JP5136394B2 - Vehicle power supply - Google Patents

Description

  The present invention relates to a vehicle power supply device, and more particularly to a vehicle power supply device including a voltage converter having a function of manipulating a duty ratio by switching using a semiconductor element.

  In recent years, hybrid vehicles and electric vehicles have attracted much attention as environmentally friendly vehicles. Some of these vehicles adopt a configuration in which a battery voltage is converted by a voltage conversion device (voltage converter) and supplied to a motor drive device. The voltage converter is a power converter that converts an input voltage from a DC power source into a desired output voltage. For example, Japanese Patent Application Laid-Open No. 2008-172966 (Patent Document 1) discloses a method for determining abnormality of such a power converter.

  A control device disclosed in Japanese Patent Application Laid-Open No. 2008-172966 is mounted on a vehicle and controls a load driving circuit that supplies power to a driving load from a converter that converts a voltage. The control device calculates the average value of the voltage values on the output side of the converter when the voltage conversion command is not output for a predetermined period or longer as the first average value, and the voltage conversion command is output. When the average value of the voltage value on the output side of the converter is calculated as the second average value, and the difference between the first average value and the second average value is smaller than the predetermined value, the converter has an abnormality. It is determined that

  According to the control device disclosed in Japanese Patent Laid-Open No. 2008-172966, for example, in the case of a boost converter, when the boost command is not output (when the upper arm of the converter is on), the output side of the converter The average value of the voltage values is calculated as the first average value. Thereafter, the average value of the voltage values on the output side of the converter when the boost command is output is calculated as the second average value. If the difference between the first average value and the second average value is smaller than the threshold value (that is, if the output voltage value of the converter after the boost command does not increase), it is determined that an abnormality has occurred in the converter. To do. At this time, the first average value when the reference boost command is not output is calculated over a predetermined period. For this reason, even if the boost command value is small, erroneous determination due to variations in accuracy of the voltage sensor can be avoided. As a result, an abnormality in the converter can be accurately determined even if the difference between the converted voltage value (step-up target voltage value or step-down target voltage value) and the voltage value before conversion is small.

  In addition to the above-mentioned Japanese Patent Application Laid-Open No. 2008-172966, various techniques for determining a power converter or an abnormality of a device related to the power converter are known.

For example, International Publication No. 2006/033163 (Patent Document 2) includes a voltage converter, a battery connected to the input side of the voltage converter, a load connected to the input side of the voltage converter, and a voltage value of the battery. In a load driving circuit including a first sensor for detecting the voltage and a second sensor for detecting a voltage value on the output side of the converter, the voltage value detected by the first sensor when the converter is not operating in a step-up / step-down manner When the absolute value of the difference between the voltage value detected by the second sensor and the voltage value detected by the second sensor is greater than or equal to a predetermined threshold value, the voltage value detected by the first sensor is outside the tolerance range of the first sensor. If the first sensor is identified as an abnormal sensor and the voltage value detected by the second sensor is outside the tolerance range of the second sensor, the second sensor is an abnormal sensor. Abnormality monitoring apparatus is disclosed for identifying a.
JP 2008-172966 A International Publication No. 2006/033163 Pamphlet JP 2003-219635 A JP 2007-330089 A

  Incidentally, a voltage sensor that detects a voltage value on the output side of the voltage converter and a voltage sensor that detects a voltage value on the input side of the voltage converter generally have detection errors. Therefore, when determining the abnormality of the voltage converter using the detection value and determination threshold value of each voltage sensor, if the determination threshold value is set in consideration of the detection error of each voltage sensor, the standards of each voltage sensor and voltage converter are set. Depending on the value, there is a risk of misjudgment. Therefore, it is desirable to set the determination threshold in consideration of the relative error of each voltage sensor.

  However, none of the above-described Patent Documents 1-4 describes a technique for setting or correcting the determination threshold in consideration of the relative error of each voltage sensor.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a vehicle power supply device capable of improving the accuracy of determination as to whether or not the voltage conversion device is normal. That is.

  A power supply apparatus for a vehicle according to the present invention has a switching element controlled by a given command duty ratio, performs voltage conversion between a DC power supply and a load circuit, and a DC power supply side of the voltage conversion apparatus A first sensor that detects the voltage of the voltage converter, a second sensor that detects a voltage on the load circuit side of the voltage converter, and a control connected to the voltage converter, the first sensor, and the second sensor to control the voltage converter. Part. The voltage conversion device is configured such that, when the switching element is controlled to a predetermined state by the command duty ratio, voltage conversion is not performed, and the voltage on the DC power supply side and the voltage on the load circuit side substantially match. . The control unit considers both the detection error of the first sensor and the detection error of the second sensor, and calculates a determination threshold value used for determining whether or not the voltage conversion device is normal. A second calculation for calculating a ratio or difference between a detection value of the first sensor and a detection value of the second sensor when the element is controlled to a predetermined state as a value indicating a relative error between the first sensor and the second sensor. Unit, a storage unit that stores a value indicating a relative error, and a storage unit that stores a value indicating a relative error, the voltage converter is normal using the determination threshold value calculated by the first calculation unit. If the value indicating the relative error is stored in the storage unit, the determination threshold value calculated by the first calculation unit is corrected based on the value indicating the relative error, and corrected. The determination threshold is used to determine whether or not the voltage converter is normal And a Nau determination unit.

  According to the present invention, when the switching element is controlled to be in a predetermined state, the switching element is in the predetermined state by utilizing the characteristic that the voltage on the DC power supply side and the voltage on the load circuit side of the voltage conversion device substantially match. The ratio or difference between the detection value of the first sensor and the detection value of the second sensor when the control is performed is calculated and stored as a value indicating the relative error between the first sensor and the second sensor. If a value indicating the relative error is stored, the determination threshold is corrected based on the stored value indicating the relative error, and whether the voltage converter is normal using the corrected determination threshold. Judgment is made. Therefore, the accuracy of the abnormality determination of the voltage converter is improved as compared with the case where only the determination threshold value calculated considering both the detection error of the first sensor and the detection error of the second sensor is used.

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

  FIG. 1 is a schematic diagram illustrating the configuration of a power supply device for a vehicle and related equipment according to the present embodiment. In FIG. 1, it is assumed that the vehicle is mounted on an electric vehicle.

  The vehicle power supply device 10 includes a configuration of a DC chopper device including a circuit unit connecting the DC power supply 12 and the inverter motor 14 and a control unit 16. The circuit unit includes a coil 18, diodes 20 and 24, transistors 22 and 26, and a capacitor 28.

  One end of a coil 18 is connected to the positive electrode of the DC power supply 12. The other end of the coil 18 is connected to an upper arm in which the diode 20 and the transistor 22 are connected in parallel, and a lower arm in which the diode 24 and the transistor 26 are connected in parallel.

  The other end of the upper arm is connected to the positive terminal of the inverter motor 14, and the other end of the lower arm is connected to the negative terminal of the inverter motor 14 and to the negative terminal of the DC power source 12. A capacitor 28 is connected between the positive terminal and the negative terminal of the inverter motor 14.

  The voltage VL (input voltage VL) of the DC power supply 12 is measured by the voltage sensor 30. The current IB of the DC power supply 12 is measured by an ammeter 32. Further, the output voltage VH output between the positive terminal and the negative terminal of the inverter motor 14 is measured by the voltage sensor 34. These measured voltage and current are sent to the control unit 16.

  In addition, power consumption information is sent from the inverter motor 14 to the control unit 16. This information can be replaced by torque command information that can calculate electric power. Further, target output power for output power control performed by control unit 16 is input from command unit 36. The command unit 36 instructs the optimum target output power at any time according to the traveling state of the electric vehicle.

  The control unit 16 includes an arithmetic control unit 38 and a storage unit 40. The arithmetic control unit 38 performs processing according to a preset program, and also performs processing such as input signals and output signals. Specifically, the arithmetic control unit 38 issues a switching command to the transistors 22 and 26. In this switching, the duty ratio relating to the on / off time is manipulated to control the output voltage close to the target output voltage. The arithmetic control unit 38 performs control using the output voltage VH of the chopper device as a control amount, and also performs arithmetic processing related to abnormality determination of the circuit unit.

  The storage unit 40 temporarily or fixedly stores information necessary for the calculation control unit 38 to perform processing. For example, information for determining abnormality of the circuit unit is stored in the storage unit 40.

  Next, the operation of the circuit unit will be briefly described. This circuit unit can operate as a step-up circuit as a forward direction conversion circuit that supplies power from the DC power source 12 to the inverter motor 14, and conversely as a step-down circuit as a reverse direction conversion circuit that regenerates to the DC power source 12. Is also operable.

  When operating as a booster circuit, the transistor 26 is turned on and off with the transistor 22 turned off. That is, when the transistor 26 is on, a current flowing from the DC power supply 12 forms a loop that returns to the DC power supply 12 via the coil 18 and the transistor 26. Magnetic energy is stored in the coil 18 as current flows through the loop.

  When the transistor 26 is turned off, a current flowing from the DC power supply 12 flows to the inverter motor 14 via the coil 18 and the diode 20 to form a loop returning to the DC power supply 12. During this time, in addition to the electric energy from the DC power supply 12, the magnetic energy stored in the coil 18 is supplied to the inverter motor 14, so that the output voltage applied to the inverter motor 14 is boosted.

  On the other hand, when operating as a step-down circuit, transistor 22 is turned on and off with transistor 26 turned off. That is, when the transistor 22 is on, the current regenerated from the inverter motor 14 flows to the transistor 22, the coil 18, and the DC power supply 12, thereby forming a loop that returns to the inverter motor 14.

  When the transistor 22 is off, a loop composed of the coil 18, the DC power supply 12, and the diode 24 is formed, and the magnetic energy stored in the coil 18 is regenerated in the DC power supply 12.

  In this reverse conversion circuit, the time during which the DC power supply 12 receives power is longer than the time during which the inverter motor 14 supplies power. As can be seen from this, the voltage in the inverter motor 14 is stepped down and regenerated in the DC power supply 12. The operation of the voltage converter is performed by appropriately controlling the power running operation and the regenerative operation.

  Here, the duty ratio will be described. For the sake of simplicity, considering the case where the voltage converter 13 includes only a booster circuit, the duty ratio is expressed as follows.

Duty ratio = ton / (ton + toff) (1)
Duty ratio = VL / VH (2)
Note that the on time of the transistor is ton and the off time of the transistor is toff. Equation (2) is derived when it is assumed that the current flowing through the circuit is always constant and the power supplied by the DC power supply and the power consumed on the output side are equal during one switching cycle. It is a formula.

  As can be seen from the equations (1) and (2), the output voltage can be set to a desired value by changing the duty ratio by changing ton and toff. In the definition of the duty ratio, it is also possible to use a theoretical formula that does not perform approximation or that improves the accuracy of approximation. In addition, when a reverse direction conversion circuit is included, the extension may be performed based on the same idea.

  With reference to FIG. 2, the abnormality determination process of the voltage conversion system which the control part 16 performs is demonstrated. FIG. 2 is a diagram for explaining an abnormality determination method of the voltage conversion system of the control unit 16. Factors that cause abnormalities in the voltage conversion system include abnormalities in the voltage sensors 30 and 34 and abnormalities in the voltage converter 13 (abnormalities in semiconductor elements such as the diodes 20 and 24 and the transistors 22 and 26).

  As can be seen from the above equation (2), the relationship of output voltage VH = input voltage VL / duty ratio is established among the input voltage VL, the output voltage VH, and the duty ratio.

  Using this relationship, the control unit 16 uses the detected value (VL sensor value) of the voltage sensor 30 and the duty command value D from the command unit 36 to allow a range of VH sensor values when the voltage conversion system is normal ( An upper limit line and a lower limit line in FIG. 2 are obtained, and abnormality determination of the voltage conversion system is performed based on whether or not the VH sensor value is included in the obtained range.

  Specifically, the control unit 16 calculates the VL sensor value / duty calculation value Duty as the calculation value (VH calculation value) of the output voltage VH, and the difference between the detection value of the voltage sensor 34 and the VH calculation value (= VH The upper limit threshold value Vupp and the lower limit threshold value Vlow of (sensor value−VH calculated value) are calculated by the following equations.

Upper limit threshold Vupp = [1 / Duty (+)] × (VL−ΔVL) + ΔVH (3)
Lower threshold Vlow = [1 / Duty (−)] × (VL + ΔVL) −ΔVH (4)
However, ΔVL is the detection error of the voltage sensor 30, ΔVH is the detection error of the voltage sensor 34, Duty (+) is the maximum value of the duty calculation value Duty in consideration of the dead time and switching delay, and Duty (−) is the dead time. And the minimum value of the duty calculation value Duty when the switching delay is taken into consideration. The duty calculation value Duty is a value obtained by adding a correction amount Dd of the duty command value D due to dead time and a correction amount Ds of the duty command value D due to switching delay to the duty command value D from the command unit 36 ( That is, Duty = D + Dd + Ds). The correction amount Dd is set to a larger value when the actual dead time is smaller than the median value. The correction amount Ds is set to a larger value when the actual switching delay is larger than the median value.

  In the above equation (3), when the error of the voltage sensor 34 is on the + side (when the voltage sensor 34 detects a value higher than the actual value by ΔVH and the VH sensor value becomes maximum), the voltage sensor 30 The upper threshold value Vupp is set on the assumption that the error is negative (when the voltage sensor 30 detects a value lower than the actual value by ΔVL and the VH calculation value is minimized). ing.

  In the above equation (4), when the error of the voltage sensor 34 is on the negative side (when a value lower than the actual value by ΔVH is output and the VH sensor value is minimum), the error of the voltage sensor 30 is The lower limit threshold Vlow is set on the assumption that the positive side (when the value higher than the actual value by ΔVL is output and the VH calculation value is maximum) occurs at the same time.

  Then, the control unit 16 determines that the voltage conversion system is normal when the VH calculated value−the lower limit threshold Vlow is the lower limit line, the VH calculated value + the upper limit threshold Vupp is the upper limit line, and the lower limit line <VH sensor value <the upper limit line. judge. When VH sensor value> upper limit line or VH sensor value <lower limit line, it is determined that the voltage conversion system is abnormal.

  As described above, the control unit 16 sets the range (upper limit line and lower limit line) that can be taken by the VH sensor value in the normal state in consideration of both the detection error ΔVL of the voltage sensor 30 and the detection error ΔVH of the voltage sensor 34. Then, abnormality determination of the voltage conversion system is performed. In such a setting method, the set upper limit line tends to approach the upper limit essential line that should be detected as abnormal, and the set lower limit line tends to approach the lower limit essential line that should be detected as abnormal (that is, FIG. 2). The upper and lower margins shown in FIG.

  Therefore, depending on the dead time of the voltage converter 13 and the magnitude of detection errors of the voltage sensors 30 and 34, the difference between the region that should be detected as abnormal and the region that can be detected normally (the size of the margin shown in FIG. 2). May be further reduced or eliminated, and there is a concern that the abnormality of the voltage conversion system may be erroneously determined.

  FIG. 3 shows the operation region of the VH sensor value when the abnormality that cannot be boosted by the voltage converter 13 occurs, the above-described upper limit line (= VH calculated value + upper limit threshold Vupp), and lower limit line (with the duty calculated value Duty as a parameter) = VH calculated value-lower threshold Vlow).

  Lines A to I in FIG. 3 show VH sensor values when an abnormality that cannot be boosted by the voltage converter 13 occurs according to the combination of errors of the voltage sensors. Note that “No VL” shown in the legend of FIG. 3 indicates a case where there is no error of the voltage sensor 30, “VL +” indicates a case where the voltage sensor 30 detects a value higher than the actual by an error ΔVL, “VL−” indicates a case where the voltage sensor 30 detects a value lower than the actual value by an error ΔVL. “No VH” indicates a case where there is no error of the voltage sensor 34, “VH +” indicates a case where the voltage sensor 34 detects a value higher than the actual value by an error ΔVH, and “VH−” indicates a voltage sensor. 34 shows a case where a value lower than the actual value by an error ΔVH is detected.

  As shown by lines A to I in FIG. 3, when an abnormality that cannot be boosted by the voltage converter 13 occurs, the VH sensor value varies according to the combination of errors of the voltage sensors. The line connecting the right ends of the lines A to I in FIG. 3 is a lower-limit essential line that should be detected as abnormal in nature, and the region closer to the VH calculation value (upper region) than the lower-limit essential line is normal. This is a possible region, and the region farther from the VH calculation value (lower region) is the region at the time of abnormality.

  As described above, the control unit 16 determines that the voltage conversion system is normal when the lower limit line <VH sensor value <the upper limit line, but this lower limit line is a VH calculated value that is lower than the lower limit essential line shown in FIG. If the lower limit line overlaps with the lines A to I in FIG. 3, the control unit 16 does not actually increase the voltage with the voltage converter 13. An erroneous determination may be made that it is determined that the voltage conversion system is normal. Such an erroneous determination can also occur on the upper limit line side.

  In order to reduce the possibility of such an erroneous determination, as shown by the arrows in FIG. 3, the upper limit line (VH calculated value + upper limit threshold Vupp) and the lower limit line (VH calculated value−lower limit threshold Vlow) are respectively set. It is necessary to reduce the possible range at normal time (to increase the margin shown in FIG. 2) close to the value when no error occurs (VH calculation value).

  Therefore, the present invention utilizes the characteristic that the output voltage VH and the input voltage VL coincide with each other when the upper arm is on, so that the relative error between the voltage sensors 30 and 34 when the upper arm is on (the error of the voltage sensor 30 and the voltage sensor 34). The ratio or difference between the upper limit threshold value Vupp and the lower limit threshold value Vlow is reduced in accordance with the stored relative error when a voltage conversion system abnormality is determined. The correction is characterized in that the upper limit line and the lower limit line are brought close to the VH calculated values (the range shown in FIG. 2 is enlarged by narrowing the possible range at normal time).

  FIG. 4 is a processing flow in the case where the control unit 16 calculates the correction coefficient K used for correcting the upper limit threshold value Vupp and the lower limit threshold value Vlow as a value indicating the relative error between the voltage sensors 30 and 34. In addition, it is desirable to implement this processing flow after confirming that a circuit (such as the voltage converter 13) constituting the boost is normal at the time of completion inspection of the vehicle. This is because the characteristic that the output voltage VH and the input voltage VL coincide with each other when the upper arm is on can be used only when it is clear that the circuit constituting the booster is normal. The above-described method for confirming that the circuit constituting the booster is normal is that the VH, VL, and VB values are acquired by an external sensor during vehicle completion inspection, and the frequency analysis is performed to obtain the switching frequency of the boost control. You may judge by not having.

  In S100, control unit 16 determines whether or not the upper arm of voltage converter 13 is on. When the upper arm is in the on state, the converter is in a non-boosted state, and the input voltage VL and the output voltage VH match. If the upper arm is on (YES in S100), the process proceeds to S102. Otherwise (NO in S100), this process ends.

In S102, control unit 16 detects a VH sensor value and a VL sensor value.
In S104, control unit 16 calculates the ratio of VH sensor value to VL sensor value (= VH sensor value / VL sensor value) as correction coefficient K. In S106, the control unit 16 stores the correction coefficient K in the storage unit 40 and ends the present process.

  When the control unit 16 subsequently performs abnormality determination of the voltage conversion system and the correction coefficient K is stored in the storage unit 40, the control unit 16 calculates the above equation (3) and equation (4). Instead of the upper limit threshold Vupp and the lower limit threshold Vlow, the upper limit line and the lower limit line are set using the upper limit threshold Vupp and the lower limit threshold Vlow calculated by the following formulas (5) and (6).

Upper limit threshold Vupp = [1 / Duty (+)] × VL × correction coefficient K (5)
Lower limit threshold Vlow = [1 / Duty (−)] × VL × correction coefficient K (6)
That is, the control unit 16 determines the ratio of the VH sensor value to the VL sensor value when the upper arm is in the on state and the input voltage VL and the output voltage VH are actually coincident with each other. It is calculated as a relative error, and the upper limit threshold Vupp and the lower limit threshold Vlow are corrected in consideration of this relative error.

  Therefore, compared with the case where the upper limit threshold value Vupp and the lower limit threshold value Vlow (that is, the threshold values calculated in consideration of the detection errors of the voltage sensors 30 and 34) calculated by the above formulas (3) and (4) are used. Thus, the absolute values of the upper limit threshold value Vupp and the lower limit threshold value Vlow can be reduced to bring the upper limit line and the lower limit line closer to the VH calculated values (the range shown in FIG. 2 can be expanded by narrowing the possible range at normal time). As a result, the accuracy of the voltage conversion system abnormality determination is improved, and the voltage conversion system abnormality can be determined earlier.

<Modification>
The processing flow shown in FIG. 4 may be replaced with the processing flow shown in FIG. Note that the processing flow shown in FIG. 5 is also executed on condition that the switching frequency of the boost control is not output, as in FIG. In the flow shown in FIG. 5, the same step number is assigned to the same process as the flow shown in FIG. 4 described above. The processing is the same for them. Therefore, detailed description thereof will not be repeated here.

  In S200, control unit 16 calculates difference VH−VL between the VH sensor value and the VL sensor value as correction amount ΔV. In S202, control unit 16 stores correction amount ΔV in storage unit 40.

  When the control unit 16 performs the subsequent abnormality determination of the voltage conversion system and the correction amount ΔV is stored in the storage unit 40, the control unit 16 calculates the above equation (3) and equation (4). Instead of the upper limit threshold value Vupp and the lower limit threshold value Vlow, abnormality determination is performed using the upper limit threshold value Vupp and the lower limit threshold value Vlow calculated by the following equations (7) and (8).

Upper limit threshold Vupp = [1 / Duty (+)] × (VL + correction amount ΔV) (7)
Lower limit threshold Vlow = [1 / Duty (−)] × (VL + correction amount ΔV) (8)
That is, the control unit 16 determines the difference between the VH sensor value and the VL sensor value when the upper arm is in the on state and the input voltage VL and the output voltage VH are actually coincident with each other. It is calculated as a relative error, and the upper limit threshold Vupp and the lower limit threshold Vlow are corrected in consideration of this relative error.

  Therefore, similarly to the above-described embodiment, the absolute values of the upper limit threshold Vupp and the lower limit threshold Vlow are reduced to bring the upper limit line and the lower limit line closer to the VH calculated values (the margin shown in FIG. Can be expanded).

  Note that the processing flow of FIG. 4 and the processing flow of FIG. 5 may be properly used depending on the characteristics of the voltage sensor. For example, when the relative error of each of the voltage sensors 30 and 34 can be expressed as a ratio, the processing flow of FIG. 4 is used, and when the relative error (offset) can be expressed, the processing flow of FIG. 5 is used. Good.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is the schematic explaining the power supply device of the vehicle which concerns on this Embodiment. It is a figure for demonstrating the abnormality determination method which the power supply device of the vehicle which concerns on embodiment of this invention performs. It is the figure which showed the relationship between the operation area | region of the VH sensor value when the abnormality which cannot raise | generate a voltage converter has occurred, and the upper limit line and lower limit line which the power supply device which concerns on this Embodiment calculates. It is a flowchart which shows the control structure of the power supply device of the vehicle which concerns on embodiment of this invention. It is a flowchart which shows the control structure of the power supply device of the vehicle which concerns on the modification of embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Power supply device, 12 DC power supply, 13 Voltage converter, 14 Inverter motor, 16 Control part, 18 Coil, 20, 24 Diode, 22, 26 Transistor, 28 Capacitor, 30, 34 Voltage sensor, 32 Ammeter, 36 Command part, 38 arithmetic control units, 40 storage units.

Claims (1)

A voltage conversion device having a switching element controlled by a given command duty ratio and performing voltage conversion between a DC power supply and a load circuit;
A first sensor for detecting a voltage on the DC power supply side of the voltage converter;
A second sensor for detecting a voltage on the load circuit side of the voltage converter;
A control unit connected to the voltage conversion device, the first sensor, and the second sensor and controlling the voltage conversion device;
When the switching element is controlled to be in a predetermined state by the command duty ratio, the voltage conversion device does not perform voltage conversion, and the voltage on the DC power supply side and the voltage on the load circuit side substantially coincide with each other. Is composed of
The controller is
A first calculation unit that calculates a determination threshold used for determining whether or not the voltage conversion device is normal in consideration of both the detection error of the first sensor and the detection error of the second sensor;
The ratio or difference between the detection value of the first sensor and the detection value of the second sensor when the switching element is controlled to the predetermined state indicates a relative error between the first sensor and the second sensor. A second calculation unit that calculates a value;
A storage unit for storing a value indicating the relative error;
When a value indicating the relative error is not stored in the storage unit, it is determined whether or not the voltage converter is normal using the determination threshold value calculated by the first calculation unit, When a value indicating the relative error is stored in the storage unit, the determination threshold value calculated by the first calculation unit is corrected based on the value indicating the relative error, and the corrected determination threshold value is used. And a determination unit that determines whether or not the voltage converter is normal.

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