Power conversion device

Abstract

Provided is a power conversion device that specifies a voltage sensor in which an abnormality has occurred, using only a voltage sensor value within the power conversion device, without using external voltage information different from voltage information within the power conversion device. Comprising a first voltage sensor for detecting the voltage of a low-voltage side capacitor, and a second voltage sensor and a third voltage sensor for detecting the voltage of a high-voltage side capacitor, comparing the voltage value of the second voltage sensor with the voltage value of the third voltage sensor, and judging whether the second voltage sensor and the third voltage sensor are abnormal or not. The presence or absence of an abnormality in the first voltage sensor and the second voltage sensor is determined by comparing a first voltage sensor estimated value estimated from the voltage value of the second sensor voltage with the voltage value of the first voltage sensor.

Description

Technical Field

[0001] The present application relates to a power conversion device. Background Art

[0002] In electric vehicles, in order to achieve high efficiency, it is necessary to control the voltage input from the low-voltage battery to the power conversion device to boost the voltage and supply power to the motor (i.e., power operation), and return the power on the motor side to the battery (i.e., regeneration). Moreover, in this control, it is necessary to detect the input voltage of the power conversion device (hereinafter referred to as the low-voltage side voltage) and the output voltage of the power conversion device (hereinafter referred to as the high-voltage side voltage) respectively. Therefore, when the voltage sensor that detects these voltages fails, accurate voltage control cannot be performed, so it becomes important to monitor the abnormality of the sensor regardless of the state of the power conversion device.

[0003] In a conventional abnormality monitoring device for a power conversion device, a voltage sensor in an abnormal state is identified by using a battery voltage of a battery connected to the power conversion device, a low voltage side voltage, and a high voltage side voltage of the power conversion device (eg, Patent Document 1). Prior art literature Patent Literature

[0004] Patent Document 1: Japanese Patent No. 3632657 Summary of the invention Technical problem to be solved by the invention

[0005] In the conventional abnormality monitoring device, the battery voltage is used to identify the voltage sensor in the abnormal state of the power conversion device. However, in the case where the control system of the battery and the control system of the power conversion device are different systems, such as in a hybrid vehicle, it is necessary to receive the battery voltage information from the outside and use it in the abnormality monitoring device of the power conversion device. In this case, if the received battery voltage is not signal processed based on the consideration of the external system processing cycle, etc., it cannot be used as reliable battery voltage information, and the voltage sensor in the abnormal state cannot be identified.

[0006] The present application discloses a technique for solving the above-mentioned problem, and an object of the present application is to obtain a power conversion device capable of determining an abnormality of a voltage sensor without using external voltage information. Technical means for solving technical problems

[0007] The power conversion device disclosed in this application, The power conversion device comprises a voltage conversion circuit for converting a first DC voltage into a second DC voltage of a different value, at least two capacitors, and a control device for controlling the voltage conversion amplitude of the voltage conversion circuit, wherein the power conversion device is characterized in that: a first capacitor connected in parallel with the first DC voltage; a second capacitor connected in parallel with the second DC voltage; a first voltage sensor configured to detect a voltage of the first capacitor; and a second voltage sensor, the second voltage sensor being used to detect a voltage of the second capacitor, and having a third voltage sensor, the third voltage sensor detecting the voltage of the third capacitor when the third capacitor is present in the voltage conversion circuit, and detecting the voltage of the first capacitor or the second capacitor when the third capacitor is not present, The control device controlling a voltage conversion amplitude of the voltage conversion circuit using a first voltage sensor value detected by the first voltage sensor, a second voltage sensor value detected by the second voltage sensor, and a third voltage sensor value detected by the third voltage sensor, calculating a first difference between the second voltage sensor value and a value obtained by multiplying the third voltage sensor value by a predetermined coefficient, and performing a first determination process to determine whether the first difference is greater than a predetermined first threshold value, In the first determination process, When the first difference is greater than the first threshold, direct connection control is performed to make the first voltage sensor value consistent with the second voltage sensor value, a second difference between the first voltage sensor value and the second voltage sensor value is calculated, and a second determination process is performed to determine whether the second difference is greater than a preset second threshold. In the second determination process, When the second difference is greater than the second threshold, it is determined that the second voltage sensor is abnormal, and when the second difference is less than the second threshold, it is determined that the third voltage sensor is abnormal. In the first determination process, When the first difference is smaller than the first threshold, a third difference is calculated as the difference between the first voltage sensor value and the first voltage sensor estimated value calculated based on the second voltage sensor value, and a third determination process is performed to determine whether the third difference is greater than a third threshold set in advance. In the third determination process, When the third difference is equal to or greater than the third threshold value, it is determined that the first voltage sensor is abnormal. When the third difference is smaller than the third threshold value, it is determined that all the voltage sensors are normal. Effects of the Invention

[0008] According to the present application, it is possible to perform abnormality determination of the voltage sensor without using external battery voltage information. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is a diagram showing the structure of the power conversion device according to the first embodiment. Figure 2A This is a flowchart showing a process for performing abnormality determination of the voltage sensor according to the first embodiment. Figure 2B This is a flowchart showing a process for performing abnormality determination of the voltage sensor according to the first embodiment. Figure 3 1 is a diagram showing gate drive signals and reactor current waveforms in the power conversion circuit according to the first embodiment. Figure 4 This is a diagram for explaining the operation mode (during power running operation) in the voltage conversion circuit according to the first embodiment. Figure 5 This is a diagram for explaining an operation mode (during regenerative operation) in the voltage conversion circuit according to the first embodiment. Figure 6 This is a diagram showing the configuration of a power conversion device according to a second embodiment. Figure 7 This is a diagram for explaining the operation mode of the voltage conversion circuit in the second embodiment. Figure 8 1 is a diagram showing gate drive signals and reactor current waveforms in the voltage conversion circuit according to the second embodiment. Fig. 9A This is a flowchart showing a process for performing abnormality determination of the voltage sensor according to the second embodiment. Fig. 9B This is a flowchart showing a process for performing abnormality determination of the voltage sensor according to the second embodiment. Fig.10 This is a configuration diagram showing an example of hardware of the control device according to the first and second embodiments. DETAILED DESCRIPTION

[0010] The following is an explanation of the embodiments of the power conversion device disclosed in the present application with reference to the accompanying drawings. In each figure, the same reference numerals represent the same or corresponding parts. Therefore, in order to avoid repetition, their detailed description is sometimes omitted.

[0011] Implementation method 1. Hereinafter, the power conversion device according to Embodiment 1 will be described with reference to the drawings. Figure 1: is a diagram showing the structure of the power conversion device involved in Embodiment 1. The power conversion device 3 is connected between the battery 1 and the load 2 to form a power supply system. That is, the power conversion device 3 is a DC / DC converter having the battery 1 connected to the terminal on the input side and the load 2 connected to the terminal on the output side, and is configured to be able to switch between a power operation action and a regeneration action, wherein the power operation action boosts the voltage of the battery 1 to a set voltage and supplies power to the load 2, and the regeneration action accumulates the power generated by the load 2 in the battery 1.

[0012] <Structure of power conversion device 3> The power conversion device 3 includes a main circuit 30 and a control device 31 . The main circuit 30 includes a low-voltage side capacitor 51, an inductor 4, a voltage conversion circuit 32, a high-voltage side capacitor 52, and also includes a first voltage sensor 61 for detecting a voltage V1 applied to the low-voltage side capacitor 51, a second voltage sensor 62 for detecting a voltage V2 applied to the high-voltage side capacitor 52, and a third voltage sensor 63.

[0013] The low voltage side capacitor 51 is connected in parallel with the battery 1, and the high voltage side capacitor 52 is connected in parallel with the load 2. The reactor 4 has a first terminal and a second terminal, and the first terminal is connected to the terminal of the battery 1 on the high potential side (positive side).

[0014] The voltage conversion circuit 32 is configured such that a first switching element 32a and a second switching element 32b are connected in series and connected in parallel with the load 2. The first switching element 32a and the second switching element 32b are respectively connected as follows: Figure 1 As shown, for example, a diode is connected in reverse parallel to an IGBT (Insulated Gate Bipolar Transistor). One terminal (emitter side terminal) of the first switching element 32a is connected to the terminal on the low potential side (negative side) of the battery 1, and one terminal (collector side terminal) of the second switching element 32b is connected to the terminal on the high potential side of the load 2. The first connection portion 32c, which is the connection point between the other terminal (collector side terminal) of the first switching element 32a and the other terminal (emitter side terminal) of the second switching element 32b, is connected to the second terminal of the reactor 4. In addition, the current sensor 40 is arranged between the reactor 4 and the first connection portion 32c to detect the current value IL flowing to the reactor 4.

[0015] The voltage information V1sen detected by the first voltage sensor 61, the voltage information V2Msen detected by the second voltage sensor 62, the voltage information V2Ssen detected by the third voltage sensor 63, and the current value IL detected by the current sensor 40 are respectively input to the control device 31. In addition, the control device 31 generates a gate drive signal for turning on and off the gates of the first switching element 32a and the second switching element 32b of the voltage conversion circuit 32, and outputs it to the voltage conversion circuit 32. The details will be described below.

[0016] <Operation of the power conversion device 3> A gate drive signal generated by the control device 31 is applied to the first switching element 32a and the second switching element 32b of the power conversion device 3. Through PWM (Pulse Width Modulation) control, the gates of the first switching element 32a and the second switching element 32b are turned on and off respectively, thereby controlling the voltage applied to the load 2. The control period Tsw is the reciprocal of the driving frequency fsw of the first switching element 32a and the second switching element 33b. Tsw=1 / fsw.

[0017] The switching mode of the first switching element 32a and the second switching element 32b connected in series is provided with a dead time in such a way that the switching element 32a and the second switching element 32b are not turned on at the same time. The duty ratio Duty in the DC / DC converter of the power conversion device 3 is defined by the ratio of the on time Ton of the gate drive signal of the first switching element 32a in one cycle of the control cycle Tsw. That is, Duty=Ton / Tsw. In addition, the boosted voltage V2 is obtained by the following equation (1). V2=V1 / (1-Duty) · · · (1) The voltage conversion amplitude (duty ratio Duty) of the voltage conversion circuit 32 is described by the voltage V1 and the voltage V2.

[0018] <Steps for Determining Abnormality of Each Voltage Sensor 61, 62, 63> Figure 2A and 2B This is a flowchart showing a procedure for determining abnormality of the first voltage sensor 61 , the second voltage sensor 62 , and the third voltage sensor 63 in the control device 31 according to the first embodiment. Figure 2A and 2B The processing shown is repeatedly performed at every set time, for example, every 1 ms. When the voltage sensor abnormality detection of step S101 starts, in step S102, the control device 31 obtains the first voltage sensor value V1sen from the first voltage sensor 61, obtains the second voltage sensor value V2Msen from the second voltage sensor 62, obtains the third voltage sensor value V2Ssen from the third voltage sensor 63, and the on-time ratio of the first switching element 32a, that is, the command duty cycle Duty as the control state of the DC / DC converter.

[0019] Next, in step S103, the control device 31 determines whether the voltage conversion circuit 32 is being controlled by "boost control". "Boost control" controls the first voltage conversion circuit 32 to boost the low-voltage side voltage to generate a high-voltage side voltage. If it is determined in step S103 that "boost control is in progress" ("Yes" in step S103), the process proceeds to step S104. If it is determined that "boost control is not in progress" ("No" in step S103), the process returns to step S103.

[0020] In step S104 , control device 31 calculates the absolute value of the difference between second voltage sensor value V2Msen and third voltage sensor value V2Ssen.

[0021] Next, in step S105, the control device 31 compares the calculation result of step S104 with the preset threshold value A1. When the calculation result of step S104 is less than the threshold value A1 ("No" in step S105), it is determined that the second voltage sensor 62 and the third voltage sensor 63 are not abnormal, and the process proceeds to step S111. On the other hand, when the calculation result of step S104 is greater than the threshold value A1 ("Yes" in step S105), it is determined that any one of the second voltage sensor 62 and the third voltage sensor 63 is abnormal, and the process proceeds to step S106. In addition, the threshold value A1 can also be determined by experiment. Alternatively, the threshold value A1 can also be set according to the error of the sensor.

[0022] In step S106 , the control device 31 performs direct connection control on the voltage conversion circuit 32 to make the low voltage side voltage and the high voltage side voltage coincide with each other, that is, to make the first voltage sensor value V1sen coincide with the second voltage sensor value V2Msen detecting the high voltage side capacitor voltage. In addition, "direct connection control" means controlling the voltage conversion circuit 32 so that the low-voltage side voltage and the high-voltage side voltage are consistent, so it is a state in which the conduction time ratio of the second switch element 32b is 1 and the conduction time ratio of the first switch element 32a is 0. Next, in step S107 , the absolute value of the difference between the first voltage sensor value V1sen detecting the voltage of the low-voltage side capacitor 51 and the second voltage sensor value V2Msen detecting the voltage of the high-voltage side capacitor 52 is calculated.

[0023] Next, in step S108, the control device 31 compares the calculation result of step S107 with the preset threshold value B1. When the calculation result of step S107 is less than the threshold value B1 ("No" in step S108), it is determined that the first voltage sensor 61 and the second voltage sensor 62 respectively normally detect the voltage of the low-voltage side capacitor 51 and the voltage of the high-voltage side capacitor 52, which are the same voltage in the case of direct connection control in step S106. As a result, it is determined that the third voltage sensor 63 is abnormal (step S109).

[0024] On the other hand, when the calculation result of step S107 is greater than or equal to the threshold value B1 ("Yes" in step S108), it is determined that an abnormality has occurred in any one of the first voltage sensor 61 and the second voltage sensor 62. Combined with the result of step S105 in which it is determined that an abnormality has occurred in any one of the second voltage sensor 62 and the third voltage sensor 63, it is determined that the second voltage sensor 62 common to the results of both is abnormal (step S110). In addition, the threshold value B1 can also be determined by experiment. Alternatively, the threshold value B1 can also be set according to the error of the sensor.

[0025] If the result of step S105 is that the calculation result of step S104 is smaller than the threshold value A1 (No in step S105 ), it is determined in step S111 whether the power conversion device 3 is in either power running operation or regeneration operation. The determination of power operation or regeneration operation uses the current value IL detected by the current sensor 40. If the current value is positive, it is determined to be in power operation, and if it is negative, it is determined to be in regeneration. If it is in regeneration, it proceeds to step S112, and if it is in power operation, it proceeds to step S113.

[0026] In step S112, the difference between the first voltage sensor value V1sen during the regeneration operation and the first voltage sensor estimated value V1estreg calculated as the estimated value of the first voltage sensor value V1sen is obtained. In step S113, the difference between the first voltage sensor value V1sen during the regeneration operation and the first voltage sensor estimated value V1estrun calculated as the estimated value of the first voltage sensor value V1sen is obtained.

[0027] Here, use Figure 3 to Figure 5 A method of calculating the first voltage sensor estimated value will be described. Figure 3 3 is a diagram showing the relationship between the gate drive signal and the reactor current IL in the voltage conversion circuit 32 . Figure 3 In (a), the gate drive signal output to the voltage conversion circuit 32 is shown, the upper side is the gate drive signal of the switch element 32b, and the lower side is the gate drive signal of the switch element 32a. When the on-time of the switch element 32b coincides with the on-time of the switch element 32a, the high potential side and the low potential side of the high voltage side capacitor 52 are short-circuited. Therefore, considering the delay of the on-time and off-time of the switch element, the dead time (Td) must be set in such a way that the switch element 32b and the switch element 32a are not turned on at the same time. Therefore, the switch element 32b and the switch element 32a are turned on alternately with the dead time.

[0028] Figure 3 (b) indicates the reactor current during power operation. Figure 3 (c) shows the behavior of the reactor current during regenerative operation, but the behaviors of the two are different. First, about Figure 3 The reactor current during power operation in (b) is the same as Figure 4 The flow of reactor current corresponding to the operation mode during power operation is explained.

[0029] In the interval of mode 1, the switch element 32b is turned off and the switch element 32a is turned on. Figure 4 As shown in mode 1 (a), current flows through the loop of the switching element 32a and the low-voltage side capacitor 51, the potential of the connection portion 32c is 0, and the reactor current increases.

[0030] In the interval of mode 2, the switch element 32b is turned on and the switch element 32a is turned off. Figure 4 As shown in mode 2 (b), the current flows through the loop of the switching element 32b, the high-voltage side capacitor 52, and the low-voltage side capacitor 51, the potential of the connection portion 32c is V2, and the current decreases.

[0031] In the interval of mode 3, both the switch element 32b and the switch element 32a are turned off. Figure 4 As shown in (c) mode 3, the current loop is the same as that in mode 2, and the current decreases. That is, during the power running operation, the current behavior is the same as that in mode 2 in which the switch element 32b is turned on during the dead time.

[0032] Next, about Figure 3 (c) The reactor current during regenerative operation is Figure 5 The flow of the reactor current corresponding to the operation mode during the regenerative operation is described. In the interval of mode 1, the switch element 32b is turned off and the switch element 32a is turned on. Figure 5 As shown in mode 1 (a), current flows through the loop of the switching element 32a and the low-voltage side capacitor 51, the potential of the connection portion 32c is 0, and the reactor current increases.

[0033] In the interval of mode 2, the switch element 32b is turned on and the switch element 32a is turned off. Figure 5 As shown in mode 2 (b), the current flows through the loop of the high-voltage side capacitor 52, the switching element 32b, and the low-voltage side capacitor 51, the potential of the connection portion 32c is V2, and the current decreases.

[0034] In the interval of mode 3, the switch element 32b is turned off, and the switch element 32a is also turned off. Figure 5 As shown in (c) mode 3, the current loop is the same as that in mode 1, and the current increases. That is, during the regenerative operation, the current behavior is the same as that in mode 1 in which the switching element 32a is turned on during the dead time.

[0035] As described above, since the relationship between voltages V1, V2, and command duty cycle Duty is affected differently by the dead time during power operation and regeneration, the calculation accuracy of the estimated value of voltage V1 used in abnormality judgment of the voltage sensor can be improved by using a different calculation formula that includes information about the dead time for correction.

[0036] In addition, a delay time is generated in the timing from the gate drive signal being turned off to being turned on, from being turned on to being turned off, and the switch being turned on and off. Figure 3 Similarly, since the influence of the switch delay time is different during power operation and regeneration, the calculation accuracy of the estimated value of the first voltage sensor can be improved by using a different calculation formula that includes information on the switch delay time to correct the calculation of the estimated value of the voltage V1 used in the abnormality judgment of the voltage sensor.

[0037] In addition, as a main reason why the calculation of the estimated value of the voltage V1 is different during the power running operation and the regeneration operation, there is the power conversion efficiency of the power conversion device 3. When the power on the battery 1 side is P1 and the power on the load side is P2, the power conversion efficiency during the power running operation is defined as Effrun=P2 / P1(<1), and the power conversion efficiency during the regeneration operation is defined as Effreg=P1 / P2(<1).

[0038] The formula for the boost voltage V2 using the power conversion efficiency Effrun during power operation is (1) V2=1 / (1-Duty)×V1×Effrun When the command duty ratio Duty is the same as that when the power conversion efficiency is 1, the V2 voltage becomes smaller.

[0039] On the other hand, if it is assumed that the voltage reduction control is performed during the regenerative operation, the equation for the reduced voltage V1 using the power conversion efficiency Effreg during the regenerative operation is obtained from (1): V1=(1-Duty)×V2×Effreg When the command duty ratio Duty is the same as that when the power conversion efficiency is 1, the voltage V1 decreases.

[0040] Therefore, in steps S112 and S113, the calculation of the estimated value of voltage V1 used in the abnormality judgment of the voltage sensor includes information on the power conversion efficiency. If different calculation formulas are used for correction during power operation and regeneration, the calculation accuracy of the estimated value of the first voltage sensor can be improved.

[0041] In steps S112 and S113 , the difference between the first voltage sensor value V1sen and the first voltage sensor estimated value V1est calculated as the estimated value of the first voltage sensor value V1sen is obtained. Ideally, the first voltage sensor estimated value V1est can be obtained by the following equation (2). V1est=V2 × (1-Duty) ·· · (2) In reality, due to the influence of dead time, switching delay time, and efficiency, the relationship between the command duty ratio Duty and the voltages V1 and V2 is different during power running and regeneration, so the estimated value is corrected.

[0042] During the power running operation, the first voltage sensor estimated value V1estrun is obtained using the following equation (3). [Mathematical formula 1] During the regenerative operation, the first voltage sensor estimated value V1estreg is obtained using the following equation (4). [Mathematical formula 2]

[0043] Here, although it is assumed that the power conversion efficiencies Effrun and Effreg during power operation and regeneration are equivalent, different values ​​may be used for each, and may be changed according to the size of the load or determined through experiments.

[0044] Here, let's return to the flowchart of FIG. 2 . In step S112 , control device 31 calculates a difference ΔV between first voltage sensor value V1sen and first voltage sensor estimated value V1estreg obtained according to equation (4), and proceeds to step S114 . Furthermore, in step S113 , the difference ΔV between the first voltage sensor value V1sen and the first voltage sensor estimated value V1estrun obtained according to equation (3) is calculated, and the process proceeds to step S114 .

[0045] In step S114, the absolute value of the difference ΔV, which is the calculation result of step S112 or the calculation result of step S113, is compared with the preset threshold value C1. When the absolute value of the difference ΔV is less than the threshold value C1 ("No" in step S114), it can be determined that the first voltage sensor estimated value V1est calculated based on the second voltage sensor value V2Msen is consistent with the first voltage sensor value V1sen. In the previous step S105, it was determined that the second voltage sensor 62 was not abnormal, so the first voltage sensor 61 was also determined to be normal, and all voltage sensors were determined to be normal (step S115).

[0046] In step S114, when the absolute value of the difference ΔV is greater than or equal to the threshold value C1 (“Yes” in step S114), it is determined that an abnormality has occurred in either the first voltage sensor 61 or the second voltage sensor 62. Since it has been determined in step S105 that the second voltage sensor 62 has no abnormality, it is determined that an abnormality has occurred in the first voltage sensor 61 (step S116).

[0047] In step S114, the threshold value C1 may be determined by experiment or may be set based on the error of the sensor and the gate drive signal and the delay time until the switching element is actually turned on or off.

[0048] In the above description, the voltage V2 of the second capacitor is measured using the third voltage sensor 63, but the voltage V1 of the first capacitor may be measured. At this time, the voltage of the first capacitor detected by the third voltage sensor 63 is set to a third voltage sensor value V1Ssen. The above determination procedure of the voltage sensor will be described below.

[0049] exist Figure 2A In step S104, the control device 31 calculates the absolute value of the difference between the first voltage sensor value V1sen and the third voltage sensor value V1Ssen. Next, in step S105, the control device 31 compares the calculation result of step S104 with a preset threshold value A1.

[0050] In addition, in step S107, the control device 31 calculates the absolute value of the difference between the first voltage sensor value V1sen and the second voltage sensor value V2Msen. Next, in step S108, when the calculation result of step S107 is less than the threshold value B1 ("No" in step S108), the control device 31 determines that the first voltage sensor 61 and the second voltage sensor 62 respectively normally detect the voltage of the low-voltage side capacitor 51 and the voltage of the high-voltage side capacitor 52, which are consistent in the direct connection control in step S106. As a result, it is determined that the third voltage sensor 63 is abnormal (step S109).

[0051] On the other hand, when the calculation result of step S107 is greater than or equal to the threshold value B1 ("YES" in step S108), it is determined that an abnormality has occurred in either the first voltage sensor 61 or the second voltage sensor 62. Combined with the result of step S105 in which it is determined that an abnormality has occurred in either the first voltage sensor 61 or the third voltage sensor 63, it is determined that the first voltage sensor 61 common to both results is abnormal (step S110).

[0052] In step S114, when the absolute value of the difference ΔV is less than the threshold value C1 ("No" in step S114), it can be determined that the first voltage sensor estimated value V1est calculated based on the second voltage sensor value V2Msen is consistent with the first voltage sensor value V1sen. In the previous step S105, it was determined that the first voltage sensor 61 is not abnormal, so the second voltage sensor 62 is also determined to be normal, and all voltage sensors are determined to be normal (step S115).

[0053] In step S114, when the absolute value of the difference ΔV is greater than or equal to the threshold value C1 ("Yes" in step S114), it is determined that an abnormality has occurred in either the first voltage sensor 61 or the second voltage sensor 62. Since it is determined in step S105 that the first voltage sensor 61 is not abnormal, it is determined that an abnormality has occurred in the second voltage sensor 62 (step S116).

[0054] As described above, according to the first embodiment, the power conversion device 3 is a DC / DC converter including a voltage conversion circuit 32 that converts the voltage of the battery 1 as a first DC voltage into a second DC voltage of a different value, at least two capacitors 51 and 52, and a control device that controls the voltage conversion width of the voltage conversion circuit 32, wherein the voltage conversion circuit 32 has a first switching element 32a and a second switching element 32b connected in series, a first capacitor 51 connected in parallel with the battery 1, a second capacitor 52 connected in parallel with the second DC voltage, a first voltage sensor 61 for detecting the voltage of the first capacitor 51, a second voltage sensor 62 for detecting the voltage of the second capacitor 52, and a third voltage sensor 63 for detecting the voltage of the first capacitor 51 or the second capacitor 52. Then, the control device controls the voltage conversion width of the voltage conversion circuit 32 by commanding the duty ratio Duty using the first voltage sensor value V1sen detected by the first voltage sensor 61, the second voltage sensor value V2Msen detected by the second voltage sensor 62, and the third voltage sensor value V2Ssen detected by the third voltage sensor 63. Furthermore, a first difference is calculated as the difference between the second voltage sensor value V2Msen and the value obtained by multiplying the third voltage sensor value V2Ssen by 1 which is a preset coefficient, and a first determination process is performed to determine whether the first difference is greater than a first threshold value A1 which is preset. When the first difference is greater than the first threshold value A1, direct connection control is performed, and a second difference is calculated as the difference between the first voltage sensor value V1sen and the second voltage sensor value V2Msen, and a second determination process is performed to determine whether the second difference is greater than a second threshold value B1 which is preset. When the second difference is greater than the second threshold value B1, it is determined that the second voltage sensor 62 is abnormal. When the second difference is less than the second threshold value B1, it is determined that the third voltage sensor 63 is abnormal. In the first determination process, when the first difference is smaller than the first threshold value A1, a third difference is calculated as the difference between the first voltage sensor value V1sen and the first voltage sensor estimated value V1est calculated based on the second voltage sensor value V2Msen, and a third determination process is performed to determine whether the third difference is greater than a third threshold value C1 set in advance. When the third difference is greater than the third threshold value C1, it is determined that the first voltage sensor 61 is abnormal, and when the third difference is less than the third threshold value C1, it is determined that all sensors are normal. Thus, it is possible to determine and determine that any one of the first voltage sensor 61, the second voltage sensor 62, and the third voltage sensor 63 is abnormal without using external voltage information.

[0055] In the first embodiment, the non-insulated step-up DC / DC converter in which the battery 1 side has a low voltage and the load side has a high voltage is described as an example, but the present invention can also be applied to a non-insulated step-down DC / DC converter.

[0056] In addition, in the above-mentioned step S103, in the case of boost control, the next step is entered, and the process of determining whether the voltage sensor is normal or abnormal is described. In the case of direct connection control, different from the workflow of Figure 2, the normality or abnormality of the first voltage sensor 61, the second voltage sensor 62, and the third voltage sensor 63 can also be determined by comparing the first voltage sensor value V1sen, the second voltage sensor value V2Msen, and the third voltage sensor value V2Ssen. That is, in the case of direct connection control, it is ideal that V1sen=V2Msen=V2Ssen, so by confirming the difference between two of the three, it is possible to determine whether an abnormality has occurred in any voltage sensor. In this way, the failure of the voltage sensor can be determined without relying on boost control or direct connection control.

[0057] Implementation method 2. Hereinafter, a power conversion device according to Embodiment 2 will be described with reference to the drawings. Figure 6 1 is a diagram showing the structure of a power conversion device according to Embodiment 2. The power conversion device 3 is connected between the battery 1 and the load 2 in the same manner as in Embodiment 1 to form a power supply system. That is, the power conversion device 3 is a DC / DC converter having the battery 1 connected to the input terminal and the load 2 connected to the output terminal. The difference from Embodiment 1 is that the DC / DC converter is a multi-level converter having an intermediate capacitor 53. The following description will focus on the differences from Embodiment 1, and the description of the same structure and operation will be omitted.

[0058] <Structure of power conversion device 3> Figure 6 In the embodiment, the power conversion device 3 includes a main circuit 30 and a control device 31 . The main circuit 30 includes a low-voltage side capacitor 51, a reactor 4, a voltage conversion circuit 33, an intermediate capacitor 53, and a high-voltage side capacitor 52, and also includes: a current sensor 40 for detecting a current flowing through the reactor 4, a first voltage sensor 61 for detecting a voltage V1 applied to the low-voltage side capacitor 51, a second voltage sensor 62 for detecting a voltage V2 applied to the high-voltage side capacitor 52, and a third voltage sensor 63 for detecting a voltage V0 applied to the intermediate sensor 53. The configuration of the low-voltage side capacitor 51, the reactor 4, the current sensor 40, and the first voltage sensor 61 is the same as that of the first embodiment.

[0059] The voltage conversion circuit 33 is connected in parallel with the load 2. The first switch element 33a, the second switch element 33b, the third switch element 33c and the fourth switch element 33d are connected in series to the voltage conversion circuit 33. The connection point between the first switch element 33a and the second switch element 33b constitutes a first connection part 33f, the connection point between the second switch element 33b and the third switch element 33c constitutes a second connection part 33e, and the connection point between the third switch element 33c and the fourth switch element 33d constitutes a third connection part 33g.

[0060] One terminal (emitter side terminal) of the first switching element 33a is connected to the terminal on the low potential side (negative side) of the battery 1, and one terminal (collector side terminal) of the fourth switching element 33d is connected to the terminal on the high potential side (positive side) of the load 2. The second connecting portion 33e is connected to the second terminal of the reactor 4. The first to fourth switching elements 33a, 33b, 33c, and 33d are similar to the first embodiment, and each has a structure in which a diode is connected in reverse parallel to the IGBT, for example.

[0061] The high voltage side capacitor 52 is connected in parallel with the load 2, the low voltage side capacitor 51 is connected in parallel with the battery 1, and the intermediate capacitor 53 is connected to the first connection portion 33f and the third connection portion 33g. The current sensor 40 is arranged between the reactor 4 and the second connection portion 33e, and detects the current value IL flowing to the reactor 4.

[0062] The voltage information V2sen detected by the second voltage sensor 61 , the voltage information V1sen detected by the first voltage sensor 61 , the voltage information V0sen detected by the third voltage sensor 63 , and the current value ILsen detected by the current sensor 40 are respectively input to the control device 31 .

[0063] <Operation Mode of Voltage Converter Circuit 33> Next, use Figure 7 illustrate Figure 6 The operation mode of the voltage conversion circuit 33 is shown. like Figure 7 As shown in (a) to (d), there are four operation modes as the on-off modes of the first to fourth switching elements 33a, 33b, 33c, and 33d, namely (a) mode 1 to (d) mode 4. In the power operation operation when power is supplied from the battery 1 to the load 2, and the regeneration operation when power is supplied from the load 2 to the battery 1, there is a difference between the IGBT of a part of the switching elements and the reverse parallel diode, but the current path recorded by the dotted line is the same in the opposite direction, so the power operation operation is described here.

[0064] In mode 1, the first switch element 33a and the third switch element 33c are turned on, and the second switch element 33b and the fourth switch element 33d are turned off. Figure 7 As shown in the current path (a), current flows through the diode of the third switching element 33 c and the IGBT of the first switching element 33 a , and energy is stored in the intermediate capacitor 53 .

[0065] In mode 2, the first switch element 33a and the third switch element 33c are turned off, and the second switch element 33b and the fourth switch element 33d are turned on. Figure 7 As shown in the current path (b), the current flows through the IGBT of the second switching element 33b and the diode of the fourth switching element 33d, and the energy of the intermediate capacitor 53 is released.

[0066] In mode 3, the first switch element 33a and the second switch element 33b are turned off, and the third switch element 33c and the fourth switch element 33d are turned on. Figure 7 As shown in the current path (c), the current flows through the diode of the third switching element 33 c and the diode of the fourth switching element 33 d , and the energy of the reactor 4 is released.

[0067] In mode 4, the first switch element 33a and the second switch element 33b are turned on, and the third switch element 33c and the fourth switch element 33d are turned off. Figure 7 As shown in the current path (d), current flows through the IGBT of the first switching element 33 a and the IGBT of the second switching element 33 b , and energy is stored in the reactor 4 .

[0068] Figure 8 1 is a diagram showing the relationship between the gate drive signal and the reactor current IL in the voltage conversion circuit 33 according to the second embodiment. Figure 8 (a) is a gate drive signal output to the voltage conversion circuit 33, and from the top are the gate drive signals of the switch element 33d, the switch element 33a, the switch element 33c, and the switch element 33b. The on-time of the switch element 33d overlaps with the on-time of the switch element 33a. In order to prevent a short circuit, the dead time (Td) must be set in such a way that the switch element 33d and the switch element 33a are not turned on at the same time, taking into account the delay of the on-time and off-time of the switch element. Similarly, the on-time of the switch element 33c overlaps with the on-time of the switch element 33b. In order to prevent a short circuit, the dead time (Td) must be set in such a way that the switch element 33c and the switch element 33b are not turned on at the same time.

[0069] In the multi-level converter in the second embodiment, the duty cycle Duty1 is defined for the first switch element 33a, and the duty cycle Duty2 is defined for the second switch element 33b. Basically, the duty cycle Duty1 and the duty cycle Duty2 are the same, but according to the control of the V0 voltage, there is also a case where the time of the duty cycle Duty1 and the duty cycle Duty2 are deliberately offset. Even in the case of a multi-level converter, the relationship between the V2 voltage and the duty cycle Duty is expressed by equation (1). In addition, the phase of the gate signal of the first switch element 33a and the second switch element 33b is offset by 180 degrees relative to the switching frequency (fsw).

[0070] By appropriately adjusting the time ratio of these operation modes, the voltage V2 applied to the load 2 can be controlled, and the voltage applied to the reactor 4 can be reduced by controlling the voltage V0 applied to the intermediate capacitor 53 to half of V2.

[0071] <Steps for Determining Abnormality of Each Voltage Sensor 61, 62, 63> Fig. 9A and 9B This is a flowchart showing a procedure for determining abnormality of the first voltage sensor 61 , the second voltage sensor 62 , and the third voltage sensor 63 in the control device 31 according to the second embodiment. Fig. 9A and 9B The processing shown is repeatedly performed at set time intervals, for example, at 1 ms intervals.

[0072] When the voltage sensor abnormality detection of step S201 starts, in step S202, the control device 31 obtains the first voltage sensor value V1sen from the first voltage sensor 61, the second voltage sensor value V2sen from the second voltage sensor 62, the third voltage sensor value V0sen from the third voltage sensor 63, and the instruction duty cycle Duty as the control state of the multi-level converter.

[0073] In step S203, the control device 31 determines whether the voltage conversion circuit 33 is being controlled by the "boost control". In step S204 , the voltage V0 applied to the intermediate capacitor 53 is controlled to be half the voltage V2 applied to the high-voltage side capacitor 52 , and therefore the control device 31 calculates the absolute value of the difference between the second voltage sensor value V2sen and twice the third voltage sensor value V0sen.

[0074] Next, in step S205, the control device 31 compares the calculation result of step S204 with a preset threshold value A2. In addition, the threshold value A2 may be determined by experiments. Alternatively, the threshold value A2 may be set according to the error of the sensor. When the calculation result of step S204 is less than the threshold value A2 ("No" in step S205), it is determined that there is no abnormality in the second voltage sensor 62 and the third voltage sensor 63, and the process proceeds to step S211. On the other hand, when the calculation result of step S204 is greater than the threshold value A2 ("Yes" in step S205), it is determined that an abnormality has occurred in any one of the second voltage sensor 62 and the third voltage sensor 63, and the process proceeds to step S206.

[0075] Since steps S206 to S216 in the second embodiment are the same as steps S106 to S116 in the first embodiment, their description is omitted. In addition, other thresholds B2 and C2 in the second embodiment can also be set in the same way as thresholds B1 and C1 in the first embodiment. Therefore, even if the power conversion device 3 has a multi-level converter, without using external voltage information, it is possible to determine abnormalities in the first voltage sensor 61 that detects the voltage of the low-voltage side capacitor arranged in the power conversion device 3, the second voltage sensor 62 that detects the voltage of the high-voltage side capacitor, and the third voltage sensor 63 that detects the voltage of the intermediate capacitor.

[0076] As described above, according to the present embodiment 2, the same effects as those of the embodiment 1 can be obtained. That is, the power conversion device 3 of the embodiment 2 is a multi-level converter including a voltage conversion circuit 33 for converting the voltage of the battery 1 as a first DC voltage into a second DC voltage of a different value, three capacitors 51, 52, 53, and a control device 31 for controlling the voltage conversion width of the voltage conversion circuit 33, wherein the voltage conversion circuit 33 has first to fourth switching elements 33a, 33b, 33c, 33d connected in series, a first capacitor 51 connected in parallel with the battery 1, a second capacitor 52 connected in parallel with the second DC voltage, an intermediate capacitor 53 having one end connected to the connection point of the first switching element 33a and the second switching element 33b and the other end connected to the connection point of the third switching element 33c and the fourth switching element 33d, a first voltage sensor 61 for detecting the voltage of the first capacitor 51, a second voltage sensor 62 for detecting the voltage of the second capacitor 52, and a third voltage sensor 63 for detecting the voltage of the intermediate capacitor 53 as the third capacitor. Then, the control device 31 controls the voltage conversion width of the voltage conversion circuit 33 by commanding the duty ratio Duty, using the first voltage sensor value V1sen detected by the first voltage sensor 61, the second voltage sensor value V2sen detected by the second voltage sensor 62, and the third voltage sensor value V0sen detected by the third voltage sensor 63. Furthermore, the control device 31 calculates the first difference between the second voltage sensor value V2sen and the value obtained by multiplying the third voltage sensor value V0sen by 2, which is a preset coefficient, and performs a first determination process to determine whether the first difference is greater than or equal to a preset first threshold value A2. If the first difference is greater than or equal to the first threshold value A2, direct connection control is performed. The control device 31 calculates the second difference between the first voltage sensor value V1sen and the second voltage sensor value V2sen, and performs a second determination process to determine whether the second difference is greater than or equal to a preset second threshold value B2. If the second difference is greater than or equal to the second threshold value B2, the control device 31 determines that the second voltage sensor 62 is abnormal. If the second difference is less than the second threshold value B2, the control device 31 determines that the third voltage sensor 63 is abnormal. In the first determination process, when the first difference is smaller than the first threshold value A2, a third difference is calculated as the difference between the first voltage sensor value V1sen and the first voltage sensor estimated value V1est calculated based on the second voltage sensor value V2sen, and a third determination process is performed to determine whether the third difference is greater than a third threshold value C2 set in advance. When the third difference is greater than the third threshold value C2, it is determined that the first voltage sensor 61 is abnormal, and when the third difference is less than the third threshold value C2, it is determined that all sensors are normal. Thus, without using external voltage information, it is possible to determine and determine that any one of the first voltage sensor 61, the second voltage sensor 62, and the third voltage sensor 63 is abnormal.

[0077] In addition, in embodiment 2, which is an example of a three-level multi-level converter, in step S204, a first difference is calculated, which is the difference between the second voltage sensor value V2sen and the value obtained by multiplying the third voltage sensor value V0sen by a predetermined coefficient, i.e., 2. However, the coefficient can be changed according to the circuit structure of the converter.

[0078] <Hardware Configuration of Control Device 31> In addition, the control device 31 is as follows Fig.10 As an example of hardware shown in FIG. 1 , the processor 100 and the storage device 101 are formed. Although the storage device is not shown, it includes a volatile storage device such as a random access memory and a non-volatile auxiliary storage device such as a flash memory. In addition, an auxiliary storage device such as a hard disk may be included instead of the flash memory.

[0079] The processor 100 is composed of, for example, a CPU (Central Processing Unit), an ASIC (Application Specific Integrated Circuit), a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), etc. The processor 100 executes a program input from the storage device 101. In this case, the program is input from the auxiliary storage device to the processor 100 via the volatile storage device. In addition, the processor 100 can output data such as calculation results to the volatile storage device of the storage device 101, and can also save the data to the auxiliary storage device via the volatile storage device.

[0080] <Other Implementation Methods> (1) Figure 1 , 6 In the example, the switch element is composed of an IGBT, but it is not limited to this structure. For example, it can also be composed of a MOSFET (Metal Oxide Semiconductor Field Effect Transistor). In addition, the switch element is not limited to being composed of Si (silicon) semiconductors, but can also be a wide bandgap semiconductor, using semiconductors such as SiC (silicon carbide) and GaN (gallium nitride). It can also be composed of a switch element such as GaN-HEMT (Gallium Nitride-High Mobility Transistor: Gallium Nitride-High Electron Mobility Transistor).

[0081] (2) In the above-mentioned embodiments 1 and 2, the first voltage sensor estimated value V1est is calculated using equations (2) to (4), but if the dead time, the switching delay time of the voltage conversion circuits 32 and 33, and the power conversion efficiency during power operation or regeneration are appropriately considered in the calculation in addition to the command duty ratio Duty related to the second voltage sensor value and the voltage conversion width, the accuracy can be improved. The combination of items can be arbitrarily selected.

[0082] Although the present application describes various exemplary embodiments and examples, various features, methods, and functions described in one or more embodiments are not limited to application in specific embodiments and may be applied to the embodiments alone or in various combinations. Therefore, it is considered that numerous modifications not shown in the examples are also included in the technical scope disclosed in the present specification, for example, including the case where at least one component is modified, added or omitted, and the case where at least one component is extracted and combined with components of other embodiments.

[0083] Hereinafter, each aspect of the present disclosure will be collectively described as a supplementary note.

[0084] (Note 1) The power conversion device comprises a voltage conversion circuit for converting a first DC voltage into a second DC voltage of a different value, at least two capacitors, and a control device for controlling the voltage conversion amplitude of the voltage conversion circuit, wherein the power conversion device is characterized in that: a first capacitor connected in parallel with the first DC voltage; a second capacitor connected in parallel with the second DC voltage; a first voltage sensor configured to detect a voltage of the first capacitor; and a second voltage sensor, the second voltage sensor being used to detect a voltage of the second capacitor, and having a third voltage sensor, the third voltage sensor detecting the voltage of the third capacitor when the third capacitor is present in the voltage conversion circuit, and detecting the voltage of the first capacitor or the second capacitor when the third capacitor is not present, The control device controlling a voltage conversion amplitude of the voltage conversion circuit using a first voltage sensor value detected by the first voltage sensor, a second voltage sensor value detected by the second voltage sensor, and a third voltage sensor value detected by the third voltage sensor, calculating a first difference between the second voltage sensor value and a value obtained by multiplying the third voltage sensor value by a predetermined coefficient, and performing a first determination process to determine whether the first difference is greater than a predetermined first threshold value, In the first determination process, When the first difference is greater than the first threshold, direct connection control is performed to make the first voltage sensor value consistent with the second voltage sensor value, a second difference between the first voltage sensor value and the second voltage sensor value is calculated, and a second determination process is performed to determine whether the second difference is greater than a preset second threshold. In the second determination process, When the second difference is greater than the second threshold, it is determined that the second voltage sensor is abnormal, and when the second difference is less than the second threshold, it is determined that the third voltage sensor is abnormal. In the first determination process, When the first difference is smaller than the first threshold, a third difference is calculated which is a difference between the first voltage sensor value and a first voltage sensor estimated value calculated based on the second voltage sensor value, and it is determined whether the third difference is greater than a third threshold set in advance. In the third determination process, When the third difference is equal to or greater than the third threshold value, it is determined that the first voltage sensor is abnormal. When the third difference is smaller than the third threshold value, it is determined that all the voltage sensors are normal. (Supplementary Note 2) The power conversion device as described in Supplementary Note 1 is characterized in that: The voltage conversion circuit has a first switching element and a second switching element. A reactor having one end connected to the positive electrode side of the first DC voltage, One terminal of the first switching element is connected to the negative side of the first DC voltage, The other terminal of the first switching element and the other end of the reactor are connected to one terminal of the second switching element. The other terminal of the second switching element is connected to the positive side of the second DC voltage, and the third voltage sensor is configured to detect a voltage of the second capacitor, The control device The coefficient for calculating the first difference is set to 1, a first difference between the second voltage sensor value and the third voltage sensor value is calculated, and a first determination process is performed to determine whether the first difference is equal to or greater than a preset first threshold value. (Supplementary Note 3) The power conversion device as described in Supplementary Note 1 is characterized in that: The voltage conversion circuit includes a first switching element, a second switching element, a third switching element, and a fourth switching element connected in series in sequence, and an intermediate capacitor having one end connected to a connection point between the first switching element and the second switching element and the other end connected to a connection point between the third switching element and the fourth switching element. A reactor having one end connected to the positive electrode side of the first DC voltage, One terminal of the first switching element is connected to the negative side of the first DC voltage, The other end of the reactor is connected to a connection point between the second switching element and the third switching element. One terminal of the fourth switching element is connected to the positive side of the second DC voltage, and The third voltage sensor is configured to detect the voltage of the intermediate capacitor, The control device The coefficient for calculating the first difference is set to 2, a first difference is calculated which is a difference between the second voltage sensor value and the third voltage sensor value multiplied by 2, and a first determination process is performed to determine whether the first difference is equal to or greater than a preset first threshold value. (Supplementary Note 4) The power conversion device as described in Supplementary Note 2 is characterized in that: The first voltage sensor estimated value is calculated using the voltage conversion width of the voltage conversion circuit and the second voltage sensor value. (Supplementary Note 5) The power conversion device as described in Supplementary Note 4 is characterized in that: The control device The first switching element and the second switching element of the voltage conversion circuit are driven by setting a dead time so that the first switching element and the second switching element are not turned on at the same time. The first voltage sensor estimated value is calculated using the second voltage sensor value, the voltage conversion width of the voltage conversion circuit, and the dead time. (Supplementary Note 6) The power conversion device as described in Supplementary Note 3 is characterized in that: The first voltage sensor estimated value is calculated using the voltage conversion width of the voltage conversion circuit and the second voltage sensor value. (Supplementary Note 7) The power conversion device as described in Supplementary Note 6 is characterized in that: The control device The voltage conversion circuit is driven by setting a dead time so that the first switching element, the second switching element, the third switching element, and the fourth switching element are not turned on at the same time, The first voltage sensor estimated value is calculated using the second voltage sensor value, the voltage conversion width of the voltage conversion circuit, and the dead time. (Supplementary Note 8) The power conversion device according to any one of Supplementary Notes 4 to 7, characterized in that: The first voltage sensor estimated value is also calculated using a switching delay time of the voltage conversion circuit. (Supplementary Note 9) The power conversion device according to any one of Supplementary Notes 4 to 8, characterized in that: The first voltage sensor estimated value is also calculated using the power conversion efficiency of the voltage conversion circuit. (Supplementary Note 10) The power conversion device according to any one of Supplementary Notes 1 to 9, characterized in that: A voltage conversion operation from the first DC voltage to the second DC voltage and a voltage switching operation from the second DC voltage to the first DC voltage can be switched. (Supplementary Note 11) The power conversion device as described in Supplementary Note 10 is characterized in that: The first voltage sensor estimated value is different between a voltage conversion operation from the first DC voltage to the second DC voltage and a voltage conversion operation from the second DC voltage to the first DC voltage. Description of symbols

[0085] 1 Battery 2 Load 3 Power conversion device 4 Reactor 30 Main circuit 31 Control device 32, 33 Voltage conversion circuit 32a, 32b, 33a, 33b, 33c, 33d switch elements 32c, 33e, 33f, 33g connection part 40 Current sensor 51 Low voltage side capacitor 52 High voltage side capacitor 53 Intermediate capacitor 61 First voltage sensor 62 Second voltage sensor 63 Third voltage sensor 100 processors 101 storage device.

Claims

1. A power conversion device, comprising a voltage conversion circuit for converting a first DC voltage into a second DC voltage of a different value, at least two capacitors, and a control device for controlling the voltage conversion amplitude of the voltage conversion circuit, wherein the power conversion device is characterized in that: a first capacitor connected in parallel with the first DC voltage; a second capacitor connected in parallel with the second DC voltage; a first voltage sensor, the first voltage sensor being used to detect a voltage of the first capacitor; as well as a second voltage sensor, the second voltage sensor being used to detect a voltage of the second capacitor, and having a third voltage sensor, the third voltage sensor detecting the voltage of the third capacitor when the third capacitor is present in the voltage conversion circuit, and detecting the voltage of the first capacitor or the second capacitor when the third capacitor is not present, The control device controlling a voltage conversion amplitude of the voltage conversion circuit using a first voltage sensor value detected by the first voltage sensor, a second voltage sensor value detected by the second voltage sensor, and a third voltage sensor value detected by the third voltage sensor, calculating a first difference between the second voltage sensor value and a value obtained by multiplying the third voltage sensor value by a predetermined coefficient, and performing a first determination process to determine whether the first difference is greater than a predetermined first threshold value, In the first determination process, When the first difference is greater than the first threshold, direct connection control is performed to make the first voltage sensor value consistent with the second voltage sensor value, a second difference between the first voltage sensor value and the second voltage sensor value is calculated, and a second determination process is performed to determine whether the second difference is greater than a preset second threshold. In the second determination process, When the second difference is greater than the second threshold, it is determined that the second voltage sensor is abnormal, and when the second difference is less than the second threshold, it is determined that the third voltage sensor is abnormal. In the first determination process, When the first difference is smaller than the first threshold, a third difference is calculated as the difference between the first voltage sensor value and the first voltage sensor estimated value calculated based on the second voltage sensor value, and a third determination process is performed to determine whether the third difference is greater than a third threshold set in advance. In the third determination process, When the third difference is equal to or greater than the third threshold value, it is determined that the first voltage sensor is abnormal. When the third difference is smaller than the third threshold value, it is determined that all the voltage sensors are normal.

2. The power conversion device according to claim 1, characterized in that: The voltage conversion circuit has a first switching element and a second switching element. A reactor having one end connected to the positive electrode side of the first DC voltage, One terminal of the first switching element is connected to the negative side of the first DC voltage, The other terminal of the first switching element and the other end of the reactor are connected to one terminal of the second switching element. The other terminal of the second switching element is connected to the positive side of the second DC voltage, and the third voltage sensor is configured to detect a voltage of the second capacitor, The control device sets a coefficient for calculating the first difference to 1, calculates a first difference between the second voltage sensor value and the third voltage sensor value, and performs a first determination process to determine whether the first difference is equal to or greater than a preset first threshold.

3. The power conversion device according to claim 1, characterized in that: The voltage conversion circuit includes a first switching element, a second switching element, a third switching element, and a fourth switching element connected in series in sequence, and an intermediate capacitor having one end connected to a connection point between the first switching element and the second switching element and the other end connected to a connection point between the third switching element and the fourth switching element. A reactor having one end connected to the positive electrode side of the first DC voltage, One terminal of the first switching element is connected to the negative side of the first DC voltage, The other end of the reactor is connected to a connection point between the second switching element and the third switching element. One terminal of the fourth switching element is connected to the positive side of the second DC voltage, and The third voltage sensor is configured to detect the voltage of the intermediate capacitor, The control device sets the coefficient for calculating the first difference to 2, calculates a first difference between the second voltage sensor value and a value obtained by multiplying the third voltage sensor value by 2, and performs a first determination process to determine whether the first difference is greater than a preset first threshold value.

4. The power conversion device according to claim 2, characterized in that: The first voltage sensor estimated value is calculated using the voltage conversion width of the voltage conversion circuit and the second voltage sensor value.

5. The power conversion device according to claim 4, characterized in that: The control device The voltage conversion circuit is driven by setting a dead time so that the first switching element and the second switching element are not turned on at the same time, The first voltage sensor estimated value is calculated using the second voltage sensor value, the voltage conversion width of the voltage conversion circuit, and the dead time.

6. The power conversion device according to claim 3, characterized in that: The first voltage sensor estimated value is calculated using the voltage conversion width of the voltage conversion circuit and the second voltage sensor value.

7. The power conversion device according to claim 6, characterized in that: The control device The voltage conversion circuit is driven by setting a dead time so that the first switching element, the second switching element, the third switching element, and the fourth switching element are not turned on at the same time, The first voltage sensor estimated value is calculated using the second voltage sensor value, the voltage conversion width of the voltage conversion circuit, and the dead time.

8. The power conversion device according to any one of claims 4 to 7, characterized in that: The first voltage sensor estimated value is also calculated using a switching delay time of the voltage conversion circuit.

9. The power conversion device according to any one of claims 4 to 7, characterized in that: The first voltage sensor estimated value is also calculated using the power conversion efficiency of the voltage conversion circuit.

10. The power conversion device according to any one of claims 1 to 7, characterized in that: A voltage conversion operation from the first DC voltage to the second DC voltage and a voltage switching operation from the second DC voltage to the first DC voltage can be switched.

11. The power conversion device according to claim 10, characterized in that: The first voltage sensor estimated value is different between a voltage conversion operation from the first DC voltage to the second DC voltage and a voltage conversion operation from the second DC voltage to the first DC voltage.

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