurs, so a transformer current ITR can flow as a result. Consequently, even if there is a voltage difference between the two primary capacitors C1 and C2, that voltage difference will decrease.

[0116] The controller 17 has a predetermined allowable voltage difference set in advance (for example, ±10V). The controller 17 determines whether the voltage difference between the two primary capacitors C1 and C2 is within the allowable voltage difference range. If the controller 17 determines that the voltage difference between the two primary capacitors C1 and C2 is within the allowable voltage difference range, it transitions to operating state St1.

[0117] In operating state St1, the control method is switched (from half-bridge mode to full-bridge mode). This corresponds to a transition from the third charging voltage range to the second charging voltage range. The controller 17 has a predetermined appropriate delay time (e.g., 0.1 seconds). After this delay time has elapsed, the system transitions to operating state St2.

[0118] In operating state St2, a soft start is performed. That is, the actual charging operation begins from operating state St2. The controller 17 outputs the power command value Pout * The control system then gradually increases the power from 0 to the rated power of the DC / DC converter 5.

[0119] Then, the output power command value Pout * When the power reaches the rated power (Prated), it transitions to operating state St3. Operating state St3 corresponds to the steady state. Therefore, after operating state St3, the controller 17 enters normal operation (steady state) after startup.

[0120] Thus, before the charging operation at startup begins, the controller 17 performs voltage balancing control to eliminate the voltage difference between the two primary capacitors C1 and C2. This effectively suppresses the DC bias phenomenon.

[0121] (Control during discharge operation by the controller) Next, we will explain the control of the discharge operation by the controller 17.

[0122] In this converter circuit 15, there is no resonant capacitor in the secondary circuit 22. However, by turning off all of the primary switching elements S1 to S6 and utilizing their freewheeling diodes 24, the converter circuit 15 can perform a discharge operation in which power is input from the secondary side and output from the primary side by switching the secondary switching elements S7 to S10 in that state.

[0123] However, in that case, only a square wave is applied to the excitation inductance Lm, so it cannot resonate with the primary side resonant capacitor Cr. Therefore, the operation becomes that of a normal series resonant type with only the primary side resonant capacitor Cr and primary side resonant inductance Lr as resonant elements during discharge. As a result, the operating range of input and output power during discharge is basically limited by the turns ratio of transformer 20. That is, the secondary side voltage Vout becomes the same as the primary side voltage Vin.

[0124] However, during discharge, the primary voltage Vin may be higher than the secondary voltage Vout. In this case, a boost operation can be achieved by performing a phase shift in the third and fourth switching elements S3 and S4 of the primary circuit 21. Therefore, in this DC / DC converter 5, the primary voltage Vin can be higher than the secondary voltage Vout. Furthermore, since the AC / DC converter 6 can maintain a constant AC output voltage during discharge, PWM control that changes the duty cycle is unnecessary.

[0125] As a result, during discharge operation, the discharge voltage range is divided into first and second ranges according to the relative magnitudes of the primary voltage Vin (output voltage) and the secondary voltage Vout (input voltage), and switching control information is set for each of them, as shown in Figure 4(b) (first and second discharge switching control information).

[0126] According to these first and second discharge switching control information, PWM control with a fixed duty cycle of 50% is performed for all switching elements S7 to S10 of the secondary circuit 22 across the entire discharge voltage range.

[0127] The first discharge voltage range is when the secondary voltage Vout and the primary voltage Vin are the same. According to the first discharge switching control information, in the first discharge voltage range, a full-bridge control method is used, and all switching elements S1 to S6 of the primary circuit 21 are kept off at all times.

[0128] The second discharge voltage range is when the primary voltage Vin is higher than the secondary voltage Vout. According to the second discharge switching control information, in the second discharge voltage range, the first, second, fifth, and sixth switching elements S1, S2, S5, and S6 of the primary circuit 21 are always turned off, and a phase shift is performed in the third and fourth switching elements S3 and S4.

[0129] Figure 8 illustrates the switching patterns of each switching element S3, S4, S7~S10 in the primary circuit 21 and secondary circuit 22 in the second discharge voltage range.

[0130] <Verification of effectiveness> (Verification 1) The effects of the charging operation during startup were verified through simulation. An example of the results is shown in Figure 9.

[0131] The uppermost graph in Figure 9 shows the time-dependent changes in the voltages Vin(LO) and Vin(HI) of the two primary capacitors C1 and C2 during startup. The graph below that shows the time-dependent changes in the transformer current ITR, and the graph below that shows the time-dependent changes in the output power command value Pout. The lowermost graph shows the time-dependent changes in the operating state (see Figure 7).

[0132] As shown in Figure 9, the voltage difference across the two primary capacitors C1 and C2 before startup is 400V. This voltage difference converged to 0V before the start of the charging operation. This confirms that the voltage difference across the two primary capacitors C1 and C2 can be eliminated before the start of the charging operation.

[0133] (Verification 2) The stability of the charging operation after startup (steady state) was verified through simulation. An example of the results is shown in Figures 10A to 10C.

[0134] Figure 10A corresponds to the third charging voltage range. In the simulation, the primary voltage Vin was set to 400V and the secondary voltage Vout to 150V. The output power Pout was set to 2kW. The output current command value Iout at this time is also shown. * This is below the upper limit of the 17f current limiter (CC mode).

[0135] Figure 10B corresponds to the second charging voltage range. In the simulation, the primary voltage Vin was set to 400V and the secondary voltage Vout to 300V. The output power Pout was set to 4kW. The output current command value Iout at this time is also shown. * This is the upper limit of the current limiter 17f (CP mode).

[0136] Figure 10C corresponds to the first charging voltage range. In the simulation, the primary voltage Vin was set to 400V and the secondary voltage Vout to 450V. The output power Pout was set to 4kW. The output current command value Iout at this time is also shown. * This is the upper limit of the current limiter 17f (CP mode).

[0137] The uppermost graph in Figures 10A to 10C shows the change in transformer voltage VTR over time, corresponding to its voltage waveform (see Figure 6B). The graph below it shows the corresponding change in transformer current ITR, etc., over time.

[0138] As shown in these figures, it was confirmed that step-up / step-down operation can be achieved with a constant input voltage, and that charging can be performed with a constant power. Although specific examples are not shown, the same applies to discharge operation. Therefore, according to the disclosed technology, the power conversion range that can be handled can be effectively expanded on both the charging and discharging sides, and a compact and highly efficient DC / DC converter can be realized.

[0139] <Another form of bidirectional isolated LLC resonant circuit> Figure 11 shows another configuration of the converter circuit 15 (T-type converter circuit 15A). The T-type converter circuit 15A differs from the converter circuit 15 described above in the configuration of the primary side circuit 21. The secondary side circuit of the T-type converter circuit 15A is the same as the secondary side circuit 22 of the converter circuit 15 described above, so the same components are referred to by the same reference numerals and their explanation is omitted.

[0140] The primary side circuit 21 of the T-type converter circuit 15A is the same as the converter circuit 15 described above in that it has primary side input / output terminals 30 and six primary side switching elements S1 to S6, and has a third leg 33 in which two primary side capacitors C1 and C2 are arranged in series, and a first leg 31 in which two primary side switching elements S3 and S4 are arranged in series.

[0141] In addition to these, the primary side circuit 21 of the T-type converter circuit 15A has a second leg 32 in which two primary side switching elements S5 and S6 are arranged in series. The first leg 31, the second leg 32, and the third leg 33 are connected in parallel between a pair of primary side main lines 36, 36, each having a primary side input / output terminal 30 at one end.

[0142] A single connecting wire 38 is connected to the area between the two primary-side switching elements S5 and S6 in the second leg 32 and to the area between the two primary-side capacitors C1 and C2 in the third leg 33. Two primary-side switching elements S1 and S2 are arranged in series on this connecting wire 38, with their current-carrying directions facing inward when both are ON.

[0143] The control details of the T-type converter circuit 15A are the same as those of the converter circuit 15 described above. In other words, the control method of the T-type converter circuit 15A, the switching patterns of each switching element S1 to S10, etc., are the same as those of the converter circuit 15 described above.

[0144] <Modified example of a bidirectional isolated LLC resonant circuit> Figure 12 shows modified versions of the converter circuit 15 and the T-type converter circuit 15A described above. Figure 12(a) is a modified version of the T-type converter circuit 15A, and Figure 12(b) is a modified version of the converter circuit 15.

[0145] These modified versions differ from the converter circuit 15 and T-type converter circuit 15A described above in that an LLC circuit is also provided on the secondary circuit 22 side. In other respects, they are the same, so the same symbols are used for the same configuration, and their explanations and reference numerals are omitted.

[0146] In other words, these modified versions further include an LLC circuit (secondary LLC circuit 60) located between the transformer 20 and the secondary circuit 22 (a so-called CLLC converter). Specifically, the secondary LLC circuit 60 has a secondary resonant capacitor 61 and a secondary resonant inductance 62 (leakage inductance) arranged in series from the sixth leg 51 side on the secondary upper relay wiring 57. A secondary excitation inductance may also be connected in parallel with the secondary coil 20b.

[0147] The secondary LLC circuit 60 is composed of a secondary resonant capacitor 61 and a secondary resonant inductance 62. Therefore, these modifications allow for an even wider power handling range during discharge operation. [Explanation of Symbols]

[0148] 1 vehicle 2 Commercial power supply 3 On-board charger 4 Batteries 5 DC / DC Converters 6 AC / DC Converters 15 Bidirectional isolated LLC resonant circuit 16 Converter mechanism 17 Controllers 17a CC / CP switching section 17b Current regulator 17c Control Unit 17d drive circuit 17e Divider 17f Current Limiter 20 transformers 21 Primary circuit 22 Secondary circuit 23 LLC circuit 25 Pair 30 Primary side input / output terminal 31 Leg 1 32 Leg 2 33 Third Leg 34 Leg 4 35 Leg 5 36 Primary side main line 37 Bypass Line 38 Connecting Line 43. Output section of intermediate voltage 45 Primary side upper relay wiring 46 Primary side lower relay wiring 50 Secondary input / output terminals 51 Leg 6 52 Leg 7 53 Leg 8 54 Secondary main line 57 Secondary side upper relay wiring 58 Lower secondary relay wiring 60 Secondary side LLC circuit 61 Secondary resonant capacitor 62 Secondary resonant inductance S1~S10 Switching elements D1, D2 diodes C1, C2 Primary side capacitors C3 Intermediate Capacitor C4 Secondary capacitor Cr Primary side resonant capacitor Lr Primary resonant inductance Lm Excitation Inductance

Claims

1. A DC / DC converter comprising a converter mechanism including a bidirectional isolated LLC resonant circuit and a controller for controlling the converter mechanism, The aforementioned bidirectional isolated LLC resonant circuit is A transformer having a primary coil and a secondary coil, A primary side circuit located on the primary side of the transformer includes a primary side input / output terminal pair and six primary side switching elements, A secondary circuit located on the secondary side of the transformer includes a pair of secondary input / output terminals and four secondary switching elements, An LLC circuit located between the transformer and the primary side circuit, It has, The primary side circuit is, Two primary capacitors are arranged in series and electrically connected between the primary input / output terminal pair, An intermediate voltage output section located between the two primary capacitors, which applies a primary half voltage, an intermediate voltage of the primary voltage which is the DC voltage input to the primary input / output terminal pair, to the LLC circuit, It has, A charging operation in which a DC voltage is input to the primary input / output terminal pair and output from the secondary input / output terminal pair, A discharge operation in which a DC voltage is input to the secondary input / output terminal pair and output from the primary input / output terminal pair, It is configured to be executable, The aforementioned controller It has switching control information regarding the duty cycle and phase shift set according to the relative magnitudes of the input and output DC voltages, A DC / DC converter configured to change the switching patterns of the primary and secondary switching elements in the charging and discharging operations based on the switching control information, and to perform voltage balancing control to eliminate the voltage difference between the two primary capacitors before the start of the charging operation at startup.

2. In the DC / DC converter according to claim 1, A DC / DC converter which, when the DC voltage output during the charging operation is greater than the primary half voltage, controls the duty cycle and switches the operation of the LLC circuit between the primary voltage and the primary half voltage.

3. In the DC / DC converter according to claim 1 or 2, The primary side circuit is, A first leg in which two primary-side switching elements are arranged in series, A second leg in which two pairs of elements, each consisting of two primary-side switching elements connected in series, are arranged in series, The third leg on which the two primary capacitors are located, The fourth leg has one intermediate capacitor, The fifth leg consists of two diodes arranged in series, The primary input / output terminal pair is located at one end, and the first leg, the second leg, and the third leg are connected in parallel between each other as a pair of primary main lines, A pair of bypass lines are connected in parallel to the portion between the primary-side switching elements included in each of the element pairs in the second leg, and the fourth and fifth legs are connected in parallel between each other, A connecting wire that is connected to the portion between the two diodes in the fifth leg and the portion between the two primary capacitors in the third leg, It has, The secondary circuit is, The sixth and seventh legs each have two of the aforementioned secondary switching elements arranged in series, The eighth leg, where one secondary capacitor is located, The secondary input / output terminal pair is located at one end, and the sixth leg, the seventh leg, and the eighth leg are connected in parallel between each other as a pair of secondary main lines, It has, A primary side upper relay wiring connects the positive electrode end of the primary side coil to the portion between the two pairs of elements in the second leg, A primary side lower relay wiring connects the negative electrode end of the primary side coil to the portion between the two primary side switching elements in the first leg, A secondary upper relay wiring connects the positive terminal end of the secondary coil to the portion between the two secondary switching elements in the sixth leg, A secondary lower relay wiring connects the negative terminal end of the secondary coil to the portion between the two secondary switching elements in the seventh leg, It further possesses, The LLC circuit is a DC / DC converter having a primary side resonant capacitor and a primary side resonant inductance arranged in series with the primary side upper relay wiring.

4. In the DC / DC converter according to claim 3, A DC / DC converter in which the bidirectional isolated LLC resonant circuit further comprises a secondary LLC circuit located between the transformer and the secondary circuit.

5. In the DC / DC converter according to claim 1 or 2, The primary side circuit is, The first leg and the second leg each have two of the primary-side switching elements arranged in series, The third leg on which the two primary capacitors are located, The primary input / output terminal pair is located at one end, and the first leg, the second leg, and the third leg are connected in parallel between each other as a pair of primary main lines, Two primary-side switching elements are arranged in series such that their current-carrying directions are opposite to each other, and a connecting wire is connected between the portion between the two primary-side switching elements in the second leg and the portion between the two primary-side capacitors in the third leg, It has, The secondary circuit is, The sixth and seventh legs each have two of the aforementioned secondary switching elements arranged in series, The eighth leg, where one secondary capacitor is located, The secondary input / output terminal pair is located at one end, and the sixth leg, the seventh leg, and the eighth leg are connected in parallel between each other as a pair of secondary main lines, It has, A primary side upper relay wiring connects the positive terminal end of the primary side coil to the portion between the two primary side switching elements in the second leg, A primary side lower relay wiring connects the negative electrode end of the primary side coil to the portion between the two primary side switching elements in the first leg, A secondary upper relay wiring connects the positive terminal end of the secondary coil to the portion between the two secondary switching elements in the sixth leg, A secondary lower relay wiring connects the negative terminal end of the secondary coil to the portion between the two secondary switching elements in the seventh leg, It further possesses, The LLC circuit is a DC / DC converter having a primary side resonant capacitor and a primary side resonant inductance arranged in series with the primary side upper relay wiring.

6. In the DC / DC converter according to claim 5, A DC / DC converter in which the bidirectional isolated LLC resonant circuit further comprises a secondary LLC circuit located between the transformer and the secondary circuit.

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