Power conversion device, power conversion system, flying object, and control method

Abstract

A power conversion device (100) according to the present disclosure is characterized by comprising: a plurality of power conversion units (20) that are connected in parallel; and a control unit (11) that counts the cumulative operation time of each of the plurality of power conversion units, performs control of operating a power conversion unit with the longest cumulative operation time first to make the cumulative operation time of at least one power conversion unit diverge from those of the other power conversion units, and changes the number of the plurality of power conversion units in operation.

Description

Power conversion device, power conversion system, flying object, and control method

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

[0002] In recent years, there has been a growing trend around the world to electrify flying objects in order to reduce carbon dioxide emissions. To meet a wide range of power demands, the electrification of flying objects requires a system in which multiple power converters are connected in parallel to increase the power capacity of the power conversion device. Even in high-capacity power conversion devices in which multiple power converters are connected in parallel, there is a demand for miniaturization, weight reduction, and high efficiency.

[0003] For example, Patent Document 1 discloses a technique for increasing the efficiency of multiple power conversion units connected in parallel, in which one of the multiple conversion units is operated according to the load current value, and the number of units in operation is switched. By switching the number of units in operation in this way, operation can be performed according to the load state, enabling highly efficient operation.

[0004] International Publication No. 2021 / 182447

[0005] Here, when electrifying flying objects, continued flight function is important, so power conversion devices are required to be highly reliable and safe in addition to being highly efficient. To maintain high reliability and safety, power conversion devices require more frequent maintenance than power conversion devices for general industrial or automotive applications. 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-described problems, and has an object to provide a power conversion device that can reduce maintenance costs.

[0007] The power conversion device according to the present disclosure includes a plurality of power conversion units connected in parallel, and a control unit 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.

[0008] The control method according to the present disclosure includes the steps of counting the cumulative operating time of a plurality of power conversion units, and operating the power conversion unit with the longest cumulative operating time among the plurality of power conversion units first, thereby controlling the cumulative operating time of at least one power conversion unit to create a difference.

[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.

[0010] FIG. 1 is a circuit diagram showing a configuration of a power conversion device according to a first embodiment of the present disclosure. FIG. 2 is a schematic diagram showing a hardware configuration of a control unit of the power conversion device according to the first embodiment of the present disclosure. FIG. 3 is a graph showing a cumulative operating time for each power conversion unit of the power conversion device according to the first embodiment of the present disclosure. FIG. 4 is a graph showing switching of operation of the power conversion device according to the first embodiment of the present disclosure. FIG. 5 is a graph showing switching of operation when the cumulative operating time of the power conversion device according to the first embodiment of the present disclosure exceeds a threshold. FIG. 6 is a graph showing switching of operation for each cumulative operating time of the power conversion device according to the first embodiment of the present disclosure. FIG. 7 is a flowchart showing a control method according to the first embodiment of the present disclosure. FIG. 8 is a circuit diagram showing a configuration of a power conversion device according to a second embodiment of the present disclosure. FIG. 9 is a flowchart showing a control method according to the second embodiment of the present disclosure. FIG. 10 is a schematic diagram showing a configuration of a flying object according to a third embodiment of the present disclosure. FIG. 11 is a schematic diagram showing a configuration of a flying object according to a fourth embodiment of the present disclosure.

[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] First Embodiment. FIG. 1 is a circuit diagram illustrating 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 and supplies power to a load 40. The central part of the power conversion device 100 is composed of four power conversion units whose inputs and outputs are connected in parallel. Note that 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 connected in parallel using a semiconductor switch. For example, the power conversion units may be an inverter (DC / AC) that converts a DC voltage to an AC voltage, a PWM converter (AC / DC) that converts an AC voltage to a DC voltage, a DC-DC converter that converts a DC voltage, or the like. The following describes an example in which a DC-DC converter is used as the power conversion unit.

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

[0014] In the following description, the first DC-DC converter 1 will be referred to as DC-DC1, the second DC-DC converter 2 as DC-DC2, the third DC-DC converter 3 as DC-DC3, the fourth DC-DC converter 4 as DC-DC4, and the four DC-DC converters as DC-DC20.

[0015] The DC source 30 may be a battery, a DC power source or other battery system 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 DC voltage to AC voltage. While FIG. 1 illustrates four parallel-connected DCDCs 20, this does not limit the present disclosure, and a configuration in which at least two or more DCDC converters are connected in parallel may also be used. Although not shown, the input sides of the DCDCs 1 to 4 may include at least one of a smoothing capacitor, a normal mode filter, and a common mode filter. Similarly, the output sides of the DCDCs 1 to 4 may also include at least one of a smoothing capacitor, a normal mode filter, and a common mode filter.

[0016] Next, the circuit configuration of the DCDC1 will be described. The DCDC2 to DCDC4 of the first embodiment have similar circuit configurations, and therefore their description will be omitted. The DCDC1 is an isolated DCDC converter that uses a transformer Tr1 for isolation. The primary side of the transformer Tr1 has a full-bridge configuration with four power semiconductor elements Q1 to Q4, the secondary side of the transformer Tr1 has a center-tap configuration and full-wave rectification with power semiconductor elements Q11 and Q12, and the filter section is configured for smoothing using a reactor Lf and a capacitor Cf. Since the interleaving operation of capacitor Cf, which will be described later, can be used to reduce the size of the filter capacitor, multiple capacitors Cf in the DCDC 20 may be integrated into a single unit. Similarly, multiple reactors Lf in the DCDC 20 may be integrated into a single unit to reduce the size, as in the case of a coupling reactor. The power semiconductor elements Q1 to Q4, Q11, and Q12 are self-extinguishing devices such as insulated gate bipolar transistors (IGBTs) and metal-oxide-semiconductor field-effect transistors (MOSFETs). FIG. 1 shows a case where a MOSFET is used.

[0017] FIG. 2 is a schematic diagram illustrating the hardware configuration of a control unit of a power conversion apparatus according to the first embodiment of the present disclosure. The control unit 11 counts the cumulative operating time of multiple power conversion units connected in parallel 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 changing the number of operating multiple power conversion units. As illustrated in FIG. 2 , the control unit 11 includes a central processing unit (CPU) or other arithmetic processing device 111 for controlling the DCDCs 1 to 4, a storage device 112 for exchanging data with the arithmetic processing device 111, and an input / output interface 113 for inputting and outputting signals between the arithmetic processing device 111 and the outside. The power conversion apparatus 100 can change the number of operating DCDCs 20 using the control unit 11. For example, by reducing the number of DCDCs 20 in operation, it is possible to improve losses during light loads 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. Furthermore, the arithmetic processing device 111 may be a plurality of the same 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 unit 111, a gate drive circuit for driving each switching element, and an alarm unit described later.

[0019] The control unit 11 controls the output voltage and the current of the DCDC1 to DCDC4 based on, for example, the input voltage, output voltage, and current information of the DCDC1 to DCDC4. The aforementioned current may be the primary current of the transformer or the current of the reactor Lf. Furthermore, the control unit 11 may detect overvoltage and overcurrent based on the detected voltage and current information, and may stop the entire DCDC 20 or at least one DCDC converter at a protection threshold for protection. A temperature sensor may be provided to input temperature information, or protection may be based on a threshold.

[0020] The control unit 11 outputs a detection signal 102 for driving the primary-side power semiconductor elements Q1 to Q4 of the DCDC1 to DCDC4 and the secondary-side power semiconductors Q11 and Q12. The gate signal is generated using a triangular wave comparison method such as PWM (Pulse Width Modulation) control. Meanwhile, the secondary-side power semiconductors Q11 and Q12 may be synchronously rectified to reduce conduction loss due to the diode VF. Instead of duty control using PWM control, PFM (Pulse Frequency Modulation) control, which controls frequency, may be used. The pulse width output by the primary-side full-bridge circuit may be controlled to output symmetric pulses, or may be controlled to output asymmetric pulses for soft switching or the like.

[0021] The control unit 11 counts the cumulative operating time of the DCDC1 to DCDC4 in the arithmetic processing unit 111 or the storage device 112. The cumulative operating time may be counted as gate output time or 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 issues a notification when the cumulative operating time of the power conversion unit with the longest cumulative operating time reaches a predetermined cumulative operating time. The predetermined cumulative operating time may be a value that the user can set appropriately, taking into account the product lifespan, etc. The notification unit may issue a notification based on the cumulative operating time via the input / output interface 113 as an external device. The notification may also be issued using a light source such as an LED, or 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, etc., by issuing a notification based on the cumulative operating time.

[0022] The control unit 11 may be configured to shift the carrier phases of the triangular waves to control DCDC1 to DCDC4. The operation of shifting the phases of multiple DCDC converters to cancel out ripples is called interleaving. This interleaving operation enables the miniaturization of input / output filters. There are various methods for interleaving, but it can be achieved by controlling the operation or stopping of multiple DCDC converters. For example, four carrier phases may be shifted by approximately 45 degrees. Two carrier phases may be shifted by approximately 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 approximately 60 degrees each. Two of the four DCDCs may be stopped, and two may be operated with two carrier phases shifted by approximately 90 degrees. The aforementioned "approximately 45 degrees" refers to a range of 50 degrees to 40 degrees, preferably 44 degrees to 46 degrees. The same applies to phase angles showing other values. Any phase shift that can suppress ripples is sufficient. 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 cumulative operation time of the power conversion device according to the first embodiment of the present disclosure. As shown in FIG. 3, t4 is the cumulative operation time of DCDC1, t3 is the cumulative operation time of DCDC2, t2 is the cumulative operation time of DCDC1, and t4 is the cumulative operation time of DCDC4. When the control unit 11 counts the cumulative operation time as shown in FIG. 3, the power conversion unit with the longest cumulative operation time is DCDC1. After identifying the power conversion unit with the longest cumulative operation time in this manner, the control unit 11 performs control such that the cumulative operation time of that 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 converters 20 is referred to as standalone operation, the operation of two of the DCDC converters 20 as dual-parallel operation, the operation of three of the DCDC converters 20 as triple-parallel operation, and the operation of all four DCDC converters 20 as full-parallel operation. The load states are defined as a first load state (single-parallel operation, dual-parallel operation, triple-parallel operation) excluding a state in which all of the power conversion devices are operating, and a second load state (full-parallel operation) excluding 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 parallel-connected DCDC converters are connected, thereby achieving a larger converter capacity. In other words, the control unit 11 can change the number of operating power conversion units in the first load state, which is a load state excluding a state in which all of the parallel-connected power conversion units are operating.

[0025] In Figure 4, the cumulative operating time of DCDC1 to DCDC4 is shown from top to bottom, with times T1 to T4 representing the cumulative operating time at the current point in time. Figure 4 shows a case where the number of operating units is changed from the next time onward after the current point in time. For the purpose of explanation, this operation is described from a light to a heavy load; operation from a heavy to a light load, or operation under a different load, is also possible. As shown in Figure 4, the number of operating units is changed in order of the longest cumulative operating time for the operation of DCDC1 to DCDC4, with the period T1a representing single-unit operation, the period T2a representing 2-parallel operation, the period T3a representing 3-parallel operation, and the period T4a representing full-parallel operation.

[0026] In this way, 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 11 can operate the multiple power conversion units, excluding the power conversion unit with the longest cumulative operating time, in order of the longest cumulative operating time. Therefore, by differentiating the cumulative operating time, the DCDCs 20 are deteriorated in order, in other words, deterioration can be suppressed in order. Note that although the explanation describes the order of longest, if the cumulative operating times are similar, the order of longest may also be used. Any control may be performed as long as there is a difference in the cumulative operating time of at least one DCDC.

[0027] If the cumulative operating time exceeds a predetermined threshold, the operation of a certain DC-DC converter can be stopped to prevent malfunction and destruction. However, in an aircraft, it is also necessary to continue operation rather than stopping it in order to maintain flight functions. As described above, after the threshold is reached, it is possible to continue operation in order of the longest cumulative operating time, but as will be explained next, the cumulative operating time of a DC-DC converter that has exceeded the predetermined threshold can also be reduced.

[0028] FIG. 5 is a graph showing switching of operation when the cumulative operating time of the power conversion device according to the first embodiment of the present disclosure exceeds a threshold. FIG. 5 shows the cumulative operating time of DCDC1 to DCDC4 from top to bottom, with times T5 to T8 representing the cumulative operating time up to the present. Similar to FIG. 4 , operation is performed with the number of operating units changed in the first load state, with single operation during the period T5a, two-parallel operation during the period T6a, three-parallel operation during the period T7a, and full-parallel operation during the period T8a. However, unlike FIG. 4 , this graph shows the operation when the cumulative operating time of DCDC1 exceeds a predetermined threshold at time T8. Until time T8 is reached, the control unit 11 operates DCDC1 to DCDC4 in descending order of cumulative operating time. However, when the predetermined threshold is reached, the control unit 11 operates DCDC2, which has the second-longest cumulative operating time and has not yet reached the predetermined threshold, 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 a power conversion unit that has exceeded its cumulative operation time to the minimum.

[0030] FIG. 6 is a graph showing operation switching for each cumulative operation time of the power conversion device according to the first embodiment of the present disclosure. Up until FIG. 5 , a case has been described in which the DCDC1 with the longest cumulative operation time is operated first, followed by the DCDCs 20 in descending order of cumulative operation time. Here, as shown in FIG. 6 , a case will be described in which the DCDC1 to DCDC4 are operated in ascending order of cumulative operation time, with the DCDC1 (here, DCDC1) being operated first, and the other DCDCs 2 to 4 being operated in descending order of cumulative operation time. Note that the period T1b is single operation, the period T2b is 2-parallel operation, the period T3b is 3-parallel operation, and the period T4b is full-parallel operation. By operating in this manner, it is possible to control at least one DCDC to have a different operating time, and the other DCDC converters can be controlled for equal periods of time. Here, "equal" refers to the cumulative operation time of the DCDC converter with the longest cumulative operation time being dominant compared to the other DCDC converters, and includes the term "approximately equal" to the extent that the other DCDC converters can be considered approximately equal even if their cumulative operation times 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 the state in which multiple power conversion units connected in parallel are all operating, the accumulated operating times of the other power conversion units, excluding the power conversion unit with the longest accumulated operating time, are operated evenly, thereby accelerating the deterioration of at least one DC-DC converter and slowing down the deterioration of the other DC-DC converters evenly.

[0032] In the above-described control, switching to another DC-DC converter during the single operation, two-parallel operation, or three-parallel operation period is not described, but switching to another DC-DC converter may also be performed.

[0033] If a DC-DC converter that has exceeded its cumulative operating time undergoes maintenance, the cumulative operating time may be reset. The number of maintenance cycles may also be input to the control unit 11. The reset process may be performed using an external signal or a button or switch on the circuit board or housing. Furthermore, the deterioration of multiple DC-DC converters may be determined based on weighted information on the current value or temperature change amount in addition to the cumulative operating time described above, and the converters may be controlled to differentiate the degree of deterioration.

[0034] 7 is a flowchart showing a control method according to the first embodiment of the present disclosure. As shown in FIG. 6, when control starts, in step S1, the control unit 11 counts the cumulative operating time of a plurality of power conversion units. Next, in step S2, based on the cumulative operating time counted in step S1, the power conversion unit with the longest cumulative operating time is operated first, and control is performed to differentiate the cumulative operating 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 operating time of a plurality of power conversion units, it is possible to perform maintenance on a power conversion unit that has exceeded its cumulative operating time. Therefore, each time maintenance is performed, it is only necessary to perform maintenance on a portion of the power conversion device and its system, rather than the entire system, thereby reducing maintenance costs.

[0038] In particular, in a device that requires frequent maintenance, such as a flying object, 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 operating time exceeds a predetermined threshold, the power conversion units that have not yet reached the predetermined threshold are operated in order, thereby minimizing the cumulative operating time of the power conversion units that have exceeded the cumulative operating time. Furthermore, by operating the power conversion units other than those with the longest cumulative operating time in order of least to most, uniform control can be achieved, thereby minimizing the cumulative operating time. By minimizing the cumulative operating 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, a case where the cumulative operation time of the DCDC1 is long is shown as an example of controlling the cumulative operation time of at least one power conversion unit so that it is different from the other power conversion units. The present disclosure is not limited to this example, and two or more power conversion units may have the longest cumulative operation time.

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

[0042] Second Embodiment In a 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 parts will be 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 operating times of multiple DC-DC converters were differentiated to enable maintenance of some of them compared to the whole. In the second embodiment, a technology is disclosed in which the failure rates are equalized from the viewpoint of reliability engineering to extend the maintenance period and reduce maintenance costs.

[0044] FIG. 8 is a circuit diagram illustrating the 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 includes multiple power conversion units connected in parallel, as in the first embodiment. However, among DCDC1 to DCDC4, only DCDC2 has a different circuit configuration. As shown in FIG. 8 , the primary side of the transformer Tr2 is different. The primary side in FIG. 8 is configured as a half-bridge including two power semiconductor elements Q5 and Q6 and two capacitors C1 and C2 that generate a neutral point potential. The circuit configurations of DCDC3 and DCDC4 are the same as DCDC1, except for the symbols. In other words, the power conversion device 100b according to the second embodiment of the present disclosure includes multiple power conversion units connected in parallel, with at least one circuit having a different number of semiconductor elements from the other circuits. Here, the semiconductor elements refer to elements 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. Reducing the number of power semiconductors reduces switching losses and other factors, resulting in higher efficiency. In addition, the fewer parts, the higher reliability tends to be achieved. Reducing the number of power semiconductors is expected to reduce costs, and the associated gate drivers and gate power supplies can also be reduced, resulting in smaller size. In other words, operating the highly efficient DCDC2 in the first load state leads to higher efficiency. However, as a disadvantage, the half-bridge configuration reduces the power capacity of DCDC2 compared to a full-bridge configuration.

[0046] Next, a control unit 11b in a power conversion device 100b according to a 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 component fails 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 represents the failure rate of a product and is the average number of failures per predetermined time, for example, the average number of failures per 1 billion (10^9) hours of operation. A 10 FIT value means that 10 components fail in 1 billion hours. Note that the FIT value can be easily understood by defining it as [components / 10^9] (10 [FIT value] × 1 billion hours = 10 components). In the following explanation, since the term "failure rate" may be ambiguous, the failure rate λ of a component in a DC-DC converter is defined as the component failure rate λp, and the average number of failures for a single DC-DC converter is defined as the FIT value. Note that the FIT value is the average number of failures per billion hours, and it is unknown where the failures will occur. In other words, a small FIT value does not necessarily mean a longer lifespan, but rather indicates 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 concept is to use a different model formula for each component and multiply it by a correction coefficient according to the environmental stress to determine 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 equations are the component basic failure rate λb, the temperature element πT, the quality element πQ, and the environmental element πE.

[0048]

[0049] The desired FIT value of the DC-DC converter can be calculated by multiplying the component failure rate λp of each component by the quantity m (Σ) as shown in equation (2). 10^3 is used to match the units. In the equation, the FIT value is expressed as FIT.

[0050]

[0051] In the DCDC1 to DCDC4 shown in FIG. 8 , the FITs of DCDC1, 3, and 4 are designated FIT_A, and DCDC2, which has a different circuit configuration, is designated FIT_B. If there are components with a predominantly high component failure rate λp, the FIT value can be calculated by prioritizing only the numerical values ​​of at least certain specific components. When the components of a DCDC converter are configured with highly reliable components, the component failure rate λp of power semiconductors tends to be the highest. In this case, the FIT value can be calculated for only the power semiconductors. In the following description, the FIT value is calculated assuming that the component failure rate of power semiconductors is predominantly high compared to other components. However, calculating the FIT value by integrating all component components is preferable in practice because it allows for a more detailed calculation of the DCDC FIT value.

[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 a pre-calculated FIT value. In the circuit of FIG. 7 , FIT_A2 is calculated based on four primary-side power semiconductors and two secondary-side power semiconductors, and FIT_B2 is calculated based on two primary-side power semiconductors and two secondary-side power semiconductors. Assuming the same component failure rate λp, the number of power semiconductors results in an FIT ratio of FIT_A2:FIT_B2 = 3:2. Therefore, when DCDC1 to DCDC4 are operated for the same period of time, the FIT value of DCDC2 is smaller than that of DCDC1, 3, and 4, resulting in higher reliability. It is preferable to pre-calculate the FIT values ​​of DCDC1 to DCDC4 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 should be noted that the FIT value may be calculated not only for the power semiconductors described above but also for other components.

[0053] Next, a method for extending the cumulative operating time and maintenance interval by equalizing the failure rates and reliability of the power conversion device 100b will be described. To equalize the failure rates based on the calculated FIT values, the ratio of the FIT values ​​must be distributed over the cumulative operating time. To achieve this distribution, the FIT value multiplied by the cumulative operating time can be controlled to be uniform. When the multiple DC-DC converters shown in FIG. 7 have different circuit configurations, controlling the failure values ​​to be uniform in the first load state increases the operating time of the efficient DC-DC converter 2, thereby achieving high efficiency and equalizing the failure rates.

[0054] Furthermore, while maintaining equalization of failure rates, multiple DC-DC converters may be operated to prioritize high efficiency under the first load condition by weighting the cumulative operating time. In particular, when operating standalone under the first load condition, equalization of failure rates and high-efficiency operation can be achieved by lengthening the cumulative operating time of a DC-DC converter with a smaller number of semiconductor elements (here, DCDC2) than the other DC-DC converters. When operating multiple DC-DC converters, it is preferable to reduce the operating time of the high-efficiency DC-DC converter. While this will of course prevent equalization of failure rates, the high-efficiency DC-DC converter may be actively operated under the first load condition, and high efficiency may be prioritized while calculating the FIT value x cumulative operating time. If the FIT value x cumulative operating time exceeds a predetermined threshold, the operation of the high-efficiency DC-DC converter may be reduced, and the FIT value x cumulative operating time may be equalized to equalize the failure rates.

[0055] Next, we will explain a calculation example in which one SBD (Schottky barrier diode) is connected in parallel to each of two secondary-side MOSFETs. Using a Schottky barrier diode can reduce VF loss relative to the MOSFET's built-in diode. The component failure rate for an SBD can also be calculated based on the MIL standard. However, we will assume that the component failure rate λp for an SBD is approximately 0.1 times that of a MOSFET. In this case, if the FIT value for a circuit with the same configuration is FIT_A3 and the FIT value for a circuit with a different configuration is FIT_B3, the FIT value ratio is calculated as FIT_A3:FIT_B3 = 6.2:4.2. To equalize these failure rates, the FIT value multiplied by the cumulative operating time can be equalized as described above.

[0056] Although the mean number of failures is equalized by equalizing the FIT value x cumulative operating time of each DCDC converter, control may also 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 operating time by the number of failures (corresponding to the FIT value). Because this MTBF value uses the cumulative operating time and the number of failures, control using the MTBF value has the same effect as control using the FIT value.

[0057] 9 is a flowchart showing a control method according to a second embodiment of the present disclosure. As shown in FIG. 9 , when control unit 11b starts control, in step S1, control unit 11b counts the cumulative operating time of multiple 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, control unit 11b changes the number of operating power conversion units so as to equalize the failure rates of the multiple power conversion units using at least one of the FIT value, which is the average number of failures per predetermined time for the multiple power conversion units, and the cumulative operating time, and the MTBF value, which is calculated from the cumulative operating 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] This configuration makes it possible to equalize the failure rate based on the mean number of failures and mean time between failures, thereby equalizing reliability. This makes it possible to extend the overall maintenance period, which has the effect of reducing maintenance costs, as in the first embodiment.

[0060] Although the power conversion device 100b according to the second embodiment of the present disclosure has been described in the above as estimating the component failure rate based on the MIL standard, the component failure rate can also be estimated by other means. For example, the component failure rate may be calculated using the reliability prediction method of Telcordia SR-332, or may be calculated based on a component failure rate calculation means and a component failure rate calculated based on manufacturer-specific test data.

[0061] Although the DC-DC converter has been described as an isolated type in the first and second embodiments of the present disclosure, it may be configured as a non-isolated boost converter, buck converter, or buck-boost converter.

[0062] In calculating the FIT value, the circuit configuration of the isolated DC-DC converter has been described in this disclosure as being different between a full-bridge and a half-bridge primary side. However, other known circuit configurations may also be used. Typical examples include a flyback converter, a forward converter, a bridge converter, and a push-pull converter. An additional parallel element may be connected to increase current capacity or reduce loss, or an additional series element may be connected to distribute voltage. It is sufficient that at least a portion of the circuit configuration or the number of components of the DC-DC converter is different, and the FIT value of one of the DC-DC converters is different.

[0063] In the power conversion device 100b according to the second embodiment of the present disclosure, an example has been described in which a DC-DC converter is used in the power conversion unit, as in the first embodiment, but it is sufficient if the power conversion unit connects inputs and outputs in parallel, using a semiconductor switch to switch the number of units in parallel.

[0064] As in embodiment 1, the control unit 11b can change the number of operating power conversion units 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.

[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] Furthermore, the power conversion device 100b according to the second embodiment of the present disclosure includes multiple parallel-connected power conversion units, at least one of which has a different number of semiconductor elements than the other circuits, and thus some of the power conversion units are more efficient than the other power conversion units. The control unit 11b can achieve even higher efficiency by lengthening the cumulative operating 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 a state in which all of the parallel-connected power conversion units are operating, relative to the cumulative operating 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 components, it is possible to reduce the size and weight of the power conversion unit.

[0067] Embodiment 3 In embodiment 3, a flying object 200 including the power conversion device 100 according to embodiment 1 or 2 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 a 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 power from the DC source 30, and a power conversion device including the multiple power conversion units and control units described in the first or second embodiment. Note that, as in the first and second embodiments of the present disclosure, the following describes an example in which a DCDC 20 is used as an example of the multiple power conversion units. The flying object 200 is an electrically powered flying object, and its propulsion power system 90 includes a power source 92, a DC source 30 connected to the power source 92, an inverter 21 connected to the DC source 30 and configured to convert DC power to a predetermined voltage using the DCDC 20 (step-down, step-up, or step-up / step-down), converting the stepped-down or stepped-down DC power into 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 together 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 power from the DC source 30. The equipment 44 is a propulsion system load for obtaining propulsion force, such as 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, an accessory that operates using power from the DC source 30, and a power conversion device that includes 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 embodiment 4, a flying object 200b including the power conversion device 100 according to embodiment 1 or 2 will be described. This 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 a fourth embodiment of the present disclosure. A flying object 200b according to the fourth embodiment of the present disclosure includes a DC source 30, an accessory 45 that operates using power from 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 that includes multiple power conversion units and a control unit 11d described in the first or second embodiment. Note that, hereinafter, as in the first and second embodiments of the present disclosure, an example using a DCDC 20 is shown as an example of multiple power conversion units. In the flying object 200b, the equipment-based 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 it 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 together constitute 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 power from the DC power 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 going 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 equipment 45 that operates using power from the DC source 30, the power source 92 including an AC power source, the AC / DC converter 93 that converts the AC power from the power source 92 into DC power, and a power conversion device including the multiple power conversion units and the control unit 11d described in the first or second embodiment. This reduces the maintenance cost of the power conversion device mounted on the flying object 200d according to the fourth 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, as in the third embodiment.

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

[0078] 1 First DC-DC converter, 2 Second DC-DC converter, 3 Third DC-DC converter, 4 Fourth DC-DC converter, 11 Control unit, 20 DCDC, 21 Inverter, 30 DC source, 40 Load, 44 45 Equipment, 90 Propulsion system power system, 92 Power source, 93 AC / DC converter, 94 Equipment system power system, 100 100b Power conversion device, 111 Processing unit, 112 Storage device, 113 Input / output interface, 200 200b Flying object, 300 300b Power conversion system

Claims

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

2. A power conversion device comprising: 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 conversion units, and controls the plurality of power conversion units to have equal failure rates using at least one of a 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 an MTBF value calculated from the cumulative operating time and the number of failures, and changes the number of operating units of the plurality of power conversion units.

3. The power conversion device according to claim 1 or 2, 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.

4. 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 having the longest accumulated operation time reaches a predetermined accumulated operation time.

5. 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, excluding the power conversion unit with the longest accumulated operating time, in order of the longest accumulated operating 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, except for the power conversion unit having the longest cumulative operating time, evenly throughout their accumulated operating times.

7. A power conversion device as described in any one of claims 1, 4, 5 and 6, 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.

8. The power conversion device according to claim 2, 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, by a time during which the power conversion unit operates alone 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.

9. A power conversion system comprising: a DC source; and a power conversion device according to any one of claims 1 to 8.

10. A flying object comprising: a DC source; equipment that operates using power from the DC source; and a power conversion device according to any one of claims 1 to 8.

11. The flying object according to claim 10, comprising: a power source including an AC power source; and an AC / DC converter that converts the AC power of the power source into DC power.

12. A control method comprising the steps of: counting a cumulative operating time of a plurality of power conversion units; and operating first one of the plurality of power conversion units that has the longest cumulative operating time, thereby controlling so as to create a difference in the cumulative operating time of at least one of the power conversion units.

13. A control method comprising the steps of: counting the cumulative operating time of multiple power conversion units connected in parallel, at least one of which has a different number of semiconductor elements than the other circuits; and changing the number of operating units of the multiple power conversion units so as to equalize the failure rates of the multiple power conversion units, using at least one of an FIT value, which is the average number of failures per predetermined time for the multiple power conversion units, and the cumulative operating time, and an MTBF value calculated from the cumulative operating time and the number of failures.

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