Power converter

Abstract

The present invention provides a power conversion device that can more accurately calculate the junction temperatures of multiple switching elements in multiple converters connected in series, while suppressing an increase in the computational load of the control device. [Solution] A power conversion device is provided comprising a main circuit section having a plurality of converters connected in series, and a control device that controls the operation of the main circuit section, each of the plurality of converters having a plurality of switching elements, the control device inputting control signals to the plurality of converters and inputting measured values ​​of the current flowing through the plurality of converters to each of the plurality of converters, the plurality of converters calculating the loss of each of the plurality of switching elements based on the control signals, measured values ​​of the current, conduction loss, turn-on loss, and turn-off loss, and calculating the temperature rise value of the junction temperature of each of the plurality of switching elements based on the loss of each of the plurality of switching elements.

Description

[Technical Field]

[0001] Embodiments of the present invention relate to a power conversion device. [Background technology]

[0002] A power converter is known that comprises a main circuit section that performs power conversion and a control device that controls the operation of the main circuit section. In such a power converter, the main circuit section is often configured as a multi-stage unit in which multiple converters are connected in series.

[0003] Each converter has multiple switching elements and charge storage elements connected in parallel to the multiple switching elements. Each converter also has a pair of connection terminals, and is connected in series via these terminals. In a power converter having a multi-stage main circuit, for example, it is possible to handle large amounts of power while suppressing the increase in the responsibilities required of each element in each converter.

[0004] In such power converters, monitoring the junction temperature of each switching element is being considered to suppress failures of each switching element in each converter. The junction temperature of a switching element needs to be estimated by calculation. For this reason, in power converters with a multi-stage main circuit, the number of converters is large, making it difficult for the control unit to monitor the junction temperature of all switching elements in all converters.

[0005] For example, instead of performing calculations for each individual switching element, it has been proposed to calculate the average junction temperature of each switching element based on switching information of the switching element, such as the carrier frequency (the average frequency of the element) and duty cycle, as well as information on the current flowing through the switching element. However, in this case, when a particular switching element is selected intensively, the element temperature may become excessive, potentially leading to element failure.

[0006] Therefore, in power converters having a multi-stage main circuit, it is desirable to be able to calculate the junction temperature of each switching element of each converter more accurately while suppressing an increase in the computational load of the control device. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] International Publication No. 2021 / 106175 [Overview of the project] [Problems that the invention aims to solve]

[0008] Embodiments of the present invention provide a power conversion device that can more accurately calculate the junction temperatures of multiple switching elements of multiple converters connected in series, while suppressing an increase in the computational load of the control device. [Means for solving the problem]

[0009] According to an embodiment of the present invention, a power conversion device is provided comprising: a main circuit unit having a plurality of converters connected in series, which converts power through the operation of the plurality of converters; and a control device that controls the operation of the main circuit unit, each of the plurality of converters having a pair of connection terminals, a plurality of switching elements, and a charge storage element connected in parallel to the plurality of switching elements, and connected in series via the pair of connection terminals; the control device generates a control signal to control the switching of the plurality of switching elements of the plurality of converters, and controls the operation of the main circuit unit by inputting the control signal to the plurality of converters, and also inputs a measured value of the current flowing through the plurality of converters to each of the plurality of converters, and the plurality of converters calculate the loss of each of the plurality of switching elements corresponding to the direction of the current flowing through the plurality of converters and the switching of the plurality of switching elements based on the control signal, the measured value of the current, the conduction loss of the plurality of switching elements, the turn-on loss of the plurality of switching elements and the turn-off loss of the plurality of switching elements, and calculates the temperature rise value of the junction temperature of each of the plurality of switching elements based on the loss of each of the plurality of switching elements. [Effects of the Invention]

[0010] A power conversion device is provided that can more accurately calculate the junction temperatures of multiple switching elements in multiple converters connected in series, while suppressing an increase in the computational load of the control device. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic block diagram showing a power conversion device according to an embodiment. [Figure 2] This is a block diagram schematically representing the converter. [Figure 3] This is a block diagram schematically representing a part of the control system. [Figure 4] Figures 4(a) and 4(b) are block diagrams schematically representing a part of the converter. [Figure 5] It is a block diagram schematically showing a part of a converter.

[0012] Each embodiment will be described below with reference to the drawings. Note that the drawings are schematic or conceptual, and the relationship between the thickness and width of each portion, the size ratio between portions, and the like are not necessarily the same as those in reality. Further, even when the same portion is illustrated, the dimensions and ratios may be different depending on the drawings. In the present specification and each drawing, the same reference numerals are given to the same elements as those described above with respect to the already shown drawings, and detailed description thereof will be omitted as appropriate.

[0013] FIG. 1 is a block diagram schematically showing a power converter according to the embodiment. As shown in FIG. 1, the power converter 10 includes a main circuit section 12 and a control device 14. The main circuit section 12 is connected to an AC power system 2 via a transformer 4, for example. The AC power of the power system 2 is three-phase AC power. More specifically, it is symmetric three-phase AC power. The transformer 4 converts the three-phase AC power of the power system 2 into AC power compatible with the main circuit section 12. The transformer 4 changes the effective value of each phase of the three-phase AC power in accordance with the main circuit section 12.

[0014] The main circuit section 12 has three arm portions 20. Each arm portion 20 is provided between each phase of the three-phase AC power of the power system 2. For example, when each phase of the three-phase AC power is defined as U phase, V phase, and W phase, one arm portion 20 is provided between the U phase and the V phase, another arm portion 20 is provided between the V phase and the W phase, and the remaining one arm portion 20 is provided between the W phase and the U phase. In other words, each arm portion 20 is delta-connected to the three-phase AC power of the power system 2.

[0015] The main circuit unit 12 performs power conversion. For example, the main circuit unit 12 performs power conversion by outputting AC power to the power system 2. For example, the main circuit unit 12 suppresses voltage fluctuations in the power system 2 by supplying reactive power to the three-phase AC power system 2. In this example, the power converter 10 is a reactive power compensator (Static Synchronous Compensator: STATCOM).

[0016] Each arm section 20 has multiple converters 22 connected in series. The main circuit section 12 is, for example, a multilevel power converter having multiple converters 22 connected in series. The main circuit section 12 is, for example, an MMC (Modular Multilevel Converter) type power converter. The main circuit section 12 is, for example, an MMC type reactive power compensation device.

[0017] The number of converters 22 connected in series in each arm section 20 is, for example, the same. However, if the number of converters 22 connected in series is large (for example, 100 or more), the number of converters 22 connected in series in each arm section 20 may differ by about 1 to 2 units.

[0018] Each converter 22 has a plurality of switching elements connected in a half-bridge or full-bridge configuration, and a charge storage element connected in parallel to each switching element. Each converter 22 outputs AC power to the power system 2 (power conversion operation) by switching each switching element.

[0019] Furthermore, the power conversion operation of the main circuit unit 12 is not limited to the output of AC power. The power conversion operation of the main circuit unit 12 may also be, for example, conversion from DC power to AC power or conversion from AC power to DC power. The configuration of the main circuit unit 12 is not limited to the above and may be any configuration having multiple converters 22 connected in series.

[0020] The control device 14 is connected to the main circuit unit 12. The control device 14 generates control signals to control the switching of each switching element in each converter 22, and controls the power conversion operation by the main circuit unit 12 by inputting the generated control signals to each converter 22.

[0021] Figure 2 is a block diagram schematically representing the converter. As shown in Figure 2, the converter 22 includes a plurality of switching elements 31 to 34, a plurality of rectifier elements 41 to 44, a charge storage element 50, and a pair of connection terminals 51 and 52.

[0022] Each switching element 31-34 has a pair of main terminals and a control terminal. The control terminal controls the current flowing between the pair of main terminals. Self-extinguishing elements such as IEGTs and IGBTs are used for each switching element 31-34. The pair of main terminals are, for example, an emitter and a collector, and the control terminal is, for example, a gate.

[0023] Each switching element 31-34 switches between an ON state, which allows current to flow between the pair of main terminals, and an OFF state, which blocks the current flowing between the pair of main terminals. The OFF state is not limited to a state in which no current flows at all between the pair of main terminals; for example, it may be a state in which a very weak current flows between the pair of main terminals, such that it does not affect the operation of the converter 22. In other words, the OFF state is a state in which the current flowing between the pair of main terminals is sufficiently small.

[0024] Each switching element 31-34 is, for example, a normally-off semiconductor element. Each switching element 31-34 is ON when the voltage at the control terminal is high and OFF when the voltage at the control terminal is low. Each switching element 31-34 is OFF when the voltage at the control terminal is lower than the ON state. Each switching element 31-34 is, for example, ON when a positive voltage is applied to the control terminal and OFF when the voltage at the control terminal is set to 0V or when a negative voltage is applied to the control terminal.

[0025] The pair of main terminals of switching element 32 are connected in series with the pair of main terminals of switching element 31. The pair of main terminals of switching element 34 are connected in series with the pair of main terminals of switching element 33. In addition, switching elements 33 and 34 are connected in parallel with switching elements 31 and 32.

[0026] Connection terminal 51 is connected between switching element 31 and switching element 32. Connection terminal 52 is connected between switching element 33 and switching element 34. Connection terminal 52 is connected to the main terminal of switching element 31 on the opposite side of the main terminal connected to switching element 32 via switching element 33.

[0027] In this example, the converter 22 is a full-bridge circuit having four switching elements 31-34 connected in a full-bridge configuration.

[0028] Multiple converters 22 within the same arm section 20 are connected in series via a pair of connection terminals 51 and 52. Switching elements 31 and 33 are so-called low-side switches, and switching elements 32 and 34 are so-called high-side switches.

[0029] Rectifier element 41 is connected in antiparallel to the pair of main terminals of switching element 31. The forward direction of rectifier element 41 is opposite to the direction of the current flowing between the pair of main terminals of switching element 31. Similarly, rectifier element 42 is connected in antiparallel to the pair of main terminals of switching element 32. Rectifier element 43 is connected in antiparallel to the pair of main terminals of switching element 33. Rectifier element 44 is connected in antiparallel to the pair of main terminals of switching element 34. Rectifier elements 41 to 44 are so-called freewheeling diodes.

[0030] The charge storage element 50 is connected in parallel to the switching elements 31 and 32, and also in parallel to the switching elements 33 and 34. The charge storage element 50 is, for example, a capacitor.

[0031] In the full-bridge converter 22, when switching elements 32 and 33 are turned ON and switching elements 31 and 34 are turned OFF, +Vc is output between the respective connection terminals 51 and 52.

[0032] When switching elements 31 and 34 are turned ON and switching elements 32 and 33 are turned OFF, -Vc is output between the respective connection terminals 51 and 52.

[0033] Furthermore, when switching elements 31 and 33 are turned on and switching elements 32 and 34 are turned off, or when switching elements 32 and 34 are turned on and switching elements 31 and 33 are turned off, a voltage of virtually 0V is output between each of the connection terminals 51 and 52.

[0034] Thus, the full-bridge converter 22 can output three levels of power, +Vc, 0, and -Vc, depending on the combination of the switching elements 31 to 34 that are turned on and off.

[0035] In the full-bridge converter 22, for example, the state where +Vc is output is the first output state, the state where -Vc is output is the second output state, the state where 0V is output is the bypass state, and the state where each switching element 31~34 is turned off is the stopped state. This converter 22 is put into the bypass state by turning on the two upper switching elements 32, 34 or the two lower switching elements 31, 33 of the four switching elements 31~34 connected in a full bridge. Switching between the states of this converter 22 can be achieved, for example, by making the control signal a three-level signal corresponding to three levels.

[0036] The converter 22 switches between an output state in which the voltage of the charge storage element 50 is output between the connection terminals 51 and 52, a bypass state in which the connection terminals 51 and 52 are conductive, and a stopped state in which the switching elements 31 to 34 are turned off, by switching the switching elements 31 to 34 based on the control signal from the control device 14.

[0037] In each arm section 20, the sum of the voltages of the converters 22 that are in the output state becomes the voltage of each arm section 20. The main circuit section 12 and the control device 14 perform multi-level power conversion by controlling the number of converters 22 that are in the output state.

[0038] Furthermore, the configuration of the converter 22 is not limited to a full-bridge circuit; it may also be a half-bridge circuit having two switching elements connected in a half-bridge configuration.

[0039] Figure 3 is a block diagram schematically representing a part of the control device. As shown in Figure 3, the control device 14 includes an absolute value calculator 60, a voltage calculator 61, a turn-on energy calculator 62, a turn-off energy calculator 63, and multipliers 64 to 66.

[0040] The control device 14 receives input of measured values ​​of the phase current I. The phase current I is the current flowing through the arm section 20. In other words, the phase current I is the current flowing through multiple converters 22 connected in series. The control device 14 receives input of the three phase currents I flowing through each of the three arm sections 20.

[0041] The control device 14 receives, for example, a measured value of the phase current I from a current measuring instrument (not shown in the figure). The current measuring instrument measures the magnitude of the phase current I flowing through the arm section 20 and inputs the measured value of the phase current I to the control device 14. The control device 14 may also receive the measured value of the phase current I from, for example, a higher-level controller. The method of inputting the measured value of the phase current I to the control device 14 is not limited to the above, and any method that allows the measured value of the phase current I to be appropriately input to the control device 14 is acceptable.

[0042] The absolute value calculator 60 calculates the absolute value of the measured phase current I. The voltage calculator 61 receives the absolute value of the measured phase current I as input from the absolute value calculator 60. The voltage calculator 61 has a correspondence between the magnitude of the phase current I and the magnitude of the voltage Vce generated between the pair of main terminals of each switching element 31-34 of the converter 22 when the phase current I flows through each switching element 31-34. This correspondence is represented, for example, by a calculation formula or table data. Based on the input absolute value of the measured phase current I, the voltage calculator 61 calculates the magnitude of the voltage Vce corresponding to the absolute value of the measured phase current I by referring to the correspondence.

[0043] The turn-on energy calculator 62 receives the absolute value of the measured phase current I as input from the absolute value calculator 60. The turn-on energy calculator 62 has a correspondence between the magnitude of the current flowing through each switching element 31-34 of the converter 22 when it transitions from the off state to the on state, and the magnitude of the turn-on energy Eon generated when each switching element 31-34 transitions from the off state to the on state. This correspondence is represented, for example, by a calculation formula or table data. Based on the input absolute value of the measured phase current I, the turn-on energy calculator 62 calculates the magnitude of the turn-on energy Eon corresponding to the absolute value of the measured phase current I by referring to the correspondence.

[0044] The turn-off energy calculator 63 receives the absolute value of the measured phase current I as input from the absolute value calculator 60. The turn-off energy calculator 63 has a correspondence between the magnitude of the current flowing through each switching element 31-34 of the converter 22 when it transitions from the ON state to the OFF state, and the magnitude of the turn-off energy Eoff generated when each switching element 31-34 transitions from the ON state to the OFF state. This correspondence is represented, for example, by a calculation formula or table data. Based on the input absolute value of the measured phase current I, the turn-off energy calculator 63 calculates the magnitude of the turn-off energy Eoff corresponding to the absolute value of the measured phase current I by referring to the correspondence.

[0045] The multiplier 64 receives the absolute value of the measured phase current I calculated by the absolute value calculator 60 and the magnitude of the voltage Vce calculated by the voltage calculator 61 as inputs, and calculates the conduction loss of each switching element 31 to 34 of the converter 22 by multiplying the absolute value of the measured phase current I by the magnitude of the voltage Vce.

[0046] The multiplier 65 receives the magnitude of the turn-on energy Eon calculated by the turn-on energy calculator 62 and the switching frequency (1 / Ts) of each switching element 31-34 of the converter 22 as inputs, and calculates the turn-on loss of each switching element 31-34 of the converter 22 by multiplying the magnitude of the turn-on energy Eon by the switching frequency.

[0047] The multiplier 66 receives the magnitude of the turn-off energy Eoff calculated by the turn-off energy calculator 63 and the switching frequency (1 / Ts) of each switching element 31-34 of the converter 22 as inputs, and calculates the turn-off loss of each switching element 31-34 of the converter 22 by multiplying the magnitude of the turn-off energy Eoff by the switching frequency.

[0048] The control device 14 inputs the measured value of the phase current I, the conduction loss, the turn-on loss, and the turn-off loss to each of the multiple converters 22 of the arm section 20 corresponding to the phase current I.

[0049] Accordingly, the control device 14 has three absolute value calculators 60, three voltage calculators 61, three turn-on energy calculators 62, three turn-off energy calculators 63, and three multipliers 64-66, corresponding to each of the three arm sections 20. The control device 14 calculates the absolute values ​​of the measured values ​​of the three phase currents I, three conduction losses, three turn-on losses, and three turn-off losses corresponding to each of the three arm sections 20.

[0050] Furthermore, as described above, the control device 14 inputs the measured value of the phase current I, conduction loss, turn-on loss, and turn-off loss to each converter 22, and also inputs control signals to each converter 22 to control the switching of each switching element 31 to 34 of each converter 22.

[0051] Figures 4(a) and 4(b) are block diagrams schematically representing a part of the converter. Figure 4(a) shows an example of the operation of the converter 22 when the magnitude of the phase current I is positive (I>0). Figure 4(b) shows an example of the operation of the converter 22 when the magnitude of the phase current I is negative (I<0). When the magnitude of the phase current I is positive, it corresponds to the direction of the current flowing from the connection terminal 52 to the connection terminal 51 via the switching element 33, the charge storage element 50, and the switching element 32. When the magnitude of the phase current I is negative, it corresponds to the direction of the current flowing from the connection terminal 51 to the connection terminal 52 via the switching element 31, the charge storage element 50, and the switching element 34.

[0052] In this case, when the magnitude of the phase current I is positive, switching elements 32 and 33 are turned on, and switching elements 31 and 34 are turned off. When the magnitude of the phase current I is negative, switching elements 31 and 34 are turned on, and switching elements 32 and 33 are turned off.

[0053] As shown in Figures 4(a) and 4(b), the converter 22 has multipliers 70 to 72. The multiplier 70 receives the magnitude Vdc of the DC voltage of the charge storage element 50 as input, as well as a reference value Vdc_base of the magnitude of the DC voltage of the charge storage element 50. The magnitude Vdc of the DC voltage of the charge storage element 50 is measured, for example, by a voltage measuring instrument (not shown in the figure) and input to the multiplier 70. The multiplier 70 calculates the ratio of the magnitude Vdc of the DC voltage of the charge storage element 50 to the reference value Vdc_base by multiplying the magnitude Vdc of the DC voltage of the charge storage element 50 by the reciprocal of the reference value Vdc_base.

[0054] The multiplier 71 receives the turn-on loss input from the control device 14, as well as the ratio of the magnitude of the DC voltage Vdc of the charge storage element 50 to the reference value Vdc_base calculated by the multiplier 70.

[0055] The multiplier 71 corrects the turn-on loss according to the magnitude of the DC voltage Vdc of the charge storage element 50 by multiplying the turn-on loss by the ratio of the magnitude Vdc of the DC voltage of the charge storage element 50 to the reference value Vdc_base.

[0056] The multiplier 72 receives the turn-off loss input from the control device 14, as well as the ratio of the magnitude of the DC voltage Vdc of the charge storage element 50 to the reference value Vdc_base calculated by the multiplier 70.

[0057] The multiplier 72 corrects the turn-off loss according to the magnitude of the DC voltage Vdc of the charge storage element 50 by multiplying the turn-off loss by the ratio of the magnitude Vdc of the DC voltage of the charge storage element 50 to the reference value Vdc_base.

[0058] As shown in Figure 4(a), the converter 22 further includes a determination unit 80a, edge detectors 81a and 82a, AND circuits 83a to 85a, switches 86a to 88a, and adders 89a and 90a.

[0059] The detector 80a outputs a logic "1" when the magnitude of the phase current I is positive, and a logic "0" when the magnitude of the phase current I is negative. A logic "0" corresponds to, for example, a low state (low voltage), and a logic "1" corresponds to, for example, a high state (high voltage).

[0060] The edge detector 81a receives a drive signal DS33, which is input to the control terminal of the switching element 33. The drive signal DS33 is generated based on a control signal input from the control device 14. The drive signal DS33 is used to switch the switching element 33 between the on and off states. For example, a logic value of "0" in the drive signal DS33 corresponds to the off state of the switching element 33, and a logic value of "1" in the drive signal DS33 corresponds to the on state of the switching element 33.

[0061] The edge detector 81a detects the rising edge of the drive signal DS33. The edge detector 81a outputs a logic "0" when it has not detected the rising edge of the drive signal DS33, and outputs a logic "1" until a predetermined time has elapsed since the detection of the rising edge of the drive signal DS33.

[0062] The edge detector 82a receives the drive signal DS33, which is input to the control terminal of the switching element 33. The edge detector 82a detects the falling edge of the drive signal DS33. The edge detector 82a outputs a logic "0" when it has not detected the falling edge of the drive signal DS33, and outputs a logic "1" until a predetermined time has elapsed since the detection of the falling edge of the drive signal DS33.

[0063] The AND gate 83a receives the output of the detector 80a as well as the drive signal DS33. The AND gate 83a outputs "1" when both the output of the detector 80a and the drive signal DS33 are "1", and outputs "0" otherwise.

[0064] The AND gate 84a receives the output of the classifier 80a as well as the output of the edge detector 81a. The AND gate 84a outputs "1" when both the output of the classifier 80a and the output of the edge detector 81a are "1", and outputs "0" otherwise.

[0065] The AND gate 85a receives the output of the classifier 80a as well as the output of the edge detector 82a. The AND gate 85a outputs "1" when both the output of the classifier 80a and the output of the edge detector 82a are "1", and outputs "0" otherwise.

[0066] The switch 86a outputs zero when the output of the AND circuit 83a is "0", and outputs the conduction loss input from the control device 14 when the output of the AND circuit 83a is "1".

[0067] The switch 87a outputs zero when the output of the AND circuit 84a is "0", and outputs the corrected turn-on loss calculated by the multiplier 71 when the output of the AND circuit 84a is "1".

[0068] Switch 88a outputs zero when the output of AND circuit 85a is "0", and outputs the corrected turn-off loss calculated by multiplier 72 when the output of AND circuit 85a is "1".

[0069] Adder 89a adds the output of switch 86a and the output of switch 87a. Adder 90a adds the output of adder 89a and the output of switch 88a.

[0070] As a result, the converter 22 converts the output of the adder 90a to the loss P of the switching element 33. LOSS33 It is calculated as follows.

[0071] As shown in Figure 4(a), the converter 22 further includes a determination unit 80b, edge detectors 81b and 82b, AND circuits 83b to 85b, switches 86b to 88b, and adders 89b and 90b.

[0072] The Detector 80b outputs a logical "1" when the magnitude of the phase current I is positive, and a logical "0" when the magnitude of the phase current I is negative. A logical "0" corresponds to, for example, a low state (low voltage), and a logical "1" corresponds to, for example, a high state (high voltage).

[0073] The edge detector 81b receives the drive signal DS32, which is input to the control terminal of the switching element 32. The drive signal DS32 is generated based on the control signal input from the control device 14. The drive signal DS32 is used to switch the switching element 32 between the on and off states. For example, a logic value of "0" in the drive signal DS32 corresponds to the off state of the switching element 32, and a logic value of "1" in the drive signal DS32 corresponds to the on state of the switching element 32.

[0074] The edge detector 81b detects the rising edge of the drive signal DS32. The edge detector 81b outputs a logic "0" when it has not detected the rising edge of the drive signal DS32, and outputs a logic "1" until a predetermined time has elapsed since the detection of the rising edge of the drive signal DS32.

[0075] The edge detector 82b receives the drive signal DS32, which is input to the control terminal of the switching element 32. The edge detector 82b detects the falling edge of the drive signal DS32. The edge detector 82b outputs a logic "0" when it has not detected the falling edge of the drive signal DS32, and outputs a logic "1" until a predetermined time has elapsed since the detection of the falling edge of the drive signal DS32.

[0076] The AND gate 83b receives the output of the detector 80b as well as the drive signal DS32. The AND gate 83b outputs "1" when both the output of the detector 80b and the drive signal DS32 are "1", and outputs "0" otherwise.

[0077] The AND gate 84b receives the output of the classifier 80b as well as the output of the edge detector 81b. The AND gate 84b outputs "1" when both the output of the classifier 80b and the output of the edge detector 81b are "1", and outputs "0" otherwise.

[0078] The AND gate 85b receives the output of the classifier 80b as well as the output of the edge detector 82b. The AND gate 85b outputs "1" when both the output of the classifier 80b and the output of the edge detector 82b are "1", and outputs "0" otherwise.

[0079] The switch 86b outputs zero when the output of the AND circuit 83b is "0", and outputs the conduction loss input from the control device 14 when the output of the AND circuit 83b is "1".

[0080] Switch 87b outputs zero when the output of AND circuit 84b is "0", and outputs the corrected turn-on loss calculated by multiplier 71 when the output of AND circuit 84b is "1".

[0081] Switch 88b outputs zero when the output of AND circuit 85b is "0", and outputs the corrected turn-off loss calculated by multiplier 72 when the output of AND circuit 85b is "1".

[0082] Adder 89b adds the output of switch 86b and the output of switch 87b. Adder 90b adds the output of adder 89b and the output of switch 88b.

[0083] As a result, the converter 22 converts the output of the adder 90b to the loss P of the switching element 32. LOSS32 It is calculated as follows.

[0084] As shown in Figure 4(b), the converter 22 further includes a determination unit 80c, edge detectors 81c and 82c, AND circuits 83c to 85c, switches 86c to 88c, and adders 89c and 90c.

[0085] The Detector 80c outputs a logical "1" when the magnitude of the phase current I is negative, and a logical "0" when the magnitude of the phase current I is positive. A logical "0" corresponds to, for example, a low state (low voltage), and a logical "1" corresponds to, for example, a high state (high voltage).

[0086] The edge detector 81c receives a drive signal DS31, which is input to the control terminal of the switching element 31. The drive signal DS31 is generated based on a control signal input from the control device 14. The drive signal DS31 is used to switch the switching element 31 between the on and off states. For example, a logic value of "0" in the drive signal DS31 corresponds to the off state of the switching element 31, and a logic value of "1" in the drive signal DS31 corresponds to the on state of the switching element 31.

[0087] The edge detector 81c detects the rising edge of the drive signal DS31. The edge detector 81c outputs a logic "0" when it has not detected the rising edge of the drive signal DS31, and outputs a logic "1" until a predetermined time has elapsed since the detection of the rising edge of the drive signal DS31.

[0088] The edge detector 82c receives the drive signal DS31, which is input to the control terminal of the switching element 31. The edge detector 82c detects the falling edge of the drive signal DS31. The edge detector 82c outputs a logic "0" when it has not detected the falling edge of the drive signal DS31, and outputs a logic "1" until a predetermined time has elapsed since the detection of the falling edge of the drive signal DS31.

[0089] The AND gate 83c receives the output of the detector 80c as well as the drive signal DS31. The AND gate 83c outputs "1" when both the output of the detector 80c and the drive signal DS31 are "1", and outputs "0" otherwise.

[0090] The AND gate 84c receives the output of the classifier 80c as well as the output of the edge detector 81c. The AND gate 84c outputs "1" when both the output of the classifier 80c and the output of the edge detector 81c are "1", and outputs "0" otherwise.

[0091] The AND gate 85c receives the output of the classifier 80c as well as the output of the edge detector 82c. The AND gate 85c outputs "1" when both the output of the classifier 80c and the output of the edge detector 82c are "1", and outputs "0" otherwise.

[0092] The switch 86c outputs zero when the output of the AND circuit 83c is "0", and outputs the conduction loss input from the control device 14 when the output of the AND circuit 83c is "1".

[0093] Switch 87c outputs zero when the output of AND circuit 84c is "0", and outputs the corrected turn-on loss calculated by multiplier 71 when the output of AND circuit 84c is "1".

[0094] Switch 88c outputs zero when the output of AND circuit 85c is "0", and outputs the corrected turn-off loss calculated by multiplier 72 when the output of AND circuit 85c is "1".

[0095] Adder 89c adds the output of switch 86c and the output of switch 87c. Adder 90c adds the output of adder 89c and the output of switch 88c.

[0096] As a result, the converter 22 converts the output of the adder 90c to the loss P of the switching element 31. LOSS31 It is calculated as follows.

[0097] As shown in Figure 4(b), the converter 22 further includes a determination unit 80d, edge detectors 81d and 82d, AND circuits 83d to 85d, switches 86d to 88d, and adders 89d and 90d.

[0098] The Detector 80d outputs a logical "1" when the magnitude of the phase current I is negative, and a logical "0" when the magnitude of the phase current I is positive. A logical "0" corresponds to, for example, a low state (low voltage), and a logical "1" corresponds to, for example, a high state (high voltage).

[0099] The edge detector 81d receives a drive signal DS34, which is input to the control terminal of the switching element 34. The drive signal DS34 is generated based on a control signal input from the control device 14. The drive signal DS34 is used to switch the switching element 34 between the on and off states. For example, a logic value of "0" in the drive signal DS34 corresponds to the off state of the switching element 34, and a logic value of "1" in the drive signal DS34 corresponds to the on state of the switching element 34.

[0100] The edge detector 81d detects the rising edge of the drive signal DS34. The edge detector 81d outputs a logical "0" when it has not detected the rising edge of the drive signal DS34, and outputs a logical "1" until a predetermined time has elapsed since the detection of the rising edge of the drive signal DS34.

[0101] The edge detector 82d receives the drive signal DS34, which is input to the control terminal of the switching element 34. The edge detector 82d detects the falling edge of the drive signal DS34. The edge detector 82d outputs a logic "0" when it has not detected the falling edge of the drive signal DS34, and outputs a logic "1" until a predetermined time has elapsed since the detection of the falling edge of the drive signal DS34.

[0102] The AND gate 83d receives the output of the detector 80d as well as the drive signal DS34. The AND gate 83d outputs "1" when both the output of the detector 80d and the drive signal DS34 are "1", and outputs "0" otherwise.

[0103] The AND gate 84d receives the output of the classifier 80d as well as the output of the edge detector 81d. The AND gate 84d outputs "1" when both the output of the classifier 80d and the output of the edge detector 81d are "1", and outputs "0" otherwise.

[0104] The AND gate 85d receives the output of the classifier 80d as well as the output of the edge detector 82d. The AND gate 85d outputs "1" when both the output of the classifier 80d and the output of the edge detector 82d are "1", and outputs "0" otherwise.

[0105] The switch 86d outputs zero when the output of the AND circuit 83d is "0", and outputs the conduction loss input from the control device 14 when the output of the AND circuit 83d is "1".

[0106] The switch 87d outputs zero when the output of the AND circuit 84d is "0", and outputs the corrected turn-on loss calculated by the multiplier 71 when the output of the AND circuit 84d is "1".

[0107] When the output of the AND circuit 85d is "0", the switcher 88d outputs zero, and when the output of the AND circuit 85d is "1", it outputs the corrected turn-off loss calculated by the multiplier 72.

[0108] The adder 89d adds the output of the switcher 86d and the output of the switcher 87d. The adder 90d adds the output of the adder 89d and the output of the switcher 88d.

[0109] Thereby, the converter 22 uses the output of the adder 90d as the loss P of the switching element 34 LOSS34 for calculation.

[0110] As described above, each converter 22 calculates each loss P of the switching elements 31 to 34 in accordance with the direction of the phase current I and the switching state of the switching elements 31 to 34 based on the control signal input from the control device 14, the measured value of the phase current I, the conduction loss, the turn-on loss, and the turn-off loss. LOSS31 to P LOSS34 is calculated.

[0111] It should be noted that the conduction loss, turn-on loss, and turn-off loss may be calculated on the side of each converter 22 based on the measured value of the phase current I. However, the conduction loss, turn-on loss, and turn-off loss are commonly used by a plurality of converters 22 of one arm unit 20. Therefore, it is more preferable that the calculation of the conduction loss, turn-on loss, and turn-off loss is performed on the control device 14 side as described above. Thereby, even when each loss P of the switching elements 31 to 34 LOSS31 to P LOSS34 is calculated on each converter 22 side, the increase in calculation load of each converter 22 can be suppressed. For example, by balancing the calculation load of the control device 14 and the calculation load on each converter 22 side, the calculation of each loss P of the switching elements 31 to 34 LOSS31 to P LOSS34 on each converter 22 side can be performed more efficiently.

[0112] Fig. 5 is a block diagram schematically showing a part of the converter. Figure 5 schematically shows an example of the temperature rise calculation unit 100 for each converter 22. Each converter 22 has a temperature rise calculation unit 100. The temperature rise calculation unit 100 calculates the respective losses P of each switching element 31 to 34. LOSS31 ~P LOSS34 Based on this, the temperature rise values ​​ΔTj1 to ΔTj4 of the junction temperature of each switching element 31 to 34 are calculated.

[0113] The temperature rise calculation unit 100 includes an arithmetic unit 102 and adders 104 and 106. The arithmetic unit 102 has information on the thermal resistance and thermal time constant of each switching element 31 to 34, and the loss P of each switching element 31 to 34. LOSS31 ~P LOSS34 Based on this, the temperature rise value of the junction temperature of each switching element 31 to 34 is calculated according to the thermal resistance and thermal time constant.

[0114] The arithmetic unit 102 has, for example, information on multiple thermal resistances and multiple thermal time constants for each switching element 31 to 34. In this example, the arithmetic unit 102 has information on four thermal resistances R1 to R4 and four thermal time constants T1 to T4 for each switching element 31 to 34.

[0115] The arithmetic unit 102 processes the information of the thermal resistance R1 and thermal time constant T1 of the switching element 31, and the loss P of the switching element 31. LOSS31 Based on the above, the temperature rise value ΔTj11 of the junction temperature of the switching element 31 is calculated according to the thermal resistance R1 and thermal time constant T1.

[0116] The arithmetic unit 102 calculates the transient thermal resistance Rth1 using, for example, the heat transfer function (R1 / (1+sT1)) of the first-order lag system, and adds the loss P of the switching element 31 to the transient thermal resistance Rth1. LOSS31 By multiplying by Rth1, the temperature rise value ΔTj11 is calculated. That is, the calculator 102 calculates ΔTj11 = Rth1 × P LOSS31 The temperature rise value ΔTj11 is calculated using the following formula.

[0117] Similarly, the arithmetic unit 102 receives information on the thermal resistance R2 and thermal time constant T2 of the switching element 31, and the loss P of the switching element 31. LOSS31 Based on the above, the temperature rise value ΔTj12 of the junction temperature of the switching element 31 is calculated according to the thermal resistance R2 and thermal time constant T2.

[0118] The arithmetic unit 102 processes the information of the thermal resistance R3 and thermal time constant T3 of the switching element 31, and the loss P of the switching element 31. LOSS31 Based on the above, the temperature rise value ΔTj13 of the junction temperature of the switching element 31 is calculated according to the thermal resistance R3 and thermal time constant T3.

[0119] The arithmetic unit 102 receives information on the thermal resistance R4 and thermal time constant T4 of the switching element 31, and the loss P of the switching element 31. LOSS31 Based on the above, the temperature rise value ΔTj14 of the junction temperature of the switching element 31 is calculated according to the thermal resistance R4 and thermal time constant T4.

[0120] The temperature rise calculation unit 100 calculates the temperature rise value ΔTj1 of the junction temperature of the switching element 31 by adding the temperature rise values ​​ΔTj11 to ΔTj14 calculated by the calculator unit 102 using adders 104 and 106. That is, the temperature rise calculation unit 100 calculates the temperature rise value ΔTj1 of the junction temperature of the switching element 31 using the formula ΔTj1 = ΔTj11 + ΔTj12 + ΔTj13 + ΔTj14.

[0121] Similarly, the arithmetic unit 102 calculates the temperature rise value ΔTj21 of the junction temperature of the switching element 32 according to the thermal resistance R1 and thermal time constant T1, the temperature rise value ΔTj22 of the junction temperature of the switching element 32 according to the thermal resistance R2 and thermal time constant T2, the temperature rise value ΔTj23 of the junction temperature of the switching element 32 according to the thermal resistance R3 and thermal time constant T3, and the temperature rise value ΔTj24 of the junction temperature of the switching element 32 according to the thermal resistance R4 and thermal time constant T4. The temperature rise value calculation unit 100 calculates the temperature rise value ΔTj2 of the junction temperature of the switching element 32 by adding the temperature rise values ​​ΔTj21 to ΔTj24 calculated by the arithmetic unit 102 using adders 104 and 106.

[0122] Similarly, the arithmetic unit 102 calculates the temperature rise value ΔTj31 of the junction temperature of the switching element 33 according to the thermal resistance R1 and thermal time constant T1, the temperature rise value ΔTj32 of the junction temperature of the switching element 33 according to the thermal resistance R2 and thermal time constant T2, the temperature rise value ΔTj33 of the junction temperature of the switching element 33 according to the thermal resistance R3 and thermal time constant T3, and the temperature rise value ΔTj34 of the junction temperature of the switching element 33 according to the thermal resistance R4 and thermal time constant T4. The temperature rise value calculation unit 100 calculates the temperature rise value ΔTj3 of the junction temperature of the switching element 33 by adding the temperature rise values ​​ΔTj31 to ΔTj34 calculated by the arithmetic unit 102 using adders 104 and 106.

[0123] Similarly, the arithmetic unit 102 calculates the temperature rise value ΔTj41 of the junction temperature of the switching element 34 according to the thermal resistance R1 and thermal time constant T1, the temperature rise value ΔTj42 of the junction temperature of the switching element 33 according to the thermal resistance R2 and thermal time constant T2, the temperature rise value ΔTj43 of the junction temperature of the switching element 33 according to the thermal resistance R3 and thermal time constant T3, and the temperature rise value ΔTj44 of the junction temperature of the switching element 33 according to the thermal resistance R4 and thermal time constant T4. The temperature rise value calculation unit 100 calculates the temperature rise value ΔTj4 of the junction temperature of the switching element 33 by adding the temperature rise values ​​ΔTj41 to ΔTj44 calculated by the arithmetic unit 102 using adders 104 and 106.

[0124] As described above, when the temperature rise value calculation unit 100 calculates the temperature rise values ​​ΔTj1 to ΔTj4 of the junction temperature of each switching element 31 to 34, it sequentially calculates each temperature rise value ΔTj11 to ΔTj14, ΔTj21 to ΔTj24, ΔTj31 to ΔTj34, and ΔTj41 to ΔTj44 in a single calculator unit 102.

[0125] The temperature rise calculation unit 100 uses, for example, information on the thermal resistance R1, information on the thermal time constant T1, and the loss P of the switching element 31. LOSS31 By setting this to the arithmetic unit 102, the arithmetic unit 102 is made to calculate the temperature rise value ΔTj11. After this, the temperature rise value calculation unit 100 takes, for example, information on the thermal resistance R2, information on the thermal time constant T2, and the loss P of the switching element 31. LOSS31 By setting this to the arithmetic unit 102, the arithmetic unit 102 is made to calculate the temperature rise value ΔTj12.

[0126] Similarly, the temperature rise calculation unit 100 calculates the temperature rise value using information on thermal resistances R1 to R4, thermal time constants T1 to T4, and the loss P of switching elements 31 to 34. LOSS31 ~P LOSS34 By sequentially setting these values ​​in the arithmetic unit 102, each temperature rise value ΔTj11~ΔTj14, ΔTj21~ΔTj24, ΔTj31~ΔTj34, and ΔTj41~ΔTj44 are sequentially calculated by a single arithmetic unit 102.

[0127] In this example, the temperature rise calculation unit 100 calculates the temperature rise values ​​ΔTj1 to ΔTj4 of the junction temperatures of each switching element 31 to 34 by having the arithmetic unit 102 perform calculations 16 times. In other words, the temperature rise calculation unit 100 performs time sharing of the arithmetic unit 102.

[0128] In this way, the temperature rise calculation unit 100 (multiple converters 22) sequentially calculates multiple temperature rise values ​​ΔTj11~ΔTj14, ΔTj21~ΔTj24, ΔTj31~ΔTj34, and ΔTj41~ΔTj44 corresponding to the information of multiple thermal resistances R1~R4 and multiple thermal time constants T1~T4 for each of the multiple switching elements 31~34 in a single calculator 102. By adding the calculated multiple temperature rise values ​​ΔTj11~ΔTj14, ΔTj21~ΔTj24, ΔTj31~ΔTj34, and ΔTj41~ΔTj44 for each of the multiple switching elements 31~34, the unit calculates the temperature rise values ​​ΔTj1~ΔTj4 for the junction temperature of each of the multiple switching elements 31~34.

[0129] This makes the configuration of the temperature rise calculation unit 100 simpler compared to, for example, a case where multiple calculation units 102 are provided to calculate each of the temperature rise values ​​ΔTj11~ΔTj14, ΔTj21~ΔTj24, ΔTj31~ΔTj34, and ΔTj41~ΔTj44. For example, it is possible to suppress the enlargement of each converter 22 and the increase in manufacturing costs.

[0130] In this example, the arithmetic unit 102 has information on the four thermal resistances R1 to R4 and the four thermal time constants T1 to T4 of each switching element 31 to 34. In other words, in this example, the arithmetic unit 102 has the heat transfer functions of the four first-order lag systems of each switching element 31 to 34.

[0131] However, the number of thermal resistance information entries and thermal time constants is not limited to four, but can be any number. For example, the number of thermal resistance information entries and thermal time constants may be as few as one. In this case, adders 104 and 106 may be omitted. For example, one temperature rise value calculated by the arithmetic unit 102 may be used as the temperature rise value ΔTj1 of the junction temperature of the switching element 31.

[0132] On the other hand, when calculating the temperature rise values ​​ΔTj1 to ΔTj4 for each switching element 31 to 34 based on information from multiple thermal resistances and multiple thermal time constants, as described above, the calculation accuracy of the temperature rise values ​​ΔTj1 to ΔTj4 for each switching element 31 to 34 can be improved compared to, for example, calculating the temperature rise values ​​ΔTj1 to ΔTj4 for each switching element 31 to 34 based on information from one thermal resistance and one thermal time constant.

[0133] Each converter 22 calculates, for example, the maximum value of the temperature rise values ​​ΔTj1 to ΔTj4 of the junction temperatures of each switching element 31 to 34, which are calculated by the temperature rise value calculation unit 100. Each converter 22 inputs the maximum value of the calculated temperature rise value to the control device 14. However, each converter 22 may also input, for example, each of the temperature rise values ​​ΔTj1 to ΔTj4 of each switching element 31 to 34 to the control device 14.

[0134] The control device 14 determines whether the temperature rise value (maximum value) input from each converter 22 is equal to or greater than a determination value. If the temperature rise value of any of the converters 22 is equal to or greater than the determination value, the control device 14 reduces the phase current I to continue the operation of the main circuit unit 12 (the operation of power conversion by the main circuit unit 12).

[0135] The control device 14 acquires, for example, temperature information for each switching element 31-34 when the temperature rise value of any of the converters 22 exceeds a certain threshold. The temperature information for each switching element 31-34 is, for example, the temperature of the cooling water used to cool each switching element 31-34. The temperature information for each switching element 31-34 may also be, for example, the temperature of the case of each switching element 31-34 or the temperature of the air surrounding each switching element 31-34. The temperature information for each switching element 31-34 may be any information relating to the temperature of each switching element 31-34.

[0136] The control device 14 calculates the actual junction temperature Tj of each switching element 31-34 based on the temperature information and temperature rise value of each switching element 31-34. For example, the control device 14 calculates the actual junction temperature Tj by adding the temperature rise value to the temperature information. For example, suppose the temperature rise value input from each converter 22 is 24K, and the temperature information of each switching element 31-34 (the switching element corresponding to the maximum value) is 50°C. In this case, the actual junction temperature Tj can be calculated to be 74°C.

[0137] The control device 14 calculates the limit value of the temperature rise based on the calculated actual junction temperature Tj. For example, suppose the actual junction temperature Tj is 50°C and the upper limit of the junction temperature for each switching element 31-34 is 150°C. In this case, the limit value of the temperature rise is 100°C (100K). For example, suppose the actual junction temperature Tj is 20°C and the upper limit of the junction temperature for each switching element 31-34 is 150°C. In this case, the limit value of the temperature rise is 130°C (100K). Thus, the limit value of the temperature rise is calculated, for example, by subtracting the actual junction temperature Tj from the upper limit of the junction temperature for each switching element 31-34.

[0138] If the temperature rise value of any of the converters 22 exceeds a certain threshold, the control device 14 reduces the phase current I so that, for example, the temperature rise values ​​ΔTj1 to ΔTj4 of each switching element 31 to 34 do not exceed a limit value, thereby continuing the operation of the main circuit section 12.

[0139] This allows, for example, setting an appropriate phase current I according to the limit value of the temperature rise. For example, it can prevent the phase current I from being excessively reduced. For example, it can raise the junction temperature of each switching element 31 to 34 to near the upper limit while preventing the temperature rise values ​​ΔTj1 to ΔTj4 of each switching element 31 to 34 from exceeding the limit value.

[0140] Even after reducing the phase current I, the control device 14 stops the operation of the main circuit unit 12 (the operation of power conversion by the main circuit unit 12) if the temperature rise value of any of the converters 22 is greater than or equal to a determination value. The control device 14 may also stop the operation of the main circuit unit 12 even after reducing the phase current I if the actual junction temperature Tj of any of the converters 22 is greater than or equal to a determination value. This helps to suppress failures of the switching elements 31 to 34 of each converter 22.

[0141] Even after reducing the phase current I, the control device 14 may, if the temperature rise value of any of the converters 22 exceeds a certain threshold, switch the converter 22 whose temperature rise value is determined to be above the threshold to a bypass state. Furthermore, the control device 14 may stop the operation of the main circuit unit 12 when the number of converters 22 in the bypass state among the multiple converters 22 connected in series in one arm unit 20 exceeds a predetermined number. This makes it possible to suppress failures of the switching elements 31 to 34 of each converter 22 while improving the continuity of operation of the main circuit unit 12.

[0142] As described above, in the power converter 10 according to this embodiment, multiple converters 22 determine the direction of the phase current I and the respective losses P of the multiple switching elements 31 to 34 based on the control signal, the measured value of the phase current I, conduction loss, turn-on loss, and turn-off loss of the multiple switching elements 31 to 34. LOSS31 ~P LOSS34 The loss P of each of the multiple switching elements 31 to 34 is calculated and calculated. LOSS31 ~P LOSS34 Based on this, the temperature rise values ​​ΔTj1 to ΔTj4 of the junction temperatures of each of the multiple switching elements 31 to 34 are calculated.

[0143] In this way, by performing the calculation of temperature rise values ​​ΔTj1 to ΔTj4 on each converter 22, it is possible to more accurately calculate the junction temperatures of multiple switching elements 31 to 34 of multiple converters 22 connected in series, while suppressing an increase in the computational load of the control device 14.

[0144] The above embodiment shows an example of calculating the junction temperatures of multiple switching elements 31 to 34. However, it is not limited to this, and the junction temperatures of multiple rectifier elements 41 to 44 can also be calculated by performing similar calculations for multiple rectifier elements 41 to 44.

[0145] In each of the above embodiments, an MMC type power converter is used in the main circuit section 12. The main circuit section 12 is not limited to the MMC type; for example, it may be a power converter of another type in which multiple converters 22 are connected in series, such as an MV (Medium Voltage) type power converter.

[0146] This embodiment includes the following aspects. (Note 1) A main circuit unit having multiple converters connected in series, which converts power through the operation of the multiple converters, A control device that controls the operation of the main circuit section, Equipped with, Each of the aforementioned plurality of converters is A pair of connection terminals, Multiple switching elements, A charge storage element connected in parallel to the plurality of switching elements, It has, and is connected in series via the pair of connection terminals, The control device generates a control signal for controlling the switching of the multiple switching elements of the multiple converters, and controls the operation of the main circuit by inputting the control signal to the multiple converters, and also inputs a measured value of the current flowing through the multiple converters to each of the multiple converters. A power conversion device comprising the plurality of converters that calculates the direction of the current flowing through the plurality of converters and the loss of each of the plurality of switching elements in accordance with the switching of the plurality of switching elements, based on the control signal, the measured value of the current, the conduction loss of the plurality of switching elements, the turn-on loss of the plurality of switching elements, and the turn-off loss of the plurality of switching elements, and calculates the temperature rise value of the junction temperature of each of the plurality of switching elements based on the loss of each of the plurality of switching elements.

[0147] (Note 2) The power conversion device according to Appendix 1, wherein the control device calculates the conduction loss of the plurality of switching elements, the turn-on loss of the plurality of switching elements, and the turn-off loss of the plurality of switching elements based on the measured value of the current, and inputs the calculated conduction loss of the plurality of switching elements, the turn-on loss of the plurality of switching elements, and the turn-off loss of the plurality of switching elements to each of the plurality of converters.

[0148] (Note 3) The plurality of converters each have a calculator that performs calculations of the temperature rise value according to the thermal resistance and thermal time constant, based on the thermal resistance information and thermal time constant information of the plurality of switching elements and the losses of the plurality of switching elements. The aforementioned arithmetic unit has a plurality of thermal resistance information and a plurality of thermal time constant information, The power conversion device according to Appendix 1 or 2, wherein the plurality of converters sequentially calculates a plurality of temperature rise values ​​corresponding to a plurality of thermal resistance information and a plurality of thermal time constant information for each of the plurality of switching elements using one calculator, and calculates the temperature rise value of the junction temperature of each of the plurality of switching elements by adding the calculated plurality of temperature rise values ​​for each of the plurality of switching elements.

[0149] (Note 4) The aforementioned plurality of converters input the temperature rise value of the junction temperature of each of the plurality of switching elements to the control device. The power conversion device according to any one of the appendices 1 to 3, wherein the control device reduces the current flowing through the plurality of converters when the temperature rise value of any of the plurality of converters exceeds a determination value, thereby continuing the operation of the main circuit section.

[0150] (Note 5) The power conversion device described in Appendix 4, wherein, when the temperature rise value of any of the plurality of converters is greater than or equal to the determination value, the control device calculates the actual junction temperature of the plurality of switching elements based on the temperature information of the plurality of switching elements and the temperature rise value, calculates a limit value for the temperature rise value based on the actual junction temperature, and reduces the current flowing through the plurality of converters so that the temperature rise value of the plurality of switching elements does not exceed the limit value, thereby continuing the operation of the main circuit section.

[0151] (Note 6) The power conversion device according to Appendix 4 or 5, wherein the control device stops the operation of the main circuit section if, even after reducing the current flowing through the plurality of converters, the temperature rise value of any of the plurality of converters is greater than or equal to the determination value.

[0152] The plurality of converters are capable of switching between an output state in which the voltage of the charge storage element is output between the pair of connection terminals, a bypass state in which the pair of connection terminals are conductive, and a stopped state in which the plurality of switching elements are turned off, by switching the plurality of switching elements. The power conversion device according to Appendix 4 or 5, wherein, even after reducing the current flowing through the plurality of converters, if the temperature rise value of any of the plurality of converters is greater than or equal to the determination value, the control device switches the converter whose temperature rise value is determined to be greater than or equal to the determination value to the bypass state, and when the number of converters in the bypass state exceeds a predetermined number, the operation of the main circuit section is stopped.

[0153] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of symbols]

[0154] 2...Power system, 4...Transformer, 10...Power converter, 12...Main circuit section, 14...Control device, 20...Arm section, 22...Converter, 31~34...Switching element, 41~44...Rectifier element, 50...Charge storage element, 51, 52...Connection terminals, 60...Absolute value calculator, 61...Voltage calculator, 62...Turn-on energy calculator, 63...Turn-off energy calculator, 64~66...Multiplier, 70~72...Multiplier, 80a~80d...Determinant, 81a~81d, 82a~82d...Edge detector, 83a~83d, 84a~84d, 85a~85d...AND circuit, 86a~86d, 87a~87d, 88a~88d...Switch, 89a-89d, 90a-90d...Adder, 100...Temperature rise calculation unit, 102...Calculator, 104, 106...Adder

Claims

1. A main circuit unit having multiple converters connected in series, which converts power through the operation of the multiple converters, A control device that controls the operation of the main circuit section, Equipped with, Each of the aforementioned plurality of converters is A pair of connection terminals, Multiple switching elements, A charge storage element connected in parallel to the plurality of switching elements, It has, and is connected in series via the pair of connection terminals, The control device generates a control signal for controlling the switching of the multiple switching elements of the multiple converters, and controls the operation of the main circuit by inputting the control signal to the multiple converters, and also inputs a measured value of the current flowing through the multiple converters to each of the multiple converters. A power conversion device comprising the plurality of converters that calculates the direction of the current flowing through the plurality of converters and the loss of each of the plurality of switching elements in accordance with the switching of the plurality of switching elements, based on the control signal, the measured value of the current, the conduction loss of the plurality of switching elements, the turn-on loss of the plurality of switching elements, and the turn-off loss of the plurality of switching elements, and calculates the temperature rise value of the junction temperature of each of the plurality of switching elements based on the loss of each of the plurality of switching elements.

2. The power conversion device according to claim 1, wherein the control device calculates the conduction loss of the plurality of switching elements, the turn-on loss of the plurality of switching elements, and the turn-off loss of the plurality of switching elements based on the measured value of the current, and inputs the calculated conduction loss of the plurality of switching elements, the turn-on loss of the plurality of switching elements, and the turn-off loss of the plurality of switching elements to each of the plurality of converters.

3. The plurality of converters each have a calculator that performs calculations of the temperature rise value according to the thermal resistance and thermal time constant, based on the thermal resistance information and thermal time constant information of the plurality of switching elements and the losses of the plurality of switching elements. The aforementioned arithmetic unit has a plurality of thermal resistance information and a plurality of thermal time constant information, The power conversion device according to claim 1, wherein the plurality of converters sequentially cause one calculator to calculate a plurality of temperature rise values ​​corresponding to a plurality of thermal resistance information and a plurality of thermal time constant information for each of the plurality of switching elements, and calculates the temperature rise value of the junction temperature of each of the plurality of switching elements by adding the calculated plurality of temperature rise values ​​for each of the plurality of switching elements.

4. The aforementioned plurality of converters input the temperature rise value of the junction temperature of each of the plurality of switching elements to the control device. The power conversion device according to claim 1, wherein the control device reduces the current flowing through the plurality of converters when the temperature rise value of any of the plurality of converters exceeds a determination value, thereby continuing the operation of the main circuit section.

5. The power conversion device according to claim 4, wherein, when the temperature rise value of any of the plurality of converters is greater than or equal to the determination value, the control device calculates the actual junction temperature of the plurality of switching elements based on the temperature information of the plurality of switching elements and the temperature rise value, calculates a limit value for the temperature rise value based on the actual junction temperature, and reduces the current flowing through the plurality of converters so that the temperature rise value of the plurality of switching elements does not exceed the limit value, thereby continuing the operation of the main circuit section.

6. The power conversion device according to claim 4, wherein the control device, after reducing the current flowing through the plurality of converters, stops the operation of the main circuit section if the temperature rise value of any of the plurality of converters is greater than or equal to the determination value.

7. The plurality of converters are capable of switching between an output state in which the voltage of the charge storage element is output between the pair of connection terminals, a bypass state in which the pair of connection terminals are conductive, and a stopped state in which the plurality of switching elements are turned off, by switching the plurality of switching elements. The power conversion device according to claim 4, wherein, even after reducing the current flowing through the plurality of converters, if the temperature rise value of any of the plurality of converters is greater than or equal to the determination value, the control device switches the converter whose temperature rise value is determined to be greater than or equal to the determination value to the bypass state, and when the number of converters in the bypass state exceeds a predetermined number, the operation of the main circuit unit is stopped.

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