Power Conversion Device

Abstract

To obtain a power conversion device capable of more appropriately detecting abnormality of a voltage detection unit.SOLUTION: A setting unit 41 sets a duty ratio of a PWM signal based on a target voltage value to output the set duty ratio to a voltage conversion circuit 20. An estimation value calculation unit 42 periodically calculates a duty ratio estimation value D based on an input-voltage detection value V1 and an output-voltage detection value V2 in a case where a relation between the input-voltage detection value V1 and the output-voltage detection value V2 is assumed. An abnormality detection unit 43 periodically calculates difference between an updated estimation value and a comparison reference value as a difference value ΔD to detect abnormality of a voltage detection unit 30 based on change in the calculated difference value ΔD. The updated estimation value is a newly calculated duty ratio estimation value D. The comparison reference value is a value based on the duty ratio estimation value D calculated in a period prior to a period in which the update estimation value is calculated.SELECTED DRAWING: Figure 9

Description

[Technical Field]

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

[0002] In a conventional voltage conversion device, the duty ratio of a PWM signal is estimated based on either the input voltage or the output voltage of a voltage conversion unit, and a target voltage. The PWM signal is a control signal input to the voltage conversion unit. The input voltage and the output voltage are detected by a voltage detection unit. When the voltage conversion unit is in a stable state, an abnormality determination unit determines whether the difference between the estimated duty ratio of the PWM signal and the actually set duty ratio has converged to less than a certain value (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-208968 Summary of the Invention [Problem to be solved by the invention]

[0004] Typically, a voltage detection unit has hardware characteristic variations. The characteristic variations include, for example, variations caused by the ambient temperature of the hardware and variations caused by aging of the hardware. In the conventional voltage conversion device described above, when detecting an abnormality in the voltage detection unit, the above variations reduce the accuracy of the abnormality detection. As a result, there is a problem in that the abnormality in the voltage detection unit cannot be detected properly.

[0005] The present disclosure has been made to solve the above-described problems, and has an object to provide a power conversion device that can more appropriately detect an abnormality in a voltage detection unit. [Means for solving the problem]

[0006] The power conversion device according to the present disclosure includes a voltage conversion circuit, a voltage detection unit having an input voltage detector that detects the input voltage to the voltage conversion circuit as an input voltage detection value and an output voltage detector that detects the output voltage from the voltage conversion circuit as an output voltage detection value, and a control unit that controls the voltage conversion circuit. The control unit includes a setting unit that sets the duty ratio of a PWM signal to be provided to the voltage conversion circuit based on a target voltage value that is a target value for the output voltage, and outputs a PWM signal based on the set duty ratio to the voltage conversion circuit, an estimate value calculation unit that periodically calculates, based on the input voltage detection value and the output voltage detection value, a duty ratio estimate value that is the duty ratio of the PWM signal that should have been output from the setting unit to the voltage conversion circuit, assuming a relationship between the input voltage detection value and the output voltage detection value, and an abnormality detection unit that periodically calculates a difference value between an updated estimate value that is a duty ratio estimate newly calculated by the estimate value calculation unit and a comparison reference value based on the duty ratio estimate value calculated by the estimate value calculation unit in a period prior to the period in which the updated estimate value was calculated, and detects an abnormality in the voltage detection unit based on a change in the calculated difference value. [Effects of the Invention]

[0007] According to the power conversion device according to the present disclosure, it is possible to more appropriately detect an abnormality in the voltage detection unit. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a configuration diagram showing, in partial blocks, a power conversion device according to a first embodiment. [Figure 2] FIG. 2 is a configuration diagram of a power conversion device in which an inverter circuit and a motor are applied as the load in FIG. [Figure 3] 2 is a diagram for explaining output variations of the output voltage detector of FIG. 1. FIG. [Figure 4] 2 is a diagram for explaining a duty ratio deviation width and a method for setting a specified range in the power conversion device of FIG. 1. FIG. [Figure 5]2 is a time chart for explaining an abnormality detection algorithm executed by the control unit of FIG. 1; [Figure 6] 4 is a time chart for explaining an abnormality detection algorithm when noise is superimposed on the input voltage detector of FIG. 1; [Figure 7] 2 is a time chart for explaining an abnormality detection algorithm when noise is superimposed on the output voltage detector of FIG. 1; [Figure 8] 4 is a flowchart showing an abnormality detection routine executed by the control unit in FIG. 1. [Figure 9] 9 is a flowchart showing a process subsequent to the process of the abnormality detection routine of FIG. 8. [Figure 10] 10 is a time chart for explaining an abnormality detection algorithm executed by a control unit of a power conversion device according to a second embodiment. [Figure 11] 10 is a flowchart showing an abnormality detection routine executed by a control unit of a power conversion device according to a second embodiment. [Figure 12] FIG. 10 is a diagram showing an example in which a two-stage multilevel step-up DC / DC converter is applied as a voltage conversion circuit. [Figure 13] FIG. 10 is a diagram illustrating an example in which a two-phase multiphase step-up DC / DC converter is applied as a voltage conversion circuit. [Figure 14] FIG. 1 is a diagram illustrating an example in which a one-phase, one-stage step-down DC / DC converter is applied as a voltage conversion circuit. [Figure 15] FIG. 1 is a diagram showing an example in which a one-phase, one-stage step-up / step-down DC / DC converter is applied as a voltage conversion circuit. [Figure 16] 1 is a configuration diagram showing a first example of a processing circuit that realizes the functions of the power conversion devices according to the first and second embodiments. FIG. [Figure 17] FIG. 10 is a configuration diagram showing a second example of a processing circuit that realizes the functions of the power conversion devices according to the first and second embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments will be described with reference to the drawings. Embodiment 1 1 is a block diagram showing a configuration of a power conversion device according to Embodiment 1. The power conversion device 10 includes a voltage conversion circuit 20, a voltage detection unit 30, and a control unit .

[0010] The voltage conversion circuit 20 is connected to a DC voltage source 50 as an external power source. The voltage conversion circuit 20 is also connected to a load 60. The voltage conversion circuit 20 converts an input voltage into an output voltage. The input voltage is a voltage input from the DC voltage source 50 to the voltage conversion circuit 20. The output voltage is a voltage output from the voltage conversion circuit 20 to the load 60.

[0011] The voltage conversion circuit 20 includes a first switching element 21, a second switching element 22, an input capacitor 23, an output capacitor 24, a reactor 25, and a drive unit .

[0012] The first switching element 21 and the second switching element 22 are each composed of a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) and a diode. The diode is connected in anti-parallel between the source and drain of the MOSFET. That is, the cathode of the diode is connected to the source of the MOSFET, and the anode of the diode is connected to the drain of the MOSFET. Therefore, this diode is called an anti-parallel diode. The anti-parallel diode is built into the MOSFET. Furthermore, the MOSFET uses a SiC (Silicon Carbide) semiconductor.

[0013] The drain terminal of the first switching element 21 is connected to the positive electrode side of the load 60. The source terminal of the first switching element 21 is connected to the drain terminal of the second switching element 22. The source terminal of the second switching element 22 is connected to the negative electrode side of the load 60.

[0014] Input capacitor 23 is connected between the positive electrode of DC voltage source 50 and the negative electrode of DC voltage source 50. Input capacitor 23 prevents noise components generated by the on / off operation of first switching element 21 and noise components generated by the on / off operation of second switching element 22 from flowing out to DC voltage source 50. Input capacitor 23 also smoothes fluctuations in the voltage generated by DC voltage source 50.

[0015] The output capacitor 24 is connected between the positive electrode side of the load 60 and the negative electrode side of the load 60. That is, the output capacitor 24 is connected between the drain terminal of the first switching element 21 and the source terminal of the second switching element 22. The output capacitor 24 covers the supply of power to the load 60 when the first switching element 21 is turned off. In addition, the output capacitor 24 prevents noise components generated by the on / off operation of the first switching element 21 and the on / off operation of the second switching element 22 from flowing out to the load 60.

[0016] One end of reactor 25 is connected to the positive electrode side of DC voltage source 50. The other end of reactor 25 is connected to the source terminal of first switching element 21 and the drain terminal of second switching element 22.

[0017] The driving unit 26 has a buffer circuit configured with a driver IC (Integrated Circuit) or the like. A PWM (Pulse Width Modulation) signal is input to the driving unit 26 from the control unit 40. The PWM signal is a signal provided to the voltage conversion circuit 20. The driving unit 26 amplifies the input PWM signal using the buffer circuit and applies it between the gate terminal and source terminal of the first switching element 21 and between the gate terminal and source terminal of the second switching element 22.

[0018] The drive unit 26 alternately turns on and off the first switching element 21 and the second switching element 22 in accordance with the input PWM signal. This alternately stores energy in the reactor 25 and supplies the stored energy to the load 60 and the output capacitor 24, thereby boosting the output voltage to a voltage higher than the input voltage. In other words, the voltage conversion circuit 20 is a boost DC / DC converter.

[0019] The voltage detection unit 30 has an input voltage detector 31 and an output voltage detector 32. The input voltage detector 31 detects the input voltage to the voltage conversion circuit 20 as an input voltage detection value V1. The output voltage detector 32 detects the output voltage from the voltage conversion circuit 20 as an output voltage detection value V2.

[0020] The input voltage detector 31 and the output voltage detector 32 each have a voltage dividing resistor, an insulating element, and an A / D converter. The voltage dividing resistor reduces the voltage of the voltage conversion circuit 20 to the operating voltage level of the control unit 40. The insulating element is an element for insulating the voltage conversion circuit 20 from the control unit 40. The A / D converter converts the detected voltage into a digital value.

[0021] The control unit 40 has a setting unit 41, an estimated value calculation unit 42, and an abnormality detection unit 43 as functional blocks.

[0022] The setting unit 41 sets the duty ratio of the PWM signal based on the target voltage value and the output voltage detection value V2. The target voltage value is a target value for the output voltage of the voltage conversion circuit 20. The target voltage value is determined by the higher-level device 70. More specifically, the setting unit 41 sets the duty ratio of the PWM signal by PI control so that the output voltage detection value V2 approaches the target voltage value. The setting unit 41 outputs the PWM signal to the drive unit 26 of the voltage conversion circuit 20.

[0023] The estimated value calculation unit 42 periodically calculates a duty ratio estimated value based on the detected input voltage value V1 and the detected output voltage value V2. The duty ratio estimated value is the duty ratio of the PWM signal that should be output from the setting unit 41 to the voltage conversion circuit 20, assuming a relationship between the detected input voltage value V1 and the detected output voltage value V2. The estimated value calculation unit 42 also stores the periodically calculated duty ratio estimated value.

[0024] If the duty ratio estimated value at period number "n" is D(n), the duty ratio estimated value D(n) is expressed by the following equation (1): where V1(n) is the input voltage detection value V1 at period number "n", and V2(n) is the output voltage detection value V2 at period number "n". Note that the duty ratio estimated value D(n) in equation (1) holds when the voltage conversion circuit 20 is a step-up DC / DC converter.

[0025] D(n)=(V2(n)-V1(n)) / V2(n) ···(1)

[0026] The abnormality detection unit 43 periodically calculates a difference between the updated estimated value and the comparison reference value as a difference value. The updated estimated value is a duty ratio estimated value newly calculated by the estimate value calculation unit 42. The comparison reference value is a value based on the duty ratio estimated value calculated by the estimate value calculation unit 42 in a period previous to the period in which the updated estimated value was calculated. The abnormality detection unit 43 detects an abnormality in the voltage detection unit 30 based on a change in the calculated difference value.

[0027] The updated estimated value for period number "n" is the duty ratio estimated value D(n) calculated for period number "n." If the comparison reference value is Cmp and the difference value for period number "n" is ΔD(n), the difference value ΔD(n) is expressed by the following equation (2).

[0028] ΔD(n)=D(n)-Cmp (2)

[0029] In the first embodiment, the comparison reference value Cmp is the duty cycle estimated value obtained in the period immediately before the period in which the updated estimated value is obtained. That is, Equation (2) is expressed by the following Equation (3).

[0030] ΔD(n)=D(n)-D(n-1) (3)

[0031] When the abnormality detection unit 43 detects an abnormality in the voltage detection unit 30, it notifies the host device 70 of the abnormality in the voltage detection unit 30. After that, when the setting unit 41 receives a command from the host device 70 in response to the abnormality notification, it controls the first switching element 21 and the second switching element 22 in accordance with the command from the host device 70. For example, the command from the host device 70 is a command to stop the switching operation of the first switching element 21 and the switching operation of the second switching element 22. Furthermore, for example, the command from the host device 70 is a command to cause the first switching element 21 and the second switching element 22 to continue switching operation at a constant duty ratio.

[0032] The DC voltage source 50 is configured by a secondary battery, such as a battery, a lithium ion battery, or a nickel cadmium battery.

[0033] The higher-level device 70 is configured by, for example, an ECU (Electronic Control Unit). The higher-level device 70 transmits a target voltage value and information relating to fluctuations in the load 60 to the control unit 40. The information relating to fluctuations in the load 60 includes, for example, a load current value.

[0034] 2 is a configuration diagram of the power conversion device 10 when an inverter circuit and a motor are applied as the load 60 in FIG. 1. The load 60 has an inverter circuit 61 and a motor 62. The inverter circuit 61 has six switching elements. In this way, when the load 60 is a load having switching elements, the output capacitor 24 prevents noise components generated by the on / off operation of the switching elements of the load 60 from flowing into the voltage conversion circuit 20.

[0035] 3 is a diagram illustrating output variations of output voltage detector 32 in a comparative example. When detecting an abnormality in voltage detection unit 30, in order to prevent erroneous detection of an abnormality, it is necessary to determine a setting margin for the threshold value for detecting an abnormality, taking into consideration variations in the characteristics of the hardware of voltage detection unit 30.

[0036] For example, when the input / output voltage conditions of the voltage conversion circuit 20 and the characteristic variations of the voltage detection unit 30 are assumed as follows, the necessary setting margin is calculated as follows.

[0037] Input voltage range: 200~400V Output voltage range: 200~650V Normal input voltage detector 31 characteristic variation: ±2% Normal output voltage detector 32 characteristic variation: ±4%

[0038] Here, as a comparative example with the abnormality detection method based on the difference value ΔD(n), a setting margin is calculated assuming a method of detecting an abnormality in the voltage detection unit 30 based on the difference between the duty ratio estimated value calculated according to the above formula (1) and the duty ratio that is actually set.

[0039] In this case, the maximum duty ratio deviation range is calculated to be 0.06. The duty ratio deviation range is the range of deviation between the duty ratio set by the setting unit 41 and the duty ratio estimated value D(n). Therefore, in this case, to avoid erroneous detection of an abnormality in the voltage detection unit 30, the setting margin needs to be set to at least ±0.06.

[0040] In Figure 3, the horizontal axis represents the actual output voltage, and the vertical axis represents the detected output voltage V2. A solid line 81 indicates that the detected output voltage V2 matches the actual output voltage. When the detected output voltage V2 is on the solid line 81, the set duty ratio and the estimated duty ratio D(n) match. That is, in this case, the duty ratio deviation is zero. Furthermore, the further the detected output voltage V2 is from the solid line 81, the larger the duty ratio deviation is considered to be.

[0041] Dashed line 82 represents the upper limit of the variation in the detected output voltage value V2 when the input voltage is 200 V. Dashed line 83 represents the lower limit of the variation in the detected output voltage value V2 when the input voltage is 200 V. Dashed line 84 represents the upper limit of the variation in the detected output voltage value V2 when the input voltage is 400 V. Dashed line 85 represents the lower limit of the variation in the detected output voltage value V2 when the input voltage is 400 V.

[0042] As described above, the variation in the output voltage detection value V2 increases as the output voltage increases. The variation in the output voltage detection value V2 also increases as the input voltage decreases. The variation in the output voltage detection value V2 reaches a maximum of 176 V when the input voltage is 200 V and the output voltage is 650 V. In other words, the right end of the dashed line 82 is 826 V. This means that the output voltage detector 32 cannot determine that an abnormality has occurred until the output voltage detection value V2 exceeds 826 V, relative to the target voltage of 650 V. Therefore, to prevent erroneous detection of an abnormality in the output voltage detector 32, it is desirable to set a setting margin 88 between the dashed and dotted lines 86 and 87.

[0043] FIG. 4 is a diagram illustrating a method for setting the duty ratio deviation width and the specified range for abnormality detection in the power conversion device 10 of FIG. 1. The specified range is a range within which the voltage detection unit 30 is determined to be normal when the difference value ΔD(n) falls within that range. The specified range is set to include a setting margin. FIG. 4 shows simulation results for the duty ratio deviation width when the input / output conditions of the voltage conversion circuit 20 are an input voltage range of 200 to 400 V and an output voltage range of 200 to 650 V. This simulation is a simulation in which the abnormality detection unit 43 periodically calculates the difference between the updated estimated value and the comparison reference value as a difference value, and detects an abnormality in the voltage detection unit 30 based on changes in the calculated difference value.

[0044] In FIG. 4, the horizontal axis indicates the target output voltage, and the vertical axis indicates the duty ratio deviation width.

[0045] The group of circular plots indicates the duty ratio deviation width when the voltage detection unit 30 is operating normally and the output power of the voltage conversion circuit 20 changes by a maximum of 5 kW due to a change in the output current of the voltage conversion circuit 20. Under these conditions, the duty ratio deviation width is maximum at an input voltage of 200 V and an output voltage of 220 V, and the value is 0.007.

[0046] On the other hand, under the same input / output conditions, the diamond plot shows the duty ratio deviation range when the output voltage detection value V2 fluctuates by 50 V, assuming an abnormality in the output voltage detector 32. Also, the rectangular plot shows the duty ratio deviation range when the output voltage detection value V2 fluctuates by 100 V, assuming an abnormality in the output voltage detector 32.

[0047] From this simulation result, it can be seen that the duty ratio deviation is 0.02 or greater whether the fluctuation in the output voltage detection value V2 is 50 V or 100 V. In this result, the voltage condition under which the duty ratio deviation is smallest is an input voltage of 200 V and an output voltage of 650 V. Based on the above simulation result, the specified range is set to 0.01, which is between 0.007, which is the maximum value of the duty ratio deviation when the voltage detection unit 30 is in a normal state, and 0.02, which is the minimum value of the duty ratio deviation when the voltage detection unit 30 is in an abnormal state.

[0048] As described above, according to the first embodiment, even when the output power changes by 5 kW, the duty ratio deviation width can be reduced by an order of magnitude compared to the comparative example. Therefore, the anomaly detection method according to the first embodiment can detect an anomaly in the voltage detection unit 30 with higher accuracy than the anomaly detection method according to the comparative example.

[0049] Fig. 5 is a time chart for explaining the abnormality detection algorithm executed by the control unit 40 of Fig. 1. The horizontal axis of Fig. 5 represents time. From top to bottom, Fig. 5 shows the period number, various voltages, duty ratio estimated value D, difference value ΔD, abnormality determination count c, and abnormality detection status. The various voltages are the target voltage value, input voltage, input voltage detection value V1, output voltage, and output voltage detection value V2.

[0050] The period number represents a control period, which is a fixed period in the control unit 40. The control unit 40 acquires the input voltage detection value V1, the output voltage detection value V2, and the target voltage value, and updates the duty ratio at fixed intervals. For example, if the control period is set to 20 μs, the horizontal axis indicates that 20 μs have elapsed for each increment of the period number. In the example shown in FIG. 5, it is assumed that the output voltage detector 32 fails in period number "6," and that the output voltage detection value V2 remains higher than the target voltage from period number "7" onward.

[0051] The target voltage value is indicated by a dashed line and is constant from cycle number "1" to "12." The input voltage is indicated by a dashed line, and the detected input voltage value V1 is indicated by a circular plot. The input voltage and the detected input voltage value V1 are consistent with each other and are constant from cycle number "1" to "12."

[0052] The output voltage is shown by a solid line, and the detected output voltage value V2 is shown by a larger circle plot than the plot of the detected input voltage value V1. The output voltage and the detected output voltage value V2 match the target voltage value and remain constant from period numbers "1" to "5." However, in period number "6," the output voltage detector 32 fails for some reason, causing the detected output voltage value V2 to increase in period number "7." Thereafter, the detected output voltage value V2 remains constant and higher than the target voltage value until period number "12."

[0053] The increase in the output voltage detection value V2 in period number "7" is reflected in the setting by the setting unit 41 in period number "8." After period number "8," the setting unit 41 reduces the duty ratio so that the output voltage detection value V2 approaches the target voltage value, and therefore the output voltage begins to decrease from the target voltage value in period number "8."

[0054] After that, since the output voltage detection value V2 remains constant and higher than the target voltage, the setting unit 41 continues to reduce the duty ratio and eventually sets the duty ratio to 0. As a result, the output voltage converges to the input voltage. Note that the control shown in FIG. 5 is merely an example, and the cycle number at which the setting unit 41 starts reducing the duty ratio does not have to be "8."

[0055] In period number "7", the detected output voltage value V2 changes suddenly. The estimated duty ratio value D(n) is calculated according to equation (1), so it changes suddenly in period number "7". Furthermore, from period number "8" onwards, the detected output voltage value V2 remains constant, so the estimated duty ratio value D also remains at the value it had in period number "7".

[0056] For example, the difference value ΔD(6) for period number "6" is the value obtained by subtracting the duty cycle estimated value D(5) for period number "5" from the duty cycle estimated value D(6) for period number "6." In this example, since there is no change in the input voltage detection value V1 and the output voltage detection value V2 from period number "1" to period number "6," the abnormality detection unit 43 continuously calculates the difference value ΔD(n) as 0.

[0057] However, at period number "7," the duty cycle estimated value D(7) changes suddenly, so the difference value ΔD(7) also changes suddenly, and the difference value ΔD(7) exceeds the predetermined excess detection threshold (0.01). Here, the excess detection threshold (0.01) is the upper limit of the specified range, and the excess detection threshold (-0.01) is the lower limit of the specified range. In other words, the excess detection threshold is a threshold for determining whether the difference value ΔD(n) exceeds the specified range.

[0058] In period number "7", the abnormality detection unit 43 detects that the difference value ΔD(n) exceeds the specified range. Since the duty cycle estimated value D(n) does not change from period number "8" onwards, the abnormality detection unit 43 continues to calculate the difference value ΔD(n) as 0.

[0059] After detecting that the difference value ΔD(n) has exceeded the specified range, the abnormality detection unit 43 determines that the voltage detection unit 30 is abnormal if the difference value ΔD(n) falls within the specified range for a specified number of five consecutive times, starting from the period following the period in which the difference value ΔD(n) exceeded the specified range.

[0060] Here, if the difference value ΔD(n) exceeds a specified range, the abnormality detection unit 43 changes the abnormality detection status from "not detected" to "detecting." When the abnormality detection status is changed to "detecting," the abnormality detection unit 43 starts the abnormality detection process. More specifically, when the abnormality detection status is changed to "detecting," the abnormality detection unit 43 sets the abnormality determination count c to 0. If the difference value ΔD(n) falls within the specified range in the period following the period in which the abnormality detection status was changed to "detecting," the abnormality detection unit 43 counts up the abnormality determination count c by one.

[0061] 5, the difference value ΔD(n) is within the specified range from cycle number "8" to "12," so the abnormality determination count c continues to count up, and at cycle number "12," the abnormality determination count c becomes "5." At this point, the abnormality detection unit 43 changes the abnormality detection status from "detecting" to "determined abnormality."

[0062] In this way, by providing an abnormality detection status and monitoring the difference value ΔD(n), the abnormality detection unit 43 can notify the upper device 70 of the possibility of an abnormality in the voltage detection unit 30 before the abnormality in the voltage detection unit 30 is confirmed.

[0063] 6 is a time chart for explaining an abnormality detection algorithm when noise is superimposed on the input voltage detector 31 of FIG. 1. When instantaneous noise is superimposed on the input voltage detector 31 in period number "7", the duty ratio estimated value D(7) in period number "7" fluctuates with respect to the duty ratio estimated value D(6) in period number "6". As a result, the difference value ΔD(7) in period number "7" exceeds the specified range.

[0064] Therefore, the anomaly detection unit 43 changes the anomaly detection status from "not detected" to "detecting" in period number "7" and starts the anomaly determination count c. However, if the excess of the difference value ΔD(7) in period number "7" was caused by noise, the duty cycle estimated value D(8) in the next period number "8" will return to the same value as the duty cycle estimated value D before period number "6". Therefore, the difference value ΔD(8) in period number "8" will exceed with the opposite polarity to the polarity of the excess of the difference value ΔD(7) in period number "7".

[0065] In this way, if the difference value ΔD(n) is detected to have exceeded the specified range consecutively and the polarities of the difference value ΔD(n) exceeding the specified range in the two consecutive detected exceedances are opposite to each other, it can be determined that the two exceedances are caused by superimposition of noise. Therefore, in this case, the abnormality detection unit 43 changes the abnormality detection status from "detecting" to "not detected" and temporarily terminates the determination of whether or not the voltage detection unit 30 is abnormal.

[0066] 7 is a time chart for explaining an abnormality detection algorithm when noise is superimposed on the output voltage detector 32 of FIG. 1. When instantaneous noise is superimposed on the output voltage detector 32 in period number "7", the duty ratio estimated value D(7) in period number "7" fluctuates with respect to the duty ratio estimated value D(6) in period number "6". As a result, the difference value ΔD(7) in period number "7" exceeds the specified range.

[0067] Therefore, the anomaly detection unit 43 changes the anomaly detection status from "not detected" to "detecting" in period number "7" and starts the anomaly determination count c. However, if the excess of the difference value ΔD(7) in period number "7" was caused by noise, the duty cycle estimated value D(8) in the next period number "8" will return to the same value as the duty cycle estimated value D before period number "6". Therefore, the difference value ΔD(8) in period number "8" will exceed with the opposite polarity to the polarity of the excess of the difference value ΔD(7) in period number "7".

[0068] In this way, if the difference value ΔD(n) is detected to have exceeded the specified range consecutively and the polarities of the difference values ​​ΔD exceeding the specified range in the two consecutive detected exceedances are opposite to each other, it can be determined that the two exceedances are caused by superimposition of noise. Therefore, in this case, the abnormality detection unit 43 changes the abnormality detection status from "detecting" to "not detected" and temporarily terminates the determination of whether or not the voltage detection unit 30 is abnormal.

[0069] Since the abnormality detection unit 43 detects an abnormality in the voltage detection unit 30 based on a change in the difference value ΔD(n), it is possible to perform abnormality detection with particularly high accuracy under the conditions where the input voltage is constant, the target voltage value is constant, and the output power fluctuation due to fluctuations in the load current is 5 kW or less. Therefore, it is preferable to disable the abnormality determination by the abnormality detection unit 43 when the input voltage, the target voltage value, and the load current are fluctuating. Therefore, the abnormality detection unit 43 temporarily disables the abnormality determination by the voltage detection unit 30 based on information about fluctuations in the input voltage detection value V1 detected by the input voltage detector 31, information about fluctuations in the target voltage value, and information about fluctuations in the load current.

[0070] Fig. 8 is a flowchart showing an abnormality detection routine executed by the control unit 40 of Fig. 1. The routine of Fig. 8 is executed, for example, every time a certain time period elapses. When the routine of Fig. 8 starts, the control unit 40 determines in step S101 whether or not there is a change in the target voltage value.

[0071] If there is a change in the target voltage value, in step S105, the control unit 40 sets the abnormality detection status to "not detected," sets the abnormality determination count c to 0, and temporarily ends this routine. On the other hand, if there is no change in the target voltage value, in step S102, the control unit 40 determines whether the state in which the fluctuation in the load current is equal to or less than the specified current value has continued for a certain period of time or more.

[0072] If the fluctuation of the load current does not remain below the specified current value for a certain period of time or more, the control unit 40 sets the abnormality detection status to "not detected" in step S105, sets the abnormality judgment count c to 0, and temporarily terminates this routine.

[0073] On the other hand, if the fluctuation in the load current remains below the specified current value for a certain period of time or more, the control unit 40 determines in step S103 whether the fluctuation in the input voltage remains below the specified voltage value for a certain period of time or more.

[0074] If the fluctuation of the input voltage does not remain below the specified voltage value for a certain period of time or more, the control unit 40 sets the abnormality detection status to "not detected" in step S105, sets the abnormality judgment count c to 0, and temporarily terminates this routine.

[0075] On the other hand, if the fluctuation of the input voltage remains below the specified voltage value for a certain period of time or more, the control unit 40 calculates the duty ratio estimated value D(n) in accordance with equation (1) in step S104 and starts the routine of FIG. 9.

[0076] Fig. 9 is a flowchart showing processing subsequent to the processing of the abnormality detection routine of Fig. 8. The routine of Fig. 9 is executed following step S104 of Fig. 8. When the routine of Fig. 9 starts, the abnormality detection unit 43 calculates the difference value ΔD(n) according to equation (3) in step S106. That is, the abnormality detection unit 43 calculates the difference value ΔD(n) using the comparison reference value Cmp as the duty ratio estimated value D(n-1) acquired in the period immediately preceding the period in which the updated estimated value is acquired.

[0077] Next, in step S107, the abnormality detection unit 43 determines whether the abnormality detection status is "detecting." If the abnormality detection status is not "detecting," that is, if the abnormality detection status is "not detected," the abnormality detection unit 43 determines in step S108 whether the absolute value |ΔD(n)| of the difference value ΔD(n) is equal to or greater than the excess detection threshold. In this example, the excess detection threshold is 0.01.

[0078] If the absolute value |ΔD(n)| is equal to or greater than the excess detection threshold, the abnormality detection unit 43 changes the abnormality detection status from "not detected" to "detecting" in step S109, sets the abnormality determination count c to 0, starts the abnormality determination count c, and temporarily ends this routine. In other words, if the difference value ΔD(n) exceeds the specified range, the abnormality detection unit 43 starts the abnormality detection process.

[0079] On the other hand, if the absolute value |ΔD(n)| is less than the excess detection threshold, the abnormality detection unit 43 sets the abnormality detection status to "not detected" and sets the abnormality determination count c to 0 in step S110. In this way, if the difference value ΔD(n) is within the specified range, the abnormality detection status remains "not detected." In this case, it is considered that the voltage detection unit 30 continues to operate normally.

[0080] Also, if it is determined in step S107 that the abnormality detection status is "detecting", the abnormality detection unit 43 determines in step S111 whether the absolute value |ΔD(n)| of the difference value ΔD(n) is less than the excess detection threshold.

[0081] If the absolute value |ΔD(n)| is less than the excess detection threshold, the abnormality detection unit 43 counts up the abnormality determination count c in step S112. Next, in step S113, the abnormality detection unit 43 determines whether the abnormality determination count c has reached "5".

[0082] If the abnormality determination count c has not reached "5," the abnormality detection unit 43 temporarily ends this routine. That is, the abnormality detection status remains "detecting."

[0083] On the other hand, if the abnormality determination count c has reached "5," the abnormality detection unit 43 changes the abnormality detection status from "detecting" to "determined abnormality" in step S114 and temporarily ends this routine. That is, in this case, the difference value ΔD(n) has behaved in the following order: "exceeds -> within specified range -> within specified range -> within specified range -> within specified range." In this case, an abnormality in the voltage detection unit 30 is determined.

[0084] When the abnormality detection status is set to "abnormality confirmed," the control unit 40 notifies the higher-level device 70 that the voltage detection unit 30 is abnormal. Thereafter, in accordance with an instruction from the higher-level device 70, the control unit 40, for example, stops the switching operation of the first switching element 21 and the switching operation of the second switching element 22. For example, the control unit 40 continues the switching operation of the first switching element 21 and the switching operation of the second switching element 22 while fixing the duty ratio to a constant value.

[0085] Furthermore, if it is determined in step S111 that the absolute value |ΔD(n)| is equal to or greater than the excess detection threshold, it means that the difference value ΔD(n) has exceeded the excess detection threshold for at least two consecutive periods. Therefore, in step S115, the abnormality detection unit 43 determines whether the polarity of the previous difference value ΔD(n-1) and the polarity of the current difference value ΔD(n) are opposite to each other.

[0086] If the polarity of the previous difference value ΔD(n-1) and the polarity of the current difference value ΔD(n) are the same, the abnormality detection unit 43 temporarily ends this routine. In this case, the operation of the voltage detection unit 30 is considered to be unstable, and there is a possibility that the voltage detection unit 30 will become abnormal thereafter. In other words, at this stage, it is considered that a possible abnormality has been detected.

[0087] On the other hand, if the polarity of the previous difference value ΔD(n-1) and the polarity of the current difference value ΔD(n) are opposite to each other, the abnormality detection unit 43 changes the abnormality detection status from "detecting" to "not detected" in step S116. Also, in step S116, the abnormality detection unit 43 sets the abnormality determination count c to 0. Thereafter, the abnormality detection unit 43 temporarily ends this routine. That is, in this case, the excess of the difference value ΔD(n) beyond the specified range is considered to be caused by momentary noise superimposition on the voltage detection unit 30.

[0088] As described above, the power conversion device 10 according to the first embodiment includes a voltage conversion circuit 20, a voltage detection unit 30, and a control unit 40. The voltage detection unit 30 includes an input voltage detector 31 and an output voltage detector 32. The input voltage detector 31 detects the input voltage to the voltage conversion circuit 20 as an input voltage detection value V1. The output voltage detector 32 detects the output voltage from the voltage conversion circuit 20 as an output voltage detection value V2. The control unit 40 controls the voltage conversion circuit 20.

[0089] The control unit 40 has a setting unit 41, an estimated value calculation unit 42, and an abnormality detection unit 43. The setting unit 41 sets the duty ratio of the PWM signal based on the target voltage value, and outputs the PWM signal based on the set duty ratio to the voltage conversion circuit 20. The target voltage value is a target value for the output voltage. The PWM signal is a signal provided to the voltage conversion circuit 20.

[0090] The estimated value calculation unit 42 periodically calculates a duty ratio estimated value D(n) based on the input voltage detection value V1 and the output voltage detection value V2, assuming a relationship between the input voltage detection value V1 and the output voltage detection value V2. The duty ratio estimated value D(n) is the duty ratio of the PWM signal that should be output from the setting unit 41 to the voltage conversion circuit 20.

[0091] The abnormality detection unit 43 periodically calculates the difference between the updated estimated value and the comparison reference value Cmp as a difference value ΔD(n), and detects an abnormality in the voltage detection unit 30 based on a change in the calculated difference value ΔD(n). The updated estimated value is a duty ratio estimated value D(n) newly calculated by the estimate value calculation unit 42. The comparison reference value Cmp is a value based on the duty ratio estimated value D(n) calculated by the estimate value calculation unit 42 in a period previous to the period in which the updated estimated value was calculated.

[0092] According to this, since the difference value ΔD(n) is the difference between the updated estimated value and the comparison reference value Cmp, the detector variation component included in the updated estimated value and the detector variation component included in the comparison reference value Cmp cancel each other out in the difference value ΔD(n). The detector variation component is a component of the characteristic variation of the voltage detection unit 30. This makes it possible to narrow the setting margin, thereby narrowing the specified range for abnormality detection. As a result, abnormalities in the voltage detection unit 30 can be detected more appropriately.

[0093] The comparison reference value Cmp is the duty ratio estimated value D(n-1) obtained in the period immediately preceding the period in which the updated estimated value is obtained.

[0094] The detector variation component depends on the temperature characteristics of the hardware in the voltage detection unit 30 and on deterioration over time of the hardware in the voltage detection unit 30. Because the comparison reference value Cmp is acquired in the cycle immediately before the updated estimated value is acquired, the change in the detector variation component due to temperature changes resulting from the difference in acquisition timing and the change in the detector variation component due to deterioration over time are negligibly small. Therefore, the specified range for anomaly detection can be narrowed, and as a result, the accuracy of detecting anomalies in the voltage detection unit 30 can be improved.

[0095] Furthermore, after detecting that the difference value ΔD(n) exceeds the specified range, the abnormality detection unit 43 determines that the voltage detection unit 30 is abnormal when it detects that the periodically calculated difference value ΔD(n) is within the specified range for five consecutive times.

[0096] This makes it possible to prevent erroneous detection of an abnormality in the voltage detection unit 30. Furthermore, before an abnormality in the voltage detection unit 30 is confirmed, the higher-level device 70 can be notified of the possibility of an abnormality in the voltage detection unit 30 at the time when the difference value ΔD(n) exceeds the specified range.

[0097] Furthermore, if the abnormality detection unit 43 detects consecutive exceedances of the specified range of the difference value ΔD(n) and the polarities with which the difference values ​​ΔD(n) exceed the specified range in the two consecutive detected exceedances are opposite to each other, the abnormality detection unit 43 temporarily terminates the determination of whether or not the voltage detection unit 30 is abnormal.

[0098] This makes it possible to prevent momentary noise superimposed on the voltage detection unit 30 from being erroneously detected as an abnormality in the voltage detection unit 30.

[0099] Furthermore, the abnormality detection unit 43 sets a specified range according to the input voltage to the voltage conversion circuit 20 and the output voltage from the voltage conversion circuit 20 .

[0100] As shown in FIG. 3, the higher the input voltage, the narrower the duty ratio deviation range. Also, the lower the output voltage, the narrower the duty ratio deviation range. Therefore, the higher the input voltage, the narrower the specified range can be, thereby improving the accuracy of detecting an abnormality in the voltage detection unit 30 when the input voltage is high. Also, the lower the output voltage, the narrower the specified range can be, thereby improving the accuracy of detecting an abnormality in the voltage detection unit 30 when the output voltage is low.

[0101] Furthermore, when the target voltage value is changed, the abnormality detection unit 43 temporarily disables the detection of an abnormality.

[0102] According to this, since the detection of an abnormality in the voltage detection unit 30 is performed in a stable state where the target voltage value is not changed, the accuracy of detecting an abnormality in the voltage detection unit 30 can be improved.

[0103] Furthermore, if the output current of the voltage conversion circuit 20 changes by a specified current value or more due to a fluctuation in the load 60, the abnormality detection unit 43 temporarily disables the detection of the abnormality.

[0104] According to this, since the abnormality of the voltage detection unit 30 is detected in a state where the fluctuation of the load 60 is suppressed, the accuracy of detecting the abnormality of the voltage detection unit 30 can be improved.

[0105] Furthermore, when the input voltage changes by a specified voltage value or more due to voltage fluctuations in DC voltage source 50, abnormality detection unit 43 temporarily disables the detection of an abnormality.

[0106] According to this, since the detection of an abnormality in voltage detection unit 30 is performed in a state where the voltage fluctuation of DC voltage source 50 is suppressed, the accuracy of detecting an abnormality in voltage detection unit 30 can be improved.

[0107] The specified range is set based on the maximum value of the duty ratio deviation range within the normal operating range of the voltage detection unit 30. The duty ratio deviation range is the range of deviation between the duty ratio estimated value and the duty ratio set based on the target voltage value and the output voltage detection value V2.

[0108] This allows the specified range to be set more appropriately, thereby preventing erroneous detection of an abnormality, and as a result, an abnormality in the voltage detection unit 30 can be detected more appropriately.

[0109] Embodiment 2 The power conversion device according to the second embodiment differs from the power conversion device 10 according to the first embodiment in that the comparison reference value calculated in the abnormality detection unit 43 is the average value of a plurality of duty ratio estimates acquired in a period prior to the period in which the updated estimate value is acquired.

[0110] The configuration other than the above is the same as that of the power conversion device 10 of embodiment 1. Hereinafter, a description of the configuration that is the same as that of the power conversion device 10 of embodiment 1 will be omitted.

[0111] In the second embodiment, the abnormality detection unit 43 calculates the difference value ΔD(n) using the comparison reference value Cmp(m) as shown in the following equation (4), where m represents the period number at which the comparison reference value Cmp(m) is updated, and m is an integer smaller than n.

[0112] ΔD(n)=D(n)-Cmp(m) (4)

[0113] The comparison reference value Cmp(m) is the average value of 10 consecutive duty cycle estimates obtained in a period prior to the period in which the updated estimate is obtained. That is,

[0114] Cmp(m)={D(m-9)+D(m-8)+…+D(m)} / 10 ···(5)

[0115] 10 is a time chart for explaining an abnormality detection algorithm executed by the control unit 40 of the power conversion device according to the second embodiment. When the calculated duty ratio estimation value D(n) falls within a certain range α, the abnormality detection unit 43 counts up the comparison reference value calculation count by one. On the other hand, when the calculated duty ratio estimation value D(n) deviates from the certain range α, the comparison reference value calculation count is cleared.

[0116] The abnormality detection unit 43 updates the comparison reference value Cmp(m) when the comparison reference value calculation count reaches "10," that is, when the duty ratio estimation value D(n) falls within the certain range α 10 times in a row. For example, in period number "4," the comparison reference value calculation count is 7, but in period number "5," the duty ratio estimation value D(5) deviates from the certain range α, so the comparison reference value calculation count is cleared.

[0117] At period number "6", the comparison reference value calculation count again counts up from 1. Between period numbers "6" and "15", the duty ratio estimated values ​​D(6) to D(15) continuously fall within the certain range α, so at period number "15", the comparison reference value calculation count reaches "10". Therefore, at period number "15", the abnormality detection unit 43 updates the comparison reference value Cmp(m).

[0118] The abnormality detection unit 43 calculates the average value of the duty cycle estimation values ​​D(6) to D(15) as the comparison reference value Cmp(m). From cycle number "16" onwards, the difference values ​​ΔD(16) to ΔD(23) are expressed by the following equations (6) to (13), respectively.

[0119] ΔD(16)=D(16)-Cmp(15) ···(6)

[0120] ΔD(17)=D(17)-Cmp(15) ···(7)

[0121] ΔD(18)=D(18)-Cmp(15) ···(8)

[0122] ΔD(19)=D(19)-Cmp(15) ···(9)

[0123] ΔD(20)=D(20)-Cmp(15) ···(10)

[0124] ΔD(21)=D(21)-Cmp(15) ···(11)

[0125] ΔD(22)=D(22)-Cmp(15) ···(12)

[0126] ΔD(23)=D(23)-Cmp(15) ···(13)

[0127] however,

[0128] Cmp(15)={D(6)+D(7)+…+D(15)} / 10 ···(14)

[0129] The method of detecting an abnormality in the voltage detection unit 30 using the difference value ΔD(n) is the same as the abnormality detection algorithm described in the first embodiment, and therefore a detailed description thereof will be omitted.

[0130] Fig. 11 is a flowchart showing an abnormality detection routine executed by the control unit 40 of the power conversion device 10 according to the second embodiment. The routine of Fig. 11 is executed following step S104 of Fig. 8. That is, the control unit 40 of the power conversion device 10 according to the second embodiment first executes the abnormality detection routine of Fig. 8.

[0131] 11 starts, the abnormality detection unit 43 calculates the difference value ΔD(n) in step S201 according to equations (4) and (5). That is, the abnormality detection unit 43 calculates the difference value ΔD(n) by setting the comparison reference value Cmp as the average value of 10 consecutive duty ratio estimates acquired in a period prior to the period in which the updated estimate value was acquired.

[0132] The subsequent processing in steps S107 to S116 is the same as the processing in steps S107 to S116 in FIG. 9, and therefore a description thereof will be omitted.

[0133] In this way, the comparison reference value Cmp is the average value of 10 consecutive duty cycle estimates obtained in a period prior to the period in which the updated estimate was obtained.

[0134] According to this method, even if noise is superimposed on any of the ten duty cycle estimates used as the comparison reference value Cmp, the influence of the noise is weakened by averaging the ten duty cycle estimates, thereby providing higher noise resistance compared to a method that uses, as the comparison reference value Cmp, the duty cycle estimate D(n-1) obtained in the period immediately preceding the period in which the updated estimate is obtained.

[0135] The comparison reference value Cmp may be calculated, for example, by substituting the average value of 10 consecutive input voltage detection values ​​V1 for V1 in equation (1) and substituting the average value of 10 consecutive output voltage detection values ​​V2 for V2 in equation (1).

[0136] Furthermore, the number of duty cycle estimated values ​​D averaged to obtain the comparison reference value Cmp is not limited to 10. Furthermore, the duty cycle estimated values ​​D averaged to obtain the comparison reference value Cmp do not necessarily have to be consecutive. For example, the duty cycle estimated values ​​D in a deviation period may be excluded from the duty cycle estimated values ​​D to be averaged. A deviation period is a period in which the duty cycle estimated values ​​D deviate from the certain range α. In the example shown in FIG. 10 , the comparison reference value Cmp may be calculated using the duty cycle estimated values ​​from period number "2" to period number "4" and the duty cycle estimated values ​​from period number "6" to period number "15."

[0137] In addition, it is preferable that the comparison reference value Cmp be updated when the input voltage to the voltage conversion circuit 20 fluctuates, and it is preferable that the comparison reference value Cmp be updated when the output voltage from the voltage conversion circuit 20 fluctuates.

[0138] Furthermore, in consideration of variations in the characteristics of the voltage detection unit 30, it is preferable that the comparison reference value Cmp be updated periodically. For example, it is preferable that the comparison reference value Cmp be updated at regular intervals in consideration of the time constant of temperature changes in the voltage detection unit 30.

[0139] Furthermore, the first and second embodiments may be combined as appropriate. For example, in the second embodiment, when the comparison reference value Cmp is updated, it takes at least 10 cycles from the start of the update process until a new comparison reference value Cmp is set. Therefore, until a new comparison reference value Cmp is set, the duty ratio estimated value D(n-1) acquired in the cycle immediately before the cycle in which the updated estimated value is acquired may be used as the comparison reference value Cmp. This makes it possible to detect an abnormality in the voltage detection unit 30 even while the comparison reference value calculation count is being counted up.

[0140] In addition, in the first and second embodiments, when the difference value ΔD(n) is detected to be within a specified range five consecutive times as a specified number of times, the voltage detection unit 30 determines that an abnormality has occurred. However, the specified number of times is not limited to five times and may be changed as appropriate.

[0141] Furthermore, in the first and second embodiments, the case where the output voltage detector 32 fails has been described as an example, but even if the input voltage detector 31 fails, the abnormality detection unit 43 can detect an abnormality in the voltage detection unit 30.

[0142] Furthermore, in the first and second embodiments, when an abnormality is detected in the voltage detection unit 30, it is not determined whether the abnormality has occurred in the input voltage detector 31 or the output voltage detector 32. Therefore, for example, it may be determined whether the abnormality has occurred in the input voltage detector 31 or the output voltage detector 32, as follows.

[0143] When an abnormality in voltage detection unit 30 is detected, abnormality detection unit 43 compares input voltage detection value V1 with the detection value of a voltage sensor for monitoring the output voltage of DC voltage source 50. The voltage sensor may be a voltage sensor provided in DC voltage source 50, or may be provided in the power conversion device.

[0144] If the difference between the input voltage detection value V1 and the detection value of the voltage sensor is equal to or greater than the input voltage determination value, the abnormality detection unit 43 can determine that the input voltage detector 31 is abnormal. The input voltage determination value is a value used to determine whether the input voltage detection value V1 indicates an abnormal value. On the other hand, if the difference between the input voltage detection value V1 and the detection value of the voltage sensor is less than the input voltage determination value, the output voltage detector 32 can be determined to be abnormal.

[0145] Furthermore, in the case of a motor load, the output voltage of the voltage conversion circuit 20 can be estimated based on the torque of the motor 62, the rotation speed of the motor 62, the capacitance value of the output capacitor 24, and the switching frequency of the voltage conversion circuit 20. Therefore, when an abnormality is detected in the voltage detection unit 30, the abnormality detection unit 43 estimates the output voltage detection value V2 based on the load current value. If the difference between the output voltage detection value V2 and the estimated output voltage is equal to or greater than the output voltage determination value, the abnormality detection unit 43 can determine that the output voltage detector 32 is abnormal. The output voltage determination value is a value used to determine whether the output voltage detection value V2 indicates an abnormal value. On the other hand, if the difference between the output voltage detection value V2 and the estimated output voltage is less than the output voltage determination value, the input voltage detector 31 can be determined to be abnormal.

[0146] Furthermore, if an abnormality is detected in the voltage detection unit 30, the abnormality detection unit 43 may instruct the setting unit 41 to set the boost ratio in the voltage conversion circuit 20 to 1, and then identify whether the abnormality is in the input voltage detector 31 or the output voltage detector 32, as follows.

[0147] When the step-up ratio is set to 1, i.e., when the duty ratio is set to 0, the abnormality detection unit 43 may compare the input voltage detection value V1, the output voltage detection value V2, and the detection value of the voltage sensor. If the input voltage detector 31 is faulty, the input voltage detection value V1 will be different from the other two detection values, and if the output voltage detector 32 is faulty, the output voltage detection value V2 will be different from the other two detection values.

[0148] Therefore, if the input voltage detection value V1 differs from the other two detection values ​​among the input voltage detection value V1, the output voltage detection value V2, and the detection value of the voltage sensor, the abnormality detection unit 43 can determine that the input voltage detector 31 is abnormal. Also, if the output voltage detection value V2 differs from the other two detection values ​​among the input voltage detection value V1, the output voltage detection value V2, and the detection value of the voltage sensor, the abnormality detection unit 43 can determine that the output voltage detector 32 is abnormal.

[0149] Furthermore, when the duty ratio is set to 0, the abnormality detection unit 43 may compare the input voltage detection value V1, the output voltage detection value V2, and the estimated output voltage. If the input voltage detector 31 is faulty, the input voltage detection value V1 will differ from the output voltage detection value V2 and the estimated output voltage, and if the output voltage detector 32 is faulty, the output voltage detection value V2 will differ from the input voltage detection value V1 and the estimated output voltage.

[0150] Therefore, when the input voltage detection value V1 differs from the output voltage detection value V2 and the estimated output voltage among the input voltage detection value V1, the output voltage detection value V2, and the estimated output voltage, the abnormality detection unit 43 can determine that the input voltage detector 31 is abnormal. Also, when the output voltage detection value V2 differs from the input voltage detection value V1 and the estimated output voltage among the input voltage detection value V1, the output voltage detection value V2, and the estimated output voltage, the abnormality detection unit 43 can determine that the output voltage detector 32 is abnormal.

[0151] Furthermore, in the first and second embodiments, the setting unit 41 sets the duty ratio of the PWM signal by PI control, but the duty ratio of the PWM signal may be set by PID control.

[0152] Furthermore, in the power conversion device 10 according to the first and second embodiments, feedback control is applied to the PWM control, but the power conversion device 10 is not limited to a device in which feedback control is applied to the PWM control. For example, fixed duty ratio control or feedforward control may be applied to the PWM control in the power conversion device 10.

[0153] In the voltage conversion circuit 20 of the first and second embodiments, in principle, only a current flows through the first switching element 21 in a direction from the source to the drain. Therefore, the first switching element 21 may be replaced with a diode. In this case, the diode may be arranged so that the anode terminal of the diode corresponds to the source terminal of the first switching element 21 and the cathode terminal of the diode corresponds to the drain terminal of the first switching element 21.

[0154] Although MOSFETs made of SiC semiconductors are used for the first switching element 21 and the second switching element 22, the MOSFETs may be made of Si semiconductors. Also, instead of MOSFETs, IGBTs (Insulated Gate Bipolar Transistors) or GaN-HEMTs (Gallium Nitride-High Electron Mobility Transistors) may be used.

[0155] Furthermore, in the first switching element 21 and the second switching element 22, the anti-parallel diodes are built into the MOSFETs, but the anti-parallel diodes may be attached externally to the MOSFETs.

[0156] Furthermore, in the first and second embodiments, the voltage conversion circuit 20 is configured as a one-phase, one-stage step-up DC / DC converter, but the configuration of the voltage conversion circuit 20 is not limited to a one-phase, one-stage step-up DC / DC converter. The voltage conversion circuit 20 may be configured as a step-down DC / DC converter or a step-up / step-down DC / DC converter. Furthermore, the voltage conversion circuit 20 may be configured as a multi-phase DC / DC converter or a multi-level DC / DC converter.

[0157] Fig. 12 is a diagram showing an example in which a two-stage multilevel step-up DC / DC converter is applied as the voltage conversion circuit 20. Fig. 13 is a diagram showing an example in which a two-phase multiphase step-up DC / DC converter is applied as the voltage conversion circuit 20. Fig. 14 is a diagram showing an example in which a one-phase one-stage step-down DC / DC converter is applied as the voltage conversion circuit 20. Fig. 15 is a diagram showing an example in which a one-phase one-stage step-up / step-down DC / DC converter is applied as the voltage conversion circuit 20.

[0158] The duty ratio estimated value D(n) in the voltage conversion circuit 20 of Figures 12 and 13 is expressed by equation (1). The duty ratio estimated value D(n) in the voltage conversion circuit 20 of Figure 14 is expressed by the following equation (15).

[0159] D(n)=V2(n) / V1(n) (15)

[0160] The duty ratio estimation value D(n) in the voltage conversion circuit 20 of FIG. 15 is expressed by equation (1) when the input voltage is smaller than the output voltage, i.e., during step-up operation, and is expressed by equation (15) when the input voltage is larger than the output voltage, i.e., during step-down operation.

[0161] 1 and 12 to 15, the duty ratio estimated value D(n) can be calculated using the input voltage and the output voltage. Therefore, in the present disclosure, the calculation formula for the duty ratio estimated value D(n) is changed as appropriate depending on the circuit configuration of the voltage conversion circuit.

[0162] Furthermore, in the first and second embodiments, a secondary battery is used as DC voltage source 50, but a fuel cell or other DC voltage source may also be used.

[0163] The functions of the power conversion devices 10 according to the first and second embodiments are realized by a processing circuit. Fig. 16 is a configuration diagram showing a first example of a processing circuit that realizes the functions of the power conversion devices 10 according to the first and second embodiments. The processing circuit 100 of the first example is dedicated hardware.

[0164] Furthermore, the processing circuit 100 may be, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination thereof.

[0165] 17 is a configuration diagram showing a second example of a processing circuit that realizes the functions of the power conversion device 10 according to the first and second embodiments. The processing circuit 200 of the second example includes a processor 201 and a memory 202.

[0166] In the processing circuit 200, the functions of the power conversion device 10 are realized by software, firmware, or a combination of software and firmware. The software and firmware are written as programs and stored in the memory 202. The processor 201 realizes the functions by reading and executing the programs stored in the memory 202.

[0167] It can also be said that the programs stored in memory 202 cause the computer to execute the procedures or methods of the above-mentioned sections. Here, memory 202 refers to non-volatile or volatile semiconductor memory, such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable Read Only Memory), and EEPROM (Electrically Erasable and Programmable Read Only Memory). Magnetic disks, flexible disks, optical disks, compact disks, minidisks, DVDs, and the like also fall under memory 202.

[0168] It should be noted that some of the functions of the power conversion device 10 described above may be realized by dedicated hardware and some by software or firmware.

[0169] In this way, the processing circuit can realize the functions of the power conversion device 10 described above by hardware, software, firmware, or a combination thereof.

[0170] The above describes in detail preferred embodiments, but the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the claims.

[0171] Various aspects of the present disclosure are summarized below as appendices.

[0172] (Appendix 1) voltage conversion circuit, a voltage detection unit having an input voltage detector that detects an input voltage to the voltage conversion circuit as an input voltage detection value, and an output voltage detector that detects an output voltage from the voltage conversion circuit as an output voltage detection value; A control unit that controls the voltage conversion circuit Equipped with The control unit a setting unit that sets a duty ratio of a PWM signal to be provided to the voltage conversion circuit based on a target voltage value that is a target value of the output voltage, and outputs the PWM signal based on the set duty ratio to the voltage conversion circuit; an estimated value calculation unit that periodically calculates a duty ratio estimated value, which is a duty ratio of a PWM signal that should be output from the setting unit to the voltage conversion circuit, based on the input voltage detection value and the output voltage detection value, assuming a relationship between the input voltage detection value and the output voltage detection value; an abnormality detection unit that periodically calculates a difference between an updated estimated value, which is the duty ratio estimated value newly calculated by the estimated value calculation unit, and a comparison reference value based on the duty ratio estimated value calculated by the estimated value calculation unit in a period prior to the period in which the updated estimated value was calculated, as a difference value, and detects an abnormality in the voltage detection unit based on a change in the calculated difference value A power conversion device having: (Appendix 2) The comparison reference value is the duty ratio estimated value obtained in the period immediately before the period in which the updated estimated value is obtained. 2. The power conversion device according to claim 1. (Appendix 3) The comparison reference value is an average value of a plurality of duty cycle estimates obtained in a period prior to the period in which the updated estimate value is obtained. 2. The power conversion device according to claim 1. (Appendix 4) The abnormality detection unit determines that the voltage detection unit is abnormal when it detects that the difference value exceeds a specified range and then detects that the periodically calculated difference value is within the specified range for a specified number of consecutive times. 4. The power conversion device according to claim 1, wherein the power conversion device is a power conversion device having a first and a second terminal. (Appendix 5) The abnormality detection unit continuously detects that the difference value exceeds the specified range, and when the polarities by which the difference value exceeds the specified range in two consecutive detected exceedsals are opposite to each other, the abnormality detection unit temporarily terminates the determination of whether or not the voltage detection unit is abnormal. 5. The power conversion device according to claim 1, wherein the power conversion device is a power conversion device having a first and a second terminal. (Appendix 6) The abnormality detection unit sets the specified range in accordance with the input voltage to the voltage conversion circuit and the output voltage from the voltage conversion circuit. 6. The power conversion device according to claim 4 or 5. (Appendix 7) When the target voltage value is changed, the abnormality detection unit temporarily disables the detection of the abnormality. 7. The power conversion device according to claim 1, wherein the power conversion device is a power conversion device having a first power supply and a second power supply. (Appendix 8) When the output current of the voltage conversion circuit changes by a specified current value or more due to a load fluctuation, the abnormality detection unit temporarily disables the detection of the abnormality. 8. The power conversion device according to claim 1, wherein the power conversion device is a power conversion device having a first power supply and a second power supply. (Appendix 9) When the input voltage changes by a specified voltage value or more due to voltage fluctuations of an external power supply, the abnormality detection unit temporarily disables the detection of the abnormality. 9. The power conversion device according to any one of Supplementary Note 1 to Supplementary Note 8. (Appendix 10) The specified range is set based on a maximum value of a duty ratio deviation width, which is a width of deviation between a duty ratio set based on a target voltage value and the output voltage detection value and the duty ratio estimated value, within a normal operating range of the voltage detection unit. 6. The power conversion device according to claim 4 or 5. [Explanation of symbols]

[0173] 10 power conversion device, 20 voltage conversion circuit, 30 voltage detection unit, 31 input voltage detector, 32 output voltage detector, 40 control unit, 41 setting unit, 42 estimated value calculation unit, 43 abnormality detection unit, 50 DC voltage source, 60 load.

Claims

1. voltage conversion circuit, a voltage detection unit having an input voltage detector that detects an input voltage to the voltage conversion circuit as an input voltage detection value, and an output voltage detector that detects an output voltage from the voltage conversion circuit as an output voltage detection value; A control unit that controls the voltage conversion circuit Equipped with The control unit a setting unit that sets a duty ratio of a PWM signal to be provided to the voltage conversion circuit based on a target voltage value that is a target value of the output voltage, and outputs the PWM signal based on the set duty ratio to the voltage conversion circuit; an estimated value calculation unit that periodically calculates a duty ratio estimated value, which is a duty ratio of a PWM signal that should be output from the setting unit to the voltage conversion circuit, based on the input voltage detection value and the output voltage detection value, assuming a relationship between the input voltage detection value and the output voltage detection value; an abnormality detection unit that periodically calculates a difference between an updated estimated value, which is the duty ratio estimated value newly calculated by the estimated value calculation unit, and a comparison reference value based on the duty ratio estimated value calculated by the estimated value calculation unit in a period prior to the period in which the updated estimated value was calculated, as a difference value, and detects an abnormality in the voltage detection unit based on a change in the calculated difference value A power conversion device having:

2. The comparison reference value is the duty ratio estimated value obtained in the period immediately before the period in which the updated estimated value is obtained. The power conversion device according to claim 1 .

3. The comparison reference value is an average value of a plurality of duty cycle estimates obtained in a period prior to the period in which the updated estimate value is obtained. The power conversion device according to claim 1 .

4. The abnormality detection unit determines that the voltage detection unit is abnormal when it detects that the difference value exceeds a specified range and then detects that the periodically calculated difference value is within the specified range for a specified number of consecutive times. The power conversion device according to claim 1 .

5. The abnormality detection unit continuously detects that the difference value exceeds the specified range, and when the polarities by which the difference value exceeds the specified range in two consecutive detected exceedsals are opposite to each other, the abnormality detection unit temporarily terminates the determination of whether or not the voltage detection unit is abnormal. The power conversion device according to claim 1 .

6. The abnormality detection unit sets the specified range in accordance with the input voltage to the voltage conversion circuit and the output voltage from the voltage conversion circuit. The power conversion device according to claim 4 or 5.

7. When the target voltage value is changed, the abnormality detection unit temporarily disables the detection of the abnormality. The power conversion device according to any one of claims 1 to 3.

8. When the output current of the voltage conversion circuit changes by a specified current value or more due to a load fluctuation, the abnormality detection unit temporarily disables the detection of the abnormality. The power conversion device according to any one of claims 1 to 3.

9. When the input voltage changes by a specified voltage value or more due to voltage fluctuations of an external power supply, the abnormality detection unit temporarily disables the detection of the abnormality. The power conversion device according to any one of claims 1 to 3.

10. The specified range is set based on a maximum value of a duty ratio deviation width, which is a width of deviation between a duty ratio set based on a target voltage value and the output voltage detection value and the duty ratio estimated value, within a normal operating range of the voltage detection unit. The power conversion device according to claim 4 or 5.

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