Insulation resistance detection system for electric vehicle and insulation resistance detection method thereof

Abstract

An insulation resistance detection system for an electric vehicle is used to detect a positive electrode insulation resistance between a positive electrode of a battery of the electric vehicle and a device ground point, and a negative electrode insulation resistance between a negative electrode of the battery and the device ground point. The insulation resistance detection system comprises a negative electrode detection circuit, a positive electrode detection circuit and a control unit. The control unit controls the negative electrode detection circuit to be charged to generate a first capacitance voltage, and controls the positive electrode detection circuit to be charged to generate a second capacitance voltage. The control unit determines whether the negative electrode insulation resistance is abnormal according to the first capacitance voltage and a battery voltage of the battery, and determines whether the positive electrode insulation resistance is abnormal according to the second capacitance voltage and the battery voltage. The present application also relates to an insulation resistance detection method for an electric vehicle.

Description

TECHNICAL FIELD

[0001] The present application relates to an insulation resistance detection system and an insulation resistance detection method thereof, and in particular, to an insulation resistance detection system and an insulation resistance detection method thereof for an electric vehicle. BACKGROUND

[0002] As the electric vehicles driven by electric power are more and more popular, the research and application of the electric vehicles are also more and more valued. Especially in the application of the electric vehicles with the batteries, it is usually necessary to ensure that the installation space of the batteries of the electric vehicles is well insulated to avoid the leakage of the batteries and the conditions of the electric shock or the continuous consumption of the battery power. Therefore, it is necessary to use a specific instrument or circuit to measure the insulation impedance of the electric vehicles to determine the leakage.

[0003] However, the insulation detection method of the electric vehicles usually only uses the resistance measurement or the capacitance measurement voltage at the detection point, and then the insulation impedance value is inversely calculated by the formula. The disadvantage is that the fluctuation of the charging voltage on the capacitor caused by the voltage variation of the battery during the use of the electric vehicles is not considered, which affects the calculation accuracy of the insulation impedance and leads to the false judgment of the system. Moreover, since the impedance value can be obtained only after the insulation impedance is calculated by the microprocessor, the calculation method is relatively complex, and the protection action of the system is slow, which cannot prevent the circuit damage and protect the safety of the personnel in time. In addition, if the main power source is used in the detection process, the frequent operation will affect the driving mileage of the electric vehicles.

[0004] Therefore, how to design an insulation resistance detection system and an insulation resistance detection method thereof for an electric vehicle to detect the insulation conditions between the positive electrode of the battery and the equipment grounding point and the insulation conditions between the negative electrode of the battery and the equipment grounding point, respectively, is a big research topic of the present application, and the detection process is fast and energy-saving. SUMMARY

[0005] To solve the above problems, the present application provides an insulation resistance detection system for an electric vehicle to overcome the problems of the prior art. The insulation resistance detection system is used to detect the positive electrode insulation resistance between the positive electrode of the battery of the electric vehicle and the equipment grounding point, and to detect the negative electrode insulation resistance between the negative electrode of the battery and the equipment grounding point. The insulation resistance detection system includes a negative electrode detection circuit, a positive electrode detection circuit, and a control unit. The negative electrode detection circuit is connected in parallel with the battery and includes a first charge-discharge circuit and a first current-limiting resistor. The first current-limiting resistor is coupled between the equipment grounding point and the negative electrode, and the first charge-discharge circuit includes a first charging circuit and a first discharging circuit. The first charging circuit includes a first capacitor and a first switch. The first capacitor is coupled between the positive electrode and the equipment grounding point, the first switch is coupled between the positive electrode and the first capacitor, and the first discharging circuit is connected in parallel with the first capacitor. The positive electrode detection circuit is connected in parallel with the battery and includes a second charge-discharge circuit and a second current-limiting resistor. The second current-limiting resistor is coupled between the equipment grounding point and the positive electrode, and the second charge-discharge circuit includes a second charging circuit and a second discharging circuit. The second charging circuit includes a second capacitor and a second switch. The second capacitor is coupled between the negative electrode and the equipment grounding point, the second switch is coupled between the negative electrode and the second capacitor, and the second discharging circuit is connected in parallel with the second capacitor. The control unit periodically turns on the first charging circuit to charge the first capacitor, periodically turns on the first discharging circuit to discharge the first capacitor, periodically turns on the second charging circuit to charge the second capacitor, and periodically turns on the second discharging circuit to discharge the second capacitor. Wherein the first capacitor generates a first capacitor voltage when it is charged, and the second capacitor generates a second capacitor voltage when it is charged. Wherein, the first charging circuit and the second discharging circuit are turned on at the same time, the second charging circuit and the first discharging circuit are turned on at the same time, and the first charging circuit and the second charging circuit are not turned on at the same time. Wherein, the control unit determines whether the negative electrode insulation resistance is abnormal according to the first capacitor voltage and the battery voltage of the battery, and determines whether the positive electrode insulation resistance is abnormal according to the second capacitor voltage and the battery voltage.

[0006] To solve the above problems, the present application provides an insulation resistance detection method for an electric vehicle to overcome the problems of the prior art. The insulation resistance detection method detects the positive electrode insulation resistance of a positive electrode of a battery of the electric vehicle to a device grounding point and the negative electrode insulation resistance of a negative electrode of the battery to the device grounding point using an insulation resistance detection system including a negative electrode detection circuit and a positive electrode detection circuit; the negative electrode detection circuit includes a first capacitor, and the positive electrode detection circuit includes a second capacitor. The insulation resistance detection method includes: measuring a battery voltage of the battery; periodically charging and discharging the first capacitor and obtaining a first capacitor voltage when the first capacitor is charged; periodically charging and discharging the second capacitor and obtaining a second capacitor voltage when the second capacitor is charged; wherein the steps of periodically charging and discharging the first capacitor and periodically charging and discharging the second capacitor include: when the first capacitor is charged, the second capacitor is discharged at the same time; and when the first capacitor is discharged, the second capacitor is charged at the same time; wherein the charging and discharging time is the same; calculating the negative electrode insulation resistance to be less than a first predetermined resistance range according to the first capacitor voltage and the battery voltage to determine that the negative electrode insulation resistance is abnormal; and calculating the positive electrode insulation resistance to be less than a second predetermined resistance range according to the second capacitor voltage and the battery voltage to determine that the positive electrode insulation resistance is abnormal.

[0007] The main purpose and technical effect of the present application is that the insulation resistance detection system can periodically charge and discharge through the negative electrode detection circuit and the positive electrode detection circuit to detect the insulation condition between the positive electrode and the negative electrode of the battery to the device grounding point path respectively, so as to prevent electric shock caused by battery leakage, avoid the continuous detection of the battery power consumption affecting the electric vehicle mileage, and the detection process is fast and timely to improve the safety technical effect.

[0008] In order to further understand the technology, means and technical effects adopted by the present application to achieve the predetermined purpose, please refer to the following detailed description and drawings of the present application. It is believed that the purpose, features and characteristics of the present application can be understood in depth and specifically from the above, however, the drawings are provided for reference and explanation only, and are not used to limit the present application. BRIEF DESCRIPTION OF DRAWINGS

[0009] Figure 1 The block diagram of the insulation resistance detection system for the electric vehicle of the present application;

[0010] Figure 2 The block diagram of the preferred embodiment of the insulation resistance detection system of the present application;

[0011] Figure 3 The method flow chart of the insulation resistance detection method for the electric vehicle of the present application;

[0012] Figure 4A The method flow chart of the first embodiment of the insulation resistance detection method of the present application;

[0013] Figure 4B Method flow chart for the second embodiment of the insulation resistance detection method of the present application; and

[0014] Figure 4C Method flow chart for the third embodiment of the insulation resistance detection method of the present application.

[0015] BRIEF DESCRIPTION OF DRAWINGS

[0016] 1 … insulation resistance detection system

[0017] 10 … negative electrode detection circuit

[0018] 12 … first charge-discharge circuit

[0019] 121 … first charging circuit

[0020] S1 … first switch

[0021] C1 … first capacitor

[0022] 122 … first discharging circuit

[0023] S3 … third switch

[0024] R1 … first discharging resistor

[0025] REN … first current-limiting resistor

[0026] 20 … positive electrode detection circuit

[0027] 22 … second charge-discharge circuit

[0028] 221 … second charging circuit

[0029] S2 … second switch

[0030] C2 … second capacitor

[0031] 222 … second discharging circuit

[0032] S4 … fourth switch

[0033] R2 … second discharging resistor

[0034] RPE … second current-limiting resistor

[0035] 30 … control unit

[0036] 40 … battery detection circuit

[0037] 42 … first detection circuit

[0038] 44 … second detection circuit

[0039] 50 … circuit breaking unit

[0040] 200 … battery

[0041] 200+ … positive electrode

[0042] 200- … negative electrode

[0043] VPN … battery voltage

[0044] 300 … electric vehicle

[0045] GND … equipment ground

[0046] RN … negative electrode insulation resistance

[0047] RP … positive electrode insulation resistance

[0048] VC1 … first capacitor voltage

[0049] VC2 … second capacitor voltage

[0050] Sbv … battery voltage signal

[0051] Sv1 … first voltage signal

[0052] Sv2 … second voltage signal

[0053] Sp … protection signal

[0054] Sc1 … first control signal

[0055] Sc2 … second control signal

[0056] Sc3 … third control signal

[0057] Sc4 … fourth control signal

[0058] Lc1 … first charging path

[0059] Ld1 … first discharging path

[0060] Lc2 … second charging path

[0061] Ld2 … second discharging path

[0062] Vth … threshold voltage DETAILED DESCRIPTION

[0063] The technical contents and detailed descriptions of the present application are described as follows in conjunction with the accompanying drawings:

[0064] Please refer to Figure 1A block diagram of an insulation resistance detection system for an electric vehicle. The insulation resistance detection system 1 is used to detect the positive insulation resistance RP between the positive terminal 200+ of a battery 200 and a ground point GND of an electric vehicle 300, and also to detect the negative insulation resistance RN between the negative terminal 200- of the battery 200 and the ground point GND of the electric vehicle 300. The electric vehicle 300 can be a mobile device powered by the battery 200, such as but not limited to an electric boat, an electric vehicle, etc. In particular, the battery 200 is usually installed in a receiving space, such as a battery slot, of the electric vehicle 300. Since the path between the battery slot and the ground point GND can be poorly insulated due to environmental or time factors, there is a risk of electric leakage of the battery 200 after installation through the path. Therefore, the insulation resistance detection system 1 is used to detect the insulation condition between the battery 200 and the ground point GND (usually the impedance between the housing of the electric vehicle 300 and the ground point GND) to avoid the risk of electric leakage of the battery 200 due to poor insulation of the device, which can harm people and system safety.

[0065] Referring back to Figure 1 , the insulation resistance detection system 1 includes a negative detection circuit 10, a positive detection circuit 20, and a control unit 30. The negative detection circuit 10 is connected in parallel to the battery 200 and includes a first charge-discharge circuit 12 and a first current-limiting resistor REN coupled between the ground point GND and the negative terminal 200-. The positive detection circuit 20 is connected in parallel to the battery 200 and includes a second charge-discharge circuit 22 and a second current-limiting resistor RPE coupled between the ground point GND and the positive terminal 200+. The control unit 30 is coupled to the battery 200, the first charge-discharge circuit 12, and the second charge-discharge circuit 22. The first charge-discharge circuit 12 and the second charge-discharge circuit 22 each have a built-in capacitor. The control unit 30 controls the first charge-discharge circuit 12 to periodically charge and discharge, so that the first charge-discharge circuit 12 generates a first capacitor voltage VC1 when charging, and controls the second charge-discharge circuit 22 to periodically charge and discharge, so that the second charge-discharge circuit 22 generates a second capacitor voltage VC2 when charging.

[0066] The control unit 30 judges whether the equivalent negative electrode insulation resistance RN (hereinafter referred to as the negative electrode insulation resistance RN) between the negative electrode 200- and the equipment ground point GND is abnormal according to the first capacitor voltage VCl and the battery voltage VPN, and judges whether the equivalent positive electrode insulation resistance RP (hereinafter referred to as the positive electrode insulation resistance RP) between the positive electrode 200+ and the equipment ground point GND is abnormal according to the second capacitor voltage VC2 and the battery voltage VPN. When the negative electrode insulation resistance RN is abnormal, it represents that the insulation between the negative electrode 200- of the battery 200 and the equipment ground point GND is poor and a leakage current is generated. When the positive electrode insulation resistance RP is abnormal, it represents that the insulation between the positive electrode 200+ of the battery 200 and the equipment ground point GND is poor and a leakage current is generated.

[0067] The insulation resistance detection system 1 further comprises a battery detection circuit 40, a first detection circuit 42 and a second detection circuit 44. The battery detection circuit 40 is coupled between the battery 200 and the control unit 30, and is used to detect the battery voltage VPN and accordingly provide a battery voltage signal Sbv to the control unit 30, so that the control unit 30 knows the magnitude of the battery voltage VPN according to the battery voltage signal Sbv. The first detection circuit 42 is coupled to the first charge-discharge circuit 12, and is used to detect the first capacitor voltage VCl and accordingly provide a first voltage signal Sv1 to the control unit 30, so that the control unit 30 knows the magnitude of the first capacitor voltage VCl according to the first voltage signal Sv1. The second detection circuit 44 is coupled to the second charge-discharge circuit 22, and is used to detect the second capacitor voltage VC2 and accordingly provide a second voltage signal Sv2 to the control unit 30, so that the control unit 30 knows the magnitude of the second capacitor voltage VC2 according to the second voltage signal Sv2. The battery detection circuit 40, the first detection circuit 42 and the second detection circuit 44 can be coupled in series or in parallel to the battery 200.

[0068] The insulation resistance detection system 1 further comprises at least one cut-off unit 50, and the cut-off unit 50 is coupled to the path between the battery 200 and the electric vehicle 300, which can be coupled to the path between the positive electrode 200+ and the electric vehicle 300, or the path between the negative electrode 200- and the electric vehicle 300, or both (as shown). Figure 1 The control unit 30 provides a protection signal Sp to the corresponding cut-off unit 50 according to the abnormal negative electrode insulation resistance RN or the abnormal positive electrode insulation resistance RP, so as to form a cut-off between the battery 200 and the electric vehicle 300 by turning off the cut-off unit 50, thereby providing a leakage protection function. When the insulation resistance detection system 1 judges that both the negative electrode insulation resistance RN and the positive electrode insulation resistance RP are normal, the control unit 30 turns on the cut-off unit 50, so that the battery voltage VPN can be supplied to the electric vehicle 300.

[0069] Please refer to Figure 2The block diagram of the preferred embodiment of the insulation resistance detection system of the present application is shown in FIG. 1. The preferred embodiment of the insulation resistance detection system of the present application is described in detail as follows. Figure 1 The first charging circuit 121 includes a first switch S1 and a first capacitor C1. The first switch S1 is coupled to the positive terminal 200+ and the first capacitor C1. The first capacitor C1 is coupled to the first switch S1 and the ground terminal GND. The positions of the first capacitor C1 and the first switch S1 can be interchanged. The first discharging circuit 122 is connected in parallel to the first capacitor C1 and the first detection circuit 42. The second charging circuit 221 includes a second switch S2 and a second capacitor C2. The second switch S2 is coupled to the negative terminal 200- and the second capacitor C2. The second capacitor C2 is coupled to the second switch S2 and the ground terminal GND. Similarly, the positions of the second capacitor C2 and the second switch S2 can be interchanged. The second discharging circuit 222 is connected in parallel to the second capacitor C2 and the second detection circuit 44.

[0070] The preferred embodiment of the first discharging circuit 122 and the second discharging circuit 222 is that the first discharging circuit 122 includes a third switch S3 and a first discharging resistor R1, and the second discharging circuit 222 includes a fourth switch S4 and a second discharging resistor R2. The third switch S3 is coupled to one end of the first capacitor C1. The first discharging resistor R1 is connected in series to the third switch S3. The first discharging resistor R1 is coupled to the other end of the first capacitor C1. The fourth switch S4 is coupled to one end of the second capacitor C2. The second discharging resistor R2 is connected in series to the fourth switch S4. The second discharging resistor R2 is coupled to the other end of the second capacitor C2. The positions of the third switch S3 and the first discharging resistor R1 can be interchanged. The positions of the fourth switch S4 and the second discharging resistor R2 can be interchanged.

[0071] The control unit 30 provides a first control signal Sc1 to control the first switch S1 to be turned on or turned off, provides a second control signal Sc2 to control the second switch S2 to be turned on or turned off, provides a third control signal Sc3 to control the third switch S3 to be turned on or turned off, and provides a fourth control signal Sc4 to control the fourth switch S4 to be turned on or turned off. The first control signal Sc1 and the third control signal Sc3 are complementary control signals to make the first capacitor C1 to be charged and discharged, respectively. The second control signal Sc2 and the fourth control signal Sc4 are complementary control signals to make the second capacitor C2 to be charged and discharged, respectively. The first control signal Sc1 and the second control signal Sc2 can be complementary control signals. That is, the control unit 30 provides the first control signal Sc1 and the fourth control signal Sc4 at the same time to control the first charging circuit 121 and the second discharging circuit 222 to be turned on at the same time. The control unit 30 provides the second control signal Sc2 which is complementary to the fourth control signal Sc4 and the third control signal Sc3 which is complementary to the first control signal Sc1 at the same time to control the second charging circuit 221 and the first discharging circuit 122 to be turned on at the same time, so that the first charging circuit 121 and the second charging circuit 221 are not turned on at the same time, and preferably the first capacitor C1 is charged at the same time when the second capacitor C2 is discharged, and vice versa. The advantage is that the first capacitor C1 and the second capacitor C2 can be alternately charged and discharged (i.e. one is charged and the other is discharged at the same time). In this way, the technical effect of improving the detection speed of the insulation resistance detection system 1 can be achieved, and the process is simplified and the system energy consumption is reduced, especially in the above-mentioned embodiment in which the battery 200 directly serves as a power supply device. In addition, the control signals Sc1-Sc4 can be fixed time periods, so that the control unit 30 can detect periodically. Since the control signals Sc1-Sc4 can be fixed time periods, the charging and discharging time of the first capacitor C1 is the same as the charging and discharging time of the second capacitor C2.

[0072] Referring again to Figure 2When the control unit 30 controls the first switch S1 to be on and the third switch S3 to be off, the battery voltage VPN will charge the first capacitor C1 to generate a first charging path Lc1. The first charging path Lc1 is a closed path composed of the battery 200, the first switch S1, the first capacitor C1 and the first current-limiting resistor REN. Since the first current-limiting resistor REN is designed to have a resistance value much smaller than the negative electrode insulation resistance RN (in a normal state), the current flowing through the negative electrode insulation resistance RN can be ignored, and the current path is equivalent to non-existent. When the control unit 30 controls the first switch S1 to be off and the third switch S3 to be on, the first capacitor C1 will discharge to generate a first discharging path Ld1. The first discharging path Ld1 is a closed path composed of the first capacitor C1, the first discharging resistor R1 and the third switch S3. The control unit 30 of the insulation resistance detection system 1 controls the on or off of the second switch S2 and the fourth switch S4 to generate the control mode and path composition of the second charging path Lc2 and the second discharging path Ld2, which are similar to the first charging path Lc1 and the first discharging path Ld1 described above, and will not be described again here.

[0073] Further, since the endurance of the electric vehicle 300 is reduced too much due to the battery voltage VPN consumed too much during the detection process of the insulation resistance detection system 1, the current flowing through the first charge-discharge circuit 12 from the battery 200 must be reduced as much as possible, so the resistance value of the first current-limiting resistor REN must be maintained at a relatively large value to reduce the current flowing through the first charge path Lc1 during detection. However, in order to avoid the charging speed of the first capacitor voltage VC1 being too slow or the charging amount being too small, causing the control unit 30 to be difficult to determine whether the negative electrode insulation resistance RN is abnormal according to the first capacitor voltage VC1, the resistance value of the first current-limiting resistor REN is not too large, so its preferred embodiment is set to a resistance value of the order of MΩ. In addition, the resistance value of the first discharge resistor R1 is related to the discharge speed of the first capacitor C1, that is, the smaller the first discharge resistor R1 (even if the first discharge resistor R1 is not installed), the faster the discharge speed of the first capacitor C1, and ideally it can be completely discharged within a predetermined time so that the first capacitor C1 starts charging from 0 potential in the next detection cycle, increasing the accuracy of the detection of the insulation resistance detection system 1. However, when the resistance value of the first discharge resistor R1 is too small, the current flowing through the first discharge path Ld1 will be too large, so the current-carrying specification of the third switch S3 needs to be improved, resulting in increased circuit cost, so the resistance value of the first discharge resistor R1 is not too small, so its preferred embodiment is set to a resistance value of the order of KΩ. The resistance values of the second current-limiting resistor RPE and the second discharge resistor R2 are also considered in this way, that is, the preferred embodiment of the second current-limiting resistor RPE is set to a resistance value of the order of MΩ, and the preferred embodiment of the second discharge resistor R2 is set to a resistance value of the order of KΩ, which will not be described here.

[0074] Please refer to Figure 3 For the method flowchart of the insulation resistance detection method for electric vehicles of the present application, please refer to Figures 1-2The insulation resistance detection method includes measuring a battery voltage VPN of a battery 200 configured in an electric vehicle 300 (S100). The control unit 30 obtains the battery voltage VPN by measuring a battery voltage signal Sbv via the battery detection circuit 40. Then, the first capacitor C1 is periodically charged and discharged, and a first capacitor voltage VC1 when the first capacitor C1 is charged is obtained (S120). The control unit 30 periodically controls the first switch S1 and the third switch S3 to be turned on and turned off, so that the first capacitor C1 is periodically charged and discharged to generate the first capacitor voltage VC1 when charged, and the first capacitor voltage VC1 is obtained by measuring a first voltage signal Sv1 via the first detection circuit 42. Then, the second capacitor C2 is periodically charged and discharged, and a second capacitor voltage VC2 when the second capacitor C2 is charged is obtained (S140). The control unit 30 periodically controls the second switch S2 and the fourth switch S4 to be turned on and turned off, so that the second capacitor C2 is periodically charged and discharged to generate the second capacitor voltage VC2 when charged, and the second capacitor voltage VC2 is obtained by measuring a second voltage signal Sv2 via the second detection circuit 44.

[0075] Then, it is determined whether the negative electrode insulation resistance RN is abnormal according to the first capacitor voltage VC1 and the battery voltage VPN (S160). The control unit 30 determines whether the negative electrode insulation resistance RN of the path between the negative electrode 200- of the battery 200 and the equipment ground point GND is abnormal according to the first capacitor voltage VC1 and the battery voltage VPN. When the negative electrode insulation resistance RN is abnormal, it represents that the path between the negative electrode 200- of the battery 200 and the equipment ground point GND is poorly insulated and causes a leakage condition. Then, it is determined whether the positive electrode insulation resistance RP is abnormal according to the second capacitor voltage VC2 and the battery voltage VPN (S180). The control unit 30 determines whether the positive electrode insulation resistance RP of the path between the positive electrode 200+ of the battery 200 and the equipment ground point GND is abnormal according to the second capacitor voltage VC2 and the battery voltage VPN. When the positive electrode insulation resistance RP is abnormal, it represents that the path between the positive electrode 200+ of the battery 200 and the equipment ground point GND is poorly insulated and causes a leakage condition. Finally, the battery 200 and the electric vehicle 300 are controlled to be disconnected according to the negative electrode insulation resistance RN being abnormal or the positive electrode insulation resistance RP being abnormal (S200). When the insulation resistance detection system 1 determines that the negative electrode insulation resistance RN and the positive electrode insulation resistance RP are normal, the control unit 30 turns on the disconnection unit 50, so that the battery voltage VPN can be supplied to the electric vehicle 300. Otherwise, the corresponding disconnection unit 50 is turned off to provide a leakage protection function.

[0076] Please refer to Figure 4A The method flowchart of the first embodiment of the insulation resistance detection method of the present application is shown in FIG. 1, and the method flowchart of the second embodiment of the insulation resistance detection method of the present application is shown in FIG. 2. Figures 1-3The determination of whether the insulation resistance is abnormal using the first capacitor voltage VCl and the second capacitor voltage VC2 can include three determination methods, Figure 4A The flowchart shown is the first determination method, and the steps include measuring the battery voltage VPN of the battery 200 (S300). Then, the first switch SI and the fourth switch S4 are turned on, and the second switch S2 and the third switch S3 are turned off (S320). When the control unit 30 controls the first switch SI and the fourth switch S4 to be turned on, the first capacitor CI is charged, and the second capacitor C2 is discharged. Then, the first capacitor voltage VCl is measured (S340). Then, the second switch S2 and the third switch S3 are turned on, and the first switch SI and the fourth switch S4 are turned off (S360). When the control unit 30 controls the second switch S2 and the third switch S3 to be turned on, the second capacitor C2 is charged, and the first capacitor CI is discharged. Then, the second capacitor voltage VC2 is measured (S380). Finally, return to step (S300) for detection in the next cycle.

[0077] When step (S340) is completed, the negative electrode insulation resistance RN can be calculated again (S400). The control unit 30 calculates the current negative electrode insulation resistance RN using the first capacitor voltage VCl and the battery voltage VPN. The negative electrode insulation resistance RN can be calculated by the formula of capacitor charging and discharging or obtained by looking up a pre-prepared first capacitor voltage and battery voltage corresponding table. When step (S380) is completed, the positive electrode insulation resistance RP can be calculated again (S420). The control unit 30 calculates the current positive electrode insulation resistance RP using the second capacitor voltage VC2 and the battery voltage VPN. The positive electrode insulation resistance RP can be calculated by the formula of capacitor charging and discharging or obtained by looking up a pre-prepared second capacitor voltage and battery voltage corresponding table. Then, it is determined whether the insulation resistance RN or RP is within a predetermined resistance range (S440). The control unit 30 obtains the current negative electrode insulation resistance RN using the calculation in step (S400), and determines whether the resistance value of the current negative electrode insulation resistance RN is within a pre-set first predetermined resistance range. When the resistance value of the current negative electrode insulation resistance RN is not within the pre-set first predetermined resistance range, a protection action is performed (S460). When the insulation resistance detection system 1 determines that the resistance value of the current negative electrode insulation resistance RN is not within the pre-set first predetermined resistance range, the control unit 30 turns off the circuit breaking unit 50 to provide the function of leakage protection. The control unit 30 obtains the resistance value of the current positive electrode insulation resistance RP using the calculation in step (S420), and can also determine whether the resistance value is within a pre-set second predetermined resistance range, and the determination method is also the same, which will not be described again here.

[0078] It is worth mentioning that the first predetermined resistance range and the second predetermined resistance range can be the resistance values of the negative electrode insulation resistance RN and the positive electrode insulation resistance RP measured in advance in the case of good insulation of the electric vehicle 300, and the resistance values are added with positive and negative percentages to become a preset range. Alternatively, the resistance values of the negative electrode insulation resistance RN and the positive electrode insulation resistance RP are obtained from the specification table of the electric vehicle 300, and the resistance values are added with positive and negative percentages to become a preset range.

[0079] Referring to Figure 4B The flowchart of the method of the second embodiment of the insulation resistance detection method of the present application is shown in FIG. 6, and the flowchart of the method of the first embodiment of the insulation resistance detection method of the present application is shown in FIG. 5. Figures 1-4A Figure 4B The steps include measuring the battery voltage VPN of the battery 200 (S500). Then, the first switch S1 and the fourth switch S4 are turned on, and the second switch S2 and the third switch S3 are turned off (S520). When the first switch S1 and the fourth switch S4 are turned on and the second switch S2 and the third switch S3 are turned off under the control of the control unit 30, the first capacitor C1 is charged and the second capacitor C2 is discharged. Then, the first capacitor voltage VC1 is measured (S540). Then, it is determined whether the negative electrode insulation resistance RN is abnormal according to the threshold voltage Vth and the first capacitor voltage VC1 (S560). In step (S500), the threshold voltage Vth is calculated by scaling down the battery voltage VPN by a certain ratio (S580), and the threshold voltage Vth is provided to step (S560) for use, i.e., the control unit 30 calculates the threshold voltage Vth by scaling down the battery voltage VPN by a certain ratio, and then compares the threshold voltage Vth with the first capacitor voltage VC1 to determine whether the negative electrode insulation resistance RN is abnormal. Then, when the control unit 30 determines that the negative electrode insulation resistance RN is abnormal, a protection action is performed (S600). When the insulation resistance detection system 1 determines that the negative electrode insulation resistance RN is abnormal, the control unit 30 turns off the circuit breaker unit 50 to provide the function of leakage protection. The above-mentioned "scaling down" is a preferred embodiment, but is not limited thereto, and can be scaled up or down according to actual needs.

[0080] Further, Figure 4B ​The determination of the abnormality of the negative insulation resistance RN is based on whether the charging amount of the fixed charging time is sufficient to charge the capacitor voltage to the threshold voltage. The control unit 30 sets a period from when the first switch S1 is turned on to a first predetermined time as a first charging period, and determines whether the negative insulation resistance RN is abnormal according to whether the first capacitor C1 can be charged to the threshold voltage Vth in the first charging period. When the first capacitor C1 can be charged to or above the threshold voltage Vth in the first charging period, it indicates that the negative insulation resistance RN is abnormal, and the process goes to step (S600). Otherwise, the process goes to step (S620). When the negative insulation resistance RN is abnormal, its resistance value becomes too small, and the power of the battery 200 bypasses the first charging path Lc1 including the first current-limiting resistor REN, and instead goes through another charging path including the battery 200, the first switch S1, the first capacitor C1, and the negative insulation resistance RN. As a result, the first capacitor C1 is charged at a speed higher than expected. It is worth mentioning that, Figure 4B The detection and determination of the abnormality of the positive insulation resistance RP in steps (S620) to (S660) are similar to those in steps (S520) to (S560), and will not be described again. In addition, steps (S620) to (S660) and steps (S520) to (S560) can be mutually adjusted, i.e., the positive insulation resistance RP is detected first, and then the negative insulation resistance RN is detected.

[0081] Please refer to Figure 4C The method flowchart of the third embodiment of the insulation resistance detection method of the application is shown in FIG. 6. Please refer to Figures 1-4B . Figure 4C The steps include measuring the battery voltage VPN of the battery 200 (S700). Then, the first switch S1 and the fourth switch S4 are turned on, and the second switch S2 and the third switch S3 are turned off (S720). When the control unit 30 controls the first switch S1 and the fourth switch S4 to be turned on, and controls the second switch S2 and the third switch S3 to be turned off, the first capacitor C1 is charged, and the second capacitor C2 is discharged. Then, the first capacitor voltage VC1 is measured (S740). Then, the second switch S2 and the third switch S3 are turned on, and the first switch S1 and the fourth switch S4 are turned off (S760). When the control unit 30 controls the second switch S2 and the third switch S3 to be turned on, and controls the first switch S1 and the fourth switch S4 to be turned off, the second capacitor C2 is charged, and the first capacitor C1 is discharged. Then, the second capacitor voltage VC2 is measured (S780).

[0082] Then, the greater of the first capacitor voltage VCl and the second capacitor voltage VC2 is compared with the threshold voltage Vth (S800). Here, the control unit 30 compares the voltage peak value of the first capacitor voltage VCl with the voltage peak value of the second capacitor voltage VC2, and compares the relatively higher one of the two voltage peak values with the threshold voltage Vth. Since the greater the voltage peak value of the capacitor voltage, the smaller the resistance value of the corresponding insulation resistance RN or RP, the condition of poor insulation is more likely to occur. At the step (S700), the threshold voltage Vth is calculated by reducing the battery voltage by a certain ratio (S820), and the threshold voltage Vth is supplied to the step (S800) for use. Then, whether at least one of the insulation resistances is abnormal is determined based on the result of the comparison at the step (S800) (S840). When the determination result is "Yes", a protection action is performed (S860); when the determination result is "No", the step (S700) is returned to for detection in the next cycle. For example, but not limited to, the control unit 30 selects the corresponding first capacitor voltage VCl to compare with the threshold voltage Vth based on the voltage peak value of the first capacitor voltage VCl being greater than the voltage peak value of the second capacitor voltage VC2, and when the first capacitor voltage VCl is greater than the threshold voltage Vth, it is determined that the negative electrode insulation resistance RN is abnormal and proceeds to the step (S860), otherwise, it proceeds to the step (S700).

[0083] It is worth mentioning that, in the above embodiment, the battery voltage VPN is reduced by a certain ratio, but the present application is not limited thereto. For example, but not limited to, the battery voltage VPN can be reduced by a certain percentage, or the battery voltage VPN can be reduced by a certain ratio and then reduced by a certain percentage. Figures 4A-4C In the above embodiment, since the battery voltage VPN is gradually reduced during the detection and consumption of the battery 200, the battery voltage VPN and the threshold voltage Vth are not fixed values, and the size of the threshold voltage Vth changes with the size of the battery voltage VPN. In addition, the charging of the capacitor is an exponential curve. When the capacitor is close to full, the change of the capacitor voltage is small, which is not conducive to the judgment of the control unit 30 on the insulation resistance, so it is preferred to set the threshold voltage Vth at 60% to 70% of the battery voltage VPN.

[0084] The above description is only a detailed description of the preferred embodiments of the present application and the accompanying drawings, and the features of the present application are not limited thereto, and are not intended to limit the present application. The scope of the present application should be based on the claims, and any embodiments that are consistent with the concept of the claims and similar changes thereof should be included in the scope of the present application. Any changes or modifications that can be easily thought of by those skilled in the art in the field of the present application can be covered by the claims of the present disclosure.

Claims

1. A system for detecting insulation resistance of a battery of an electric vehicle, comprising: a negative electrode detection circuit in parallel with the battery, comprising a first charge-discharge circuit and a first current-limiting resistor; the first current-limiting resistor is coupled between a device ground and a negative electrode of the battery, and the first charge-discharge circuit comprises: a first charging circuit, comprising: a first capacitor coupled between the positive electrode and the device ground; and a first switch coupled between the positive electrode and the first capacitor; and a first discharging circuit in parallel with the first capacitor; a positive electrode detection circuit in parallel with the battery, comprising a second charge-discharge circuit and a second current-limiting resistor; the second current-limiting resistor is coupled between the device ground and the positive electrode, and the second charge-discharge circuit comprises: a second charging circuit, comprising: a second capacitor coupled between the negative electrode and the device ground; and a second switch coupled between the negative electrode and the second capacitor; and a second discharging circuit in parallel with the second capacitor; and a control unit, periodically turning on the first charging circuit to charge the first capacitor, periodically turning on the first discharging circuit to discharge the first capacitor, periodically turning on the second charging circuit to charge the second capacitor, and periodically turning on the second discharging circuit to discharge the second capacitor; wherein the first capacitor generates a first capacitor voltage when charged, and the second capacitor generates a second capacitor voltage when charged; wherein the first charging circuit and the second discharging circuit are turned on at the same time, the second charging circuit and the first discharging circuit are turned on at the same time, and the first charging circuit and the second charging circuit are not turned on at the same time; wherein the control unit determines whether the negative electrode insulation resistance is abnormal according to the first capacitor voltage and a battery voltage of the battery, and determines whether the positive electrode insulation resistance is abnormal according to the second capacitor voltage and the battery voltage, wherein the first discharging circuit comprises: a third switch; and a first discharging resistor in series with the third switch; wherein the battery, the first switch, the first capacitor and the first current-limiting resistor form a first charging path for charging the first capacitor when the first switch is turned on and the third switch is turned off, and the first capacitor, the third switch and the first discharging resistor form a first discharging path for discharging the first capacitor when the third switch is turned on and the first switch is turned off; and wherein the second discharging circuit comprises: a fourth switch; and a second discharging resistor in series with the fourth switch; wherein the battery, the second switch, the second capacitor and the second current-limiting resistor form a second charging path for charging the second capacitor when the second switch is turned on and the fourth switch is turned off, and the second capacitor, the fourth switch and the second discharging resistor form a second discharging path for discharging the second capacitor when the fourth switch is turned on and the second switch is turned off. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2. The insulation resistance detection system of claim 1, wherein, The first current-limiting resistor is set to have a resistance value in the order of MΩ, and the first discharging resistor is set to have a resistance value in the order of KΩ, so that the discharging speed of the first capacitor is greater than the charging speed. And The second current-limiting resistor is set to have a resistance value in the order of MΩ, and the second discharging resistor is set to have a resistance value in the order of KΩ, so that the discharging speed of the second capacitor is greater than the charging speed.

3. The insulation resistance detection system of claim 1, wherein, The control unit provides a first control signal to control the first switch to be turned on or turned off, provides a second control signal to control the second switch to be turned on or turned off, provides a third control signal which is complementary to the first control signal to control the first discharging circuit to be turned on or turned off, and provides a fourth control signal which is complementary to the second control signal to control the second discharging circuit to be turned on or turned off, wherein the first control signal and the second control signal are complementary signals, and the time for the switches to be turned on or turned off is the same.

4. The insulation resistance detection system of claim 1, further comprising: a disconnection unit coupled to the battery and the electric vehicle; wherein the control unit turns off the disconnection unit according to the abnormal negative electrode insulation resistance or the abnormal positive electrode insulation resistance, so that the battery and the electric vehicle are disconnected.

5. An insulation resistance detection method for an electric vehicle, used in the insulation resistance detection system of any one of claims 1 to 4, the insulation resistance detection method using an insulation resistance detection system to detect a positive electrode insulation resistance from a positive electrode of a battery to a device ground point of an electric vehicle, and to detect a negative electrode insulation resistance from a negative electrode of the battery to the device ground point, the insulation resistance detection system comprising a negative electrode detection circuit and a positive electrode detection circuit, the negative electrode detection circuit comprising a first capacitor, and the positive electrode detection circuit comprising a second capacitor, the insulation resistance detection method comprising: measuring a battery voltage of the battery; periodically charging and discharging the first capacitor, and obtaining a first capacitor voltage when the first capacitor is charged; periodically charging and discharging the second capacitor, and obtaining a second capacitor voltage when the second capacitor is charged; wherein the steps of periodically charging and discharging the first capacitor and periodically charging and discharging the second capacitor comprise: charging the first capacitor while discharging the second capacitor; and discharging the first capacitor while charging the second capacitor; wherein the time for charging and discharging is the same; judging that the negative electrode insulation resistance is abnormal according to the first capacitor voltage and the battery voltage, if the negative electrode insulation resistance is less than a first predetermined resistance range; and judging that the positive electrode insulation resistance is abnormal according to the second capacitor voltage and the battery voltage, if the positive electrode insulation resistance is less than a second predetermined resistance range.

6. The insulation resistance detection method of claim 5, further comprising: calculating a threshold voltage from the battery voltage by a ratio; judging that the negative electrode insulation resistance is less than the first predetermined resistance range according to the first capacitor voltage reaching the threshold voltage, and further judging that the negative electrode insulation resistance is abnormal; and judging that the positive electrode insulation resistance is less than the second predetermined resistance range according to the second capacitor voltage reaching the threshold voltage, and further judging that the positive electrode insulation resistance is abnormal. ​ 7. The insulation resistance detection method of claim 6, further comprising: determining that the negative electrode insulation resistance is abnormal according to the first capacitor charging to the threshold voltage within a first charging period; and determining that the positive electrode insulation resistance is abnormal according to the second capacitor charging to the threshold voltage within a second charging period.

8. The insulation resistance detection method of claim 6, further comprising: comparing a larger one of a voltage peak value of the first capacitor voltage and a voltage peak value of the second capacitor voltage with the threshold voltage; and determining that at least one of the negative electrode insulation resistance and the positive electrode insulation resistance is abnormal according to the capacitor voltage corresponding to the larger voltage peak value being greater than the threshold voltage, and performing a protection action.

9. The insulation resistance detection method of claim 6, wherein the ratio is 60% to 70%.

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