JP6063282B2 - Insulation state detector - Google Patents

Description

  The present invention relates to an insulation state detection device that can be mounted on a vehicle.

  For example, in a vehicle that uses electric power as propulsion energy, such as an electric vehicle, a DC power supply device that outputs a high voltage of about 200 V may be mounted. In the case of a vehicle equipped with such a high-voltage DC power supply device, it is used in a state where the positive and negative power supply lines of the DC power supply device and the vehicle body are electrically insulated. That is, the vehicle body is not used as a ground for a power source that outputs a high voltage.

  In such a vehicle, it is necessary to inspect and confirm that the high-voltage DC power output wiring and the vehicle body are sufficiently electrically insulated in order to ensure safety. For example, Patent Literature 1, Patent Literature 2, and Patent Literature 3 disclose conventional techniques of an insulation state detection device used when performing such an inspection.

  This type of insulation state detection device uses a flying capacitor. That is, a detection capacitor (referred to as a flying capacitor) is connected between a high-voltage positive / negative power supply line and a ground electrode (vehicle body) for a certain period of time via a switching element. The charging voltage of the flying capacitor is monitored, and the ground fault resistance, that is, the insulation resistance between the power supply line and the ground electrode is calculated from the charging voltage.

  For example, a film capacitor or a ceramic capacitor may be used as a detection capacitor of such an insulation state detection device. However, while film capacitors are highly accurate, they are difficult to downsize and have low moisture resistance. Therefore, in the case of an in-vehicle insulation state detection device, it is assumed that a ceramic capacitor having a small size is used.

However, when using a ceramic capacitor, there is a problem in terms of accuracy. That is, there are the following problems.
(1) There is a large variation in capacitance among components.
(2) The capacitance when actually used varies due to the influence of a DC (direct current) bias voltage.
(3) Capacitance during actual use varies according to temperature changes.

  Therefore, Patent Document 1 discloses a technique for removing the influence of DC bias characteristics when a ceramic capacitor is used as a detection capacitor. Specifically, all charging voltages and charging time constants when the ground fault resistance RL is the alarm threshold value RLx are made the same. Thereby, in the vicinity of the alarm threshold value RLx, the influence of the DC bias characteristic can be reduced, and the measurement accuracy can be prevented from being lowered.

  In Patent Document 2, the measurement timing of the power supply charging voltage V0 and the negative side ground fault resistance measurement voltage VC1n and the measurement timing of the power supply charging voltage V0 and the positive side ground fault resistance measurement voltage VC1p are the same. . As a result, even when the voltage of the power supply fluctuates, the influence of the fluctuation can be reduced.

  Patent Document 3 discloses a technique for shortening measurement time while ensuring detection accuracy. Specifically, a sample hold circuit is connected in front of the analog input port of the CPU, and the timing for measuring the voltage is controlled to prevent a decrease in detection accuracy.

JP 2009-281986 A JP 2009-281987 A JP 2011-102788 A

  When a ceramic capacitor is used as a detection capacitor of an insulation state detection device, there are problems (1), (2), (3), etc., but since it is a special environment for measuring insulation resistance, These multiple factors affect each other and are intertwined in a complicated manner, which adversely affects measurement accuracy.

  For example, when the capacitance of the detection capacitor changes, the voltage rise curve when the capacitor is charged and the time required from the start of charging to full charge change. Therefore, there is a great difference in the DC bias voltage applied between the terminals of the capacitor at each timing when the capacitor is charged. This difference further causes fluctuations in the capacitance of the capacitor, which causes further measurement errors.

  Therefore, it is not easy to eliminate the influence on the problem of the DC bias voltage characteristic (2). For example, by using the technique disclosed in Patent Document 1, the measurement accuracy can be increased in the vicinity of the alarm threshold value RLx. However, in the region where the ground fault resistance value is significantly different from the alarm threshold value RLx, the measurement accuracy is reduced. Unavoidable. Further, by using the technique disclosed in Patent Document 2, it is possible to reduce the influence of the DC bias voltage characteristic on the ratio of V0 / VC1n and V0 / VC1p. However, the influence of the DC bias voltage characteristic on individual voltage measurement values such as VC1n and VC1p cannot be reduced.

  For example, even if the temperature of the actual detection capacitor can be grasped using a temperature sensor, it is not easy to correctly correct the measurement result of the ground fault resistance by reflecting this temperature change. Therefore, the measurement accuracy of the ground fault resistance is lowered due to the influence of the temperature characteristic (3).

  The present invention has been made in view of the above-described circumstances, and its purpose is to reduce the influence of the DC bias voltage characteristics even when a component such as a ceramic capacitor whose characteristics are easily changed is adopted as a detection capacitor. An object of the present invention is to provide an insulation state detecting device capable of measuring ground fault resistance with high accuracy.

In order to achieve the above-described object, an insulation state detection device according to the present invention is characterized by the following (1) to (4).
(1) A positive-side input terminal and a negative-side input terminal connected to a positive-side power line and a negative-side power line for a predetermined high-voltage DC power output, respectively, and a ground electrode, and based on the charging voltage of the flying capacitor An insulation state detection device for grasping an insulation state between the positive electrode side power line and the negative electrode side power line and the ground electrode as a ground fault resistance,
A first voltage measurement value obtained when the flying capacitor is charged through a first energization path not affected by the ground fault resistance, and a second energization affected by the ground fault resistance. A charging voltage measuring unit for measuring each of the second voltage measurement values obtained when charging via the path;
A ground fault resistance value calculation unit that calculates a value of the ground fault resistance based on the first voltage measurement value and the second voltage measurement value measured by the charging voltage measurement unit;
The charging time length of the flying capacitor for measuring the second voltage measurement value is variable, and the first voltage measurement value obtained before measuring the second voltage measurement value is used as the charge time. A charging time length control unit that automatically reflects the length,
Be provided.
(2) The insulation state detection device according to (1) above,
The charging time length control unit has a constant table that associates and holds each of a plurality of voltage ranges and information on a coefficient related to the charging time length, and the charging voltage measurement unit detects the first Based on the voltage measurement value of 1, using the constant table, the charging time length when measuring the second voltage measurement value is automatically corrected.
(3) The insulation state detection device according to (1) above,
A temperature detector for detecting a temperature in the vicinity of the flying capacitor;
A temperature compensation controller that reflects the temperature parameter detected by the temperature detector in the charging time length of the flying capacitor;
Is further provided.
(4) The insulation state detection device according to (3) above,
The temperature compensation control unit includes a temperature compensation table that holds each of a plurality of temperature ranges in association with information on a coefficient corresponding to a length of time for charging the flying capacitor, and the temperature detection unit Based on the detected temperature, the charging time length is automatically corrected using the temperature compensation table.

According to the insulation state detection device having the configuration (1), it is possible to reduce the influence of the DC bias voltage characteristic and to measure the ground fault resistance with high accuracy. That is, since the first voltage measurement value corresponds to the maximum value of the voltage actually applied to the flying capacitor, by performing compensation according to the first voltage measurement value, the DC bias voltage characteristic The impact can be reduced. Further, the DC bias voltage characteristic can be compensated by controlling the charging time length of the flying capacitor when measuring the second voltage measurement value.
According to the insulation state detection apparatus having the configuration (2), a coefficient necessary for correctly correcting the charging time length can be obtained by simple processing. Therefore, even when the measurement is repeatedly executed in a short time period, the influence of the fluctuation of the first voltage measurement value obtained at the immediately previous measurement timing is immediately reflected in the charging time length used in the immediately following measurement. It becomes possible to reflect.
According to the insulation state detection apparatus having the configuration (3), not only the DC bias voltage characteristic of the flying capacitor but also the influence of the temperature characteristic can be compensated. Further, since compensation control is performed with a common charging time length as a control object for the DC bias voltage characteristic and the temperature characteristic, high-precision compensation is possible only by simple control.
According to the insulation state detection apparatus having the configuration (4), it is possible to obtain a coefficient necessary for correctly correcting the charging time length according to the temperature of the flying capacitor by a simple process.

  According to the insulation state detection device of the present invention, even when a component such as a ceramic capacitor whose characteristics are easily changed is adopted as a detection capacitor, the influence of the DC bias voltage characteristic is reduced, and the ground fault resistance is reduced with high accuracy. It becomes possible to measure.

  The present invention has been briefly described above. Further, the details of the present invention will be further clarified by reading through a mode for carrying out the invention described below (hereinafter referred to as “embodiment”) with reference to the accompanying drawings. .

FIG. 1 is an electric circuit diagram illustrating a configuration example of an insulation state detection device and its peripheral circuits according to the embodiment. FIG. 2 is a flowchart showing the main control contents of the insulation state detection apparatus shown in FIG. FIG. 3 is a time chart showing a specific example of the operation timing of the insulation state detection device shown in FIG. FIG. 4 is a schematic diagram showing a configuration example of a constant table that holds compensation values according to temperature. FIG. 5 is a graph showing a specific example of the relationship between the voltage applied to the capacitor, the charge charge, and the temperature. FIG. 6 is a graph showing a specific example of compensation characteristics corresponding to a temperature change. FIG. 7 is a schematic diagram illustrating a configuration example of a DC bias voltage compensation constant table. FIG. 8 is a graph showing a specific example of the relationship between the voltage applied to the capacitor and the charge charge. FIG. 9 is a time chart showing the operation timing of the basic measurement cycle.

  Specific embodiments relating to the insulation state detection device of the present invention will be described below with reference to the drawings.

<Overview of overall configuration and operation>
FIG. 1 shows the configuration of an insulation state detection device 10 mounted on a vehicle and its peripheral circuits.
The insulation state detection device 10 shown in FIG. 1 can be used by being mounted on a vehicle such as an electric vehicle or a hybrid vehicle including an engine and an electric motor as drive sources. The in-vehicle DC high-voltage power supply 50 outputs high-voltage DC power of about 200V, for example. The electric motor that generates the driving force of the vehicle can be driven by the electric power output from the in-vehicle DC high-voltage power supply 50.

  The positive electrode side power supply line 111 of the output of the in-vehicle DC high voltage power supply 50 and the ground electrode 103 are electrically insulated. The negative power supply line 112 and the ground electrode 103 are also electrically insulated. The ground electrode 103 corresponds to an earth part such as a vehicle body. Here, the insulation state between the positive power line 111 and the ground electrode 103 can be expressed as a ground fault resistance RLp. Further, the insulation state between the negative power supply line 112 and the ground electrode 103 can be expressed as a ground fault resistance RLn.

  In order to reduce common mode noise, as shown in FIG. 1, a Y capacitor 101 is connected between the positive power line 111 and the ground electrode 103, and between the negative power line 112 and the ground electrode 103. A Y capacitor 102 is connected to this.

  By mounting the insulation state detection device 10 shown in FIG. 1 on a vehicle, the insulation state of the vehicle can be monitored at any time as necessary. That is, the insulation state detection device 10 can be used to detect the ground fault resistances RLp and RLn at the output of the in-vehicle DC high voltage power supply 50 and grasp the insulation state.

  Therefore, as shown in FIG. 1, the positive input terminal 13 and the negative input terminal 14 of the insulation state detection device 10 are connected to the positive power supply line 111 and the negative power supply line 112, respectively. The ground electrode 15 of the insulation state detection device 10 is connected to the ground electrode 103.

  An output terminal 21 is provided as shown in FIG. 1 in order to output the measurement result of the insulation state detection device 10 and alarm information. The output terminal 21 can be connected to, for example, a vehicle-side electronic control unit (ECU).

<Configuration Example of Insulation State Detection Device 10>
As shown in FIG. 1, the circuit of the insulation state detection device 10 is provided with a detection capacitor C1 that operates as a flying capacitor. A ceramic capacitor is employed as the detection capacitor C1 in consideration of being used in a vehicle.

  Further, in order to control charging and discharging of the detection capacitor C1, four switching elements S1 to S4 are provided in the vicinity thereof. Each of these switching elements S1 to S4 is a switch that can switch the open / close (off / on) state of a contact by controlling an insulated signal, such as an optical MOSFET.

  The switching element S <b> 1 is connected to the positive input terminal 13 and the other end is connected to the wiring 31. The switching element S2 has one end connected to the negative input terminal 14 and the other end connected to the wiring 32 via the resistor R2.

  The switching element S <b> 3 has one end connected to the wiring 33 and the other end connected to the wiring 35. The switching element S4 has one end connected to the wiring 32 and the other end connected to the ground electrode 15 via the resistor R4.

  The detection capacitor C <b> 1 has a negative terminal connected to the wiring 32. The positive terminal of the detection capacitor C1 is connected to the wiring 31 through a series circuit including a diode D1 and a resistor R1. The positive terminal of the detection capacitor C1 is connected to the wiring 33 via a series circuit including a diode D3 and a resistor R3, and is further connected to the wiring 33 via a diode D2. The diode D2 is connected with a polarity that allows energization in the direction from the wiring 33 to the wiring 34, and the diode D3 is connected with a polarity that allows energization in the direction from the wiring 34 to the wiring 33.

  Note that the wiring 34 may be grounded via a special switch and resistor (not shown) in order to discharge the electric charge accumulated in the detection capacitor C1. However, such a special discharge circuit can be omitted by using components having relatively small resistance values for the resistors R3, R4, and R5.

  As shown in FIG. 1, a thermistor 25 is disposed in the vicinity of the detection capacitor C1. Since the resistance value of the thermistor 25 changes according to the temperature of the detection capacitor C1, it is possible to output an electric signal whose level changes according to this temperature.

  The microcomputer (CPU) 11 executes various controls required for the insulation state detection device 10 by executing a program incorporated in advance. Specifically, the microcomputer 11 controls the switching elements S1 to S4 individually to control charging and discharging of the detection capacitor C1. Further, the microcomputer 11 inputs an analog level corresponding to the charging voltage of the detection capacitor C1 from one analog input port AD1 via the wiring 36, performs calculation based on this input level, and performs ground fault resistance RLp and Know RLn.

  The input circuit 20 is connected between the wiring 35 and the wiring 36. The input circuit 20 performs signal processing for converting a signal appearing on the wiring 35 into a signal suitable for the processing of the microcomputer 11. Although various functions and configurations are conceivable for the input circuit 20, a sample hold circuit is assumed as a typical input circuit 20.

  For example, an analog switch is connected between the wiring 35 and the wiring 36, and a capacitor (capacitor) that holds a signal level is connected between the wiring 36 and the ground electrode 15. When the microcomputer 11 temporarily turns on (conducts) the analog switch at a specific timing, the signal level input at that timing can be sampled and held by the capacitor in the input circuit 20. . Of course, the function of such a sample and hold circuit can be omitted.

  The other analog input port AD <b> 2 of the microcomputer 11 is connected to one end of the thermistor 25 via a wiring 37. Therefore, the microcomputer 11 can acquire the temperature information of the detection capacitor C1 detected by the thermistor 25 by measuring the input level of the analog input port AD2.

<Measurement of ground fault resistance>
<Description of Charging / Discharging of Capacitor for Detection (Flying Capacitor) C1>
<Timing for switching>
A specific example of the switching timing of the switching elements S1 to S4 at the time of measurement is shown in FIG. That is, when measuring the ground fault resistances RLp and RLn, the microcomputer 11 controls on / off of the switching elements S1 to S4 according to the schedule of the basic measurement cycle as shown in FIG. Get the necessary measurements.

  The basic measurement cycle shown in FIG. 9 includes “V0 charge”, “measurement”, “discharge”, “Vc1n charge”, “measurement”, “discharge”, “V0 charge”, “measurement”, “discharge”, “ It is composed of a series of sections of “Vc1p charge”, “measurement”, and “discharge”.

  In the “V0 charging” section at time t1-t2, the switching elements S1 and S2 are turned on (contacts closed), and the other switching elements are turned off (contacts open). In the “measurement” section at time t2-t3, the switching elements S3 and S4 are turned on, and the other switching elements are turned off.

  In the “discharge” section from time t3 to t4, the switching elements S3 and S4 are turned on, and the other switching elements are turned off. In the “Vc1p charging” section at time t4-t5, the switching elements S1 and S4 are turned on, and the other switching elements are turned off.

  The “measurement” section at time t5-t6 is the same as the “measurement” section at time t2-t3. Further, the “discharge” section at time t6-t7 is the same as the “discharge” section at time t3-t4. The “V0 charging” section from time t7 to t8 is the same as the “V0 charging” section from time t1 to t2. The subsequent “measurement” section from time t8 to t9 is the same as the “measurement” section from time t2 to t3. Further, the “discharge” section from time t9 to t10 is the same as the “discharge” section from time t3 to t4.

  In the “Vc1p charge” section from time t10 to t11, the switching elements S2 and S3 are turned on, and the other switching elements are turned off. The “measurement” section at time t11-t12 is the same as the “measurement” section at time t2-t3. The “discharge” section from time t12 to t13 is the same as the “discharge” section from time t3 to t4.

<Energization path and operation in each section of measurement cycle>
"V0 charge" section:
Since the contact of the switching element S1 is closed, a current flows from the positive power supply line 111 to the positive terminal of the detection capacitor C1 through the positive input terminal 13, the switching element S1, the wiring 31, the diode D1, and the resistor R1. Flowing. Further, since the contact of the switching element S2 is closed, a current flows from the negative terminal of the detection capacitor C1 to the wiring 32, the resistor R2, the switching element S2, the negative input terminal 14, and the negative power line 112. Therefore, the electric charge is charged in the detection capacitor C1 by this current.

“Measurement” section:
Since the contact of the switching element S4 is closed, the negative terminal of the detection capacitor C1 is connected to the ground electrode 15 via the resistor R4. Since the contact of the switching element S3 is closed, the positive terminal of the detection capacitor C1 is connected to the microcomputer 11 via the diode D3, the resistor R3, the switching element S3, the wiring 35, the input circuit 20, and the wiring 36. Connected to analog input port. Therefore, the microcomputer 11 can detect an analog level proportional to the charging voltage of the detection capacitor C1.

“Discharge” section:
Since the contact of the switching element S4 is closed, the negative terminal of the detection capacitor C1 is connected to the ground electrode 15 via the resistor R4. Since the contact of the switching element S3 is closed, the positive terminal of the detection capacitor C1 is connected to the ground electrode 15 via the diode D3, the resistor R3, the switching element S3, and the resistor R5. Accordingly, the charge accumulated in the detection capacitor C1 is naturally discharged.

"Vc1n charge" section:
Since the contact of the switching element S1 is closed, a current flows from the positive power supply line 111 to the positive terminal of the detection capacitor C1 through the positive input terminal 13, the switching element S1, the wiring 31, the diode D1, and the resistor R1. Flowing. Further, since the contact of the switching element S4 is closed, the negative power supply line from the negative terminal of the detection capacitor C1 passes through the switching element S4, the resistor R4, the ground electrode 15, the ground electrode 103, and the ground fault resistor RLn. A current flows through 112. This current charges the detection capacitor C1. The charging voltage at this time is a result reflecting the influence of the ground fault resistance RLn.

"Vc1p charge" section:
Since the contact of the switching element S3 is closed, the positive electrode of the detection capacitor C1 passes from the positive power supply line 111 through the ground fault resistance RLp, the ground electrode 103, the ground electrode 15, the resistor R5, the switching element S3, and the diode D2. Current flows through the side terminals. Further, since the contact of the switching element S2 is closed, a current flows from the negative terminal of the detection capacitor C1 to the wiring 32, the resistor R2, the switching element S2, the negative input terminal 14, and the negative power line 112. This current charges the detection capacitor C1. The charging voltage at this time is a result reflecting the influence of the ground fault resistance RLp.

<Basic grounding resistance measurement operation>
Regarding the operation of the insulation state detection device 10 shown in FIG. 1, the following relational expression is basically established.
(RLp + RLn) / (RLp × RLn) = {(Vc1p) + (Vc1n)} / V0
However,
V0: Charge voltage Vc1n of the detection capacitor C1 corresponding to the output voltage of the in-vehicle DC high-voltage power supply 50: Charge voltage Vc1p of the detection capacitor C1 affected by the negative ground fault resistance RLn: Positive ground fault resistance RLp Voltage RLp, RLn of the capacitor C1 for detection affected by the resistance: resistance value of the local resistance

  Therefore, the microcomputer 11 grasps each charging voltage “V0”, “Vc1n”, “Vc1p” from the signal level inputted to the analog input port (AD1) in each state, and the ground fault resistance based on the above relational expression. RLp and RLn can be calculated.

<Explanation of compensation of temperature characteristic of detection capacitor C1>
A specific example of the relationship between the voltage applied to the capacitor, the charge charged, and the temperature is shown in FIG. A specific example of compensation characteristics corresponding to temperature changes is shown in FIG.

  When using a ceramic capacitor, the characteristics change as shown in FIG. That is, when the charging time is constant, the capacitance decreases when the temperature of the capacitor itself (generally equivalent to the ambient temperature) becomes higher than the normal temperature (for example, 20 ° C.) (80 ° C.). Charge charge decreases. Further, when the temperature of the capacitor itself becomes lower than the normal temperature (−30 ° C.), the capacitance increases and the charge charge also increases.

  When a ceramic capacitor whose characteristics change in accordance with the temperature as described above is used as the detection capacitor C1 of the insulation state detection device 10, the charge charge, that is, the measured value of the voltage changes due to the influence of the temperature. It becomes a factor of resistance measurement error.

  Therefore, the insulation state detection apparatus 10 controls temperature compensation as shown in FIG. That is, when the capacitance decreases due to a temperature rise, the charging time of the detection capacitor C1 is changed to be shorter than usual, and when the capacitance increases due to a temperature drop, the charging time of the detection capacitor C1. The length of is changed to be longer than usual.

  By such control, even when a ceramic capacitor having the characteristics shown in FIG. 5 is used as the detection capacitor C1, a state close to the ideal characteristic F0 can be obtained as in the characteristic F1 shown in FIG. That is, the influence of temperature can be compensated by changing the length of the charging time according to the temperature. Further, by performing another compensation according to the difference in the DC bias voltage of the detection capacitor C1 as will be described later, a state closer to the ideal characteristic F0 than the characteristic F1 shown in FIG. 6 can be obtained.

<Description of Constant Table Used for Temperature Compensation of Detection Capacitor C1>
FIG. 4 shows a configuration example of the constant table TB1 that holds a compensation value corresponding to the temperature. The constant table TB1 shown in FIG. 4 holds constants of the length of charging time associated with each of a plurality of temperature ranges.

  In the example shown in FIG. 4, the lowest temperature range (−A ° C. or lower),..., 0 to 10 [° C.], 10 to 20 [° C.], 20 to 30 [° C.], 30 to 40 [° C.] , 40 to 50 [° C.],..., Constants for the length of the charging time associated with the highest temperature range (+ B ° C. or higher) are held in the constant table TB1.

  The constant of the charging time length associated with each temperature range is determined as a result of multiplying the reference time length (T0 [sec]) by a predetermined coefficient. For example, the constant in the temperature range of 0 to 10 [° C.] is 1.2 times the reference time length (T0), and the constant in the temperature range of 30 to 40 [° C.] is 0.9 of the reference time length (T0). Is double.

  That is, the temperature range of 20-30 [° C.] is set as a reference state, the charging time is changed longer than the reference time length (T0) at a temperature lower than this range, and the charging time is shorter than the reference at a higher temperature. Means to change.

  In the insulation state detection device 10 shown in FIG. 1, the constant table TB1 having the configuration shown in FIG. 4 is held in advance in an internal memory (ROM or nonvolatile memory) of the microcomputer 11. Therefore, the microcomputer 11 can easily obtain the optimum value of the charging time length necessary for temperature compensation using the constant table TB1.

<Description of compensation of DC bias voltage characteristic of capacitor C1 for detection>
A specific example of the relationship between the voltage applied to the capacitor and the charging voltage is shown in FIG. A specific example of the operation timing of the insulation state detection device shown in FIG. 1 is shown in FIG.

  When the detection capacitor C1 is a ceramic capacitor, the voltage due to the charge of the capacitor changes according to the difference in applied voltage, for example, as shown by the characteristic F2 shown in FIG. However, the characteristic F2 includes the influence of the DC bias characteristic of the detection capacitor C1 itself. When there is no influence of the DC bias characteristic, the characteristic F2 is as shown in the characteristic F3 of FIG.

  That is, if the capacitance of the detection capacitor C1 is constant (standard value) regardless of the DC bias voltage, the ideal characteristic F3 is obtained. However, since the capacitance actually varies according to the difference in the DC bias voltage, the actual characteristic F2 is deviated from the ideal characteristic F3. Moreover, the amount of deviation varies greatly depending on the magnitude of the applied voltage as shown in FIG.

  When measuring the ground fault resistance, the calculation is performed on the assumption that the capacitance of the detection capacitor C1 is constant. Therefore, the deviation of the characteristic F2 from the ideal characteristic F3 becomes a measurement error of the ground fault resistance. Connected. In addition, since the deviation amount varies according to the applied voltage as shown in FIG. 8, it is not easy to eliminate the influence of the DC bias characteristics.

  Actually, when the above-described basic measurement cycle schedule is executed in order to measure the voltages V0, Vc1n, and Vc1p necessary for the calculation of the ground fault resistance, the voltage between the terminals is increased by charging and discharging the detection capacitor C1. The absolute value changes like the waveform of | Vc | shown in FIG. That is, the voltage between the terminals of the detection capacitor C1 gradually rises to a voltage | Vc | according to an exponential function from the relationship between the resistances of the resistors R1 and R2 and the capacitance of the detection capacitor C1. It becomes saturated and constant when fully charged.

  That is, if the capacitance of the detection capacitor C1 changes, the rising curve of | Vc | at the time of charging also changes and affects the measured voltage value. Further, in the process of charging the detection capacitor C1, the voltage between the terminals of the detection capacitor C1 changes as shown by the rising curve shown in FIG. 3, so that the influence of the DC bias characteristic of the detection capacitor C1 also varies at each time point. Change. Furthermore, the influence of the DC bias characteristic changes with the fluctuation of the high voltage applied to the insulation state detection device 10 from the positive power supply line 111 and the negative power supply line 112.

  Therefore, in order to reduce the influence of the DC bias characteristic of the detection capacitor C1, control as shown in FIG. 3 is performed. That is, the charging time length Tc1n when charging the detection capacitor C1 in the Vc1n measurement section is variable, and the charging time length Tc1n is automatically set based on the charging time length T1 and the V0 measurement value in the immediately preceding T0 measurement section. adjust. Further, the charging time length Tc1p for charging the detection capacitor C1 in the Vc1p measurement section is variable, and the charging time length Tc1p is automatically set based on the charging time length T1 and the V0 measurement value in the immediately preceding T0 measurement section. adjust. The adjustment amounts of the charging time lengths Tc1n and Tc1p are determined so as to compensate for the deviation between the characteristics F2 and F3 in FIG. 8 due to the influence of the DC bias characteristics. Actually, the adjustment amount is determined using a constant table TB2 for DC bias voltage compensation described later.

  For example, assuming that the charging time length T1 of the T0 measurement section is constant, the fluctuation amount of the high voltage applied to the insulation state detection device 10 from the positive power supply line 111 and the negative power supply line 112, and the detection capacitor C1 The influence of the DC bias characteristic is reflected in the V0 measurement value. Therefore, if the charging time length Tc1n in the Vc1n measurement section is corrected according to the V0 measurement value, it is possible to obtain the result of eliminating the characteristic deviation due to the influence of the high voltage fluctuation and the DC bias characteristic as the Vc1n measurement value. . Similarly, if the charging time length Tc1p in the Vc1p measurement section is corrected according to the V0 measurement value, it is possible to obtain the result of eliminating the characteristic deviation due to the influence of the high voltage fluctuation and the DC bias characteristic as the Vc1p measurement value. Become.

  Note that the actual charging time length T1 in the T0 measurement section is automatically adjusted according to the temperature as shown in FIG. 3 in order to correct the variation in characteristics due to the temperature of the detection capacitor C1.

<Description of Constant Table Used for DC Bias Voltage Compensation of Detection Capacitor C1>
A configuration example of a constant table for DC bias voltage compensation is shown in FIG.

  In the constant table TB2 shown in FIG. 7, information on correction coefficients associated with each of a plurality of ranges of the voltage measurement value of the detection capacitor C1 is held. In other words, “A-100 ± 25 [V]”, “A-50 ± 25 [V]”, “A ± 25 [], based on a predetermined reference value A [V] of the V0 measurement value of the detection capacitor C1. V] ”,“ A + 50 ± 25 [V] ”,“ A + 100 ± 25 [V] ”, etc., each has a charging time length correction coefficient.

  In the constant table TB2 of FIG. 7, for example, the charging time length T1 is set to “T1 × 1.1 [sec] for the range of“ A-50 ± 25 [V] ”of the V0 measurement value of the detection capacitor C1. ] ”Is assigned a correction coefficient (1.1). Further, for the range of “A + 100 ± 25 [V]” of the V0 measurement value of the detection capacitor C1, a correction coefficient (0 for correcting the charging time length T1 to “T1 × 0.8 [sec]” .8) is assigned.

  The reference value A [V] in the constant table TB2 of FIG. 7 corresponds to a voltage at which the characteristics F2 and F3 shown in FIG. Therefore, in the voltage range of “A ± 25 [V]”, it is not necessary to correct the charging time length, and “1” is assigned as the correction coefficient. Further, in the range of “A−50 ± 25 [V]” of the V0 measurement value, the characteristic F2 shifts to the negative side with respect to the characteristic F3 as shown in FIG. 8, and therefore, the voltage of Vc1n and Vc1p is adjusted to increase. Therefore, a correction coefficient larger than “1” is assigned. Further, in the range of “A + 100 ± 25 [V]” of the measured value V0, the characteristic F2 shifts to the plus side with respect to the characteristic F3 as shown in FIG. 8, so that the voltages Vc1n and Vc1p are adjusted to decrease. , A correction coefficient smaller than “1” is assigned.

  The constant table TB2 is held in advance on the internal memory (ROM or nonvolatile memory) of the microcomputer 11. Therefore, the microcomputer 11 can instantaneously obtain an optimum correction coefficient for eliminating the influence of the DC bias voltage of the detection capacitor C1 when measuring the voltages Vc1n and Vc1p from the constant table TB2. Therefore, when the Vc1n measurement interval is executed, the V0 measurement value obtained in the immediately preceding V0 measurement interval can be immediately reflected in the charging time length Tc1n. Further, when the Vc1p measurement interval is executed, the V0 measurement value obtained in the immediately preceding V0 measurement interval can be immediately reflected in the charging time length Tc1p.

<Control Operation in Insulation State Detection Device 10>
<Processing contents of microcomputer 11>
FIG. 2 shows the main control contents of the insulation state detection apparatus 10 shown in FIG. That is, the microcomputer 11 executes the process of FIG. A specific example of the operation timing of the insulation state detection device shown in FIG. 1 is shown in FIG.

The contents of the control shown in FIG. 2 will be described below.
When the power source of the insulation state detection apparatus 10 is turned on, the microcomputer 11 performs a predetermined initialization in step S11 and then proceeds to the process of S12.

  In step S12, the microcomputer 11 inputs the analog level of the signal output from the thermistor 25 from the analog input port AD2 via the wiring 37 and converts it into digital information. Thereby, the temperature information in the vicinity of the detection capacitor C1 can be grasped.

  In step S13, the microcomputer 11 obtains the correction coefficient for the charging time of the detection capacitor C1 according to the temperature measurement value from the constant table TB1 shown in FIG. 4, and determines the charging time length T1. For example, when the temperature is 35 [° C.], a value of (0.9) is acquired from the constant table TB1 as a correction coefficient, and the charging time length T1 is determined to be (T0 × 0.9). The reference time length T0 is a constant.

  In step S14, the microcomputer 11 executes the schedule of the basic measurement cycle, and acquires each measurement value of V0, Vc1n, and Vc1p. In other words, the switching elements S1 to S4 are controlled as shown in FIG. Measure and acquire each.

  In this case, the absolute value of the voltage appearing between the terminals of the detection capacitor C1 has a waveform such as | Vc | shown in FIG. The time length (T1) from the start of charging of the detection capacitor C1 in the “V0 measurement section” to the timing of measuring the voltage corresponds to the charging time length T1 determined in step S13.

  The charging time length Tc1n of the “Vc1n measurement section” and the charging time length Tc1p of the “Vc1p measurement section” are determined based on the charging time length T1. Therefore, the timing for actually measuring each voltage (V0, Vc1n, Vc1p) is automatically adjusted according to the temperature of the detection capacitor C1.

  Further, when executing the basic measurement cycle schedule in step S14, the microcomputer 11 simultaneously executes the processes of steps S21 to S26 shown in FIG. The processing of S21 to S26 will be described later.

  In step S15, the microcomputer 11 calculates the resistance value RL of the ground fault resistance based on the measured value of each voltage (V0, Vc1n, Vc1p) acquired in S14 and a predetermined calculation formula.

  In step S16, the microcomputer 11 compares the resistance value RL of the ground fault resistance acquired in S15 with a predetermined ground fault resistance alarm value (lower limit value) RLref. If the condition “RL <RLref” is satisfied, the process proceeds to S17. If the condition is not satisfied, the process proceeds to S18.

  In step S <b> 17, the microcomputer 11 outputs a ground fault resistance alarm to the output terminal 21 because the resistance value RL of the ground fault resistance detected by the insulation state detection device 10 is less than the ground fault resistance alarm value RLref.

  In step S18, the microcomputer 11 outputs information indicating the resistance value RL of the ground fault resistance acquired in S15 to the output terminal 21.

Next, steps S21 to S26 shown in FIG. 2 will be described.
In step S21, the microcomputer 11 identifies whether or not it is the timing when the measurement of the latest voltage V0 is completed in each “V0 measurement section” shown in FIG. That is, when the measurement of the voltage V0 is completed, the process proceeds from S21 to S22.

  In step S22, the microcomputer 11 acquires a DC bias voltage compensation correction coefficient from the constant table TB2 shown in FIG. 7 based on the latest V0 measurement value acquired immediately before, and determines the charging time length T2.

  In step S23, the microcomputer 11 identifies whether or not it is the timing corresponding to the “Vc1n measurement section” shown in FIG. That is, when the “Vc1n measurement section” is executed, the process proceeds to the next step S24.

  In step S24, the microcomputer 11 determines the latest charging time length T2 determined immediately before by the processing of S22 as the charging time length Tc1n of this section.

  In step S25, the microcomputer 11 identifies whether or not the timing corresponds to the “Vc1p measurement section” shown in FIG. That is, when the “Vc1p measurement section” is executed, the process proceeds to the next step S26.

  In step S26, the microcomputer 11 determines the latest charging time length T2 determined immediately before by the processing of S22 as the charging time length Tc1p of the current section.

  Therefore, when the microcomputer 11 executes the process shown in FIG. 2, the operation shown in FIG. 3 is realized. That is, the charging time length Tc1n of the detection capacitor C1 when executing the “Vc1n measurement section” shown in FIG. 3 is based on the V0 measurement value obtained in the immediately preceding “V0 measurement section” and the constant table TB2. It is automatically adjusted using a correction factor that can be acquired. The charging time length Tc1p of the detection capacitor C1 when executing the “Vc1p measurement section” shown in FIG. 3 is based on the V0 measurement value obtained in the immediately preceding “V0 measurement section” and the constant table TB2. It is automatically adjusted using a correction factor that can be acquired.

  As shown in FIG. 8, the influence of the DC bias characteristic of the detection capacitor C1 varies depending on the magnitude of the applied voltage. The magnitude of the applied voltage is detected as a V0 measurement value in the “V0 measurement section”. By acquiring an appropriate correction coefficient based on the V0 measurement value and the constant table TB2 and adjusting the charging time lengths Tc1n and Tc1p, the influence of the DC bias characteristic can be eliminated. Further, since the correction coefficient is acquired using the V0 measurement value detected immediately before the “Vc1n measurement interval” and the “Vc1p measurement interval”, the charging time lengths Tc1n and Tc1p can be adjusted in real time. Therefore, even when the high voltage output from the in-vehicle DC high voltage power supply 50 fluctuates, appropriate correction can be performed based on the current voltage (V0), and the measurement accuracy of the ground fault resistance is improved.

  Although not shown in FIG. 2, steps S12 and S13 can be executed again every time a predetermined time elapses while steps S14 to S26 are being executed. Thereby, the influence of the temperature change with time can also be compensated.

By performing the control as shown in FIG. 2, the following advantages can be obtained.
(1) Even when a ceramic capacitor is employed as the detection capacitor C1, improvement in detection accuracy of the ground fault resistance can be expected.
(2) By performing appropriate correction, it is possible to improve not only the relative value but also the voltage detection accuracy as an absolute value. Therefore, the ground fault resistance can be detected with high accuracy.
(3) Since the charging time length (T1, Tc1n, Tc1p) of the detection capacitor C1 is automatically adjusted, correction can be made to increase the charge amount under the condition that the charged charge is small. Thereby, measurement in a lower voltage region and a higher resistance region becomes possible. The noise margin can be improved by raising the threshold value for failure determination. Moreover, it can correct | amend so that the amount of electric charges may be reduced on the conditions in which charging charge is large. As a result, the voltage dividing ratio of the voltage dividing circuit constituted by the resistors R3, R4, and R5 can be increased, and the dynamic range of the A / D conversion input can be utilized more effectively.

  In addition, about the detailed circuit structure of the insulation state detection apparatus 10 shown in FIG. 1, various deformation | transformation can be considered as disclosed by patent document 3, for example. What is necessary is just to change about a detailed circuit structure as needed.

<Supplementary explanation>
(1) The insulation state detection device (10) shown in FIG. 1 is connected to the positive power supply line (111) and the negative power supply line (112) of a predetermined on-vehicle high-voltage DC power supply (50), respectively. An input terminal (13), a negative electrode side input terminal (14), and a ground electrode (15), and based on the charging voltage of the flying capacitor (C1), the positive electrode side power line, the negative electrode side power line, and the ground electrode Grasping the insulation state between them as ground fault resistance. In addition, a first voltage measurement value (V0) obtained when the flying capacitor is charged through a first energization path (energization path of the V0 measurement section) that is not affected by the ground fault resistance, and the flying capacitor Are measured through the second energization path (Vc1n measurement section or the energization path of the Vc1p measurement section) that is affected by the ground fault resistance, respectively, and second voltage measurement values (Vc1n, Vc1p) obtained when the battery is charged. A charging voltage measurement unit (S14) and a ground fault resistance value calculation unit that calculates the value of the ground fault resistance based on the first voltage measurement value and the second voltage measurement value measured by the charging voltage measurement unit. (S15) and before changing the charging time length (Tc1n, Tc1p) of the flying capacitor for measuring the second voltage measurement value and measuring the second voltage measurement value Was the first voltage measured value (V0), and includes automatic charging time length control unit that reflects the (S21 to S26) in the charging time length.

  (2) Further, as shown in FIG. 7, the charging time length control unit associates and holds each of a plurality of voltage ranges and information on coefficients related to the charging time length (TB2). And the charging time length when measuring the second voltage measurement value is automatically calculated using the constant table based on the first voltage measurement value detected by the charging voltage measurement unit. Correction is performed (S22).

  (3) Further, a temperature detection unit (25) that detects a temperature in the vicinity of the flying capacitor, and a temperature compensation control unit that reflects the temperature parameter detected by the temperature detection unit in the charging time length of the flying capacitor ( S12, S13).

  (4) Further, the temperature compensation control unit has a temperature compensation table (TB1) that holds each of the plurality of temperature ranges in association with information on a coefficient corresponding to a length of time for charging the flying capacitor. And the charging time length is automatically corrected using the temperature compensation table based on the temperature detected by the temperature detector (S13).

DESCRIPTION OF SYMBOLS 10 Insulation state detection apparatus 11 Microcomputer 13 Positive electrode side input terminal 14 Negative electrode side input terminal 15 Ground electrode 20 Input circuit 21 Output terminal 25 Thermistor 31-37 Wiring 50 In-vehicle DC high voltage power supply 101, 102 Y capacitor 103 Ground electrode 111 Positive electrode side power supply Line 112 Negative power supply line C1 Capacitor for detection (flying capacitor)
D1, D2, D3 Diode R1, R2, R3, R4, R5 Resistor RLp, RLn Ground fault resistance S1, S2, S3, S4 Switching element SWx Operation switch TB1 Constant table (for temperature compensation)
TB2 constant table (for DC bias voltage compensation)

Claims (4)

A positive-side input terminal and a negative-side input terminal connected to a positive-side power line and a negative-side power line of a predetermined high-voltage DC power output, respectively, and a ground electrode, and the positive-side based on the charging voltage of the flying capacitor An insulation state detection device for grasping an insulation state between a power line and a negative side power line and the ground electrode as a ground fault resistance,
A first voltage measurement value obtained when the flying capacitor is charged through a first energization path not affected by the ground fault resistance, and a second energization affected by the ground fault resistance. A charging voltage measuring unit for measuring each of the second voltage measurement values obtained when charging via the path;
A ground fault resistance value calculation unit that calculates a value of the ground fault resistance based on the first voltage measurement value and the second voltage measurement value measured by the charging voltage measurement unit;
The charging time length of the flying capacitor for measuring the second voltage measurement value is variable, and the first voltage measurement value obtained before measuring the second voltage measurement value is used as the charge time. A charging time length control unit that automatically reflects the length,
An insulation state detection device comprising: The charging time length control unit has a constant table that associates and holds each of a plurality of voltage ranges and information on a coefficient related to the charging time length, and the charging voltage measurement unit detects the first 2. The insulation according to claim 1, wherein the charging time length when the second voltage measurement value is measured is automatically corrected based on the voltage measurement value of 1 using the constant table. State detection device. A temperature detector for detecting a temperature in the vicinity of the flying capacitor;
A temperature compensation controller that reflects the temperature parameter detected by the temperature detector in the charging time length of the flying capacitor;
The insulation state detection device according to claim 1, further comprising: The temperature compensation control unit includes a temperature compensation table that holds each of a plurality of temperature ranges in association with information on a coefficient corresponding to a length of time for charging the flying capacitor, and the temperature detection unit The insulation state detection device according to claim 3, wherein the charging time length is automatically corrected based on the detected temperature using the temperature compensation table.

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