JP2017122662A - Ground fault detection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ground fault detection circuit with which it is possible to improve resistance to current noise and improve the accuracy of detecting a ground fault.SOLUTION: The ground fault detection circuit comprises: a measurement unit for measuring, when electrical continuity to third and fourth switch elements is established, the charge voltage of a first capacitor charged when electrical continuity to first and second switch elements is established, and also finding ground fault resistance between a DC high voltage power source and ground on the basis of the charge voltage of the first capacitor affected by negative-side ground fault resistance occurring between a second line and ground when electrical continuity to the first and fourth switch elements is established, and the charge voltage of the first capacitor affected by positive-side ground fault resistance occurring between a first line and ground when electrical continuity to the second and third switch elements is established; a first diode provided on a path leading from the first switch element to the second switch element; second and third diodes provided between a first contact point to the third switch element and connected in parallel in reverse to each other; and a second capacitor connected in parallel to the first diode.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a ground fault detection circuit.

  Conventionally, a ground fault detection circuit has been proposed in which a flying path in a state floating from the ground potential and four switching elements form different paths in the same circuit and determine the insulation state of a power supply mounted on the vehicle. (For example, refer to Patent Document 1).

  The technique described in Patent Document 1 is to prevent erroneous charging due to reverse connection of a power supply that supplies a high voltage, or to prevent reverse voltage from being applied when the flying capacitor has polarity. A diode is connected to the flying capacitor. With such a circuit configuration, the direction of the current charged in the flying capacitor is limited, and the above matters are prevented.

Japanese Patent No. 4759018

  However, in an environment where current noise such as motor current leakage enters the ground fault detection circuit via the ground potential, current noise is limited to the charging direction by the diode connected to the flying capacitor. The

  Therefore, when measuring the ground-fault resistance on the negative electrode side, the measured value varies because the charging current due to current noise increases.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a ground fault detection circuit capable of improving resistance to current noise and improving ground fault detection accuracy.

  A ground fault detection circuit according to the present invention includes a first line on a positive potential side and a second line on a negative potential side of a DC high-voltage power supply, a third line connecting these lines, a first capacitor on the third line, and A first switching element provided before the first connection point with the third line in the first line; and provided before the second connection point with the third line in the second line. A ground fault detection circuit comprising a second switch element, a third switch element provided at a stage subsequent to the first connection point, and a fourth switch element provided at a stage subsequent to the second connection point, And the charging voltage of the first capacitor charged when the second switch element is turned on is measured when the third and fourth switch elements are turned on, and the first and fourth switch elements are turned on. Between the two lines and the ground The influence of the charging voltage of the first capacitor affected by the negative-side ground fault resistance and the positive-side ground fault resistance generated between the first line and the ground when the second and third switch elements are turned on Provided on the path from the first switch element to the second switch element, and a measuring unit for obtaining a ground fault resistance between the DC high-voltage power supply and the ground based on the charged voltage of the first capacitor The first diode, the second and third diodes provided between the first connection point and the third switch element and reversely connected in parallel to each other, and connected in parallel to the first diode And a second capacitor.

  ADVANTAGE OF THE INVENTION According to this invention, the tolerance of a current noise can be improved and the fall of a ground fault detection accuracy can be prevented.

It is a figure which shows the structural example of the ground fault detection circuit 1 which concerns on this embodiment, and its peripheral circuit. It is a figure which shows the circuit network at the time of charge of charging voltage V0, V01. It is a figure which shows the circuit network at the time of measurement of charging voltage V0, V01. It is a figure which shows the circuit network at the time of discharge of charging voltage V0, V01. It is a figure which shows the circuit network at the time of charge of the charging voltage VC1n which receives the influence of negative electrode side ground fault resistance RLn. It is a figure which shows the circuit network at the time of charge of charging voltage VC1p which receives to the influence of the positive side ground fault resistance RLp. It is a time chart explaining an example of a basic measurement cycle. It is the schematic of the motor 33 and its peripheral circuit. It is a figure explaining the current noise mixed in the circuit network at the time of charge of charge voltage VC1n influenced by negative electrode side ground fault resistance RLn. It is a figure explaining the current noise mixed in the circuit network at the time of charge of the charging voltage VC1p affected by the positive electrode side ground fault resistance RLp. It is a prior art example in which Y capacitors Yp and Yn are provided, and is a diagram showing a circuit network at the time of charging a charging voltage VC1n affected by a negative-side ground fault resistance RLn.

  FIG. 1 is a diagram illustrating a configuration example of the ground fault detection circuit 1 and its peripheral circuits according to the present embodiment. The ground fault detection circuit 1 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 a motor 33 (described later) as a drive source. As shown in FIG. 1, the ground fault detection circuit 1 is connected to a DC high-voltage power supply 5 and diagnoses the insulation state of the DC high-voltage power supply 5. The DC high-voltage power supply 5 outputs high-voltage DC power of about 200V, for example. The motor 33 that generates the driving force of the vehicle can be driven by the electric power output from the DC high-voltage power supply 5.

  The positive electrode side line 111 of the DC high-voltage power supply 5 and the ground G are electrically insulated. The negative electrode side line 112 of the DC high-voltage power supply 5 and the ground G are also electrically insulated. The ground G corresponds to a ground portion such as a vehicle body. Here, the insulation state between the positive electrode side line 111 and the ground G can be expressed as a positive electrode side ground fault resistance RLp. Further, the insulation state between the negative electrode side line 112 and the ground G can be expressed as a negative electrode side ground fault resistance RLn. The positive side ground fault resistance RLp and the negative side ground fault resistance RLn are collectively referred to as a ground fault resistance RL.

  By mounting the ground fault detection circuit 1 of FIG. 1 on a vehicle, the insulation state of the DC high-voltage power supply 5 can be monitored. Therefore, the ground fault detection circuit 1 mounted on the vehicle can monitor the insulation state of the vehicle. That is, the ground fault detection circuit 1 can diagnose the insulation state of the vehicle by obtaining the ground fault resistance RL between the DC high-voltage power supply 5 and the ground G.

  Therefore, as shown in FIG. 1, the positive input terminal 6 and the negative input terminal 7 of the ground fault detection circuit 1 are connected to the positive line 111 and the negative line 112, respectively. The ground fault detection circuit 1 is connected to the ground G.

  In order to output the diagnosis result or alarm information of the ground fault detection circuit 1, an output terminal 8 is provided as shown in FIG. The output terminal 8 can be connected to, for example, an unillustrated vehicle-side electronic control unit (ECU).

  Next, the ground fault detection circuit 1 will be specifically described.

  The ground fault detection circuit 1 connects the first line L1 on the positive potential side of the DC high-voltage power supply 5, the second line L2 on the negative potential side of the DC high-voltage power supply 5, and the first line L1 and the second line L2. And a third line L3. The ground fault detection circuit 1 includes a first capacitor C1 on the third line L3.

  In the ground fault detection circuit 1, the first switch element S1 is provided in a stage preceding the first connection point T1 with the third line L3 in the first line L1. In the ground fault detection circuit 1, the second switch element S2 is provided in the previous stage of the second connection point T2 with the third line L3 in the second line L2. In the ground fault detection circuit 1, a third switch element S3 is provided after the first connection point T1. In the ground fault detection circuit 1, a fourth switch element S4 is provided at the subsequent stage of the second connection point T2.

  The first capacitor C1 operates as a flying capacitor. The first capacitor C1 is not particularly limited, and a film capacitor or a ceramic capacitor may be employed.

  Each of the first switch element S1, the second switch element S2, the third switch element S3, and the fourth switch element S4 is made of, for example, an optical MOSFET, has high voltage resistance, and has insulating characteristics. The first switch element S1, the second switch element S2, the third switch element S3, and the fourth switch element S4 are collectively referred to as an insulated switch S.

  The ground fault detection circuit 1 is provided with a measurement unit 10. The measuring unit 10 measures the charging voltage V0 of the first capacitor C1 charged when the first switch element S1 and the second switch element S2 are turned on when the third switch element S3 and the fourth switch element S4 are turned on.

  The measuring unit 10 is affected by the charging voltage V0 and the negative-side ground fault resistance RLn generated between the second line L2 and the ground G when the first switch element S1 and the fourth switch element S4 are conductive. Charging of the first capacitor C1 affected by the charging voltage VC1n of C1 and the positive side ground fault resistance RLp generated between the first line L1 and the ground G when the second switch element S2 and the third switch element S3 are conducted. Based on the voltage VC1p, the ground fault resistance RL between the DC high-voltage power supply 5 and the ground G is obtained.

  Next, the ground fault detection circuit 1 will be described more specifically.

  The first switch element S1 has a first end connected to the positive input terminal 6 via the resistor R01, and a second end connected to the anode side of the first diode D1 via the seventh connection point T7. It is connected. A resistor R1 is connected to the cathode side of the first diode D1. The resistor R1 is connected to the first capacitor C1 via the first connection point T1. A second capacitor C2 is connected in parallel to the first diode D1. The second switch element S2 has a first end connected to the negative input terminal 7 via the resistor R02 and a second end connected to the resistor R2. The resistor R2 is connected to the first capacitor C1 via the second connection point T2.

  The third switch element S3 has a first end connected to the third connection point T3 and a second end connected to the fifth connection point T5. Between the third connection point T3 and the fourth connection point T4, a parallel circuit in which a second diode D2 and a third diode D3 opposite to the second diode D2 are connected in parallel is provided. In this parallel circuit, a resistor R3 is connected between the cathode side of the third diode D3 and the third connection point T3. The anode side of the third diode D3 and the cathode side of the second diode D2 are connected via a fourth connection point T4. The first connection point T1 and the fourth connection point T4 are at the same potential.

  The fourth switch element S4 has a first end connected to the second connection point T2. Between the second connection point T2 and the first connection point T1, the first capacitor C1 described above is provided. The resistor R2 described above is provided between the second connection point T2 and the second switch element S2. The fourth switch element S4 has a second end connected to the resistor R4. The resistor R4 is connected to the sixth connection point T6. The sixth connection point T6 is connected to the ground G and the resistor R5. The resistor R5 is provided between the sixth connection point T6 and the fifth connection point T5.

  The first end of the switch Sa is connected to the fifth connection point T5. The second end of the switch Sa is connected to the A / D port of the measurement unit 10. A third capacitor C3 is connected to an eighth connection point T8 between the second end of the switch Sa and the A / D port of the measurement unit 10. The measurement unit 10 supplies the diagnosis result of the insulation state of the DC high-voltage power supply 5 by the ground fault detection circuit 1 to the outside through the output terminal 8.

  In addition, when any of the resistors R01, R02, R1 to R5 is not particularly specified, it is referred to as a resistor R.

  Next, when the ground fault detection circuit 1 determines the insulation state of the power source, the first switch element S1, the second switch element S2, the third switch element S3, and the fourth switch element S4 are controlled, Different paths formed in the same circuit will be described with reference to FIGS.

  FIG. 2 is a diagram illustrating a circuit network during charging with charging voltages V0 and V01. FIG. 3 is a diagram showing a circuit network at the time of measuring the charging voltages V0 and V01. FIG. 4 is a diagram showing a circuit network at the time of discharging the charging voltages V0 and V01. FIG. 5 is a diagram showing a circuit network at the time of charging with the charging voltage VC1n affected by the negative side ground fault resistance RLn. FIG. 6 is a diagram showing a circuit network during charging of the charging voltage VC1p affected by the positive-side ground fault resistance RLp. FIG. 7 is a time chart for explaining an example of the basic measurement cycle.

  As shown in FIG. 2, when the charging voltages V0 and V01 are charged, the first switch element S1 and the first diode D1 are turned on when the first switch element S1 and the second switch element S2 are turned on. A circuit network in which the first capacitor C1 and the second switch element S2 are electrically connected in order is formed. Note that description of the resistor R included in this network is omitted.

  As shown in FIG. 3, when the charging voltages V0 and V01 are measured, when the third switch element S3 and the fourth switch element S4 are turned on, that is, turned on, the first capacitor C1, the third diode D3, A circuit network in which the third switch element S3 and the fourth switch element S4 are electrically connected in order is formed, and the circuit network and the measurement unit 10 are electrically connected through the switch Sa. Note that description of the resistor R included in this network is omitted.

  As shown in FIG. 4, when the charging voltages V0 and V01 are discharged, the third switch element S3 and the fourth switch element S4 are turned on, that is, turned on, whereby the first capacitor C1, the third diode D3, A circuit network in which the third switch element S3 and the fourth switch element S4 are electrically connected in order is formed, and the circuit network and the measuring unit 10 are electrically disconnected by the switch Sa. Note that description of the resistor R included in this network is omitted.

  As shown in FIG. 5, when the charging voltage VC1n affected by the negative-side ground fault resistance RLn is charged, the first switch element S1 and the fourth switch element S4 are turned on, that is, the first switch element S4 is turned on. A circuit network is formed in which the switch element S1, the first diode D1, the first capacitor C1, the fourth switch element S4, and the negative-side ground fault resistor RLn are sequentially connected, and the first diode D1 includes a first network. Two capacitors C2 are connected in parallel. Note that description of the resistor R included in this network is omitted.

  As shown in FIG. 6, during charging of the charging voltage VC1p affected by the positive side ground fault resistance RLp, the positive side ground fault resistance RLp, the third switch element S3, the second diode D2, the first capacitor C1, and the second A circuit network in which the switch elements S2 are electrically connected in order is formed. Note that description of the resistor R included in this network is omitted.

  As shown in FIG. 7, the measurement of the charging voltage V0, the charging voltage V01, the charging voltage VC1n, the charging voltage V0, the charging voltage V01, and the charging voltage VC1p is repeated. Here, the positive side ground fault resistors RLp and RLn and the charging voltages V0, VC1n, V0, V01, and VC1p have the following correlation.

(RLp + RLn) / (RLp × RLn) = f [(VC1p + VC1n) / V0]
However,
V0: charging voltage VC1n of the first capacitor C1 according to the output voltage of the DC high-voltage power supply 5: charging voltage VC1p of the first capacitor C1 affected by the negative side ground fault resistance RLn: influence of the positive side ground fault resistance RLp Receiving charging voltage RLp, RLn of first capacitor C1: resistance value of local fault resistance RL

  In the following description, if any one of the charging voltage V0, the charging voltage V01, the charging voltage VC1n, the charging voltage V0, the charging voltage V01, and the charging voltage VC1p is not particularly specified, it is referred to as a charging voltage V.

  From the above description, the measurement unit 10 detects the charging voltages V0, VC1p, and VC1n from the signal level input to the A / D port in each circuit network at the time of measuring the charging voltage V described above, and performs the above correlation. Based on the relationship, the positive side ground fault resistance RLp and the negative side ground fault resistance RLn can be obtained. For example, the ground fault resistance RL can be calculated from a converted ground fault resistance map in which the value of (VC1p + VC1n) / V0 is stored in advance.

Next, a case where current noise such as motor noise is mixed in each circuit network will be described. FIG. 8 is a schematic diagram of the motor 33 and its peripheral circuits. As shown in FIG. 8, the wiring portion 30 has stray inductances f _L1 and f _L2 and stray capacitances C _f1 and C _f2 . The motor 33 includes stray capacitances C _{f3 to} C _f5 . When current noise such as motor noise is mixed into the ground fault _detection circuit 1 via the floating capacitances C _{f3 to} C _{f5 and the} like, the charging current increases.

Specifically, since stray capacitances C _{f3 to} C _{f5 and the} like exist between the motor 33 and the ground G, current noise such as motor noise is grounded via the stray capacitances C _{f3 to} C _{f5 and the} like. G may flow. On the other hand, the ground fault detection circuit 1 is electrically connected to the ground G, and the ground G connected to the motor 33 and the ground G connected to the ground fault detection circuit 1 have the same potential. Therefore, if current noise flows from the motor 33 to the ground G, the current noise may flow into the ground fault detection circuit 1 via the ground G.

  As a result, the measured value fluctuates in the direction of decreasing insulation. Therefore, the influence of current noise in the conventional ground fault detection circuit 1 will be specifically described with reference to FIG. FIG. 11 is a conventional example in which Y capacitors Yp and Yn are provided, and is a diagram showing a circuit network at the time of charging the charging voltage VC1n affected by the negative-side ground fault resistance RLn. In FIG. 11, there is no second capacitor C2 connected in parallel with the first diode D1. In the description of FIG. 11, the influence of the Y capacitors Yp and Yn on the circuit network is ignored, and in particular, the capacitance of the Y capacitors Yp and Yn is also ignored on the circuit network.

  As shown in FIG. 11, the C1 discharge current due to current noise such as motor noise is interrupted by the first diode D1. Therefore, current noise is not mixed in the C1 discharge direction. On the other hand, the C1 charging current due to current noise such as motor noise is mixed in the C1 charging direction because there is no blocking element. Therefore, since the current noise is mixed only in the C1 charging direction, the charge accumulated in the first capacitor C1 increases and affects the measured value of the ground fault resistance RL.

  Therefore, a circuit configuration in which the C1 charging current due to current noise is not interrupted will be specifically described. FIG. 9 is a diagram for explaining current noise mixed in the circuit network during charging of the charging voltage VC1n affected by the negative side ground fault resistance RLn.

  As described above, the second capacitor C2 is connected in parallel to the first diode D1. Therefore, since the C1 discharge current due to the current noise can pass through the second capacitor C2, the current noise is mixed not only in the C1 charging direction but also in the C1 discharging direction. As a result, current noise is mixed in both the C1 charging direction and the C1 discharging direction, and is offset as an influence on the measured value of the negative side ground fault resistance RLn. Does not affect the value.

  Of the purposes in which the first diode D1 is provided, the first purpose is to prevent reverse connection of the charging voltages V0 and V01, and the second purpose is to apply a reverse voltage to the first capacitor C1. It is to prevent being done.

  Specifically, the first object is to prevent erroneous connection between the positive electrode side of the DC high voltage power source 5 and the negative electrode side of the DC high voltage power source 5 when connecting the ground fault detection circuit 1 to the DC high voltage power source 5. It is. The second purpose is to prevent erroneous connection when the first capacitor C1 has polarity.

  Further, the circuit network at the time of measuring the charging voltage VC1n is a current noise such as motor noise without affecting the first and second purposes even if the second capacitor C2 is connected in parallel with the first diode D1. To escape.

  Thereby, since the current noise mixed in the first capacitor C1 can be equal in the charging direction and the discharging direction, it is possible to prevent the measurement value of the negative side ground fault resistance RLn from being lowered due to the mixing of the current noise. it can. The second capacitor C2 preferably has a smaller capacity than the first capacitor C1. Specifically, the capacitance of the second capacitor C2 is preferably 1/10 to 1/100 compared to the capacitance of the first capacitor C1. That is, it is preferable that the capacitance value of the second capacitor C2 is a capacitance value that is orders of magnitude smaller than the capacitance value of the first capacitor C1. Thereby, the capacitance of the second capacitor C2 can be ignored when the charging voltage V is measured while using the second capacitor C2 as a bypass path.

  Next, measurement of the charging voltage VC1p by the positive side ground fault resistance RLp between the positive side of the power source and the ground G will be described. FIG. 10 is a diagram for explaining current noise mixed in the circuit network during charging of the charging voltage VC1p affected by the positive-side ground fault resistance RLp.

  As described above, the third diode D3 and the resistor R3 are connected in parallel to the second diode D2, and in particular, the third diode D3 is connected in the opposite direction to the second diode D2. Therefore, the C1 discharge current due to current noise can pass through the third diode D3. Also, the C1 charging current due to current noise can pass through the second diode D2. As a result, current noise is mixed not only in the C1 charging direction but also in the C1 discharging direction. As a result, current noise is mixed in the C1 charging direction and the C1 discharging direction, and is offset as an influence on the measured value of the positive side ground fault resistance RLp. Therefore, the measurement of the positive side ground fault resistance RLp is performed. Does not affect the value.

  In the measurement of each charging voltage V, it is preferable that the first diode D1, the second diode D2, and the third diode D3 have the same forward voltage drop. In particular, the second diode D2 and the third diode D3 are provided to make the combined impedance of the circuit network formed in the measurement of the charging voltage VC1p and the circuit network formed in the measurement of the charging voltage VC1n the same. Is preferred.

  From the above description, the ground fault detection circuit 1 can cancel the influence of current noise in both directions of charge and discharge by the second capacitor C2 connected in parallel with the first diode D1. Noise resistance can be improved and a decrease in ground fault detection accuracy can be prevented.

  As described above, in the present embodiment, the ground fault detection circuit 1 includes the measurement unit 10 for obtaining the ground fault resistance RL between the DC high-voltage power supply 5 and the ground G, and the path from the first switch element S1 to the second switch element S2. The first diode D1 provided above, the second diode D2 and the third diode D3 provided between the first connection point T1 and the third switch element S3 and reversely connected in parallel to each other, and the first diode D1 And a second capacitor C2 connected in parallel.

  With such a configuration, the ground fault detection circuit 1 can improve the resistance to current noise and prevent a decrease in ground fault detection accuracy.

  In the ground fault detection circuit 1 according to the present embodiment, the first diode D1 is connected with the anode side facing the first connection point T1, and the first switch element S1, the first diode D1, the first capacitor C1, When a series circuit including the 4-switch element S4 and the negative-side ground fault resistor RLn is formed, current noise that has entered through the ground G is released to the path including the first diode D1 or the path including the second capacitor C2. be able to.

  Therefore, even when the ground fault detection circuit 1 measures the charging voltage VC1n of the first capacitor C1 affected by the negative side ground fault resistance RLn, the resistance to current noise is improved and the ground fault detection accuracy is improved. A decrease can be prevented.

  As mentioned above, although this invention was demonstrated based on this embodiment, this invention is not limited to the said embodiment, You may add in the range which does not deviate from the meaning of this invention.

  For example, in the present embodiment, the case where the resistance component is the resistor R has been described.

  In addition, a configuration that improves the resistance to current noise and improves the ground fault detection accuracy without using the second capacitor C2 is also possible. In such a configuration, a current sensor is provided in the ground fault detection circuit 1 described in the conventional example of FIG. 11, and this current sensor detects a current flowing into and out of the first capacitor C1 when each charging voltage V is measured. I just need it. Thereby, the current flowing into and out of the first capacitor C1 can be monitored. Therefore, by performing the process of subtracting the influence of current noise based on the monitoring result, it is possible to prevent the ground fault detection accuracy from being lowered, as in the configuration described above.

  Specifically, a current sensor is provided in either or both of the current path flowing into the first capacitor C1 and the current path flowing out from the first capacitor C1. The current sensor is composed of, for example, a Hall element. The current sensor is sampled a plurality of times at a predetermined timing from when charging of the first capacitor C1 is started until the charging voltage V is measured. Of the current values detected by the current sensor, for example, a high-frequency component is extracted by a high-pass filter, and if there is a deviation in the fluctuation of the high-frequency component, the deviation corresponds to current noise.

  Therefore, the influence of the current noise can be canceled by correcting the deviation, specifically, the current value corresponding to the current noise. Therefore, even with such a configuration, it is possible to prevent a decrease in ground fault detection accuracy, similarly to the configuration described above.

1: Ground fault detection circuit 5: DC high voltage power supply 6: Positive electrode side input terminal 7: Negative electrode side input terminal 10: Measuring unit 30: Wiring unit 32: Inverter 33: Motor

Claims (1)

The first line on the positive potential side and the second line on the negative potential side of the DC high-voltage power source, the third line connecting these lines, the first capacitor on the third line, and the third line of the first lines A first switch element provided before the first connection point with the line; a second switch element provided before the second connection point with the third line of the second line; and the first connection point. A ground fault detection circuit including a third switch element provided at a subsequent stage and a fourth switch element provided at a subsequent stage of the second connection point;
The charging voltage of the first capacitor charged when the first and second switch elements are conductive is measured when the third and fourth switch elements are conductive, and the first and fourth switch elements are conductive. Sometimes the charging voltage of the first capacitor affected by the negative side ground fault resistance generated between the second line and the ground, and the first line and the ground when the second and third switch elements are conductive. A measurement unit for determining a ground fault resistance between the DC high-voltage power supply and the ground based on the charging voltage of the first capacitor affected by the positive-side ground fault resistance generated between;
A first diode provided on a path from the first switch element to the second switch element;
Second and third diodes provided between the first connection point and the third switch element and reversely connected in parallel to each other;
A second capacitor connected in parallel to the first diode;
A ground fault detection circuit comprising:

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