Failure diagnosis method for power conversion unit and failure diagnosis device for power conversion unit

Abstract

This failure diagnosis method is a method for diagnosing a failure of a power conversion unit (10) for converting power input from a power supply (210). In this method, a state signal indicating the on / off state of a switch (220) that connects a power supply to a power conversion unit, and an output signal from a sensor (120) that detects the input voltage (Vin) of the power conversion unit are acquired. When the state of the switch indicated by the acquired state signal is on, it is determined whether or not the input voltage indicated by the acquired output signal deviates from the normal range of the input voltage. When it is determined that the input voltage indicated by the output signal is out of the normal range when the state of the switch indicated by the state signal is on, it is diagnosed that there is a possibility of failure in the sensor.

Description

Fault diagnosis method and fault diagnosis device for power conversion unit

[0001] The present invention relates to a fault diagnosis method and a fault diagnosis device for a power conversion unit.

[0002] Patent Document 1 describes a power conversion device that includes a control circuit that drives an inverter circuit, a power supply circuit that outputs an applied voltage to the control circuit, and a voltage detection unit that detects the input voltage of the inverter circuit. In this power conversion device, the voltage detection unit is diagnosed based on the switching period and on-time of a switching signal input to a switching circuit of the power supply circuit.

[0003] International Publication No. 2018 / 079299

[0004] In Patent Document 1, the period of the switching signal is fixed, so the input voltage of the inverter circuit can be calculated from the on-time of the switching signal, which changes in response to the input voltage. In power conversion units for electric vehicles, the on-time of the switching circuit changes depending on the voltage of the low-voltage battery that supplies the converted power, so the method of Patent Document 1 cannot be used to detect the input voltage for fault diagnosis. The present invention has been made in consideration of the above circumstances, and an object of the present invention is to diagnose faults in power conversion units without relying on the switching signal.

[0005] In order to solve the above-mentioned problems, one aspect of the present invention provides a fault diagnosis method for a power conversion unit that converts power input from a power source. In this method, a status signal indicating the on / off state of a switch connecting the power source to the power conversion unit and an output signal of a sensor that detects the input voltage of the power conversion unit are acquired. When the switch state indicated by the acquired status signal is on, it is determined whether the input voltage indicated by the acquired output signal is outside a normal range of input voltage. If it is determined that the input voltage indicated by the output signal is outside the normal range when the switch state indicated by the status signal is on, it is diagnosed that there is a possibility of a fault in the sensor.

[0006] According to the present invention, a fault in a power conversion unit can be diagnosed without using a switching signal.

[0007] Fig. 1 is a configuration diagram of a power conversion unit according to an embodiment of the present invention. Fig. 2 is a flowchart of a sensor fixation diagnosis process. Fig. 3 is a timing chart showing the transition of the diagnosis content of the diagnosis unit when the state of the main relay in Fig. 1 switches from on to off. Fig. 4 is a flowchart of a terminal state diagnosis process. Fig. 5 is a flowchart of an efficiency diagnosis process. Fig. 6 is a flowchart of a differential voltage diagnosis process.

[0008] [Configuration of a Power Conversion Unit According to an Embodiment] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings, identical components are designated by the same reference numerals, and their description will be omitted. FIG. 1 is a diagram showing an example of the configuration of a power conversion unit in which a fault diagnosis device according to an embodiment of the present invention is implemented. The power conversion unit 10 according to the embodiment is mounted on an electric vehicle (EV; not shown) having a high-voltage battery unit 20, a low-voltage battery 30, and a first controller 40. A third controller 140 (described later) of the power conversion unit 10, a second controller 230 (described later) of the high-voltage battery unit 20, and the first controller 40 may be configured, for example, by an ECU (Electronic Control Unit) of the electric vehicle. When each is configured by an ECU, each may be configured by a separate ECU. The ECUs can transmit and receive signals to each other via an in-vehicle network such as a Controller Area Network (CAN).

[0009] For example, signals indicating the status of each part of the electric vehicle are input to the first controller 40. The first controller 40 generates a relay control signal that controls the on / off of the main relay 220 based on the status of each part of the electric vehicle. The first controller 40 transmits the relay control signal to the second controller 230. The signals input to the first controller 40 include a status signal of the main relay 220 input from the second controller 230. The status signal indicates the on / off state of the main relay 220. The first controller 40 can output the status signal input from the second controller 230 to the third controller 140 of the power conversion unit 10. The high-voltage battery unit 20 includes a high-voltage battery 210, a main relay 220, and a second controller 230. The high-voltage battery 210 can be configured using, for example, a lithium-ion battery. The high-voltage battery 210 constitutes the power source of the electric vehicle. The high-voltage battery 210 can supply high-voltage DC power to a propulsion motor (not shown) of the electric vehicle via the main relay 220. The high-voltage battery 210 can be charged by regenerative power supplied from the propulsion motor via the main relay 220. The main relay 220 constitutes a switch that connects the high-voltage battery 210 to the power conversion unit 10. The second controller 230 outputs a relay drive signal to the main relay 220 based on a relay control signal received by the second controller 230 from the first controller 40. The main relay 220 is turned on and off based on the relay drive signal. The second controller 230 can detect the on / off state of the main relay 220, for example, based on the relay drive signal. The second controller 230 transmits a status signal indicating the detected on / off state of the main relay 220 to the first controller 40. The low-voltage battery 30 supplies low-voltage power for operation to the first controller 40, the second controller 230, the third controller 140, and a low-voltage load 50 serving as a load on the electric vehicle. The low-voltage load 50 refers to accessories in the electric vehicle that operate using the low-voltage power from the low-voltage battery 30. The low-voltage battery 30 can be configured using, for example, a lead battery.

[0010] The power conversion unit 10 has a high-voltage terminal 101 as an input terminal to which high-voltage DC power is input from the high-voltage battery unit 20. In addition to the high-voltage terminal 101, the power conversion unit 10 also has a power conversion device 110, an input voltage sensor 120, an output voltage sensor 130, and a third controller 140. The power conversion device 110 converts DC power from the high-voltage battery 210 from high voltage to low voltage and supplies the converted power to the low-voltage battery 30. The low-voltage battery 30 is charged with the low-voltage power supplied from the power conversion device 110. In this embodiment, a case will be described in which the power conversion device 110 is configured using a DC-DC converter. The power conversion device 110 of this embodiment has a primary side circuit 111, an isolation transformer 112, and a secondary side circuit 113 that configure the DC-DC converter. The primary circuit 111 causes a current resulting from high-voltage DC power input from the high-voltage battery 210 to the high-voltage terminal 101 to flow through the primary winding of the isolation transformer 112 while switching the direction of the current. The secondary circuit 113 outputs low-voltage DC power obtained from an induced current flowing through the secondary winding in accordance with the turns ratio of the isolation transformer 112. The power output from the secondary circuit 113 of the power conversion device 110 is supplied to the low-voltage battery 30 as charging power and also to the low-voltage load 50. The input voltage sensor 120 detects the voltage of the high-voltage DC power input to the high-voltage terminal 101 as the input voltage of the power conversion device 110. The output voltage sensor 130 detects the voltage of the low-voltage DC power output by the secondary circuit 113 to the low-voltage battery 30 and the low-voltage load 50 as the output voltage of the power conversion device 110.

[0011] The power conversion unit fault diagnosis method according to the embodiment of the present invention can be executed by a third controller 140. The third controller 140 includes a general-purpose microcontroller equipped with a calculation unit and an input / output unit. The calculation unit includes a central processing unit (CPU) and a memory. The memory includes a read-only memory (ROM) and a readable / writable random access memory (RAM). The calculation unit of the third controller 140 can virtually configure multiple information processing circuits by having the CPU execute a program stored in the ROM. One of the information processing circuits configured in the calculation unit of the third controller 140 outputs a switching signal to a switching circuit (not shown) in the primary circuit 111 of the power conversion device 110. The direction of the current flowing through the primary winding of the isolation transformer 112 can be switched by the switching signal output by the third controller 140. The multiple information processing circuits configured in the calculation unit of the third controller 140 can constitute, for example, an acquisition unit 141, a determination unit 142, and a diagnosis unit 143 of the third controller 140. The information processing circuit of the third controller 140 may be configured with dedicated hardware. The dedicated hardware may include devices such as an application-specific integrated circuit (ASIC) or conventional circuit components arranged to perform the required information processing functions. The third controller 140 receives a status signal of the main relay 220 from the first controller 40, as well as output signals from the input voltage sensor 120 and the output voltage sensor 130. The acquisition unit 141 acquires the signals input to the third controller 140. The acquisition unit 141 acquires at least the output signal of the input voltage sensor 120, and, if necessary, the output signal of the output voltage sensor 130 and the status signal of the main relay 220. The determination unit 142 makes a determination on the signals acquired by the acquisition unit 141. The determination made by the determination unit 142 will be described later. The diagnosis unit 143 performs a diagnosis on the power conversion unit 10 based on the determination made by the determination unit 142. The diagnosis made by the diagnosis unit 143 includes a diagnosis of sensor failure.The sensor to be diagnosed is the input voltage sensor 120 that detects the voltage of the high voltage DC power input to the high voltage terminal 101. The details of the diagnosis performed by the diagnosing unit 143 will be described later.

[0012] First Embodiment In the first embodiment, the third controller 140 performs a sensor sticking diagnostic process. "Sensor sticking" refers to a state in which the sensor output is stuck and does not fluctuate. When the sensor output is stuck, even if the physical quantity detected by the sensor changes, the sensor output does not change accordingly, and the sensor enters a state of output sticking fault. The sensor sticking diagnostic process is performed on the input voltage sensor 120 of the power conversion unit 10 as the diagnostic target. When the input voltage sensor 120 experiences an output sticking fault, the output of the input voltage sensor 120 does not change in response to fluctuations in the input voltage of the power conversion device 110.

[0013] FIG. 2 is a flowchart showing an example of the sensor sticking diagnosis process. In the sensor sticking diagnosis process, the acquisition unit 141 acquires a status signal of the main relay 220 and an output signal of the input voltage sensor 120 (step S101). The third controller 140 checks whether the state of the main relay 220 indicated by the status signal acquired by the acquisition unit 141 is on (step S102). If the state of the main relay 220 is off (NO in step S102), the sensor sticking diagnosis process ends. If the state of the main relay 220 is on (YES in step S102), the determination unit 142 determines whether the input voltage of the power conversion device 110 indicated by the output signal of the input voltage sensor 120 is outside the normal input voltage range (step S103). The normal input voltage range refers to the input voltage range in which the connection between the high-voltage battery 210 and the power conversion unit 10 is permitted when the main relay 220 is on. If the input voltage is not outside the normal range (NO in step S103), the sensor sticking diagnosis process ends. The acquisition unit 141 can intermittently and repeatedly acquire the output signal of the input voltage sensor 120 by repeating the procedure of FIG. 2 . Each time the acquisition unit 141 acquires the output signal of the input voltage sensor 120, the determination unit 142 determines whether the input voltage of the power conversion device 110 is outside the normal range. If the determination unit 142 determines that the input voltage is outside the normal range (YES in step S103), it checks whether it has determined that the input voltage has been outside the normal range a predetermined number of times in a row (step S104). If the determination unit 142 has not determined that the input voltage is outside the normal range a predetermined number of times in a row (NO in step S104), it terminates the sensor sticking diagnosis process. If the determination unit 142 determines that the input voltage is outside the normal range a predetermined number of times in a row (YES in step S104), the diagnosis unit 143 diagnoses that the input voltage sensor 120 may be faulty (step S105) and terminates the sensor sticking diagnosis process. Specifically, the possibility of a failure of the input voltage sensor 120 may be the possibility of a stuck output failure of the input voltage sensor 120. Step S104 of the sensor stuck diagnosis process may be omitted.If step S104 is omitted, once determination unit 142 determines in step S103 that the input voltage is outside the normal range, diagnosis unit 143 immediately diagnoses in step S105 that there is a possibility of a malfunction in input voltage sensor 120. Execution of step S104 is significant in improving the diagnostic accuracy of diagnosis unit 143, for example, in the case described below.

[0014] 3 is a timing chart showing an example of the transition of the diagnosis content of the diagnoser 143 when the state of the main relay 220 switches from on to off. Vth indicates a threshold value on the upper side of the normal range for the input voltage Vin of the power conversion device 110. The on / off state of the main relay 220 indicated by the state signal of the main relay 220 switches with a slight delay after the on / off state of the main relay 220 actually switches. This delay occurs, for example, due to the communication time it takes for the state signal of the main relay 220 to be input from the second controller 230 via the first controller 40 to the third controller 140. For example, assume a case in which the input voltage Vin of the power conversion device 110 increases for some reason during the delay time Tdl between when the main relay 220 actually switches from on to off and when the state signal of the main relay 220 switches from on to off. Possible circumstances include, for example, noise generated in the power conversion unit 10 or the power-on of a peripheral device (not shown) of the power conversion unit 10. In this case, even after the actual main relay 220 is turned off, the status signal of the main relay 220 indicates the on state for the delay time Tdl. If the input voltage Vin exceeds the upper threshold value Vth during the delay time Tdl, the determination unit 142 determines that the input voltage Vin of the power conversion device 110 indicated by the output signal is outside the normal range while the main relay 220 is on. If the determination unit 142 determines once that the input voltage Vin is outside the normal range, and the diagnosis unit 143 immediately diagnoses that the input voltage sensor 120 may have an output fixation fault, the diagnostic accuracy of the diagnosis unit 143 may be lower in the above-described case than in other cases. By not omitting step S104 and executing it, the diagnostic accuracy of the diagnosis unit 143 can be improved in the above-described case.

[0015] The predetermined number of times used in the determination of step S104 in FIG. 2 can be determined based on the delay time Tdl. For example, as shown in FIG. 3 , if the period during which the output signal of the input voltage sensor 120 is intermittently and repeatedly acquired is an acquisition period T, the predetermined number of times used in the determination of step S104 may be a positive integer number that is at least one greater than the value obtained by dividing the delay time Tdl by the acquisition period T. In the example of FIG. 3 , the delay time Tdl is longer than one acquisition period T but shorter than two acquisition periods T. In this case, the timing for acquiring the output signal of the input voltage sensor 120 occurs up to two times during the delay time Tdl. Due to the delay between the on / off state switching of the main relay 220 and the on / off state switching indicated by the status signal of the main relay 220, there is a possibility that the input voltage Vin indicated by the output signal of the input voltage sensor 120 will fall outside the normal range up to two consecutive times. The value obtained by dividing the delay time Tdl by the acquisition period T is greater than one and less than two. If the predetermined number of times is set to three or more times, which is one or more times greater than this value, it is possible to prevent the diagnostic unit 143 from making an erroneous diagnosis even if the input voltage Vin indicated by the output signal of the input voltage sensor 120 falls outside the normal range due to the influence of a delay in the status signal. The acquisition period T of the output signal of the input voltage sensor 120 may be set to a time length that exceeds the delay time Tdl, and the predetermined number of times may be set to two or more times. In this case, it is possible to prevent the diagnostic unit 143 from making an erroneous diagnosis due to the influence of a delay in the status signal.

[0016] In the power conversion unit 10 of the first embodiment, the time during which the switching circuit of the primary side circuit 111 of the power conversion device 110 is turned on by the switching signal varies depending not only on the input voltage of the power conversion device 110 but also on the voltage of the low-voltage battery 30. The input voltage of the power conversion device 110 cannot be calculated from the on time of the switching signal. When the status signal of the main relay 220 indicates that the main relay 220 is on, the second controller 230 receives a relay control signal to turn on the main relay 220. The first controller 40, which outputs this relay control signal, determines that there is no problem in turning on the main relay 220 and connecting the high-voltage battery 210 to the power conversion unit 10. Since the main relay 220 is turned on based on this determination, the input voltage of the power conversion device 110, to which power from the high-voltage battery 210 is input via the main relay 220, should be within the normal range for the input voltage of the power conversion device 110. If the output signal of the input voltage sensor 120 indicates an abnormal voltage value outside the normal range of the input voltage of the power conversion device 110 while the status signal of the main relay 220 is in the ON state, a reasonable doubt arises as to the normality of the input voltage sensor 120. In the power conversion unit 10 of the first embodiment, a fault in the input voltage sensor 120 can be diagnosed without using a switching signal. In the first embodiment, if the output signal of the input voltage sensor 120 indicates an abnormal voltage value when the status signal of the main relay 220 is on, there is a possibility that the output of the input voltage sensor 120 is not changing in accordance with fluctuations in the input voltage of the power conversion device 110. In this case, it can be diagnosed that the input voltage sensor 120 has a possible fault, specifically, a fixed output fault. In the first embodiment, when the high-voltage battery 210 is connected to the power conversion unit 10 by turning on the main relay 220, the first controller 40 should have determined in advance that it is safe to connect the high-voltage battery 210 to the power conversion unit 10. Based on this determination, the main relay 220 is turned on, and therefore the input voltage Vin of the power conversion device 110 to which the high-voltage battery 210 is connected via the turned-on main relay 220 should be a normal value.For example, whether the input voltage Vin of the power conversion device 110 is normal can be easily determined by determining whether the input voltage Vin is within a normal range, which is the range of the input voltage Vin when the high-voltage battery 210 can be connected to the power conversion unit 10 without any problems. In the first embodiment, when step S104 of FIG. 2 is executed, the possibility of a malfunction of the input voltage sensor 120 is diagnosed when the input voltage Vin of the power conversion device 110 falls outside the normal range not just once but a predetermined number of times in succession, thereby improving the accuracy of the diagnosis. In the first embodiment, when the input voltage Vin indicated by the output signal of the input voltage sensor 120 exceeds the upper threshold Vth, the determination unit 142 determines that the input voltage Vin exceeded the upper threshold Vth while the main relay 220 was on, even if this occurs during the delay time Tdl. In this case, the diagnosis unit 143 erroneously diagnoses that the input voltage sensor 120 may be malfunctioning, even if the input voltage sensor 120 is operating normally. When the delay time Tdl has elapsed, the status signal of the main relay 220 changes to OFF, and the determination unit 142 no longer determines that the input voltage Vin has exceeded the upper threshold value Vth while the main relay 220 was ON, which may cause an erroneous diagnosis by the diagnosing unit 143. If the input voltage Vin indicated by the output signal falls outside the normal range and continues to fall outside the normal range for longer than the delay time Tdl while the status signal of the main relay 220 is ON, it is possible to diagnose that there is a possibility of a malfunction in the input voltage sensor 120, thereby preventing erroneous diagnosis due to the delay time Tdl.

[0017] Second Embodiment In the power conversion unit 10 of the second embodiment, the third controller 140 performs at least one of a terminal state diagnosis, an efficiency diagnosis, and a differential voltage diagnosis in addition to the sensor stuck diagnosis described in the first embodiment. The terminal state diagnosis and the efficiency diagnosis are performed with the main relay 220 turned on and the low voltage load 50 of the electric vehicle not being driven. The differential voltage diagnosis is performed with the main relay 220 turned on and the low voltage load 50 being driven. The order in which the terminal state diagnosis, the efficiency diagnosis, the sensor stuck diagnosis, and the differential voltage diagnosis are performed is not particularly specified.

[0018] The terminal state diagnosis is a process for diagnosing the connection state of the high-voltage battery unit 20 to the high-voltage terminal 101 of the power conversion unit 10. The efficiency diagnosis and the differential voltage diagnosis are processes for diagnosing the possibility of a malfunction of the input voltage sensor 120, similar to the sensor stuck diagnosis.

[0019] The "terminal state" in the terminal state diagnosis process refers to the state of the high-voltage terminal 101 to which the high-voltage battery 210 of the power conversion unit 10 is connected. The terminal state diagnosis process diagnoses whether the high-voltage terminal 101 is short-circuited or open-circuited. For example, if the input voltage Vin of the power conversion device 110 is 0 even though the main relay 220 is turned on, there is a possibility that the high-voltage terminal 101 is short-circuited or open-circuited.

[0020] FIG. 4 is a flowchart showing an example of the terminal status diagnosis process. In the terminal status diagnosis process, the third controller 140 checks whether the state of the main relay 220 indicated by the state signal acquired by the acquisition unit 141 is on (step S001). If the main relay 220 is off (NO in step S001), the terminal status diagnosis process ends. If the main relay 220 is on (YES in step S001), the third controller 140 stops driving the low-voltage load 50 to which low-voltage DC power is supplied from the power conversion device 110 (step S002). If the low-voltage load 50 is not driving, the process of step S002 is unnecessary. By stopping the driving of the low-voltage load 50, the low-voltage load 50 can be electrically disconnected from the high-voltage terminal 101, and the process for diagnosing the state of the high-voltage terminal 101, which will be described later, can be performed. The acquisition unit 141 acquires the output signal of the input voltage sensor 120 while driving of the low-voltage load 50 is stopped (step S003). The third controller 140 checks whether the input voltage Vin of the power conversion device 110 indicated by the output signal of the input voltage sensor 120 is 0 (step S004). If the input voltage Vin is not 0 (NO in step S004), the terminal status diagnosis process ends. The acquisition unit 141 can intermittently and repeatedly acquire the output signal of the input voltage sensor 120, for example, by repeating the procedure of FIG. 4 . Each time the acquisition unit 141 acquires the output signal of the input voltage sensor 120, the third controller 140 checks whether the input voltage Vin of the power conversion device 110 is 0. If the input voltage Vin is 0 (YES in step S004), the determination unit 142 determines whether the state of input voltage Vin = 0 has continued for a predetermined period (step S005). If the determination unit 142 does not determine that the state of input voltage Vin = 0 has continued for a predetermined period (NO in step S005), the terminal status diagnosis process ends. If the judgment unit 142 judges that the state of input voltage Vin = 0 has continued for a predetermined period (YES in step S005), the diagnosis unit 143 diagnoses that the high voltage terminal 101 may be short-circuited or open (step S006), and terminates the terminal state diagnosis process.

[0021] If there is a possibility that the high voltage terminal 101 of the power conversion device 110 is short-circuited or open, even if a diagnosis of a possible failure of the input voltage sensor 120 is made in that state, a highly accurate diagnosis may not be possible. For example, when performing terminal state diagnosis processing in the power conversion unit 10 of the second embodiment, if the terminal state diagnosis processing does not diagnose a possibility of a short-circuit or open circuit in the high voltage terminal 101, the efficiency diagnosis processing, the sensor sticking diagnosis processing, and the differential voltage diagnosis processing may be performed. By performing the terminal state diagnosis processing first, it is possible to perform highly accurate diagnoses based on the diagnosis results of the terminal state diagnosis processing in the subsequent efficiency diagnosis processing, the sensor sticking diagnosis processing, and the differential voltage diagnosis processing.

[0022] The "efficiency" in the efficiency diagnosis process refers to the power conversion efficiency of the DC-DC converter of the power conversion unit 10. The power conversion efficiency can be calculated by dividing the input voltage Vin of the power conversion device 110, indicated by the output signal of the input voltage sensor 120, by the output voltage Vout of the power conversion device 110, indicated by the output signal of the output voltage sensor 130. In the efficiency diagnosis process, the third controller 140 calculates the power conversion efficiency while the power conversion device 110 is operating without driving the low-voltage load 50. For example, if the power conversion efficiency calculated by the third controller 140 is too low considering the expected loss in the power conversion device 110, the input voltage sensor 120 may be faulty. A failure of the input voltage sensor 120 may also occur when the calculated power conversion efficiency is too high compared to the expected value. If the power conversion efficiency significantly deviates from the expected value, the input voltage sensor 120 may be experiencing an offset failure, in which the input voltage Vin indicated by the output signal deviates from the true value.

[0023] 5 is a flowchart showing an example of the efficiency diagnosis process. In the efficiency diagnosis process, the third controller 140 checks whether the state of the main relay 220 indicated by the state signal acquired by the acquisition unit 141 is on (step S011). If the state of the main relay 220 is off (NO in step S011), the efficiency diagnosis process ends. If the state of the main relay 220 is on (YES in step S011), the third controller 140 stops driving the low-voltage load 50 to which low-voltage DC power is supplied from the power conversion device 110 (step S012). If the low-voltage load 50 is not driving, the process of step S012 is unnecessary. The acquisition unit 141 acquires output signals from the input voltage sensor 120 and the output voltage sensor 130 while driving of the low-voltage load 50 is stopped (step S013). The acquisition unit 141 performs the process of step S013 while the third controller 140 operates the power conversion device 110 for a short period of time and the secondary-side circuit 113 is outputting low-voltage DC power. The third controller 140 divides the input voltage Vin of the power conversion device 110, indicated by the output signal of the input voltage sensor 120, by the output voltage Vout of the power conversion device 110, indicated by the output signal of the output voltage sensor 130, to obtain an evaluation value of the power conversion efficiency (step S014). When the secondary-side circuit 113 outputs low-voltage DC power, the increase in the output voltage Vout of the power conversion device 110 detected by the output voltage sensor 130 is delayed relative to the output of the low-voltage DC power due to the presence of the low-voltage battery 30 connected to the secondary-side circuit 113. Taking this delay into account, the third controller 140 may, in step S014, obtain the evaluation value of the power conversion efficiency using the output signal of the output voltage sensor 130 obtained a predetermined time after the output signal of the input voltage sensor 120 was obtained. The predetermined time may be, for example, a time corresponding to the rate at which the terminal voltage of the low-voltage battery 30, which is charged by the low-voltage DC power converted by the power conversion device 110, changes due to charging by the low-voltage DC power of the power conversion device 110. The output voltage Vout used to determine the evaluation value may be, for example, the output voltage Vout indicated by the output signal of the output voltage sensor 130 acquired a predetermined time after the output signal of the input voltage sensor 120 is acquired.The output voltage Vout used to calculate the evaluation value may be, for example, a time-corrected output voltage obtained by correcting the output voltage Vout indicated by the output signal output from the output voltage sensor 130 at the time the output signal from the input voltage sensor 120 is acquired with a value corresponding to a predetermined time. A map may be used for the time correction of the output voltage Vout. For example, the map may associate the output voltage Vout indicated by the output signal output from the output voltage sensor 130 at the time the output signal from the input voltage sensor 120 is acquired with the time-corrected output voltage. Instead of the time-corrected output voltage, the map may also associate a correction value or correction content for calculating the time-corrected output voltage from the output voltage Vout indicated by the output signal output from the output voltage sensor 130. The map may be based on, for example, data acquired in advance through experiments. Performing time correction of the output voltage Vout based on experimental data can improve the diagnostic accuracy of the efficiency diagnostic process based on the evaluation value. The determination unit 142 determines whether the evaluation value calculated by the third controller 140 is outside a predetermined range (step S015). The predetermined range refers to the range of evaluation values ​​corresponding to the rated power conversion efficiency of the power conversion device 110. If the evaluation value is not outside the predetermined range (NO in step S015), the efficiency diagnosis process ends. If the determination unit 142 determines that the evaluation value is outside the predetermined range (YES in step S015), the diagnosis unit 143 diagnoses that there is a possibility of a malfunction in the input voltage sensor 120 (step S016). Specifically, the possibility of a malfunction in the input voltage sensor 120 can be determined as the possibility of an offset malfunction in the input voltage sensor 120.

[0024] The "differential voltage" in the differential voltage diagnosis process refers to the differential voltage between the voltage of the high-voltage battery 210 detected by another unit 60 of the electric vehicle shown in FIG. 1 and the input voltage Vin of the power conversion device 110 indicated by the output signal of the input voltage sensor 120. The other unit 60 refers to a unit other than the power conversion unit 10 that receives high-voltage DC power from the high-voltage battery 210 and is capable of communicating with the third controller 140 via the in-vehicle network. The other unit 60 may be, for example, a high-voltage battery unit 20 that includes the high-voltage battery 210. The other unit 60 may be, for example, an inverter unit or an on-board charger (not shown). The inverter unit is disposed between the high-voltage battery unit 20 and an electric motor (not shown), which is the propulsion source of the electric vehicle. The on-board charger is installed on the electric vehicle as a charger for the high-voltage battery 210. The other unit 60 is not limited to the above examples. The other units 60 to which high-voltage DC power from the high-voltage battery 210 is input may independently detect the voltage of the high-voltage battery 210. The third controller 140 acquires a detection signal indicating the voltage of the high-voltage battery 210 detected in the other units 60 from the other units 60 via the in-vehicle network. In a differential voltage diagnosis process, the third controller 140 compares the input voltage Vin of the power conversion device 110 indicated by the output signal of the input voltage sensor 120 with the voltage of the high-voltage battery 210 detected in the other units 60. The third controller 140 diagnoses the possibility of a malfunction of the input voltage sensor 120 based on the result of this comparison.

[0025] FIG. 6 is a flowchart showing an example of the differential voltage diagnosis process. In the differential voltage diagnosis process, the third controller 140 checks whether the input voltage sensor 120 has been diagnosed as possibly malfunctioning in the efficiency determination process or the sensor sticking diagnosis process (step S111). If the input voltage sensor 120 has not been diagnosed as possibly malfunctioning (NO in step S111), the process proceeds to step S119, which will be described later. If the input voltage sensor 120 has been diagnosed as possibly malfunctioning (YES in step S111), the third controller 140 drives the low voltage load 50 (step S112). While the low voltage load 50 is being driven, the acquisition unit 141 acquires the output signal of the input voltage sensor 120 and the voltage of the high-voltage battery 210 detected in the other unit 60 (step S113). The acquisition unit 141 acquires the output signal of the input voltage sensor 120 and the voltage of the high-voltage battery 210 detected in the other unit 60 at the same time. The acquisition unit 141 performs the process of step S113 while the third controller 140 is operating the power conversion device 110 and the secondary-side circuit 113 is outputting low-voltage DC power. The third controller 140 calculates a differential voltage between the voltage of the high-voltage battery 210 acquired from the other unit 60 and the input voltage Vin of the power conversion device 110 indicated by the output signal of the input voltage sensor 120 (step S114). The differential voltage may be the absolute value of the difference. The determination unit 142 determines whether the differential voltage calculated by the third controller 140 exceeds a predetermined voltage (step S115). The predetermined voltage is a threshold indicating an acceptable range for the differential voltage. If the determination unit 142 determines that the evaluation value exceeds the predetermined voltage (YES in step S115), the diagnosis unit 143 diagnoses that the input voltage sensor 120 may be faulty (step S116). Specifically, the possibility of a failure of the input voltage sensor 120 can be the possibility of a voltage monitor abnormality failure of the input voltage sensor 120. A voltage monitor abnormality failure is a failure in which the input voltage sensor 120 outputs, as an output signal, a signal indicating a voltage different from the actual input voltage Vin of the power conversion device 110.The third controller 140 operates the power conversion device 110 diagnosed by the diagnosing unit 143 as having a possible malfunction in the input voltage sensor 120 at less than the rated maximum capacity through derating operation (step S117). If the determining unit 142 determines that the evaluation value is equal to or less than a predetermined voltage (NO in step S115), the diagnosing unit 143 diagnoses the input voltage as abnormal (step S118) and proceeds to step S119. An "input voltage abnormality" refers to an abnormality in the high-voltage DC power input from the high-voltage battery unit 20 to the high-voltage terminal 101 of the power conversion unit 10. If the evaluation value is a value other than 0 that is equal to or less than a predetermined voltage, it is considered that the input voltage sensor 120 is not malfunctioning, but that the actual input voltage Vin of the power conversion device 110 deviates from its intended voltage value. In step S119, the third controller 140 operates the power conversion device 110 diagnosed by the diagnosing unit 143 as having an input voltage abnormality at the rated maximum capacity through normal operation. After step S119, the differential voltage diagnosis process ends. Multiple predetermined voltages may be set for the determination in step S115 of FIG. 6 depending on the magnitude of the differential voltage. If multiple predetermined voltages are set, the determination unit 142 determines whether the differential voltage calculated by the third controller 140 exceeds each predetermined voltage in step S115. If the differential voltage exceeds at least one predetermined voltage (YES in step S115), the third controller 140 may set the derating operation in step S117 to the largest predetermined voltage among the predetermined voltages exceeded by the differential voltage. In this case, the derating operation of the power conversion device 110 can be changed according to the severity of the potential voltage monitor abnormality, thereby improving the robustness of the power conversion unit 10 against failures. If the differential voltage diagnosis process is not performed, a procedure for changing the operation of the power conversion device 110 in accordance with the diagnosis of a failure of the power conversion unit 10 in the differential voltage diagnosis process may be added to the sensor stuck diagnosis process or the efficiency diagnosis process. For example, in the case of the sensor sticking diagnosis process of FIG. 2, after the diagnosis of step S105, the process of step S117 of FIG. 6 is performed, and if the result of the confirmation or determination is NO in any of steps S102 to S104, the process of step S119 of FIG. 6 is performed.For example, in the case of the efficiency diagnosis process of FIG. 5, after the diagnosis of step S016, the process of step S117 of FIG. 6 is performed, and if the result of confirmation or judgment is NO in either step S011 or step S015, the process of step S119 of FIG. 6 is performed.

[0026] In the power conversion unit 10 of the second embodiment, the acquisition unit 141 acquires the output voltage Vout of the power conversion device 110 while the drive of the low-voltage load 50 is stopped. The acquired output voltage Vout is lower than the calculated output voltage corresponding to the winding ratio of the isolation transformer 112 of the power conversion device 110, which constitutes the DC-DC converter of the power conversion device 110, by a voltage corresponding to the power loss due to self-consumption of the power conversion unit 10. The power conversion efficiency of the power conversion device 110 can be evaluated using an evaluation value calculated based on the input voltage Vin and output voltage Vout of the power conversion device 110. Because the power conversion device 110 has a rated power conversion efficiency, the evaluation value of the power conversion efficiency should be within a predetermined range corresponding to the rated power conversion efficiency of the power conversion device 110. In the second embodiment, when the efficiency diagnosis process is performed, it is possible to accurately diagnose whether the input voltage sensor 120 is likely to be faulty by determining whether the evaluation value is outside the predetermined range. In the second embodiment, if the evaluation value of the power conversion efficiency is outside a predetermined range when the status signal is on, the input voltage Vin indicated by the output signal of the input voltage sensor 120 may be offset beyond an allowable range relative to the true value of the input voltage Vin. In this case, the efficiency diagnosis process can diagnose the input voltage sensor 120 as having a possible fault, i.e., an offset fault in the input voltage sensor 120. In the second embodiment, the low-voltage battery 30 is connected to the power conversion device 110 even when the low-voltage load 50 is stopped from being driven. When the output voltage Vout of the power conversion device 110 changes, the terminal voltage of the low-voltage battery 30 changes with a delay relative to the change in the output voltage Vout of the power conversion device 110. This delay corresponds to the time width corresponding to the difference between the rate at which the output voltage Vout of the power conversion device 110 changes and the rate at which the terminal voltage of the low-voltage battery 30 changes due to charging. In the second embodiment, in the efficiency diagnosis process, this time width is set to a predetermined time, and the evaluation value of the power conversion efficiency of the power conversion device 110 is calculated using the input voltage Vin of the power conversion device 110 at a certain point in time and the output voltage Vout at a point in time a predetermined time after that point in time.By calculating an evaluation value using the input voltage Vin at a certain time point and the output voltage Vout at a certain time point after a predetermined time, it is possible to accurately diagnose a possible malfunction of the input voltage sensor 120 using the evaluation value in the efficiency diagnosis process. In the second embodiment, the evaluation value can be calculated using a time-corrected output voltage obtained by correcting the output voltage Vout indicated by the output voltage sensor 130 at the time of acquisition of the input voltage sensor 120 with content corresponding to the predetermined time. In this case, in the efficiency diagnosis process, the evaluation value can be calculated using the output signal of the input voltage sensor 120 and the output signal of the output voltage sensor 130 acquired at the same time point. In the second embodiment, the input voltage Vin acquired by the input voltage sensor 120 when the operation of the low voltage load 50 is stopped should be the same as the voltage of the high-voltage battery 210 detected in another unit 60 to which high-voltage DC power from the high-voltage battery 210 is input. When the input voltage sensor 120 is diagnosed as possibly having a malfunction, if the differential voltage between the voltage of the high-voltage battery 210 and the input voltage Vin, as indicated by the detection signal acquired from the other unit 60, exceeds a predetermined voltage, it is considered that there is an abnormality in the output signal of the input voltage sensor 120. In the second embodiment, when performing the differential voltage diagnosis process, the input voltage sensor 120 is diagnosed as having a malfunction based on the abnormality in the output signal of the input voltage sensor 120, thereby improving the accuracy of the diagnosis. In the second embodiment, even if the input voltage sensor 120 of a power conversion unit 10 malfunctions, the power conversion function of the power conversion device 110 in the same power conversion unit 10 can be maintained. When the input voltage sensor 120 is diagnosed as having a malfunction, the power conversion device 110 is operated in a derating mode, thereby allowing the power conversion unit 10 to continue operating at less than the rated maximum capacity without suspending operation, while taking into account the malfunction of the input voltage sensor 120. In the second embodiment, if the difference between the voltage of the high-voltage battery 210 indicated by the detection signal acquired from the other unit 60 and the input voltage Vin indicated by the output signal of the input voltage sensor 120 is equal to or less than a predetermined voltage, it is considered that there is an abnormality in the input voltage Vin, not a failure of the input voltage sensor 120. In this case, by diagnosing that the input voltage Vin of the power conversion device 110 is abnormal, it is possible to diagnose an abnormality caused by a factor other than the power conversion unit 10.In the second embodiment, if the input voltage Vin of the power conversion device 110 is diagnosed as abnormal, the diagnosis made before that diagnosis, which indicated a possible malfunction of the input voltage sensor 120, is considered to be caused by the abnormality of the input voltage Vin of the power conversion device 110 itself. In this case, the power conversion device 110 is operated at its rated maximum capacity through normal operation, thereby suppressing a decrease in the power conversion efficiency of the power conversion device 110. In the second embodiment, when the terminal status diagnosis process is performed, the output signal of the input voltage sensor 120 can be used to diagnose the possibility of a short circuit or open circuit in the high-voltage terminal 101 of the power conversion device 110, to which the high-voltage battery 210 is connected. This diagnosis can be performed before the low-voltage load 50 is driven by the low-voltage DC power supplied from the power conversion device 110, thereby avoiding a situation in which the low-voltage load 50 is driven in a short-circuit or open state of the high-voltage terminal 101.

[0027] In the first and second embodiments, the present invention is applied to a power conversion unit 10 that converts high-voltage power input from a high-voltage battery 210 serving as a power source for an electric vehicle into low-voltage power that is supplied by a low-voltage battery 30 of the electric vehicle to a low-voltage load 50 of the electric vehicle. The present invention can also be applied to fault diagnosis of a power conversion unit that converts power input from a power source and is used for purposes other than electric vehicles. Even when the present invention is applied to fault diagnosis of a power conversion unit used for purposes other than electric vehicles, the same effects as those of the first and second embodiments can be obtained.

[0028] The above-described embodiment and its modifications are merely examples of the present invention. Therefore, the present invention is not limited to the above-described embodiment, and various modifications can be made to the design and other aspects of the present invention without departing from the technical concept of the present invention.

[0029] 1 Electric vehicle, 10 Power conversion unit, 30 Low voltage battery, 50 Low voltage load, 60 Other units, 101 High voltage terminal, 120 Input voltage sensor, 141 Acquisition unit, 142 Determination unit, 143 Diagnosis unit, 210 High voltage battery, 220 Main relay, T Acquisition period, Tdl Delay time, Vin Input voltage, Vout Output voltage.

Claims

1. A method for diagnosing a fault in a power conversion unit that converts power input from a power source, comprising: acquiring a status signal indicating the on / off state of a switch connecting the power source to the power conversion unit, and an output signal of a sensor that detects the input voltage of the power conversion unit; determining whether the input voltage indicated by the acquired output signal is outside a normal range of the input voltage when the switch state indicated by the acquired status signal is on; and diagnosing a possible fault in the sensor if it is determined that the input voltage indicated by the output signal is outside the normal range when the switch state indicated by the status signal is on.

2. A fault diagnosis method for a power conversion unit as described in claim 1, in which, when the state of the switch indicated by the state signal is on and it is determined that the input voltage indicated by the output signal is outside the normal range, the sensor is diagnosed as having a possible output fixation fault, in which the output of the sensor does not change in response to fluctuations in the input voltage.

3. A fault diagnosis method for a power conversion unit according to claim 1 or 2, wherein the normal range is the range of input voltage that allows connection between the power supply and the power conversion unit when the switch is turned on.

4. A fault diagnosis method for a power conversion unit according to any one of claims 1 to 3, in which the output signal is intermittently and repeatedly acquired, and when the state of the switch indicated by the status signal is on, if it is determined that the input voltage indicated by the output signal is outside the normal range a predetermined number of times in succession, a diagnosis is made that there is a possibility of a fault in the sensor.

5. A fault diagnosis method for a power conversion unit according to claim 4, wherein the delay time of the status signal is the time from when the on / off state of the switch is actually changed until the on / off state of the switch indicated by the status signal is changed, and the predetermined number of times is the number of times that exceeds the value obtained by dividing the delay time by the acquisition period of the output signal by one or more, or the acquisition period is set to a time length that exceeds the delay time and the predetermined number of times is set to two.

6. A fault diagnosis method for a power conversion unit according to any one of claims 1 to 5, comprising: acquiring an output voltage of the power conversion unit while stopping the drive of a load to which power is supplied from the power conversion unit when the state signal indicates that the switch is on; determining an evaluation value of the power conversion efficiency of the power conversion unit based on the acquired output voltage and the input voltage indicated by the output signal acquired at a time point corresponding to the time point at which the output voltage was acquired; determining whether the obtained evaluation value is outside a predetermined range corresponding to the rated power conversion efficiency of the power conversion unit; and diagnosing a possible fault in the sensor if it is determined that the evaluation value is outside the predetermined range.

7. A fault diagnosis method for a power conversion unit as described in claim 6, wherein if it is determined that the evaluation value is outside the specified range when the state of the switch indicated by the state signal is on, it is diagnosed that there is a possibility of an offset fault in the sensor, in which the input voltage indicated by the output signal is offset beyond an allowable range with respect to the true value of the input voltage.

8. A fault diagnosis method for a power conversion unit as described in claim 7, wherein the evaluation value is calculated using the output voltage at a time a predetermined time after the time the output signal is acquired, and the predetermined time is set to a time corresponding to the rate at which the terminal voltage of a battery charged by the power converted by the power conversion unit changes due to the charging.

9. A fault diagnosis method for a power conversion unit as described in claim 8, wherein the output voltage obtained at the time of acquisition of the output signal is corrected with a content corresponding to the specified time, and the time-corrected output voltage is set to the output voltage at a time that is the specified time after the time of acquisition of the output signal.

10. A fault diagnosis method for a power conversion unit according to any one of claims 1 to 9, wherein, when it is diagnosed that the sensor may have a fault, the output signal is acquired while a load supplied with power from the power conversion unit is driven, and a detection signal indicating the voltage of the power supply detected in another unit connected to the power supply is acquired, and it is determined whether or not a differential voltage between the voltage of the power supply indicated by the detection signal acquired while the load is driven and the input voltage indicated by the output signal exceeds a predetermined voltage, and if it is determined that the differential voltage exceeds the predetermined voltage, the sensor diagnosed as having a possible fault is diagnosed as having a fault.

11. The fault diagnosis method for a power conversion unit according to claim 10, wherein, when the sensor is diagnosed as faulty, the power conversion unit is operated at less than its rated maximum capacity by derating.

12. A fault diagnosis method for a power conversion unit according to claim 10 or 11, wherein the input voltage is diagnosed as abnormal if it is determined that the differential voltage is equal to or less than the predetermined voltage.

13. The fault diagnosis method for a power conversion unit according to claim 12, wherein, when the input voltage is diagnosed as abnormal, the power conversion unit is operated in a normal operation mode at a rated maximum capacity.

14. A fault diagnosis method for a power conversion unit according to any one of claims 1 to 13, wherein the output signal is intermittently and repeatedly acquired, and when the state of the switch indicated by the status signal is on, the input terminal of the power conversion unit to which the power supply is connected is diagnosed as possibly being short-circuited or open-circuited if it is determined that the input voltage indicated by the output signal remains at 0 for a predetermined period of time while the drive of a load to which power is supplied from the power conversion unit is stopped.

15. A device for diagnosing a fault in a power conversion unit that converts power input from a power source, comprising: an acquisition unit that acquires a status signal indicating the on / off state of a switch that connects the power source to the power conversion unit and an output signal of a sensor that detects the input voltage of the power conversion unit; a determination unit that determines whether the input voltage indicated by the acquired output signal is outside a normal range of the input voltage when the state of the switch indicated by the acquired status signal is on; and a diagnosis unit that diagnoses that there is a possibility of a fault in the sensor when it is determined that the input voltage indicated by the output signal is outside the normal range.

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