Earth leakage detection device and vehicle power supply system

Abstract

In order to quickly and accurately perform failure analysis on a coupling capacitor of an earth leakage detection device, a voltage output unit (11a, OP1) generates a periodical voltage that changes periodically and applies the voltage to the other end of the coupling capacitor (Cc) via a first resistor (R1). A second resistor (R2) and a third resistor (R3) are connected in series between the connection point between the coupling capacitor (Cc) and the first resistor (R1) and a predetermined fixed potential. A voltage measurement unit (11b) measures the voltage at the voltage-dividing point between the second resistor (R2) and the third resistor (R3). A diagnosis unit (11d) determines whether the coupling capacitor (Cc) is normal or not, on the basis of the voltage measured when switches (MRp, MRm, MRpp) are turned on in a state in which a fixed voltage is output from the voltage output unit (11a, OP1).

Description

TECHNICAL FIELD

[0001] The present invention relates to an earth leakage detection device that detects anearth leakage from a load insulated from a ground, and a vehicle power supply system.BACKGROUND ART

[0002] In recent years, hybrid vehicles (HV), plug-in hybrid vehicles (PHV), and electricvehicles (EV) have become widespread. In these electric vehicles, a high-voltage drivingbattery (traction battery) is mounted separately from an auxiliary battery (generally, a leadbattery having an output of 12 V). In order to prevent an electric shock, a high-voltage circuitincluding a high-voltage driving battery, an inverter, and a drive motor are insulated from abody (chassis ground) of a vehicle.

[0003] Y capacitors are inserted between a positive wiring of the high-voltage circuit on avehicle side and the chassis ground and between a negative wiring of the high-voltage circuiton the vehicle side and the chassis ground, respectively, so that a power source suppliedfrom the high-voltage driving battery to the load on the vehicle side is stabilized. An earthleakage detection device that monitors an insulation resistance between the high-voltagecircuit and the chassis ground, and detects an earth leakage is mounted.

[0004] In an AC type earth leakage detection device, a pulse voltage is applied to a positiveelectrodeterminal or a negative-electrode terminal of a driving battery via a resistor and acoupling capacitor, a voltage at a node between the resistor and the coupling capacitor ismeasured, and presence or absence of an earth leakage is detected.

[0005] In the AC type earth leakage detection device, as a method of diagnosing a failureof the coupling capacitor, there is a method of diagnosing based on a fluctuation in crestvalue when a relay (contactor) between a battery and a vehicle is opened and closed. Whenthe fluctuation in crest value is less than or equal to a specified value, it is determined thatan abnormality has occurred in the coupling capacitor (see, for example, PTL 1).Citation ListPatent Literature

[0006] PTL 1: Unexamined Japanese Patent Publication No. 2004-53367SUMMARY OF THE INVENTIONTechnical problem

[0007] In the above-described coupling capacitor failure diagnosis method, it is necessaryto measure the fluctuation of the crest value, and thus it is necessary to specify a voltage ofa lower peak value as an upper peak value of the crest value. If the measurement timing ofthe upper peak value or the lower peak value deviates, an accurate crest value cannot bemeasured. In addition, since the crest value is not determined unless both the upper peakvalue and the lower peak value are measured, there is a time restriction on a measurementcycle of the crest value. It takes time to make a plurality of determinations. The same appliesto a case of diagnosing the failure of the coupling capacitor based on the fluctuation of theupper peak value of the crest value or the fluctuation of the lower peak value of the crestvalue.

[0008] The present disclosure has been made in view of such a situation, and an object ofthe present disclosure is to provide a technique for quickly and accurately performing failurediagnosis of a coupling capacitor of an earth leakage detection device.Solutions to problem

[0009] In order to solve the above problem, an earth leakage detection device according toan aspect of the present disclosure is an earth leakage detection device mounted on a vehicle,including a power storage unit that is mounted in a state of being insulated from a chassisground of the vehicle and supplies electric power to a load in the vehicle, and a switchinserted into a wiring connecting the power storage unit and the load, the earth leakagedetection device including: a coupling capacitor including one end connected to a currentpath of the power storage unit connected to the load in a state of being insulated from aground; a voltage output unit that generates a periodically changing periodic voltage andapplies the periodic voltage to the other end of the coupling capacitor via a first resistor; asecond resistor and a third resistor connected in series between a connection point betweenthe coupling capacitor and the first resistor, and a predetermined fixed potential; a voltagemeasurement unit that measures a voltage at a voltage dividing point between the secondresistor and the third resistor; an earth leakage determination unit that determines presenceor absence of an earth leakage between the current path of the power storage unit and theground based on a voltage measured by the voltage measurement unit in a state where theperiodic voltage is output from the voltage output unit; and a diagnosis unit that determineswhether or not the coupling capacitor is normal based on a voltage measured by the voltagemeasurement unit when the switch is turned on in a state where a fixed voltage is outputfrom the voltage output unit.Advantageous effect of invention

[0010] According to the present disclosure, the failure diagnosis of the coupling capacitorof the earth leakage detection device can be performed quickly and with high accuracy.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Fig. 1 is a diagram for explaining a configuration of a power supply systemincluding an earth leakage detection device according to a comparative example.Fig. 2 is a diagram illustrating an example of an applied pulse waveform and ameasured voltage waveform.Fig. 3 is a diagram illustrating an example of a measured waveform at the time offailure diagnosis of coupling capacitor Cc according to the comparative example.Fig. 4 is a diagram for explaining a configuration of a power supply systemincluding an earth leakage detection device according to an exemplary embodiment.Fig. 5 is a diagram illustrating an example of a measured waveform at the time offailure diagnosis of coupling capacitor Cc according to the exemplary embodiment.DESCRIPTION OF EMBODIMENT

[0012] (Comparative example)Fig. 1 is a diagram for explaining a configuration of power supply system 5including earth leakage detection device 10 according to a comparative example. Powersupply system 5 is mounted on an electric vehicle. Power supply system 5 is providedseparately from an auxiliary battery (typically, a lead battery with 12 V output is used) in theelectric vehicle. Power supply system 5 includes high-voltage power storage unit 20 andearth leakage detection device 10. Power storage unit 20 includes a plurality of cells E1 toEn connected in series. As the cells, a lithium ion battery cell, a nickel metal hydride batterycell, a lead battery cell, an electric double layer capacitor cell, a lithium ion capacitor cell,or the like can be used. Hereinafter, an example using a lithium ion battery cell (nominalvoltage: 3.6 V to 3.7 V) is assumed in the present specification.

[0013] The electric vehicle includes inverter 2 and motor 3 as high-voltage loads. Apositive electrode of power storage unit 20 and one end of inverter 2 are connected bypositive wiring Lp, and a negative electrode of power storage unit 20 and the other end ofinverter 2 are connected by negative wiring Lm. Large-capacity capacitor 4 is connected inparallel with inverter 2. Positive-side main relay MRp is inserted into positive wiring Lp,and negative-side main relay MRm is inserted into negative wiring Lm.

[0014] Precharge relay MRpp and precharge resistor Rp connected in series are connectedin parallel with positive-side main relay MRp. Precharge relay MRpp is turned on (closed)before positive-side main relay MRp is turned on (closed), whereby capacitor 4 can beprecharged with a limited current, and an inrush current can be suppressed. Note that theprecharge relay and the precharge resistor connected in series may be connected in parallelto negative-side main relay MRm.

[0015] Positive-side main relay MRp, precharge relay MRpp, and negative-side main relayMRm function as contactors that control conduction and cutoff between power storage unit20 and a high-voltage load in the electric vehicle. Note that, instead of the relay, asemiconductor switch having a high withstand voltage and a high insulation can be used.

[0016] Inverter 2 is a bidirectional inverter connected between power storage unit 20 andmotor 3. At the time of power running, inverter 2 converts DC power supplied from powerstorage unit 20 into AC power, and supplies the AC power to motor 3. At the time ofregeneration, the AC power supplied from motor 3 is converted into DC power, and the DCpower is supplied to power storage unit 20. For example, a three-phase AC motor is used asmotor 3. Motor 3 rotates in accordance with AC power supplied from inverter 2 at the timeof power running. At the time of regeneration, a rotational energy due to deceleration isconverted into AC power, and the AC power is supplied to inverter 2.

[0017] Power storage unit 20 is mounted on the electric vehicle in a state of being insulatedfrom a chassis ground of the electric vehicle. The auxiliary battery is mounted on the electricvehicle in a state where a negative electrode is electrically connected to the chassis ground.Note that positive wiring Lp on a side of inverter 2 with respect to positive-side main relayMRp and the chassis ground are connected via positive-side Y capacitor Cp. In addition,negative wiring Lm on the side of inverter 2 with respect to negative-side main relay MRmand the chassis ground are connected via negative-side Y capacitor Cm. Positive-side Ycapacitor Cp and negative-side Y capacitor Cm have a function of galvanically insulatingpositive wiring Lp and the chassis ground, and negative wiring Lm and the chassis ground,respectively, and stabilizing the voltages of positive wiring Lp and negative wiring Lm.

[0018] When power storage unit 20 is ideally insulated from the chassis ground, anintermediate potential of power storage unit 20 is maintained near the potential of the chassisground. For example, when the voltage across power storage unit 20 is 250 V, a positiveelectrode potential of power storage unit 20 is maintained around +125 V, and a negativeelectrode potential is maintained around -125 V. In a state in which high-voltage powerstorage unit 20 and the chassis ground are electrically connected to each other, there is a riskof an electric shock when a human touches an exposed conducting part of the electric vehicle.Therefore, in the electric vehicle on which high-voltage power storage unit 20 is mounted,it is necessary to mount earth leakage detection device 10 and monitor an insulation statebetween the current path of power storage unit 20 connected to the high-voltage vehicle load,and the chassis ground. In Fig. 1, an insulation state between positive wiring Lp and thechassis ground is represented as positive-side earth leakage resistance Rlp, and an insulationstate between negative wiring Lm and the chassis ground is represented as negative-sideearth leakage resistance Rlm.

[0019] In the comparative example, earth leakage detection device 10 includes couplingcapacitor Cc, first resistor R1, first operational amplifier OP1, second resistor R2, smoothingcapacitor C1, second operational amplifier OP2, and controller 11. Controller 11 includesoscillation unit 11a, voltage measurement unit 11b, earth leakage determination unit 11c,and diagnosis unit 11d. Controller 11 can include, for example, a microcomputer and anonvolatile memory (for example, an electrically erasable programmable read-only memory(EEPROM) and a flash memory).

[0020] One end of coupling capacitor Cc is connected to a current path of power storageunit 20. In the example illustrated in Fig. 1, one end of coupling capacitor Cc is connectedto the negative electrode of power storage unit 20. Note that one end of coupling capacitorCc may be connected to the positive electrode of power storage unit 20, or may be connectedto any node of the plurality of cells E1 to En in power storage unit 20. The other end ofcoupling capacitor Cc is connected to an output end of a voltage output unit via first resistorR1. A connection point between the other end of coupling capacitor Cc and first resistor R1is measurement point A. Note that another impedance element may be used instead of firstresistor R1.

[0021] In Fig. 1, an aluminum electrolytic capacitor capable of increasing the capacity at arelatively low cost is used as coupling capacitor Cc. The aluminum electrolytic capacitor haspolarity, and in Fig. 1, the positive electrode of the aluminum electrolytic capacitor isconnected to measurement point A, and the negative electrode of the aluminum electrolyticcapacitor is connected to the negative electrode of power storage unit 20. Coupling capacitorCc may be configured by connecting a plurality of aluminum electrolytic capacitors in series.In this case, even if a short-circuit failure occurs in one capacitor, galvanic insulation can bemaintained by the remaining capacitors.

[0022] The voltage output unit described above generates a periodically changing periodicvoltage, and applies the generated periodic voltage to the other end of coupling capacitor Ccvia first resistor R1. Hereinafter, an example in which a rectangular wave voltage is used asthe periodic voltage is assumed in the present specification.

[0023] The voltage output unit includes oscillation unit 11a and first operational amplifierOP1. Oscillation unit 11a includes a multivibrator and a local oscillator, and generates arectangular wave having a preset frequency. The rectangular wave voltage generated byoscillation unit 11a is input to a non-inverting input terminal of first operational amplifierOP1. An output terminal of first operational amplifier OP1 is connected to first resistor R1.An inverting input terminal and the output terminal of first operational amplifier OP1 areconnected. A positive power source terminal of first operational amplifier OP1 is connectedto a first fixed potential (power source potential Vcc), and a negative power source terminalof first operational amplifier OP1 is connected to a second fixed potential (ground potentialGND). Hereinafter, in the present specification, an example in which power source potentialVcc is 5 V and ground potential GND is 0 V is assumed.

[0024] First operational amplifier OP1 functions as a voltage follower that performs onlyimpedance conversion with an amplification factor of one time. Note that, instead of firstoperational amplifier OP1, an AND gate having one input terminal connected to the firstfixed potential or an OR gate having one input terminal connected to the second fixedpotential may be used. First operational amplifier OP1 can be substituted as long as theelement functions as a buffer that separates the impedance of controller 11 and theimpedance of measurement point A.

[0025] Measurement point A is connected to a non-inverting input terminal of secondoperational amplifier OP2 via second resistor R2. An inverting input terminal and an outputterminal of second operational amplifier OP2 are connected. Second operational amplifierOP2 also functions as a voltage follower that performs only impedance conversion with anamplification factor of one time. Smoothing capacitor C1 is connected between the noninvertinginput terminal of second operational amplifier OP2 and the second fixed potential(ground potential GND). Smoothing capacitor C1 removes noise of the voltage input to thenon-inverting input terminal of second operational amplifier OP2.

[0026] Second operational amplifier OP2 outputs a voltage at measurement point A tovoltage measurement unit 11b. Voltage measurement unit 11b measures the voltage atmeasurement point A. Voltage measurement unit 11b includes an A / D converter, and theA / D converter samples an analog voltage at measurement point A at timing synchronizedwith the timing of a rising edge and a falling edge of the rectangular wave voltage generatedby oscillation unit 11a, and converts the sampled analog voltage into a digital value. Thevoltage sampled at the timing of the rising edge of the rectangular wave voltage correspondsto a lower peak value of the measured voltage waveform, and the voltage sampled at thetiming of the falling edge of the rectangular wave voltage corresponds to an upper peak valueof the measured voltage waveform. Note that, in consideration of the blunting of therectangular wave voltage, the timing at which the lower peak value should be sampled andthe timing at which the upper peak value should be sampled may be adjusted. Voltagemeasurement unit 11b outputs the voltage at measurement point A to earth leakagedetermination unit 11c and diagnosis unit 11d.

[0027] Earth leakage determination unit 11c determines the presence or absence of an earthleakage between the current path of power storage unit 20 and the chassis ground based onthe voltage at measurement point A measured by voltage measurement unit 11b. When apeak-to-peak value indicated by a difference between an upper peak value and a lower peakvalue is smaller than a set value, earth leakage determination unit 11c determines that anearth leakage occurs between the current path of power storage unit 20 and the chassisground. The set value is determined on the basis of a peak-to-peak value of a measuredvoltage waveform at the time of occurrence of an earth leakage derived in advance by anexperiment or simulation by a designer. When an earth leakage occurs between the currentpath of power storage unit 20 and the chassis ground, an AC current flows from firstoperational amplifier OP1 to coupling capacitor Cc via first resistor R1 acting as a detectionresistor. When the current flows through first resistor R1, the voltage amplitude atmeasurement point A decreases due to a voltage drop.

[0028] Fig. 2 is a diagram illustrating an example of an applied pulse waveform and ameasured voltage waveform. In a pulse waveform applied from the voltage output unit tomeasurement point A, a high-side potential is set to 5 V, and a low-side potential is set to 0V. Earth leakage determination unit 11c specifies an upper peak value Vp1 and a lower peakvalue Vp2 of the voltage waveform measured during a period in which the pulse voltage isapplied to measurement point A, and determines the presence or absence of the earth leakagebased on the peak-to-peak value defined by a difference between the upper peak value Vp1and the lower peak value Vp2.

[0029] Returning to Fig. 1. Diagnosis unit 11d performs a failure diagnosis as to whetheror not coupling capacitor Cc is normal based on the voltage at measurement point Ameasured by voltage measurement unit 11b. Specifically, in a state where a pulse voltage isapplied from the voltage output unit to measurement point A, diagnosis unit 11d diagnosescoupling capacitor Cc on the basis of a change amount of a measured voltage before andafter positive-side main relay MRp is turned on (closed), before and after positive-side mainrelay MRp is turned off (opened), before and after negative-side main relay MRm is turnedon, or before and after negative-side main relay MRm is turned off.

[0030] Fig. 3 is a diagram illustrating an example of a measured waveform at the time offailure diagnosis of coupling capacitor Cc according to the comparative example. Fig. 3illustrates an example in which coupling capacitor Cc is diagnosed based on an amount ofchange in the measured voltage before and after positive-side main relay MRp is turned onand before and after positive-side main relay MRp is turned off.

[0031] Diagnosis unit 11d determines that coupling capacitor Cc is normal when a decreaseamount of a peak-to-peak value Vppc of the measured voltage immediately after positivesidemain relay MRp is turned on from a peak-to-peak value Vppr (specified value) of themeasured voltage immediately before positive-side main relay MRp is less than or equal toa specified value, and determines that coupling capacitor Cc is abnormal when the decreaseamount is not less than or equal to the specified value. When coupling capacitor Cc isnormally connected to the vehicle, a change in an earth leakage state on the vehicle appearsas a decrease in the measured waveform as positive-side main relay MRp is turned on. Whencoupling capacitor Cc is abnormal, this decrease in the measured waveform does not appear.

[0032] Further, diagnosis unit 11d may diagnose coupling capacitor Cc when positive-sidemain relay MRp is turned off. Diagnosis unit 11d determines that coupling capacitor Cc isnormal when an increase amount of the peak-to-peak value Vppo of the measured voltageimmediately after positive-side main relay MRp is turned off from the peak-to-peak valueVppr (reference value) of the measured voltage immediately before positive-side main relayMRp is turned off is greater than or equal to a specified value, and determines that couplingcapacitor Cc is abnormal when the increase amount is not greater than or equal to thespecified value. When coupling capacitor Cc is normally connected to the vehicle, a changein an earth leakage state on the vehicle appears as an increase in the measured waveform aspositive-side main relay MRp is turned off. When coupling capacitor Cc is abnormal, thisincrease in the measured waveform does not appear.

[0033] Note that diagnosis unit 11d may determine that coupling capacitor Cc is normalwhen detecting fluctuations greater than or equal to respective specified values both whenpositive-side main relay MRp is turned on and off. In addition, in Fig. 3, coupling capacitorCc is diagnosed based on the fluctuation in the measured voltage of the peak-to-peak valuewhen positive-side main relay MRp is turned on or off, but coupling capacitor Cc may bediagnosed based on the fluctuation in the peak-to-peak value of the measured voltage whennegative-side main relay MRm is turned on or off.

[0034] (Exemplary embodiment)Fig. 4 is a diagram for describing a configuration of power supply system 5including earth leakage detection device 10 according to an exemplary embodiment.Hereinafter, differences from the configuration of power supply system 5 according to thecomparative example illustrated in Fig. 1 will be described. In the exemplary embodiment,third resistor R3 and third operational amplifier OP3 are added. Controller 11 furtherincludes constant voltage output unit 11e. Constant voltage output unit 11e can output a fixedvoltage of at least one of a first reference voltage (5 V in the present exemplary embodiment)and a second reference voltage (0 V in the present exemplary embodiment).

[0035] In the present exemplary embodiment, oscillation unit 11a and first operationalamplifier OP1 constitute a first voltage output unit, and constant voltage output unit 11e andthird operational amplifier OP3 constitute a second voltage output unit. In the presentexemplary embodiment, the first voltage output unit is also configured to be able to outputa fixed voltage of at least one of the first reference voltage and the second reference voltage.

[0036] Second resistor R2 and third resistor R3 are connected in series between connectionpoint A between coupling capacitor Cc and first resistor R1, and second voltage output unit.More specifically, a constant voltage output from constant voltage output unit 11e is inputto a non-inverting input terminal of third operational amplifier OP3. An output terminal ofthird operational amplifier OP3 is connected to third resistor R3. An inverting input terminaland the output terminal of third operational amplifier OP3 are connected. Third operationalamplifier OP3 also functions as a voltage follower that performs only impedance conversionwith an amplification factor of one time.

[0037] In the present exemplary embodiment, a voltage at a voltage dividing point ofsecond resistor R2 and third resistor R3 is input to the non-inverting input terminal of secondoperational amplifier OP2. That is, voltage measurement unit 11b measures a voltage atmeasurement point A with a compressed voltage by measuring the voltage at the voltagedividing point of second resistor R2 and third resistor R3. Earth leakage determination unit11c calculates an earth leakage resistance value with reference to an earth leakage resistanceconversion table based on an amplitude value of the voltage measured by voltagemeasurement unit 11b, and determines the presence or absence of an earth leakage betweenthe current path of power storage unit 20 and the chassis ground. In the present exemplaryembodiment, the voltage at measurement point A is divided and measured, so that a periodduring which the voltage at measurement point A deviates from a measurement range (0 Vto 5 V in the present exemplary embodiment) can be reduced. That is, it is possible to reducea period during which the earth leakage determination cannot be performed.

[0038] Diagnosis unit 11d diagnoses whether or not coupling capacitor Cc is normal basedon the voltage measured by voltage measurement unit 11b during an on-sequence ofpositive-side main relay MRp, negative-side main relay MR, and precharge relay MRpp ina state where the fixed voltage is output from the first voltage output unit. Specifically,diagnosis unit 11d determines that coupling capacitor Cc is normal when a fluctuation rangeof a voltage measured during the on-sequence exceeds a specified value, and determines thatcoupling capacitor Cc is abnormal when the fluctuation range of the voltage measured duringthe on-sequence is less than or equal to the specified value.

[0039] The specified value is set based on data obtained by experiments or simulations bya designer.

[0040] Diagnosis unit 11d may diagnose coupling capacitor Cc when positive-side mainrelay MRp, negative-side main relay MR, and precharge relay MRpp are first turned on afterthe vehicle is started (key-on). In this case, the first voltage output unit outputs a fixedvoltage from the first voltage output unit after the vehicle is started. An electronic controlunit (ECU) (not illustrated) on the vehicle starts an on-sequence of positive-side main relayMRp, negative-side main relay MRm, and precharge relay MRpp after a predetermined timehas elapsed from the start of the vehicle. Diagnosis unit 11d diagnoses coupling capacitorCc during the on-sequence. After the end of the on-sequence, the first voltage output unitswitches the output voltage from the fixed voltage to the pulse voltage, and earth leakagedetermination unit 11c starts monitoring an earth leakage.

[0041] Fig. 5 is a diagram illustrating an example of a measured waveform at the time offailure diagnosis of coupling capacitor Cc according to the exemplary embodiment. The firstvoltage output unit outputs a fixed voltage after the vehicle is started. For example, when aresistance value of first resistor R1 is 200 kW, a resistance value of second resistor R2 is1000 kW, and a resistance value of third resistor R3 is 1000 kW, and 5 V is output from thefirst voltage output unit and 0 V is output from the second voltage output unit, a fixed voltagemeasured by voltage measurement unit 11b is about 2.27 V as shown in the following(Formula 1). When 0 V is output from the first voltage output unit and 5 V is output fromthe second voltage output unit with similar circuit constants, the fixed voltage measured byvoltage measurement unit 11b is about 2.73 V as shown in the following (Formula 2).

[0042] 5 x (1000 / (200 + 1000 + 1000)) » 2.27 (Formula 1)5 x ((200 + 1000) / (200 + 1000 + 1000)) » 2.73 (Formula 2)

[0043] In the example illustrated in Fig. 5, the ECU on the vehicle starts the on-sequenceof positive-side main relay MRp, negative-side main relay MR, and precharge relay MRppafter several hundred ms have elapsed from the start of the vehicle. Elapsed time t1 is a timefor eliminating the influence of blunting of the measured waveform by smoothing capacitorC1, and is a time until the measured waveform is stabilized.

[0044] In the example illustrated in Fig. 5, on-sequence period t2 is set to several hundredms, and the ECU on the vehicle side turns on negative-side main relay MRm, prechargerelay MRpp, and positive-side main relay MRp in this order during on-sequence period t2.Note that, when the precharge relay is connected to a side of the negative electrode, the ECUturns on positive-side main relay MRp, the precharge relay, and negative-side main relayMRm in this order.

[0045] Diagnosis unit 11d determines that coupling capacitor Cc is normal whenfluctuation range DV of the measured voltage during on-sequence period t2 exceeds aspecified value, and determines that coupling capacitor Cc is abnormal when fluctuationrange DV of the measured voltage during on-sequence period t2 is less than or equal to thespecified value. Fluctuation range DV is defined by a difference between a maximum valueand a minimum value of the measured voltage during on-sequence period t2.

[0046] As described above, according to the present exemplary embodiment, the failurediagnosis of coupling capacitor Cc is performed based on fluctuation range DV of themeasured voltage during on-sequence period t2 in a state where the fixed voltage is applied.As a result, the failure diagnosis of coupling capacitor Cc can be performed quickly and withhigh accuracy.

[0047] In the present exemplary embodiment, since the voltage at the voltage dividingpoint of second resistor R2 and third resistor R3 is measured, when a fixed voltage is applied,the fixed voltage can be measured in the vicinity of the middle of the measurement range.Therefore, even if the measured voltage increases or decreases, the fluctuation can bemeasured with high accuracy. On the other hand, in the circuit configuration according tothe comparative example illustrated in Fig. 1, it is difficult to detect a decrease in themeasured voltage when a fixed voltage of 0 V is applied, and it is difficult to detect anincrease in the measured voltage when a fixed voltage of 5 V is applied.

[0048] Note that it is also conceivable to perform the failure diagnosis of coupling capacitorCc based on the fluctuation of the upper peak value or the fluctuation of the lower peak valueof the peak-to-peak value measured in a state where the pulse voltage is applied. However,since the peak-to-peak value usually varies in a cycle of several hundred ms or more, theupper peak value or the lower peak value can be detected only in a cycle of several hundredms or more, and it takes time to sample the peak values at a plurality of points.

[0049] In this regard, with a fixed voltage, the value can be measured at a cycle of severaltens of ms or less, and thus, it is possible to quickly determine the presence or absence of avoltage fluctuation exceeding a specified value. Even if initial stabilization time t1 isincluded, the diagnosis of coupling capacitor Cc can be completed within less than or equalto 1 s.

[0050] The present disclosure has been described above based on the exemplaryembodiment. It is to be understood by the person of ordinary skill in the art that theexemplary embodiment is a merely example, that various modified examples can be madeto combinations of the respective configuration elements and the respective processingprocesses, and that such modified examples are also within the scope of the presentdisclosure.

[0051] In the circuit configuration illustrated in Fig. 1, the voltage output unit may outputa fixed voltage set to a value near a center of the measurement range of voltage measurementunit 11b, and diagnosis unit 11d may determine whether or not coupling capacitor Cc isnormal based on a voltage measured during an on-sequence period of a contactor. The valuenear the center of the measurement range of voltage measurement unit 11b may be a valueset within a range of ±1 V of the center voltage of the measurement range. For example,when the measurement range is 0 V to 5 V, the fixed voltage is set to a value within a rangeof 1.5 V to 3.5 V. Note that the value of the fixed voltage may be set outside a range of ±1V of a center voltage of the measured range as long as the measured voltage is suppressedfrom sticking to an upper limit or a lower limit of the measurement range due to verticalfluctuation. Also in the above method, the same effects as those of the above exemplaryembodiment can be obtained.

[0052] In the above exemplary embodiment, an example has been described in which thefailure diagnosis of coupling capacitor Cc is performed at the time of starting the vehicle. Inthis regard, the failure diagnosis of coupling capacitor Cc may be performed after the vehicleis parked. In that case, since there is a margin in terms of time, on and off of the contactormay be repeated a plurality of times, and final diagnosis may be performed based on thedetermination results of the plurality of times.

[0053] In the above exemplary embodiment, precharge relay MRpp and precharge resistorRp are connected in parallel with positive-side main relay MRp. However, in a case wherethe load is small, precharge relay MRpp and precharge resistor Rp may be omitted.

[0054] In the above exemplary embodiment, the example has been described in which therectangular wave voltage is applied from the first voltage output unit to coupling capacitorCc via first resistor R1. In this regard, a sinusoidal voltage may be applied to couplingcapacitor Cc. Also in this case, earth leakage determination unit 11c can specify a peak-topeakvalue from the voltage waveform at measurement point A, and determine the presenceor absence of the earth leakage in the same manner as in the above exemplary embodiment.

[0055] In the above exemplary embodiment, an example in which earth leakage detectiondevice 10 is mounted on an electric vehicle and used has been described. In this respect,earth leakage detection device 10 according to the above exemplary embodiment can alsobe applied to applications other than in-vehicle applications. The load may be any load aslong as the load that receives power supply from power storage unit 20, and power storageunit 20 are insulated from the ground. For example, the load may be a load used in a railwayvehicle.

[0056] Note that the exemplary embodiment may be specified by the following items.

[0057] [Item 1]Earth leakage detection device (10) mounted on a vehicle, including power storageunit (20) that is mounted in a state of being insulated from a chassis ground of the vehicleand supplies electric power to load (2) in the vehicle, and switch (MRp, MRm, MRpp)inserted into a wiring connecting power storage unit (20) and load (2), the earth leakagedetection device including:coupling capacitor (Cc) including one end connected to a current path of powerstorage unit (20) connected to load (2) in a state of being insulated from a ground;voltage output unit (11a, OP1) that generates a periodically changing periodicvoltage and applies the periodic voltage to the other end of coupling capacitor (Cc) via firstresistor (R1);second resistor (R2) and third resistor (R3) connected in series between aconnection point between coupling capacitor (Cc) and first resistor (R1), and apredetermined fixed potential;voltage measurement unit (11b) that measures a voltage at a voltage dividing pointbetween second resistor (R2) and third resistor (R3);earth leakage determination unit (11c) that determines presence or absence of anearth leakage between the current path of power storage unit (20) and the ground based on avoltage measured by voltage measurement unit (11b) in a state where the periodic voltage isoutput from voltage output unit (11a, OP1); anddiagnosis unit (11d) that determines whether or not coupling capacitor (Cc) isnormal based on a voltage measured by voltage measurement unit (11b) when switch (MRp,MRm, MRpp) is turned on in a state where a fixed voltage is output from voltage output unit(11a, OP1).Therefore, the failure diagnosis of coupling capacitor (Cc) can quickly beperformed with high accuracy.[Item 2]Earth leakage detection device (10) mounted on a vehicle, including power storageunit (20) that is mounted in a state of being insulated from a chassis ground of the vehicleand supplies electric power to load (2) in the vehicle, and switch (MRp, MRm, MRpp)inserted into a wiring connecting power storage unit (20) and load (2), the earth leakagedetection device including:voltage output unit (11a, OP1) that generates a periodically changing periodicvoltage and applies the periodic voltage to the other end of coupling capacitor (Cc) viaresistor (R1);voltage measurement unit (11b) that measures a voltage at a connection pointbetween coupling capacitor (Cc) and resistor (R1);earth leakage determination unit (11c) that determines presence or absence of anearth leakage between a current path of power storage unit (20) and the ground based on avoltage measured by voltage measurement unit (11b) in a state where the periodic voltage isoutput from voltage output unit (11a, OP1); anddiagnosis unit (11d) that determines whether or not coupling capacitor (Cc) isnormal based on a voltage measured by voltage measurement unit (11b) when switch (MRp,MRm, MRpp) is turned on in a state where voltage output unit (11a, OP1) outputs a fixedvoltage set to a value near a center of a measurement range of voltage measurement unit(11b).Therefore, the failure diagnosis of coupling capacitor (Cc) can quickly beperformed with high accuracy.[Item 3]Earth leakage detection device (10) according to Item 1 or 2, wherein when switch(MRp, MRm, MRpp) is turned on, diagnosis unit (11d) determines that coupling capacitor(Cc) is abnormal when a fluctuation range of a voltage measured by voltage measurementunit (11b) is less than or equal to a specified value.Therefore, the failure diagnosis of coupling capacitor (Cc) can quickly beperformed with high accuracy.[Item 4]Earth leakage detection device (10) according to Item 3, whereinswitch (MRp, MRm, MRpp) includes:positive electrode relay (MRp) inserted into a positive wiring, the positive wiringconnecting a positive electrode of power storage unit (20) and one end of load (2);negative electrode relay (MRm) inserted into a negative wiring, the negative wiringconnecting a negative electrode of power storage unit (20) and the other end of load (2); andprecharge relay (MRpp) connected in parallel to positive electrode relay (MRp) ornegative electrode relay (MRm), anddiagnosis unit (11d) determines that coupling capacitor (Cc) is abnormal when afluctuation range of the measured voltage in a period from when one of three relays (MRp,MRm, MRpp) is turned on to when the three relays are turned on is less than or equal to thespecified value.According to this, in the configuration in which a contactor including the prechargerelay is connected to load (2) on the vehicle side, the failure diagnosis of coupling capacitor(Cc) can be performed quickly and with high accuracy.[Item 5]Vehicle power supply system (5) including:power storage unit (20) that is mounted in a state of being insulated from a chassisground of the vehicle and supplies electric power to load (2) in the vehicle; andearth leakage detection device (10) according to any one of Items 1 to 4.According to this, it is possible to achieve vehicle power supply system (5)including earth leakage detection device (10) capable of quickly and accurately performingthe failure diagnosis of coupling capacitor (Cc).[Item 6]Vehicle power supply system (5) according to Item 5, wherein diagnosis unit (11d)determines whether or not coupling capacitor (Cc) is normal when switch (MRp, MRm,MRpp) is first turned on after the vehicle is started.According to this, the failure diagnosis of coupling capacitor (Cc) can be performedwithout setting a special diagnosis period.REFERENCE MARKS IN THE DRAWINGS

[0058] 2: inverter3: motor4: capacitorLp: positive wiringLm: negative wiringCp: positive-side Y capacitorCm: negative-side Y capacitorRlp: positive-side earth leakage resistanceRlm: negative-side earth leakage resistanceMRp: positive-side main relayMRm: negative-side main relayMRpp: precharge relayRp: precharge resistor5: power supply system20: power storage unitE1 to En: cell10: earth leakage detection device11: controller11a: oscillation unit11b: voltage measurement unit11c: earth leakage determination unit11d: diagnosis unit11e: constant voltage output unitCc: coupling capacitorR1: first resistorR2: second resistorR3: third resistorC1: smoothing capacitorOP1: first operational amplifierOP2: second operational amplifierOP3: third operational amplifier

Claims

1. An earth leakage detection device mounted on a vehicle, the earth leakage detection device including a power storage unit that is mounted in a state of being insulated from a chassis ground of the vehicle and supplies electric power to a load in the vehicle, and a switch inserted into a wiring connecting the power storage unit to the load, the earth leakage detection device comprising: a coupling capacitor including one end connected to a current path of the power storage unit connected to the load in a state of being insulated from a ground; a voltage output unit that generates a periodic voltage periodically changing and applies the periodic voltage to another end of the coupling capacitor via a first resistor; a second resistor and a third resistor connected in series between a connection point between the coupling capacitor and the first resistor, and a predetermined fixed potential; a voltage measurement unit that measures a voltage at a voltage dividing point between the second resistor and the third resistor; an earth leakage determination unit that determines whether or not an earth leakage occurs between the current path of the power storage unit and the ground based on a voltage measured by the voltage measurement unit in a state where the periodic voltage is output from the voltage output unit; and a diagnosis unit that determines whether or not the coupling capacitor is normal based on a voltage measured by the voltage measurement unit when the switch is turned on in a state where a fixed voltage is output from the voltage output unit.

2. An earth leakage detection device mounted on a vehicle, including a power storage unit that is mounted in a state of being insulated from a chassis ground of the vehicle and supplies electric power to a load in the vehicle, and a switch inserted into a wiring connecting the power storage unit and the load, the earth leakage detection device comprising: a coupling capacitor including one end connected to a current path of the power storage unit connected to the load in a state of being insulated from a ground; a voltage output unit that generates a periodically changing periodic voltage and applies the periodic voltage to another end of the coupling capacitor via a resistor; a voltage measurement unit that measures a voltage at a connection point between the coupling capacitor and the resistor; an earth leakage determination unit that determines whether or not an earth leakage occurs between the current path of the power storage unit and the ground based on a voltage measured by the voltage measurement unit in a state where the periodic voltage is output from the voltage output unit; and a diagnosis unit that determines whether or not the coupling capacitor is normal based on a voltage measured by the voltage measurement unit when the switch is turned on in a state where the voltage output unit outputs a fixed voltage set to a value near a center of a measurement range of the voltage measurement unit.

3. The earth leakage detection device according to Claim 1 or 2, wherein when the switch is turned on, the diagnosis unit determines that the coupling capacitor is abnormal when a fluctuation range of a voltage measured by the voltage measurement unit is less than or equal to a specified value.

4. The earth leakage detection device according to Claim 3, wherein the switch includes three relays that are: a positive electrode relay inserted into a positive wiring, the positive wiring connecting a positive electrode of the power storage unit and one end of the load; a negative electrode relay inserted into a negative wiring, the negative wiring connecting a negative electrode of the power storage unit and another end of the load; and a precharge relay connected in parallel to the positive electrode relay or the negative electrode relay, and the diagnosis unit determines that the coupling capacitor is abnormal when a fluctuation range of the measured voltage in a period from when one of the three relays is turned on to when the three relays are turned on is less than or equal to the specified value.

5. A vehicle power supply system comprising: a power storage unit that is mounted in a state of being insulated from a chassis ground of the vehicle and supplies electric power to a load in the vehicle; and the earth leakage detection device according to any one of Claims 1 to 4.

6. The vehicle power supply system according to Claim 5, wherein the diagnosis unit determines whether or not the coupling capacitor is normal when the switch is first turned on after the vehicle is started.