Power conversion device

Abstract

To provide a power conversion device that can identify a voltage sensor that has failed using only the voltage sensor values within the power conversion device without using external voltage information other than the voltage information within the power conversion device.SOLUTION: The power conversion device includes a first voltage sensor that detects the voltage of a low-voltage side capacitor and a second voltage sensor and a third voltage sensor that detect the voltage of a high-voltage side capacitor. By comparing the voltage value detected by the second voltage sensor with the voltage value detected by the third voltage sensor, the power conversion device determines whether there is a problem with the second voltage sensor or the third voltage sensor. By comparing the estimated value of the first voltage sensor, which is estimated from the voltage value detected by the second voltage sensor, with the voltage value detected by the first voltage sensor, the power conversion device determines whether there is a problem with the first voltage sensor or the second voltage sensor.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] In order to achieve high efficiency in an electric vehicle, it is necessary to control the boosting of the voltage input from a low-voltage battery to a power conversion device to supply power to the motor (i.e., power running) and returning the power from the motor side to the battery (i.e., regeneration). This control requires the detection of the input voltage (hereinafter, low-voltage side voltage) of the power conversion device and the output voltage (hereinafter, high-voltage side voltage) of the power conversion device. Therefore, if a failure occurs in the voltage sensors that detect these voltages, accurate voltage control becomes impossible, so technology that monitors sensor abnormalities regardless of the state of the power conversion device is important.

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

[0004] [Patent Document 1] Patent No. 3632657 Summary of the Invention [Problem to be solved by the invention]

[0005] In the conventional abnormality monitoring device, it was necessary to use the battery voltage to identify the voltage sensor in the power conversion device that has become abnormal. However, in the case of a hybrid vehicle in which the battery control system and the power conversion device control system are separate systems, it is necessary to receive battery voltage information from the outside and use it in the abnormality monitoring device for the power conversion device. In that case, unless the received battery voltage is signal-processed while taking into consideration 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 technology for solving the above-mentioned problems, and aims to obtain a power conversion device that can determine an abnormality in a voltage sensor without using external voltage information. [Means for solving the problem]

[0007] The power conversion device disclosed in the present application is A power conversion device comprising a voltage conversion circuit that converts a first DC voltage into a second DC voltage having a different value, at least two capacitors, and a control device that controls a voltage conversion width of the voltage conversion circuit, a first capacitor connected in parallel to the first DC voltage; a second capacitor connected in parallel to the second DC voltage; a first voltage sensor that detects a voltage of the first capacitor; a second voltage sensor that detects a voltage of the second capacitor; a third voltage sensor that detects a voltage of the third capacitor when the third capacitor is present in the voltage conversion circuit, and detects a voltage of the first capacitor or the second capacitor when the third capacitor is not present; The control device includes: a voltage conversion width of the voltage conversion circuit is controlled 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 second voltage sensor value by a preset coefficient, and performing a first determination process to determine whether the first difference is equal to or greater than a preset first threshold value; In the first determination process, when the first difference is equal to or greater than the first threshold value, a direct control is performed to make the first voltage sensor value equal to the second voltage sensor value, a second difference is calculated which is the difference between the first voltage sensor value and the second voltage sensor value, and a second determination process is performed to determine whether the second difference is equal to or greater than a second threshold value set in advance; In the second determination process, determining that the second voltage sensor is abnormal when the second difference is equal to or greater than the second threshold value, and determining that the third voltage sensor is abnormal when the second difference is smaller than the second threshold value; In the first determination process, if 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 from the second voltage sensor value, and a third determination process is performed to determine whether the third difference is equal to or larger than a preset third threshold; In the third determination process, determining that the first voltage sensor is abnormal when the third difference is equal to or greater than the third threshold value; If the third difference is smaller than the third threshold value, it is determined that both of the voltage sensors are normal. Effect of the Invention

[0008] According to the present application, it is possible to determine whether or not a voltage sensor has an abnormality without using external battery voltage information. [Brief description of the drawings]

[0009] [Figure 1] 1 is a diagram showing a configuration of a power conversion device according to a first embodiment. [Figure 2A]4 is a flowchart showing a process for determining an abnormality in the voltage sensor according to the first embodiment. [Figure 2B] 4 is a flowchart showing a process for determining an abnormality in the voltage sensor according to the first embodiment. [Diagram 3] 4A and 4B are diagrams illustrating waveforms of a gate drive signal and a reactor current in the voltage conversion circuit according to the first embodiment. [Figure 4] 4 is a diagram for explaining an operation mode (during powering operation) in the voltage conversion circuit according to the first embodiment. FIG. [Diagram 5] 4 is a diagram illustrating an operation mode (during regenerative operation) in the voltage conversion circuit according to the first embodiment. FIG. [Figure 6] FIG. 11 is a diagram showing a configuration of a power conversion device according to a second embodiment. [Figure 7] 11 is a diagram for explaining an operation mode of the voltage conversion circuit in the second embodiment. FIG. [Figure 8] 13A and 13B are diagrams illustrating waveforms of a gate drive signal and a reactor current in a voltage conversion circuit according to a second embodiment. [Figure 9A] 10 is a flowchart showing a process for determining an abnormality in a voltage sensor according to the second embodiment. [Figure 9B] 10 is a flowchart showing a process for determining an abnormality in a voltage sensor according to the second embodiment. [Figure 10] FIG. 2 is a configuration diagram showing an example of hardware of a control device according to the first and second embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of a power conversion device disclosed in the present application will be described with reference to the drawings. In each drawing, the same reference numerals indicate the same or corresponding parts. Therefore, detailed descriptions thereof may be omitted to avoid duplication.

[0011] Embodiment 1 The power conversion device according to the first embodiment will be described below with reference to the drawings. FIG. 1 is a diagram showing the configuration of the power conversion device according to the first embodiment. The power conversion device 3 is connected between a battery 1 and a load 2 to form a power supply system. That is, the power conversion device 3 is a DC / DC converter having an input terminal connected to the battery 1 and an output terminal connected to the load 2, and is configured to be able to switch between a power running operation in which the voltage of the battery 1 is boosted to a set voltage and power is supplied to the load 2, and a regenerative operation in which power generated by the load 2 is stored in the battery 1.

[0012] <Configuration 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, a reactor 4, a voltage conversion circuit 32, and a high-voltage side capacitor 52, and further includes a first voltage sensor 61 that detects a voltage V1 applied to the low-voltage side capacitor 51, and a second voltage sensor 62 and a third voltage sensor 63 that detect a voltage V2 applied to the high-voltage side capacitor 52.

[0013] Low-voltage side capacitor 51 is connected in parallel to battery 1, and high-voltage side capacitor 52 is connected in parallel to load 2. Reactor 4 has a first terminal and a second terminal, and the first terminal is connected to the high potential side (positive electrode side) terminal of battery 1.

[0014] The voltage conversion circuit 32 has a configuration in which a first switching element 32a and a second switching element 32b are connected in series, and is connected in parallel to the load 2. As shown in FIG. 1, the first switching element 32a and the second switching element 32b each have a configuration in which, for example, an IGBT (Insulated Gate Bipolar Transistor) and a diode are connected in inverse parallel. The first switching element 32a has one terminal (emitter side terminal) connected to a low potential side (negative side) terminal of the battery 1, and the second switching element 32b has one terminal (collector side terminal) connected to a high potential side terminal of the load 2. A first connection part 32c, which is a 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 a second terminal of the reactor 4. The current sensor 40 is disposed between the reactor 4 and the first connection part 32c, and detects a current IL flowing through the reactor 4.

[0015] The control device 31 receives voltage information V1sen detected by the first voltage sensor 61, voltage information V2Msen detected by the second voltage sensor 62, voltage information V2Ssen detected by the third voltage sensor 63, and a current value IL detected by the current sensor 40. The control device 31 also generates gate drive signals 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 the gate drive signals to the voltage conversion circuit 32. Details will be described below.

[0016] <Operation of 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, and the gates of the first switching element 32a and the second switching element 32b are turned on and off by PWM (Pulse Width Modulation) control, thereby controlling the voltage applied to the load 2. The control period Tsw is the reciprocal of the drive frequency fsw of the first and second switching elements 32a and 33b. Tsw=1 / fsw It is.

[0017] The switching pattern of the first switching element 32a and the second switching element 32b connected in series has a dead time provided so that the switching element 32a and the second switching element 32b are not turned on at the same time. The duty in the DC / DC converter of the power conversion device 3 is defined as the ratio of the on time Ton of the gate drive signal of the first switching element 32a in one control period Tsw. That is, Duty=Ton / Tsw In addition, the boosted voltage V2 is calculated by the following formula (1). V2 = V1 / (1 - Duty) (1) The voltage conversion width (duty) of the voltage conversion circuit 32 is described by voltage V1 and voltage V2.

[0018] <Procedure for determining whether each of the voltage sensors 61, 62, and 63 is abnormal> 2A and 2B are flowcharts showing a procedure for performing an abnormality determination for 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. The process shown in Figs. 2A and 2B is repeatedly performed at set time intervals, for example, every 1 ms. When voltage sensor abnormality detection starts in step S101, in step S102, the control device 31 acquires the first voltage sensor value V1sen from the first voltage sensor 61, the second voltage sensor value V2Msen from the second voltage sensor 62, the third voltage sensor value V2Ssen from the third voltage sensor 63, and the on-time ratio of the first switching element 32a, i.e., the command duty Duty, which is 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 under "boost control". "Boost control" refers to controlling the first voltage conversion circuit 32 to boost the low-side voltage to generate a high-side voltage. If it is determined in step S103 that "boost control is underway" (YES in step S103), the process proceeds to step S104, and if it is determined that "boost control is not underway" (NO in step S103), the process returns to step S103.

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

[0021] Next, in step S105, the control device 31 compares the calculation result of step S104 with a preset threshold value A1. If the calculation result of step S104 is smaller than the threshold value A1 (NO in step S105), 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 S111. On the other hand, if the calculation result of step S104 is equal to or greater than the threshold value A1 (YES in step S105), it is determined that an abnormality has occurred in either the second voltage sensor 62 or the third voltage sensor 63, and the process proceeds to step S106. The threshold value A1 may be determined by testing. Alternatively, the threshold value A1 may be set based on a sensor error.

[0022] In step S106, control device 31 performs direct control on voltage conversion circuit 32 to make the low-voltage side voltage and the high-voltage side voltage equal to each other. That is, control is performed so that the first voltage sensor value V1sen and the second voltage sensor value V2Msen that detects the high-voltage side capacitor voltage are equal to each other. It should be noted that "direct control" refers to controlling the voltage conversion circuit 32 so that the low-voltage side voltage and the high-voltage side voltage are the same, and is a state in which the on-time ratio of the second switching element 32b is 1 and the on-time ratio of the first switching element 32a is 0. Next, in step S107, the absolute value of the difference between first voltage sensor value V1sen detecting the voltage of low-voltage side capacitor 51 and second voltage sensor value V2Msen detecting the voltage of high-voltage side capacitor 52 is calculated.

[0023] Next, in step S108, control device 31 compares the calculation result of step S107 with a preset threshold value B1. If the calculation result of step S107 is smaller than threshold value B1 (NO in step S108), it is determined that first voltage sensor 61 and second voltage sensor 62 are normally detecting the voltages of low-voltage side capacitor 51 and high-voltage side capacitor 52, whose voltages match under the direct coupling control of step S106. As a result, it is determined that third voltage sensor 63 is abnormal (step S109).

[0024] On the other hand, if the calculation result in step S107 is equal to or greater than 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. Taking this into consideration the result of step S105 in which it was determined that an abnormality has occurred in either the second voltage sensor 62 or the third voltage sensor 63, it is determined that the second voltage sensor 62, which is common to both results, is abnormal (step S110). Note that threshold value B1 may be determined by testing. Alternatively, threshold value B1 may be set based on sensor error.

[0025] If it is determined in step S105 that the calculation result in step S104 is smaller than threshold A1 (NO in step S105), it is determined in step S111 whether the power conversion device 3 is in a power running operation or a regenerative operation. The determination of powering operation or regenerative operation is made using the current value IL detected by the current sensor 40. If the current value is positive, it is determined that powering operation is in progress, and if the current value is negative, it is determined that regenerative operation is in progress. If regenerative operation is in progress, the process proceeds to step S112, and if powering operation is in progress, the process proceeds to step S113.

[0026] In step S112, the difference between the first voltage sensor value V1sen during regenerative operation and a first voltage sensor estimate V1estreg obtained by calculating an estimate of the first voltage sensor value V1sen is calculated. In step S113, the difference between the first voltage sensor value V1sen during powering operation and a first voltage sensor estimate V1estrun obtained by calculating an estimate of the first voltage sensor value V1sen is calculated.

[0027] Here, a method for calculating the first voltage sensor estimated value will be described with reference to FIGS. 3 is a diagram showing the relationship between the gate drive signal and the reactor current IL in the voltage conversion circuit 32. In FIG. 3(a), the gate drive signal output to the voltage conversion circuit 32 is shown, with the upper side showing the gate drive signal for the switching element 32b and the lower side showing the gate drive signal for the switching element 32a. If the on-time of the switching element 32b and the on-time of the switching element 32a overlap, the high-potential side and the low-potential side of the high-voltage side capacitor 52 are short-circuited. Therefore, taking into consideration the delay in turning on and off the switching elements, a dead time (Td) is provided so that the switching elements 32b and 32a are not turned on at the same time. Therefore, the switching elements 32b and 32a are alternately turned on with the dead time in between.

[0028] FIG. 3(b) shows the reactor current during power running, and FIG. 3(c) shows the reactor current during regenerative operation, but the two behaviors are different. First, the reactor current during power running in FIG. 3(b) will be described using the flow of the reactor current corresponding to the operation mode during power running in FIG.

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

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

[0031] In the section of mode 3, both the switching element 32b and the switching element 32a are turned off. As shown in (c) mode 3 of Fig. 4, the same current loop as in mode 2 is formed, and the current decreases. In other words, during powering operation, the current behavior during the dead time period is the same as in mode 2, where the switching element 32b is turned on.

[0032] Next, the reactor current during regenerative operation in FIG. 3(c) will be described using the flow of the reactor current corresponding to the operation mode during regenerative operation in FIG. During the mode 1 section, switching element 32b is turned off and switching element 32a is turned on, and as shown in mode 1 of FIG. 5(a), a current flows through the loop of switching element 32a and low-voltage side capacitor 51, the potential of connection point 32c becomes 0, and the reactor current increases.

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

[0034] In the section of mode 3, the switching element 32b is turned off, the switching element 32a is also turned off, and as shown in (c) mode 3 of Fig. 5, the same current loop as in mode 1 is formed, and the current increases. In other words, during the regenerative operation, the current behavior during the dead time period is the same as in mode 1 where the switching element 32a is turned on.

[0035] From the above, since the relationship between the voltages V1, V2, and the command duty Duty differs during powering operation and regenerative operation due to the influence of the dead time, the calculation accuracy of the first voltage sensor estimate can be improved by correcting the calculation of the estimate of the voltage V1 used to determine an abnormality in the voltage sensor using a different calculation formula that includes information about the dead time.

[0036] In addition, there is a delay in the timing when the gate drive signal is switched from off to on and from on to off. As with the effect of the dead time described in Fig. 3, the effect of this switching delay time differs between powering operation and regenerative operation, so the calculation accuracy of the first voltage sensor estimate value can be improved by including information on the switching delay time in the calculation of the estimate value of voltage V1 used to determine an abnormality in the voltage sensor and correcting it using a different calculation formula.

[0037] Furthermore, the difference in the calculation of the estimated value of voltage V1 during power running and regenerative operation is due to the efficiency of power conversion in the power conversion device 3. If the power on the battery 1 side is P1 and the power on the load side is P2, the power conversion efficiency during power running is defined as Effrun=P2 / P1 (<1), and the power conversion efficiency during regenerative operation is defined as Effreg=P1 / P2 (<1).

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

[0039] On the other hand, if we consider that the step-down control is performed during regenerative operation, the equation for the step-down voltage V1 using the power conversion efficiency Effreg during regenerative operation is given by (1): V1=(1-Duty)×V2×Effreg Thus, when the command duty is the same as when the power conversion efficiency is 1, the voltage V1 becomes smaller.

[0040] Therefore, in steps S112 and S113, the calculation of the estimated value of voltage V1 used to determine an abnormality in the voltage sensor includes information on the power conversion efficiency, and the calculation accuracy of the first voltage sensor estimated value can be improved by correcting it using different calculation formulas during powering operation and regenerative operation.

[0041] In steps S112 and S113, the difference between the first voltage sensor value V1sen and a first voltage sensor estimate value V1est, which is a calculated estimate of the first voltage sensor value V1sen, is calculated. Ideally, the first voltage sensor estimate value V1est can be calculated using the following equation (2). V1est=V2 × (1-Duty) ···(2) In reality, there are effects of dead time, switching delay time, and efficiency, and the relationship between the command duty Duty and the voltages V1 and V2 differs during powering operation and during regenerative operation, so a correction is made to the estimated value.

[0042] During powering operation, the first voltage sensor estimated value V1estrun is calculated using the following equation (3).

number

number

[0043] Here, the power conversion efficiencies Effrun and Effreg during power running and regeneration are assumed to be equivalent, but different values ​​may be used for each. They may also be changed according to the size of the load, or may be determined by testing.

[0044] Now, returning to the flowchart of FIG. In step S112, control device 31 calculates the difference ΔV between first voltage sensor value V1sen and first voltage sensor estimated value V1estreg obtained from 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 calculated from the 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 result of the calculation in step S112 or the result of the calculation in step S113, is compared with a preset threshold C1. If the absolute value of the difference ΔV is smaller than the threshold C1 (NO in step S114), it can be determined that the first voltage sensor estimate value V1est calculated from the second voltage sensor value V2Msen matches the first voltage sensor value V1sen. Since it has been determined in the previous step S105 that there is no abnormality in the second voltage sensor 62, it is also determined that there is no abnormality in the first voltage sensor 61, and all the voltage sensors are determined to be normal (step S115).

[0046] In step S114, if the absolute value of the difference ΔV is equal to or greater than 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 already been determined in step S105 that there is no abnormality in the second voltage sensor 62, it is determined that an abnormality has occurred in the first voltage sensor 61 (step S116).

[0047] In step S114, the threshold C1 may be determined by testing, or may be set based on the sensor error and the delay time between the gate drive signal and the switching element actually being 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 instead. In this case, the voltage of the first capacitor detected by the third voltage sensor 63 is taken as a third voltage sensor value V1Ssen, and a procedure for determining whether or not the voltage sensor is at its normal state will be described below.

[0049] 2A, 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] Furthermore, in step S107, control device 31 calculates the absolute value of the difference between first voltage sensor value V1sen and second voltage sensor value V2Msen. Next, in step S108, if the calculation result in step S107 is smaller than threshold value B1 (NO in step S108), control device 31 determines that first voltage sensor 61 and second voltage sensor 62 are normally detecting the voltages of low-voltage side capacitor 51 and high-voltage side capacitor 52, whose voltages match under the direct coupling control in step S106. As a result, control device 31 determines that third voltage sensor 63 is abnormal (step S109).

[0051] On the other hand, if the calculation result in step S107 is equal to or greater than 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 was 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, which is common to both results, is abnormal (step S110).

[0052] In step S114, if the absolute value of the difference ΔV is smaller than the threshold value C1 (NO in step S114), it can be determined that the first voltage sensor estimated value V1est calculated from the second voltage sensor value V2Msen matches the first voltage sensor value V1sen. Since it has been determined in the previous step S105 that the first voltage sensor 61 is not abnormal, it is also determined that the second voltage sensor 62 is not abnormal, and all the voltage sensors are determined to be normal (step S115).

[0053] In step S114, if the absolute value of the difference ΔV is equal to or greater than 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 there is no abnormality in the first voltage sensor 61, 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, which is a first DC voltage, into a second DC voltage of a different value, at least two capacitors 51, 52, and a control device that controls the voltage conversion width of the voltage conversion circuit 32, and 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 to the battery 1, a second capacitor 52 connected in parallel to the second DC voltage, a first voltage sensor 61 that detects the voltage of the first capacitor 51, a second voltage sensor 62 that detects the voltage of the second capacitor 52, and a third voltage sensor 63 that detects 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 using a command duty 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, which is the difference between the second voltage sensor value V2Msen and the third voltage sensor value V2Ssen multiplied by a preset coefficient of 1, 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 A1. If the first difference is equal to or greater than the first threshold value A1, direct connection control is performed, and a second difference, which is the difference between the first voltage sensor value V1sen and the second voltage sensor value V2Msen, is calculated, and a second determination process is performed to determine whether the second difference is equal to or greater than a preset second threshold value B1. If the second difference is equal to or greater than the second threshold value B1, it is determined that the second voltage sensor 62 is abnormal, and if the second difference is smaller than the second threshold value B1, it is determined that the third voltage sensor 63 is abnormal.In the first determination process, if the first difference is smaller than the first threshold A1, a third difference is calculated, which is the difference between the first voltage sensor value V1sen and the first voltage sensor estimated value V1est calculated from the second voltage sensor value V2Msen, and a third determination process is performed to determine whether the third difference is equal to or larger than a preset third threshold C1. If the third difference is equal to or larger than the third threshold C1, it is determined that the first voltage sensor 61 is abnormal, and if the third difference is smaller than the third threshold C1, it is determined that all the voltage sensors are normal. This makes it possible to identify and determine which 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 above-mentioned first embodiment, a non-insulated step-up DC / DC converter in which the battery 1 side is at a low voltage and the load side is at a high voltage has been described as an example, but the present invention may also be applied to a non-insulated step-down DC / DC converter.

[0056] In the above description, in step S103, in the case of boost control, the flow proceeds to the next step and determines whether the voltage sensors are normal or abnormal. In the case of direct control, the first voltage sensor value V1sen, the second voltage sensor value V2Msen, and the third voltage sensor value V2Ssen may be compared to determine whether the first voltage sensor 61, the second voltage sensor 62, and the third voltage sensor 63 are normal or abnormal, separately from the workflow of FIG. 2. That is, in the case of direct control, ideally V1sen=V2Msen=V2Ssen, so by checking the difference between two of the three, it is possible to determine whether an abnormality has occurred in any of the voltage sensors. In this way, it is possible to identify a failure of the voltage sensor regardless of whether the control is boost control or direct control.

[0057] Embodiment 2 A power conversion device according to the second embodiment will be described below with reference to the drawings. FIG. 6 is a diagram showing the configuration of the power conversion device according to the second embodiment. The power conversion device 3 is connected between the battery 1 and the load 2 as in the first embodiment to form a power supply system. That is, the power conversion device 3 is a DC / DC converter having the battery 1 connected to an input terminal and the load 2 connected to an output terminal. The difference from the first embodiment is that the DC / DC converter is a multilevel converter having an intermediate capacitor 53. The following description will focus on the differences from the first embodiment, and will omit a description of the same configuration and operation.

[0058] <Configuration of power conversion device 3> In FIG. 6, the power conversion device 3 includes a main circuit 30 and a control device 31. Main circuit 30 includes low-voltage side capacitor 51, reactor 4, voltage conversion circuit 33, intermediate capacitor 53, and high-voltage side capacitor 52, and further includes a current sensor 40 that detects a current flowing through reactor 4, a first voltage sensor 61 that detects a voltage V1 applied to low-voltage side capacitor 51, a second voltage sensor 62 that detects a voltage V2 applied to high-voltage side capacitor 52, and a third voltage sensor 63 that detects a voltage V0 applied to intermediate capacitor 53. The arrangement of low-voltage side capacitor 51, reactor 4, current sensor 40, and first voltage sensor 61 is the same as in the first embodiment.

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

[0060] One terminal (emitter side terminal) of the first switching element 33a is connected to the low potential side (negative side) terminal of the battery 1, and one terminal (collector side terminal) of the fourth switching element 33d is connected to the high potential side (positive side) terminal of the load 2. The second connection part 33e is connected to a second terminal of the reactor 4. The first to fourth switching elements 33a, 33b, 33c, and 33d are each configured, for example, in such a manner that a diode is connected in inverse parallel to an IGBT, as in the first embodiment.

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

[0062] The control device 31 receives voltage information V2sen detected by the second voltage sensor 62, voltage information V1sen detected by the first voltage sensor 61, voltage information V0sen detected by the third voltage sensor 63, and a current value ILsen detected by the current sensor 40.

[0063] <Operation mode of voltage conversion circuit 33> Next, the operation mode of the voltage conversion circuit 33 shown in FIG. 6 will be described with reference to FIG. 7(a) to (d), there are four operating modes, which are on / off patterns of the first to fourth switching elements 33a, 33b, 33c, and 33d: (a) mode 1 to (d) mode 4. In the powering operation in which power is supplied from the battery 1 to the load 2 and in the regenerative operation in which power is supplied from the load 2 to the battery 1, there is a difference between whether the current passes through the IGBT of some of the switching elements or the diode connected in anti-parallel, but since the current paths indicated by the dashed lines are the same but in the opposite direction, the powering operation will be described here.

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

[0065] In mode 2, the first switching element 33a and the third switching element 33c are off, and the second switching element 33b and the fourth switching element 33d are on. This operation causes a current to flow through the IGBT of the second switching element 33b and the diode of the fourth switching element 33d, as shown in the current path in Fig. 7(b), and the energy of the intermediate capacitor 53 is released.

[0066] In mode 3, the first switching element 33a and the second switching element 33b are off, and the third switching element 33c and the fourth switching element 33d are on. This operation causes a current to flow through the diode of the third switching element 33c and the diode of the fourth switching element 33d, as shown in the current path in Fig. 7(c), and the reactor 4 enters a state in which energy is released.

[0067] In mode 4, the first switching element 33a and the second switching element 33b are on, and the third switching element 33c and the fourth switching element 33d are off. This operation causes a current to flow through the IGBT of the first switching element 33a and the IGBT of the second switching element 33b, as shown in the current path in Fig. 7(d), and energy is stored in the reactor 4.

[0068] FIG. 8 is a diagram showing the relationship between the gate drive signal and the reactor current IL in the voltage conversion circuit 33 of the second embodiment. FIG. 8(a) shows the gate drive signal output to the voltage conversion circuit 33, which is the gate drive signal of the switching element 33d, the switching element 33a, the switching element 33c, and the switching element 33b from the top. In order to prevent the ON time of the switching element 33d and the ON time of the switching element 33a from overlapping and causing a short circuit, a dead time (Td) is provided so that the switching elements 33d and 33a are not turned on at the same time, taking into consideration the delay in turning on and off the switching elements. Similarly, in order to prevent the ON time of the switching element 33c and the ON time of the switching element 33b from overlapping and causing a short circuit, a dead time (Td) is provided so that the switching elements 33c and 33b are not turned on at the same time.

[0069] In the multilevel converter in the second embodiment, a duty 1 is defined for the first switching element 33a, and a duty 2 is defined for the second switching element 33b. Basically, the duty 1 and the duty 2 are the same, but the time of the duty 1 and the duty 2 may be intentionally shifted depending on the control of the V0 voltage. Even in the case of the multilevel converter, the relationship between the V2 voltage and the duty 2 is expressed using the formula (1). Also, the gate signals of the first switching element 33a and the second switching element 33b are out of phase with each other by 180 degrees with respect to the switching frequency (fsw).

[0070] By appropriately adjusting the time ratio of these operation modes, it is possible to control the voltage V2 applied to the load 2 and to control the voltage V0 applied to the intermediate capacitor 53 to half of V2 in order to reduce the voltage applied to the reactor 4.

[0071] <Procedure for determining whether each of the voltage sensors 61, 62, and 63 is abnormal> 9A and 9B are flowcharts showing a procedure for performing an abnormality determination for 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. The process shown in Figs. 9A and 9B is repeatedly performed at set time intervals, for example, every 1 ms.

[0072] When voltage sensor abnormality detection starts in step S201, in step S202, the control device 31 acquires 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 a command duty Duty, which is the control state of the multi-level converter.

[0073] In step S203, the control device 31 determines whether the voltage conversion circuit 33 is under "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, so that 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. The threshold value A2 may be determined by testing. Alternatively, the threshold value A2 may be set based on the error of the sensor. If the calculation result in step S204 is smaller than threshold value A2 (NO in step S205), it is determined that there is no abnormality in second voltage sensor 62 and third voltage sensor 63, and the process proceeds to step S211. On the other hand, if the calculation result in step S204 is equal to or larger than threshold value A2 (YES in step S205), it is determined that an abnormality has occurred in either second voltage sensor 62 or third voltage sensor 63, and the process proceeds to step S206.

[0075] Steps S206 to S216 in the second embodiment are similar to steps S106 to S116 in the first embodiment, and therefore the description will be omitted. The other thresholds B2 and C2 in the second embodiment may be set in the same manner as the thresholds B1 and C1 in the first embodiment. In this way, even in a power conversion device 3 equipped with a multi-level converter, abnormalities in the first voltage sensor 61 that detects the voltage of the low-voltage side capacitor, 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 provided in the power conversion device 3 can be identified without using external voltage information.

[0076] As described above, according to the second embodiment, the same effects as those of the first embodiment are achieved. That is, the power conversion device 3 according to the second embodiment is a multilevel converter including a voltage conversion circuit 33 that converts the voltage of the battery 1, which is a first DC voltage, into a second DC voltage of a different value, three capacitors 51, 52, and 53, and a control device 31 that controls the voltage conversion width of the voltage conversion circuit 33. The voltage conversion circuit 33 has first to fourth switching elements 33a, 33b, 33c, and 33d connected in series, and includes a first capacitor 51 connected in parallel to the battery 1, a second capacitor 52 connected in parallel to the second DC voltage, an intermediate capacitor 53 having one end connected to the connection point between the first switching element 33a and the second switching element 33b and the other end connected to the connection point between the third switching element 33c and the fourth switching element 33d, a first voltage sensor 61 that detects the voltage of the first capacitor 51, a second voltage sensor 62 that detects the voltage of the second capacitor 52, and a third voltage sensor 63 that detects the voltage of the intermediate capacitor 53, which is a third capacitor. Then, the control device 31 controls the voltage conversion width of the voltage conversion circuit 33 by a command duty 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, a first difference, which is the difference between the second voltage sensor value V2sen and the value obtained by multiplying the second voltage sensor value V0sen by 2, which is a preset coefficient, 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 A2. If the first difference is equal to or greater than the first threshold value A2, direct connection control is performed, and a second difference, which is the difference between the first voltage sensor value V1sen and the second voltage sensor value V2sen, is calculated, and a second determination process is performed to determine whether the second difference is equal to or greater than a preset second threshold value B2. If the second difference is equal to or greater than the second threshold value B2, it is determined that the second voltage sensor 62 is abnormal, and if the second difference is smaller than the second threshold value B2, it is determined that the third voltage sensor 63 is abnormal.In the first determination process, if the first difference is smaller than the first threshold A2, a third difference is calculated, which is the difference between the first voltage sensor value V1sen and the first voltage sensor estimated value V1est calculated from the second voltage sensor value V2sen, and a third determination process is performed to determine whether the third difference is equal to or larger than a preset third threshold C2, and if the third difference is equal to or larger than the third threshold C2, it is determined that the first voltage sensor 61 is abnormal, and if the third difference is smaller than the third threshold C2, it is determined that all the voltage sensors are normal. This makes it possible to identify and determine which of the first voltage sensor 61, the second voltage sensor 62, and the third voltage sensor 63 is abnormal, without using external voltage information.

[0077] Note that the second embodiment is an example of a three-level multilevel converter, and in step S204, the first difference is calculated as the 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. However, the coefficient may be changed depending on the circuit configuration of the converter.

[0078] <Hardware configuration of the control device 31> The control device 31 is configured with a processor 100 and a storage device 101, as shown in Fig. 10, which is an example of hardware. 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. Also, instead of the flash memory, a hard disk auxiliary storage device may be included.

[0079] The processor 100 is composed of, for example, a central processing unit (CPU), an application specific integrated circuit (ASIC), a digital signal processor (DSP), a field programmable gate array (FPGA), 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 a volatile storage device. The processor 100 may output data such as a calculation result to the volatile storage device of the storage device 101, or may store the data in the auxiliary storage device via the volatile storage device.

[0080] <Other embodiments> (1) In the examples shown in Figs. 1 and 6, the switching elements are configured with IGBTs, but the present invention is not limited to this configuration. For example, the switching elements may be configured with MOSFETs (Metal Oxide Semiconductor Field Effect Transistors). The switching elements are not limited to those configured with Si (silicon) semiconductors, and may be semiconductors such as SiC (silicon carbide) and GaN (gallium nitride), which are wide band gap semiconductors. The switching elements may be configured with GaN-HEMTs (Gallium Nitride-High Mobility Transistors).

[0081] (2) In the above first and second embodiments, the first voltage sensor estimated value V1est is calculated using formulas (2) to (4), but the accuracy can be improved by appropriately considering the following items in the calculation: dead time, switching delay time of the voltage conversion circuits 32 and 33, and power conversion efficiency during power running or regenerative operation in addition to the second voltage sensor value and the command duty Duty related to the voltage conversion width. Items to be combined may be selected arbitrarily.

[0082] Although the present application describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to application to a particular embodiment, but may be applied to the embodiments alone or in various combinations. Therefore, countless modifications not exemplified are assumed within the scope of the technology disclosed in the present specification, including, for example, modifying, adding, or omitting at least one component, and further, extracting at least one component and combining it with a component of another embodiment.

[0083] Various aspects of the present disclosure are summarized below as appendices.

[0084] (Appendix 1) A power conversion device comprising a voltage conversion circuit that converts a first DC voltage into a second DC voltage having a different value, at least two capacitors, and a control device that controls a voltage conversion width of the voltage conversion circuit, a first capacitor connected in parallel to the first DC voltage; a second capacitor connected in parallel to the second DC voltage; a first voltage sensor that detects a voltage of the first capacitor; a second voltage sensor that detects a voltage of the second capacitor; a third voltage sensor that detects a voltage of the third capacitor when the third capacitor is present in the voltage conversion circuit, and detects a voltage of the first capacitor or the second capacitor when the third capacitor is not present; The control device includes: a voltage conversion width of the voltage conversion circuit is controlled 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 second voltage sensor value by a preset coefficient, and performing a first determination process to determine whether the first difference is equal to or greater than a preset first threshold value; In the first determination process, when the first difference is equal to or greater than the first threshold value, a direct control is performed to make the first voltage sensor value equal to the second voltage sensor value, a second difference is calculated which is the difference between the first voltage sensor value and the second voltage sensor value, and a second determination process is performed to determine whether the second difference is equal to or greater than a second threshold value set in advance; In the second determination process, determining that the second voltage sensor is abnormal when the second difference is equal to or greater than the second threshold value, and determining that the third voltage sensor is abnormal when the second difference is smaller than the second threshold value; In the first determination process, if 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 from the second voltage sensor value, and a third determination process is performed to determine whether the third difference is equal to or larger than a preset third threshold; In the third determination process, determining that the first voltage sensor is abnormal when the third difference is equal to or greater than the third threshold value; The power conversion device determines that both of the voltage sensors are normal when the third difference is smaller than the third threshold value. (Appendix 2) the voltage conversion circuit includes a first switching element and a second switching element; a reactor having one end connected to a positive electrode side of the first DC voltage, one terminal of the first switching element is connected to a negative electrode 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 electrode side of the second DC voltage, the third voltage sensor is positioned to detect a voltage across the second capacitor; The control device includes: The power conversion device described in Appendix 1 performs a first determination process to calculate a first difference, which is the difference between the second voltage sensor value and the third voltage sensor value, using a coefficient for calculating the first difference as 1, and to determine whether the first difference is equal to or greater than a predetermined first threshold value. (Appendix 3) 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, and an intermediate capacitor having one end connected to a connection point between the first switching element and the second switching element and another end connected to a connection point between the third switching element and the fourth switching element; a reactor having one end connected to a positive electrode side of the first DC voltage, one terminal of the first switching element is connected to a negative electrode 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 electrode side of the second DC voltage; the third voltage sensor is positioned to detect a voltage across the intermediate capacitor; The control device includes: The power conversion device described in Appendix 1 performs a first determination process to calculate a first difference, which is the difference between the second voltage sensor value and the third voltage sensor value multiplied by 2, using a coefficient for calculating the first difference as 2, and to determine whether the first difference is greater than or equal to a predetermined first threshold value. (Appendix 4) 3. The power conversion device according to claim 2, wherein the first voltage sensor estimate value is calculated using the second voltage sensor value and a voltage conversion width of the voltage conversion circuit. (Appendix 5) The control device includes: driving the first switching element and the second switching element of the voltage conversion circuit while providing a dead time so that the first switching element and the second switching element are not turned on at the same time; 5. The power conversion device according to claim 4, wherein the first voltage sensor estimate value is calculated using the second voltage sensor value, a voltage conversion width of the voltage conversion circuit, and the dead time. (Appendix 6) 4. The power conversion device according to claim 3, wherein the first voltage sensor estimate value is calculated using the second voltage sensor value and a voltage conversion width of the voltage conversion circuit. (Appendix 7) The control device includes: driving the first switching element, the second switching element, the third switching element, and the fourth switching element of the voltage conversion circuit while providing a dead time so that they are not turned on simultaneously; 7. The power conversion device according to claim 6, wherein the first voltage sensor estimate value is calculated using the second voltage sensor value, a voltage conversion width of the voltage conversion circuit, and the dead time. (Appendix 8) The power conversion device according to any one of appendixes 4 to 7, wherein the first voltage sensor estimate is further calculated using a switching delay time of the voltage conversion circuit. (Appendix 9) The power conversion device according to any one of appendixes 4 to 8, wherein the first voltage sensor estimate is further calculated using a power conversion efficiency of the voltage conversion circuit. (Appendix 10) A voltage conversion operation from the first DC voltage to the second DC voltage; 10. The power conversion device according to claim 1, wherein a voltage conversion operation from the second DC voltage to the first DC voltage is switchable. (Appendix 11) The power conversion device described in Appendix 10, wherein 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. [Explanation 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: switching elements, 32c, 33e, 33f, 33g: connection portions, 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: processor, 101: storage device.

Claims

1. A power conversion device including a voltage conversion circuit that converts a first DC voltage into a second DC voltage having a different value, at least two capacitors, and a control device that controls a voltage conversion width of the voltage conversion circuit, a first capacitor connected in parallel to the first DC voltage; a second capacitor connected in parallel to the second DC voltage; a first voltage sensor that detects a voltage of the first capacitor; a second voltage sensor that detects a voltage of the second capacitor; a third voltage sensor that detects a voltage of the third capacitor when the third capacitor is present in the voltage conversion circuit, and detects a voltage of the first capacitor or the second capacitor when the third capacitor is not present; The control device includes: a voltage conversion width of the voltage conversion circuit is controlled 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 second voltage sensor value by a preset coefficient, and performing a first determination process to determine whether the first difference is equal to or greater than a preset first threshold value; In the first determination process, When the first difference is equal to or greater than the first threshold value, a direct control is performed to make the first voltage sensor value equal to the second voltage sensor value, a second difference is calculated which is the difference between the first voltage sensor value and the second voltage sensor value, and a second determination process is performed to determine whether the second difference is equal to or greater than a preset second threshold value; In the second determination process, determining that the second voltage sensor is abnormal when the second difference is equal to or greater than the second threshold value, and determining that the third voltage sensor is abnormal when the second difference is smaller than the second threshold value; In the first determination process, if 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 from the second voltage sensor value, and a third determination process is performed to determine whether the third difference is equal to or greater than a preset third threshold; In the third determination process, If the third difference is equal to or greater than the third threshold value, it is determined that the first voltage sensor is abnormal; The power conversion device determines that both of the voltage sensors are normal when the third difference is smaller than the third threshold value.

2. the voltage conversion circuit includes a first switching element and a second switching element; a reactor having one end connected to a positive electrode side of the first DC voltage, one terminal of the first switching element is connected to a negative electrode 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 electrode side of the second DC voltage, the third voltage sensor is positioned to detect a voltage across the second capacitor; The control device includes:

2. The power conversion device according to claim 1, further comprising: a coefficient for calculating the first difference being set to 1; and a first determination process being performed to determine whether the first difference is equal to or greater than a first threshold value set in advance.

3. 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, and an intermediate capacitor having one end connected to a connection point between the first switching element and the second switching element and another end connected to a connection point between the third switching element and the fourth switching element; a reactor having one end connected to a positive electrode side of the first DC voltage, one terminal of the first switching element is connected to a negative electrode 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 electrode side of the second DC voltage; the third voltage sensor is positioned to detect a voltage across the intermediate capacitor; The control device includes:

2. The power conversion device according to claim 1, further comprising: a coefficient for calculating the first difference being set to 2; a first difference being the difference between the second voltage sensor value and the third voltage sensor value multiplied by 2; and a first determination process being performed to determine whether the first difference is equal to or greater than a preset first threshold value.

4. The power conversion device according to claim 2 , wherein the first voltage sensor estimate value is calculated using the second voltage sensor value and a voltage conversion width of the voltage conversion circuit.

5. The control device includes: driving the first switching element and the second switching element of the voltage conversion circuit while providing a dead time so that the first switching element and the second switching element are not turned on at the same time; The power conversion device according to claim 4 , wherein the first voltage sensor estimate value is calculated using the second voltage sensor value, a voltage conversion width of the voltage conversion circuit, and the dead time.

6. The power conversion device according to claim 3 , wherein the first voltage sensor estimate value is calculated using the second voltage sensor value and a voltage conversion width of the voltage conversion circuit.

7. The control device includes: driving the first switching element, the second switching element, the third switching element, and the fourth switching element of the voltage conversion circuit while providing 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 simultaneously; The power conversion device according to claim 6 , wherein the first voltage sensor estimate value is calculated using the second voltage sensor value, a voltage conversion width of the voltage conversion circuit, and the dead time.

8. The power conversion device according to claim 4 , wherein the first voltage sensor estimate value is calculated further using a switching delay time of the voltage conversion circuit.

9. The power conversion device according to claim 4 , wherein the first voltage sensor estimate value is calculated further using a power conversion efficiency of the voltage conversion circuit.

10. A voltage conversion operation from the first DC voltage to the second DC voltage; The power conversion device according to claim 1 , wherein a voltage conversion operation from the second DC voltage to the first DC voltage is switchable.

11. The power conversion device according to claim 10 , wherein the first voltage sensor estimate 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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