JP2004104923A - Method and apparatus for detecting insulation resistance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To judge in a short time whether the insulation resistance between a high-voltage circuit and a chassis when a vehicle is started, and detect the insulation resistance with accuracy and stability without the influences of a high-voltage battery while the vehicle is running. <P>SOLUTION: A first coupling capacitor 341 and a second coupling capacitor 342 either ends of which are respectively connected with the total negative portion and the total positive portion of the high-voltage battery 12 are provided. Thus, the offset voltage of a resistor 33 is prevented from being produced due to fluctuation in the voltage of the high-voltage battery. Further, drop in insulation resistance is detected at an insulation resistance detecting portion 381 in a short time. This detection is carried out based on the difference between a first amplitude level computed at some point in time from the peak level of signals sampled by an analog-to-digital converter 37 every half cycle of a signal generated by a signal generator 31, and a second amplitude level computed a half cycle later. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention converts DC power from a battery pack, which is a high-voltage battery mounted on an electric vehicle such as an electric vehicle (PEV) or a hybrid vehicle (HEV), into AC power by an inverter via a relay through a relay, and converts the DC power into a motor. The present invention relates to a technology for detecting an insulation resistance of an electric vehicle that travels while being supplied.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in an electric vehicle (PEV), a so-called hybrid vehicle (HEV) having an engine and a motor, and the like, a high energy density (that is, energy can be stored compactly) as a main power source for driving the motor. In view of high power density, nickel-hydrogen (Ni-MH) secondary batteries are mainly used. In such PEVs and HEVs, a plurality of cells are combined into one assembled battery so that a sufficient output can be supplied to the motor, and the assembled battery is mounted as a high-voltage battery.
[0003]
Such an HEV or the like has a high-voltage circuit for driving and controlling a motor using a high-voltage battery as a driving source, and a low-voltage circuit for driving electronic devices such as audio equipment using a low-voltage battery as a driving source. are doing. Further, the high-voltage circuit includes an inverter for driving the motor.
[0004]
In an electric vehicle such as an HEV, in order to ensure safety to the human body, it is detected whether or not the value of the insulation resistance between the high-voltage circuit and the chassis of the vehicle is sufficiently large. Warn the driver or shut off the power from the high-voltage battery.
[0005]
FIG. 4 is a functional block diagram showing a partial configuration of a conventional electric vehicle. In FIG. 4, an electric vehicle 100 includes a high-voltage circuit 10 that drives and controls a high-voltage load 11 such as a motor, a low-voltage circuit 20 that drives a low-voltage load 21 such as various electronic devices, a high-voltage circuit 10 and a chassis. And an insulation resistance detecting device 300 for detecting insulation resistance between the two.
[0006]
The high-voltage circuit 10 includes a high-voltage battery 12, a second switch unit 13 that conducts or cuts off power from the high-voltage battery 12 to the high-voltage load 11, and an inverter that drives and controls the high-voltage load 11. 14, a resistor 15 connected between the high potential input terminal of the inverter 14 and the chassis, and a resistor 16 connected between the low potential input terminal of the inverter 14 and the chassis.
[0007]
The high-voltage battery 12 includes a plurality of secondary batteries (for example, Ni-MH secondary batteries) 121 connected in series, and is used to rotationally drive a motor as a drive source for driving the electric vehicle 100. A required high voltage (for example, 288 V) can be output. The second switch section 13 is configured by a relay or the like, and has a predetermined or more current capacity necessary for driving the high-voltage load 11 such as a motor. The inverter 14 has a function of converting a DC current from the high-voltage battery 12 into an AC current in order to rotationally drive a motor (for example, a three-phase AC motor). , A large-capacity smoothing capacitor 141 is provided. The resistor 15 (resistance value R1) and the resistor 16 (resistance value R2) have a large resistance value because the end of precharging of the smoothing capacitor 141 of the inverter 14 is determined based on the charging voltage. The detection circuit is not shown).
[0008]
The low-voltage circuit 20 includes a low-voltage battery 22 and a first switch unit 23 that enables connection control between the low-voltage battery 22 and the low-voltage load 21.
[0009]
The low-voltage battery 22 includes a plurality of rechargeable batteries 221 connected in series. The low-voltage battery 22 includes a low-voltage load 21 such as an illumination display unit 211 and an acoustic device 212 (for example, a radio or a stereo) as an electronic device. A low voltage (for example, 12 V) necessary for driving can be output. The first switch unit 23 is an ignition key switch, and controls on / off of an electric system of the entire vehicle. The first switch unit 23 is interlocked with the second switch unit 13, and when the first switch unit 23 is turned on, the second switch unit 13 is also turned on, and the first switch unit 23 is turned off. Accordingly, the second switch section 13 is also turned off.
[0010]
The insulation resistance detecting device 300 includes a signal generator 31 that outputs a sine wave or a square wave signal of a predetermined frequency (for example, 1 Hz), an amplifier 32 that amplifies a signal from the signal generator 31 to a predetermined level, A resistor 33 for attenuating a signal from the amplifier 32 according to an insulation resistance (not shown) between the voltage circuit 10 and the chassis, and a resistor 33 between one end of the resistor 33 and all negative terminals of the high-voltage battery 12. A coupling capacitor 34 connected thereto, a low-pass filter (LPF) 35 for removing a high-frequency component of the signal from the amplifier 32 via the resistor 33, an amplifier 36 for amplifying the signal from the LPF 35 to a predetermined level, and an amplifier 36 An A / D converter 37 that updates data from the signal at one cycle interval (for example, 1 second when the signal frequency is 1 Hz) and converts the data into a digital signal. Includes a microcomputer (μCOM) 38 which receives the digital signal from the A / D converter 37. The μCOM 38 includes an insulation resistance detection unit 381 ′ that compares the digital signal from the A / D converter 37 with a predetermined threshold to determine whether insulation resistance has decreased.
[0011]
Further, 40 receives the ON operation signal of the first switch unit 23, and sets the second switch unit 13 to the ON state when the detection end signal from the insulation resistance detection unit 381 ′ indicates that the insulation resistance has not decreased. When the detection end signal from the insulation resistance detection unit 381 ′ indicates that the insulation resistance has decreased, the switch control unit turns off the second switch unit 13.
[0012]
The insulation resistance detector 381 ′ first keeps the second switch 13 in the off state via the switch controller 40 at the time of starting the vehicle, compares the digital signal from the A / D converter 37 with a predetermined threshold, When the insulation resistance between the high-voltage battery 12 and the chassis becomes equal to or less than a predetermined value (for example, 100 kΩ) and the digital signal decreases and becomes equal to or less than the threshold value, the decrease in insulation resistance is detected. The signal is output to the switch control unit 40 and is output to the illumination display unit 211 to turn on the display lamp.
[0013]
The switch control unit 40 receives the ON operation signal of the first switch unit 23, and sets the second switch unit 13 to the ON state when the detection signal from the insulation resistance detection unit 381 ′ indicates that the insulation resistance has not decreased. When the detection signal from the insulation resistance detection unit 381 ′ indicates that the insulation resistance has decreased, the second switch unit 13 is kept off.
[0014]
If the insulation resistance between the high-voltage battery 12 and the chassis is normal when the vehicle starts, the second switch unit 13 is turned on, and the DC power from the high-voltage battery 12 is converted into AC power by the inverter 14. Then, the electric vehicle 100 is supplied to the motor and becomes ready to run. Even when the vehicle is running, the insulation resistance detection unit 381 ′ determines whether the insulation resistance between the path from the second switch unit 13 to the inverter 14 and the chassis is reduced.
[0015]
[Problems to be solved by the invention]
When the vehicle is started, the second switch unit 13 is turned off, and even if it is determined that the insulation resistance between the high-voltage battery 12 and the chassis does not decrease and that the high-voltage battery 12 is normal, the second switch unit 13 supplies the inverter to the inverter. In some cases, the insulation resistance between the path up to 14 and the chassis is reduced.
[0016]
In this case, at the moment when the second switch section 13 is turned on, a charge / discharge current flows through the coupling capacitor 34, and the level of the input signal to the A / D converter 37 exceeds the A / D conversion range, and the signal level Is considered to be zero, and it is erroneously determined that the insulation resistance is abnormal. This problem will be described below with reference to FIGS. 5A, 5B, and 5C.
[0017]
5A, 5B, and 5C show that the insulation resistance between the high potential input side of the inverter 14 and the chassis decreases when the insulation resistance between the input side of the inverter 14 and the chassis is normal. FIG. 4 is a waveform diagram of an input signal to the A / D converter 37 when the power supply is turned on and when the insulation resistance between the low potential input side of the inverter 14 and the chassis is reduced.
[0018]
If the insulation resistance between the high-potential input side of the inverter 14 and the chassis is reduced to some extent, if not abnormally, the resistance 15 (resistance R1) and the reduced insulation resistance (RL) are connected in parallel, The combined resistance value R1 // RL becomes smaller than the resistance value R2 of the resistor 16.
[0019]
Therefore, at the moment when the second switch section 13 is turned on, the voltage VC applied to the coupling capacitor 34 changes from the equilibrium state (FIG. 5A) where the voltage VC is equal to の of the voltage VB of the high-voltage battery 12. The voltage VC becomes equal to the voltage VB of the high-voltage battery 12, and the current for charging the coupling capacitor 34 from the resistor 33 to the chassis via the coupling capacitor 34 and the resistor 16 flows instantaneously, as shown in FIG. 5B. In addition, the bias level of the input signal to the A / D converter 37 is significantly lower than the A / D conversion range (VT-VB).
[0020]
As a result, the charging of the coupling capacitor 34 becomes substantially saturated. As a result, it takes a long time until the bias level of the signal reaches the vicinity of the intermediate value (VM) of the conversion range of the A / D converter 37. Become. As a result, there is a possibility that the insulation resistance is erroneously detected as being reduced to a degree determined to be abnormal (for example, 100 kΩ).
[0021]
On the other hand, when the insulation resistance between the low-potential input side of the inverter 14 and the chassis is reduced to some extent, if not abnormal, the resistance 16 (resistance R2) and the reduced insulation resistance (RL) are connected in parallel. Thus, the combined resistance value R2 // RL becomes smaller than the resistance value R1 of the resistor 15.
[0022]
Therefore, at the moment when the second switch section 13 is turned on, the voltage VC applied to the coupling capacitor 34 changes from the equilibrium state (FIG. 5A) where the voltage VC is equal to の of the voltage VB of the high-voltage battery 12. When the voltage VC becomes zero, a current for discharging the coupling capacitor 34 from the chassis to the resistor 33 via the resistor 15 and the coupling capacitor 34 flows instantaneously, and flows to the A / D converter 37 as shown in FIG. 5C. The input signal bias level greatly exceeds the A / D conversion range (VT-VB).
[0023]
Also in this case, the discharge to the coupling capacitor 34 becomes almost saturated, and as a result, it takes a long time until the bias level of the signal reaches the vicinity of the intermediate value (VM) of the conversion range of the A / D converter 37. become. As a result, there is a possibility that the insulation resistance is erroneously detected as being reduced to a degree determined to be abnormal (for example, 100 kΩ).
[0024]
To avoid the erroneous detection as described above, the detection confirmation time may be set longer, but in that case, it is not a preferable measure from the viewpoint of safety for the human body.
[0025]
Further, in the above-described conventional example, since the signal from the amplifier 36 is sampled at one cycle interval by the A / D converter 37 to determine the decrease in insulation resistance, the time required for the determination becomes longer.
[0026]
In addition to the above-mentioned problems, during traveling of the vehicle, charging and discharging of the high-voltage battery 12 is performed, and the voltage VB of the high-voltage battery 12 fluctuates. There is also a problem that the detection accuracy by the insulation resistance detecting unit 381 ′ is deteriorated. This problem will be described below with reference to FIGS. 6A, 6B, and 6C.
[0027]
6A, 6B, and 6C show the case where the voltage of the high voltage battery 12 does not fluctuate, the case where the voltage of the high voltage battery 12 increases due to charging, and the case where the voltage of the high voltage battery 12 decreases due to discharging, respectively. 3 is a waveform diagram of an input signal to the A / D converter 37. FIG.
[0028]
When the high-voltage battery 12 is charged during vehicle braking, the voltage VB increases with the ground potential of the chassis as an intermediate value, and the increased voltage causes a charging current to flow to the coupling capacitor 34 via the resistor 33. When the charging current flows through the resistor 33, as shown in FIG. 6B, the bias level of the input signal to the A / D converter 37 by the offset voltage (the resistance value of the resistor 33 × the value of the charging current) is increased as shown in FIG. From the state, it becomes difficult to accurately detect the insulation resistance.
[0029]
On the other hand, when discharging from the high-voltage battery 12 at the time of vehicle acceleration or climbing a slope, the voltage VB decreases with the ground potential of the chassis as an intermediate value. Discharge current flows. When the discharge current flows through the resistor 33, as shown in FIG. 6C, the bias level of the input signal to the A / D converter 37 by the offset voltage (the resistance value of the resistor 33 × the value of the charging current) is increased as shown in FIG. From the state, it becomes difficult to accurately detect the insulation resistance.
[0030]
The present invention has been made in view of such a problem, and an object thereof is to detect whether or not an insulation resistance between a high-voltage circuit and a chassis is normal at the time of starting a vehicle in a time as short as possible, It is another object of the present invention to provide an insulation resistance detection method and apparatus capable of detecting an insulation resistance accurately and stably without being affected by a voltage fluctuation of a high-voltage battery during running of a vehicle.
[0031]
[Means for Solving the Problems]
In order to achieve the above object, an insulation resistance detecting method according to the present invention provides a method for detecting a DC power from a battery pack (high-voltage battery) formed by combining a plurality of nickel-hydrogen secondary batteries. A signal generator that generates a signal of a predetermined frequency (for example, 1 Hz), which is applied to an electric vehicle having a high-voltage circuit that converts the power into AC power by an inverter via an inverter and supplies the power to the motor, and an output of the signal generator. One end is connected to the terminal to cooperate with the insulation resistance between the high-voltage circuit (path from the battery pack to the relay, path from the relay to the inverter) and the chassis to attenuate the output signal of the signal generator A method for detecting an insulation resistance using a resistive element of the type described above and a capacitive element for capacitively coupling the other end of the resistive element and a path from the battery pack to the relay, comprising the steps of: Calculating the amplitude level for each half cycle (T / 2), a first amplitude level V (i) calculated at a certain time point ti, and a second amplitude level calculated at a time point ti + T / 2 half a cycle after the first amplitude level V (i). Comparing the second amplitude level V (i + 1) with the level V (i + 1) by a predetermined value Vt below the first amplitude level V (i). Detecting a decrease.
[0032]
According to this insulation resistance detection method, when the vehicle is started, when the relay is turned on, it is determined in a short time as to whether the insulation resistance between the path from the relay to the inverter and the chassis is normal or abnormal. can do.
[0033]
In the insulation resistance detection method according to the present invention, the capacitive element includes a first capacitive element connected between the other end of the resistive element and one terminal of the battery pack, and the other end of the resistive element. It is preferable that a second capacitive element is connected between the other terminal of the battery pack and has the same capacitance as the first capacitive element.
[0034]
As a result, even when the voltage of the high-voltage battery fluctuates during running of the vehicle, the charge / discharge current flowing through the resistive element is reduced to compensate for the offset voltage due to the resistive element, thereby biasing the signal to be detected. Since the level can be stabilized, the insulation resistance can be accurately detected.
[0035]
In order to achieve the above object, an insulation resistance detecting device according to the present invention provides a relay (a second switch) using DC power from an assembled battery (high-voltage battery) formed by combining a plurality of nickel-hydrogen secondary batteries, for example. Section) between the high-voltage circuit (the path from the battery pack to the relay, the path from the relay to the inverter) and the chassis in an electric vehicle having a high-voltage circuit that is converted into AC power by the inverter via the inverter and supplied to the motor. A signal generator for generating a signal of a predetermined frequency (for example, 1 Hz), one end of which is connected to an output terminal of the signal generator, and cooperating with the insulation resistance. Resistive element for attenuating the output signal of the above, a first capacitive element connected between the other end of the resistive element and one terminal of the battery pack, the other end of the resistive element and the battery pack The other of A second capacitive element connected between the second capacitive element and the first capacitive element and having the same capacitance value as the first capacitive element; and an insulation for detecting a decrease in insulation resistance according to an amplitude level of a signal passing through the resistive element. And a resistance detector.
[0036]
According to this insulation resistance detection device, even when the voltage of the high-voltage battery fluctuates while the vehicle is running, the charge / discharge current flowing through the resistive element is reduced, and the offset voltage due to the resistive element is compensated for. Since the bias level of the signal to be detected can be stabilized, the insulation resistance can be accurately detected.
[0037]
In the insulation resistance detection device according to the present invention, the insulation resistance detection unit calculates an amplitude level of a signal passing through the resistive element for each half cycle (T / 2) (A / D converter, insulation resistance detection unit) Is compared with a first amplitude level V (i) calculated at a certain time point ti and a second amplitude level V (i + 1) calculated at a time point ti + T / 2 half a cycle later. When the amplitude level V (i + 1) is lower than the first amplitude level V (i) by a predetermined value Vt, it is preferable to include a means (insulation resistance detector) for detecting a decrease in insulation resistance.
[0038]
Thus, when the relay is turned on at the time of starting the vehicle, it is possible to determine in a short time as to whether the insulation resistance between the path from the relay to the inverter and the chassis is normal or abnormal.
[0039]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
[0040]
FIG. 1 is a functional block diagram showing a partial configuration of an electric vehicle to which an insulation resistance detecting device 30 according to one embodiment of the present invention is applied. In FIG. 1, portions having the same functions and configurations as those in FIG. 4 showing a conventional example are denoted by the same reference numerals, and description thereof will be omitted.
[0041]
The present embodiment is different from the conventional example in that the insulation resistance detecting device 30 has one end connected to the entire minus portion of the high-voltage battery 12 and the other end connected to the other end of the resistor 33, as in the conventional case. In addition to the first coupling capacitor 341 (first capacitive element), a second coupling capacitor 342 (which has one end connected to the total positive portion of the high-voltage battery 12 and the other end connected to the other end of the resistor 33) (A second capacitive element) and an insulation resistance detector 381 having a function different from that of the conventional insulation resistance detector 381 ′.
[0042]
Hereinafter, the operation of the insulation resistance detecting device thus configured will be described with reference to FIG. FIG. 2 is a flowchart illustrating a processing procedure of an insulation resistance detection routine according to the present embodiment.
[0043]
In FIG. 2, when the first switch unit 23, which is an ignition key switch, is turned on (S201), first, the insulation resistance of the high-voltage battery 12 is reduced while the second switch unit 13 is kept off. It is confirmed whether or not it is normal (S202). Note that the confirmation processing in step S202 is the same as the processing in steps S204 and S205 described later, and a description thereof will not be repeated.
[0044]
In step S202, when it is confirmed that the insulation resistance on the high-voltage battery 12 side is normal, the insulation resistance detection unit 381 in the μCOM 38 turns on the second switch unit 13 via the switch control unit 40. Then, the timer is started (S204), and the process proceeds to the process of detecting the insulation resistance in the path from the second switch section 13 to the input side of the inverter 14.
[0045]
A signal of a predetermined frequency (for example, 1 Hz) from the signal generator 31 is input to an A / D converter 37 in the μCOM 38 via a resistor 33 (resistive element), an LPF 35, and an amplifier 36, and a half cycle (T / The peak level is sampled every 2, for example, 0.5 seconds (S205). At this time, it is determined whether or not the peak level is sampled normally (S206). If the result of this determination is that the peak level cannot be sampled (No), it is determined whether or not the count value Count of the clock timer is equal to or greater than a predetermined value Ct. Is determined (S207). Here, in step S207, when the insulation resistance has decreased enough to be judged as abnormal, the signal from the amplifier 36 greatly exceeds the A / D conversion range, and charging / discharging of the coupling capacitors 341 and 342 occurs. It is determined whether the time until the saturation level is reached is within a specified time in consideration of safety.
[0046]
If the result of the determination in step S207 is that the count value Count is equal to or greater than the predetermined value Ct (Yes), the processing of steps S211, S212, and S213 described below is performed. On the other hand, if the result of the determination in step S207 is that the count value Count is less than the predetermined value Ct, steps S206 and S207 are repeated, and the process waits until the signal peak level enters the A / D conversion range.
[0047]
As a result of the determination in step S206, when the peak level has been sampled normally (Yes), the insulation resistance detecting unit 381 determines at a certain time ti a half cycle before the time ti (that is, a time ti-T / 2). An amplitude level V (i) (first amplitude level) is calculated from the difference between the maximum or minimum peak level and the minimum or maximum peak level at time ti, and then at time ti + T / 2, which is a half cycle after time ti. The amplitude level V (i + 1) (second amplitude level) from the difference between the minimum or maximum peak level half a cycle before the time point ti + T / 2 (that is, the time point ti) and the maximum or minimum peak level at the time point ti + T / 2. Is calculated (S208).
[0048]
Next, in the insulation resistance detecting section 381, the first amplitude level V (i) and the second amplitude level V (i + 1) are compared, and the absolute value obtained by calculating the difference between V (i) and V (i + 1) is obtained. It is determined whether the value is less than a predetermined value Vth (S209). If the result of the determination in step S209 is that the absolute value of the difference between V (i) and V (i + 1) is equal to or greater than a predetermined value Vth (No), it is determined that the insulation resistance value is normal (S210). Exit the routine.
[0049]
On the other hand, as a result of the determination in step S209, when the absolute value of the difference between V (i) and V (i + 1) is less than the predetermined value Vth, the insulation resistance detection unit 381 determines that the insulation resistance is abnormal ( (S211), the second switch section 13 is turned off via the switch control section 40 (S212), and the abnormality display lamp in the illumination display section 211 is turned on (S213).
[0050]
If it is determined in step S210 that the insulation resistance is normal, the vehicle is ready to run.
[0051]
Next, the principle that the insulation resistance can be accurately and stably detected even when there is a voltage fluctuation due to charging and discharging of the high-voltage battery 12 during traveling of the vehicle will be described with reference to FIGS. 3A and 3B. FIGS. 3A and 3B are equivalent circuit diagrams showing paths of the charging current Ic flowing through the coupling capacitor in the conventional example and the present embodiment, respectively, when the voltage of the high-voltage battery 12 increases due to charging while the vehicle is traveling. .
[0052]
First, in the conventional example, as shown in FIG. 3A, when the voltage of the high-voltage battery 12 increases due to charging, the charging current Ic flows through the coupling capacitor 34 via the resistor 33 (resistance value R). Therefore, an offset voltage (R × Ic) is generated, and as shown in FIG. 6B, the bias level (DC level) of the input signal to the A / D converter 37 is changed from the intermediate value VM in the A / D conversion range. As a result, the insulation resistance cannot be accurately detected.
[0053]
However, in the present embodiment, as shown in FIG. 1, in addition to the first coupling capacitor 341 as in the related art, one end is connected to the total positive portion of the high-voltage battery 12, and the other end is connected to the other end of the resistor 33. Is connected to the second coupling capacitor 342. Therefore, as shown in FIG. 3B, the charging current Ic does not flow through the resistor R33, so that no offset voltage is generated. Therefore, since the bias level (DC level) of the input signal to the A / D converter 37 is set to the intermediate value VM of the A / D conversion range, the insulation resistance can be detected accurately and stably.
[0054]
Although the case where the voltage of the high-voltage battery 12 increases has been illustrated and described, the insulation resistance can also be accurately and stably detected in the case where the voltage of the high-voltage battery 12 decreases due to discharge.
[0055]
【The invention's effect】
As described above, according to the present invention, it is possible to detect whether or not the insulation resistance between the high-voltage circuit and the chassis is normal at the time of starting the vehicle in the shortest possible time, and In this case, the insulation resistance can be accurately and stably detected without being affected by the voltage fluctuation.
[Brief description of the drawings]
FIG. 1 is a functional block diagram showing a partial configuration of an electric vehicle to which an insulation resistance detection device according to an embodiment of the present invention is applied. FIG. 2 is a flowchart showing a processing procedure of an insulation resistance detection routine in the embodiment. 3A is an equivalent circuit diagram showing the path of charging current Ic flowing through the coupling capacitor in the conventional example when the voltage of high-voltage battery 12 increases due to charging during vehicle running. FIG. 4 is an equivalent circuit diagram showing the path of the charging current Ic flowing through the coupling capacitor in the present embodiment when the voltage of the reference numeral 12 increases. FIG. 4 is a functional block diagram showing a partial configuration of an electric vehicle to which a conventional insulation resistance detecting device is applied. FIG. 5A is a waveform diagram of an input signal to the A / D converter 37 when the insulation resistance between the input side of the inverter 14 and the chassis is normal. 5B: A waveform diagram of an input signal to the A / D converter 37 when the insulation resistance between the high potential input side of the inverter 14 and the chassis is reduced. [FIG. 5C] The low potential input side of the inverter 14 and the chassis FIG. 6A is a waveform diagram showing an input signal to the A / D converter 37 when the insulation resistance during the period is low. FIG. 6B is a waveform diagram of an input signal in the conventional example when the voltage of the high-voltage battery 12 is increased by charging. FIG. 6C is a waveform diagram of an input signal in the conventional example. Waveform diagram of an input signal to the A / D converter 37 when the voltage of the battery 12 decreases.
1 electric vehicle 10 high voltage circuit 11 high voltage load (motor)
12. High voltage battery (assembled battery)
121 Rechargeable Battery 13 Second Switch Unit 14 Inverter 141 Smoothing Capacitors 15 and 16 Resistor for Charging Voltage Detection of Smoothing Capacitor 141 Low Voltage Circuit 21 Low Voltage Load 211 Illumination Display Unit 212 Sound Equipment 22 Low Voltage Battery 23 First switch unit 30 Insulation resistance detector 31 Signal generator 32, 36 Amplifier 33 Resistance (resistive element)
341 first coupling capacitor (first capacitive element)
342 second coupling capacitor (second capacitive element)
35 Low Pass Filter (LPF)
37 A / D converter 38 Microcomputer (μCOM)
381 Insulation resistance detector 40 Switch controller

Claims (6)

Applied to an electric vehicle having a high voltage circuit that converts DC power from a battery pack composed of a plurality of secondary batteries into AC power by an inverter via a relay and supplies the AC power to a motor, and generates a signal of a predetermined frequency. A signal generator having one end connected to an output terminal of the signal generator and cooperating with an insulation resistor between the high-voltage circuit and a chassis to attenuate the output signal of the signal generator. A method of detecting the insulation resistance using a capacitive element and a capacitive element that capacitively couples the other end of the resistive element and a path from the battery pack to the relay,
Calculating the amplitude level of the signal passing through the resistive element every half cycle, and comparing the first amplitude level calculated at a certain time point with the second amplitude level calculated at a time point after the half cycle. Steps and
Detecting a decrease in the insulation resistance when the second amplitude level is lower than the first amplitude level by a predetermined value as a result of the comparing step. . The capacitive element includes:
A first capacitive element connected between the other end of the resistive element and one terminal of the battery pack;
And a second capacitive element connected between the other end of the resistive element and the other terminal of the battery pack and having the same capacitance value as the first capacitive element. Item 2. An insulation resistance detection method according to Item 1. In an electric vehicle having a high-voltage circuit that converts DC power from a battery pack formed by combining a plurality of secondary batteries into AC power by an inverter via a relay and supplies the AC power to a motor, the high-voltage circuit and the chassis A device for detecting insulation resistance between
A signal generator for generating a signal of a predetermined frequency;
One end connected to an output terminal of the signal generator, a resistive element for attenuating an output signal of the signal generator in cooperation with the insulation resistance;
A first capacitive element connected between the other end of the resistive element and one terminal of the battery pack;
A second capacitive element connected between the other end of the resistive element and the other terminal of the battery pack and having the same capacitance value as the first capacitive element;
An insulation resistance detection device, comprising: an insulation resistance detection unit that detects a decrease in the insulation resistance according to an amplitude level of a signal passed through the resistive element. The insulation resistance detection unit,
Means for calculating the amplitude level of the signal through the resistive element every half cycle,
The first amplitude level calculated at a certain time is compared with the second amplitude level calculated at a time half a cycle after the first amplitude level, and as a result of the comparison, the second amplitude level is more predetermined than the first amplitude level. 3. The insulation resistance detecting device according to claim 2, further comprising: means for detecting a decrease in the insulation resistance when the value decreases by a value. 2. The method according to claim 1, wherein the secondary battery is a nickel-hydrogen secondary battery. The insulation resistance detecting device according to claim 3, wherein the secondary battery is a nickel-hydrogen secondary battery.

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