JP2016101040A - Ground fault detection circuit for vehicle having high voltage power source system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ground fault detection circuit for a vehicle having a high voltage power source system that is able to appropriately achieve detection frequency and detection accuracy of ground fault of a high voltage power source system.SOLUTION: A ground fault detection circuit 10 that detects ground fault of a high voltage power source system electrically insulated from a vehicle body comprises: a coupling capacitor Cs connected to the high voltage power source system and configured to insulate a DC component; a resistance element Rs connected to the coupling capacitor Cs in series; an oscillation circuit 12 connected to the resistance element Rs in series and configured to apply AC voltage of predetermined frequency to the resistance element Rs; detecting means 11, 13 that detect ground fault of the high voltage power source system on the basis of voltage at a connection point P between the coupling capacitor Cs and the resistance element Rs; and varying means 11 that changes the predetermined frequency fc of AC voltage output from the oscillation circuit 20 according to the state of connection between a battery 20 included in the high voltage power source system and other electric apparatus included in the high voltage power source system.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a vehicle ground fault detection circuit including a high voltage power supply system.

  In recent years, the importance of protection against ground faults has been recognized in hybrid vehicles, electric vehicles, and the like that employ high-voltage batteries, and various ground fault detection circuits have been proposed.

  For example, the ground fault detection circuit described in Patent Document 1 is connected to a coupling capacitor connected to a DC power supply circuit installed through a high electrical resistance (insulation resistance) in a vehicle body, with an AC of a predetermined frequency via an output impedance. A voltage is applied to detect the ground voltage at the connection point between the coupling capacitor and the output impedance. This ground voltage is a voltage obtained by dividing an alternating voltage by an output impedance and an insulation resistance. In the detection circuit, a ground fault of the DC power supply circuit is detected based on the variation of the partial pressure.

Japanese Patent No. 378289

  In the detection circuit, the ground fault is detected for each waveform of the AC voltage. Therefore, in order to detect a ground fault at an early stage, the frequency of the AC voltage may be increased and the frequency of detection of leakage may be increased.

  However, there is a stray capacitance in parallel with the insulation resistance. When the frequency of the alternating voltage is increased, the impedance of the stray capacitance is reduced, so that the effect of the stray capacitance is increased, and the detection accuracy of the partial pressure corresponding to the insulation resistance may be lowered. As a result, the detection accuracy of the ground fault may be lowered.

  In view of the above circumstances, the present invention provides a ground fault detection circuit for a vehicle including a high voltage power supply system capable of appropriately balancing the detection frequency and detection accuracy of a ground fault in a high voltage power supply system. Main purpose.

  In order to solve the above problems, the present invention is a ground fault detection circuit for detecting a ground fault of a high voltage power supply system that is electrically insulated from a vehicle body, and is connected to the high voltage power supply system to insulate a DC component. An insulating means connected in series to the insulating means, an oscillating means connected in series to the resistive means for applying an AC voltage of a predetermined frequency to the resistive means, and the insulating means and the resistive means Based on the voltage at the connection point, the detection means for detecting the ground fault, the battery included in the high-voltage power supply system and the other electrical equipment included in the high-voltage power supply system, according to the connection state, Variable means for changing a predetermined frequency of the AC voltage output by the oscillating means.

  According to the present invention, the ground fault of the high voltage power supply system is detected based on the voltage at the connection point between the insulating means connected to the high voltage power supply system and the resistance means connected in series to the insulation means. The voltage at the connection point is a voltage obtained by dividing the AC voltage applied to the resistance means by the insulation resistance of the high voltage power supply system and the resistance means. If stray capacitance exists in parallel with the insulation resistance of the high-voltage power supply system, the higher the AC voltage frequency, the greater the effect of stray capacitance, and the smaller the voltage drop corresponding to the insulation resistance. The detection accuracy of the system ground fault decreases. On the other hand, the higher the frequency of the AC voltage, the greater the number of ground fault detection opportunities.

  Here, the frequency of occurrence of a ground fault in the high-voltage power supply system varies depending on the connection state between the battery included in the high-voltage power supply system and other electrical devices. When the occurrence frequency of ground faults is high, it is desirable to increase the detection frequency of ground faults than when the occurrence frequency of ground faults is low. Therefore, by changing the predetermined frequency of the AC voltage according to the connection state between the battery included in the high-voltage power supply system and other electrical devices, the detection frequency and detection accuracy of the ground fault of the high-voltage power supply system are appropriately set. Can be compatible.

The figure which shows schematic structure of the ground fault detection circuit which concerns on this embodiment. The figure which shows the characteristic of an insulation resistance and the voltage of the connection point P. FIG. The figure which shows schematic structure of the ground fault detection circuit in driving | running | working. The figure which shows schematic structure of the ground fault detection circuit during a stop. The figure which shows schematic structure of the ground fault detection circuit during charge. The figure which shows the noise amount with respect to the connection pattern of a battery and an electric equipment, a stray capacity, the generation degree of an electrical leakage, and the frequency of alternating voltage. The figure which shows schematic structure of the high voltage power supply system which concerns on other embodiment.

  Hereinafter, an embodiment in which a ground fault detection circuit for a vehicle including a high voltage power supply system is embodied will be described. Vehicles to which the ground fault detection circuit 10 according to the present embodiment is applied are assumed to be hybrid vehicles, electric vehicles, fuel cell vehicles, and the like that have a high-voltage power supply system and use a traveling motor as a drive source.

  First, the configuration of a high-voltage power supply system for a vehicle according to the present embodiment will be described with reference to FIG. The high-voltage power supply system of the vehicle includes a battery 20 and a plurality of electric devices, and is electrically insulated from the vehicle body. The plurality of electrical devices includes a converter 31, an inverter 32, an MG 33, and a power converter 34.

  The battery 20 is a high-voltage (for example, several hundreds V) assembled battery configured by connecting a plurality of battery cells in series, and is, for example, a lithium ion secondary battery. Battery 20 is connected to converter 31 via switches SW1 and SW2. An inverter 32 is connected to the converter 31, and an MG 33 is connected to the inverter 32.

  The MG 33 (traveling motor) is a motor generator that operates as an electric motor that applies traveling power to the vehicle and operates as a generator that performs regenerative power generation when the vehicle is decelerated. The inverter 32 drives the MG 33 as a generator or an electric motor. Converter 31 boosts the power supplied from battery 20 and supplies it to inverter 32 when MG 33 operates as an electric motor. Further, converter 31 boosts the power supplied from inverter 32 to charge battery 20 when MG 33 operates as a generator.

  Further, the battery 20 is connected to the power converter 34 via the switches SW3 and SW4. The power converter 34 is an electrical device that is used for a different purpose from the driving of the MG 33. In the present embodiment, the power converter 34 is a charger that has a plug opening for an external power supply, converts the voltage of power supplied from the outside of the vehicle, and supplies the converted voltage to the battery 20. Note that the power converter 34 may be a device that has a plug insertion port for an external load, converts the power of the battery 20 to a voltage, and supplies the voltage to the external load.

  Between the battery 20, the converter 31, the inverter 32, the MG 33 and the power converter 34 included in the high-voltage power supply system and the vehicle body, there are ground insulation resistances 41a to 41e and ground floating capacitors 42a to 42e, respectively. In particular, since the power converter 34 has a large amount of noise, a noise countermeasure capacitor is often connected between the power converter 34 and the vehicle body. Here, for convenience, a noise countermeasure capacitor is also included in the ground stray capacitance 42e. Therefore, the ground stray capacitance 42e is larger than the ground stray capacitances 42b to 42d. Further, among the ground stray capacitances 42b to 42d, the ground stray capacitance 42c of the inverter 32 is large, and the ground stray capacitances 42b and 42d of the converter 31 and the MG 33 are small. Hereinafter, when at least one of the ground insulation resistances 41a to 41e is shown, the ground insulation resistance 41 is used, and when at least one of the ground stray capacitances 42a to 42e is shown, the ground stray capacitance 42 is used.

  Next, the configuration of the ground fault detection circuit 10 according to the present embodiment will be described with reference to FIG. The ground fault detection circuit 10 includes a coupling capacitor Cs, a resistance element Rs, an oscillation circuit 12, a detection circuit 13, and a CPU 11, and detects a ground fault to the vehicle body in the high voltage power supply system.

  The coupling capacitor Cs (insulating means) is connected to the negative terminal side of the battery 20 and insulates a direct current component. The resistance element Rs (resistance means) is connected in series to the coupling capacitor Cs and is connected in series to the oscillation circuit 12.

  The oscillation circuit 12 (oscillation means) generates a pulse voltage with a predetermined frequency (which may be an AC voltage) and applies the pulse voltage with a predetermined frequency to the resistance element Rs. The predetermined frequency is set by the CPU 11.

  The detection circuit 13 is connected to a connection point P between the coupling capacitor Cs and the resistance element Rs, extracts the ground voltage at the connection point P, and outputs it to the CPU 11. Specifically, the detection circuit 13 includes a band pass filter circuit and an amplifier circuit. The band-pass filter circuit removes noise components such as fluctuation components associated with voltage fluctuations of the battery 20 from the ground voltage at the connection point P, and inputs the ground voltage at the connection point P from which the noise component has been removed to the amplifier circuit. The amplifier circuit amplifies the difference between the peak value of the ground voltage at the connection point P and the reference voltage and inputs the amplified difference to the CPU 11.

  The ground voltage at the connection point P is a voltage obtained by dividing the AC voltage applied to the resistance element Rs by the resistance element Rs and the ground insulation resistance of the high-voltage power supply system. The ground insulation resistance of the high-voltage power supply system is a value obtained by synthesizing the ground insulation resistance 41 a of the battery 20 and the ground insulation resistance 41 of the electrical equipment connected to the battery 20. Also, the ground stray capacitance of the high voltage power supply system is a value obtained by combining the ground stray capacitance 42 a of the battery 20 and the ground stray capacitance 42 of the electrical equipment connected to the battery 20.

  The CPU 11 is a microcomputer that controls on / off of the SW1 to SW4 and sets a predetermined frequency of the AC voltage. Further, the CPU 11 detects a ground fault of the high voltage power supply system based on the voltage input from the detection circuit 13. Specifically, the CPU 11 determines that there is a ground fault when the ground voltage at the connection point P is lower than the reference voltage. The insulation resistance may be calculated from the ground voltage at the connection point P and a map of the ground voltage and the insulation resistance prepared in advance.

  Here, when the predetermined frequency of the AC voltage is fc and the capacitance value of the ground stray capacitance 42 is C, the impedance X of the ground stray capacitance 42 is X = 1 / (2π × fc × C). That is, the impedance X decreases as the predetermined frequency fc increases, and the impedance X decreases as the capacitance value C increases. As the impedance X decreases, the influence of the ground stray capacitance 42 on the ground insulation resistance 41 increases, the voltage drop corresponding to the ground insulation resistance 41 decreases, and the ground voltage at the connection point P decreases.

  Therefore, as shown in FIG. 2, even if the actual ground insulation resistance 41 has the same value, the detected value of the ground voltage at the connection point P decreases as the predetermined frequency fc increases or the capacitance value C increases. That is, as the predetermined frequency fc increases, the ground insulation resistance 41 appears smaller than the actual value.

  Therefore, when the predetermined frequency fc is high, the CPU 11 can easily determine that there is a ground fault even when the ground fault is not actually occurred. On the other hand, the CPU 11 determines whether or not there is a ground fault for each waveform of the AC voltage output from the oscillation circuit 12. For this reason, the higher the predetermined frequency fc, the greater the number of ground fault detection opportunities. Moreover, the occurrence frequency of a ground fault changes with the connection state of the battery 20 and another electric equipment. When the frequency of occurrence of ground faults is high, it is desirable to increase the number of ground fault detection opportunities.

  Therefore, the CPU 11 changes the predetermined frequency fc of the AC voltage output from the oscillation circuit 12 in accordance with the connection state between the battery 20 and other electrical devices included in the high-voltage power supply system. However, by changing the predetermined frequency fc, there is a possibility that a signal component cannot be appropriately extracted only by an analog bandpass filter. Therefore, the CPU 11 configures a digital filter that cuts off frequency components outside the predetermined pass band, and changes the predetermined pass band of the digital filter according to the predetermined frequency fc of the AC voltage. In this embodiment, the CPU 11 and the detection circuit 13 constitute detection means, and the CPU 11 constitutes a variable means and digital filter means.

  Next, a mode in which the predetermined frequency fc of the AC voltage is changed according to the connection state in the high-voltage power supply system will be described with reference to FIGS.

  There are three connection states: pattern A, pattern B, and pattern C. As shown in FIG. 3, the pattern A is a pattern in which the vehicle is running, and is a state in which the switches SW1 and SW2 are turned on and the switches SW3 and SW4 are turned off. A portion surrounded by an alternate long and short dash line indicates the battery 20 and an electric device connected to the battery 20. In the pattern A, the MG 33 is connected to the battery 20 via the converter 31 and the inverter 32.

  Pattern B is a pattern in which the vehicle is stopped as shown in FIG. 4 and is a state in which all switches SW1 to SW4 are turned off. In the pattern B, no other electrical device is connected to the battery 20. The vehicle is stopped when the vehicle is stopped at a parking lot or an intersection.

  As shown in FIG. 5, the pattern C is a pattern in which the battery 20 is being charged by the external power source, and is a state in which the switches SW1 and SW2 are turned off and the switches SW3 and SW4 are turned on. In the pattern C, the power converter 34 is connected to the battery 20. Note that, even when the power converter 34 is an electric device other than the charger, the pattern C is a state in which the power converter 34 is connected to the battery 20 and the power converter 34 is used.

  As shown in FIG. 6A, in the pattern C, since the power converter 34 to which the external plug is connected is connected to the battery 20, the noise amount is the largest among the three patterns. On the other hand, in pattern B, since no other electrical device is connected to battery 20, the amount of noise is the smallest among the three patterns.

  Further, as shown in FIG. 6 (b), in pattern C, a noise countermeasure capacitor is installed between the power converter 34 and the vehicle body, and therefore the ground floating capacitance 42 is the largest among the three patterns. . On the other hand, in the pattern B, since no other electrical device is connected to the battery 20, the ground stray capacitance 42 is the smallest among the three patterns.

  In addition, when the vehicle vibration is large and large, a ground fault occurs between the high-voltage power supply system and the vehicle body, and electric leakage is likely to occur. As shown in FIG. 6 (c), in the pattern A, the vehicle is running, so the vibration of the vehicle is large, and the occurrence frequency of electric leakage is the highest among the three patterns. On the other hand, in the pattern C, since the vehicle is stopped and charged in a parking lot or the like, the vibration of the vehicle is small and little, and the frequency of occurrence of electric leakage is the lowest among the three patterns. Even when the power converter 34 is an electric device other than the charger, it is used by stopping at a parking lot or the like, and therefore, the occurrence frequency of electric leakage is the lowest among the three patterns. In pattern B, when stopping at an intersection, as shown in FIG. 6C, the occurrence frequency of leakage is lower than pattern A and higher than pattern C. When stopping at a parking lot or the like, the occurrence frequency of leakage is Similar to pattern C.

  In pattern A, since the occurrence frequency of electric leakage is relatively high, it is desirable that the predetermined frequency fc be relatively high. On the other hand, in the pattern C, the occurrence frequency of leakage is relatively low and the ground floating capacitance 42 is relatively large. Therefore, in the pattern C, it is desired that the predetermined frequency fc is relatively low in order to reduce the influence of the ground stray capacitance 42. Therefore, the predetermined frequency fc in the pattern C is set lower than the predetermined frequency fc in the pattern A.

  In addition, when the vehicle stops at a parking lot or the like and does not use an electrical device, the CPU 11 is generally in a sleep state and periodically starts for a short time to execute a predetermined process. Therefore, in pattern B, it is desirable to increase the number of ground fault detection opportunities so that the CPU 11 can detect the ground fault in a short time when the CPU 11 starts from the sleep state. Therefore, the predetermined frequency fc in the pattern B is set to be higher than the predetermined frequency fc when another electric device is connected to the battery 20. That is, the predetermined frequency fc in the pattern B is higher than the predetermined frequency fc in the pattern A, and is set to the highest frequency among the three patterns.

  According to this embodiment described above, the following effects are obtained.

  The frequency of detection of a ground fault in the high-voltage power supply system by changing the predetermined frequency fc of the AC voltage output from the oscillation circuit 12 according to the connection state between the battery 20 included in the high-voltage power supply system and other electrical devices. And detection accuracy can both be achieved appropriately.

  The pass band of the digital filter is changed according to the predetermined frequency fc of the AC voltage. As a result, since the signal component can be extracted according to the predetermined frequency fc of the AC voltage, the detection accuracy of the voltage at the connection point P corresponding to the ground insulation resistance 41 of the high-voltage power supply system, and hence the detection accuracy of the ground fault can be improved. Can do.

  When the MG 33 is connected to the battery 20, the vehicle is traveling, the vehicle vibration is large, and the occurrence frequency of the ground fault is high. On the other hand, the power converter 34 is connected to the battery 20 when the vehicle is parked and charged at a parking lot or the like, and the vibration of the vehicle is small and the occurrence frequency of the ground fault is low. Therefore, by setting the predetermined frequency fc of the AC voltage to be lower when the power converter 34 is connected to the battery 20 than when the MG 33 is connected to the battery 20, the ground fault of the high voltage power supply system is reduced. The detection frequency and the detection accuracy can be appropriately balanced.

  Generally, since a noise countermeasure capacitor is connected to the power converter 34, the capacitance value of the ground stray capacitance 42 is larger than that of other electric devices. As the capacitance value increases, the impedance X of the ground stray capacitance 42 decreases, and the influence of the ground stray capacitance 42 on the ground insulation resistance 41 increases. Therefore, by setting the predetermined frequency fc of the AC voltage to be lower when the power converter 34 is connected to the battery 20 than when the MG 33 is connected to the battery 20, the ground fault of the high voltage power supply system is reduced. Detection accuracy can be increased.

  When no other electrical device is connected to the battery 20, the vehicle is stopped at a parking lot or an intersection. When the vehicle is parked at the parking lot, the CPU 11 is generally in a sleep state and is periodically activated to detect a ground fault. For this reason, when no other electrical device is connected to the battery 20, it is desirable to increase the detection frequency of the ground fault so that the ground fault can be detected in a short time when the CPU 11 is activated. Therefore, by increasing the predetermined frequency fc of the AC voltage when the electric power converter 34 is connected to the battery 20 when no other electrical device is connected to the battery 20, the high voltage power supply system The detection frequency of ground fault and the detection accuracy can be made compatible appropriately.

  By setting the predetermined frequency fc of the AC voltage higher when no other electrical device is connected to the battery 20 than when the other electrical device is connected to the battery 20, It is possible to more appropriately balance the detection frequency and the detection accuracy of the fault.

(Other embodiments)
The periodic startup time from the sleep state of the CPU 11 may be long, but the predetermined frequency fc in the pattern B may be any frequency as long as it can be output from the oscillation circuit 12. The predetermined frequency fc in the pattern B may be any frequency as long as the predetermined frequency fc in the pattern C is lower than the predetermined frequency fc in the pattern A.

  In pattern B, the predetermined frequency fc may be changed between when the signal stops and when the vehicle stops in a parking lot or the like. That is, in the pattern B, the predetermined frequency fc may be changed between when the CPU 11 is always activated and when activated from the sleep state. For example, the predetermined frequency fc when the signal is stopped is set to a frequency between the predetermined frequency fc in the pattern A and the predetermined frequency fc in the pattern C, and the predetermined frequency fc when the vehicle is stopped in a parking lot or the like is set to the highest frequency.

  The power converter 34 may not be included in the high voltage power supply system. In this case, the predetermined frequency fc is changed between a pattern in which the MG 33 is connected to the battery 20 and a pattern in which the MG 33 is not connected to the battery 20.

  The coupling capacitor Cs may be connected to the positive terminal side of the battery 20 or the inside of the battery 20.

  The other electric devices included in the high-voltage power supply system are not limited to two systems, that is, a traveling power system including the converter 31, the inverter 32, and the MG 33, and a non-traveling power system including the power converter 34. Two or more electric power systems may be included. FIG. 7 shows the configuration of a high-voltage power supply system that includes three electric power systems including electric equipment 35 in addition to converter 31, inverter 32, MG 33, and power converter 34 as other electric equipment. The electrical device 35 may be a traveling power system including a converter, an inverter, and an MG, or may be an electrical device used for purposes other than traveling. For example, when the power device 35 is a traveling power system, the same processing as the pattern A is performed when SW5 and SW6 are on. In the case where the electric power device 35 is an electric device used for purposes other than traveling, the same processing as the pattern C is performed when SW5 and SW6 are on.

  DESCRIPTION OF SYMBOLS 10 ... Ground fault detection circuit, 11 ... CPU, 12 ... Oscillation circuit, 13 ... Detection circuit, 20 ... Battery, 33 ... MG, 34 ... Power converter, Cs ... Coupling capacitor, Rs ... Resistance element.

Claims (7)

A ground fault detection circuit (10) for detecting a ground fault of a high voltage power supply system electrically insulated from a vehicle body,
An insulating means (Cs) connected to the high-voltage power supply system and insulating a DC component;
Resistance means (Rs) connected in series to the insulation means;
Oscillating means (12) connected in series to the resistance means and applying an alternating voltage of a predetermined frequency to the resistance means;
Detection means (11, 13) for detecting the ground fault based on a voltage at a connection point between the insulation means and the resistance means;
The predetermined AC voltage output by the oscillating means is determined according to the connection state between the battery (20) included in the high-voltage power supply system and the other electrical devices (33, 34) included in the high-voltage power supply system. A vehicle ground fault detection circuit comprising a high-voltage power supply system, comprising variable means (11) for changing the frequency. Comprising digital filter means (11) for cutting off frequency components outside the predetermined passband;
2. The vehicle ground fault detection circuit having a high-voltage power supply system according to claim 1, wherein the variable means changes a predetermined pass band of the filter means in accordance with a predetermined frequency of the AC voltage. The other electric device includes a traveling motor (33) and a power converter (34) used for a purpose different from the driving of the traveling motor,
The variable means makes the predetermined frequency when the power converter is connected to the battery lower than the predetermined frequency when the traveling motor is connected to the battery. A ground fault detection circuit for a vehicle comprising the high-voltage power supply system described in 1.   The vehicle ground fault detection circuit having a high-voltage power supply system according to claim 3, wherein a noise countermeasure capacitor is connected between the power converter and the vehicle body.   The variable means makes the predetermined frequency when the other electric device is not connected to the battery higher than the predetermined frequency when the other electric device is connected to the battery. A vehicle ground fault detection circuit comprising the high-voltage power supply system according to any one of? The other electric device includes a traveling motor,
The variable means makes the predetermined frequency when the other electric device is not connected to the battery higher than the predetermined frequency when the traveling motor is connected to the battery. A vehicle ground fault detection circuit comprising the high-voltage power supply system described. The other electric devices include a travel motor, and a power converter used in a different application from the drive of the travel motor,
The variable means makes the predetermined frequency when the other electric device is not connected to the battery higher than the predetermined frequency when the traveling motor is connected to the battery, and the battery. The high-voltage power supply system according to claim 1 or 2, wherein the predetermined frequency when the power converter is connected to the battery is lower than the predetermined frequency when the traveling motor is connected to the battery. A ground fault detection circuit for a vehicle.

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