Power conversion device and program

Abstract

To provide a power conversion apparatus and a program in which deterioration of the accuracy of estimating an inductance can be suppressed.SOLUTION: A power conversion apparatus 100 includes first, second, and third full-bridge circuits 10, 20, 30, first and second transformers 60, 70, and a control device 110. For example, by performing switching control of the first and second full-bridge circuits 10 and 20, the control device 110 performs a power transmission process of transmitting power between the first full-bridge circuit 10 and the second full-bridge circuit 20 via the first transformer 60. In addition, the control device 110 performs an estimation process of the excitation inductances of the first and second transformers 60 and 70. The frequency of a fundamental wave component of a test voltage that is used in the estimation process is set to be lower than the frequency of a fundamental wave component of a voltage that is outputted to the first and second transformers 60 and 70 in the power transmission process.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a power conversion device and a program. [Background technology]

[0002] Conventionally, a known power conversion device includes a first circuit that is a bridge circuit connected to a first external terminal, a second circuit that is a bridge circuit connected to a second external terminal, and a transformer that connects a first AC terminal of the first circuit and a second AC terminal of the second circuit. Patent Document 1, for example, describes a multi-port converter as an embodiment of this power conversion device. The power conversion device described in Patent Document 1 is capable of estimating the inductance of the transformer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-85704 Summary of the Invention [Problem to be solved by the invention]

[0004] In addition to the device described in Patent Document 1, there is also a power conversion device that can reduce switching loss by utilizing LC resonance. More specifically, the power conversion device is a device that connects a first AC terminal of a first circuit and a second AC terminal of a second circuit. Rui inductance element and ,stomach Capacitor connected to an inductance element and In this power conversion device ,stomach Inductance required Natural When estimating inductance, Inductance Outputs a test voltage to the element. If the frequency of the test voltage is not set properly, Inductance The accuracy of the estimation of the element's inductance may be reduced.

[0005] A main object of the present invention is to provide a power conversion device and a program that can suppress a decrease in the accuracy of inductance estimation. [Means for solving the problem]

[0006] The present invention provides a power supply comprising: a first circuit which is a bridge circuit connected to a first external terminal; a second circuit which is a bridge circuit connected to the second external terminal; A first AC terminal of the first circuit and a second AC terminal of the second circuit are connected Rui an inductance element; before Note I a resonant capacitor connected to the inductance element; system With the Minister, Equipped with The control unit By controlling the switching of at least one of the first circuit and the second circuit, Note I a power transfer process for transferring power between the first external terminal and the second external terminal via an inductance element; before Note I Inductance required Simply By outputting a test voltage, Inductance an estimation process for estimating the inductance of the element; and The frequency of the fundamental component of the test voltage is Inductance The frequency is set to be lower than the frequency of the fundamental component of the voltage output to the element.

[0007] The impedance of a resonant capacitor tends to increase as the frequency decreases, while the impedance of an inductance element tends to decrease as the frequency decreases. ,stomach Inductance required Simply The frequency of the fundamental wave component of the output test voltage is Resonant Capacitor By setting the frequency low enough to minimize current flow, Inductance It is believed that this can suppress a decrease in the estimation accuracy of the element inductance.

[0008] In this regard, in the present invention, the frequency of the fundamental wave component of the test voltage is Inductance The frequency is set to be lower than the frequency of the fundamental component of the voltage output to the element. Resonant Capacitor As a result, it is possible to output a test voltage having a low frequency that minimizes the flow of current. Inductance This makes it possible to suppress a decrease in the accuracy of estimating the inductance of the element. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is an overall configuration diagram of a power conversion device according to a first embodiment. [Figure 2] FIG. 4 is a diagram showing a circuit state in a process of estimating the excitation inductance of the first transformer. [Figure 3] 4 is a time chart showing the transition of test voltage, etc. [Figure 4] FIG. 10 is a diagram showing a circuit state in the process of estimating the excitation inductance of the second transformer. [Figure 5] FIG. 10 is a diagram showing impedance frequency characteristics of a resonant capacitor and an exciting inductance. [Figure 6] FIG. 4 is a diagram showing impedance frequency characteristics of first and second closed loop circuits. [Figure 7] 10 is a flowchart showing the procedure of a process for estimating an exciting inductance. [Figure 8] FIG. 10 is a diagram showing calculation results of the effect of improving estimation accuracy. [Figure 9] FIG. 10 is an overall configuration diagram of a power conversion device according to a second embodiment. [Figure 10] 10 is a flowchart showing the procedure of a process for estimating an exciting inductance. [Figure 11] FIG. 10 is an overall configuration diagram of a power conversion device according to a third embodiment. [Figure 12] FIG. 10 is a diagram showing an output mode of a test voltage according to the fourth embodiment. [Figure 13] 4 is a time chart showing the transition of test voltage, etc. [Figure 14] FIG. 4 is a diagram showing an example of current sampling timing. [Figure 15] FIG. 4 is a diagram showing an example of current sampling timing. [Figure 16] FIG. 10 is an overall configuration diagram of a power conversion device according to a fifth embodiment. [Figure 17] FIG. 13 is an overall configuration diagram of a power conversion device according to a modification of the fifth embodiment. [Figure 18] FIG. 13 is an overall configuration diagram of a power conversion device according to a modification of the fifth embodiment. [Figure 19] FIG. 10 is a diagram illustrating the overall configuration of a power conversion device according to another embodiment. [Figure 20] FIG. 10 is a diagram illustrating the overall configuration of a power conversion device according to another embodiment. [Figure 21] FIG. 10 is a diagram illustrating the overall configuration of a power conversion device according to another embodiment. [Figure 22] FIG. 10 is a diagram illustrating the overall configuration of a power conversion device according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Several embodiments will be described with reference to the drawings. In several embodiments, functionally and / or structurally corresponding and / or associated parts may be assigned the same reference numerals or reference numerals that differ in the hundredth or more digit. For corresponding and / or associated parts, reference may be made to the descriptions of other embodiments.

[0011] First Embodiment A first embodiment of a power conversion device according to the present invention will be described below with reference to the drawings. The power conversion device of this embodiment is a multi-port type. The power conversion device is mounted on a moving object such as a vehicle, an aircraft, or a ship. The vehicle may be, for example, a hybrid vehicle, an electric vehicle, or a railroad car.

[0012] 1, the power conversion device 100 includes a plurality of external terminals and full-bridge circuits provided corresponding to the respective external terminals. Power is transmitted between at least two of the external terminals by switching control of the full-bridge circuits.

[0013] The power conversion device 100 includes a first external terminal, a second external terminal, and a third external terminal. A chargeable / dischargeable storage battery, an AC-DC converter, an electric load, etc. are connected to the first external terminal, the second external terminal, and the third external terminal. A system is configured by the chargeable / dischargeable storage battery, the AC-DC converter, the electric load, etc., and the power conversion device 100. The power conversion device 100 includes a first full-bridge circuit 10 as a full-bridge circuit corresponding to the first external terminals, that is, a first high-potential side terminal CH1 and a first low-potential side terminal CL1.

[0014] The first full-bridge circuit 10 includes firstA to fourthA switches QA1 to QA4. In this embodiment, the firstA to fourthA switches QA1 to QA4 are N-channel MOSFETs and have body diodes. A first high potential terminal CH1 is connected to the drains, which are high potential terminals, of the first switch QA1 and the thirdA switch QA3. A drain of the secondA switch QA2 is connected to the source, which is a low potential terminal, of the firstA switch QA1, and a drain of the fourthA switch QA4 is connected to the source of the thirdA switch QA3. A first low potential terminal CL1 is connected to the sources of the secondA switch QA2 and the fourthA switch QA4. A first terminal of a first capacitor 11 included in the power conversion device 100 is connected to the first high potential terminal CH1. A second terminal of the first capacitor 11 is connected to the first low potential terminal CL1. The first capacitor 11 serves as a smoothing capacitor and a noise eliminator. The first capacitor 11 may be built into the first full-bridge circuit 10.

[0015] The power conversion device 100 includes a second full bridge circuit 20 as a full bridge circuit corresponding to the second high potential side terminal CH2 and the second low potential side terminal CL2, which are second external terminals. The second full bridge circuit 20 includes first to fourth B switches QB1 to QB4. In this embodiment, the first to fourth B switches QB1 to QB4 are N-channel MOSFETs and have body diodes. In this embodiment, the configuration of the second full bridge circuit 20 is similar to the configuration of the first full bridge circuit 10, so a detailed description of the second full bridge circuit 20 will be omitted.

[0016] A first terminal of a second capacitor 21 included in the power conversion device 100 is connected to the second high potential side terminal CH2. A second terminal of the second capacitor 21 is connected to the second low potential side terminal CL2. The second capacitor 21 serves as a smoothing capacitor and a noise remover. The second capacitor 21 may be built into the second full bridge circuit 20.

[0017] The power conversion device 100 includes a third full bridge circuit 30 as a full bridge circuit corresponding to the third high potential side terminal CH3 and the third low potential side terminal CL3, which are third external terminals. The third full bridge circuit 30 includes first to fourth C switches QC1 to QC4. In this embodiment, the first to fourth C switches QC1 to QC4 are N-channel MOSFETs and have body diodes. In this embodiment, the configuration of the third full bridge circuit 30 is similar to the configuration of the first full bridge circuit 10, so a detailed description of the third full bridge circuit 30 will be omitted.

[0018] A first terminal of a third capacitor 31 included in the power conversion device 100 is connected to the third high potential side terminal CH3. A second terminal of the third capacitor 31 is connected to the third low potential side terminal CL3. The third capacitor 31 serves as a smoothing capacitor and a noise remover. The third capacitor 31 may be built into the third full bridge circuit 30.

[0019] The power conversion device 100 includes a first transformer 60 (corresponding to a "first inductance element") for transmitting power between the first full-bridge circuit 10 and the second full-bridge circuit 20. The first transformer 60 includes a first coil 61, a second coil 62, and a core around which the first coil 61 and the second coil 62 are wound. The first coil 61 and the second coil 62 are magnetically coupled via the core.

[0020] A first end of the first coil 61 is connected to the firstA AC terminal CA1 of the first full-bridge circuit 10. A source of the firstA switch QA1 and a drain of the secondA switch QA2 are connected to the firstA AC terminal CA1. A second end of the first coil 61 is connected to the firstB AC terminal CB1 of the first full-bridge circuit 10. A source of the thirdA switch QA3 and a drain of the fourthA switch QA4 are connected to the firstB AC terminal CB1.

[0021] A first end of second coil 62 is connected to a first end of first resonant capacitor 63 included in power conversion device 100. A second end of first resonant capacitor 63 is connected to secondA AC terminal CA2 of second full-bridge circuit 20. A second end of second coil 62 is connected to secondB AC terminal CB2 of second full-bridge circuit 20. Leakage inductances 61a and 62a of first and second coils 61 and 62 are also shown in FIG.

[0022] When the potential of the first end of the first coil 61 is higher than that of the second end, an induced voltage is generated in the second coil 62 such that the potential of the first end is higher than that of the second end. On the other hand, when the potential of the second end of the first coil 61 is higher than that of the first end, an induced voltage is generated in the second coil 62 such that the potential of the second end is higher than that of the first end.

[0023] The power conversion device 100 includes a second transformer 70 (corresponding to a "second inductance element") for transmitting power between the second full-bridge circuit 20 and the third full-bridge circuit 30. The second transformer 70 includes a first coil 71 (corresponding to a "third coil"), a second coil 72 (corresponding to a "fourth coil"), and a core around which the first coil 71 and the second coil 72 are wound. The first coil 71 and the second coil 72 are magnetically coupled via the core.

[0024] The second A AC terminal CA2 is connected to a first end of the first coil 71. The second B AC terminal CB2 is connected to a second end of the first coil 71. In other words, the first coil 71 of the second transformer 70 is connected in parallel to the series connection of the second coil 62 and the first resonant capacitor 63 of the first transformer 60.

[0025] A first end of a second resonant capacitor 64 included in the power conversion device 100 is connected to a first end of a second coil 72 of the second transformer 70. A second end of the second resonant capacitor 64 is connected to a third A AC terminal CA3 of the third full bridge circuit 30. A second end of the second coil 72 is connected to a third B AC terminal CB3 of the third full bridge circuit 30. Leakage inductances 71a and 72a of the first and second coils 71 and 72 are also shown in FIG.

[0026] When the potential of the first end of the first coil 71 is higher than that of the second end, an induced voltage is generated in the second coil 72 such that the potential of the first end is higher than that of the second end. On the other hand, when the potential of the second end of the first coil 71 is higher than that of the first end, an induced voltage is generated in the second coil 72 such that the potential of the second end is higher than that of the first end.

[0027] The power conversion device 100 includes a first voltage sensor 12, a second voltage sensor 22, and a third voltage sensor 32. The first voltage sensor 12 detects the voltage of the first capacitor 11, the second voltage sensor 22 detects the voltage of the second capacitor 21, and the third voltage sensor 32 detects the voltage of the third capacitor 31.

[0028] The power conversion device 100 includes a first current sensor 13, a second current sensor 23, and a third current sensor 33. The first current sensor 13 detects the current flowing between the first full-bridge circuit 10 and the first low-potential side terminal CL1. The second current sensor 23 detects the current flowing between the second full-bridge circuit 20 and the second low-potential side terminal CL2. The third current sensor 33 detects the current flowing between the third full-bridge circuit 30 and the third low-potential side terminal CL3.

[0029] Taking the first current sensor 13 as an example, the first current sensor 13 may detect, for example, the current flowing between the first full-bridge circuit 10 and the first high potential side terminal CH1.

[0030] The detected values ​​Vdc1, Vdc2, and Vdc3 of the first, second, and third voltage sensors 12, 22, and 33 and the detected values ​​I1, I2, and I3 of the first, second, and third current sensors 13, 23, and 33 are input to a control device 110, which serves as a control unit included in the power conversion apparatus 100. The control device 110 is mainly configured with a microcomputer 111, which includes a CPU. The functions provided by the microcomputer 111 can be provided by software stored in a physical memory device and a computer that executes the software, software alone, hardware alone, or a combination thereof. For example, when the microcomputer 111 is implemented as a hardware electronic circuit, the electronic circuit can be implemented as a digital circuit including multiple logic circuits or an analog circuit. For example, the microcomputer 111 executes a program stored in a non-transitory tangible storage medium that serves as a memory unit included in the microcomputer 111. The program includes, for example, a program for processing the processing shown in FIG. 7, which will be described later. A method corresponding to a program is executed by executing the program installed in the control device 110. The storage unit is, for example, a non-volatile memory. The program stored in the storage unit can be downloaded and updated via a communication network such as the Internet, for example, via OTA (Over The Air) or the like.

[0031] Next, the power transmission process performed by the control device 110 will be described.

[0032] The power transfer process is a process of transferring power between at least two of the first to third external terminals, and utilizes an LC series resonant circuit made up of a resonant capacitor and a leakage inductance.

[0033] A closed loop circuit including the first full-bridge circuit 10, the first transformer 60, the first resonant capacitor 63, and the second full-bridge circuit 20 is referred to as a first closed loop circuit. In the first closed loop circuit, an LC series resonant circuit is formed, which is made up of the first resonant capacitor 63 and leakage inductances 61a and 62a of the first transformer 60. In this embodiment, the values ​​of the leakage inductances 61a and 62a are equal.

[0034] The closed loop circuit including the second full-bridge circuit 20, the second transformer 70, the second resonant capacitor 64, and the third full-bridge circuit 30 is referred to as the second closed loop circuit. In the second closed loop circuit, an LC series resonant circuit is formed, consisting of the second resonant capacitor 64 and the leakage inductances 71a and 72a of the second transformer 70. In this embodiment, the values ​​of the leakage inductances 71a and 72a are equal. Furthermore, in this embodiment, the values ​​of the leakage inductances 61a, 62a, 71a, and 72a of the transformers 60 and 70 are equal.

[0035] In the first and second closed loop circuits, an additional inductor that is a passive element may be provided as an inductance that constitutes the LC series resonant circuit, instead of a leakage inductance.

[0036] A case where power is transmitted between the first external terminal and the second external terminal will be described. The power transmission control method can employ, for example, the method described in JP 2021-145407 A.

[0037] The control device 110 alternately turns on the set of the firstA switch QA1 and the fourthA switch QA4 and the set of the secondA switch QA2 and the thirdA switch QA3. The control device 110 also alternately turns on the set of the firstB switch QB1 and the fourthB switch QB4 and the set of the secondB switch QB2 and the thirdB switch QB3. The control device 110 can control the direction and amount of power transmission by adjusting the phase difference between the timing at which the firstA switch QA1 is switched off and the timing at which the firstB switch QB1 is switched off.

[0038] Next, a case where power is transferred between the second external terminal and the third external terminal will be described. The control device 110 alternately turns on the set of the firstB switch QB1 and the fourthB switch QB4 and the set of the secondB switch QB2 and the thirdB switch QB3. The control device 110 also alternately turns on the set of the firstC switch QC1 and the fourthC switch QC4 and the set of the secondC switch QC2 and the thirdC switch QC3. The control device 110 can control the direction and amount of power transfer by adjusting the phase difference between the timing at which the firstB switch QB1 is switched off and the timing at which the firstC switch QC1 is switched off.

[0039] The switching frequency fβ of each of the switches QA1 to QA4, QB1 to QB4, and QC1 to QC4 in the power transfer process is set to a frequency (e.g., 100 kHz) higher than the higher of the resonant frequencies of the first and second closed loop circuits. For example, when the capacitance of the first resonant capacitor 63 is equal to the capacitance of the second resonant capacitor 64, the resonant frequencies of the first and second closed loop circuits are equal. In this embodiment, the switching periods Tβ (=1 / fβ) of each of the switches QA1 to QA4, QB1 to QB4, and QC1 to QC4 are set to the same value. The closer the switching frequency fβ is to the resonant frequency, the greater the effect of reducing the switching loss of the switches. Note that the switching frequency fβ may be set to, for example, a frequency equal to or higher than 1.3 times the resonant frequency and equal to or lower than twice the resonant frequency.

[0040] Next, the process of estimating the magnetizing inductance of the transformer executed by the control device 110 will be described.

[0041] First, a method for estimating the excitation inductance of the first transformer 60 will be described with reference to Fig. 2. In Fig. 2, AC terminals and the like are not shown.

[0042] The excitation inductance of the first transformer 60 is the inductance of the magnetic flux (excitation magnetic flux) that interlinks both the first and second coils 61, 62, among the magnetic flux generated by energizing either one of the first and second coils 61, 62.

[0043] The control device 110 turns off all of the switches included in the full bridge circuits other than the full bridge circuit that outputs the test voltage Vtest among the full bridge circuits 10, 20, and 30. Specifically, the control device 110 turns off all of the switches QB1 to QB4 of the second full bridge circuit 20 and turns off all of the switches QC1 to QC4 of the third full bridge circuit 30.

[0044] The control device 110 has a function of setting the frequency of the test voltage Vtest. The frequency of the test voltage Vtest is set so that the fundamental wave component of the test voltage Vtest has a frequency described below. The control device 110 alternately turns on the pair of the first A switch QA1 and the fourth A switch QA4 and the pair of the second A switch QA2 and the third A switch QA3 while keeping the switches QB1 to QB4 and QC1 to QC4 off. This causes the test voltage Vtest to be output from the first full-bridge circuit 10 to the first coil 61 of the first transformer 60. As shown in FIG. 3 , the test voltage Vtest is an AC voltage having an amplitude Va, specifically a square-wave voltage. Va is a voltage equivalent to the terminal voltage of the first capacitor 11. In this embodiment, the control device 110 detects the detection value Vdc1 of the first voltage sensor 12 as the test voltage Vtest and uses the detected test voltage Vtest to estimate the exciting inductance. In FIG. 3, Tsw represents the switching period of each of the switches QA1 to QA4 of the first full-bridge circuit 10 in the estimation process.

[0045] When the test voltage Vtest is applied to the first coil 61, a current flows through the first coil 61. The current flowing through the first coil 61 is detected by the first current sensor 13. The control device 110 estimates the excitation inductance L1 of the first transformer 60 based on the test voltage Vtest detected by the first voltage sensor 12 and the current Itest (corresponding to the "first estimation current") detected by the first current sensor 13. In detail, the control device 110 estimates the excitation inductance L1 of the first transformer 60 by dividing the amplitude Va of the detected test voltage Vtest by the rate of change (e.g., the rate of increase or decrease) of the detected current Itest.

[0046] Next, a method for estimating the excitation inductance of the second transformer 70 will be described with reference to FIG.

[0047] The control device 110 turns off all of the switches QA1 to QA4 of the first full-bridge circuit 10, and turns off all of the switches QC1 to QC4 of the third full-bridge circuit 30. With the switches QA1 to QA4 and QC1 to QC4 turned off, the control device 110 alternately turns on the set of the firstB switch QB1 and the fourthB switch QB4 and the set of the secondB switch QB2 and the thirdB switch QAB. As a result, the test voltage Vtest shown in FIG. 3 is output from the second full-bridge circuit 20 to the first coil 71 of the second transformer 70.

[0048] When the test voltage Vtest is applied to the first coil 71, a current flows through the first coil 71. The current flowing through the first coil 71 is detected by the second current sensor 23. In the process of estimating the excitation inductance of the second transformer 70, the control device 110 detects the detection value Vdc2 of the second voltage sensor 22 as the test voltage Vtest and uses the detected test voltage Vtest to estimate the excitation inductance. The control device 110 estimates the excitation inductance L2 of the second transformer 70 based on the test voltage Vtest detected by the second voltage sensor 22 and the current Itest (corresponding to the "second estimation current") detected by the second current sensor 23. More specifically, the control device 110 estimates the excitation inductance L2 of the second transformer 70 by dividing the amplitude Va of the detected test voltage Vtest by the rate of change (e.g., the rate of increase or decrease) of the detected current Itest.

[0049] If the frequency of the test voltage Vtest is too low, the first coil may become magnetically saturated, which may cause an overcurrent to flow in the closed circuit including the first coil when the test voltage Vtest is applied. Furthermore, if magnetic saturation occurs, the excitation inductance may temporarily decrease, which may reduce the accuracy of estimating the excitation inductance. Therefore, it is desirable to set the frequency of the test voltage Vtest to a frequency that does not cause magnetic saturation.

[0050] This embodiment is characterized by the method for setting the frequency of the fundamental component of the test voltage Vtest, which will be described below with reference to FIG.

[0051] Figure 5 shows the impedance frequency characteristics of the resonant capacitor and the transformer's excitation inductance that make up the LC series resonant circuit. As shown in the following equation (eq1), the impedance Zc of the capacitor increases as the frequency decreases. Therefore, the lower the frequency, the more difficult it is for current to flow through the capacitor. On the other hand, as shown in the following equation (eq2), the impedance ZL determined from the excitation inductance decreases as the frequency decreases. Therefore, the lower the frequency, the more easily current flows through the coil. In the equations below, ω represents each frequency, C represents the capacitance of the capacitor, and L represents the excitation inductance.

[0052]

number

[0053]

number

[0054] In contrast, in a comparative example in which the frequency of the fundamental component of the test voltage Vtest is set to a frequency higher than the reference frequency fα, when the test voltage is applied to the first coil 61, current tends to flow toward the second coil 62. Specifically, current flows through a closed loop circuit including the second coil 62, the first resonant capacitor 63, and the body diodes of the switches of the second full-bridge circuit 20, or through a closed loop circuit including the second coil 62, the first resonant capacitor 63, and the first coil 71 of the second transformer 70. As a result, the current detected by the first current sensor 13 becomes larger than in the present embodiment. This reduces the accuracy of estimating the excitation inductance L1 of the first transformer 60. Furthermore, loss occurs due to the current flow.

[0055] In addition, in the process of estimating the excitation inductance of the first transformer 60, it is desirable that the frequency of the fundamental wave component of the test voltage Vtest be set to a frequency at which the impedance ZL determined from the excitation inductance is 1 / 5 or less or 1 / 10 or less of the impedance Zc of the first resonant capacitor 63.

[0056] On the other hand, the frequency at which the impedance ZL determined from the excitation inductance of the second transformer 70 becomes equal to the impedance Zc of the second resonant capacitor 64 is defined as the reference frequency fα. In the process of estimating the excitation inductance of the second transformer 70, the frequency of the fundamental component of the test voltage Vtest is set to a frequency lower than the reference frequency fα. Specifically, the frequency of the fundamental component of the test voltage Vtest is set to a frequency at which the impedance ZL determined from the excitation inductance of the second transformer 70 becomes equal to or less than one-third of the impedance Zc of the second resonant capacitor 64. This makes it difficult for current to flow on the second coil 72 side when the test voltage is applied to the first coil 71. As a result, it is possible to suitably suppress a decrease in the estimation accuracy of the excitation inductance L2 of the second transformer 70.

[0057] In addition, in the process of estimating the excitation inductance of the second transformer 70, it is desirable that the frequency of the fundamental wave component of the test voltage Vtest be set to a frequency at which the impedance ZL determined from the excitation inductance is 1 / 5 or less or 1 / 10 or less of the impedance Zc of the first and second resonant capacitors 63, 64.

[0058] Fig. 6 shows the impedance frequency characteristic K1 of the first closed loop circuit and the impedance frequency characteristic K2 of the second closed loop circuit. K1 is calculated from the impedance (Vdc1 / I1) calculated based on the detected value Vdc1 of the first voltage sensor 12 and the detected value I1 of the first current sensor 13 when the test voltage Vtest is applied in the state shown in Fig. 2. K2 is calculated from the impedance (Vdc2 / I2) calculated based on the detected value Vdc2 of the second voltage sensor 22 and the detected value I2 of the second current sensor 23 when the test voltage Vtest is applied in the state shown in Fig. 4.

[0059] It is assumed that the first and second transformers 60 and 70 have the same excitation inductance value (e.g., 1.36 mH) when new, but the actual excitation inductance of the second transformer 70 decreases due to deterioration (e.g., 250 μH).

[0060] When the frequency of the fundamental component of the test voltage Vtest in the estimation process is set to the switching frequency fβ during the power transmission process, the inductances K1 and K2 have the same value, as shown in FIG. 6. This indicates that the excitation inductances of the first and second transformers 60 and 70 cannot be estimated correctly. In contrast, in this embodiment, the frequency of the fundamental component is set to a frequency lower than the reference frequency fα. In this case, the excitation inductance can be estimated correctly.

[0061] 6, the resonant frequency of each closed loop circuit and the reference frequency fα are the same or equivalent. In the process of estimating the excitation inductance of each transformer 60, 70, the frequency of the fundamental wave component of the test voltage Vtest may be set to a value greater than or equal to 1 / 5 and less than or equal to 1 / 3 of the reference frequency fα, or greater than or equal to 1 / 10 and less than or equal to 1 / 5 of the reference frequency fα.

[0062] FIG. 7 shows a flowchart of the process of estimating the magnetizing inductance executed by the control device 110.

[0063] In step S10, a transformer to be estimated is selected from the first and second transformers 60 and 70. In this embodiment, the first transformer 60 (corresponding to the "target element") is first selected as the target element to be estimated.

[0064] In step S11, as shown in FIG. 2, all of the switches QB1 to QB4 of the second full-bridge circuit 20 are turned off, and all of the switches QC1 to QC4 of the third full-bridge circuit 30 are turned off.

[0065] In step S12, the current test voltage Vtest is acquired, and in step S13, the detection value Itest of the first current sensor 13 when the test voltage Vtest is being applied is acquired.

[0066] In step S14, the magnetizing inductance L1 of the first transformer 60 is estimated based on the acquired test voltage Vtest and current Itest.

[0067] In step S15, it is determined whether or not estimation of the excitation inductances of both the first and second transformers 60, 70 has been completed. If the determination in step S15 is negative, the process proceeds to step S10, where the second transformer 70 (corresponding to the "target element") is selected as the target for estimating the excitation inductance. Then, steps S11 to S14 are performed in the same manner as in the process of estimating the excitation inductance of the first transformer 60.

[0068] If the determination in step S15 is affirmative, the process proceeds to step S16, where the mode is changed to one in which the power transmission process is executed.

[0069] The order of selection of the first and second transformers 60, 70 for estimating the excitation inductance is not limited to a specific order and may be changed as appropriate, such as selecting the first transformer 60 and then the second transformer 70.

[0070] FIG. 8 shows the results of the excitation inductance estimation process for this embodiment and the comparative example. In the example shown in FIG. 8, the true values ​​of the excitation inductances of the first and second transformers 60 and 70 are the same. According to this embodiment, the estimated values ​​of the excitation inductances of the first and second transformers 60 and 70 are close to the true values. In contrast, in the comparative example, the frequency of the fundamental wave component of the test voltage Vtest is set higher than the reference frequency fα, so the first coil 71 of the second transformer 70 is equivalently connected in parallel to the second coil 62 of the first transformer 60. As a result, the estimated values ​​of the excitation inductances of the first and second transformers 60 and 70 are approximately half of the true values, significantly reducing the estimation accuracy.

[0071] According to the present embodiment described above in detail, it is possible to suitably suppress a decrease in the estimation accuracy of the exciting inductance of the transformer.

[0072] <Modification of the first embodiment> The first resonant capacitor 63 may be connected in series to the first coil 61 of the first transformer 60 instead of the second coil 62 .

[0073] The second resonant capacitor 64 may be connected in series to the first coil 71 of the second transformer 70 instead of the second coil 72.

[0074] The switching frequency fsw of each of the switches QA1 to QA4, QB1 to QB4, and QC1 to QC4 may be set to a frequency lower than the lower of the resonant frequencies of the first and second closed loop circuits.

[0075] The estimation process shown in FIG. 7 may be executed immediately after startup of the control device 110, or may be executed during a period other than immediately after startup, provided that the period is other than the period during which the power transmission process is being executed.

[0076] For example, in the estimation process executed immediately after the start-up of the control device 110, the transformers to be subjected to the estimation of the excitation inductance are not limited to all the transformers included in the power conversion device 100, but may be only some of the transformers. In this case, the part of the transformers to be subjected to the estimation may be changed each time the control device 110 is started up.

[0077] When the control device 110 determines that the estimated value of the magnetizing inductance is outside the normal range, it may determine that an abnormality has occurred in the transformer corresponding to the estimated value that is outside the normal range. In this case, the control device 110 may prohibit the execution of the power transmission process or may notify the user that an abnormality has occurred. Here, the notification process may be, for example, a process of notifying the user by controlling a notification unit (e.g., a sound generating unit such as a buzzer, or a light generating unit such as a lamp) provided in the system.

[0078] Prior to executing the estimation process, the control device 110 may cut off the electrical connection between each external terminal and the electrical load connected to the external terminal.

[0079] The energy loss caused by the switching control of the full-bridge circuit during the estimation process and the current flowing through the full-bridge circuit during the estimation process may be greater than the electrostatic energy stored in the capacitor on the external terminal side of the full-bridge circuit (for example, the first capacitor 11 in the circuit state of FIG. 2). In this case, the control device 110 may perform control to supply the power required for the estimation process to the capacitor from a voltage source connected to the external terminal.

[0080] Second Embodiment The second embodiment will be described below with reference to the drawings, focusing on differences from the first embodiment. In this embodiment, as shown in Fig. 9, a power conversion device 100 includes a first voltage adjustment circuit 15 and a second voltage adjustment circuit 25. For convenience, a third full-bridge circuit 30 and the like are not shown in Fig. 9.

[0081] In this embodiment, the first voltage adjustment circuit 15 includes a series connection of a first discharge resistor 15a and a first discharge switch 15b, and is a discharge circuit for the first capacitor 11. The second voltage adjustment circuit 25 also includes a series connection of a second discharge resistor 25a and a second discharge switch 25b, and is a discharge circuit for the second capacitor 21. The first voltage adjustment circuit 15 is connected in parallel to the first capacitor 11, and the second voltage adjustment circuit 25 is connected in parallel to the second capacitor 21. In this embodiment, each of the voltage adjustment circuits 15 and 25 is used to prevent the transformer from becoming magnetically saturated during the estimation process.

[0082] The power conversion device 100 includes a first cutoff switch SMR1 (e.g., a relay) for electrically connecting or disconnecting the first high potential side terminal CH1 and the first low potential side terminal CL1 to or from the first voltage adjustment circuit 15. The power conversion device 100 also includes a second cutoff switch SMR2 ​​(e.g., a relay) for electrically connecting or disconnecting the second high potential side terminal CH2 and the second low potential side terminal CL2 to or from the second voltage adjustment circuit 25. Fig. 9 shows an example in which a first storage battery B1 is connected to the first high potential side terminal CH1 and the first low potential side terminal CL1, and a second storage battery B2 is connected to the second high potential side terminal CH2 and the second low potential side terminal CL2.

[0083] The control device 110 controls the first discharge switch 15b to discharge the charge from the first capacitor 11 while keeping the first shutoff switch SMR1 off. This makes the terminal voltage of the first capacitor 11 during the estimation process of the exciting inductance of the first transformer 60 lower than the terminal voltage (specifically, the rated voltage) of the first capacitor 11 during the power transfer process. As a result, the amplitude of the fundamental component of the test voltage Vtest during the estimation process becomes smaller than the amplitude of the fundamental component of the voltage output from the first full-bridge circuit 10 during the power transfer process.

[0084] As described above, the frequency of the fundamental component of the test voltage Vtest during the estimation process is set to a low frequency. This makes it easy for magnetic saturation to occur in the first transformer 60. If magnetic saturation occurs, there is a concern that an overcurrent may flow in the closed loop circuit including the first full-bridge circuit 10 and the first coil 61. Therefore, by reducing the amplitude of the fundamental component of the test voltage Vtest, the occurrence of magnetic saturation in the first transformer 60 is suppressed.

[0085] Similarly, the control device 110 controls the second discharge switch 25b to discharge the electric charge from the second capacitor 21 while keeping the second cutoff switch SMR2 ​​off. As a result, the terminal voltage of the second capacitor 21 during the estimation process of the exciting inductance of the second transformer 70 is made lower than the terminal voltage of the second capacitor 21 during the power transmission process.

[0086] If the terminal voltages of the first and second capacitors 11 and 21 are reduced too much during the estimation process, the change in the current flowing through the transformer coil will be small, which may reduce the estimation accuracy of the exciting inductance. Therefore, it is desirable to set the terminal voltages of the first and second capacitors 11 and 21 during the estimation process to values ​​that take into consideration preventing magnetic saturation and ensuring estimation accuracy.

[0087] Fig. 10 shows a flowchart of the process of estimating the magnetizing inductance executed by the control device 110. In Fig. 10, the same processes as those shown in Fig. 7 are denoted by the same reference numerals for convenience.

[0088] After completing the process of step S10, the process proceeds to step S17. If the first transformer 60 is selected as the estimation target, in step S17, the first discharge switch 15b is controlled to discharge the charge from the first capacitor 11 while the first shut-off switch SMR1 is turned off. As a result, the amplitude of the fundamental component of the test voltage Vtest in step S12 is made smaller than the amplitude of the fundamental component of the voltage output from the first full-bridge circuit 10 during the power transfer process.

[0089] If the second transformer 70 is selected as the estimation target, in step S17, the second discharge switch 25b is controlled to discharge the charge from the second capacitor 21 while the second shutoff switch SMR2 ​​is turned off. As a result, the amplitude of the fundamental component of the test voltage Vtest in step S12 is made smaller than the amplitude of the fundamental component of the voltage output from the second full-bridge circuit 20 during the power transfer process.

[0090] According to the present embodiment described above, it is possible to prevent the transformer from becoming magnetically saturated during the estimation process.

[0091] <Modification of the second embodiment> The voltage adjustment circuit for adjusting the terminal voltage of the capacitor is not limited to a discharge circuit, and may be, for example, a DC-DC converter.

[0092] 2, the control device 110 may control the first discharge switch 15b to make the terminal voltage of the second capacitor 21 higher than the terminal voltage of the first capacitor 11 multiplied by the turns ratio of the first transformer 60. This makes it possible to prevent current from flowing through a closed loop circuit including the second coil 62, the first resonant capacitor 63, and the body diodes of the switches of the second full-bridge circuit 20 when the test voltage Vtest is applied to the first coil 61.

[0093] 4, the control device 110 may control the second discharge switch 25b so as to make the terminal voltage of the third capacitor 31 higher than the value obtained by multiplying the terminal voltage of the second capacitor 21 by the turns ratio of the second transformer 70. Furthermore, when the control device 110 performs the estimation process in the circuit state shown in FIG. 4, the control device 110 may control the second discharge switch 25b so as to make the terminal voltage of the first capacitor 11 higher than the value obtained by multiplying the terminal voltage of the second capacitor 21 by the turns ratio of the first transformer 60.

[0094] In the process shown in FIG. 10, voltage adjustment is performed in step S17 each time a transformer to be estimated is selected in step S10. However, this is not limited to this. For example, voltage adjustment may be performed on all of the first, second, and third capacitors 11, 21, and 31 at the start of the process shown in FIG. 10.

[0095] <Third embodiment> The third embodiment will be described below with reference to the drawings, focusing on differences from the first embodiment. As shown in FIG. 11 , a power conversion device 100 includes a first switch 16, a second switch 26, and a third switch 36. In this embodiment, the switches 16, 26, and 36 are relays. The first switch 16 is provided on an electrical path from the first-A AC terminal CA1 to the first-B AC terminal CB1 via the first coil 61. The second switch 26 is provided on an electrical path from the second-A AC terminal CA2 to the second-B AC terminal CB2 via the first resonant capacitor 63 and the second coil 62. The third switch 36 is provided on an electrical path from the third-A AC terminal CA3 to the third-B AC terminal CB3 via the second resonant capacitor 64 and the second coil 72.

[0096] 2 , the control device 110 turns on the first switch 16 and turns off the second switch 26 and the third switch 36. This prevents current from flowing through the closed loop circuit including the second coil 62, the first resonant capacitor 63, and the body diode of the second full-bridge circuit 20, and the closed loop circuit including the second coil 72, the second resonant capacitor 64, and the body diode of the third full-bridge circuit 30, when the test voltage Vtest is applied to the first coil 61.

[0097] 4, the control device 110 turns on the second switch 26 and turns off the first switch 16 and the third switch 36. This prevents current from flowing through the closed loop circuit including the first coil 61 and the body diode of the first full-bridge circuit 10 and the closed loop circuit including the second coil 72, the second resonant capacitor 64, and the body diode of the third full-bridge circuit 30 when the test voltage Vtest is applied to the first coil 71.

[0098] <Fourth embodiment> The fourth embodiment will be described below with reference to the drawings, focusing on the differences from the first embodiment.

[0099] As shown in Fig. 6, peaks appear in the impedance frequency characteristics due to the LC resonance of the LC series resonant circuit. In the example shown in Fig. 6, peaks appear around 5 kHz to 10 kHz. Note that Fig. 6 shows the impedance frequency characteristics of a three-port power conversion device, but as the number of ports increases, the number of peaks that appear also increases.

[0100] When the test voltage Vtest used in the excitation inductance estimation process is a square wave voltage, the square wave contains harmonic components. As a result, the frequency of the harmonic components becomes the resonant frequency of the LC resonance or a frequency close to it, causing a resonant current to flow. In this case, there is a concern that the accuracy of the excitation inductance estimation may decrease or that an overcurrent may flow in the transformer coil, etc.

[0101] Therefore, as shown in the upper part of FIG. 12, the control device 110 performs switching control of the full-bridge circuit at a switching frequency (e.g., 100 kHz) higher than the resonant frequency of the first and second closed loop circuits in the estimation process, thereby outputting the test voltage Vtest from the full-bridge circuit. Specifically, the control device 110 performs PWM control of the full-bridge circuit based on a magnitude comparison between a triangular carrier signal SgC and a sinusoidal modulating wave SgM. The modulating wave SgM is a signal having a frequency (e.g., 1 kHz) lower than the resonant frequency, and the carrier signal SgC is a signal having a switching frequency higher than the resonant frequency of the first and second closed loop circuits. This prevents the frequency of harmonic components included in the test voltage Vtest from being at or near the resonant frequency, thereby preventing the flow of resonant current. Note that Tvt in FIG. 12 represents one period of the fundamental component of the test voltage Vtest.

[0102] Taking the estimation process of the excitation inductance of the first transformer 60 as an example, when the PWM process is performed, the current I1 detected by the first current sensor 13 contains high-frequency ripples, as shown in Fig. 13. On the other hand, the waveform of the current IL flowing through the first coil 61 of the first transformer 60 is significantly different from the waveform of the current I1 detected by the first current sensor 13.

[0103] Therefore, the control device 110 sets the timing when the carrier signal SgC reaches its minimum value or its maximum value as the current sampling timing for the first current sensor 13. As a result, the detection value Itest of the first current sensor 13 used to estimate the exciting inductance becomes close to the current IL flowing through the first coil 61. As a result, it is possible to suppress a decrease in the estimation accuracy of the exciting inductance.

[0104] Fig. 14 shows an example in which current sampling is performed at timing ta when the carrier signal SgC reaches its minimum value, and Fig. 15 shows an example in which current sampling is performed at timing tb when the carrier signal SgC reaches its maximum value. Figs. 14 and 15 show the changes in the test voltage Vtest, the current IL flowing through the first coil 61 of the first transformer 60, the current Itest detected by the first current sensor 13, the carrier signal SgC, and the modulated wave SgM.

[0105] According to the current sampling timing described above, it is possible to detect a value near the median of the current IL that includes current ripple and flows through the first coil 61. This makes it possible to suppress a decrease in the estimation accuracy of the exciting inductance.

[0106] Fifth Embodiment The fifth embodiment will be described below with reference to the drawings, focusing on differences from the first embodiment. The number of ports of the power conversion device 100 is not limited to three, and may be four as shown in Fig. 16. Note that, for convenience, the control device 110 and the like are not shown in Fig. 16.

[0107] The power conversion device 100 includes a fourth high potential side terminal CH4 and a fourth low potential side terminal CL4 as fourth external terminals. The power conversion device 100 also includes a fourth full bridge circuit 40 and a fourth capacitor 41. The fourth full bridge circuit 40 includes first to fourth D switches QD1 to QD4. In this embodiment, the first to fourth D switches QD1 to QD4 are N-channel MOSFETs and have body diodes. In this embodiment, the configuration of the fourth full bridge circuit 40 is similar to the configuration of the first full bridge circuit 10, so a detailed description of the fourth full bridge circuit 40 will be omitted.

[0108] In this embodiment, the second resonant capacitor 64 is connected in series to the first coil 71 of the second transformer 70.

[0109] The power conversion device 100 includes a third transformer 80 and a third resonant capacitor 65 as components for transmitting power between the third full-bridge circuit 30 and the fourth full-bridge circuit 40. The third transformer 80 includes a first coil 81, a second coil 82, and a core around which the first coil 81 and the second coil 82 are wound. The first coil 81 and the second coil 82 are magnetically coupled via the core.

[0110] A first end of the first coil 81 is connected to the third A AC terminal CA3 via a third resonant capacitor 65. A second end of the first coil 81 is connected to the third B AC terminal CB3. A first end of the second coil 82 is connected to the fourth A AC terminal CA4 of the fourth full bridge circuit 40. A second end of the second coil 82 is connected to the fourth B AC terminal CB4 of the fourth full bridge circuit 40. Note that FIG. 16 also shows leakage inductances 81a and 82a of the first and second coils 81 and 82.

[0111] The power conversion device 100 includes a fourth voltage sensor 42 and a fourth current sensor 43. The fourth voltage sensor 42 detects the voltage of the fourth capacitor 41. The fourth current sensor 43 detects the current flowing between the fourth full-bridge circuit 40 and the fourth low potential side terminal CL4. A detection value Vdc4 of the fourth voltage sensor 42 and a detection value I4 of the fourth current sensor 43 are input to the control device 110.

[0112] As shown in Fig. 17, the number of ports of the power conversion device 100 may be five or more. In this case, the power conversion device 100 is required to include at least a fourth transformer 90 having a first coil 91 and a second coil 92, and a fourth resonant capacitor 66. Fig. 17 also shows leakage inductances 91a and 92a of the first and second coils 91 and 92.

[0113] 17 may also be modified as shown in FIG. 18. The power conversion device 100 includes a first module 18, a second module 28, a third module 38, and a fourth module 48. The first module 18 is a modularized device in which a first full-bridge circuit 10, a first capacitor 11, a first coil 61 and a portion of the core of a first transformer 60, a first voltage sensor 12, and a first current sensor 13 are housed in a first housing. The second module 28 is a modularized device in which a second full-bridge circuit 20, a second capacitor 21, a second coil 62 and a portion of the core of a first transformer 60, a first coil 71 and a portion of the core of a second transformer 70, a second resonant capacitor 64, a second voltage sensor 22, and a second current sensor 23 are housed in a second housing.

[0114] A portion of the core around which the first coil 61 of the first transformer 60 is wound is exposed from the abutting surface of the first housing of the first module 18 with the second housing of the second module 28. Furthermore, a portion of the core around which the second coil 62 of the first transformer 60 is wound is exposed from the abutting surface of the second housing of the second module 28 with the first housing of the first module 18. When the abutting surfaces of the first housing and the second housing abut and the first and second housings are integrated, a portion of the core around which the first coil 61 of the first transformer 60 is wound abuts against a portion of the core around which the second coil 62 of the first transformer 60 is wound. As a result, the first coil 61 and the second coil 62 of the first transformer 60 are magnetically coupled.

[0115] The third module 38 is a modularized device in which the third full-bridge circuit 30, the third capacitor 31, the second coil 72 and part of the core of the second transformer 70, the first coil 81 and part of the core of the third transformer 80, the third resonant capacitor 65, the third voltage sensor 32, and the third current sensor 33 are housed in a third housing.

[0116] A portion of the core around which the first coil 71 of the second transformer 70 is wound is exposed from the abutting surface of the second housing of the second module 28 with the third housing of the third module 38. Furthermore, a portion of the core around which the second coil 72 of the second transformer 70 is wound is exposed from the abutting surface of the third housing of the third module 38 with the second housing of the second module 28. When the abutting surface of the second housing abuts the abutting surface of the third housing to integrate the second and third housings, a portion of the core around which the first coil 71 of the second transformer 70 is wound abuts against a portion of the core around which the second coil 72 of the second transformer 70 is wound. As a result, the first coil 71 and the second coil 72 of the second transformer 70 are magnetically coupled.

[0117] The fourth module 48 is a modularized device in which the fourth full-bridge circuit 40, the fourth capacitor 41, the second coil 82 and part of the core of the third transformer 80, the first coil 91 and part of the core of the fourth transformer 90, the fourth resonant capacitor 66, the fourth voltage sensor 42, and the fourth current sensor 43 are housed in a fourth housing.

[0118] A portion of the core around which the first coil 81 of the third transformer 80 is wound is exposed from the abutting surface of the third housing of the third module 38 with the fourth housing of the fourth module 48. Furthermore, a portion of the core around which the second coil 82 of the third transformer 80 is wound is exposed from the abutting surface of the fourth housing of the fourth module 48 with the third housing of the third module 38. When the abutting surface of the third housing and the abutting surface of the fourth housing abut against each other to integrate the third and fourth housings, a portion of the core around which the first coil 81 of the third transformer 80 is wound abuts against a portion of the core around which the second coil 82 of the third transformer 80 is wound. As a result, the first coil 81 and the second coil 82 of the third transformer 80 are magnetically coupled.

[0119] 18, it is possible to realize a power conversion device 100 according to the number of ports desired by the user. In the configuration shown in Fig. 18, it is desirable that one of the modules 18, 28, 38, and 48 is a master module that determines the estimation order of the exciting inductance of the transformer, etc.

[0120] <Other embodiments> The above-described embodiments may be modified as follows.

[0121] As shown in Fig. 19, the number of ports of the power conversion device 200 may be two. Even in this case, the frequency of the fundamental wave component of the test voltage Vtest output from the first full-bridge circuit 10 is set to a frequency lower than the reference frequency fα, thereby preventing a decrease in the estimation accuracy of the excitation inductance. In the configuration shown in Fig. 19, the first coil 71 corresponds to the "second inductance element."

[0122] The switches in the full-bridge circuit are not limited to N-channel MOSFETs, but may be, for example, IGBTs with freewheeling diodes connected in reverse parallel. In this case, the high-potential terminal of the switch is the collector, and the low-potential terminal of the switch is the emitter.

[0123] As shown in FIG. 20, the number of ports of the power conversion device 300 may be two.

[0124] As shown in FIG. 21, the power conversion device 400 may include relays SR1 and SR2 so that current flows only through the coil of the transformer that is the subject of estimation.

[0125] In the estimation process of each of the above embodiments, the frequency of the fundamental wave component of the test voltage Vtest may be set higher than the reference frequency fα.

[0126] 22, the power conversion device 500 may include current sensors CT1, CT2, CT3, and CT4 that individually detect the currents flowing through the coils 61, 62, 71, and 72. In this case, in the estimation process, the frequency of the fundamental component of the test voltage Vtest may be set to a frequency higher than the reference frequency fα.

[0127] The bridge circuit is not limited to a full bridge circuit, but may be any other bridge circuit as long as it can output a voltage whose polarity alternates (for example, an AC voltage) to the transformer coil.

[0128] The control unit and the method described herein may be implemented by a special-purpose computer configured by configuring a processor and memory programmed to perform one or more functions embodied in a computer program. Alternatively, the control unit and the method described herein may be implemented by a special-purpose computer configured by configuring a processor with one or more dedicated hardware logic circuits. Alternatively, the control unit and the method described herein may be implemented by one or more special-purpose computers configured by combining a processor and memory programmed to perform one or more functions with a processor configured with one or more hardware logic circuits. Furthermore, the computer program may be stored as instructions executed by a computer on a computer-readable non-transitory tangible storage medium. [Explanation of symbols]

[0129] 10, 20, 30...first, second, third full bridge circuits, 60...first transformer, 63...first resonant capacitor, 64...second resonant capacitor, 70...second transformer, 100...power conversion device.

Claims

1. a first circuit (10) that is a bridge circuit connected to first external terminals (CH1, CL1); a second circuit (20) that is a bridge circuit connected to second external terminals (CH2, CL2); an inductance element (60) connecting first AC terminals (CA1, CB1) of the first circuit and second AC terminals (CA2, CB2) of the second circuit; a resonant capacitor (63) connected to the inductance element; A control unit (110); Equipped with The control unit a power transmission process of transmitting power between the first external terminal and the second external terminal via the inductance element by switching control of at least one of the first circuit and the second circuit; an estimation process for estimating an inductance of the inductance element by outputting a test voltage to the inductance element; and A power conversion device (100, 200, 300) in which the frequency of the fundamental component of the test voltage is set to a frequency lower than the frequency of the fundamental component of the voltage output to the inductance element in the power transmission process.

2. A first transformer (60) having a first coil (61) connected to the first AC terminal and a second coil (62) connected to the second AC terminal is provided as the inductance element, the resonant capacitor is a first resonant capacitor connected in series to the first coil or the second coil, a third circuit (30) that is a bridge circuit connected to third external terminals (CH3, CL3); a second transformer (70) having a third coil (71) connected to the second AC terminal and a fourth coil (72) connected to third AC terminals (CA3, CB3) of the third circuit; a second resonant capacitor (64) connected in series with the fourth coil; the power transmission process is a process of transmitting power between at least two of the first external terminal, the second external terminal, and the third external terminal by switching control of at least one of the first circuit, the second circuit, and the third circuit, The control unit acquiring an estimation current that is a current that flows through a path that is closer to the second external terminal than the second AC terminal, among a current flow path from the second external terminal through the second circuit to the third coil; In the estimation process, when a test voltage is output from the second AC terminal by switching control of the second circuit, an exciting inductance of the second transformer is estimated based on the test voltage and the acquired current for estimation; 2. The power conversion device (100) according to claim 1, wherein the frequency of the fundamental component of the test voltage is set to a frequency lower than the frequency of the fundamental component of the voltage output from the second AC terminal in the power transmission process.

3. the estimation current is a second estimation current, the first resonant capacitor is connected in series with the second coil; The control unit a first estimation current is acquired, the first estimation current being a current flowing through a path that is closer to the first external terminal than the first AC terminal, among current flow paths from the first external terminal through the first circuit to the first coil; 3. The power conversion device according to claim 2, wherein, in the estimation process, when the test voltage is output from the first AC terminal by switching control of the first circuit, an excitation inductance of the first transformer is estimated based on the test voltage and the first estimation current.

4. a first circuit (10) that is a bridge circuit connected to first external terminals (CH1, CL1); a second circuit (20) that is a bridge circuit connected to second external terminals (CH2, CL2); a third circuit (30) that is a bridge circuit connected to third external terminals (CH3, CL3); a first transformer (60) having a first coil (61) connected to first AC terminals (CA1, CB1) of the first circuit and a second coil (62) connected to second AC terminals (CA2, CB2) of the second circuit; a first resonant capacitor (63) connected in series with the second coil; a second transformer (70) having a third coil (71) connected to the second AC terminal and a fourth coil (72) connected to third AC terminals (CA3, CB3) of the third circuit; a second resonant capacitor (64) connected in series to the third coil or the fourth coil; A control unit (110); Equipped with The control unit a power transmission process of transmitting power between at least two of the first external terminal, the second external terminal, and the third external terminal by switching control of at least one of the first circuit, the second circuit, and the third circuit; an estimation process for estimating an exciting inductance of the first transformer; and acquiring an estimation current that is a current that flows through a path that is closer to the first external terminal than the first AC terminal, among a current flow path from the first external terminal through the first circuit to the first coil; In the estimation process, when a test voltage is output from the first AC terminal by switching control of the first circuit, an exciting inductance of the first transformer is estimated based on the test voltage and the estimation current; A power conversion device (100) in which the frequency of the fundamental component of the test voltage is set to a frequency lower than the frequency of the fundamental component of the voltage output from the first AC terminal in the power transmission process.

5. a transformer (60) having a first coil (61) connected to the first AC terminal and a second coil (62) connected to the second AC terminal is provided as the inductance element; the resonant capacitor is connected in series with the second coil; a third coil (71) connected to the second AC terminal; the power transmission process is a process of transmitting power between the first external terminal and the second external terminal by switching control of at least one of the first circuit and the second circuit, When a test voltage is output from the first AC terminal by switching control of the first circuit in the estimation process, the control unit estimates an exciting inductance of the transformer based on the test voltage and an estimation current that is a current flowing through the first coil; 2. The power conversion device (200) according to claim 1, wherein the frequency of the fundamental component of the test voltage is set to a frequency lower than the frequency of the fundamental component of the voltage output from the first AC terminal in the power transmission process.

6. 3. The power conversion device according to claim 2, wherein the frequency of the fundamental wave component of the test voltage when estimating the excitation inductance of the second transformer is set to a frequency at which an impedance determined from the excitation inductance of the second transformer is smaller than the impedances of the first resonant capacitor and the second resonant capacitor.

7. 7. The power conversion device according to claim 6, wherein the frequency of the fundamental wave component of the test voltage when estimating the excitation inductance of the second transformer is set to a frequency at which the impedance determined from the excitation inductance of the second transformer is 1 / 3 or less of the impedance of the first resonant capacitor and the second resonant capacitor.

8. 5. The power conversion device according to claim 3, wherein a frequency of a fundamental wave component of the test voltage when estimating the excitation inductance of the first transformer is set to a frequency at which an impedance determined from the excitation inductance of the first transformer is smaller than an impedance of the first resonant capacitor.

9. 9. The power conversion device according to claim 8, wherein a frequency of a fundamental wave component of the test voltage when estimating the excitation inductance of the first transformer is set to a frequency at which an impedance determined from the excitation inductance of the first transformer is ⅓ or less of an impedance of the first resonant capacitor.

10. a first circuit (10) that is a bridge circuit connected to first external terminals (CH1, CL1); a second circuit (20) that is a bridge circuit connected to second external terminals (CH2, CL2); a third circuit (30) that is a bridge circuit connected to third external terminals (CH3, CL3); a first transformer (60) having a first coil (61) connected to first AC terminals (CA1, CB1) of the first circuit and a second coil (62) connected to second AC terminals (CA2, CB2) of the second circuit; a first resonant capacitor (63) connected in series to the first coil or the second coil; a second transformer (70) having a third coil (71) connected to the second AC terminal and a fourth coil (72) connected to third AC terminals (CA3, CB3) of the third circuit; a second resonant capacitor (64) connected in series with the fourth coil; A control unit (110); Equipped with The control unit acquiring an estimation current that is a current that flows through a path that is closer to the second external terminal than the second AC terminal, among a current flow path from the second external terminal through the second circuit to the third coil; When a test voltage is output from the second AC terminal by switching control of the second circuit, an estimation process is performed to estimate an exciting inductance of the second transformer based on the test voltage and the estimation current; A power conversion device (100) in which the frequency of the fundamental wave component of the test voltage when estimating the excitation inductance of the second transformer is set to a frequency at which the impedance determined from the excitation inductance of the second transformer is smaller than the impedance of the first resonant capacitor and the second resonant capacitor.

11. a first circuit (10) that is a bridge circuit connected to first external terminals (CH1, CL1); a second circuit (20) that is a bridge circuit connected to second external terminals (CH2, CL2); a third circuit (30) that is a bridge circuit connected to third external terminals (CH3, CL3); a first transformer (60) having a first coil (61) connected to first AC terminals (CA1, CB1) of the first circuit and a second coil (62) connected to second AC terminals (CA2, CB2) of the second circuit; a first resonant capacitor (63) connected in series with the second coil; a second transformer (70) having a third coil (71) connected to the second AC terminal and a fourth coil (72) connected to third AC terminals (CA3, CB3) of the third circuit; a second resonant capacitor (64) connected in series to the third coil or the fourth coil; A control unit (110); Equipped with The control unit acquiring an estimation current that is a current that flows through a path that is closer to the first external terminal than the first AC terminal, among a current flow path from the first external terminal through the first circuit to the first coil; When a test voltage is output from the first AC terminal by switching control of the first circuit, an estimation process is performed to estimate an exciting inductance of the first transformer based on the test voltage and the estimation current; A power conversion device (100) in which the frequency of the fundamental wave component of the test voltage when estimating the excitation inductance of the first transformer is set to a frequency at which the impedance determined from the excitation inductance of the first transformer is smaller than the impedance of the first resonant capacitor.

12. The power conversion device according to any one of claims 2 to 7, wherein the control unit makes the amplitude of the fundamental wave component in the estimation process smaller than the amplitude of the fundamental wave component of the output voltage in the power transfer process.

13. a voltage adjustment circuit (15, 25) that adjusts at least one of an input voltage on the first external terminal side of the first circuit and an input voltage on the second external terminal side of the second circuit, The power conversion device according to claim 12 , wherein the control unit controls the voltage adjustment circuit so that the input voltage in the estimation process is lower than the input voltage in the power transfer process.

14. The power conversion device according to any one of claims 2 to 7, wherein the control unit, in the estimation process, uses the fundamental wave component as a modulated wave, and sets a switching frequency in the switching control to a frequency higher than a resonant frequency of a resonant circuit including the resonant capacitor by PWM processing using the modulated wave and a carrier signal.

15. the carrier signal is a triangular wave signal, The power conversion device according to claim 14 , wherein the control unit sets, in the estimation process, a timing at which the carrier signal reaches a maximum value or a timing at which the carrier signal reaches a minimum value as a detection timing of the estimation current.

16. a first circuit (10) that is a bridge circuit connected to first external terminals (CH1, CL1); a second circuit (20) that is a bridge circuit connected to second external terminals (CH2, CL2); an inductance element (60) connecting first AC terminals (CA1, CB1) of the first circuit and second AC terminals (CA2, CB2) of the second circuit; a capacitor (63) connected to the inductance element; A control unit (110); A program applied to a power conversion device (100, 200, 300) comprising: The control unit a power transmission process of transmitting power between the first external terminal and the second external terminal via the inductance element by switching control of at least one of the first circuit and the second circuit; an estimation process for estimating an inductance of the inductance element by outputting a test voltage to the inductance element; Execute The program, wherein the frequency of the fundamental component of the test voltage is set to a frequency lower than the frequency of the fundamental component of the voltage output to the inductance element in the power transmission process.

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