JP5926677B2 - Ground fault detector - Google Patents

Description

  The present invention relates to a ground fault detection device.

  Generally, in an electric vehicle or a hybrid vehicle, as a motor drive system, a battery as a motor drive energy supply source, a circuit for monitoring the battery state, an inverter that converts DC power supplied from the battery into AC power Circuits etc. are installed. These are insulated from the vehicle body so as not to form a closed circuit with the vehicle body. As a result, even when a person accidentally contacts the motor drive system, it is possible to prevent electric current from flowing through the human body and electric shock.

  In the motor drive system as described above, as a conventional technique for verifying that the insulation resistance with respect to the vehicle body is above a certain level, an AC waveform with a constant period is applied to the connection line between the battery and a load such as an inverter circuit. A method of detecting a voltage change corresponding to this using a smoothing filter and a comparator is well known. However, when such a conventional method is used, it is known that a malfunction occurs due to potential fluctuation of the connection line.

  Thus, as a solution to the above-described problem, for example, a method has been proposed in which when a potential fluctuation of a connection line is detected, ground fault detection is stopped for a certain period thereafter (see Patent Document 1).

JP 2004-286523 A

  In the method disclosed in Patent Document 1, it is preferable to set the period during which ground fault detection is stopped according to the time from when the potential of the connection line fluctuates until it settles within a certain range. In general, this time depends on the stray capacitance of the connection line and the size of the insulation resistance, and a longer time is required as these values increase. Therefore, when the insulation state with respect to the vehicle body is normally maintained, it is difficult to quickly restart the ground fault detection after the potential fluctuation occurs in the connection line between the battery and the load and the ground fault detection is stopped.

A ground fault detection device according to the present invention detects a ground fault of a connection line between a battery and a load, generates an AC signal, and applies an AC signal to the connection line via a coupling capacitor. Reduces the insulation resistance of the connection line when the potential of the generation line, the ground fault detection part that detects the response signal to the AC signal, detects the ground fault of the connection line based on the response signal, and the potential of the connection line fluctuates and an insulation resistance change portion, the connecting line, is connected to a relay for cutting or conduction between the battery and the load in accordance with the switching control from the outside, the insulation resistance change portion, one end of which is grounded A resistor and a switch connected between the resistor and the connection line, and when the relay is connected between the battery and the load, the switch is switched from the disconnected state to the conductive state, thereby connecting the connection line. lowering the insulation resistance And wherein the door.

  According to the present invention, the ground fault detection can be quickly restarted after the potential fluctuation occurs in the connection line between the battery and the load and the ground fault detection is stopped.

It is a figure which shows the structural example of the motor drive system which concerns on one Embodiment of this invention. It is a figure which shows the circuit structure regarding the ground fault detection which concerns on one Embodiment of this invention. It is a figure which shows the mode of the change of the voltage value and resistance value of each site | part at the time of not applying this invention. It is a figure which shows the mode of the change of the voltage value and resistance value of each site | part at the time of applying this invention.

  FIG. 1 is a diagram illustrating a configuration example of a motor drive system according to an embodiment of the present invention. The motor drive system shown in FIG. 1 is used in, for example, an electric vehicle or a hybrid vehicle, and includes a monitoring device 100, a battery module 112, a drive circuit 113, and a motor 140.

  The battery module 112 is configured by electrically connecting a plurality of battery groups each having a predetermined number of battery cells electrically connected in series. The battery module 112 is connected to the drive circuit 113 via the positive electrode connection line 160 and the negative electrode connection line 161, and supplies DC power generated by the discharge of each battery cell to the drive circuit 113. Each battery cell of the battery module 112 may be a chargeable / dischargeable secondary battery. In this case, each battery cell of the battery module 112 is charged by converting AC power generated by the regenerative power generation of the motor 140 into DC power by the drive circuit 113 and outputting the DC power to the battery module 112.

  The drive circuit 113 drives the motor 140 by converting the DC power supplied from the battery module 112 into AC power and outputting the AC power to the motor 140. Although FIG. 1 shows a configuration example of a three-phase inverter provided with switching elements (transistors) for three phases as the driving circuit 113, the configuration of the driving circuit 113 is not limited to this. Depending on the structure of the motor 140 and the like, the drive circuit 113 having various configurations can be used.

  The motor 140 is driven to rotate by receiving AC power output from the drive circuit 113, thereby generating a driving force of a vehicle on which the motor drive system of FIG. 1 is mounted. As described above, when each battery cell of the battery module 112 is a secondary battery, the motor 140 performs regenerative power generation using the kinetic energy of the vehicle at the time of braking, so that AC power is generated by the motor 140. Good. The AC power obtained by the regenerative power generation is converted into DC power by the drive circuit 113 and output to the battery module 112, whereby each battery cell of the battery module 112 is charged.

  The drive circuit 113 and the motor 140 are insulated from the battery module 112 and the monitoring device 100 when the relays 150 and 151 are opened. These are also insulated from the ground potential. Therefore, when the relays 150 and 151 are open, the drive circuit 113 and the motor 140, the battery module 112, and the monitoring device 100 may have different ground potentials.

  The monitoring device 100 is a device for monitoring the state of the battery module 112, and includes a battery state monitoring integrated circuit 120, a ground fault detection device 121, a communication circuit 130, a control unit 131, and a communication unit 132.

  The battery state monitoring integrated circuit 120 is connected to each battery cell of the battery module 112, and according to a control command transmitted from the control unit 131 via the communication circuit 130, voltage measurement and balancing control of each battery cell. Etc. The measurement result of each battery cell by the battery state monitoring integrated circuit 120 is transmitted to the control unit 131 via the communication circuit 130. The battery state monitoring integrated circuit 120 may be provided corresponding to each battery group of the battery module 112.

  The control unit 131 controls the activation of the battery state monitoring integrated circuit 120 by transmitting a control command to the battery state monitoring integrated circuit 120 via the communication circuit 130, and the operation of the battery state monitoring integrated circuit 120. And the state of each battery cell of the battery module 112 is monitored. Moreover, the state monitoring result of each battery cell of the battery module 112 is reported by performing communication with an external host controller via the communication unit 132.

  The ground fault detection device 121 is a device that detects a ground fault between the drive circuit 113 and the battery module 112. The ground fault detection result by the ground fault detection device 121 is notified to the control unit 131. Details of the ground fault detection device 121 will be described later with reference to FIG.

  In the monitoring device 100, the battery state monitoring integrated circuit 120 and the control unit 131 are connected to each other in an insulated state via the communication circuit 130 and the ground fault detection device 121. Therefore, hereinafter, as shown in FIG. 1, the portion of the monitoring device 100 on the high potential side that is connected to the battery module 112 and includes the integrated circuit 120 for monitoring the battery state is referred to as a monitoring device (HV side) 110. A portion of the monitoring device 100 on the low potential side that is connected to the host controller and includes the control unit 131 and the communication unit 132 is referred to as a monitoring device (LV side) 111. Since the monitoring device (LV side) 111 is grounded to the ground of the vehicle via the grounding circuit 114, its ground potential is zero.

  FIG. 2 is a diagram showing a circuit configuration relating to ground fault detection according to an embodiment of the present invention. In FIG. 2, the drive circuit 113 and the motor 140 that act as a load of the battery module 112 are connected to the positive side of the battery module 112 via a positive connection line 160 provided with a relay 150. Moreover, it is connected to the negative electrode side of the battery module 112 via the negative electrode connection line 161 provided with the relay 151.

  A stray capacitance 211 and an insulation resistance 212 corresponding to the insulation state exist between the drive circuit 113 and the motor 140 and the ground potential. Similarly, a stray capacitance 201 and an insulation resistance 202 corresponding to the insulation state exist between the battery module 112 and the ground potential.

  As shown in FIG. 2, the positive connection line 160 that connects the drive circuit 113 and the motor 140 to the positive side of the battery module 112 is also connected to the ground fault detection device 121. The ground fault detection device 121 includes a coupling capacitor 220, a ground fault detection unit 221, an AC signal generation unit 222, and an insulation resistance change unit 250.

  The AC signal generator 222 generates and outputs an AC signal (for example, a pulse signal) having a predetermined amplitude. The AC signal output from the AC signal generator 222 is applied to the positive electrode connection line 160 via the voltage dividing circuit and the coupling capacitor 220.

  When the AC signal generated by the AC signal generator 222 is applied to the positive connection line 160, a response signal having an amplitude corresponding to the insulation state with respect to the ground potential is generated in the positive connection line 160. That is, if the ground resistance value of the positive connection line 160 is high, the waveform of the response signal with respect to the AC signal has a large amplitude. Conversely, if the ground resistance value of the positive connection line 160 is low, the waveform of the response signal with respect to the AC signal is The amplitude is small. This response signal is detected by the ground fault detector 221 via the coupling capacitor 220 and the voltage dividing circuit.

  The ground fault detection unit 221 detects a response signal to the AC signal from the AC signal generation unit 222, and detects a ground fault of the positive electrode connection line 160 based on the response signal. For example, it is determined whether or not the amplitude of the detected response signal is less than a predetermined threshold, and if it is less than the threshold, it is determined that the ground resistance value of the positive connection line 160 is lower than the reference value. Detect a ground fault. The ground fault detection result by the ground fault detection unit 221 is notified from the ground fault detection device 121 to the control unit 131 of FIG.

  The insulation resistance changing unit 250 is connected between the coupling capacitor 220 and the positive electrode connection line 160 and includes a switch 251 and a resistor 252. The resistor 252 has a resistance value Rq, and one end thereof is grounded. The switch 251 is connected between the non-grounded side of the resistor 252 and the positive connection line 160, and performs a switching operation of these connection states. The switching operation by the switch 251 is controlled as follows according to the state of the relays 150 and 151.

  Relays 150 and 151 are connected to the positive connection line 160 and the negative connection line 161, respectively. The relays 150 and 151 disconnect (OFF) or conduct (ON) between the battery module 112 and the drive circuit 113 and the motor 140, which are loads, according to switching control from an external host controller.

  When the relays 150 and 151 are OFF and the drive circuit 113 and the battery module 112 are disconnected, the switch 251 is in the disconnected (OFF) state in the insulation resistance changing unit 250 of the ground fault detector 121. . When the relays 150 and 151 are switched on from this state and the drive circuit 113 and the battery module 112 are connected, the switch 251 is turned on (ON) for a predetermined time. After the predetermined time has elapsed, the switch 251 is disconnected again.

  In the ground fault detection device 121, the switching timing of the relays 150 and 151 is notified from the control unit 131 shown in FIG. The ground fault detection device 121 can control the operation of the switch 251 of the insulation resistance changing unit 250 according to the switching timing notified from the control unit 131. Note that the control unit 131 can specify the switching timing of the relays 150 and 151 based on information transmitted from a host controller (not shown) via the communication unit 132, for example.

  Here, it is assumed that there is a difference between the ground potential of the drive circuit 113 and the motor 140 and the ground potential of the battery module 112 and the monitoring device (HV side) 110 when the relays 150 and 151 are OFF. In this case, the both-ends voltage of the stray capacitance 211 between the drive circuit 113 and the motor 140 and the ground potential and the both-ends voltage of the stray capacitance 201 between the battery module 112 and the monitoring device (HV side) 110 and the ground potential are: Is different. Therefore, when the relays 150 and 151 are switched from OFF to ON as described above and the drive circuit 113 and the battery module 112 are connected, the voltage across the stray capacitance 211 and the stray capacitance 201 coincides with each other. Current flows between the two. For example, when the voltage across the stray capacitance 211 is higher than that of the stray capacitance 201, current flows from the stray capacitance 211 to the stray capacitance 201 as indicated by an arrow in FIG. As a result, the voltage across the stray capacitances 201 and 211 changes. This is equivalent to a change in ground potential in the drive circuit 113 and the battery module 112.

  When the ground potential of the battery module 112 varies as described above, the potential of the positive electrode connection line 160 also varies. Therefore, the response signal detected via the coupling capacitor 220 changes from the state when the relays 150 and 151 are OFF, and the ground fault detection unit 221 cannot perform correct ground fault detection. In order to eliminate the influence on the response signal due to the fluctuation of the ground potential, the battery after the coupling capacitor 220 is charged or discharged and the accumulated charge amount is connected to the drive circuit 113 It is necessary to increase or decrease the charge amount according to the ground potential difference between the module 112 (monitoring device (HV side) 110) and the monitoring device (LV side) 111.

  Here, as a conventional technique to which the present invention is not applied, a case where the insulation resistance change unit 250 is not provided in the ground fault detection device 121 is considered. In this case, the coupling capacitor 220 is charged or discharged by the insulation resistance 212 between the drive circuit 113 and the motor 140 and the ground potential, or the insulation between the battery module 112 and the monitoring device (HV side) 110 and the ground potential. This is done via the resistor 202. For this reason, it takes a long time for the charge amount of the coupling capacitor 220 to increase or decrease to the above-described charge amount, and it is difficult to calculate and estimate the time in advance.

  On the other hand, according to the above embodiment to which the present invention is applied, in the ground fault detection device 121, the insulation resistance changing unit 250 is provided between the coupling capacitor 220 and the positive electrode connection line 160. As described above, the insulation resistance changing unit 250 turns on the switch 251 for a predetermined time when the relays 150 and 151 are switched from OFF to ON and the potential of the positive connection line 160 fluctuates. As a result, the resistor 252 acts as the insulation resistance of the positive connection line 160, and the charging or discharging of the coupling capacitor 220 in accordance with the potential fluctuation of the positive connection line 160 has a resistance value Rq lower than that of the insulation resistances 202 and 212. This is done via a resistor 252 having the same. Therefore, compared with the case where the insulation resistance change unit 250 is not provided, the period during which the ground fault detection unit 221 cannot detect the ground fault can be shortened, and the ground fault detection can be resumed in a short time.

  The difference in operation of the ground fault detection device 121 depending on the presence / absence of the insulation resistance changing unit 250 as described above will be described below with a specific example. FIG. 3 is a diagram showing how the voltage value and resistance value of each part change when the present invention is not applied. 3, (a) shows the switching state of the relays 150 and 151, (b) shows the ground potential of the battery module 112, (c) shows the insulation resistance value between the battery module 112 and the ground potential, d) shows the voltage across the coupling capacitor 220, and (e) shows the voltage of the response signal detected by the ground fault detector 221.

  As shown in FIG. 3A, when the relays 150 and 151 are switched from OFF to ON at time t0, the ground potential of the battery module 112 changes as shown in FIG. 3B. On the other hand, as shown in FIG. 3C, the insulation resistance value between the battery module 112 and the ground potential does not change before and after time t0. In FIG. 3B, the ground potential of the drive circuit 113 and the motor 140 is lower than the ground potential of the battery module 112 and the monitoring device (HV side) 110 before time t0, and therefore the ground of the battery module 112 at time t0. An example in which the potential is lowered is shown.

  When the ground potential of the battery module 112 decreases at time t0, the coupling capacitor 220 starts to be discharged accordingly. This discharge is performed via the insulation resistance 202 and the insulation resistance 212 as described above. For this reason, as shown in FIG. 3D, the voltage across the coupling capacitor 220 gradually decreases.

  As shown in FIG. 3E, since the response signal is not correctly output while the voltage across the coupling capacitor 220 is changing, the ground fault detection unit 221 cannot perform ground fault detection. When the voltage across the coupling capacitor 220 becomes substantially constant at time t1, the response signal is output again correctly, and the ground fault detection can be resumed. Thus, when the present invention is not applied, the period during which the ground fault detection unit 221 cannot detect the ground fault is the period from time t0 to time t1 shown in FIG.

  FIG. 4 is a diagram showing how the voltage value and resistance value of each part change when the present invention is applied. 4, (a) shows the switching state of the relays 150 and 151, (b) shows the ground potential of the battery module 112, and (c) shows the insulation between the battery module 112 and the ground potential. The resistance value is shown, (d) shows the voltage across the coupling capacitor 220, and (e) shows the voltage of the response signal detected by the ground fault detector 221.

  As shown in FIG. 4A, when the relays 150 and 151 are switched from OFF to ON at time t0, the ground potential of the battery module 112 changes as shown in FIG. 4B. This is the same as in FIGS. 3A and 3B.

  Here, immediately before time t0, when the switch 251 of the insulation resistance changing unit 250 is turned on as described above, the positive connection line 160 is connected to the ground potential via the resistor 252, and the positive connection line 160 is insulated. Resistor 252 acts as a resistor. Thereby, as shown in FIG.4 (c), the insulation resistance value between the battery module 112 and ground potential falls. Thereafter, when the ground potential of the battery module 112 decreases at time t0, the coupling capacitor 220 starts to be discharged accordingly. Unlike the case of FIG. 3, the coupling capacitor 220 is discharged through the resistor 252 instead of the insulation resistor 202 and the insulation resistor 212. Therefore, as shown in FIG. 4D, the voltage between both ends of the coupling capacitor 220 decreases quickly as compared with FIG. 3D, and becomes substantially constant at time t2.

  When the voltage across the coupling capacitor 220 becomes substantially constant at time t2, the output of the response signal is restored and the ground fault detection can be resumed as shown in FIG. 4 (e). Therefore, when the present invention is applied, the period during which the ground fault detection unit 221 cannot detect the ground fault is the period from time t0 to time t2 shown in FIG. 4 (e), which is shown in FIG. 3 (e). It can be seen that it is shorter than the period from time t0 to time t1 when the ground fault cannot be detected.

As described above, the start point of the period during which the switch 251 is turned on in the insulation resistance changing unit 250 is the time before the time t0 when the relays 150 and 151 are switched from OFF to ON, or at the same time as the time t0. Preferably there is. Moreover, the time T shown in FIG.4 (c) represents the time from the time t0 to the end point of this period, and it is preferable that this satisfy | fills the following formula | equation (1). In Expression (1), C is the capacitance value of the coupling capacitor 220, Rq is the resistance value of the resistor 252, VL is the amplitude of the AC signal generated from the AC signal generator 222, and VH is the maximum that the battery module 112 can take. Each voltage is shown. However, in Formula (1), ln {VH / (VH−VL)} represents a natural logarithm of VH / (VH−VL).
T ≧ C × Rq × ln {VH / (VH−VL)} (1)

  According to the embodiment of the present invention described above, the following operational effects are obtained.

(1) The ground fault detection device 121 causes the insulation resistance changing unit 250 to reduce the insulation resistance of the positive connection line 160 when the potential of the positive connection line 160 varies. Since it did in this way, after a potential fluctuation arises in the connection line between the battery and the load and the ground fault detection is stopped, the ground fault detection can be restarted quickly.

(2) The insulation resistance changing unit 250 includes a resistor 252 whose one end is grounded, and a switch 251 connected between the resistor 252 and the positive electrode connection line 160. By switching the switch 251 from the disconnected state to the conductive state, the insulation resistance of the positive electrode connection line 160 is reduced, so that the insulation resistance can be reliably reduced with a simple circuit.

(3) Relays 150 and 151 that disconnect or connect between the battery module 112 and the drive circuit 113 that is a load and the motor 140 are connected to the positive electrode connection line 160 in accordance with switching control from the outside. The insulation resistance changing unit 250 switches the switch 251 from the disconnected state to the conductive state when the relays 150 and 151 are connected between the battery module 112 and the load. Since it did in this way, when an electric potential fluctuation | variation arises in the positive electrode connection line 160, the insulation resistance of the positive electrode connection line 160 can be reduced reliably.

(4) The insulation resistance changing unit 250 may reduce the insulation resistance of the positive electrode connection line 160 during the time T represented by the above-described formula (1) after the battery module 112 and the load are conducted. preferable. In this way, the insulation resistance of the positive electrode connection line 160 can be reliably reduced until the coupling capacitor 220 is charged or discharged and the voltage at both ends becomes constant.

  In the above-described embodiment, the example in which the insulation resistance of the positive electrode connection line 160 is reduced by switching the switch 251 from the disconnected state to the conductive state in the insulation resistance changing unit 250 has been described. However, other circuit configurations may be used as long as the insulation resistance can be reduced when the potential of the positive electrode connection line 160 fluctuates.

  In the above embodiment, the ground fault detection device 121 is connected to the positive electrode side of the battery module 112, and the AC signal from the AC signal generator 222 is applied to the positive electrode connection line 160. However, the ground fault detection device 121 may be connected to the negative electrode side of the battery module 112 and the AC signal from the AC signal generator 222 may be applied to the negative electrode connection line 161. Even in this case, ground fault detection can be performed in the same manner as in the above embodiment, and the insulation resistance can be reduced when the potential of the negative electrode connection line 161 changes, thereby shortening the period during which ground fault detection is not possible. it can.

  The embodiment and various modifications described above are merely examples, and the present invention is not limited to these contents as long as the features of the invention are not impaired.

100 monitoring device 112 battery module 113 drive circuit 114 grounding circuit 120 battery state monitoring integrated circuit 121 ground fault detection device 130 communication circuit 131 control unit 132 communication unit 140 motor 150 relay 151 relay 160 positive connection line 161 negative connection line 201 floating Capacitance 202 Insulation resistance 211 Floating capacitance 212 Insulation resistance 220 Coupling capacitor 221 Ground fault detection unit 222 AC signal generation unit 250 Insulation resistance change unit 251 Switch 252 Resistor

Claims (2)

A ground fault detection device for detecting a ground fault of a connection line between a battery and a load,
An AC signal generator that generates an AC signal and applies the AC signal to the connection line via a coupling capacitor;
Detecting a response signal to the AC signal, and detecting a ground fault of the connection line based on the response signal;
When the potential of the connection line varies, and an insulation resistance changing portion to decrease the insulation resistance of the connection line,
A relay that disconnects or conducts between the battery and the load according to switching control from the outside is connected to the connection line,
The insulation resistance changing unit includes a resistor having one end grounded, and a switch connected between the resistor and the connection line, and when the battery and the load are connected by the relay. In addition, the ground fault detection device is characterized in that the insulation resistance of the connection line is lowered by switching the switch from a disconnected state to a conductive state . In the ground fault detection apparatus according to claim 1 ,
The insulation resistance changing unit is connected between the battery and the load based on a capacitance value C of the coupling capacitor, a resistance value Rq of the resistor, an amplitude VL of the AC signal, and a maximum voltage VH of the battery. After that, during the time T expressed by the following formula, the ground fault detection device reduces the insulation resistance of the connection line.
T ≧ C × Rq × ln {VH / (VH−VL)}
In the above formula, ln {VH / (VH−VL)} represents the natural logarithm of VH / (VH−VL).

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