JP6309979B2 - Insulation detector - Google Patents

Description

  The present invention relates to an insulation detection device that detects a ground fault or an insulation state with respect to a ground potential portion of a DC power source based on a charging voltage of a flying capacitor charged by a DC power source insulated from a ground potential portion.

  As a conventional insulation detection device, for example, a flying capacitor type insulation detection device has been proposed.

  In this conventional insulation detection device, when detecting the insulation state of a DC high-voltage power supply, the voltage of the high-voltage power supply was charged to a capacitor (that is, a flying capacitor) in a state of floating from the ground, and the voltage at both ends thereof was measured. In the state where one of the capacitors is grounded via a resistor, the high-voltage power supply voltage is charged to the capacitor in the same way, and the ground fault resistance is calculated by calculating the ground fault resistance based on the measured value at both ends. The insulation state of the power source is detected (see Patent Document 1).

  For example, in a vehicle that uses electric power as propulsion energy, it is normal to insulate a high-voltage (eg, 200 V) DC power source from the vehicle body and use it as a non-grounded power source. The insulation detection device having the above-described configuration is used to detect a ground fault or an insulation state with respect to the ground potential portion.

JP 2004-170103 A (JP 2004-170103 A)

  By the way, as the power of the object to be inspected (vehicles, etc.) of the insulation detection device becomes higher (for example, 400V), the semiconductor relays such as optical MOS-FETs used in the flying capacitor type ground fault measuring circuit are also increased. There is a demand for pressure resistance.

  However, optical MOS-FETs with high breakdown voltage (for example, withstand voltage of about 900 V) have the disadvantage that they are technically difficult to manufacture and the unit cost of components is high, increasing the cost of the entire device.

  In addition, when a high breakdown voltage optical MOS-FET or the like is used, there is a problem in that the energization current decreases.

  In other words, in the flying capacitor type ground fault measurement circuit, if the energization current of the optical MOS-FET or the like is limited to a low level as the ground fault measurement circuit has a high withstand voltage, charge / discharge is reduced due to the ground fault measurement circuit method. Current is limited to be low. Along with this, the required time for charging / discharging has to be changed for a long time, and the measurement cycle becomes slow, so there is a problem that it is not possible to meet the demand for high-speed measurement of ground faults and insulation states of vehicles etc. It was.

  The present invention has been made in view of the above problems, and provides an insulation detection device capable of achieving a high breakdown voltage without using a high breakdown voltage semiconductor relay and ensuring an energization current. Objective.

  In order to achieve the above object, a ground fault measuring circuit according to an aspect of the present invention is for detecting an insulation state of a DC power source, and includes a positive terminal and a negative terminal of the DC power source insulated from a ground potential portion. Are connected to each other, and the flying capacitor is charged with a charge amount corresponding to the power supply voltage of the DC power supply, the changeover switch for switching between charging and discharging of the flying capacitor, and the charging voltage when the flying capacitor is charged. A detectable voltage detection device and an arithmetic device for detecting an insulation state of the DC power source based on a charging voltage of the flying capacitor detected by the voltage detection device. The changeover switch is connected in parallel to each of a plurality of switches having semiconductor relays and one or more of the plurality of switches, and the maximum voltage applied to the connected semiconductor relays is set to a constant voltage. A protective element to keep.

  The changeover switch may include a first switch to a fourth switch. In this case, the first switch is connected to one terminal of the flying capacitor via a first diode and a first resistor connected in series to the positive terminal, and the second switch has a negative terminal connected to the other terminal of the flying capacitor. The third switch is connected in series between the wiring connecting the first switch and the first diode and the voltage detection device and connected in series to one terminal of the flying capacitor. The fourth switch is connected to the voltage detection device via the second diode and the third resistor, and the fourth switch has the other terminal of the flying capacitor connected to the ground potential portion via the fourth resistor.

The semiconductor relay may be composed of an optical MOS-FET relay, and the protection element may be composed of, for example, a Zener diode connected in parallel to the optical MOS-FET relay of each switch. In this case, the Zener diode or the like of the first switch is provided in a direction opposite to the current flowing from the positive terminal of the DC power supply, and the Zener diode or the like of the second switch flows toward the negative terminal of the DC power supply. The zener diode of the third switch is provided so as to be in the same forward direction as the zener diode of the first switch, and is opposite to the zener diode. Is provided with a diode for preventing reverse current, and the Zener diode of the fourth switch is provided so as to be in the same forward direction as the Zener diode of the second switch, and so on. A diode for preventing reverse current may be provided. At this time, the withstand voltage condition of each optical MOS-FET relay is:
Vds> Vz
However, Vds: the breakdown voltage of each optical MOS-FET relay, Vz: the Zener voltage of the Zener diode, and the condition of the Zener voltage (Vz) of the Zener diode are:
Vz1 + Vz3> Vd
Where Vz1 is the Zener voltage of the Zener diode of the first switch, Vz3 is the Zener voltage of the Zener diode of the third switch, Vd is the required breakdown voltage between the high voltage and the low voltage,
Vz2 + Vz4> Vd
However, Vz2: Zener voltage of the Zener diode of the second switch, Vz4: Zener voltage of the Zener diode of the fourth switch, and Vd: Dielectric breakdown voltage between required high voltage and low voltage.

  According to the aspect of the present invention, it is possible to provide an insulation detection device that can achieve a high breakdown voltage without using a high-breakdown-voltage semiconductor relay and can ensure an energization current.

FIG. 1 is a circuit diagram illustrating a basic configuration of an insulation detection device according to an embodiment. FIGS. 2A to 2D are circuit diagrams illustrating a configuration example of a first switch to a fourth switch applied to the insulation detection device according to the embodiment. FIG. 3 is a circuit diagram illustrating a configuration example of the insulation detection device according to the embodiment. FIG. 4 is a circuit diagram illustrating a configuration example of an insulation detection device according to a comparative example. FIG. 5 is a circuit diagram illustrating a configuration example of an insulation detection device according to a modification of the embodiment.

  The insulation detection device 11 according to the embodiment will be described with reference to FIGS.

(About the configuration of the insulation detector)
An insulation detection device (ground fault sensor) 11 according to the embodiment is connected between a positive terminal and a negative terminal of a high-voltage DC power supply B insulated from a ground potential portion, and has a charge corresponding to a power supply voltage of the high-voltage DC power supply B. This is an insulation detection device that detects the insulation state of the high-voltage DC power supply B by detecting the charging voltage when the flying capacitor C1 is charged in quantity by the voltage detection device 15.

  The changeover switch for switching between charging and discharging of the flying capacitor C1 includes a semiconductor relay 50 and a protection element (such as a Zener diode ZD1) that is connected in parallel to the semiconductor relay 50 and maintains the maximum voltage applied to the semiconductor relay at a constant voltage. Prepare.

  In FIGS. 1 and 3, the change-over switch is shown as having four switches (first switch S <b> 1 to fourth switch S <b> 4), but the present invention is not limited to this. You may make it comprise with five or more switches.

  The insulation detection device 11 according to the embodiment is for detecting the insulation state of the high-voltage DC power supply B insulated from the ground potential portion in a vehicle body or the like of a vehicle.

  In FIG. 1, the reference sign RLp indicates the ground fault resistance on the positive electrode side of the high-voltage DC power supply B, and the reference sign RLn indicates the ground fault resistance on the negative electrode side of the high-voltage DC power supply B.

  The insulation detection device 11 includes a bipolar flying capacitor C1, a first switch S1 to a fourth switch S4 as changeover switches, a sample hold circuit 14 that samples and holds a charging voltage and a discharge voltage of the flying capacitor C1, and a sample hold A microcomputer (hereinafter abbreviated as “microcomputer”) 15 is provided as a voltage detection device for detecting the hold value of the circuit 14 and measuring the charging voltage and discharging voltage of the flying capacitor C1. A ceramic capacitor or the like can be used as the flying capacitor C1.

  The changeover switch connects the flying capacitor C1 to the positive electrode of the high-voltage DC power supply B, the second switch S2 that connects the flying capacitor C1 to the negative electrode of the high-voltage DC power supply B, and connects the flying capacitor C1 to the microcomputer 15. And a fourth switch S4 for connecting the flying capacitor C1 to the ground potential portion. A first resistor R1 is connected in series between the flying capacitor C1 and the first switch S1, and a second resistor R2 is connected in series between the flying capacitor C1 and the second switch S2.

  In order to ensure insulation against the high-voltage DC power source B when the microcomputer 15 measures the charging voltage and discharging voltage of the flying capacitor C1, the first resistor R1 and the second resistor R2 have relatively high resistance values. A resistance (eg 300 kΩ) is used.

  For each of the first switch S1 to the fourth switch S4, for example, a semiconductor relay 50 such as an optical MOS-FET relay is used, and the microcomputer 15 can perform on / off control (open / close control).

  Here, an optical MOS-FET is an element that transmits light while electrically insulating using light, and is a complete solid state relay (semiconductor relay) that employs a light emitting diode on the drive side and a MOS-FET on the contact point. ). An optical MOS-FET relay using an optical MOS-FET is not only smaller and lighter than a conventional mechanical relay, but also has a characteristic that it is easy to drive, high speed, and hardly generates noise. On the other hand, in the optical MOS-FET, when a high breakdown voltage (for example, a breakdown voltage of 900 V) is to be achieved, the unit unit price is considerably higher than that of a normal breakdown voltage (for example, about 600 V) due to technical difficulties. There is a difficulty.

  A specific configuration example of the first switch S1 to the fourth switch S4 will be described later with reference to FIG.

  The microcomputer 15 is operated by a low-voltage auxiliary battery lower than the high-voltage DC power supply B. The high-voltage DC power source B is also insulated from the ground potential of the microcomputer 15.

  The first A / D conversion port A / D1 of the microcomputer 15 is connected to the third switch S3 via the sample hold circuit 14. A connection point between the sample hold circuit 14 and the third switch S3 is grounded via a fifth resistor R4. A fourth resistor R5 is connected between the fourth switch S4 and the ground potential portion. The first switch S1 and the third switch S3 on one end (upper pole in FIG. 1) side of the flying capacitor C1 are connected in series. A current direction switching circuit X is connected between a connection point between the first switch S1 and the third switch S3 and one end of the flying capacitor C1.

  The current direction switching circuit X is a parallel circuit, and includes a series circuit of a first diode D0 and a first resistor R1 that are forward from the first switch S1 toward one end of the flying capacitor C1, and a third circuit from one end of the flying capacitor C1. A series circuit of a second diode D2 and a third resistor R3 that are forward toward the switch S3, and a third diode D1 that is forward from the third switch S3 toward one end of the flying capacitor C1.

  In the embodiment, the high-voltage DC power supply B is provided with Y capacitors Y + and Y− for countermeasure against common mode noise between the positive and negative poles and the ground potential portion.

  The positive-side Y capacitor Y + is connected between the positive-side power supply line 111 of the high-voltage power supply output and the ground electrode 113. The negative-side Y capacitor Y− is connected between the negative-side power line 112 for high-voltage power output and the ground electrode 113. The insulation state between the positive power line 111 and the ground electrode 113 is represented as a ground fault resistance RLp, and the insulation state between the negative power line 112 and the ground electrode 113 is represented as a ground fault resistance RLn.

(About operation of insulation detector)
Next, an operation procedure for detecting a ground fault or an insulation state in the insulation detection device 11 having the above-described configuration will be described.

  First, under the control of the microcomputer 15, the first switch S1 and the second switch S2 are turned on for a predetermined time, and the third switch S3, the fourth switch S4, and the sample hold circuit 14 are turned on. Turn off the switch. Here, the predetermined time is a time shorter than the time required for the flying capacitor C1 to be fully charged.

  Thereby, from the positive electrode of the high-voltage DC power supply B, the main circuit wiring 1p on the positive terminal side, the first switch S1, the first diode D0, the first resistor R1, one end of the flying capacitor C1 (the upper terminal in FIG. 1), etc. A charging circuit is formed that passes through the end (the lower terminal in FIG. 1), the second resistor R2, the second switch S2, and the main circuit wiring 1n on the negative terminal side to reach the negative electrode of the high-voltage DC power supply B. Hereinafter, the charging circuit of this path is referred to as a first charging circuit.

  In the first charging circuit, the flying capacitor C1 is charged with a charge amount corresponding to the voltage of the high-voltage DC power supply B. By charging in the first charging circuit, one end of the flying capacitor C1 becomes a positive electrode and the other end becomes a negative electrode.

  Subsequently, under the control of the microcomputer 15, the first switch S1 and the second switch S2 are turned off, and the third switch S3 and the fourth switch S4 are turned on. Thereby, the positive electrode of the flying capacitor C1 is connected to the sample hold circuit 14 via the second diode D2, the third resistor R3, and the third switch S3, and the negative electrode of the flying capacitor C1 is connected to the fourth switch S4 and the fourth switch S4. The resistor R5 is connected to the ground potential portion. As a result, the flying capacitor C1 is discharged.

  At the same time when the third switch S3 and the fourth switch S4 are turned on, the switch of the sample hold circuit 14 is turned on for a short time (for example, 200 to 300 μs) under the control of the microcomputer 15. As a result, the reading capacitor 17 is charged at a potential corresponding to the difference between the voltages at both ends of the third resistor R3 among the divided voltages of the flying capacitor C1 by the third resistor R3 and the fifth resistor R4.

  Here, at the start of discharging of the flying capacitor C1, the flying capacitor C1 is charged with a charge amount corresponding to the voltage of the high-voltage DC power supply B. Therefore, the reading capacitor 17 charged with the discharge voltage immediately after the start of discharging of the flying capacitor C1 has a voltage dividing ratio between the fifth resistor R4 and the fourth resistor R5 in the amount of charge corresponding to the voltage of the high-voltage DC power supply B. The amount of charge corresponding to is accumulated.

  Then, when the switch of the sample hold circuit 14 is turned off under the control of the microcomputer 15, the potential obtained by dividing the charging voltage of the reading capacitor 17 becomes the first A / D conversion port A / D of the microcomputer 15 via the sample hold circuit 14. D1 is input and measured. Therefore, the charging of the flying capacitor C1 according to the voltage of the high-voltage DC power supply B is obtained from this measured value, the voltage dividing ratio of the third resistor R3 and the fifth resistor R4, and the voltage dividing ratio of the fifth resistor R4 and the fourth resistor R5. The voltage Vc1 is measured by the microcomputer 15.

  Since the third switch S3 and the fourth switch S4 remain turned on while the charging voltage of the flying capacitor C1 is measured after the sample hold circuit 14 is turned off, the flying capacitor C1 continues to be turned on. It is in a discharged state.

  Further, after the measurement of the charging voltage of the flying capacitor C1 is completed, the sample hold circuit 14 is switched on under the control of the microcomputer 15. As a result, the flying capacitor C1 and the reading capacitor 17 are discharged. When the flying capacitor C1 and the reading capacitor 17 are completely discharged, the third switch S3, the fourth switch S4, and the switch of the sample hold circuit 14 are turned off under the control of the microcomputer 15.

  Then, after the flying capacitor C1 and the reading capacitor 17 are completely discharged, the first switch S1 and the fourth switch S4 are turned on over the predetermined time described above under the control of the microcomputer 15, and the second The switch switch S2 and the third switch S3 are turned off.

  Thereby, from the positive electrode of the high-voltage DC power source B, the main circuit wiring 1p on the positive terminal side, the first switch S1, the first diode D0, the first resistor R1, one end and the other end of the flying capacitor C1, the fourth switch S4, the second switch A charging circuit is formed on the path leading to the negative electrode of the high-voltage DC power supply B through the four resistors R5, the (ground potential portion) ground fault resistor RLn on the negative terminal side, and the main circuit wiring 1n on the negative terminal side. Hereinafter, the charging circuit of this path is referred to as a second charging circuit.

  In the second charging circuit, the flying capacitor C1 is charged with an amount of charge corresponding to the ground terminal resistance RLn on the negative terminal side. By charging in the second charging circuit, one end of the flying capacitor C1 becomes a positive electrode and the other end becomes a negative electrode.

  Subsequently, under the control of the microcomputer 15, the first switch S1 and the second switch S2 are turned off, the third switch S3 and the fourth switch S4 are turned on, and the switch of the sample hold circuit 14 is turned on for a short time ( For example, 200 to 300 μs) is turned on.

  After that, until the switch of the sample hold circuit 14 is turned on again under the control of the microcomputer 15, the ground on the negative terminal side is measured in the same manner as the measurement of the charging voltage of the flying capacitor C1 according to the voltage of the high-voltage DC power supply B. The microcomputer 15 measures the charging voltage of the flying capacitor C1 in accordance with the resistance RLn.

  Then, after the flying capacitor C1 and the reading capacitor 17 are completely discharged, the second switch S2 and the third switch S3 are turned on for the predetermined time described above under the control of the microcomputer 15, and the first The switch S1 and the fourth switch S4 are turned off.

  Thereby, from the positive electrode of the high-voltage DC power supply B, the main circuit wiring 1p on the positive terminal side, the ground fault resistance RLp on the positive terminal side, the (ground potential part) fifth resistor R4, the third switch S3, the third diode D1, A charging circuit is formed on the path leading to the negative electrode of the high-voltage DC power supply B through one end and the other end of the flying capacitor C1, the second resistor R2, the second switch S2, and the main circuit wiring 1n on the negative terminal side. Hereinafter, the charging circuit of this path is referred to as a third charging circuit.

  In this third charging circuit, the flying capacitor C1 is charged with a charge amount corresponding to the ground fault resistance RLp on the positive terminal side. By charging in the third charging circuit, one end of the flying capacitor C1 becomes a positive electrode and the other end becomes a negative electrode.

  Subsequently, under the control of the microcomputer 15, the first switch S1 and the second switch S2 are turned off, the third switch S3 and the fourth switch S4 are turned on, and the switch of the sample hold circuit 14 is turned on for a short time ( For example, 200 to 300 μs) is turned on.

  Thereafter, during the measurement of the charging voltage Vc1 of the flying capacitor C1 corresponding to the voltage of the high-voltage DC power supply B, or the ground fault resistance on the negative terminal side until the switch of the sample hold circuit 14 is turned on again under the control of the microcomputer 15. Similarly to the measurement of the charging voltage of the flying capacitor C1 according to RLn, the microcomputer 15 measures the charging voltage of the flying capacitor C1 according to the ground fault resistance RLp on the positive terminal side. Then, the flying capacitor C1 and the reading capacitor 17 are completely discharged.

  Here, regarding the measurement of the ground fault resistance in the insulation detection device 11 shown in FIG. 1, the composite ground fault resistance “(RLp × RLn) / (RLp + RLn)” can be derived based on (Vc1p + Vc1n) / Vc1. .

  Where Vc1: charging voltage of the flying capacitor C1 according to the output voltage of the high-voltage DC power supply B, Vc1n: charging voltage of the flying capacitor C1 affected by the negative side ground fault resistance RLn, Vc1p: positive side ground fault resistance The charging voltage of the flying capacitor C1 affected by RLp, RLp, RLn: resistance values of the local fault resistors.

  Thereby, the microcomputer 15 grasps each charging voltage “Vc1”, “Vc1n”, “Vc1p” from the signal level input to the analog input port (A / D1) in each state, and based on the above relational expression, The tangential resistances RLp and RLn can be calculated.

  Therefore, the microcomputer 15 can calculate the parallel combined resistance value of the ground fault resistance RLp on the positive terminal side and the ground fault resistance RLn on the negative terminal side, and detect the ground fault and the insulation state of the high-voltage DC power supply B.

(Regarding the configuration example of the first switch S1 to the fourth switch S4)
Next, a configuration example of the first switch S1 to the fourth switch S4 will be described with reference to FIGS.

  First, the first switch S1 applied to the insulation detection device 11 according to the embodiment has a configuration shown in the circuit diagram of FIG.

  That is, the first switch S1 is connected to the optical MOS-FET relay 50 in parallel with the optical MOS-FET relay 50, and a Zener diode ZD1 as a protection element that keeps the maximum voltage applied to the optical MOS-FET relay 50 at a constant voltage. And an IC 20 as a switch control device for performing on / off control (opening / closing control) of the optical MOS-FET relay 50.

  Zener diode ZD1 is provided in the opposite direction to the current flowing from the positive terminal of high-voltage DC power supply B.

  The second switch S2 has a configuration shown in the circuit diagram of FIG.

  That is, the second switch S2 is connected to the optical MOS-FET relay 50 in parallel with the optical MOS-FET relay 50, and a Zener diode ZD2 as a protective element that keeps the maximum voltage applied to the optical MOS-FET relay 50 at a constant voltage. And an IC 20 as a switch control device for performing on / off control (opening / closing control) of the optical MOS-FET relay 50.

  The Zener diode ZD2 is provided in the opposite direction to the current flowing toward the negative terminal of the high-voltage DC power supply B.

  The third switch S3 has a configuration shown in the circuit diagram of FIG.

  That is, the third switch S3 includes the optical MOS-FET relay 50 and a Zener diode ZD3a as a protective element that is connected in parallel to the optical MOS-FET relay 50 and keeps the maximum voltage applied to the optical MOS-FET relay 50 at a constant voltage. As a switch control device that performs on / off control (open / close control) of the optical MOS-FET relay 50 and a series circuit of a reverse current prevention diode (Zener diode) ZD3b provided in the opposite direction to the Zener diode ZD3a IC20.

  The Zener diode ZD3a is provided in the same forward direction as the Zener diode ZD1 of the first switch S1.

  In the example shown in FIG. 2C, the case where the Zener diode ZD3b is used as the diode for preventing the reverse current is shown. However, the present invention is not limited to this, and a normal diode may be used.

  The fourth switch S4 has a configuration shown in the circuit diagram of FIG.

  That is, the fourth switch S4 includes the optical MOS-FET relay 50 and a Zener diode ZD4b as a protective element that is connected in parallel to the optical MOS-FET relay 50 and keeps the maximum voltage applied to the optical MOS-FET relay 50 at a constant voltage. As a switch control device that performs on / off control (open / close control) of the optical MOS-FET relay 50 and a series circuit of a reverse current prevention diode (Zener diode) ZD4a provided in the opposite direction to the Zener diode ZD4b IC20.

  Note that the Zener diode ZD4b is provided in the same forward direction as the Zener diode ZD2 of the second switch S2.

  In the example shown in FIG. 2D, the case where the Zener diode ZD4a is used as the reverse current prevention diode has been described. However, the present invention is not limited to this, and a normal diode may be used.

Here, the withstand voltage condition of each optical MOS-FET relay 50 is:
Withstand voltage (Vds) of each optical MOS-FET relay> Zener voltage (Vz) of Zener diodes (ZD1, ZD2, ZD3a, ZD4b) (for example, about 550V to 600V)
And the condition of the Zener voltage of the Zener diode (ZD1, ZD2, ZD3a, ZD4b) is
(Zener voltage (Vz1) of the Zener diode ZD1 of the first switch S1 + Zener voltage (Vz3) of the Zener diode ZD3a of the third switch S3)> Required high-voltage to low-voltage dielectric breakdown voltage (Vd) (for example, 900 V to 1000V)
(Zener voltage (Vz2) of the Zener diode ZD2 of the second switch S2 + Zener voltage (Vz4) of the Zener diode ZD4b of the fourth switch S4) >> required withstand voltage (Vd) between high voltage and low voltage (for example, 900 V to 1000V)
It is good to do.

  As described above, when the required withstand voltage between the high voltage and the low voltage is 900 V to 1000 V, for example, the Zener voltage of the Zener diode (ZD1, ZD2, ZD3a, ZD4b) may be about 550 V to 600 V, for example. Further, it is calculated that the withstand voltage of the optical MOS-FET relay 50 is about 600V. Therefore, a general-purpose product with a withstand voltage of about 600V can be used as each optical MOS-FET relay 50, and it is not necessary to use a high withstand voltage type with a withstand voltage of about 900V, which increases the unit price, and the cost of the apparatus can be reduced.

  As described above, a relatively high resistance value of about 300 kΩ is used for the first resistance R1 and the second resistance R2, so that, for example, a voltage of about 900 V is applied to the circuit when an abnormality occurs. In addition, about 300 V can be consumed by the voltage drop caused by the first resistor R1 and the second resistor R2. Therefore, even when such an abnormal voltage (about 900 V) is generated, it is possible to avoid a situation where a voltage with a withstand voltage of 600 V or more is applied to the optical MOS-FET relay 50.

  Even when the changeover switch is composed of 2 to 3 switches or 5 or more switches, the configuration of each switch can be the same as described above.

(Configuration example of insulation detection device according to comparative example)
FIG. 4 is a circuit diagram illustrating a configuration example of the insulation detection device 100 according to the comparative example.

  In addition, about the structure similar to the insulation detection apparatus 11 which concerns on embodiment, the same code | symbol is attached | subjected and the overlapping description is abbreviate | omitted.

  The insulation detection device 100 according to the comparative example is different from the insulation detection device 11 according to the embodiment in that instead of the first switch S1 to the fourth switch S4 of the circuit configuration shown in FIG. The switches S11 to S14 are provided.

  In the high voltage DC power supply B, Y capacitors Y + and Y− for countermeasure against common mode noise are interposed between the positive and negative poles and the ground potential portion.

  Here, the optical MOS-FET relays S <b> 11 to S <b> 14 used in the flying capacitor type ground fault measurement circuit as the power of the object to be inspected (vehicle or the like) such as the insulation detection device 100 according to the comparative example increases. There is also a demand for higher breakdown voltage (for example, a breakdown voltage of 900 V or higher).

  However, since it is technically difficult to increase the breakdown voltage of the optical MOS-FETs (S11 to S14), the number of manufacturers that can be manufactured is limited.

  In addition, when a high-breakdown-voltage optical MOS-FET (S11 to S14) is used, there is a problem in that the energization current decreases. In other words, in the flying capacitor type ground fault measuring circuit, if the energizing current of the optical MOS-FETs (S11 to S14) is limited to a low level as the circuit withstands a high voltage, charging / discharging is performed due to such a circuit type. Current for is limited low. Along with this, it is necessary to change the time required for charging / discharging for a long time, and the measurement cycle becomes slow, so that it becomes impossible to meet the demand for high-speed measurement of ground faults and insulation states of vehicles and the like.

  On the other hand, in the insulation detection device 11 according to the embodiment, as each of the optical MOS-FET relays 50 of the first switch S1 to the fourth switch S4, a device corresponding to a so-called general-purpose product having a withstand voltage of about 600V is used. Protection elements (Zener diodes (ZD1, ZD2, ZD3a, ZD4b)) that keep the maximum voltage applied to each optical MOS-FET relay 50 at a constant voltage are connected in parallel.

  Thereby, it is possible to prevent each optical MOS-FET relay 50 from being applied with a voltage higher than a withstand voltage (for example, about 600 V). Therefore, even if a general-purpose product having a breakdown voltage of about 600 V is used as each optical MOS-FET relay 50, the overall breakdown voltage of the first switch S1 to the fourth switch S4 can be increased. Therefore, the insulation detection device 11 can be provided at a relatively low cost without increasing the component cost as in the insulation detection device 100 according to the comparative example.

  In addition, since the energization current can be secured through the Zener diodes (ZD1, ZD2, ZD3a, ZD4b), it is possible to meet the demand for high-speed measurement of ground faults and insulation states of vehicles and the like.

(Modification)
Next, with reference to FIG. 5, an insulation detection apparatus 11A according to a modification of the embodiment will be described.

  As shown in FIG. 5, the insulation detection device 11 </ b> A according to the modification is applied to a high voltage battery system provided with a booster 18. Here, in the high voltage battery system, the output voltage (for example, 200V) of the high voltage DC power source B as the primary side high voltage is boosted to the secondary side high voltage output voltage (for example, 600V) by the booster 18. It is a system. Here, the insulation state between the primary high-voltage positive electrode and the ground electrode is represented as a ground fault resistance RLp1, and the insulation state between the primary high-voltage negative electrode and the ground electrode is represented as a ground fault resistance RLn1. ing. Similarly, the insulation state between the secondary high-voltage positive electrode and the ground electrode is represented as a ground fault resistance RLp2, and the insulation state between the secondary high-voltage negative electrode and the ground electrode is represented as a ground fault resistance RLn2. ing.

  The basic configuration and operation of the insulation detection device 11A according to the modification are similar to those of the insulation detection device 11 according to the embodiment. Therefore, hereinafter, the insulation detection device 11A according to the modification will be described only with respect to differences from the insulation detection device 11 according to the embodiment, and the same reference numerals are given to the same configurations as those of the insulation detection device 11 according to the embodiment. A duplicate description will be omitted.

  In the insulation detection device 11A according to the modification, the protection elements can be provided only in the second switch S2 and the fourth switch S4, and the protection elements of the first switch S1 and the third switch S3 can be omitted.

  Specifically, the second switch S2 includes a Zener diode ZD2b and a Zener diode ZD2b, which are connected in parallel to the optical MOS-FET relay 50 and serve as protective elements that keep the maximum voltage applied to the optical MOS-FET relay 50 at a constant voltage. A series circuit with a reverse current preventing diode (Zener diode) ZD2a provided in the reverse direction is provided. Further, the third switch S3 is connected in parallel to the optical MOS-FET relay 50, and is in a direction opposite to the Zener diode ZD4b and the Zener diode ZD4b as protective elements that keep the maximum voltage applied to the optical MOS-FET relay 50 at a constant voltage. A series circuit with a reverse current preventing diode (Zener diode) ZD4a provided as described above is provided. In the first switch S1 and the third switch S3, a Zener diode as a protection element is omitted.

  In such a configuration, it is assumed that the output voltage 200V of the high-voltage DC power source B, which is the primary side high voltage, is boosted to 600V by the booster 18 as the secondary side high voltage. Here, it is assumed that a ground fault (short circuit) has occurred on the positive side of the secondary high voltage. Then, the ground fault resistance RLp2 between the secondary high-voltage positive electrode and the ground electrode becomes 0Ω, and the point c in FIG. As a result, a voltage of 600V−0V = 600V is applied between the points b and c in FIG. 5, that is, the path between the second switch S2 and the fourth switch S4. On the other hand, a voltage of 600V−200V = 400V is applied between the points a and c in FIG. 5, that is, the path between the first switch S1 and the third switch S3.

  Therefore, when the insulation detection device 11A is applied to the high voltage battery system provided with the booster 18, the path that requires the most withstand voltage is between the points b and c, that is, the second switch S2. This is the path of the fourth switch S4.

  For this reason, for example, even when a general-purpose product having a withstand voltage of about 600 V is used as the optical MOS-FET relay 50 of each switch S1-S4, only the second switch S2 and the fourth switch S4 have protective elements (zener diodes ZD2a). , ZD2b, ZD4a, ZD4b), and the protective elements of the first switch S1 and the third switch S3 can be omitted.

  In the insulation detection device 11A according to the modification, the protective elements of the first switch S1 and the third switch S3 are omitted. However, like the insulation detection device 11 according to the embodiment, the first switch S1 and the third switch S3 are omitted. You may provide a protection element in each or one of these.

  As mentioned above, although the insulation detection apparatus which concerns on embodiment was demonstrated based on drawing, this invention is not limited to this, The structure of each part can be substituted to the thing of the arbitrary structures which have the same function. .

  For example, in the embodiment, a Zener diode is used as the protection element, but instead, a varistor, a TVS (Transient Voltage Suppressor) diode, or the like can be used.

  ADVANTAGE OF THE INVENTION According to this invention, while being able to achieve high withstand voltage without using a high withstand voltage semiconductor relay, the insulation detection apparatus which can ensure an energization current can be provided.

Claims (2)

An insulation detection device for detecting an insulation state of a DC power source,
A flying capacitor connected between a positive terminal and a negative terminal of a DC power source insulated from a ground potential unit, and charged with a charge amount according to a power source voltage of the DC power source;
A changeover switch for switching between charging and discharging of the flying capacitor;
A voltage detection device capable of detecting a charging voltage when the flying capacitor is charged;
An arithmetic unit for detecting an insulation state of the DC power source based on a charging voltage of the flying capacitor detected by the voltage detection device;
The changeover switch is connected in parallel corresponding to each of the plurality of switches including a semiconductor relay and the semiconductor relay of one or more of the plurality of switches,
The changeover switch includes a first switch, a second switch, a third switch, and a fourth switch,
The first switch is connected to one terminal of the flying capacitor via a first diode and a first resistor connected in series to the positive terminal,
The second switch has the negative terminal connected to the other terminal of the flying capacitor via a second resistor,
The third switch is connected in series between a wiring connecting the first switch and the first diode and the voltage detection device, and is connected in series to one terminal of the flying capacitor. And connected to the voltage detection device via a third resistor,
The fourth switch has the other terminal of the flying capacitor connected to the ground potential portion through a fourth resistor,
One or more protection elements for keeping the maximum voltage applied to the connected semiconductor relay at a constant voltage are provided only in the second switch and the fourth switch. The insulation detection device according to claim 1 ,
The semiconductor relay is composed of an optical MOS-FET relay,
The protection element includes a Zener diode connected in parallel to each of the optical MOS-FET relays of the first switch, the second switch, the third switch, and the fourth switch,
The Zener diode of the first switch is provided to be in a reverse direction with respect to a current flowing from a positive terminal of the DC power supply,
The Zener diode of the second switch is provided to be in a reverse direction with respect to a current flowing toward the negative terminal of the DC power supply,
The Zener diode of the third switch is provided so as to be in the same forward direction as the Zener diode of the first switch, and a reverse current preventing diode is provided so as to be opposite to the Zener diode.
The Zener diode of the fourth switch is provided so as to be in the same forward direction as the Zener diode of the second switch, and a diode for preventing reverse current is provided so as to be opposite to the Zener diode,
The breakdown voltage condition of each optical MOS-FET relay is as follows:
Vds> Vz
Where Vds is the breakdown voltage of each optical MOS-FET relay, Vz is the Zener voltage of the Zener diode, and
The condition of the Zener voltage (Vz) of the Zener diode is:
Vz1 + Vz3> Vd
Where Vz1: Zener voltage of the Zener diode of the first switch, Vz3: Zener voltage of the Zener diode of the third switch, Vd: Dielectric withstand voltage between required high voltage and low voltage Vz2 + Vz4> Vd
Where Vz2 is the Zener voltage of the Zener diode of the second switch, Vz4 is the Zener voltage of the Zener diode of the fourth switch, and Vd is the required withstand voltage between the high voltage and the low voltage.

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