Power conversion device and aircraft

Abstract

A power conversion device comprises a first power converter (1007), at least one second power converter (1007b), and a control device (10000). The first power converter (1007) is connected between a power source (2000) and a load (1001). The at least one second power converter (1007b) is connected between the power source (2000) and the load (1001), in parallel with the first power converter (1007). The control device (10000) operates the first power converter (1007) and the at least one second power converter (1007b) in parallel. The control device (10000) is configured to operate the at least one second power converter (1007b) alone when there is a failure in the first power converter (1007). During parallel operation, the at least one second power converter (1007b) has a lower rate of failure caused by neutrons than the first power converter (1007).

Description

[Technical Field]

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

[0002] Japanese Patent Application Laid-Open Publication No. 2019-77361 (Patent Document 1) discloses an aircraft that obtains propulsion force by the rotation of a propeller connected to an electric motor. In Patent Document 1, a redundant configuration is applied to the inverter that supplies power to the electric motor. Specifically, two inverters are connected in parallel to the electric motor via a switch circuit. In the event of a failure of the first inverter, the switch circuit switches the inverter that supplies power to the electric motor to the second backup inverter, thereby allowing the electric motor to continue operating.

[0003] Japanese Patent No. 6877660 (Patent Document 2) describes random failure of semiconductor elements due to neutrons as one of the causes of failure in power conversion equipment installed in aircraft. The failure rate of semiconductor elements due to neutrons is correlated with the type of semiconductor element and the voltage applied to the semiconductor element. In Patent Document 2, in a power conversion equipment equipped with multiple semiconductor elements, the failure rates of multiple semiconductor elements are made equal by adjusting the voltage applied to the semiconductor elements, the withstand voltage of the semiconductor elements, or the type of semiconductor element. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-77361 [Patent Document 2] Patent No. 6877660 Summary of the Invention [Problem to be solved by the invention]

[0005] In the configuration of Patent Document 1, even if the first inverter fails, the backup second inverter can continue to supply power to the electric motor. However, because the neutron failure rates of the first inverter and the second inverter are not taken into consideration, if the neutron failure rates of the first inverter and the second inverter are the same, the second inverter must continue to operate with the same failure rate as the first inverter even after the first inverter fails. In this case, there is a concern that the second inverter may fail immediately after the first inverter.

[0006] In the configuration of Patent Document 2, although the power conversion device does not have a redundant configuration, the failure rate of multiple semiconductor devices can be reduced by lowering the voltage applied to the semiconductor devices as the aircraft increases in altitude. However, lowering the voltage applied to the semiconductor devices also reduces the voltage supplied from the power conversion device to the electric motor, which reduces the torque that the electric motor can output. As a result, there is a concern that the propulsion force required for the aircraft to increase in altitude may not be obtained.

[0007] The present disclosure has been made to solve such problems, and an object of the present disclosure is to improve the reliability of a power conversion device having a redundant configuration 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 that converts DC power from a power source into power to be supplied to a load, the power conversion device including a first power converter, at least one second power converter, and a control device. The first power converter is connected between the power source and the load. The at least one second power converter is connected in parallel with the first power converter between the power source and the load. The control device operates the first power converter and the at least one second power converter in parallel. The control device is configured to operate the at least one second power converter independently in the event of a failure of the first power converter. During parallel operation, the at least one second power converter has a lower failure rate due to neutrons than the first power converter. [Effects of the Invention]

[0009] According to the present disclosure, it is possible to improve the reliability of a power conversion device having a redundant configuration 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] FIG. 2 is a diagram illustrating a mechanism for generating neutrons. [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. 10 is a diagram showing an example of a neutron ratio calculated based on altitude, latitude, and longitude data when an aircraft flew on an arbitrary date. [Figure 25] FIG. 1 is a diagram illustrating the correlation between the FIT and the neutron ratio of a three-phase two-level inverter circuit. [Figure 26] FIG. 10 is a diagram showing an example of the neutron ratio, the first FIT data of the three-phase two-level inverter circuit, and the input voltage when an aircraft is flying on an arbitrary date. [Figure 27]FIG. 1 is a diagram illustrating an example of adjustment of an input voltage of a three-phase two-level inverter circuit. [Figure 28] 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 29] FIG. 2 is a diagram illustrating a hardware configuration of a computer. [Figure 30] 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 31] 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 32] FIG. 1 is a diagram illustrating an example of the configuration of a power system having power converters with a redundant configuration. [Figure 33] FIG. 1 is a diagram illustrating an example of the configuration of an aircraft used for prediction. [Figure 34] FIG. 1 is a diagram illustrating an example of the configuration of an aircraft in which a redundant configuration is applied to power converters. [Figure 35] FIG. 2 is a diagram showing a first example configuration of a power system for realizing a first method. [Figure 36] FIG. 10 is a diagram showing a second example configuration of a power system for realizing the first method. [Figure 37] FIG. 10 is a diagram illustrating a third example configuration of a power system for implementing the first method. [Figure 38] FIG. 10 is a diagram illustrating a fourth example configuration of a power system for implementing the first method. [Figure 39] FIG. 10 is a diagram illustrating a fifth example configuration of a power system for implementing the first method. [Figure 40] FIG. 10 is a diagram illustrating a sixth example configuration of a power system for implementing the first method. [Figure 41] FIG. 10 is a diagram illustrating a seventh example configuration of a power system for implementing the first method. [Figure 42] FIG. 10 is a diagram illustrating a configuration example of a power system according to a third embodiment. [Figure 43] FIG. 10 is a diagram illustrating a configuration example of a power system according to a fourth embodiment. 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] The propulsion system 2001 supplies the electric power generated by the power supply 2000 to the propulsion motor 1001. Specifically, the propulsion system 2001 includes a DC / DC converter 1008 and a DC / AC converter 1007. The DC / DC converter 1008 changes the voltage of the DC voltage supplied from the power supply 2000. The DC / DC converter 1008 is configured to control the input voltage to the DC / AC converter 1007. The DC / AC converter 1007 converts the transformed DC voltage into an AC voltage and supplies the converted AC voltage to the propulsion motor 1001.

[0017] The control device 10000 controls the power conversion operations of 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.

[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.

[0027] (Fifth configuration example) Fig. 5 is a schematic diagram showing a fifth configuration example of an aircraft power system. The fifth configuration example of the power system differs from the first configuration example shown in Fig. 1 in that it has an electrical equipment system 2004 and electrical equipment 1002b instead of the propulsion system 2001 and motor 1001.

[0028] 5, the electrical component system 2004 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.

[0029] Specifically, the electrical component system 2004 includes a DC / DC converter 1010. The DC / DC converter 1010 changes the DC voltage supplied from the power supply 2000 and supplies the changed voltage to the electrical component 1002b. The electrical component 1002b is driven by the DC voltage supplied from the electrical component system 2004.

[0030] (Sixth configuration example) Figure 6 is a schematic diagram showing a sixth configuration example of an aircraft power system. The sixth configuration example of the power system is obtained by adding electrical equipment systems 2002-2004 and electrical components 1002a and 1002b to the first configuration example shown in Figure 1. The electrical equipment systems 2002-2004 and electrical components 1002a and 1002b are the same as those shown in Figures 3 to 5, so their explanation will be omitted.

[0031] In the composite system shown in FIG. 6, the power source 2000, which is the power supply for the propulsion system 2001 and the electrical component systems 2002 to 2004, is shared. The propulsion system 2001 and the electrical component systems 2002 to 2004 convert the DC voltage supplied from the power source 2000 into a voltage for driving the corresponding loads (propulsion system motor 1001, electrical components 1002a, 1002b) and supply it to the loads.

[0032] Note that the aircraft 1000 does not necessarily include all of the systems 2001 to 2004 shown in FIG. 6. Instead, at least one of the systems 2001 to 2004 is appropriately selected according to the loads mounted on the aircraft 1000. Also, a battery may be further connected to the DC bus connecting the power converters. Additionally, circuit breakers (CB: Circuit Breaker), not shown in the figure, are arranged within and between each system.

[0033] <Configuration Example of DC / DC Converter> Next, using FIGS. 7 to 11, a circuit configuration example of the DC / DC converter included in the above-described power system will be described. Hereinafter, the DC / DC converter 1008 of the propulsion system 2001 will be described as an example.

[0034] 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 the output voltage Vout to the output positive bus 5p and the output negative bus 5n.

[0035] The non-insulated step-down chopper circuit 5000 includes first semiconductor elements 1a, 1b which are switching elements, a reactor 2, and smoothing capacitors 7, 8.

[0036] 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."

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] Since the MOSFET has a parasitic diode, it is not necessary to connect a separate freewheeling diode in anti-parallel to the MOSFET, but 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 7, 9, and 10 show circuit configuration examples of a non-isolated step-down chopper circuit having a half-bridge circuit, the DC / DC conversion circuit 1008 may also be configured by a non-isolated chopper circuit having a full-bridge circuit. Also, instead of the non-isolated step-down chopper circuit, an isolated step-down chopper circuit using a transformer or a capacitor may be adopted.

[0049] Also, in FIGS. 7, 9, and 10, although the non-insulated step-down chopper circuit has been exemplified assuming that the DC / DC converter circuit 1008 is a step-down circuit, when the DC / DC converter circuit 1008 is a boost circuit, a non-insulated boost chopper circuit as shown in FIG. 11 can be adopted.

[0050] 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 boost chopper circuit 5000d. The difference between the non-insulated boost 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.

[0051] In the non-insulated boost chopper circuit 5000d, the boost 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.

[0052] [[ID=!]]<DC / AC converter configuration example> 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.

[0053] 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.

[0054] The three-phase two-level inverter circuit 5001 includes second semiconductor elements 10a to 10f, which are switching elements, and a smoothing capacitor 13.

[0055] 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."

[0056] Smoothing capacitor 13 is connected between input positive bus 9p and input negative bus 9n, and smoothes the DC voltage including the ripple voltage.

[0057] The three-phase two-level inverter circuit 5001 is provided with sensors 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.

[0058] 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.

[0059] 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.

[0060] Since the MOSFET has a parasitic diode, it is not necessary to connect a separate freewheeling diode in anti-parallel to the MOSFET, but 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. The number of diodes 10s may be one or more.

[0061] 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 a single package.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] In addition, in each of the semiconductor elements 1 and 10, a MOSFET is used as the switching element, and a 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.

[0069] <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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] <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.

[0076] FIG. 17 is a diagram illustrating the mechanism by which neutrons are generated, which can be a cause of accidental failures in semiconductor devices.

[0077] 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).

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 19, when a 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.

[0085] From the total number of the second semiconductor elements 10 used in the experiment, the failure times of each of the second semiconductor elements 10, and the number of the failed second semiconductor elements 10, the failure rate of the second semiconductor elements 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 1 failure occurs during 10 to the 9th power of time. The lower the FIT, the lower the failure rate.

[0086] In the experiment shown in FIG. 18, the number of neutrons irradiated per unit time and per unit area is more than the number of neutrons per unit time and per unit area actually falling in nature. Therefore, the experiment is substantially an accelerated test. Thus, the FIT in the environment where the second semiconductor element 10 is placed is corrected using the number of neutrons per unit time and per unit area in that environment.

[0087] The FIT per second semiconductor element 10 increases as the voltage applied to the second semiconductor element 10 increases. FIG. 20 is a diagram showing the relationship between the voltage applied to the second semiconductor element 10 and the FIT per second semiconductor element 10. The horizontal axis in FIG. 20 indicates the applied voltage, and the vertical axis indicates the FIT.

[0088] In FIG. 20, a FIT curve 38 of the second semiconductor element 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 element 10 can be controlled by adjusting the voltage applied to the second semiconductor element 10.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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。

[0094] According to Fig. 22, 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。

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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 the altitude.

[0103] In the FIT calculation described above, an example of calculating the 7th FIT curve 45 of the three-phase 2-level inverter circuit 5001 based on the 1st FIT curve 38 of each second semiconductor element 10 has been shown. 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 curve of the semiconductor elements mounted in the power converter.

[0104] <Neutron altitude, latitude, and longitude dependence> Next, the altitude, latitude, and longitude dependence of neutrons will be described.

[0105] 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.

[0106] 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.

[0107] 24 is a diagram showing an 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.

[0108] In Figure 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 the range of 0 to 12,000 m. Latitude data 47 indicating the aircraft's latitude varies from 35 degrees to 20 degrees. Longitude data 48 indicating the aircraft's longitude varies from -118 degrees to -120 degrees.

[0109] 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 moment. From FIG. 24, it can be seen that the neutron ratio 49 changes within the range of 0 to 200 following the changes in the altitude data 46, latitude data 47, and longitude data 48. Note that the higher the number of neutrons, the larger the neutron ratio 49. Thus, the neutron ratio 49 changes significantly according to the altitude, latitude, and longitude of the aircraft.

[0110] The neutron ratio 49 is directly related to the failure rate of the semiconductor device. Hereinafter, the relationship between the neutron ratio 49 and the failure rate will be described by taking the three-phase two-level inverter circuit 5001 as an example.

[0111] Equation (2) showing the 7th FIT curve 45 of the three-phase two-level inverter circuit 5001 can be transformed as shown in Equation (3) considering the neutron ratio 49. 7th FIT curve 45 = 6th FIT curve 44 × number of mounted 2nd power semiconductor modules 14 × neutron ratio 49 ···(3) However, in Equation (3), the 6th FIT curve 44 is the FIT curve at an altitude of 0 m above sea level.

[0112] FIG. 25 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. 25, 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.

[0113] According to FIG. 25, 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 higher the neutron ratio 49, the higher the FIT of the three-phase two-level inverter circuit 5001.

[0114] Fig. 26 is a diagram showing an example of the neutron ratio 49, the first FIT data 54 of the three-phase two-level inverter circuit 5001, and the input voltage 50 when an aircraft flies on an arbitrary date. Note that the neutron ratio 49 shown in Fig. 26 is calculated based on the altitude data 46, latitude data 47, and longitude data 48 shown in Fig. 24. The first FIT data 54 is calculated using the neutron ratio 49 and equation (3).

[0115] In FIG. 26, 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.

[0116] 26 shows that when the neutron ratio 49 changes while the input voltage 50 is at a constant voltage Va, the first FIT data 54 of the three-phase two-level inverter circuit 5001 also changes 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.

[0117] 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 54 is 1 FIT or less at time t0 and time t5, but remains 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 the reliability of the SEB is reduced.

[0118] 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.

[0119] Fig. 27 is a diagram showing an example of adjustment of the input voltage of the three-phase two-level inverter circuit 5001. Fig. 27 is obtained by adding second FIT data 56 and input voltage 55 to Fig. 26.

[0120] As shown in Figure 27, during the flight of the aircraft 1000, the input voltage 55 to the three-phase two-level inverter circuit 5001 is maintained at a voltage Vb that is lower than the voltage Va. The second 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 second FIT data 56 is kept below 1 FIT during the flight of the aircraft. Therefore, the reliability of the three-phase two-level inverter circuit 5001 against SEB is guaranteed during the flight of the aircraft.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] 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. That is, the output voltage of the DC / DC converter 1008c is adjusted.

[0125] In the fifth configuration example of the power system (see FIG. 5), the input voltage of the DC / DC converter 1010 included in the electrical equipment system 2004 is adjusted according to the neutron ratio 49. In other words, the output voltage of the AC / DC converter 1004 included in the power supply 2000 is adjusted.

[0126] 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 27.

[0127] On the other hand, if the aircraft's flight path is not known in advance, it is necessary to acquire altitude data 46, latitude data 47, and longitude data 48 during the aircraft's flight and determine the input voltage of each power converter based on the acquired data.

[0128] Fig. 28 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. 28 is obtained by adding a GPS (Global Positioning System) 61 and an altimeter 62 to the sixth example of the configuration of the power system shown in Fig. 6. The power supply 2000, propulsion system 2001, electrical equipment systems 2002-2004, propulsion motor 1001, and electrical equipment 1002a and 1002b are the same as those shown in Fig. 6, so their explanation will be omitted.

[0129] 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 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.

[0130] 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 adjusts the input voltage of each power converter to the determined input voltage.

[0131] Fig. 29 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.

[0132] 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.

[0133] The I / F device 73 receives measurement data from various sensors including 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.

[0134] 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 and 25. The memory device 74 is, for example, a hard disk drive (HDD) or a solid state drive (SSD).

[0135] 30 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 control intervals while aircraft 1000 is in flight.

[0136] As shown in FIG. 30, 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).

[0137] 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.

[0138] 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).

[0139] 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).

[0140] 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.

[0141] 31 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 each predetermined control period while aircraft 1000 is in flight.

[0142] In the flowchart shown in FIG. 31, the processes of S20 to S40 in the flowchart shown in FIG. 30 are replaced with the process of S60.

[0143] 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 referring to 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. 29).

[0144] 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).

[0145] As described above, by determining the input voltage of each power converter using a FIT curve corrected based on the neutron ratio calculated from the altitude, latitude, and longitude of the aircraft 1000's route, the reliability of each power converter's SEB can be ensured during the flight of the aircraft 1000.

[0146] On the other hand, depending on the route of the aircraft 1000, the upper limit of the input voltage of each power converter will be limited if the FIT satisfies the safety design value, as shown in Fig. 27. This will also limit the upper limit of the output voltage of the power converter, which could result in a decrease in the torque that the propulsion motor 1001 can output.

[0147] One way to relax the input voltage limit is to reduce the number of power semiconductor modules mounted on each power converter and the number of semiconductor elements mounted on each power semiconductor module, thereby lowering the FIT and increasing the upper limit of the input voltage accordingly. However, there is a concern that the reduction in the current that can flow through the power converter will limit the power that can be supplied to the propulsion motor.

[0148] Therefore, in this embodiment, a redundant configuration is applied to each power converter, in which multiple power converters are arranged in parallel as backup, thereby ensuring reliability for the SEB and easing the restrictions on the input voltage of each power converter.

[0149] Fig. 32 is a diagram showing an example of the configuration of a power system having redundant power converters. The example of the configuration of the power system shown in Fig. 32 has the same basic configuration as the first example of the configuration shown in Fig. 1, but differs in that it has a GPS 61, an altimeter 62, and a computer 63, and in that it has a propulsion system 2001b instead of propulsion system 2001.

[0150] The configurations and operations of the GPS 61, altimeter 62, and control device 10000 are the same as those described in Figures 28 to 30. That is, the computer 63 determines the input voltage of the DC / AC converter 1007 included in the propulsion system 2001b based on measurement data of the altitude, latitude, and longitude of the aircraft 1000 obtained from the altimeter 62 and GPS 61. The computer 63 outputs the determined input voltage to the control unit 65. The control unit 65 controls the power supply 2000 and the power converter included in the propulsion system 2001b.

[0151] Propulsion system 2001b has the same basic configuration as propulsion system 2001 shown in FIG. 1, but differs in that it includes DC / AC converter 1007b and circuit breakers (CB) 3000 and 3000b.

[0152] DC / AC converter 1007b is connected in parallel to DC / AC converter 1007 with respect to the output node of DC / DC converter 1008. DC / AC converter 1007b constitutes a redundant DC / AC converter for DC / AC converter 1007. In other words, propulsion system 2001b has a redundant configuration in which two DC / AC converters 1007, 1007b are arranged in parallel. Hereinafter, DC / AC converter 1007b will also be referred to as "redundant DC / AC converter 1007b." DC / AC converter 1007 corresponds to an example of a "first power converter." Redundant DC / AC converter 1007b corresponds to an example of a "second power converter."

[0153] The CB3000 is disposed between the output node of the DC / AC converter 1008 and the input node of the DC / AC converter 1007. The CB3000 is disposed between the output node of the DC / AC converter 1007 and the propulsion motor 1001.

[0154] CB3000b is disposed between the output node of DC / AC converter 1008 and the input node of redundant DC / AC converter 1007b. CB3000b is disposed between the output node of redundant DC / AC converter 1007b and propulsion motor 1001. CB3000 and CB3000b have the same configuration, and are opened by control device 10000 to cut off the current flowing through the corresponding DC / AC converter.

[0155] In the redundant configuration, for example, if the DC / AC converter 1007 fails, the CB 3000 is opened and the DC / AC converter 1007 is disconnected from the power transmission path. Thereafter, the operation of the propulsion motor 1001 continues with the power supply from the redundant DC / AC converter 1007b.

[0156] During normal operation, when both the DC / AC converter 1007 and the redundant DC / AC converter 1007b are functioning normally, the DC / AC converter 1007 and the redundant DC / AC converter 1007b perform power conversion. Therefore, the sum of the output powers from the DC / AC converters 1007 and 1007b operating in parallel is supplied to the propulsion motor 1001, enabling propulsion power to be maintained even during altitude ascent. For example, when the sum of the powers supplied to the propulsion motor 1001 is 1 MW, the power output from the DC / AC converter 1007 and the redundant DC / AC converter 1007b is 0.5 MW during normal operation. Alternatively, depending on the FIT reduction method described below, the DC / AC converter 1007 can be driven with lower loss than the redundant DC / AC converter 1007b, and therefore the proportion of the output power from the DC / AC converter 1007 may be higher than the proportion of the output power from the redundant DC / AC converter 1007b.

[0157] However, if the DC / AC converter 1007 fails, the DC / AC converter 1007 is disconnected from the power transmission path by opening the CB 3000, and power is supplied solely by the redundant DC / AC converter 1007b. If the DC / AC converter 1007 and the redundant DC / AC converter 1007b each operate at an output power of 0.5 MW during normal operation, it is expected that the propulsion motor 1001 will continue to operate with only the 0.5 MW power output from the redundant DC / AC converter 1007b. Alternatively, it is expected that a redundant DC / AC converter 1007b with a maximum output power of 1 MW will be installed, and the propulsion motor 1001 will continue to operate while maintaining propulsion force by increasing the output voltage of the redundant DC / AC converter 1007b.

[0158] If the DC / AC converter 1007 and the redundant DC / AC converter 1007b have the same configuration and the same input voltage, the DC / AC converter 1007 and the redundant DC / AC converter 1007b will have the same failure rate due to neutrons.

[0159] Here, the number of power converters that will fail within a certain number of years of use per aircraft is predicted based on the aircraft's service life, the number of power converters installed, and the neutron failure rate of the power converters. FIG. 33 is a diagram showing an example of the configuration of an aircraft used for this prediction. For example, assume that the service life per aircraft is 10 years, that is, 24 hours × 365 days × 10 years = 87,600 hours. Also, as shown in FIG. 33, assume that each aircraft is equipped with four DC / AC converters 1007. Furthermore, assume that the failure rate of each DC / AC converter 1007 is 100 FIT. Note that 100 FIT means the probability that 100 DC / AC converters 1007 will fail within 10 to the power of 9 hours.

[0160] To simplify the calculation, it is assumed that voltage is applied to the four DC / AC converters 1007 throughout the service life (87,600 hours) and that there is no fluctuation in FIT due to fluctuations in the neutron ratio.

[0161] Since each aircraft is equipped with four DC / AC converters 1007, the probability that a DC / AC converter 1007 will fail in one aircraft is 400 FIT. As a result, the number of DC / AC converters 1007 that will fail within the service life (10 years) is 400 FIT ÷ 10 to the power of 9 hours × 87,600 hours = 0.035 units. In other words, the number of DC / AC converters 1007 that will fail in 10 years is less than one.

[0162] Thus, when considering only one aircraft, even if the failure rate of DC / AC converter 1007 due to neutrons is 100 FIT, it appears that there is no problem with reliability. However, if there are 1,000 of the same aircraft, for example, the number of DC / AC converters 1007 that will fail will be 0.035 units x 1,000 units = 35 per 1,000 aircraft, and the number of DC / AC converters 1007 that will fail over a 10-year period will increase. Therefore, as the number of aircraft on the market increases, even if each aircraft is safe, the possibility of DC / AC converters 1007 failing increases when considering the total number of aircraft.

[0163] In the aircraft shown in Fig. 33, if even one of the four DC / AC converters 1007 fails, the propulsive force of the entire aircraft will decrease, which may make it difficult to operate the aircraft. Therefore, in order to reduce the possibility of a DC / AC converter 1007 failing, it is necessary to reduce the FIT of the DC / AC converter 1007 or to apply a redundant configuration to each DC / AC converter 1007 as shown in Fig. 32.

[0164] Fig. 34 is a diagram showing an example of the configuration of an aircraft in which a redundant configuration is applied to power converters. The configuration example shown in Fig. 34 differs from the configuration example shown in Fig. 32 in that a redundant configuration is applied in which two DC / AD converters 1007, 1007b are arranged in parallel for each of four DC / AC converters 1007.

[0165] In this redundant configuration, first consider a case where the DC / AC converter 1007 and the redundant DC / AC converter 1007b have the same configuration, the input voltages are the same between the DC / AC converters 1007 and 1007b, and the failure rates due to neutrons are the same.

[0166] As shown in Fig. 34, if one aircraft is equipped with four DC / AC converters 1007 and four redundant DC / AC converters 1007b, then the aircraft will effectively be equipped with eight DC / AC converters 1007. Therefore, if we assume that the failure rate of each DC / AC converter 1007 is 100 FIT, as in the aircraft shown in Fig. 33, then if there are 1,000 aircraft, the number of DC / AC converters 1007 that will fail will be 0.035 × 1,000 × 2 = 70 per 1,000 aircraft. In other words, applying a redundant configuration to the DC / DC converters will increase the number of DC / AC converters that will fail over a 10-year period.

[0167] In reality, while the probability of an event occurring during aircraft flight in which both the DC / AC converter 1007 and the redundant DC / AC converter 1007b arranged in parallel with one propulsion motor 1001 fail and the power supply to that propulsion motor 1001 stops is considered low, the possibility of such an event occurring is not necessarily zero.

[0168] Therefore, in this embodiment, redundant DC / AC converter 1007b is designed to have a lower failure rate than DC / AC converter 1007. This reduces the possibility that both DC / AC converter 1007 and redundant DC / AC converter 1007b, which are arranged in parallel, will fail while the aircraft is in flight.

[0169] For example, in the aircraft shown in Fig. 34, if the failure rate of DC / AC converter 1007 is 100 FIT and the failure rate of redundant DC / AC converter 1007b is 1 FIT, the number of redundant DC / AC converters 1007b that will fail within the service life (10 years) will be 0.00035 units x 1000 = 0.35 per 1000 aircraft. In other words, the number of redundant DC / AC converters 1007b that will fail in 1000 aircraft will be less than one. This means that the possibility of both DC / AC converter 1007 and redundant DC / AC converter 1007b failing while the aircraft is in flight is extremely low.

[0170] Next, a method for reducing the failure rate of the redundant DC / AC converter 1007b below the failure rate of the DC / AC converter 1007 will be described. The following four methods are possible for reducing the failure rate of the redundant DC / AC converter 1007b. However, each method involves a trade-off with the failure rate, and therefore reducing the failure rate may result in disadvantages.

[0171] (1) First Method A first method for reducing the failure rate of the redundant DC / AC converter 1007b is to reduce the input voltage of the redundant DC / AC converter 1007b below the input voltage of the DC / AC converter 1007. The first method utilizes the FIT curve 38 of the second semiconductor element 10, which shows that the FIT decreases as the applied voltage decreases (see FIG. 20).

[0172] According to the first method, even if redundant DC / AC converter 1007b and DC / AC converter 1007 have the same configuration and the same failure rate relative to the neutron fraction, it is possible to make the failure rate of redundant DC / AC converter 1007b lower than the failure rate of DC / AC converter 1007. However, because the output voltage of redundant DC / AC converter 1007b also drops due to the lower input voltage, there is a possibility that the torque of propulsion motor 1001 will decrease when redundant DC / AC converter 1007b is operating alone. There is a concern that this torque decrease will reduce the propulsion force of the aircraft.

[0173] (2) Second Method A second method for reducing the failure rate of the redundant DC / AC converter 1007b is to use a second semiconductor element 10 used in the redundant DC / AC converter 1007b that has a higher dielectric strength voltage than the second semiconductor element 10 used in the DC / AD converter 100. The second method utilizes the fact that the higher the dielectric strength voltage of a semiconductor element, the lower the FIT for the same applied voltage (see FIG. 22).

[0174] However, while the second method can equalize the input voltages of the redundant DC / AC converter 1007b and the DC / AC converter 1007, increasing the withstand voltage increases the on-resistance of the second semiconductor element 10, which may lead to increased power loss in the second semiconductor element 10. The increased power loss in the redundant DC / AC converter 1007b increases the amount of heat generated inside the aircraft. Increasing the cooling capacity of the redundant DC / AC converter 1007b may increase the size and weight of the redundant DC / AC converter 1007b. Furthermore, there is a concern that the increased weight of the redundant DC / AC converter 1007b may worsen the fuel efficiency of the aircraft.

[0175] (3) Third Method A third method for reducing the failure rate of the redundant DC / AC converter 1007b is to reduce the number of second semiconductor elements 10 mounted in the redundant DC / AC converter 1007b compared to the number of second semiconductor elements 10 mounted in the DC / AD converter 1007. The third method utilizes the fact that the fewer the number of semiconductor elements mounted, the lower the FIT for the same applied voltage (see FIG. 23 ). For example, the number of second power semiconductor modules 14 mounted in the redundant DC / AC converter 1007b is reduced compared to the number of second power semiconductor modules 14 mounted in the DC / AC converter 1007. Alternatively or in addition to this, the number of second semiconductor elements 10 mounted in each second power semiconductor module 14 of the redundant DC / AC converter 1007b is reduced compared to the number of second semiconductor elements 10 mounted in each second power semiconductor module 14 of the DC / AC converter 1007.

[0176] However, with the third method, there is a concern that a reduction in the number of second semiconductor elements 10 constituting each arm of the redundant DC / AC converter 1007b will increase the on-resistance of each arm, leading to increased power loss. As with the second method, increased power loss in the redundant DC / AC converter 1007b may require an increase in the size and weight of the redundant DC / AC converter 1007b in order to ensure sufficient cooling capacity. There is also a concern that the increased weight of the redundant DC / AC converter 1007b will worsen the fuel efficiency of the aircraft.

[0177] (4) The fourth method A fourth method for reducing the failure rate of the redundant DC / AC converter 1007b is to make the temperature of the second semiconductor element 10 mounted on the redundant DC / AC converter 1007b higher than the temperature of the second semiconductor element 10 mounted on the DC / AD converter 1007. The fourth method utilizes the fact that as the temperature (junction temperature) of the semiconductor element increases, the FIT for the same applied voltage decreases (see FIG. 22).

[0178] However, according to the fourth method, the temperature of the second semiconductor element 10 mounted on the redundant DC / AC converter 1007b needs to be maintained higher than the temperature of the second semiconductor element 10 mounted on the DC / AC converter 1007. This is advantageous against neutron failures, but is disadvantageous against mechanical failures.

[0179] The first to fourth methods described above each have their own disadvantages. Therefore, in this embodiment, in the redundant configuration, the DC / AC converter 1007 is designed with a focus on supplying power to the propulsion motor 1001 efficiently and with low loss, and the redundant DC / AC converter 1007b is designed with a focus on maintaining a low failure rate while supplying power to the propulsion motor 1001. This configuration achieves an efficient and highly reliable power converter.

[0180] Next, a specific configuration of the power system for implementing the first to fourth methods described above will be described.

[0181] (1) Configuration example of the first method FIG. 35 is a diagram showing a first configuration example of the power system for implementing the first method. The configuration example of the power system shown in FIG. 35 has the same basic configuration as the configuration example shown in FIG. 31, but the configuration of the propulsion system 2001b is different.

[0182] In the propulsion system 2001b shown in FIG. 35, the DC / DC converter 1008 is configured to be able to generate two different output voltages. For example, the DC / DC converter 1008 is configured to include a non-insulated step-down chopper circuit 5000 (see FIG. 7), a first output transformer TR1, and a second output transformer TR2.

[0183] The first output transformer TR1 is provided between the output positive bus 5p and the output negative bus 5n of the non-insulated step-down chopper circuit 5000 and the CB3000. The first output transformer TR1 generates an output voltage Vou1 from the output voltage Vout of the non-insulated step-down chopper circuit 5000 and outputs it to the DC / AC converter 1007. The second output transformer TR2 generates an output voltage Vou2 from the output voltage Vout of the non-insulated step-down chopper circuit 5000 and outputs it to the redundant DC / AC converter 1007b. Note that Vout2 < Vout1. According to this, the input voltage of the redundant DC / AC converter 1007b can be made lower than the input voltage of the DC / AC converter 1007.

[0184] FIG. 36 is a diagram showing a second configuration example of the power system for implementing the first method. The configuration example of the power system shown in FIG. 36 has the same basic configuration as the configuration example shown in FIG. 31, but the configuration of the propulsion system 2001b is different.

[0185] The propulsion system 2001b shown in Fig. 36 differs from the propulsion system 2001b shown in Fig. 31 in that it includes two DC / DC converters 1008, 1008d. The DC / DC converter 1008 is configured to receive a DC voltage supplied from a power supply 2000 and control the input voltage to a DC / AC converter 1007. The DC / AC converter 1007 converts the transformed DC voltage into an AC voltage and supplies the converted AC voltage to the propulsion motor 1001. The DC / DC converter 1008d is configured to receive a DC voltage supplied from the power supply 2000 and control the input voltage to a redundant DC / AC converter 1007b. The redundant DC / AC converter 1007b converts the transformed DC voltage into an AC voltage and supplies the converted AC voltage to the propulsion motor 1001.

[0186] 35 and 36, if the output node of DC / AC converter 1007 is connected to the output node of redundant DC / AC converter 1007b, the potential of the output node of redundant DC / AC converter 1007b will be raised to the potential of the output node of DC / AC converter 1007, which may cause redundant DC / AC converter 1007b to malfunction. Therefore, propulsion motor 1001 is configured as a double-winding motor having two sets of windings, with the output node of DC / AC converter 1007 connected to the first set of windings and the output node of redundant DC / AC converter 1007b connected to the second set of windings. Because the output voltage of redundant DC / AC converter 1007b is lower than the output voltage of DC / AC converter 1007, the torque of the double-winding motor may be ensured by lowering the winding impedance of the double-winding motor connected to redundant DC / AC converter 1007b to allow a large current to flow.

[0187] Alternatively, the propulsion motor 1001 may be divided into two propulsion motors 1001a and 1001b as shown in Fig. 37. Fig. 37 is a diagram showing a third example configuration of a power system for realizing the first method. The example configuration of the power system shown in Fig. 37 has the same basic configuration as the example configuration shown in Fig. 36, but differs in that it has two propulsion motors 1001a and 1001b.

[0188] As shown in FIG. 37, the DC / AC converter 1007 is connected to the propulsion motor 1001a via the CB 3000. The propulsion motor 1001a is driven by power supplied from the DC / AC converter 1007. The redundant DC / AC converter 1007b is connected to the propulsion motor 1001b via the CB 3000b. The propulsion motor 1001b is driven by power supplied from the redundant DC / AC converter 1007b. The propulsion motor 1001b may have a motor design that is different from that of the propulsion motor 1001a and is suited to the output voltage and output current of the redundant DC / AC converter 1007b.

[0189] (2) Example of the second method The second method can be realized by using a third semiconductor element 10c having a higher dielectric strength than the second semiconductor element 10 mounted on the DC / AC converter 1007 as the redundant DC / AC converter 1007b.

[0190] Specifically, when the DC / AC converter 1007 and the redundant DC / AC converter 1007b each include a three-phase two-level inverter circuit 5001b (see FIG. 14), each of the multiple second power semiconductor modules 14 included in the redundant DC / AC converter 1007b is configured using multiple third semiconductor elements 10c.

[0191] In this case, the FIT curve of the third semiconductor element 10c becomes the second FIT curve 40 shown in FIG. 21, and the FIT for the same applied voltage is smaller than that of the first FIT curve 38 of the second semiconductor element 10. Therefore, the failure rate of the redundant DC / AC converter 1007b can be made lower than that of the DC / AC converter 1007. Furthermore, it is not necessary to divide the output voltage of the DC / DC converter 1008 or to add a DC / DC converter 1008d, as shown in FIGS. 34 and 35.

[0192] (3) Example of the third method The third method is to make the number of second semiconductor elements 10 mounted in the redundant DC / AC converter 1007b smaller than the number of second semiconductor elements 10 mounted in the DC / AD converter 1007. Specifically, each of the multiple arms in the DC / AC converter 1007 is configured by connecting N second semiconductor elements 10 in parallel, and each of the multiple arms in the redundant DC / AC converter 1007b is configured by connecting M second semiconductor elements 10 in parallel. In the above configuration, N is an integer equal to or greater than 2, and M is an integer equal to or greater than 1 and smaller than N.

[0193] For example, when the DC / AC converter 1007 and the redundant DC / AC converter 1007b each include a three-phase two-level inverter circuit 5001b (see FIG. 14), the number of second semiconductor elements 10 included in the second power semiconductor module 14 constituting each phase arm in the redundant DC / AC converter 1007b is reduced from two to one.

[0194] In this case, the FIT curve of the redundant DC / AC converter 1007b has a smaller FIT for the same applied voltage than the FIT curve of the DC / AC converter 1007. Therefore, the failure rate of the redundant DC / AC converter 1007b can be made lower than the failure rate of the DC / AC converter 1007. Furthermore, it is no longer necessary to divide the output voltage of the DC / DC converter 1008 or to add a DC / DC converter 1008d, as shown in FIGS.

[0195] (4) Example of the fourth method The fourth method can be realized by making the junction temperature of the second semiconductor element 10 mounted on the redundant DC / AC converter 1007b higher than the junction temperature of the second semiconductor element 10 mounted on the DC / AD converter 1007.

[0196] Specifically, when the DC / AC converter 1007 and the redundant DC / AC converter 1007b each include a three-phase two-level inverter circuit 5001b (see FIG. 14), the cooling performance of the cooling device that cools the redundant DC / AC converter 1007b is made lower than the cooling performance of the cooling device that cools the DC / AC converter 1007. For example, when the DC / AC converter 1007 and the redundant DC / AC converter 1007b each include a water-cooling device 23a (see FIG. 16), the cooling performance can be made different between the DC / AC converter 1007 and the redundant DC / AC converter 1007b by making the amount or temperature of the refrigerant flowing through the cooling pipe 23b different.

[0197] Alternatively, the fourth method can be realized by lowering the gate voltage of the second semiconductor element 10 mounted in the three-phase two-level inverter circuit 5001b of the redundant DC / AC converter 1007b below the gate voltage of the second semiconductor element 10 mounted in the three-phase two-level inverter circuit 5001b of the DC / AC converter 1007. Lowering the gate voltage of the second semiconductor element 10 increases the on-resistance of the second semiconductor element 10, and therefore, the power loss occurring in the redundant DC / AC converter 1007b can be increased.

[0198] The first to fourth methods described above can be combined as appropriate, including combinations not mentioned in the specification, as long as no inconvenience or contradiction occurs.

[0199] <Other configuration examples> The configuration examples shown in FIGS. 35 and 36 are not limited to the propulsion system 2001b, but can also be applied to the electrical equipment systems 2002 to 2004.

[0200] Fig. 38 is a diagram showing a fourth example configuration of an electric power system for realizing the first method. In the example configuration of the electric power system shown in Fig. 38, the propulsion system 2001b in the example configuration shown in Fig. 35 is replaced with an electrical equipment system 2002b.

[0201] The electrical equipment system 2002b shown in Figure 38 differs from the propulsion system 2001b shown in Figure 35 in that it has a DC / AC converter 1009 and a redundant DC / AC converter 1009b instead of the DC / AC converter 1007 and the redundant DC / AC converter 1007b, and a DC / DC converter 1008b instead of the DC / DC converter 1008.

[0202] The DC / DC converter 1008b has a configuration similar to that of the DC / DC converter 1008, and is configured to be able to generate two different output voltages. As a result, in the electrical equipment system 2002b, as in the propulsion system 2001b, the input voltage of the redundant DC / AC converter 1009b can be made lower than the input voltage of the DC / AC converter 1009. Therefore, even if the redundant DC / AC converter 1009b and the DC / AC converter 1009 have the same configuration and the same failure rate relative to the neutron fraction, it is possible to make the failure rate of the redundant DC / AC converter 1009b lower than the failure rate of the DC / AC converter 1009.

[0203] Fig. 39 is a diagram showing a fifth example configuration of an electric power system for realizing the first method. In the example configuration of the electric power system shown in Fig. 39, the propulsion system 2001b in the example configuration shown in Fig. 36 is replaced with an electrical equipment system 2002b.

[0204] The electrical equipment system 2002b shown in Figure 39 differs from the propulsion system 2001b shown in Figure 36 in that it has a DC / AC converter 1009 and a redundant DC / AC converter 1009b instead of the DC / AC converter 1007 and the redundant DC / AC converter 1007b, and that it has DC / DC converters 1008b and 1008e instead of the DC / DC converters 1008 and 1008d.

[0205] The DC / DC converter 1008b is configured to receive a DC voltage supplied from the power supply 2000 and control the input voltage to the DC / AC converter 1009. The DC / DC converter 1008e is configured to receive a DC voltage supplied from the power supply 2000 and control the input voltage to the redundant DC / AC converter 1009b. As a result, in the electrical equipment system 2002b as well, the input voltage to the redundant DC / AC converter 1009b can be made lower than the input voltage of the DC / AC converter 1009, similar to the propulsion system 2001b.

[0206] Fig. 40 is a diagram showing a sixth example configuration of a power system for realizing the first method. The example configuration of the power system shown in Fig. 40 is obtained by replacing the propulsion system 2001b in the example configuration shown in Fig. 35 with an electrical equipment system 2003b.

[0207] The electrical equipment system 2003b shown in Figure 40 differs from the propulsion system 2001b shown in Figure 35 in that it has a DC / DC converter 1010 and a redundant DC / DC converter 1010b instead of the DC / AC converter 1007 and the redundant DC / AC converter 1007b, and a DC / DC converter 1008c instead of the DC / DC converter 1008.

[0208] The DC / DC converter 1008c has a configuration similar to that of the DC / DC converter 1008, and is configured to be able to generate two different output voltages. As a result, in the electrical component system 2003b, as in the propulsion system 2001b, the input voltage of the redundant DC / DC converter 1010b can be made lower than the input voltage of the DC / DC converter 1010. Therefore, even if the redundant DC / DC converter 1010b and the DC / DC converter 1010 have the same configuration and the same failure rate relative to the neutron fraction, it is possible to make the failure rate of the redundant DC / DC converter 1010b lower than the failure rate of the DC / DC converter 1010.

[0209] Fig. 41 is a diagram showing a seventh example configuration of an electric power system for realizing the first method. The example configuration of the electric power system shown in Fig. 41 is obtained by replacing the propulsion system 2001b in the example configuration shown in Fig. 35 with an electrical equipment system 2004b. The example configuration of the electric power system shown in Fig. 41 also differs from the example configuration shown in Fig. 35 in the configuration of the power source 2000.

[0210] 41, the power supply 2000 includes a generator 1003 and two AC / DC converters 1004 and 1004b. The generator 1003 generates an AC voltage. The AC / DC converters 1004 and 1004b convert the AC voltage generated by the generator 1003 into a DC voltage and supply it to an electrical component system 2004b.

[0211] The electrical component system 2004b includes a DC / DC converter 1010, a redundant DC / DC converter 1010b, a CB 3000, and a CB 300b. The CB 3000 is disposed between the output node of the AC / DC converter 1004 and the input node of the DC / DC converter 1010. The CB 3000 is disposed between the output node of the DC / DC converter 1007 and the electrical component 1002b. The CB 3000b is disposed between the output node of the AC / DC converter 1004b and the input node of the redundant DC / DC converter 1010b. The CB 3000b is disposed between the output node of the redundant DC / DC converter 1010b and the electrical component 1002b.

[0212] The AC / DC converter 1004b is configured to receive the AC voltage supplied from the generator 1003 and control the input voltage to the DC / DC converter 1010. The AC / DC converter 1004b is configured to receive the AC voltage supplied from the generator 1003 and control the input voltage to the redundant DC / DC converter 1010b. As a result, in the electrical equipment system 2004b as well, the input voltage to the redundant DC / DC converter 1010b can be made lower than the input voltage of the DC / DC converter 1010, similar to the propulsion system 2001b.

[0213] As described above, according to the power conversion device of embodiment 1, each power converter is configured in a redundant manner with the first power converter and the second power converter arranged in parallel, and the failure rate of the second power converter, which is used as a redundancy for the first power converter, is configured to be lower than the failure rate of the first power converter, thereby reducing the possibility of each power converter failing during operation of the power conversion device.

[0214] Embodiment 2 In the above-described first embodiment, a redundant configuration in which two DC / AC converters 1007 and 1007b are arranged in parallel to the DC / AC converter 1007 of the propulsion system 2001 has been described.

[0215] However, in propulsion system 2001b shown in FIG. 35, if DC / DC converter 1008 fails before DC / AC converters 1007 and 1007b fail, voltage will no longer be supplied to DC / AC converters 1007 and 1007b.

[0216] Therefore, the failure rate of DC / DC converter 1008 is designed to be lower than the failure rate of DC / AC converters 1007 and 1007b, thereby further improving the reliability of propulsion system 2001b.

[0217] The first to fourth methods described in the first embodiment can be applied to reduce the failure rate of DC / DC converter 1008.

[0218] Embodiment 3 In the above-described first embodiment, a redundant configuration in which two DC / AC converters 1007, 1007b are arranged in parallel to the DC / AC converter 1007 of the propulsion system 2001 is applied, but a redundant configuration can also be applied to the DC / DC converter 1008.

[0219] Fig. 42 is a diagram showing an example of the configuration of an electric power system according to embodiment 3. In the example of the configuration of the electric power system shown in Fig. 42, propulsion system 2001b in the example of the configuration shown in Fig. 35 is replaced with propulsion system 2001c.

[0220] The propulsion system 2001c has the same basic configuration as the propulsion system 2001b, but differs in that it has a redundant DC / DC converter 1008d and circuit breakers 3001, 3001b, and 3002.

[0221] Redundant DC / DC converter 1008d is connected in parallel to DC / DC converter 1008 with respect to the output node of AC / DC converter 1004. DC / AC converter 1007b constitutes a redundant DC / AC converter for DC / AC converter 1007. In other words, propulsion system 2001c has a redundant configuration in which two DC / DC converters 1008, 1008b are arranged in parallel.

[0222] CB3001 is arranged between the output node of AC / DC converter 1004 and the input node of DC / DC converter 1008. CB3001 is arranged in series with CB3000 between the output node of DC / DC converter 1008 and the input node of DC / DC converter 1007.

[0223] CB3001b is arranged between the output node of AC / DC converter 1004 and the input node of redundant DC / DC converter 1008d. CB3001b is arranged in series with CB3000b between the output node of redundant DC / DC converter 1008d and the input node of redundant DC / AC converter 1007b.

[0224] CB3002 is connected between the connection node of CB3001 and CB3000 and the connection node of CB3001b and CB3000b.

[0225] In the configuration example shown in Fig. 41, during normal operation when both the DC / DC converter 1008 and the redundant DC / DC converter 1008d are functioning normally, the DC / DC converter 1008 and the redundant DC / DC converter 1008d perform voltage conversion with CBs 3001 and 3001b closed and CB 3002 open. If the DC / DC converter 1008 fails, CBs 3001 and 3002 are opened to disconnect the DC / DC converter 1008 from the power transmission path. This allows the redundant DC / DC converter 1008d to supply voltage to the DC / AC converters 1007 and 1007b.

[0226] In this embodiment as well, by designing redundant DC / DC converter 1008d to have a lower failure rate than DC / DC converter 1008, it is possible to reduce the possibility of failures in both DC / DC converter 1008 and redundant DC / DC converter 1008d, which are arranged in parallel, during aircraft flight.

[0227] Embodiment 4 In the first to third embodiments described above, examples of a power converter having a redundant configuration in which one redundant power converter is used have been described, but a configuration in which multiple redundant power converters are provided may also be used.

[0228] Fig. 43 is a diagram showing an example of the configuration of an electric power system according to embodiment 3. In the example of the configuration of the electric power system shown in Fig. 43, propulsion system 2001b in the example of the configuration shown in Fig. 35 is replaced with propulsion system 2001d.

[0229] The propulsion system 2001d has the same basic configuration as the propulsion system 2001b, but differs in that it has two redundant DC / AC converters 1007b and 1007c.

[0230] In the configuration example shown in FIG. 43, the failure rates of the DC / AC converter 1007 and the redundant DC / AC converter 1007b can be set to be the same, and the failure rate of the redundant DC / AC converter 1007c can be set to be lower than the failure rates of the DC / AC converters 1007 and 1007b.

[0231] Alternatively, the failure rate of the redundant DC / AC converters 1007b and 1007c can be set lower than the failure rate of the DC / AC converter 1007.

[0232] Alternatively, the DC / AC converter 1007, the redundant DC / AC converter 1007b, and the redundant DC / AC converter 1007c can be designed to have different failure rates.

[0233] Embodiment 5 The junction temperature of the second semiconductor element 10 constituting the DC / AC converter 1007 varies depending on the power loss occurring in the second semiconductor element 10 and the cooling performance of the cooling device. In the fifth embodiment, a method for acquiring the junction temperature of the second semiconductor element 10 will be described.

[0234] 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.

[0235] 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.

[0236] 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.

[0237] 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.

[0238] 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.

[0239] 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.

[0240] Embodiment 6 In the above-described first to fifth 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.

[0241] 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.

[0242] 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.

[0243] 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]

[0244] 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 bonding agent, 18 back electrode, 19 insulating material, 20 front 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 dividing 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 Input voltage, 54, 56 FIT data, 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, 1001a, 1001b Propulsion 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, 2002b, 2003, 2003b, 2004, 2004b electrical equipment system, 3001, 3001b, 3002 circuit breaker, 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, TR1, TR2 output transformer.

Claims

1. A power conversion device that converts DC power from a power source into power to be supplied to a load, a first power converter connected between the power source and the load; at least one second power converter, which is any power converter connected in parallel with the first power converter between the power source and the load; a control device that operates the first power converter and the at least one second power converter in parallel, the control device is configured to operate the at least one second power converter alone when the first power converter fails; During the parallel operation, the at least one second power converter has a lower failure rate due to neutrons than the first power converter.

2. the at least one second power converter includes a plurality of second power converters; The power conversion device according to claim 1 , wherein the failure rates of the second power converters are different from one another during the parallel operation.

3. a third power converter that converts the voltage of DC power from the power supply and supplies the converted voltage to the first power converter and the at least one second power converter; the first power converter and the at least one second power converter are configured so that the failure rates are equivalent when the input voltage is the same; 3. The power conversion device according to claim 1, wherein the third power converter converts a DC voltage of the power supply into a first DC voltage and supplies the first DC voltage to the first power converter, and converts the DC voltage into a second DC voltage lower than the first DC voltage and supplies the second DC voltage to the at least one second power converter.

4. the first power converter includes a plurality of first semiconductor elements having a first dielectric strength voltage; 3. The power conversion device according to claim 1, wherein the at least one second power converter includes a plurality of second semiconductor elements having a second dielectric strength voltage higher than the first dielectric strength voltage.

5. each of the first power converter and the at least one second power converter is configured to convert DC power from the power source to power supplied to the load by switching a plurality of arms; each of the plurality of arms of the first power converter includes N first semiconductor devices connected in parallel; each of the plurality of arms of the at least one second power converter includes M second semiconductor devices connected in parallel; the first semiconductor element and the second semiconductor element are configured so that the failure rates are equivalent when the same applied voltage is applied thereto; 3. The power conversion device according to claim 1, wherein N is an integer of 2 or more, and M is an integer of 1 or more and smaller than N.

6. a third power converter that converts the voltage of DC power from the power supply and supplies the converted voltage to the first power converter and the at least one second power converter; The power conversion device according to claim 1 , wherein the third power converter has a lower failure rate than the first power converter and the at least one second power converter.

7. the first power converter, the at least one second power converter, and the third power converter are configured so that the failure rates are equivalent when an input voltage is the same; the third power converter converts a DC voltage of the power supply into a first DC voltage and supplies the first DC voltage to the first power converter, and converts the DC voltage into a second DC voltage lower than the first DC voltage and supplies the second DC voltage to the at least one second power converter; The power conversion device according to claim 6 , wherein the power supply supplies a third DC voltage lower than the second DC voltage to the third power converter.

8. the first power converter includes a plurality of first semiconductor elements having a first dielectric strength voltage; the at least one second power converter includes a plurality of second semiconductor elements having a second dielectric strength voltage higher than the first dielectric strength voltage; The power conversion device according to claim 6 , wherein the third power converter includes a plurality of third semiconductor elements having a third dielectric strength voltage higher than the second dielectric strength voltage.

9. the first power converter includes X first semiconductor devices; the at least one second power converter includes Y second semiconductor devices; the third power converter includes Z third semiconductor devices; the first semiconductor element, the second semiconductor element, and the third semiconductor element are configured so that the failure rates are equivalent when the same applied voltage is applied thereto; The power conversion device according to claim 6 , wherein X is an integer equal to or greater than 2, Y is an integer equal to or greater than 2 and smaller than X, and Z is an integer equal to or greater than 1 and smaller than Y.

10. a third power converter that converts the voltage of DC power from the power supply and supplies the converted power to the first power converter and the at least one second power converter; at least one fourth power converter connected in parallel with the third power converter between the power source and the parallel circuit of the first power converter and the at least one second power converter; the control device is configured to operate the third power converter and the at least one fourth power converter in parallel, and to operate the at least one fourth power converter independently when a failure occurs in the third power converter; The power conversion device according to claim 1 , wherein the at least one fourth power converter has a lower failure rate than the third power converter.

11. the power source; The power conversion device according to any one of claims 1 to 10; and the load.

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