Power conversion device and aircraft

Abstract

This power conversion device comprises a first power converter (1007), a second power converter (1008), and a control device (10000). The first power converter (1007) receives the input of a DC voltage to generate a voltage supplied to a load. The second power converter (1008) generates an input voltage to the first power converter (1007) from the DC voltage of a power supply. The control device (10000) controls the second power converter (1008). The control device (10000) determines an input voltage to the first power converter (1007) on the basis of position data indicating the height, latitude, and longitude of the power conversion device and data of the failure rate of the first power converter (1007) attributable to neutrons. The control device (10000) controls the second power converter (1008) so as to generate the determined input voltage.

Description

[Technical Field]

[0001] The present disclosure relates to a power conversion device and an aircraft. [Background technology]

[0002] U.S. Patent Application Publication No. 2019 / 152617 (Patent Document 1) and Patent No. 6877660 (Patent Document 2) disclose aircraft that obtains propulsion force through the rotation of a propeller connected to an electric motor. Such aircraft are equipped with a power conversion device that supplies power to the electric motor to drive the electric motor.

[0003] One of the causes of failure in power conversion equipment installed in aircraft is random failure of semiconductor elements due to neutrons from cosmic rays. Since the amount of neutrons increases with altitude, the failure rate of semiconductor elements also increases as the aircraft altitude increases.

[0004] It is known that the failure rate of semiconductor elements due to neutrons is correlated with the voltage applied to the semiconductor elements. Therefore, in Patent Documents 1 and 2, when the altitude of the aircraft exceeds a threshold, the input voltage of the power conversion device is reduced to suppress failure of the power conversion device. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] U.S. Patent Application Publication No. 2019 / 152617 [Patent Document 2] Patent No. 6877660 Summary of the Invention [Problem to be solved by the invention]

[0006] The amount of neutrons not only depends on the altitude but also varies depending on the latitude and longitude. Therefore, in order to reliably prevent the power conversion device from being damaged by neutrons, it is necessary to take into account the altitude, latitude, and longitude of the environment in which the power conversion device is placed when controlling the input voltage of the power conversion device.

[0007] The present disclosure has been made to solve such problems, and an object of the present disclosure is to provide a power conversion device that can improve reliability against failures caused by neutrons. [Means for solving the problem]

[0008] In one aspect of the present disclosure, there is provided a power conversion device connected between a power source and a load, the power conversion device including a first power converter, a second power converter, and a control device. The first power converter receives a DC voltage input and generates a voltage to be supplied to the load. The second power converter generates an input voltage for the first power converter from the DC voltage of the power source. The control device controls the second power converter. The control device determines the input voltage of the first power converter based on location data indicating the altitude, latitude, and longitude of the power conversion device and data related to a neutron-induced failure rate of the first power converter. The control device controls the second power converter to generate the determined input voltage. [Effects of the Invention]

[0009] According to the present disclosure, it is possible to provide a power conversion device that can improve reliability against failures caused by neutrons. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram showing a first configuration example of an aircraft power system. FIG. [Figure 2] FIG. 4 is a schematic diagram showing a second configuration example of an aircraft power system. [Figure 3] FIG. 10 is a schematic diagram showing a third example configuration of an aircraft power system. [Figure 4]FIG. 10 is a schematic diagram showing a fourth example configuration of an aircraft power system. [Figure 5] FIG. 10 is a schematic diagram showing a fifth example configuration of an aircraft power system. [Figure 6] FIG. 10 is a schematic diagram showing a sixth example configuration of an aircraft power system. [Figure 7] FIG. 2 is a diagram illustrating a first circuit configuration example of a DC / DC converter. [Figure 8] FIG. 2 is a diagram illustrating a configuration example of a first semiconductor element. [Figure 9] FIG. 10 is a diagram illustrating a second circuit configuration example of a DC / DC converter. [Figure 10] FIG. 10 is a diagram illustrating a third circuit configuration example of a DC / DC converter. [Figure 11] FIG. 10 is a diagram illustrating a fourth circuit configuration example of a DC / DC converter. [Figure 12] FIG. 2 is a diagram illustrating a first circuit configuration example of a DC / AC converter. [Figure 13] FIG. 4 is a diagram illustrating a configuration example of a second semiconductor element. [Figure 14] FIG. 10 is a diagram illustrating a second circuit configuration example of a DC / AC converter. [Figure 15] FIG. 10 is a diagram illustrating a third circuit configuration example of a DC / AC converter. [Figure 16] FIG. 2 is a schematic configuration diagram of a first power semiconductor module. [Figure 17] 1A and 1B are diagrams illustrating the mechanism by which neutrons are generated, which may cause accidental failures in semiconductor elements. [Figure 18] 10A and 10B are diagrams illustrating an example of an experiment on the failure rate of a semiconductor element. [Figure 19] FIG. 10 is a diagram showing a change in leakage current when neutrons are irradiated. [Figure 20] FIG. 10 is a diagram showing the relationship between the voltage applied to the second semiconductor element and the FIT of each second semiconductor element. [Figure 21] FIG. 1 is a diagram illustrating the correlation between the dielectric strength voltage and FIT of a semiconductor element. [Figure 22] FIG. 10 is a diagram illustrating the correlation between the junction temperature and FIT of the second semiconductor element. [Figure 23] 10 is a diagram illustrating the FIT of each of a second semiconductor element, a second power semiconductor module, and a three-phase two-level inverter circuit. FIG. [Figure 24] FIG. 1 is a diagram showing a first example of a neutron ratio calculated based on altitude, latitude, and longitude data when an aircraft flew on an arbitrary date. [Figure 25] FIG. 10 is a diagram showing a second example of a neutron ratio calculated based on altitude, latitude, and longitude data when an aircraft flew on an arbitrary date. [Figure 26] FIG. 1 is a diagram illustrating the correlation between the FIT and the neutron ratio of a three-phase two-level inverter circuit. [Figure 27] FIG. 10 is a diagram showing a first example of the neutron ratio, first FIT data of the three-phase two-level inverter circuit, and input voltage when the aircraft is flown on an arbitrary date. [Figure 28] FIG. 10 is a diagram showing a second example of the neutron ratio, second FIT data of the three-phase two-level inverter circuit, and input voltage when the aircraft is flown on an arbitrary date. [Figure 29] FIG. 10 is a diagram showing a comparison between first FIT data and second FIT data. [Figure 30] FIG. 1 is a diagram illustrating an example of adjustment of an input voltage of a three-phase two-level inverter circuit. [Figure 31] 1 is a diagram illustrating an example of the configuration of a power system having a function of adjusting the input voltage of a power converter. [Figure 32] FIG. 2 is a diagram illustrating a hardware configuration of a control device. [Figure 33] 10 is a flowchart illustrating an example of a procedure for a process of determining an input voltage of each power converter in a power system. [Figure 34] 10 is a flowchart illustrating another example of a processing procedure for determining an input voltage of each power converter in a power system. [Figure 35] FIG. 10 is a diagram showing an example of a change in FIT when the input voltage of a DC / AC converter in a propulsion system is adjusted. [Figure 36] FIG. 1 is a diagram showing an example of the change in FIT due to the change in outside air temperature during an aircraft flight. [Figure 37]FIG. 10 is a diagram showing an example of a change in FIT when the input voltage of a DC / AC converter of a propulsion system is adjusted in accordance with the outside air temperature. [Figure 38] FIG. 10 is a diagram illustrating a configuration example of a power system according to a second embodiment. [Figure 39] 10 is a flowchart illustrating an example of a procedure for a process of determining an input voltage of each power converter in a power system. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0012] Embodiment 1 <Example of aircraft power system configuration> First, with reference to FIGS. 1 to 6, a configuration example of an aircraft power system to which a power conversion device according to a first embodiment of the present disclosure is applied will be described.

[0013] (First configuration example) 1 is a schematic diagram showing a first configuration example of an aircraft power system. The aircraft may be, for example, a manned or unmanned airplane, a helicopter, a drone, etc. In the following description, an airplane will be exemplified as the aircraft 1000.

[0014] As shown in FIG. 1, the first configuration example of the power system includes a power source 2000, a propulsion system 2001, a propulsion system motor 1001, and a control device 10000.

[0015] The power supply 2000 generates a DC voltage. Specifically, the power supply 2000 includes a generator 1003 and an AC / DC converter 1004. The generator 1003 generates an AC voltage. The AC / DC converter 1004 converts the AC voltage generated by the generator 1003 into a DC voltage. The AC / DC converter 1004 supplies the generated DC voltage to the propulsion system 2001.

[0016] Propulsion system 2001 supplies power generated by power supply 2000 to propulsion motor 1001. Specifically, propulsion system 2001 includes DC / DC converter 1008 and DC / AC converter 1007. DC / DC converter 1008 changes the DC voltage supplied from power supply 2000. DC / DC converter 1008 is configured to control the input voltage to DC / AC converter 1007. DC / AC converter 1007 converts the transformed DC voltage into AC voltage and supplies the converted AC voltage to propulsion motor 1001. DC / AC converter 1007 corresponds to an embodiment of a "first power converter." DC / DC converter 1008 corresponds to an embodiment of a "second power converter."

[0017] The control device 10000 controls the AC / DC converter 1004, the DC / DC converter 1008, and the DC / AC converter 1007. Sensor information indicating the detected values ​​of various sensors provided in the AC / DC converter 1004, the DC / DC converter 1008, and the DC / AC converter 1007 is input to the control device 10000. The sensor information includes the detected values ​​of the current, voltage, and temperature of each power converter, as well as an abnormality detection signal.

[0018] Although not shown in the drawings, the control device 10000 may be configured to further control the generator 1003 and the propulsion motor 1001. Furthermore, a configuration may be adopted in which a plurality of control devices 10000 are provided in the power system, and the plurality of control devices 10000 control the power source 2000, the propulsion system 2001, and the propulsion motor 1001, respectively, by exchanging signals with each other.

[0019] (Second configuration example) 2 is a schematic diagram showing a second example of the configuration of an aircraft power system. The second example of the configuration of the power system has the same basic configuration as the first example of the configuration shown in FIG. 1, but differs in the configuration of the power source 2000.

[0020] 2, in the second configuration example, the power supply 2000 further includes a battery 1005 and a DC / DC converter 1006 in addition to the generator 1003 and the AC / DC converter 1004. The DC / DC converter 1006 changes the DC voltage of the battery 1005 and supplies it to the propulsion system 2001. In other words, the power supply 2000 is configured to generate a DC voltage from the power generated by the generator 1003 and the power of the battery 1005. Note that in the configuration examples shown in FIG. 3 and subsequent figures, the battery 1005 and the DC / DC converter 1006 are not shown.

[0021] (Third configuration example) Fig. 3 is a schematic diagram showing a third example of the configuration of an aircraft power system. The third example of the configuration of the power system differs from the first example of the configuration shown in Fig. 1 in that it has an electrical equipment system 2002 and an electrical equipment 1002a instead of the propulsion system 2001 and the propulsion motor 1001.

[0022] 3, the electrical component system 2002 supplies the power generated by the power supply 2000 to the electrical component 1002a. The electrical component 1002a is an electrical component that is driven by AC voltage, such as a pump, an actuator, a light, a display, or a control panel.

[0023] Specifically, the electrical component system 2002 includes a DC / DC converter 1008b and a DC / AC converter 1009. The DC / DC converter 1008b changes the DC voltage supplied from the power supply 2000. The DC / DC converter 1008b is configured to control the input voltage to the DC / AC converter 1009. The DC / AC converter 1009 converts the transformed DC voltage into an AC voltage and supplies the converted AC voltage to the electrical component 1002a. The electrical component 1002a is driven by the AC voltage supplied from the electrical component system 2002. The DC / AC converter 1009 corresponds to an example of a "first power converter." The DC / DC converter 1008b corresponds to an example of a "second power converter."

[0024] (Fourth configuration example) Fig. 4 is a schematic diagram showing a fourth configuration example of an aircraft power system. The fourth configuration example of the power system differs from the first configuration example shown in Fig. 1 in that it has an electrical equipment system 2003 and electrical equipment 1002b instead of the propulsion system 2001 and motor 1001.

[0025] 4, the electrical component system 2003 supplies the power generated by the power supply 2000 to the electrical component 1002b. The electrical component 1002b is an electrical component that is driven by a DC voltage.

[0026] Specifically, the electrical component system 2003 includes a DC / DC converter 1008c and a DC / DC converter 1010. The DC / DC converter 1008c changes the voltage of the DC voltage supplied from the power supply 2000. The DC / DC converter 1008c is configured to control the input voltage to the DC / DC converter 1010. The DC / DC converter 1010 changes the voltage of the transformed DC voltage and supplies it to the electrical component 1002b. The electrical component 1002b is driven by the DC voltage supplied from the electrical component system 2003. The DC / DC converter 1010 corresponds to an example of a "first power converter." The DC / DC converter 1008c corresponds to an example of a "second power converter."

[0027] (Fifth configuration example) Figure 5 is a schematic diagram showing a fifth configuration example of an aircraft power system. The fifth configuration example of the power system is obtained by adding electrical equipment systems 2002 and 2003 and electrical equipment 1002a and 1002b to the first configuration example shown in Figure 1. The electrical equipment systems 2002 and 2003 and the electrical equipment 1002a and 1002b are the same as those shown in Figures 3 and 4, so their explanation will be omitted.

[0028] 5, a power supply 2000 is shared as a power source for the propulsion system 2001 and the electrical equipment systems 2002 and 2003. The propulsion system 2001 and the electrical equipment systems 2002 and 2003 convert the DC voltage supplied from the power supply 2000 into a voltage for driving the corresponding loads (propulsion motor 1001, electrical equipment 1002a, 1002b) and supply the voltage to the loads.

[0029] (Sixth Configuration Example) FIG. 6 is a schematic configuration diagram showing a sixth configuration example of the power system of an aircraft. The sixth configuration example of the power system is obtained by adding DC / DC converters 1008b and 1010, a DC / AC converter 1009, and electrical components 1002a and 1002b to the configuration example shown in FIG. 1. Since the DC / DC converters 1008b and 1010, the DC / AC converter 1009, and the electrical components 1002a and 1002b are the same as those shown in FIGS. 3 and 4, the description thereof is omitted.

[0030] In the composite system shown in FIG. 6, in the electrical component system, a DC / DC converter for adjusting the input voltages of the DC / AC converter 1009 and the DC / DC converter 1010 is shared.

[0031] Note that the aircraft 1000 does not necessarily include all of the systems 2001 to 2003, and at least one of the systems 2001 to 2003 can be appropriately selected according to the load mounted on the aircraft 1000. In addition, a battery may be further connected to the DC bus connecting the power converters. Also, circuit breakers (CBs) not shown are arranged within each system and between the systems.

[0032] <Configuration Example of DC / DC Converter> Next, a circuit configuration example of the DC / DC converter included in the above-described power system will be described with reference to FIGS. 7 to 11. Hereinafter, the DC / DC converter 1008 of the propulsion system 2001 will be described as an example.

[0033] FIG. 7 is a diagram showing a first circuit configuration example of the DC / DC converter 1008. As shown in FIG. 7, the DC / DC converter 1008 is constituted by a non-insulated step-down chopper circuit 5000. The non-insulated step-down chopper circuit 5000 steps down the DC voltage input from the input positive bus 3p and the input negative bus 3n, and outputs the stepped-down DC voltage as an output voltage Vout to the output positive bus 5p and the output negative bus 5n.

[0034] The non-insulated step-down chopper circuit 5000 includes first semiconductor elements 1a and 1b which are switching elements, a reactor 2, and smoothing capacitors 7 and 8.

[0035] The first semiconductor elements 1a and 1b are connected in series between the input positive bus 3p and the input negative bus 3n. The first semiconductor element 1a constitutes the upper arm, and the first semiconductor element 1b constitutes the lower arm. The first semiconductor elements 1a and 1b are collectively referred to as the "first semiconductor elements 1."

[0036] Reactor 2 is connected between the connection node of first semiconductor elements 1a and 1b and output positive bus 5p. Smoothing capacitor 7 is connected between input positive bus 3p and input negative bus 3n. Smoothing capacitor 8 is connected between output positive bus 5p and output positive bus 5n. Each of smoothing capacitors 7 and 8 smoothes the DC voltage including the ripple voltage.

[0037] In the non-isolated step-down chopper circuit 5000, step-down control of the input voltage is ideally performed by adjusting the impedance of the reactor 2 and the switching duty ratio (ratio of on-period to off-period) of the first semiconductor element 1a (upper arm). However, the output voltage Vout may fluctuate due to the impedance of the wiring and the first semiconductor element 1, and the influence of a power converter or load connected between the output positive bus 5p and the output negative bus 5n. For this reason, the output voltage Vout, the current flowing through the reactor 2, the inter-terminal voltage and temperature of the first semiconductor element 1, etc. are detected by sensors (not shown), and these detected values ​​are provided to the control device 10000 as sensor information. The control device 10000 feeds back the sensor information to control the switching operation of the first semiconductor element 1a.

[0038] Fig. 8 is a diagram showing a configuration example of the first semiconductor element 1 included in the DC / DC converter 1008 shown in Fig. 7. As shown in Fig. 8, the first semiconductor element 1 has a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) 1m, which is a switching element, and a diode 1d. The diode 1d is a freewheeling diode (FWD) and is connected in anti-parallel to the switching element. When the switching element is a MOSFET, the diode 1d can be configured by a parasitic diode (body diode) of the MOSFET.

[0039] When a large current flows through each arm of the non-isolated step-down chopper circuit 5000, it is common to configure each arm by connecting multiple first semiconductor elements 1 in parallel to divide the current. Even when a large current does not flow through each arm, multiple first semiconductor elements 1 may be connected in parallel to reduce conduction loss of the first semiconductor elements 1.

[0040] Since the MOSFET has a parasitic diode, a separate freewheeling diode is required. S Although it is not necessary to connect in anti-parallel to the FET, a configuration may be adopted in which a diode 1s is connected in anti-parallel to the first semiconductor element 1, as shown in Fig. 8. The number of diodes 1s may be one or more.

[0041] When the non-isolated step-down chopper circuit 5000 does not perform bidirectional voltage conversion, the first semiconductor element 1b (lower arm) performs only rectification, and therefore does not need a switching function. Therefore, the first semiconductor element 1b may be configured with only a diode.

[0042] As described above, when multiple first semiconductor elements 1 are connected in parallel to form each arm, the non-isolated step-down chopper circuit 5000 may be formed using a power semiconductor module in which multiple first semiconductor elements 1 are mounted in a single package.

[0043] Fig. 9 is a diagram showing a second circuit configuration example of the DC / DC converter 1008. As shown in Fig. 9, the DC / DC converter 1008 is configured by a non-insulated step-down chopper circuit 5000b. The non-insulated step-down chopper circuit 5000b differs from the non-insulated step-down chopper circuit 5000 shown in Fig. 7 in that each of the upper arm and the lower arm has a plurality of first semiconductor elements 1 connected in parallel.

[0044] 9, each of the upper arm and the lower arm has a first power semiconductor module 6 having two parallel-connected first semiconductor elements 1. Note that the number of first semiconductor elements 1 included in the first power semiconductor module 6 may be three or more.

[0045] Fig. 10 is a diagram showing a third circuit configuration example of the DC / DC converter 1008. As shown in Fig. 10, the DC / DC converter 1008 is configured by a non-insulated step-down chopper circuit 5000c. The non-insulated step-down chopper circuit 5000c differs from the non-insulated step-down chopper circuit 5000 shown in Fig. 7 in that each of the upper arm and the lower arm has a plurality of first power semiconductor modules 6 connected in parallel.

[0046] 10, each of the upper arm and the lower arm has two first power semiconductor modules 6 connected in parallel. Each first power semiconductor module 6 has two first semiconductor elements 1 connected in parallel. Note that the number of first power semiconductor modules 6 included in each arm and the number of first semiconductor elements 1 included in each first power semiconductor module 6 may both be three or more.

[0047] Although Figs. 7, 9 and 10 show examples of circuit configurations of non-isolated step-down chopper circuits having half-bridge circuits, non-isolated step-down chopper circuits having full-bridge circuits may also be used. blood pressure reduction A chopper circuit may be used to configure the DC / DC conversion circuit 1008. Also, instead of the non-insulated step-down chopper circuit, an isolated step-down chopper circuit using a transformer or a capacitor may be used.

[0048] Also, in FIGS. 7, 9, and 10, a non-insulated step-down chopper circuit has been exemplified assuming that the DC / DC converter circuit 1008 is a step-down circuit. However, when the DC / DC converter circuit 1008 is a step-up circuit, a non-insulated step-up chopper circuit as shown in FIG. 11 can be adopted.

[0049] FIG. 11 is a diagram showing a fourth circuit configuration example of the DC / DC converter 1008. As shown in FIG. 11, the DC / DC converter 1008 is constituted by a non-insulated step-up chopper circuit 5000d. The difference between the non-insulated step-up chopper circuit 5000d and the non-insulated step-down chopper circuit 5000 shown in FIG. 7 is that a reactor 2 is connected between the input positive bus 3p and the connection node of the first semiconductor elements 1a and 1b.

[0050] In the non-insulated step-up chopper circuit 5000d, the step-up control for the input voltage is ideally executed by adjusting the impedance of the reactor 2 and the switching duty ratio of the first semiconductor element 1b (lower arm). However, since the output voltage fluctuates in the same manner as in the non-insulated step-down chopper circuit 5000, the control device 10000 feeds back the sensor information to the control of the switching operation of the first semiconductor element 1b.

[0051] <Configuration Example of DC / AC Converter> Next, with reference to FIGS. 12 to 15, a circuit configuration example of the DC / AC converter included in the above-described power system will be described. Hereinafter, the DC / AC converter 1007 of the propulsion system 2001 will be described as an example.

[0052] FIG. 12 is a diagram showing a first circuit configuration example of the DC / AC converter 1007. As shown in FIG. 12, the DC / AC converter 1007 is constituted by a three-phase two-level inverter circuit 5001. The three-phase two-level inverter circuit 5001 converts the DC voltage input from the input positive bus 9p and the input negative bus 9n into an AC voltage of three phases (U phase, V phase, W phase) and outputs it to the AC output terminals 11u, 11v, 11w.

[0053] The three-phase two-level inverter circuit 5001 includes second semiconductor elements 10a to 10f, which are switching elements, and a smoothing capacitor 13.

[0054] The second semiconductor elements 10a and 10b are connected in series between the input positive bus 9p and the input negative bus 9n. The connection node of the second semiconductor elements 10a and 10b is connected to the U-phase output terminal 11u. The second semiconductor elements 10c and 10d are connected in series between the input positive bus 9p and the input negative bus 9n. The connection node of the second semiconductor elements 10c and 10d is connected to the V-phase output terminal 11v. The second semiconductor elements 10e and 10f are connected in series between the input positive bus 9p and the input negative bus 9n. The connection node of the second semiconductor elements 10e and 10f is connected to the W-phase output terminal 11w. The second semiconductor elements 10a and 10b form a U-phase leg, the second semiconductor elements 10c and 10d form a V-phase leg, and the second semiconductor elements 10e and 10f form a W-phase leg. The second semiconductor elements 10a to 10f are collectively referred to as "second semiconductor elements 10."

[0055] Smoothing capacitor 13 is connected between input positive bus 9p and input negative bus 9n, and smoothes the DC voltage including the ripple voltage.

[0056] The three-phase two-level inverter circuit 5001 is provided with sensors (not shown) for detecting currents flowing through the U-phase output terminal 11u, the V-phase output terminal 11v, and the W-phase output terminal 11w, inter-phase voltages between the U-phase output terminal 11u, the V-phase output terminal 11v, and the W-phase output terminal 11w, and inter-terminal voltages and temperatures of each second semiconductor element 10. The detection values ​​of these sensors are provided to the control device 10000 as sensor information. The control device 10000 feeds back the sensor information to control the switching operation of the second semiconductor element 10.

[0057] Fig. 13 is a diagram showing a configuration example of the second semiconductor element 10 included in the DC / AC converter 1007 shown in Fig. 12. As shown in Fig. 13, the second semiconductor element 10 has a MOSFET 10m, which is a switching element, and a diode 10d. The diode 10d is a freewheeling diode, and is connected in anti-parallel to the switching element. When the switching element is a MOSFET, the diode 10d can be configured by a parasitic diode of the MOSFET.

[0058] When a large current flows through each arm of each leg of the three-phase two-level inverter circuit 5001, it is common to configure each arm by connecting a plurality of second semiconductor elements 10 in parallel to divide the current. Even when a large current does not flow through each arm, a plurality of second semiconductor elements 10 may be connected in parallel to reduce the conduction loss of the second semiconductor elements 10.

[0059] Since the MOSFET has a parasitic diode, a separate freewheeling diode is required. S Although it is not necessary to connect in anti-parallel to the FET, a configuration may be adopted in which a diode 10s is connected in anti-parallel to the second semiconductor element 10 as shown in Fig. 13. Furthermore, the number of diodes 10s may be one or more.

[0060] As with the non-isolated step-down chopper circuit 5000 described above, when multiple second semiconductor elements 10 are connected in parallel to form each arm, the three-phase two-level inverter circuit 5001 may be formed using a power semiconductor module in which multiple second semiconductor elements 10 are mounted in one package.

[0061] Fig. 14 is a diagram showing a second circuit configuration example of the DC / AC converter 1007. As shown in Fig. 14, the DC / AC converter 1007 is configured by a three-phase two-level inverter circuit 5001b. The three-phase two-level inverter circuit 5001b differs from the three-phase two-level inverter circuit 5001 shown in Fig. 12 in that each of the upper arm and the lower arm has a plurality of second semiconductor elements 10 connected in parallel.

[0062] 14, each of the upper arm and the lower arm has a second power semiconductor module 14 having two second semiconductor elements 10 connected in parallel. Note that the number of second semiconductor elements 10 included in the second power semiconductor module 14 may be three or more.

[0063] Fig. 15 is a diagram showing a third circuit configuration example of the DC / AC converter 1007. As shown in Fig. 15, the DC / AC converter 1007 is configured by a three-phase two-level inverter circuit 5001c. The three-phase two-level inverter circuit 5001c differs from the three-phase two-level inverter circuit 5001 shown in Fig. 12 in that each of the upper arm and the lower arm has a plurality of second power semiconductor modules 14 connected in parallel.

[0064] 15, each of the upper arm and the lower arm has two second power semiconductor modules 14 connected in parallel. Although not shown, each second power semiconductor module 14 has a plurality of second semiconductor elements 10 connected in parallel. Note that the number of second power semiconductor modules 14 included in each arm may be three or more.

[0065] The three-phase two-level inverter circuits 5001, 5001b, and 5001c may be configured using discrete semiconductor elements. The DC / AC converter 1007 is not limited to a three-phase two-level inverter circuit as long as it has a DC / AC conversion function. The DC / AC converter 1007 may be a multilevel circuit, such as a three-phase three-level inverter circuit, a three-phase five-level inverter circuit, or a three-phase gradation inverter circuit.

[0066] Up to this point, examples of circuit configurations of power converters included in a power system have been described using DC / DC converter 1008 and DC / AC converter 1007 as examples, but DC / DC converters 1008b, 1008c, and 1010 can have a circuit configuration similar to that of DC / DC converter 1008. DC / AC converter 1009 can have a circuit configuration similar to that of DC / AC converter 1007. However, the rated voltage and rated current of the semiconductor elements that make up the power converters differ depending on the capacity of the load.

[0067] In addition, in each of the semiconductor elements 1 and 10, a MOSFET is used as the switching element, and the parasitic diode of the MOSFET is used as the freewheeling diode, or the freewheeling diode is connected in anti-parallel to the switching element. However, the switching element may be a Si (silicon)-MOSFET, a SiC (silicon carbide)-MOSFET, a Si-IGBT (Insulated Gate Bipolar Transistor), a SiC-IGBT, a GaN-HEMT (High Electron Mobility Transistor), or the like. The freewheeling diode may be a Si-diode, a SiC-diode, a SiC-SBD (Schottky Barrier Diode), or the like. Note that when an IGBT is used as the switching element, it is necessary to connect the freewheeling diode in anti-parallel to the switching element. However, when an RC-IGBT is used as the switching element, it is not necessary to connect the freewheeling diode to the switching element. Alternatively, a high-voltage semiconductor element using GaO (gallium oxide) or diamond may be used.

[0068] <Configuration example of a power semiconductor module> Next, a configuration example of the power semiconductor modules 6, 14 will be described with reference to Fig. 16. Below, the first power semiconductor module 6 will be described as an example.

[0069] Fig. 16 is a schematic configuration diagram of the first power semiconductor module 6. As shown in Fig. 16, the first power semiconductor module 6 includes a first semiconductor element 1, bonding materials 17 and 21, a front surface electrode 20, an insulating material 19, a back surface electrode 18, a base plate 16, and a water cooling device 23a.

[0070] The first semiconductor element 1 is bonded to the front surface electrode 20 by a bonding material 21. The bonding materials 17, 21 are, for example, paste made of Ag (silver) or Cu (copper), solder, or the like. The front surface electrode 20 and the back surface electrode 18 are formed from Cu, Al (aluminum), or the like. The front surface electrode 20 and the back surface electrode 18 are attached to an insulating material 19 by a brazing material or the like. The insulating material 19 is formed from Si3N4 (silicon nitride), Al2O3 (alumina), AlN (aluminum nitride), a resin material, or the like.

[0071] The back electrode 18 is bonded to the base plate 16 by a bonding material 21. The base plate 16 is made of Al-SiC (aluminum-silicon carbide), Mg-SiC (magnesium-silicon carbide), Al, Cu, an Al alloy, a Cu alloy, or the like. The base plate 16 is bonded to a water cooling device 23a by screws, caulking, or the like. A cooling pipe 23b is formed in the water cooling device 23a.

[0072] 16, a water-cooling device 23a is illustrated as the cooling device, but an air-cooling device with fins may also be used. Also, a configuration may be adopted in which grease or a heat spreader is sandwiched between the base plate 16 and the water-cooling device 23a to diffuse heat dissipation.

[0073] Furthermore, the configuration of the power semiconductor module is not limited to the example of Figure 16, and it is possible to adopt a configuration in which the base plate 16 and the water cooling device 23a are directly joined, or a configuration in which the first semiconductor element 1 is cooled from both sides, etc.

[0074] <Random failure of semiconductor devices> Next, a random failure of a semiconductor element will be described with reference to Fig. 17. A random failure of the second semiconductor element 10 will be representatively described below.

[0075] FIG. 17 is a diagram illustrating the mechanism by which neutrons are generated, which can be a cause of accidental failures in semiconductor devices.

[0076] As shown in FIG. 17, cosmic rays 30 exist in space 27 and are constantly raining down on the Earth. When the cosmic rays 30 enter the Earth's atmosphere 28, they collide with the atmosphere, generating neutrons 31. These neutrons 31 may collide with a second semiconductor element 10 operating on the Earth's surface 29 or mounted on an aircraft flying in the sky. If a high voltage is applied to the second semiconductor element 10, the collision with the neutrons 31 may cause the second semiconductor element 10 to fail. This phenomenon is called SEB (Single Event Burnout).

[0077] The failure rate of a semiconductor element due to SEB can be determined experimentally. Fig. 18 is a diagram illustrating an experimental example of the failure rate of a semiconductor element. As shown in Fig. 18, a plurality of (e.g., three) second semiconductor elements 10 are connected in parallel between the positive and negative electrodes of a DC power supply 33. A voltage dividing resistor 35 and a leakage measurement resistor 36 are connected in series with each second semiconductor element 10 between the positive and negative electrodes of the DC power supply 33.

[0078] When the second semiconductor element 10 includes a MOSFET, a DC power supply 33 is electrically connected between the drain and source of the MOSFET. The drain and source of the MOSFET are kept in a high resistance state by short-circuiting the gate and source of the MOSFET or by applying a negative bias between the gate and source.

[0079] At this time, the DC voltage of the DC power supply 33 is divided by the second semiconductor element 10, the voltage-dividing resistor 35, and the resistor 36. A relationship is established between the drain-source resistance of the second semiconductor element 10, the voltage-dividing resistor 35, and the resistor 36 such that the resistance value of the resistor 36 is sufficiently smaller than the resistance value of the voltage-dividing resistor 35, and the resistance value of the voltage-dividing resistor 35 is sufficiently smaller than the resistance value of the drain-source resistance of the second semiconductor element 10. Therefore, most of the DC voltage of the DC power supply 33 is applied to the second semiconductor element 10. On the other hand, if the second semiconductor element 10 fails and the resistance value of the drain-source resistance decreases, most of the DC voltage of the DC power supply 33 will be applied to the voltage-dividing resistor 35.

[0080] The voltage across the resistor 36 is detected by a data logger (not shown). The leakage current can be calculated from the detected value of the voltage across the resistor 36 and the resistance value of the resistor 36. When the second semiconductor element 10 is normal, the leakage current is small, and when the second semiconductor element 10 fails, the leakage current increases.

[0081] In the experiment, neutrons 31 are irradiated from an accelerator 32 toward the second semiconductor element 10 while a DC voltage is applied to the second semiconductor element 10 from a DC power supply 33. When the neutrons 31 collide with the second semiconductor element 10, SEB occurs stochastically, causing the second semiconductor element 10 to fail.

[0082] Fig. 19 is a diagram showing changes in leakage current when irradiated with neutrons 31. Three leakage current waveforms 37 are shown in Fig. 19. These three waveforms 37 represent the leakage currents flowing through the three second semiconductor elements 10 shown in Fig. 18, respectively.

[0083] 19, when a DC voltage is applied to the second semiconductor elements 10, the leakage current is small at the start of neutron irradiation. When the second semiconductor elements 10 are continuously irradiated with neutrons, SEB occurs in each second semiconductor element 10. Because SEB occurs accidentally, the times at which SEB occurs differ among the three second semiconductor elements 10.

[0084] From the total number of the second semiconductor devices 10 used in the experiment, the failure times of each of the second semiconductor devices 10, and the number of the failed second semiconductor devices 10, the failure rate of the second semiconductor devices 10 can be calculated. Note that the failure rate is generally calculated using an index called "FIT (Failure-in-Time)". FIT is a unit representing the failure rate and indicates how many failures occur within 10 to the 9th power of time. For example, "1 FIT" means the probability that one failure occurs during 10 to the 9th power of time. The lower the FIT, the lower the failure rate.

[0085] In the experiment shown in FIG. 18, the number of neutrons irradiated per unit time and per unit area is larger than the number of neutrons per unit time and per unit area actually pouring in the natural world. Therefore, the experiment is substantially an accelerated test. Thus, the FIT in the environment where the second semiconductor device 10 is placed is corrected using the number of neutrons per unit time and per unit area in that environment.

[0086] The FIT of each second semiconductor device 10 increases as the voltage applied to the second semiconductor device 10 increases. FIG. 20 is a diagram showing the relationship between the voltage applied to the second semiconductor device 10 and the FIT of each second semiconductor device 10. The horizontal axis of FIG. 20 indicates the applied voltage, and the vertical axis indicates the FIT.

[0087] In FIG. 20, a FIT curve 38 of the second semiconductor device 10 is shown. According to this FIT curve 38, the FIT when the voltage V1 is applied is Y1, and the FIT when the voltage V2 is applied is Y2. If V1 < V2, then Y1 < Y2. From this, it can be understood that the FIT of the second semiconductor device 10 can be controlled by adjusting the voltage applied to the second semiconductor device 10.

[0088] It is known that FIT correlates with the dielectric strength voltage of a semiconductor element, and that the higher the dielectric strength voltage of a semiconductor element, the lower the FIT. Figure 21 is a diagram illustrating the correlation between the dielectric strength voltage of a semiconductor element and FIT. Figure 21 shows a first FIT curve 38 that shows the relationship between the applied voltage and FIT of a second semiconductor element 10, and a second FIT curve 40 that shows the relationship between the applied voltage and FIT of a high dielectric strength voltage semiconductor element 39 that has a higher dielectric strength voltage than the second semiconductor element 10.

[0089] Comparing the first FIT curve 38 and the second FIT curve 40, the FIT of the second semiconductor element 10 when voltage V1 is applied is Y1, whereas the FIT of the high dielectric strength voltage semiconductor element 39 is W1, which is lower than Y1. Note that the correlation between the dielectric strength voltage and FIT of the semiconductor elements shown in Fig. 21 remains unchanged regardless of the altitude at which the semiconductor elements are placed.

[0090] 21, it is assumed that the second semiconductor element 10 and the high dielectric strength semiconductor element 39 are both MOSFETs and have the same element area. The only difference between the second semiconductor element 10 and the high dielectric strength semiconductor element 39 is the thickness or concentration of the drift layer that maintains the withstand voltage of the MOSFET.

[0091] When the element structures of multiple MOSFETs with different dielectric strength voltages differ significantly, the electric field distributions within the MOSFETs may differ significantly. As a result, the first FIT curve 38 and the second FIT curve 40 may intersect or their vertical relationships may be reversed. For example, when the second semiconductor element 10 and the high dielectric strength voltage semiconductor element 39 are made of different semiconductor materials, the first FIT curve 38 and the second FIT curve 40 may intersect or their vertical relationships may be reversed. In anticipation of these cases, the above-described experiment (see FIG. 19) should be performed for each semiconductor element to obtain an FIT curve, thereby confirming the relationship between the applied voltage and the FIT of the semiconductor element.

[0092] Furthermore, FIT is also correlated with the temperature (junction temperature) of the semiconductor element, and the higher the junction temperature, the lower the FIT tends to be. FIG. 22 is a diagram illustrating the correlation between the junction temperature of the second semiconductor element 10 and FIT. FIG. 22 shows FIT curves 41 to 43 that indicate the relationship between the junction temperature of the second semiconductor element 10 and FIT. The third FIT curve 41 is the FIT curve when the junction temperature is A [°C]. The fourth FIT curve 42 is the FIT curve when the junction temperature is B [°C]. The fifth FIT curve 43 is the FIT curve when the junction temperature is C [°C]. Note that A [°C] <B[℃]<C[℃]とする。

[0093] According to Fig. 21, when a voltage V1 is applied to the second semiconductor element 10, the FIT is YA when the junction temperature is A [°C], the FIT is YB when the junction temperature is B [°C], and the FIT is YC when the junction temperature is C [°C]. <YB<YAとなっている。

[0094] Generally, as the junction temperature of a semiconductor element increases, the dielectric strength voltage increases, and as the junction temperature decreases, the dielectric strength voltage decreases. Therefore, in Figure 22, when the junction temperature is high, the dielectric strength voltage increases, and so the FIT decreases. Conversely, when the junction temperature is low, the dielectric strength voltage decreases, and so the FIT increases.

[0095] This correlation between the junction temperature of a semiconductor element and FIT remains constant regardless of the altitude at which the semiconductor element is located. However, since the correlation between junction temperature and FIT is not necessarily proportional, the relationship between the applied voltage of the semiconductor element and FIT should be confirmed by changing the junction temperature in the above-mentioned experiment (see Figure 19) and obtaining an FIT curve that depends on the junction temperature for each semiconductor element.

[0096] Next, the FIT of the second power semiconductor module 14 and the three-phase two-level inverter circuit 5001 on which the second semiconductor element 10 is mounted will be described.

[0097] 23 is a diagram illustrating the FIT of each of the second semiconductor element 10, the second power semiconductor module 14, and the three-phase two-level inverter circuit 5001. In FIG. 23, a first FIT curve 38 is the FIT curve for one second semiconductor element 10. A sixth FIT curve 44 is the FIT curve for one second power semiconductor module 14. A seventh FIT curve 45 is the FIT curve for one three-phase two-level inverter circuit 5001.

[0098] The FIT of the second power semiconductor module 14 on which a plurality of second semiconductor elements 10 are mounted increases in proportion to the number of mounted second semiconductor elements 10. Specifically, the sixth FIT curve 44 of each second power semiconductor module 14 is calculated by the following formula (1) using the first FIT curve 38 of each second semiconductor element 10. 6th FIT curve 44 = 1st FIT curve 38 × number of mounted second semiconductor elements 10 (1) However, in equation (1), the sixth FIT curve 44 and the first FIT curve 38 are both FIT curves at an altitude of 0 m above sea level.

[0099] The FIT of the three-phase two-level inverter circuit 5001 configured with a plurality of second power semiconductor modules 14 increases in proportion to the number of mounted second power semiconductor modules 14. Specifically, the seventh FIT curve 45 of each three-phase two-level inverter circuit 5001 is calculated by the following equation (2) using the sixth FIT curve 44 of each second power semiconductor module 14. The seventh FIT curve 45 = the sixth FIT curve 44 × the number of second power semiconductor modules 14 mounted (2) However, in equation (2), the seventh FIT curve 45 and the sixth FIT curve 44 are both FIT curves at an altitude of 0 m above sea level.

[0100] According to the above formulas (1) and (2), the 1st FIT curve 38, the 6th FIT curve 44, and the 7th FIT curve 45 have the relationship as shown in FIG. 23. For example, when a voltage V1 is applied to each of the second semiconductor element 10, the second power semiconductor module 14, and the bus of the three-phase 2-level inverter circuit 5001, among the FIT XC of the second semiconductor element 10, the FIT XB of the second power semiconductor module 14, and the FIT XA of the three-phase 2-level inverter circuit 5001, the relationship XC < XB < XA holds.

[0101] Note that both the correlation between the number of the second semiconductor elements 10 mounted in the second power semiconductor module 14 and the FIT, and the correlation between the number of the second power semiconductor modules 14 mounted in the three-phase 2-level inverter circuit 5001 and the FIT are invariant regardless of altitude.

[0102] In the FIT calculation described above, an example was shown in which the 7th FIT curve 45 of the three-phase 2-level inverter circuit 5001 was calculated based on the 1st FIT curve 38 of each second semiconductor element 10. However, the FIT of each of the DC / DC converters 1008, 1008b, 1008c, 1010 and the DC / AC converters 1007, 1009 can be calculated using the FIT curves of the semiconductor elements mounted in the power converter.

[0103] <Neutron altitude, latitude, and longitude dependence> Next, the altitude, latitude, and longitude dependence of neutrons will be described.

[0104] The number of neutrons per unit time and per unit area [number / (hour·area)] varies depending on the altitude, latitude, and longitude of the location where the neutrons are located. In the following description, the number of neutrons per unit time and per unit area will also be simply referred to as the "number of neutrons". The number of neutrons corresponds to the neutron quantity.

[0105] The neutron spectrum, which depends on altitude, latitude, and longitude, can be calculated using, for example, EXPACS (Excel-based Program for calculating Atmospheric Cosmic-ray Spectrum). EXPACS is a program that can calculate the cosmic ray flux and its energy at any point and time in the atmosphere. The neutron spectrum is data that represents the number of neutrons present per unit time and unit area across a wide energy band. From the neutron spectrum obtained by EXPACS, data can be obtained that shows the dependence of the number of neutrons with a given energy on altitude, latitude, and longitude.

[0106] 24 is a diagram showing a first example of a neutron ratio 49 calculated based on altitude data 46, latitude data 47, and longitude data 48 when an aircraft flew on an arbitrary date. In this specification, "neutron ratio" means the ratio of the number of neutrons per unit time and unit area calculated from altitude, latitude, and longitude to the number of neutrons per unit time and unit area at a point 0 m above sea level at an arbitrary coordinate.

[0107] 24, time t0 indicates the time before the aircraft takes off, time t1 indicates the time during which the aircraft is ascending, time t2 indicates the time when the aircraft reaches its maximum altitude, time t3 indicates the time during which the aircraft is cruising at its maximum altitude, time t4 indicates the time before the aircraft descends, and time t5 indicates the time after the aircraft lands. During the period from before the aircraft takes off (time t0) to after the aircraft lands (time t5), altitude data 46 indicating the aircraft's altitude varies within a range of 0 to 12,000 m. Meanwhile, latitude data 47 indicating the aircraft's latitude and longitude data 48 indicating the aircraft's longitude are both constant.

[0108] The neutron ratio 49 is calculated based on the number of neutrons calculated from the altitude data 46, latitude data 47, and longitude data 48 at each time. From FIG. 24, it can be seen that the neutron ratio 49 changes within a range of 0 to 200, following the change in the altitude data 46. Note that the greater the number of neutrons, the greater the neutron ratio 49. In this way, the neutron ratio 49 changes significantly depending on the altitude of the aircraft.

[0109] Fig. 25 is a diagram showing a second example of a neutron ratio 49 calculated based on altitude data 46, latitude data 47, and longitude data 48 when an aircraft flew on an arbitrary date. The second example shown in Fig. 25 differs from the first example shown in Fig. 24 in that in addition to the altitude data 46, the latitude data 47 and longitude data 48 have changed.

[0110] It can be seen that the neutron ratio 49 varies within the range of 0 to 200, following not only the changes in the altitude data 46 but also the latitude data 47 and longitude data 48. In this way, the neutron ratio 49 varies greatly depending on the altitude, latitude, and longitude of the aircraft.

[0111] The neutron ratio 49 is directly linked to the failure rate of the semiconductor device. The relationship between the neutron ratio 49 and the failure rate will be explained below using a three-phase two-level inverter circuit 5001 as an example.

[0112] Equation (2) showing the seventh FIT curve 45 of the three-phase two-level inverter circuit 5001 can be transformed into equation (3) when the neutron ratio 49 is taken into consideration. 7th FIT curve 45 = 6th FIT curve 44 × number of second power semiconductor modules 14 × neutron ratio 49 (3) However, in equation (3), the sixth FIT curve 44 is the FIT curve at an altitude of 0 m above sea level.

[0113] FIG. 26 is a diagram for explaining the correlation between the FIT of the three-phase two-level inverter circuit 5001 and the neutron ratio 49. In FIG. 26, the 8th FIT curve 51 is the FIT curve of the three-phase two-level inverter circuit 5001 per unit when the neutron ratio 49 is the first value. The 9th FIT curve 52 is the FIT curve of the three-phase two-level inverter circuit 5001 per unit when the neutron ratio 49 is the second value larger than the first value.

[0114] According to FIG. 26, when the input voltage 50 to the three-phase two-level inverter circuit 5001 is Va, the FIT when the neutron ratio 49 is the second value is ZA, and the FIT when the neutron ratio 49 is the first value is ZB. Note that ZB < ZA. That is, when the input voltages are equal, the larger the neutron ratio 49, the higher the FIT of the three-phase two-level inverter circuit 5001.

[0115] FIG. 27 is a diagram showing a first example of the neutron ratio 49, the first FIT data 53 of the three-phase two-level inverter circuit 5001, and the input voltage 50 when the aircraft flies on an arbitrary date. The neutron ratio 49 shown in FIG. 27 is Figure 24 calculated based on the altitude data 46, the latitude data 47, and the longitude data 48 shown in. The first FIT data 53 is calculated using the neutron ratio 49 and Equation (3).

[0116] In FIG. 27, the input voltage 50 to the three-phase two-level inverter circuit 5001 indicates the voltage applied between the input positive bus 9p and the input negative bus 9n of the three-phase two-level inverter circuit 5001, and is maintained at a constant voltage Va.

[0117] FIG. 28 is a diagram showing a second example of the neutron ratio 四十二, the second FIT data 54 of the three-phase two-level inverter circuit 5001, and the input voltage 50 when the aircraft flies on an arbitrary date. The neutron ratio 49 shown in FIG. 28 is Figure 25The second FIT data 54 was calculated using the neutron ratio 49 and equation (3).

[0118] In FIG. 28, the input voltage 50 to the three-phase two-level inverter circuit 5001 indicates the voltage applied between the input positive bus 9p and the input negative bus 9n of the three-phase two-level inverter circuit 5001, and is maintained at a constant voltage Va.

[0119] 27 and 28 show that when the neutron ratio 49 changes while the input voltage 50 is kept at a constant voltage Va, the first FIT data 53 and the second FIT data 54 also change in accordance with the change in the neutron ratio 49. As the neutron ratio 49 increases, the FIT increases, and as the neutron ratio 49 decreases, the FIT decreases.

[0120] Fig. 29 is a diagram showing a comparison between the first FIT data 53 and the second FIT data 54. As shown in Fig. 29, the change in FIT of the three-phase two-level inverter circuit 5001 can be obtained more accurately when the altitude data 46, latitude data 47, and longitude data 48 are taken into consideration than when only the altitude data 46 is taken into consideration.

[0121] Here, let us assume that the safety design value of the three-phase two-level inverter circuit 5001 is set to 1 FIT or less. When the input voltage 50 is a constant voltage Va, the first FIT data 53 and the second FIT data 54 are both 1 FIT or less at time t0 and time t5, but remain higher than 1 FIT while the aircraft is in flight. This indicates that the three-phase two-level inverter circuit 5001 does not satisfy the safety design value, and reliability of the SEB is reduced.

[0122] Therefore, in this embodiment, when the aircraft route is known in advance, the neutron ratio 49 is calculated using altitude data 46, latitude data 47, and longitude data 48 of the route, and the input voltage 50 of the three-phase two-level inverter circuit 5001 is adjusted based on the calculated neutron ratio 49.

[0123] Fig. 30 is a diagram showing an example of adjustment of the input voltage of the three-phase two-level inverter circuit 5001. Fig. 30 is obtained by adding third FIT data 56 and input voltage 55 to Fig. 28.

[0124] As shown in Figure 30, during aircraft flight, the input voltage 55 of the three-phase two-level inverter circuit 5001 is maintained at a voltage Vb that is lower than the voltage Va. The third FIT data 56 shows the change in FIT when the neutron ratio 49 changes while the input voltage 55 is kept at a constant voltage Vb. By lowering the input voltage 55, the third FIT data 56 is kept below 1 FIT during aircraft flight. Therefore, the reliability of the three-phase two-level inverter circuit 5001 against SEB is guaranteed during aircraft flight.

[0125] Next, adjustment of the input voltage of the power converter in the power system of aircraft 1000 shown in FIGS. 1 to 6 will be described.

[0126] In the first configuration example (see FIG. 1) and the second configuration example (see FIG. 2) of the power system, the input voltage of DC / AC converter 1007 included in propulsion system 2001 is adjusted according to neutron ratio 49 calculated from route altitude data 46, latitude data 47, and longitude data 48. In other words, the output voltage of DC / DC converter 1008 is adjusted.

[0127] In the third configuration example of the power system (see FIG. 3), the input voltage of the DC / AC converter 1009 included in the electrical equipment system 2002 is adjusted according to the neutron ratio 49. In other words, the output voltage of the DC / DC converter 1008b is adjusted.

[0128] In the fourth configuration example of the power system (see FIG. 4), the input voltage of the DC / DC converter 1010 included in the electrical equipment system 2003 is adjusted according to the neutron ratio 49. In other words, the output voltage of the DC / DC converter 1008c is adjusted.

[0129] In the fifth configuration example (see FIG. 5) and the sixth configuration example (see FIG. 6) of the power system, the input voltages of DC / AC converters 1007 and 1009 and DC / DC converter 1010 are adjusted according to neutron ratio 49. That is, the output voltages of DC / DC converters 1008, 1008b, and 1008c are adjusted.

[0130] In any of the configuration examples described above, if the route of the aircraft 1000 is determined before the flight, the input voltage of each power converter can be determined in advance from the route altitude data 46, latitude data 47, and longitude data 48, as shown in Figure 28.

[0131] On the other hand, if the aircraft's route is not known in advance, it is necessary to acquire altitude data 46, latitude data 47, and longitude data 48 during the flight of aircraft 1000 and determine the input voltage of each power converter based on the acquired data.

[0132] Fig. 31 is a diagram showing an example of the configuration of a power system having a function of adjusting the input voltage of a power converter. The example of the configuration of the power system shown in Fig. 31 is obtained by adding a GPS (Global Positioning System) 61 and an altimeter 62 to the fifth example of the configuration of the power system shown in Fig. 5. The power supply 2000, propulsion system 2001, electrical equipment systems 2002 and 2003, propulsion motor 1001, and electrical equipment 1002a and 1002b are the same as those shown in Fig. 5, and therefore their explanation will be omitted.

[0133] The GPS 61 measures the latitude and longitude of the current position of the aircraft 1000 while the aircraft 1000 is flying, and outputs the measurement values ​​to the control device 10000. The altimeter 62 measures the altitude of the current position of the aircraft 1000, and outputs the measurement values ​​to the control device 10000. Note that if the altitude of the aircraft 1000 can be calculated from the measurement values ​​of the GPS 61, the altimeter 62 is not necessary.

[0134] The control device 10000 includes a calculator 63 and a control unit 65. The calculator 63 calculates the neutron ratio at the current position of the aircraft 1000 based on measurements input from the GPS 61 and the altimeter 62. The calculator 63 determines the input voltage of each power converter using the calculated neutron ratio, and outputs the determined input voltage to the control unit 65. The control unit 65 uses the input voltage received from the calculator 63 as a target value and adjusts the input voltage of each power converter to reach the target value.

[0135] Fig. 32 is a diagram showing the hardware configuration of the control device 10000. As shown in Fig. 29, the control device 10000 includes a CPU (Central Processing Unit) 70, a RAM (Random Access Memory) 71, a ROM (Read Only Memory) 72, an I / F (Interface) device 73, and a storage device 74. The CPU 70, RAM 71, ROM 72, I / F device 73, and storage device 74 exchange various data via a communication bus 75.

[0136] The CPU 70 loads a program stored in the ROM 72 into the RAM 71 and executes it. The program stored in the ROM 72 describes the processes to be executed by the control device 10000.

[0137] The I / F device 73 receives measurement data of various measurements including those from the GPS 61 and the altimeter 62. The I / F device 73 also transmits control signals to each power converter for controlling the power converter.

[0138] The memory device 74 is a storage for storing various types of information, and stores information about each power converter. The information about each power converter includes information about the power semiconductor modules and semiconductor elements that make up the power converter. The memory device 74 also stores information about the failure rates of the power converters, power semiconductor modules, and semiconductor elements. This information about the failure rates includes information about the FIT curves shown in Figures 20 to 23. The memory device 74 is, for example, a hard disk drive (HDD) or a solid state drive (SSD).

[0139] 33 is a flowchart showing an example of a processing procedure for determining the input voltage of each power converter in the power system. The series of processing shown in this flowchart is executed by control device 10000 at predetermined intervals while aircraft 1000 is in flight.

[0140] As shown in FIG. 32, first, the control device 10000 acquires measurement data of the altitude of the aircraft 1000 measured by the altimeter 62, and also acquires measurement data of the latitude and longitude of the current position of the aircraft 1000 measured by the GPS 61 (step S10).

[0141] Next, the control device 10000 calculates the neutron ratio at the current position of the aircraft 1000 using the measurement data of the altitude, latitude, and longitude of the aircraft 1000 (step S20). In S20, the control device 10000 calculates the number of neutrons at the current position of the aircraft 1000 based on the acquired measurement data of the altitude, latitude, and longitude. Then, the calculator 63 calculates the ratio of the number of neutrons at the current position of the aircraft 1000 to the number of neutrons at a point 0 m above sea level as the neutron ratio.

[0142] Next, the control device 10000 corrects the FIT curve acquired in advance for each power converter using the calculated neutron ratio (step S30). In S30, the control device 10000 corrects the FIT curve for each power converter by substituting the neutron ratio calculated in S20 into the above-mentioned formula (3).

[0143] Next, the control device 10000 calculates an input voltage for each power converter using the corrected FIT curve (step S40). In S40, the control device 10000 calculates, from the corrected FIT curve, an input voltage at which the FIT can satisfy a safety design value (for example, 1 FIT or less).

[0144] Finally, the control device 10000 sets the calculated input voltage as a target value and adjusts the input voltage of each power converter so that the input voltage becomes the target value (step S50). For example, the control device 10000 controls the output voltage of the DC / DC converter 1008 so that the input voltage of the DC / AC converter 1007 included in the propulsion system 2001 becomes the target value.

[0145] 34 is a flowchart showing another example of the processing procedure for determining the input voltage of each power converter in the power system. The series of processes shown in this flowchart is executed by control device 10000 at predetermined intervals while aircraft 1000 is in flight.

[0146] In the flowchart shown in FIG. 34, the processes of S20 to S40 in the flowchart shown in FIG. 33 are replaced with the process of S60.

[0147] When the control device 10000 acquires measurement data of the altitude, latitude, and longitude of the aircraft 1000 in S10, it calculates the input voltage based on the measurement data by referencing a map created in advance for each power converter (step S60). The map defines the relationship between the altitude, longitude, and latitude and the input voltage of the power converter. The map can be created by correcting the FIT curve using the neutron ratio calculated from the altitude, longitude, and latitude, and then determining the input voltage at which the FIT satisfies the safety design value on the corrected FIT curve. The map is created in advance and stored in the storage device 74 of the control device 10000 (see FIG. 32).

[0148] The control device 10000 sets the calculated input voltage as a target value and adjusts the input voltage of each power converter so that the input voltage reaches the target value (step S50).

[0149] 35 is a diagram showing an example of a transition of FIT when adjusting the input voltage of DC / AC converter 1007 in propulsion system 2001. The adjustment of the input voltage of DC / AC converter 1007 shown in FIG. 35 is achieved by controlling the output voltage of DC / DC converter 1008.

[0150] Note that Fig. 35 shows neutron ratio 49 calculated based on altitude data 46, latitude data 47, and longitude data 48 shown in Fig. 25, as well as second FIT data 54 calculated using neutron ratio 49 and input voltage 50 (constant voltage Va). Fig. 35 also shows third FIT data 56 calculated using neutron ratio 49 and input voltage 55 (constant voltage Vb).

[0151] In S20 of Fig. 33, the control device 10000 calculates the neutron ratio using measurement data of the altitude, latitude, and longitude of the aircraft 1000 for each predetermined control period. Then, in S30 of Fig. 33, the computer 63 corrects the FIT curve of the DC / AC converter 1007, which has been acquired in advance, using the calculated neutron ratio. In S30, the control device 10000 corrects the FIT curve of the DC / AC converter 1007 by substituting the neutron ratio calculated in S20 into the above-mentioned equation (3). In this way, the correlation between the input voltage of the DC / AC converter 1007 and the FIT is obtained.

[0152] Next, in S40 of Fig. 33, the control device 10000 uses the corrected FIT curve to calculate the input voltage when the FIT becomes the safe design value (1 FIT or less). In S50 of Fig. 33, the control device 10000 controls the output voltage of the DC / DC converter 1008 so that it matches the calculated input voltage.

[0153] 35 shows the input voltage 57 of the DC / AC converter 1007, which fluctuates due to the control of the DC / DC converter 1008, and the fourth FIT data 58 of the DC / AC converter 1007 corresponding to the input voltage 57. The input voltage 57 of the DC / AC converter 1007 changes in accordance with fluctuations in the neutron ratio 49. Specifically, the higher the neutron ratio 49, the lower the input voltage 57. As a result, the fourth FIT data 58 fluctuates near the upper limit of the safety design value (1 FIT or less) while the aircraft 1000 is flying.

[0154] As described above, according to the power conversion device of embodiment 1, the input voltage of the DC / AC converter 10007 can be adjusted using an FIT curve based on the neutron ratio calculated from the altitude, latitude, and longitude of the aircraft 1000, thereby ensuring the reliability of the SEB of the DC / AC converter 1007 while the aircraft 1000 is flying.

[0155] The propulsion motor 1001 of the aircraft 1000 generally requires high output when the aircraft 1000 ascends in altitude after takeoff and when it descends in altitude to land. On the other hand, after ascending in altitude, the aircraft 1000 flies with a constant load, so the output of the propulsion motor 1001 may be lower than when ascending in altitude and when descending in altitude. Because there is a correlation between the motor output and the motor input voltage, when the input voltage of the propulsion motor 1001 is low, the output of the propulsion motor 1001 decreases. Therefore, when the aircraft 1000 ascends in altitude after takeoff and when it descends in altitude to land, it is desirable that the input voltage of the propulsion motor 1001 be higher than after ascending in altitude.

[0156] 35 also corresponds to such a load state of the aircraft 1000. Therefore, during the period when the neutron ratio is low, that is, when the aircraft 1000 is ascending or descending in altitude, the input voltage 57 of the DC / AC converter 1007 is set to a high voltage, and the required motor output can be ensured.

[0157] On the other hand, some electrical components require a certain amount of power during the flight of the aircraft 1000. In such cases, the input voltages of the corresponding DC / AC converter 1009 and DC / DC converter 1010 may be determined in advance before the aircraft 1000 takes flight, and the input voltages may be maintained at the determined voltages during flight.

[0158] Embodiment 2 In the second embodiment, a configuration will be described in which the input voltage of the DC / AC converter 1007 of the propulsion system 2001 is adjusted in accordance with the temperature of the DC / AC converter 1007.

[0159] Fig. 36 is a diagram showing an example of changes in FIT due to changes in outside air temperature 59 during flight of aircraft 1000. Fig. 36 assumes a case where the temperature of second semiconductor element 10 constituting DC / AC converter 1007 changes at the same temperature as outside air temperature 59 during adjustment of input voltage 57 shown in Fig. 35. Fig. 36 also shows fifth FIT data 60 of DC / AC converter 1007.

[0160] According to the fifth FIT data 60, it can be seen that as the outside air temperature 59 decreases during the flight of the aircraft 1000 and the temperature of the second semiconductor element 10 decreases, the FIT of the DC / AC converter 1007 increases. This is because, as shown in FIG. 22 , as the temperature of the semiconductor element decreases, the dielectric strength voltage of the semiconductor element decreases, and therefore the FIT increases.

[0161] Here, as in Figure 35, if the safety design value is set to 1 FIT or less, as the outside temperature 59 drops, FIT will exceed the safety design value, and the reliability of the SEB of the DC / AC converter 1007 cannot be guaranteed.

[0162] Therefore, in this embodiment, the input voltage of the DC / AC converter 1007 is further adjusted in accordance with the outside air temperature 59. Fig. 37 is a diagram showing an example of the transition of FIT when the input voltage of the DC / AC converter 1007 is adjusted in accordance with the outside air temperature 59 in the propulsion system 2001.

[0163] FIG. 37 shows input voltage 57b of DC / AC converter 1007 adjusted in accordance with changes in outside air temperature 59, and fifth FIT data 60b of DC / AC converter 1007 relative to changes in input voltage 57b.

[0164] 37, by adjusting the input voltage 57b, the fifth FIT data 60b fluctuates near the upper limit of the design safety value (1 FIT or less) during the flight of the aircraft 1000, similar to the fourth FIT data 58. This makes it possible to ensure the reliability of the SEB of the DC / AC converter 1007 during the flight of the aircraft 1000.

[0165] Fig. 38 is a diagram illustrating an example of the configuration of a power system according to embodiment 2. The example of the configuration of the power system illustrated in Fig. 38 is obtained by adding a thermometer 67 to the example of the configuration of the power system illustrated in Fig. 31.

[0166] The thermometer 67 measures the temperature of each power converter while the aircraft 1000 is flying, and outputs the measurement value to the control device 10000. The control device 10000 determines the input voltage of each power converter based on the measurement values ​​input from the GPS 61, the altimeter 62, and the thermometer 67.

[0167] Figure 39 is a flowchart showing an example of the processing procedure for determining the input voltage of each power converter in the power system. The series of processes shown in this flowchart is executed by control device 10000 at each predetermined control cycle while aircraft 1000 is flying. The flowchart shown in Figure 39 is obtained by replacing S30 and S40 in the flowchart shown in Figure 33 with S70 and S80, respectively.

[0168] As shown in Figure 39, first, the control device 10000 acquires measurement data of the altitude of the aircraft 1000 measured by the altimeter 62, and also acquires measurement data of the latitude and longitude of the current position of the aircraft 1000 measured by the GPS 61 (step S10).

[0169] Next, the control device 10000 calculates the neutron ratio using the measurement data of the altitude, latitude, and longitude of the aircraft 1000 (step S20). In S20, the control device 10000 calculates the number of neutrons at the current position of the aircraft 1000 based on the acquired measurement data of the altitude, latitude, and longitude. Then, the control device 10000 calculates the ratio of the number of neutrons at the current position of the aircraft 1000 to the number of neutrons at a point 0 m above sea level as the neutron ratio.

[0170] Next, the control device 10000 acquires temperature information of each power converter measured by the thermometer 67 (step S70).

[0171] The control device 10000 corrects the pre-acquired FIT curve for each power converter using the neutron ratio calculated in S20 and the temperature information acquired in S30 (step S80). In S80, the control device 10000 corrects the FIT curve by substituting the neutron ratio calculated in S20 into the above-mentioned equation (3). Furthermore, the control device 10000 corrects the FIT curve using the temperature information acquired in S70.

[0172] Next, the control device 10000 calculates an input voltage for each power converter using the corrected FIT curve (step S40). In S40, the control device 10000 calculates, from the corrected FIT curve, an input voltage at which the FIT can satisfy a safety design value (for example, 1 FIT or less).

[0173] Finally, the control device 10000 adjusts the input voltage of each power converter so that the input voltage calculated in S40 becomes the target value. For example, the control device 10000 controls the output voltage of the DC / DC converter 1008 so that the input voltage of the DC / AC converter 1007 included in the propulsion system 2001 becomes the target value.

[0174] As described above, according to the power conversion device of the second embodiment, the neutron ratio calculated from the altitude, latitude, and longitude of the aircraft 1000 and the FIT curve corrected based on the temperature of the DC / AC converter 1007 are used to calculate the neutron ratio. 7 By adjusting the input voltage, the reliability of the SEB of the DC / AC converter 1007 can be ensured while the aircraft 1000 is flying.

[0175] Embodiment 3 The junction temperature of the second semiconductor element 10 constituting the DC / AC converter 1007 does not necessarily synchronize with the outside air temperature, but also fluctuates depending on the power loss occurring in the second semiconductor element 10 and the cooling performance of the cooling device. Therefore, in the third embodiment, a method for acquiring the junction temperature of the second semiconductor element 10 will be described.

[0176] 16 , in order to monitor the heat generation of the second semiconductor element 10, a thermocouple 24 can be installed between the base plate 16 and the water cooling device 23a and configured to detect the case temperature Tc using the thermocouple 24. In this configuration, the junction temperature of the second semiconductor element 10 can be estimated from the detected value of the case temperature Tc, the power input to the second semiconductor element 10, and the thermal resistance from the second semiconductor element 10 to the base plate 16.

[0177] Alternatively, a thermistor 25 may be placed on the surface electrode 20 in the vicinity of the second semiconductor element 10, and the junction temperature may be estimated by detecting a change in the resistance value of the thermistor 25.

[0178] Alternatively, a temperature sensor 26 made up of a diode may be installed inside the second semiconductor element 10, and the junction temperature may be estimated by detecting a change in the electrical characteristics of the temperature sensor 26.

[0179] Alternatively, the junction temperature can be estimated by passing a weak current through the second semiconductor element 10 and detecting changes in electrical characteristics due to temperature changes.

[0180] Alternatively, the junction temperature can be estimated by detecting a change in the electrical characteristics of the gate resistance of the second semiconductor element 10 due to a change in temperature.

[0181] Alternatively, the temperature of the second semiconductor element 10 can be estimated based on the detected temperature of the housing of the DC / AC converter 1007.

[0182] Embodiment 4 In the above-described first to third embodiments, neutrons are used as cosmic rays, and cases where SEBs are generated by neutron collisions have been described. However, SEBs can also be generated by collisions with high-energy heavy particles, protons, etc. Furthermore, the effects of collisions with muons or pions, etc., are also being discussed in the field of micro-semiconductors such as memories.

[0183] In view of these, if it is possible to obtain FIT curves experimentally by simulating cosmic rays such as heavy particles, protons, muons, and pions that fall in nature, similar effects can be obtained by applying the first to fifth embodiments to the SEB caused by these cosmic rays.

[0184] It should be noted that, with regard to the above-mentioned embodiments and modified examples, it has been planned from the beginning of the application that the configurations described in the embodiments may be appropriately combined, including combinations not mentioned in the specification, within the scope that does not cause inconvenience or contradiction.

[0185] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The technical scope of the present disclosure is defined by the claims, not by the description of the above embodiments, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0186] 1, 1a, 1b first semiconductor element, 1d, 1s, 10d, 10s diode, 2 reactor, 3p, 9p input positive bus, 3n, 9n input negative bus, 5p output positive bus, 5n output negative bus, 6 first power semiconductor module, 7, 8, 13 smoothing capacitor, 10, 10a to 10f second semiconductor element, 10m MOSFET, 11u, 11v, 11w AC output terminal, 14 second power semiconductor module, 16 base plate, 17, 21 junction Material, 18 Back electrode, 19 Insulator, 20 Surface electrode, 23a Water cooling device, 23b Cooling pipe, 24 Thermocouple, 25 Thermistor, 26 Temperature sensor, 27 Space, 28 Atmosphere, 29 Earth's surface, 30 Cosmic rays, 31 Neutrons, 32 Accelerator, 33 DC power supply, 35 Voltage divider resistor, 36 Resistor for leak measurement, 38, 40-45, 51, 52 FIT curve, 39 High-voltage semiconductor element, 46 Altitude data, 47 Latitude data, 48 Longitude data, 49 Neutron ratio, 50, 55, 57, 57b Input voltage, 53, 54, 56, 58, 60, 60b FIT data, 59 Outside temperature, 61 GPS, 62 Altimeter, 63 Computer, 65 Control unit, 67 Thermometer, 70 CPU, 71 RAM, 72 ROM, 73 I / F device, 74 storage device, 75 communication bus, 1000 aircraft, 1001 propulsion system motor, 1002a, 1002b electrical equipment, 1003 generator, 1004 AC / DC converter, 1005 battery, 1006, 1008, 1008b, 1008c, 1010 DC / DC converter, 1007, 1009 DC / AC converter, 2000 power supply, 2001 propulsion system, 2002, 2003 electrical equipment system, 5000, 5000b, 5000c non-isolated step-down chopper circuit, 5000d non-isolated step-up chopper circuit, 5001, 5001b, 5001c three-phase two-level inverter circuit, 10000 control device.

Claims

1. A power conversion device connected between a power source and a load, a first power converter that receives a DC voltage input and generates a voltage to be supplied to the load; a second power converter that generates an input voltage for the first power converter from a DC voltage of the power supply; a control device that controls the second power converter, the control device is configured to determine the input voltage of the first power converter based on location data indicating an altitude, latitude, and longitude of the power conversion device and data related to a neutron-induced failure rate of the first power converter, and to control the second power converter to generate the determined input voltage; a measuring device that collects the position data of the power converter; a detector that acquires temperature information of the first power converter; The control device calculates the amount of neutrons to be irradiated to the power conversion device using the position data acquired from the measuring device, calculates correlation data between the input voltage and the failure rate of the first power converter for the calculated amount of neutrons, corrects the correlation data using the temperature information acquired from the detector, and determines the input voltage based on the corrected correlation data.

2. The power conversion device according to claim 1 , wherein the control device determines the input voltage based on a voltage value when the failure rate in the correlation data is equal to or less than a predetermined design value.

3. The power conversion device according to claim 1 , wherein the detector detects an outside air temperature of the power conversion device or a temperature of a semiconductor element mounted in the first power converter.

4. the power source, the load, and the power conversion device are installed on an aircraft, The power conversion device according to claim 1 , wherein the control device calculates the amount of neutrons using the position data for each control period while the aircraft is in flight, and determines the input voltage.

5. A power conversion device connected between a power source and a load, a first power converter that receives a DC voltage input and generates a voltage to be supplied to the load; a second power converter that generates an input voltage for the first power converter from a DC voltage of the power supply; a control device that controls the second power converter, the control device is configured to determine the input voltage of the first power converter based on location data indicating an altitude, latitude, and longitude of the power conversion device and data related to a neutron-induced failure rate of the first power converter, and to control the second power converter to generate the determined input voltage; a measuring device that collects the position data of the power converter; a storage device that stores a map indicating a relationship between a position of the first power converter and the input voltage; The control device uses the map to determine the input voltage from the position data acquired from the measuring device.

6. the power source, the load, and the power conversion device are installed on an aircraft, The power conversion device according to claim 5 , wherein the control device determines the input voltage from the position data using the map for each control period while the aircraft is in flight.

7. the power source; The power conversion device according to any one of claims 1 to 6; and the load.

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