POWER CONVERSION DEVICE, POWER CONVERSION SYSTEM, FLYING OBJECT, AND CONTROL METHOD

Abstract

The power conversion device (100) according to the present disclosure is characterized by comprising a plurality of power conversion units (20) connected in parallel, and a control unit (11) that counts the cumulative operating time of the plurality of power conversion units and operates the power conversion unit with the longest cumulative operating time first, thereby controlling the cumulative operating time of at least one power conversion unit to be different from the other power conversion units, and changes the number of operating power conversion units of the plurality of power conversion units.

Description

[Technical field]

[0001] The present disclosure relates to a power conversion device, a power conversion system, a flying object, and a control method. [Background technology]

[0002] In recent years, there has been a strong movement in countries around the world to electrify flying objects in order to reduce carbon dioxide emissions. In the electrification of flying objects, a method is used in which multiple power conversion units are connected in parallel to increase the capacity of the power conversion device in order to meet a wide range of power demands. Even in a power conversion device in which multiple power conversion units are connected in parallel and has a large capacity, there is a demand for it to be compact, lightweight, and highly efficient.

[0003] For example, Patent Document 1 discloses a technique for increasing the efficiency of multiple power converters connected in parallel by operating one of the multiple converters according to the load current value and switching the number of units in operation. By switching the number of units in operation in this way, operation can be performed according to the load state, making it possible to operate with high efficiency. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2021 / 182447 Summary of the Invention [Problem to be solved by the invention]

[0005] Here, in the electrification of flying objects, it is important to continue the flying function, so the power conversion device is required to have high reliability and safety in addition to high efficiency. In order to maintain high reliability and safety of this power conversion device, more frequent maintenance is required compared to power conversion devices for general industrial or automotive use. Therefore, technology to reduce maintenance costs is required for power conversion devices used in flying objects.

[0006] The present disclosure has been made to solve the above-mentioned problems, and has an object to provide a power conversion device capable of reducing maintenance costs. [Means for solving the problem]

[0007] The power conversion device according to the present disclosure includes a plurality of power conversion units connected in parallel, and counts a cumulative operation time of the plurality of power conversion units, When changing the number of the plurality of power conversion units in operation, By first operating the power conversion unit having the longest cumulative operation time among the plurality of power conversion units, the cumulative operation time of at least one of the power conversion units is controlled to be different from that of the other power conversion units. do and a control unit.

[0008] The control method according to the present disclosure includes: Parallel connected Counting a cumulative operation time of a plurality of power conversion units; When changing the number of the plurality of power conversion units in operation, the power conversion unit having the longest cumulative operation time among the plurality of power conversion units is operated first, thereby controlling so that the cumulative operation time of at least one of the power conversion units is differentiated from the other power conversion units. Steps. Effect of the Invention

[0009] According to the power conversion device according to the present disclosure, the maintenance costs of a highly efficient, large-capacity power conversion device can be reduced. [Brief description of the drawings]

[0010] [Figure 1] 1 is a circuit diagram showing a configuration of a power conversion device according to a first embodiment of the present disclosure. [Diagram 2] 2 is a schematic diagram illustrating a hardware configuration of a control unit of a power conversion device according to a first embodiment of the present disclosure. [Diagram 3] 4 is a graph showing an accumulated operation time for each power conversion unit of the power conversion device according to the first embodiment of the present disclosure. [Figure 4] 4 is a graph showing switching of operations of the power conversion device according to the first embodiment of the present disclosure. [Diagram 5] 4 is a graph showing switching of operations when a cumulative operation time of the power conversion device according to the first embodiment of the present disclosure exceeds a threshold value. [Figure 6]4 is a graph showing switching of operation for each accumulated operation time of the power conversion device according to the first embodiment of the present disclosure. [Figure 7] 4 is a flowchart showing a control method according to the first embodiment of the present disclosure. [Figure 8] 10 is a circuit diagram showing a configuration of a power conversion device according to a second embodiment of the present disclosure. FIG. [Figure 9] 10 is a flowchart showing a control method according to a second embodiment of the present disclosure. [Figure 10] FIG. 11 is a schematic diagram showing the configuration of a flying object according to a third embodiment of the present disclosure. [Figure 11] FIG. 11 is a schematic diagram showing the configuration of a flying object according to a fourth embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, a power conversion device, a power conversion system, a flying object, and a control method according to the present disclosure will be described with reference to the drawings.

[0012] Embodiment 1 FIG. 1 is a circuit diagram showing a configuration of a power conversion device according to a first embodiment of the present disclosure. As shown in FIG. 1, the power conversion device 100 is a device that converts a DC voltage of a DC source 30 into a different DC voltage for a load 40 and supplies power, and its central part is composed of four power conversion units whose inputs and outputs are connected in parallel. The power conversion units in the power conversion device 100 according to the first embodiment of the present disclosure may be any power conversion units that connect inputs and outputs in parallel and switch the number of units in parallel with a semiconductor switch. For example, the power conversion units may be inverters (DC / AC) that convert DC voltages to AC voltages, PWM converters (AC / DC) that convert AC voltages to DC voltages, DC-DC converters that convert DC voltages, and the like. In the following, an example in which a DC-DC converter is used as a power conversion unit is shown.

[0013] 1 includes a first DCDC converter 1, a second DCDC converter 2, a third DCDC converter 3, and a fourth DCDC converter 4 as a plurality of power conversion units. Furthermore, the power conversion device 100 includes a control unit 11 that controls the first to fourth DCDC converters as described later and performs a predetermined function of the power conversion device 100.

[0014] In the following description, the first DCDC converter 1 will be referred to as DCDC1, the second DCDC converter 2 as DCDC2, the third DCDC converter 3 as DCDC3, the fourth DCDC converter 4 as DCDC4, and the four DCDC converters as DCDC20.

[0015] The DC source 30 may be a battery, a DC power source and other battery systems such as a solar cell, a DC voltage obtained by rectifying an AC voltage, or a DC power distribution network. The load 40 may be a DC load, or an AC load such as a motor may be connected using an inverter that converts a DC voltage to an AC voltage. In FIG. 1, the number of parallel DCDC 20 is described as four, but this does not limit the present disclosure, and a configuration in which at least two or more DCDC converters are connected in parallel may be used. Although not shown, the input side of DCDC 1 to 4 may be provided with at least one of a smoothing capacitor, a normal mode filter, and a common mode filter. Similarly, the output side of DCDC 1 to 4 may be provided with at least one of a smoothing capacitor, a normal mode filter, and a common mode filter.

[0016] Next, the circuit configuration of DCDC1 will be described. The circuit configurations of DCDC2 to DCDC4 in the first embodiment are the same, so the description will be omitted. DCDC1 is an insulated DCDC converter that is insulated using a transformer Tr1. The primary side of the transformer Tr1 is a full-bridge configuration with four power semiconductor elements Q1 to Q4, the secondary side of the transformer Tr1 is a center tap configuration and a configuration in which full-wave rectification is performed by power semiconductor elements Q11 and Q12, and the filter section is configured to smooth by a reactor Lf and a capacitor Cf. Since the filter capacitor Cf can be miniaturized by an interleaving operation described later, the multiple capacitors Cf in the DCDC20 may be integrated into one body. The reactor Lf may also be integrated into one body and miniaturized like a coupling reactor. The power semiconductor elements Q1 to Q4, Q11, and Q12 are self-extinguishing devices such as IGBTs (Insulated Gate Bipolar Transistors) and MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors). Figure 1 shows the case where MOSFETs are used.

[0017] FIG. 2 is a schematic diagram of a hardware configuration of a control unit of a power conversion device according to the first embodiment of the present disclosure. The control unit 11 counts the cumulative operation time of a plurality of power conversion units connected in parallel, and controls the cumulative operation time of at least one power conversion unit to be different from the other power conversion units by first operating the power conversion unit with the longest cumulative operation time, and changes the number of operation units of the plurality of power conversion units. As shown in FIG. 2, the control unit 11 includes an arithmetic processing unit 111 such as a CPU (Central Processing Unit) in order to control the DCDC1 to DCDC4, a storage device 112 that exchanges data with the arithmetic processing unit 111, an input / output interface 113 that inputs and outputs signals between the arithmetic processing unit 111 and the outside, and the like. The power conversion device 100 can change the number of operation units of the DCDC20 by the control unit 11. For example, by operating with a reduced number of units among the plurality of DCDC20, it is possible to improve loss during light load and achieve high efficiency.

[0018] The arithmetic processing device 111 may be an ASIC (Application Specific Integrated Circuit), an IC (Integrated Circuit), a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), various signal processing circuits, etc. Also, the arithmetic processing device 111 may be a plurality of devices of the same type or different types, and each process may be shared and executed. The storage device 112 may be a RAM (Random Access Memory) configured to be able to read and write data from the arithmetic processing device 111, a ROM (Read Only Memory) configured to be able to read data from the arithmetic processing device 111, etc. The input / output interface 113 is composed of, for example, voltage detection means provided in DCDC1 to DCDC4, an A / D converter that inputs detection signals 102 output from current detection means, etc., to the arithmetic processing device 111, a gate drive circuit for driving each switching element, and a notification unit described later.

[0019] The control unit 11 performs output voltage control and current control of DCDC1 to DCDC4 based on, for example, the input voltage, output voltage, and current information of DCDC1 to DCDC4. The above-mentioned current may be the primary current of the transformer or the current of the reactor Lf. Also, an overvoltage and an overcurrent may be detected based on the detected voltage and current information, and the entire DCDC20 or at least one DCDC converter may be stopped and protected at a protection threshold. A temperature sensor may be provided to input temperature information, or protection may be performed by a threshold.

[0020] The control unit 11 outputs a detection signal 102 for driving the power semiconductor elements Q1 to Q4 on the primary side of DCDC1 to DCDC4 and the power semiconductors Q11 and Q12 on the secondary side. The gate signal is generated using a triangular wave comparison method such as PWM (Pulse Width Modulation) control. On the other hand, the power semiconductors Q11 and Q12 on the secondary side may be synchronously rectified in order to reduce the conduction loss of the VF of the diode. Note that instead of duty control by PWM control, PFM (Pulse Frequency Modulation) control for frequency control may be used. The pulse width output by the full bridge circuit on the primary side may be controlled to output a symmetrical pulse, or an asymmetrical pulse may be output for soft switching or the like.

[0021] The control unit 11 counts the cumulative operation time of DCDC1 to DCDC4 in the arithmetic processing device 111 or the storage device 112. The cumulative operation time may be counted as the gate output time or may be estimated based on accumulated data of temperature or current detection information. The power conversion device 100 according to the first embodiment of the present disclosure may also include a notification unit (not shown) that notifies the user when the cumulative operation time of the power conversion unit having the longest cumulative operation time reaches a predetermined cumulative operation time. The predetermined cumulative operation time may be a value that the user can appropriately set in consideration of the product life or the like. The notification unit may notify the user based on the cumulative operation time using the input / output interface 113 as an external device. The notification may also be made using a light source such as an LED, or may be made by voice announcement. In this way, the power conversion device 100 according to the first embodiment of the present disclosure can prompt the user to the need for maintenance or the like by notifying the user based on the cumulative operation time.

[0022] The control unit 11 may be configured to shift the carrier phase of the triangular wave in order to control the DCDC1 to DCDC4. The operation of shifting the phases of multiple DCDC converters to cancel out the ripples is called an interleaving operation. This interleaving operation makes it possible to miniaturize the input / output filter. There are various methods for the interleaving operation, but it can be realized by controlling to drive or stop multiple DCDC converters. For example, there is an operation in which four carrier phases are shifted by about 45 degrees. Two carrier phases may be shifted by about 90 degrees and four DCDC converters may be operated with two carrier phases. One of the four DCDCs may be stopped and the carrier phases of three may be shifted by about 60 degrees each. Two of the four DCDCs may be stopped and two may be operated with two carrier phases shifted by about 90 degrees. The above-mentioned approximately 45 degrees is 50 degrees or more and 40 degrees or less, and preferably 44 degrees or more and 46 degrees or less. The same applies to phase angles showing other values. Any phase shift that can suppress ripples is acceptable. Note that a sawtooth wave carrier may be used instead of the triangular wave carrier used for PWM switching control.

[0023] 3 is a graph showing the accumulated operation time of the power conversion device according to the first embodiment of the present disclosure. As shown in FIG. 3, t4 is the accumulated operation time of DCDC1, t3 is the accumulated operation time of DCDC2, t2 is the accumulated operation time of DCDC1, and t4 is the accumulated operation time of DCDC4. When the control unit 11 counts the accumulated operation time as shown in FIG. 3, the power conversion unit with the longest accumulated operation time is DCDC1. After identifying the power conversion unit with the longest accumulated operation time in this way, the control unit 11 performs control so that the accumulated operation time of the power conversion unit is differentiated from the other power conversion units.

[0024] FIG. 4 is a graph showing switching of the operation of the power conversion device according to the first embodiment of the present disclosure. The operation of one of the DCDC 20 is defined as a single operation, the operation of two of the DCDC 20 as a 2-parallel operation, the operation of three of the DCDC 20 as a 3-parallel operation, and the operation of all four of the DCDC 20 as a full parallel operation. The load state is defined as a first load state (single operation, 2-parallel operation, 3-parallel operation) except for a state in which all of the power conversion devices are operating, and a second load state (full parallel operation) except for a state in which all of the parallel-connected power conversion units are operating. In the power conversion device according to the first embodiment of the present disclosure, the heavier the load, the more the number of parallel DCDC converters is increased, thereby realizing a large capacity converter. That is, the control unit 11 can change the number of operating power conversion units in the first load state, which is a load state except for a state in which all of the parallel-connected power conversion units are operating.

[0025] In FIG. 4, the cumulative operation time of DCDC1 to DCDC4 is shown from the top of the figure, and the time T1 to T4 is the cumulative operation time at the current time. FIG. 4 shows the case where the number of operating units is changed after the next time from the current time. For the purpose of explanation, this operation is only described from light to heavy load, and operation from heavy to light load or operation with another load can also be performed. As shown in FIG. 4, the number of operating units is changed in order of the longest cumulative operation time as the operation operation of DCDC1 to DCDC4, and the period T1a is single operation, the period T2a is 2-parallel operation, the period T3a is 3-parallel operation, and the period T4a is full parallel operation.

[0026] In this way, when the multiple power conversion units are operating in the first load state, which is a load state other than the state in which all of the multiple power conversion units connected in parallel are operating, the control unit 11 can operate the multiple power conversion units, except for the power conversion unit with the longest cumulative operation time, in order of the cumulative operation time. Therefore, by making a difference in the cumulative operation time, the DCDC 20 is deteriorated in order, in other words, it is possible to suppress deterioration in order. Note that, although it is described in the explanation that it is in order of the longest, if the cumulative operation times are similar, it may be in order of the longest, and any control may be performed as long as a difference is generated in the cumulative operation time of at least one DCDC.

[0027] In addition, when the cumulative operation time exceeds a predetermined threshold, the operation of a certain DCDC converter can be stopped in consideration of the risk of failure and destruction. However, in an aircraft, it is necessary to continue operation rather than stopping in order to maintain flight functions. As for the operation after the threshold is reached, it is possible to continue operation in order of the cumulative operation time, as described above, but the cumulative operation time of the DCDC converter that exceeds the predetermined threshold may be suppressed as described next.

[0028] FIG. 5 is a graph showing switching of operations when the accumulated operation time of the power conversion device according to the first embodiment of the present disclosure exceeds a threshold. FIG. 5 shows the accumulated operation time of DCDC1 to DCDC4 from the top of the figure, and the accumulated operation time from time T5 to T8 is the accumulated operation time up to the present. As in FIG. 4, an operation is performed with the number of operating units changed in the first load state, and the period T5a is a single operation, the period T6a is a 2-parallel operation, the period T7a is a 3-parallel operation, and the period T8a is a full parallel operation. However, unlike FIG. 4, this is an operation when the accumulated operation time of DCDC1 exceeds a predetermined threshold at time T8. The control unit 11 operates DCDC1 to DCDC4 in order of the longest accumulated operation time until time T8 is reached, but when the predetermined threshold is reached, the control unit 11 operates DCDC2, which has the second longest accumulated operation time and has not reached the predetermined threshold, in order as the next operation, rather than DCDC1, which has exceeded the predetermined threshold.

[0029] In this way, when the power conversion unit with the longest cumulative operation time exceeds a predetermined cumulative operation time, the control unit 11 does not operate the power conversion unit with the longest cumulative operation time in the first load state, which is a load state other than the state in which all of the multiple power conversion units connected in parallel are operating. This makes it possible to limit the cumulative operation time of the power conversion unit that has exceeded its cumulative operation time to the minimum.

[0030] FIG. 6 is a graph showing switching of operation for each accumulated operation time of the power conversion device according to the first embodiment of the present disclosure. In the previous figures up to FIG. 5, the case was described where the DCDC1 with the longest accumulated operation time is operated first, and then the DCDC20 are operated in order of the longest accumulated operation time. Here, as shown in FIG. 6, a case will be described where the DCDC converter with the longest accumulated operation time (here, DCDC1) is operated first as the operation of DCDC1 to DCDC4, and the other DCDC2 to 4 are operated in order of the least accumulated operation time. Note that the period T1b is a single operation, the period T2b is a 2-parallel operation, the period T3b is a 3-parallel operation, and the period T4b is a full parallel operation. By operating in this way, it is possible to control so that at least one DCDC's operation time is different, and the other DCDC converters can be controlled with equal times. Here, "equal" means that the accumulated operation time of the DCDC converter with the longest accumulated operation time is dominant compared to the other DCDC converters, and includes an approximately equal degree of uniformity that can be considered to be approximately equal even if the accumulated operation times of the other DCDC converters vary slightly.

[0031] In this way, when the control unit 11 is operating multiple power conversion units in a first load state, which is a load state other than a state in which multiple power conversion units connected in parallel are all operating, the control unit 11 operates the other power conversion units, except for the power conversion unit with the longest accumulated operating time, evenly throughout their accumulated operating times, thereby accelerating the deterioration of at least one DCDC converter and equally slowing down the deterioration of the other DCDC converters.

[0032] In the above-described control, switching to another DCDC converter during the operation period of single operation, 2-parallel operation, or 3-parallel operation is not described, but switching to another DCDC converter may be performed.

[0033] In addition, when a DC-DC converter that has exceeded the cumulative operation time is subjected to maintenance, the cumulative operation time may be reset. The number of maintenance times may be input to the control unit 11. The reset process may be performed by changing the value by an external signal or by changing the value via a button or switch on a board or a case. Furthermore, in addition to the cumulative operation time described above, the deterioration of multiple DC-DC converters may be determined based on weighted information on the current value or the temperature change amount, and the deterioration may be differentiated.

[0034] Fig. 7 is a flowchart showing a control method according to the first embodiment of the present disclosure. As shown in Fig. 6, when control is started, in the control unit 11, in step S1, the accumulated operation time of the plurality of power conversion units is counted. Next, in step S2, based on the accumulated operation time counted in step S1, the power conversion unit with the longest accumulated operation time is operated first, and control is performed so as to differentiate the accumulated operation time of at least one power conversion unit.

[0035] As described above, the power conversion device 100 according to embodiment 1 includes a plurality of power conversion units connected in parallel, and a control unit that counts the cumulative operating time of the power conversion units and operates the power conversion unit with the longest cumulative operating time first, thereby controlling the cumulative operating time of at least one power conversion unit to be different from the other power conversion units, and changes the number of operating power conversion units.

[0036] Moreover, the power conversion system 300 according to the first embodiment of the present disclosure includes a DC source 30 and a power conversion device 100.

[0037] According to the power conversion device 100, the power conversion system 300, and the control method according to the first embodiment of the present disclosure, by creating a difference (bias) in the cumulative operation time of a plurality of power conversion units, it is possible to perform maintenance on a power conversion unit whose cumulative operation time has exceeded. Therefore, since it is only necessary to perform maintenance on a part of the power conversion device and its system each time maintenance is performed, rather than on the whole, it is possible to reduce maintenance costs.

[0038] In particular, in a vehicle that requires frequent maintenance, such as an aircraft, by installing the power conversion device 100, it is only necessary to maintain part of the system instead of the entire system, which has the effect of reducing maintenance costs.

[0039] When the cumulative operation time exceeds a predetermined threshold, the power conversion units that have not yet reached the predetermined threshold are operated in order, which has the effect of minimizing the cumulative operation time of the power conversion units that have exceeded the cumulative operation time. In addition, by operating the power conversion units other than those with the longest cumulative operation time in order of increasing cumulative operation time, it is possible to control them evenly and suppress the cumulative operation time. By suppressing the cumulative operation time, the risk of a malfunction can be prevented.

[0040] In the power conversion device 100 according to the first embodiment of the present disclosure, the case where the cumulative operation time of the DCDC1 is long is shown as an example of controlling so that the cumulative operation time of at least one power conversion unit is differentiated from other power conversion units. The present disclosure is not limited to this example, and there may be two or more power conversion units with the longest cumulative operation times.

[0041] In order to further improve the maintainability of the power conversion device 100, the multiple power conversion units may be unitized, such as a one-touch unit, so that the input / output units can be easily removed.

[0042] Embodiment 2 In the second embodiment, the same components as those in the first embodiment of the present disclosure are designated by the same reference numerals, and descriptions of the same or corresponding portions are omitted. Hereinafter, a power conversion device 100b according to the second embodiment will be described with reference to the drawings.

[0043] In the first embodiment, a means for reducing maintenance costs was described in which the cumulative operation time of multiple DC-DC converters is differentiated to enable maintenance of some of them compared to the whole. In the second embodiment, a technology is disclosed for extending the maintenance period and reducing maintenance costs by equalizing the failure rate from the viewpoint of reliability engineering.

[0044] FIG. 8 is a circuit diagram showing a configuration of a power conversion device according to a second embodiment of the present disclosure. The power conversion device 100b according to the second embodiment of the present disclosure has a plurality of power conversion units connected in parallel as in the first embodiment, but only the DCDC2 has a different circuit configuration among the DCDC1 to DCDC4. As shown in FIG. 8, the primary side of the transformer Tr2 is different, and the primary side in FIG. 8 is a half-bridge configuration consisting of two power semiconductor elements Q5 and Q6 and two capacitors C1 and C2 that create a neutral point potential. The circuit configurations of DCDC3 and DCDC4 are the same as that of DCDC1, except that the symbols are different. In other words, the power conversion device 100b according to the second embodiment of the present disclosure includes a plurality of power conversion units connected in parallel, in which at least one circuit has a different number of semiconductor elements from the other circuits. Here, the semiconductor elements refer to those used for power conversion, such as power semiconductor elements.

[0045] Of the DCDC1 to DCDC4 shown in Figure 8, only DCDC2 has a different circuit configuration in order to further improve efficiency in the first load state. By reducing the number of power semiconductors, switching losses can be reduced and efficiency can be improved. In addition, since the number of parts is small, there is a tendency for reliability to be high. Since the number of power semiconductors can be reduced, costs can be reduced, and since the associated gate drivers and gate power supplies can be reduced, miniaturization can also be expected. In other words, the operation of the highly efficient DCDC2 in the first load state leads to higher efficiency. However, as a disadvantage, the power capacity of DCDC2 is lower when configured as a half bridge compared to a full bridge.

[0046] Next, the control unit 11b in the power conversion device 100b according to the second embodiment of the present disclosure will be described. The control unit 11b uses an index called a failure rate. This failure rate is the frequency at which a part breaks down, and is expressed as the number of failures per unit time. It is generally represented by the Greek letter λ, and is often used in reliability engineering. The FIT value (Failure In Time) is an index and unit that indicates the failure rate of a product, and is the average number of failures for a predetermined time, for example, the average number of failures per 1 billion (10^9) hours of operation. A 10 FIT value means that 10 pieces fail in 1 billion hours. Note that it is easier to understand if the [FIT value] is [pieces / 10^9] (10 [FIT value] × 1 billion hours = 10 pieces). In the following description, since the term failure rate may be ambiguous, the failure rate λ of a part in a DC-DC converter is defined as a part failure rate λp, and the average number of failures for a single DC-DC converter is defined as a FIT value. The FIT value is the average number of failures per billion hours, and it is unclear where the failure will occur. In other words, a small FIT value does not necessarily mean a longer lifespan, but rather high reliability.

[0047] The component failure rate λp can be estimated based on, for example, the MIL standard (MIL-HDBK-217F). Note that the unit of MIL-HDBK-217F is a value per 1 million (10^6) operating hours. The basic idea is to use a different model formula for each component, and multiply it by a correction coefficient according to the environmental stress to obtain the component failure rate λp. The correction coefficient for environmental stress differs for each component. For example, the model formula for a transistor that operates at a high frequency is defined by equation (1), which also applies to the MOSFET shown in Figure 7. The component basic failure rate is λb, the temperature element is πT, the quality element is πQ, and the environmental element is πE.

[0048]

number

[0049] In addition, the FIT value of the desired DC-DC converter can be calculated by multiplying (Σ) the component failure rate λp and the quantity m of each component, as shown in formula (2). The 10^3 is the unit of measure. In the formula, the FIT value is written as FIT.

[0050]

number

[0051] In the DCDC1 to DCDC4 shown in FIG. 8, the FITs of DCDC1, 3, and 4 are FIT value_A, and the FIT of DCDC2, which has a different circuit configuration, is FIT value_B. If there is a component with a predominantly high component failure rate λp, the FIT value can be calculated by prioritizing only the numerical value of at least a specific component. When the components of a DCDC converter are composed of highly reliable components, the component failure rate λp of the power semiconductor tends to be the highest. In that case, the FIT value may be calculated only for the power semiconductor. In the following explanation, the FIT value is calculated assuming that the component failure rate of the power semiconductor is higher and predominant than that of other components, but it is preferable to calculate the FIT value by accumulating all the component components, since the FIT value of the DCDC can be calculated in detail.

[0052] The control unit 11b of the power conversion device 100b according to the second embodiment of the present disclosure controls DCDC1 to DCDC4 based on the FIT value calculated in advance. In the circuit of FIG. 7, FIT_A2 is calculated assuming that there are four power semiconductors on the primary side and two power semiconductors on the secondary side, and FIT_B2 is calculated assuming that there are two power semiconductors on the primary side and two on the secondary side. If the component failure rate λp is the same, the number of power semiconductors results in an FIT ratio of FIT_A2:FIT_B2=3:2. Therefore, if DCDC1 to DCDC4 are operated for the same time, the FIT value of DCDC2 is smaller than that of DCDC1, 3, and 4, and therefore the reliability is high. It is preferable to calculate the FIT values ​​of DCDC1 to DCDC4 in advance and store them as storage variable information in the storage device 112 of the control unit 11b. The information may be a specific FIT value or a ratio as described above. It is to be noted that the FIT value may be calculated not only for the power semiconductors described above, but also including other components.

[0053] Next, a method of extending the cumulative operation time and extending the maintenance period by equalizing the failure rate of the power conversion device 100b and equalizing the reliability will be described. In order to equalize the failure rate based on the calculated FIT value, it is necessary to distribute the ratio of the FIT value by the cumulative operation time. To distribute them, it is sufficient to control so that the FIT value x the cumulative operation time is equalized. In the case where the circuit configurations of the multiple DCDC converters shown in FIG. 7 are different, controlling the failure value to be equalized in the first load state increases the operation time of the efficient DCDC2, thereby realizing high efficiency and equalization of the failure rate.

[0054] In addition, the failure rate may be equalized, and multiple DCDC converters may be operated to prioritize high efficiency in the first load state by weighting the cumulative operation time. In particular, when operating alone in the first load state, the cumulative operation time of the DCDC converter with a smaller number of semiconductor elements (here, DCDC2) may be made longer than the other DCDC converters, thereby realizing equalization of failure rates and high efficiency operation. When operating multiple units, it is preferable to suppress the operation time of the highly efficient DCDC converter. Of course, it is not possible to equalize the failure rates, but the highly efficient DCDC converter may be actively operated in the first load state, and the FIT value x cumulative operation time may be calculated, while the highest priority may be given to high efficiency. In addition, when the FIT value x cumulative operation time exceeds a predetermined threshold, the operation of the highly efficient DCDC converter may be suppressed, and the FIT value x cumulative operation time may be equalized so that the failure rates are equalized.

[0055] Next, we will explain a calculation example in which one SBD (Schottky Barrier Diode) is connected in parallel to each of the two MOSFETs on the secondary side. By using a Schottky Barrier Diode, the VF loss in the built-in diode of the MOSFET can be reduced. The component failure rate of the SBD can also be calculated based on the MIL standard, but we will explain it assuming that the component failure rate of the SBD is approximately 0.1 times the component failure rate λp when the component failure rate of the MOSFET is 1. In this case, if the FIT value of the same circuit configuration is FIT_A3 and the FIT value of a different circuit configuration is FIT_B3, the ratio of the FIT values ​​is calculated as FIT_A3:FIT_B3=6.2:4.2. In order to equalize these failure rates, it is sufficient to equalize the FIT value x cumulative operating time as described above.

[0056] Although the average number of failures is equalized by equalizing the FIT value x cumulative operation time of each DCDC converter, control may be performed by equalizing the MTBF (Mean Time Between Failure) value, which is a value indicating the mean time between failures obtained by dividing the cumulative operation time by the number of failures (corresponding to the FIT value). Since this MTBF value uses the cumulative operation time and the number of failures, control using the MTBF value has the same effect as control using the FIT value.

[0057] Fig. 9 is a flowchart showing a control method according to the second embodiment of the present disclosure. As shown in Fig. 9, when the control unit 11b starts control, in step S1, the control unit 11b counts the cumulative operation time of a plurality of parallel-connected power conversion units, at least one of which has a circuit configuration different from that of the other power conversion units. Next, in step S2, the control unit 11b changes the number of operating power conversion units so as to equalize the failure rates of the plurality of power conversion units, using at least one of the FIT value, which is the average number of failures per predetermined time for the plurality of power conversion units, and the cumulative operation time, and the MTBF value calculated from the cumulative operation time and the number of failures.

[0058] As described above, the power conversion device 100b according to the second embodiment of the present disclosure includes a plurality of power conversion units connected in parallel, with at least one circuit having a different number of semiconductor elements than the other circuits, and a control unit that counts the cumulative operating time of the plurality of power units, and controls the plurality of power conversion units to have equal failure rates using at least one of the FIT value, which is the average number of failures per predetermined time for the plurality of power conversion units, and the cumulative operating time, and the MTBF value calculated from the cumulative operating time and the number of failures, and changes the number of operating power conversion units.

[0059] By configuring in this way, it is possible to equalize the failure rate based on the mean number of failures and the mean time between failures, and to equalize the reliability. This makes it possible to extend the overall maintenance period, and has the effect of reducing maintenance costs, similar to the first embodiment.

[0060] In the power conversion device 100b according to the second embodiment of the present disclosure, the component failure rate is estimated based on the MIL standard, but it can be estimated by other means. For example, it can be calculated using the reliability prediction method of Telcordia SR-332, or it can be calculated based on the component failure rate calculated based on the manufacturer's unique test data and the component failure rate calculation means.

[0061] In the first and second embodiments of the present disclosure, the DC-DC converter has been described as an isolated type, but it may be configured as a non-isolated boost converter, a step-down converter, a step-up / step-down converter, or the like.

[0062] In addition, when calculating the FIT value, the circuit configuration of the isolated DCDC converter has been described in this disclosure as a circuit configuration in which the primary side of the DCDC converter is a full bridge or a half bridge, but other known circuit configurations may be used. For example, typical examples include a flyback converter, a forward converter, a bridge converter, and a push-pull converter. In addition, an additional parallel element may be connected to increase the current capacity or reduce loss, or an additional series element that distributes the voltage may be connected. It is sufficient that at least a part of the circuit configuration or the number of parts of the DCDC is different, and the FIT value of any of the DCDC converters is different.

[0063] In the power conversion device 100b according to the second embodiment of the present disclosure, as in the first embodiment, an example has been described in which a DC-DC converter is used in the power conversion section. However, any power conversion section that connects inputs and outputs in parallel and switches the number of parallel units using a semiconductor switch may be used.

[0064] As in the first embodiment, the control unit 11b can change the number of operating power conversion units in a first load state, which is a load state other than the state in which all of the multiple power conversion units connected in parallel are operating.

[0065] Moreover, a power conversion system 300b according to the second embodiment of the present disclosure includes a DC source 30 and a power conversion device 100b.

[0066] Moreover, the power conversion device 100b according to the second embodiment of the present disclosure has a plurality of parallel-connected power conversion units, at least one of which has a different number of semiconductor elements from the other circuits, and therefore some of the power conversion units are more efficient than the other power conversion units. The control unit 11b can achieve further high efficiency by lengthening the cumulative operation time of the power conversion unit having a different number of semiconductor elements from the other power conversion units in a first load state, which is a load state other than the state in which all of the parallel-connected power conversion units are operating, relative to the cumulative operation time of the other power conversion units. Furthermore, by configuring the power conversion units having some different circuit configurations with power conversion units having a smaller number of parts, it is possible to reduce the size and weight.

[0067] Embodiment 3 In the third embodiment, a flying object 200 including the power converter 100 according to the first or second embodiment will be described. The flying object 200 is, for example, an airplane, a helicopter, a drone, a flying car, or the like.

[0068] FIG. 10 is a schematic diagram showing the configuration of a flying object according to the third embodiment of the present disclosure. As shown in FIG. 10, the flying object 200 according to the third embodiment of the present disclosure includes a DC source 30, an accessory 44 that operates using the power of the DC source 30, and a power conversion device including a plurality of power conversion units and a control unit described in the first or second embodiment. In the following, an example using a DCDC 20 is shown as an example of a plurality of power conversion units, as in the first and second embodiments of the present disclosure. The flying object 200 is an electrically powered flying object, and includes, as its propulsion power system 90, a power source 92, a DC source 30 connected to the power source 92, an inverter 21 connected to the DC source 30 and converting the DC power to a predetermined voltage by the step-down, step-up, or step-down DCDC 20, an inverter 21 that converts the stepped-down or stepped-down DC power to AC power, and an accessory 44 to which power is supplied as a load of the inverter 21.

[0069] In the flying object 200 according to the third embodiment of the present disclosure, the control unit 11c may have a function of controlling the inverter 21 in addition to controlling the DCDC 20. The control unit 11c and the DCDC 20 constitute the power conversion device according to the first and second embodiments of the present disclosure. In this case, the control unit 11c may be provided inside the DCDC or may be provided in a device separate from the DCDC 20. The equipment 44 is an equipment that uses the power of the DC source 30. The equipment 44 is a propulsion load for obtaining propulsive force, for example, an electric motor.

[0070] The flying object 200 of this embodiment 3 uses the power generated by the power conversion device according to the first and second embodiments of the present disclosure as a power supply source for the inverter 21 and equipment 44 mounted on the flying object 200.

[0071] As described above, the flying object 200 according to the third embodiment of the present disclosure includes the DC source 30, the accessories that operate using the power of the DC source 30, and a power conversion device including a plurality of power conversion units and a control unit described in the first or second embodiment. This reduces the maintenance cost of the power conversion device mounted on the flying object 200 according to the third embodiment of the present disclosure. The reduced maintenance cost allows the safety and reliability of the flying object 200 to be ensured at low cost.

[0072] Embodiment 4 In the fourth embodiment, a flying object 200b including the power converter 100 according to the first or second embodiment will be described. The flying object 200b is, for example, an airplane, a helicopter, a drone, a flying car, or the like.

[0073] 11 is a schematic diagram showing the configuration of a flying object according to the fourth embodiment of the present disclosure. The flying object 200b according to the fourth embodiment of the present disclosure includes a DC source 30, an accessory 45 that operates using the power of the DC source 30, a power source 92 including an AC power source, an AC / DC converter 93 that converts the AC power of the power source 92 into DC power, and a power conversion device including a plurality of power conversion units and a control unit 11d described in the first or second embodiment. In the following, an example using a DCDC 20 will be shown as an example of a plurality of power conversion units, as in the first and second embodiments of the present disclosure. In the flying object 200b, the equipment power system 94 includes a power source 92 including an AC power source, an AC / DC converter 93 that converts the AC power of the power source 92 into DC power, a DC source 30 connected to the AC / DC converter 93, a DCDC 20 that is connected to the DC source 30 and converts the voltage to a predetermined voltage by stepping down, stepping up, or stepping up / down, an inverter 21 that converts the DC power converted by the DCDC 20 into AC power, and equipment 45 to which power is supplied as a load of the inverter 21.

[0074] In the flying object according to the fourth embodiment of the present disclosure, the control unit 11d may have a function of controlling the inverter 21 and the AC / DC converter 93 in addition to controlling the DCDC 20. The control unit 11d and the DCDC 20 configure the power conversion device according to the first and second embodiments of the present disclosure. The control unit 11d may be provided inside the DCDC 20 or may be provided in a device separate from the DCDC 20.

[0075] The equipment 45 is an equipment that uses the power of the DC source 30, and refers to, for example, an air conditioner, an engine starter, an electric motor used to drive an auxiliary power device, etc. DC power may be supplied to the equipment 45 without passing through the inverter 21.

[0076] As described above, the flying object 200b according to the fourth embodiment of the present disclosure includes the DC source 30, the accessory 45 that operates using the power of the DC source 30, the power source 92 including an AC power source, the AC / DC converter 93 that converts the AC power of the power source 92 into DC power, and a power conversion device including a plurality of power conversion units and the control unit 11d described in the first or second embodiment. This can reduce the maintenance cost of the power conversion device mounted on the flying object 200d according to the fourth embodiment of the present disclosure. By reducing the maintenance cost, the safety and reliability of the flying object 200 can be ensured at low cost, as in the third embodiment.

[0077] The configurations shown in the above embodiments are merely examples of the contents of the present disclosure, and may be combined with other known techniques. Furthermore, parts of the configurations may be omitted or modified without departing from the scope of the present disclosure. [Explanation of symbols]

[0078] 1 first DCDC converter, 2 second DCDC converter, 3 third DCDC converter, 4 fourth DCDC converter, 11 control unit, 20 DCDC, 21 inverter, 30 DC source, 40 load, 44 45 equipment, 90 propulsion power system, 92 power source, 93 AC / DC converter, 94 equipment power system, 100 100b power conversion device, 111 arithmetic processing device, 112 storage device, 113 input / output interface, 200 200b flying object, 300 300b power conversion system

Claims

1. A plurality of power conversion units connected in parallel; a control unit that counts the cumulative operating time of the multiple power conversion units, and when changing the number of operating power conversion units, controls the cumulative operating time of at least one of the power conversion units to be different from the other power conversion units by first operating the power conversion unit among the multiple power conversion units that has the longest cumulative operating time.

2. A plurality of power conversion units connected in parallel, at least one of which has a different number of semiconductor elements from the other circuits; a control unit that counts the cumulative operating time of each of the multiple power conversion units, and when changing the number of operating power conversion units, uses an FIT value, which is an average number of failures per predetermined time for each of the multiple power conversion units, to calculate a multiplication value of the FIT value and the cumulative operating time for each of the multiple power conversion units, and controls the multiplication values ​​of the multiple power conversion units to be equal.

3. A plurality of power conversion units connected in parallel, at least one of which has a different number of semiconductor elements than the other circuits; a control unit that counts a cumulative operating time of each of the multiple power conversion units, and when changing the number of operating units of the multiple power conversion units, calculates an MTBF value for each of the multiple power conversion units by dividing the cumulative operating time by the number of failures using a predetermined number of failures for each of the multiple power conversion units, and controls the MTBF values ​​of the multiple power conversion units to be equal.

4. The power conversion device according to any one of claims 1 to 3, characterized in that the control unit changes the number of operating power conversion units in a first load state, which is a load state other than a state in which all of the multiple power conversion units connected in parallel are operating.

5. The power conversion device according to claim 1 , further comprising: a notification unit that notifies when the accumulated operation time of the power conversion unit with the longest accumulated operation time reaches a predetermined accumulated operation time.

6. The power conversion device according to claim 1, characterized in that when the multiple power conversion units are operating in a first load state, which is a load state other than a state in which all of the multiple power conversion units connected in parallel are operating, the control unit operates the other power conversion units among the multiple power conversion units, except for the power conversion unit having the longest accumulated operating time, in order of the longest accumulated operating time.

7. The power conversion device according to claim 1, characterized in that when the multiple power conversion units are operating in a first load state, which is a load state other than a state in which all of the multiple power conversion units connected in parallel are operating, the control unit operates the other power conversion units, except for the power conversion unit having the longest cumulative operating time, evenly throughout their accumulated operating times.

8. The power conversion device according to any one of claims 1 and 5 to 7, characterized in that when the power conversion unit with the longest cumulative operating time exceeds a predetermined cumulative operating time, the control unit does not operate the power conversion unit with the longest cumulative operating time in a first load state, which is a load state other than a state in which all of the multiple power conversion units connected in parallel are operating.

9. The power conversion device according to claim 2 or 3, characterized in that the control unit extends the cumulative operating time of the power conversion unit in which the number of semiconductor elements is different from the circuits of the other power conversion units, relative to the cumulative operating time of the other power conversion units, in a first load state, which is a load state excluding a state in which all of the multiple power conversion units connected in parallel are operating.

10. A direct current source; A power conversion system comprising the power conversion device according to any one of claims 1 to 3 or 5 to 7.

11. A direct current source; An equipment that operates using power from the DC source; A flying object comprising the power conversion device according to any one of claims 1 to 3 or 5 to 7.

12. a power source including an AC power source; The flying object according to claim 11 , further comprising an AC / DC converter for converting the AC power of the power source into DC power.

13. A step of counting a cumulative operation time of a plurality of power conversion units connected in parallel; When changing the number of operating power conversion units of the plurality of power conversion units, a control step is performed in which the power conversion unit having the longest cumulative operating time is operated first among the plurality of power conversion units, thereby controlling the cumulative operating time of at least one of the power conversion units to be different from the other power conversion units.

14. Counting an accumulated operation time of each of a plurality of parallel-connected power conversion units, at least one of which has a different number of semiconductor elements from the other circuits; A control method comprising a step of, when changing the number of operating units of the plurality of power conversion units, calculating a multiplication value of the FIT value and the accumulated operating time for each of the plurality of power conversion units using an FIT value, which is an average number of failures per predetermined time for each of the plurality of power conversion units, and controlling so that the multiplication values ​​of the plurality of power conversion units are equal.

15. A step of counting a cumulative operating time of each of a plurality of parallel-connected power conversion units, at least one of which has a different number of semiconductor elements from the other circuits; a step of controlling the number of operating power conversion units of the plurality of power conversion units so that the MTBF values ​​of the plurality of power conversion units are equal, the step of calculating an MTBF value for each of the plurality of power conversion units by dividing the cumulative operating time by the number of failures, using a predetermined number of failures for each of the plurality of power conversion units, when changing the number of operating power conversion units of the plurality of power conversion units.

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