Insulation resistance detection circuit, method and electric vehicle

Abstract

An embodiment of the present invention provides an insulation resistance detection circuit, method, and electric vehicle. The insulation resistance detection circuit includes a first relay, a second relay, a third relay, a first resistor, a second resistor, a third resistor, a fourth resistor, and a controller. The controller controls the operating states of the first relay, the second relay, and the third relay to determine the stabilization time during which the insulation detection voltage is in a stable state. The target insulation resistance is determined based on the stabilization time and the capacitance value of the capacitor, rather than based on the voltage value across a power battery. This decouples the insulation resistance detection from the voltage across the power battery, reduces the influence of voltage fluctuations across the power battery, and thereby improves the accuracy of the insulation resistance detection.

Description

Technical Field

[0001] The present invention relates to the technical field of insulation resistance detection, and in particular to an insulation resistance detection circuit, method and electric vehicle. Background Art

[0002] Currently, there are two methods for testing the insulation resistance of electric vehicles in my country: one method uses signal injection, and the other uses external resistor switching. The detection principle of the external resistor switching measurement circuit is to collect the voltage across the resistor and use simultaneous equations to calculate the insulation resistance between the positive and negative electrodes of the power battery and the vehicle body shell.

[0003] However, the voltage collected from each resistor in the external resistor switching measurement circuit is a voltage divider related to the power battery voltage. Under different operating conditions of electric vehicles, the battery voltage will change with the change of charging and discharging conditions, causing the collected voltage to change in real time, thereby affecting the resistance accuracy of the calculated insulation resistance. Summary of the Invention

[0004] Embodiments of the present invention provide an insulation resistance detection circuit, method, and electric vehicle, for improving the detection accuracy of insulation resistance.

[0005] In a first aspect, an embodiment of the present invention provides an insulation resistance detection circuit, comprising: a first relay, a second relay, a third relay, a first resistor, a second resistor, a third resistor, a fourth resistor, and a controller;

[0006] a first end of the first relay is electrically connected to the first end of the first resistor, the first end of the second resistor, the first end of the second relay, and the first end of the third relay, and a second end of the first relay is grounded; a second end of the first resistor is electrically connected to the first end of the third resistor; a second end of the third resistor is electrically connected to the second end of the second relay; a second end of the second resistor is electrically connected to the first end of the fourth resistor; and a second end of the fourth resistor is electrically connected to the second end of the third relay;

[0007] The controller is signal-connected to the control terminals of the first relay, the second relay, and the third relay, and is configured to:

[0008] In response to an insulation resistance detection request, controlling the switching states of the first relay, the second relay, and the third relay based on a resistance switching measurement method to determine a first capacitance of a first equivalent capacitor between a positive electrode of the power battery and a ground terminal and a second capacitance of a second equivalent capacitor between a negative electrode of the power battery and the ground terminal;

[0009] controlling the first relay to close, and alternately closing the second relay and the third relay to determine a first stable time duration during which a first insulation detection voltage is in a stable state within the closed time duration of the second relay, and determining a second stable time duration during which a second insulation detection voltage is in a stable state within the closed time duration of the third relay, wherein the first insulation detection voltage is a voltage between the positive electrode of the power battery and the ground terminal, and the second insulation detection voltage is a voltage between the negative electrode of the power battery and the ground terminal;

[0010] Based on the first stable time, the second stable time, the first capacitance, and the second capacitance, a target resistance value of a first insulation resistance between the positive electrode of the power battery and the ground terminal and a target resistance value of a second insulation resistance between the negative electrode of the power battery and the ground terminal are calculated.

[0011] Optionally, a DC-DC regulated power supply is also included;

[0012] The positive input terminal of the DC-DC regulated power supply is electrically connected to the positive electrode of the power battery, the negative input terminal of the DC-DC regulated power supply is electrically connected to the negative electrode of the power battery, the positive output terminal of the DC-DC regulated power supply is electrically connected to the second end of the first resistor, and the negative output terminal of the DC-DC regulated power supply is electrically connected to the second end of the second resistor.

[0013] In a second aspect, an embodiment of the present invention provides an insulation resistance detection method, applied to the circuit as described in any one of the first aspects, the method comprising:

[0014] In response to an insulation resistance detection request, controlling the switching states of the first relay, the second relay, and the third relay based on a resistance switching measurement method to determine a first capacitance of a first equivalent capacitance between a positive electrode of the power battery and a ground terminal and a second capacitance of a second equivalent capacitance between a negative electrode of the power battery and the ground terminal;

[0015] controlling the first relay to close, and alternately closing the second relay and the third relay to determine a first stable time duration during which a first insulation detection voltage is in a stable state within the closed time duration of the second relay, and determining a second stable time duration during which a second insulation detection voltage is in a stable state within the closed time duration of the third relay, wherein the first insulation detection voltage is a voltage between the positive electrode of the power battery and the ground terminal, and the second insulation detection voltage is a voltage between the negative electrode of the power battery and the ground terminal;

[0016] Based on the first stable time, the second stable time, the first capacitance, and the second capacitance, a target resistance value of a first insulation resistance between the positive electrode of the power battery and the ground terminal and a target resistance value of a second insulation resistance between the negative electrode of the power battery and the ground terminal are calculated.

[0017] Optionally, controlling the switching states of the first relay, the second relay, and the third relay based on a resistance switching measurement method to determine a first capacitance of a first equivalent capacitor between the positive electrode of the power battery and the ground terminal and a second capacitance of a second equivalent capacitor between the negative electrode of the power battery and the ground terminal includes:

[0018] Controlling the first relay to close, determining that the first insulation detection voltage or the second insulation detection voltage is in a stable state, obtaining a first voltage of the first insulation detection voltage and a second voltage of the second insulation detection voltage, controlling the second relay to close, and starting timing, determining that the first insulation detection voltage or the second insulation detection voltage is in a stable state, obtaining a third voltage of the second insulation detection voltage, and stopping timing to determine a third stabilization time;

[0019] controlling the second relay to open, and after determining that the first insulation detection voltage or the second insulation detection voltage is in a stable state, controlling the third relay to close and start timing, and after determining that the first insulation detection voltage or the second insulation detection voltage is stable, obtaining a fourth voltage of the first insulation detection voltage, and stopping timing to determine a fourth stabilization time;

[0020] determining an initial resistance value of the first insulation resistor and an initial resistance value of the second insulation resistor based on the first voltage, the second voltage, the third voltage, the fourth voltage, the first resistance, the second resistance, the third resistance, and the fourth resistance;

[0021] The first capacitance and the second capacitance are determined based on the initial resistance of the first insulation resistor, the initial resistance of the second insulation resistor, the third stabilization time, and the fourth stabilization time.

[0022] Optionally, determining whether the first insulation detection voltage is in a stable state is performed in the following manner:

[0023] Determining that the first insulation detection voltage is stable when a ratio of a difference between the first insulation detection voltage at a current moment and the first insulation detection voltage at a previous moment to the first insulation detection voltage at the current moment is less than a set value;

[0024] Determine whether the second insulation detection voltage is in a stable state by the following method:

[0025] When it is determined that the ratio of the difference between the second insulation detection voltage at the current moment and the second insulation detection voltage at the previous moment to the second insulation detection voltage at the current moment is less than a set value, the second insulation detection voltage is stable.

[0026] Optionally, determining the first capacitance and the second capacitance based on the initial resistance of the first insulation resistor, the initial resistance of the second insulation resistor, the third stable time, and the fourth stable time includes:

[0027] A first product of a preset value and an initial resistance value of the first insulation resistor is calculated, and a ratio of the third stabilization time to the first product is determined as the first capacitance; and a second product of the preset value and the initial resistance value of the second insulation resistor is calculated, and a ratio of the fourth stabilization time to the second product is determined as the second capacitance.

[0028] Optionally, the calculating, based on the first stable time period, the second stable time period, the first capacitance, and the second capacitance, a target insulation resistance value of a first insulation resistance between the positive electrode of the power battery and the ground terminal and a target insulation resistance value of a second insulation resistance between the negative electrode of the power battery and the ground terminal includes:

[0029] A third product of the preset value and the first capacitance is calculated, and a ratio of the first stabilization time to the third product is determined as a target resistance of the first insulation resistor; and a fourth product of the preset value and the second capacitance is calculated, and a ratio of the second stabilization time to the fourth product is determined as a target resistance of the second insulation resistor.

[0030] Optionally, determining an initial resistance value of the first insulation resistor and an initial resistance value of the second insulation resistor based on the first voltage, the second voltage, the third voltage, the fourth voltage, the first resistor, the second resistor, the third resistor, and the fourth resistor includes:

[0031] determining an uncorrected resistance value of the first insulation resistor based on the first voltage, the second voltage, the third voltage, and the fourth resistance;

[0032] determining an initial resistance value of the first insulation resistor based on the uncorrected resistance value of the first insulation resistor and the first resistor;

[0033] and determining an uncorrected resistance value of the second insulation resistor based on the first voltage, the second voltage, the fourth voltage, and the third resistance;

[0034] An initial resistance value of the second insulation resistor is determined based on the uncorrected resistance value of the second insulation resistor and the second resistance.

[0035] Optionally, before controlling the switch states of the first relay, the second relay, and the third relay based on the resistance switching measurement method to determine a first capacitance of a first equivalent capacitor between the positive electrode of the power battery and the ground terminal and a second capacitance of a second equivalent capacitor between the negative electrode of the power battery and the ground terminal, the method further includes:

[0036] A change in the operating mode of the electric vehicle is detected.

[0037] In a third aspect, an embodiment of the present invention further provides an electric vehicle, comprising the resistance detection circuit as described in any one of the first aspects.

[0038] An embodiment of the present invention provides an insulation resistance detection circuit, method, and electric vehicle. The insulation resistance detection circuit includes a first relay, a second relay, a third relay, a first resistor, a second resistor, a third resistor, a fourth resistor, and a controller. The controller controls the operating states of the first relay, the second relay, and the third relay to determine the stabilization time during which the insulation detection voltage is in a stable state. The target insulation resistance is determined based on the stabilization time and the capacitance value of the capacitor, rather than based on the voltage value across a power battery. This decouples the insulation resistance detection from the voltage across the power battery, reduces the influence of voltage fluctuations across the power battery, and thereby improves the accuracy of the insulation resistance detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0040] Figure 1 A schematic diagram of the circuit structure of an insulation resistance detection circuit provided by an embodiment of the present invention;

[0041] Figure 2 A schematic diagram of the circuit structure of another insulation resistance detection circuit provided by an embodiment of the present invention;

[0042] Figure 3 A schematic flow chart of an insulation resistance detection method provided by an embodiment of the present invention;

[0043] Figure 4 A schematic diagram of a curve showing changes in voltage and current during an insulation resistance test according to an embodiment of the present invention;

[0044] Figure 5 A schematic flow chart of a method for determining a first capacitance and a second capacitance provided in an embodiment of the present invention;

[0045] Figure 6 The present invention provides an overall flow chart of an insulation resistance detection method. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solutions and advantages of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field are within the scope of protection of this application.

[0047] Insulation resistance is the equivalent insulation resistance between the positive and negative terminals of an electric vehicle's power battery and the vehicle's exterior. It plays a crucial role in vehicle safety. When testing insulation resistance in electric vehicles, the insulation resistance is typically measured by switching the resistance circuit using an external resistor. The insulation resistance value is then calculated using simultaneous equations. During insulation resistance testing, the insulation test voltage is affected by the Y-capacitor (Y-capacitor, which primarily originates from the equivalent capacitance formed by the battery and the tray, as well as the filter capacitor in the power battery management system (BMS), with a capacitance ranging from nanofarads to microfarads). Therefore, the insulation test process takes time. The greater the insulation resistance or the larger the Y-capacitor, the longer the insulation test voltage takes to stabilize, and the corresponding insulation test cycle increases. The insulation test voltage is a voltage divided by the power battery voltage. Under different operating conditions, the battery voltage in electric vehicles varies with charging and discharging conditions, and the insulation test voltage also changes in real time, resulting in significant deviations in the calculated insulation resistance value.

[0048] In order to improve the accuracy of insulation resistance detection, an embodiment of the present invention provides an insulation resistance detection circuit, which is applied to electric vehicles, such as Figure 1 As shown, the circuit includes: a first relay K1, a second relay K2, a third relay K3, a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4 and a controller 100;

[0049] A first end of the first relay K1 is electrically connected to a first end of the first resistor R1, a first end of the second resistor R2, a first end of the second relay K2, and a first end of the third relay K3, and a second end of the first relay K1 is grounded; a second end of the first resistor R1 is electrically connected to a first end of the third resistor R3; a second end of the third resistor R3 is electrically connected to a second end of the second relay K2; a second end of the second resistor R2 is electrically connected to a first end of the fourth resistor R4; and a second end of the fourth resistor R4 is electrically connected to a second end of the third relay K3.

[0050] The controller 100 is signal-connected to the control terminals of the first relay K1, the second relay K2, and the third relay K3, and is used to:

[0051] In response to an insulation resistance detection request, controlling the switching states of the first relay K1, the second relay K2, and the third relay K3 based on a resistance switching measurement method to determine a first capacitance C1 of a first equivalent capacitor Cp between the positive electrode of the power battery and the ground terminal and a second capacitance C2 of a second equivalent capacitor Cn between the negative electrode of the power battery and the ground terminal;

[0052] Controlling the first relay K1 to close, and alternately closing the second relay K2 and the third relay K3 to determine a first stable time duration t1 during which the first insulation detection voltage is in a stable state within the closed time duration of the second relay K2, and to determine a second stable time duration t2 during which the second insulation detection voltage is in a stable state within the closed time duration of the third relay K3, wherein the first insulation detection voltage is the voltage between the positive electrode of the power battery and the ground terminal, and the second insulation detection voltage is the voltage between the negative electrode of the power battery and the ground terminal;

[0053] Based on the first stabilization time t1, the second stabilization time t2, the first capacitance C1 and the second capacitance C2, a target resistance value of the first insulation resistance Rp between the positive electrode of the power battery and the ground terminal and a target resistance value of the second insulation resistance Rn between the negative electrode of the power battery and the ground terminal are calculated.

[0054] An insulation resistance detection circuit provided by an embodiment of the present invention includes a first relay, a second relay, a third relay, a first resistor, a second resistor, a third resistor, a fourth resistor, and a controller. The controller controls the operating states of the first relay, the second relay, and the third relay to determine the stabilization time during which the insulation detection voltage is in a stable state. The target insulation resistance is determined based on the stabilization time and the capacitance value of the capacitor, rather than based on the voltage value across the power battery. This decouples the insulation resistance detection from the voltage across the power battery, reduces the impact of voltage fluctuations across the power battery, and thereby improves the accuracy of the insulation resistance detection.

[0055] It is worth noting that the first resistor R1, the second resistor R2, the third resistor R3 and the fourth resistor R4 in the embodiment of the present invention are resistors with known resistance values, the first insulation resistor Rp is the equivalent resistance between the positive electrode of the power battery and the ground terminal, the second insulation resistor Rn is the equivalent resistance between the negative electrode of the power battery and the ground terminal, the first equivalent capacitor Cp is the equivalent capacitance between the positive electrode of the power battery and the ground terminal, and the second equivalent capacitor Cn is the equivalent capacitance between the negative electrode of the power battery and the ground terminal.

[0056] In a specific implementation, the insulation resistance detection circuit provided by the embodiment of the present invention may further include a DC-DC regulated power supply, such as Figure 2 As shown:

[0057] The positive input terminal of the DC-DC regulated power supply is electrically connected to the positive electrode of the power battery, the negative input terminal of the DC-DC regulated power supply is electrically connected to the negative electrode of the power battery, the positive output terminal of the DC-DC regulated power supply is electrically connected to the second end of the first resistor R1, and the negative output terminal of the DC-DC regulated power supply is electrically connected to the second end of the second resistor R2.

[0058] The insulation resistance detection circuit provided by the embodiment of the present invention can stabilize the voltage output by the battery at a fixed value or within a fixed range because a DC-DC regulated power supply is connected in parallel at both ends of the battery. As a result, during insulation resistance detection, the insulation detection voltage is not affected by battery voltage fluctuations under various external operating conditions. The insulation detection voltage is divided based on a constant voltage, thereby avoiding deviations in insulation resistance calculation caused by battery voltage fluctuations, and improving the accuracy of insulation resistance detection.

[0059] Based on the same inventive concept, the embodiment of the present invention also provides an insulation resistance detection method, which is applied to Figure 1 or Figure 2 The insulation detection circuit shown in Figure 3 As shown, the method includes:

[0060] S301, in response to an insulation resistance detection request, controlling the switching states of the first relay K1, the second relay K2, and the third relay K3 based on a resistance switching measurement method to determine a first capacitance C1 of a first equivalent capacitor Cp between the positive electrode of the power battery and the ground terminal and a second capacitance C2 of a second equivalent capacitor Cn between the negative electrode of the power battery and the ground terminal;

[0061] S302, controlling the first relay K1 to close, and alternately closing the second relay K2 and the third relay K3 to determine a first stable time duration t1 during which the first insulation test voltage is in a stable state within the closed time duration of the second relay K2, and to determine a second stable time duration t2 during which the second insulation test voltage is in a stable state within the closed time duration of the third relay K3, wherein the first insulation test voltage is the voltage between the positive electrode and the ground terminal of the power battery, and the second insulation test voltage is the voltage between the negative electrode and the ground terminal of the power battery;

[0062] S303: Calculate a target resistance value of a first insulation resistance Rp between the positive electrode of the power battery and the ground and a target resistance value of a second insulation resistance Rn between the negative electrode of the power battery and the ground based on the first stable time t1, the second stable time t2, the first capacitance C1, and the second capacitance C2.

[0063] The insulation resistance detection method provided in an embodiment of the present invention controls the operating states of a first relay, a second relay, and a third relay to determine the stabilization time during which the insulation detection voltage is in a stable state. The target insulation resistance is determined based on the stabilization time and the capacitance value of the capacitor, rather than based on the voltage value across the power battery. This decouples the insulation resistance detection from the voltage across the power battery, reduces the impact of voltage fluctuations across the power battery, and thereby improves the accuracy of the insulation resistance detection.

[0064] Since the insulation resistance detection circuit includes a first equivalent capacitor and a second equivalent capacitor, the embodiment of the present invention performs insulation resistance detection based on the principle of the first-order circuit response equation of the RC circuit. The principle is explained below. The change curves of voltage and current during the insulation resistance detection process are shown in FIG. Figure 4 As shown, according to the first-order circuit response equation of the RC circuit, it is calculated as follows:

[0065] Among them, Uc represents the voltage across the capacitor, Uo represents the voltage across the capacitor in the initial state, Us represents the final stable voltage across the capacitor, t represents the voltage stabilization time, τ represents the time constant (τ=RC), R represents the insulation resistance, and C represents the capacitance of the equivalent capacitor.

[0066] According to the above equation, the voltage stabilization time is proportional to RC. The larger the resistance, the longer the stabilization time, and the larger the capacitance, the longer the stabilization time. When the insulation resistance detection circuit starts working, the voltage Uc on the equivalent capacitor becomes higher and higher. When it approaches the stable voltage Us (that is, the difference between Us and Uc is small enough, for example, it can be set to less than 0.4% of Us), the voltage can be considered to be basically stable. At this time, t / (RC) = 5.521. The preset value in the embodiment of the present invention can be 5.521, which represents that the voltage Uc is basically stable. Then, the insulation resistance value R can be calculated based on the stabilization time t and the current equivalent capacitance value C.

[0067] It is worth noting that the preset value 5.521 in the embodiment of the present invention is calculated based on the above-mentioned first-order circuit response equation under the condition of Us-Uc=0.4%Us. The preset value in the embodiment of the present invention can also be other values. Generally, after t=5RC, it can be considered that the voltage is basically stable. That is, the preset value can be 5 or a value greater than 5.

[0068] In a specific implementation, it can be determined that the first insulation detection voltage is in a stable state by the following method:

[0069] Determine that the first insulation detection voltage is stable when the ratio of the difference between the first insulation detection voltage at the current moment and the first insulation detection voltage at the previous moment to the first insulation detection voltage at the current moment is less than a set value. For example, the set value may be 0.01.

[0070] You can confirm that the second insulation detection voltage is in a stable state by the following methods:

[0071] When it is determined that the ratio of the difference between the second insulation detection voltage at the current moment and the second insulation detection voltage at the previous moment to the second insulation detection voltage at the current moment is less than a set value, the second insulation detection voltage is stable.

[0072] In a specific implementation, the first capacitance C1 and the second capacitance C2 are determined by the following steps: Figure 5 As shown:

[0073] S501: Control the first relay K1 to close, and after determining that the first insulation test voltage or the second insulation test voltage is in a stable state, obtain a first voltage U1 of the first insulation test voltage and a second voltage U2 of the second insulation test voltage. Control the second relay K2 to close and start timing. After determining that the first insulation test voltage or the second insulation test voltage is in a stable state, obtain a third voltage U3 of the second insulation test voltage and stop timing to determine a third stabilization time t3.

[0074] S502: Control the second relay K2 to open, and after determining that the first insulation test voltage or the second insulation test voltage is in a stable state, control the third relay K3 to close, and start timing. After determining that the first insulation test voltage or the second insulation test voltage is stable, obtain a fourth voltage U4 of the first insulation test voltage, and stop timing to determine a fourth stabilization time t4.

[0075] S503, determining an initial resistance value of the first insulation resistor Rp and an initial resistance value of the second insulation resistor Rn based on the first voltage U1, the second voltage U2, the third voltage U3, the fourth voltage U4, the first resistor R1, the second resistor R2, the third resistor R3, and the fourth resistor R4;

[0076] Specifically, the uncorrected resistance value Rp1 of the first insulation resistor Rp may be determined based on the first voltage U1, the second voltage U2, the third voltage U3, and the fourth resistor R4, and the formula may be:

[0077]

[0078] The initial resistance value Rp0 of the first insulation resistor Rp is determined based on the uncorrected resistance value Rp1 of the first insulation resistor Rp and the first resistor R1, and the formula may be:

[0079]

[0080] And based on the first voltage U1, the second voltage U2, the fourth voltage U4 and the third resistor R3, the uncorrected resistance value Rn1 of the second insulation resistor Rn is determined, and the formula can be:

[0081]

[0082] The initial resistance Rn0 of the second insulation resistor Rn is determined based on the uncorrected resistance value of the second insulation resistor Rn and the second resistance R2. The formula may be:

[0083]

[0084] S504 , determining a first capacitance C1 and a second capacitance C2 based on an initial resistance Rp0 of the first insulation resistor Rp, an initial resistance Rn0 of the second insulation resistor Rn, a third stabilization time t3 , and a fourth stabilization time t4 .

[0085] Specifically, the first product 5.521*Rp0 of the preset value (for example, 5.521) and the initial resistance Rp0 of the first insulation resistor can be calculated, and the ratio of the third stable time t3 to the first product 5.521*Rp0 is determined as the first capacitance C1, that is, C1=t3 / (5.521*Rp0); and the second product 5.521*Rn0 of the preset value and the initial resistance of the second insulation resistor is calculated, and the ratio of the fourth stable time t4 to the second product 5.521*Rn0 is determined as the second capacitance C2, that is, C2=t4 / (5.521*Rn0).

[0086] In a specific implementation, calculating the target resistance value of the first insulation resistance Rp between the positive electrode of the power battery and the ground terminal and the target resistance value of the second insulation resistance Rn between the negative electrode of the power battery and the ground terminal based on the first stable time t1, the second stable time t2, the first capacitance C1 and the second capacitance C2 may include: calculating a third product 5.521*C1 of the preset value and the first capacitance, and determining the ratio t1 / (5.521*C1) of the first stable time to the third product as the target resistance value of the first insulation resistance; and calculating a fourth product 5.521*C2 of the preset value and the second capacitance, and determining the ratio t2 / (5.521*C2) of the second stable time to the fourth product as the target resistance value of the second insulation resistance.

[0087] Since the Y capacitance value (i.e., the first capacitance C1 of the first equivalent capacitance Cp and the second capacitance C2 of the second equivalent capacitance Cn in the embodiment of the present invention) is basically unchanged in a working mode (only related to whether the upper and lower high voltages are present, the driving mode or the charging mode, and the Y capacitance of different fast charging piles will also be different), a working mode only needs to update the Y capacitance value once for the first time, lock the Y capacitance value in the intermediate process, and recalculate and update it after the working mode is switched. Therefore, in the insulation resistance detection method provided by the embodiment of the present invention, before controlling the switching states of the first relay K1, the second relay K2, and the third relay K3 based on the resistance switching measurement method to determine the first capacitance C1 of the first equivalent capacitance Cp between the positive pole and the ground terminal of the power battery and the second capacitance C2 of the second equivalent capacitance Cn between the negative pole and the ground terminal of the power battery, it can also include: detecting that the working mode of the electric vehicle has changed.

[0088] The overall process of the insulation detection method provided by the embodiment of the present invention is summarized as follows: Figure 6 As shown, the following steps are included:

[0089] S601. Responding to an insulation resistance test request, after detecting a change in the operating mode of the electric vehicle, controlling the first relay K1 to close, determining that the first insulation test voltage or the second insulation test voltage is in a stable state, obtaining a first voltage U1 of the first insulation test voltage and a second voltage U2 of the second insulation test voltage, controlling the second relay K2 to close, and starting timing. After determining that the first insulation test voltage or the second insulation test voltage is in a stable state, obtaining a third voltage U3 of the second insulation test voltage, and stopping timing to determine a third stabilization time t3.

[0090] S602: Control the second relay K2 to open, and after determining that the first insulation test voltage or the second insulation test voltage is in a stable state, control the third relay K3 to close, and start timing. After determining that the first insulation test voltage or the second insulation test voltage is stable, obtain a fourth voltage U4 of the first insulation test voltage, and stop timing to determine a fourth stabilization time t4.

[0091] S603, determining an uncorrected resistance value of the first insulation resistor Rp based on the first voltage U1, the second voltage U2, the third voltage U3, and the fourth resistor R4; determining an initial resistance value of the first insulation resistor Rp based on the uncorrected resistance value of the first insulation resistor Rp and the first resistor R1; and determining an uncorrected resistance value of the second insulation resistor Rn based on the first voltage U1, the second voltage U2, the fourth voltage U4, and the third resistor R3; determining an initial resistance value of the second insulation resistor Rn based on the uncorrected resistance value of the second insulation resistor Rn and the second resistor R2;

[0092] S604: Calculate a first product of the preset value and the initial resistance value of the first insulation resistor, 5.521*Rp0, and determine a first capacitance C1 as a ratio t3 / (5.521*Rp0) of the third stabilization time and the first product; and calculate a second product of the preset value and the initial resistance value of the second insulation resistor, 5.521*Rn0, and determine a second capacitance C2 as a ratio t4 / (5.521*Rn0) of the fourth stabilization time and the second product;

[0093] S605: Control the first relay K1 to close, and alternately close the second relay K2 and the third relay K3 to determine a first stable time duration t1 during which the first insulation test voltage remains stable while the second relay K2 is closed, and to determine a second stable time duration t2 during which the second insulation test voltage remains stable while the third relay K3 is closed, wherein the first insulation test voltage is the voltage between the positive electrode and the ground of the power battery, and the second insulation test voltage is the voltage between the negative electrode and the ground of the power battery;

[0094] S606. Calculate the third product 5.521*C1 of the preset value and the first capacitance, and determine the ratio t1 / (5.521*C1) of the first stabilization time to the third product as the target resistance of the first insulation resistor; and calculate the fourth product 5.521*C2 of the preset value and the second capacitance, and determine the ratio t2 / (5.521*C2) of the second stabilization time to the fourth product as the target resistance of the second insulation resistor.

[0095] Based on the same inventive concept, an embodiment of the present invention further provides an electric vehicle comprising any one of the above insulation resistance detection circuits. The implementation of the electric vehicle can refer to the implementation of the above circuits, and the repeated parts will not be repeated.

[0096] An embodiment of the present invention provides an insulation resistance detection circuit, method, and electric vehicle. The insulation resistance detection circuit includes a first relay, a second relay, a third relay, a first resistor, a second resistor, a third resistor, a fourth resistor, and a controller. The controller controls the operating states of the first relay, the second relay, and the third relay to determine the stabilization time during which the insulation detection voltage is in a stable state. The target insulation resistance is determined based on the stabilization time and the capacitance value of the capacitor, rather than based on the voltage value across a power battery. This decouples the insulation resistance detection from the voltage across the power battery, reduces the influence of voltage fluctuations across the power battery, and thereby improves the accuracy of the insulation resistance detection.

[0097] Those skilled in the art may make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is intended to include such modifications and variations.

Claims

1. An insulation resistance detection circuit, characterized in that: include: a first relay, a second relay, a third relay, a first resistor, a second resistor, a third resistor, a fourth resistor, and a controller; a first end of the first relay is electrically connected to the first end of the first resistor, the first end of the second resistor, the first end of the second relay, and the first end of the third relay, and a second end of the first relay is grounded; a second end of the first resistor is electrically connected to the first end of the third resistor; a second end of the third resistor is electrically connected to the second end of the second relay; a second end of the second resistor is electrically connected to the first end of the fourth resistor; and a second end of the fourth resistor is electrically connected to the second end of the third relay; The controller is signal-connected to the control terminals of the first relay, the second relay, and the third relay, and is configured to: In response to an insulation resistance detection request, controlling the switching states of the first relay, the second relay, and the third relay based on a resistance switching measurement method to determine a first capacitance of a first equivalent capacitor between a positive electrode of the power battery and a ground terminal and a second capacitance of a second equivalent capacitor between a negative electrode of the power battery and the ground terminal; controlling the first relay to close, and alternately closing the second relay and the third relay to determine a first stable time duration during which a first insulation detection voltage is in a stable state within the closed time duration of the second relay, and determining a second stable time duration during which a second insulation detection voltage is in a stable state within the closed time duration of the third relay, wherein the first insulation detection voltage is a voltage between the positive electrode of the power battery and the ground terminal, and the second insulation detection voltage is a voltage between the negative electrode of the power battery and the ground terminal; Calculating a target resistance value of a first insulation resistance between the positive electrode of the power battery and the ground terminal and a target resistance value of a second insulation resistance between the negative electrode of the power battery and the ground terminal based on the first stable time period, the second stable time period, the first capacitance, and the second capacitance; The first insulation detection voltage is determined to be in a stable state by: Determining that the first insulation detection voltage is stable when a ratio of a difference between the first insulation detection voltage at a current moment and the first insulation detection voltage at a previous moment to the first insulation detection voltage at the current moment is less than a set value; Determine whether the second insulation detection voltage is in a stable state by the following method: When it is determined that the ratio of the difference between the second insulation detection voltage at the current moment and the second insulation detection voltage at the previous moment to the second insulation detection voltage at the current moment is less than a set value, the second insulation detection voltage is stable.

2. The circuit according to claim 1, wherein It also includes a DC-DC regulated power supply; The positive input terminal of the DC-DC regulated power supply is electrically connected to the positive electrode of the power battery, the negative input terminal of the DC-DC regulated power supply is electrically connected to the negative electrode of the power battery, the positive output terminal of the DC-DC regulated power supply is electrically connected to the second end of the first resistor, and the negative output terminal of the DC-DC regulated power supply is electrically connected to the second end of the second resistor.

3. A method for detecting insulation resistance, characterized in that: Applied to the circuit according to claim 1 or 2, the method comprises: In response to an insulation resistance detection request, controlling the switching states of the first relay, the second relay, and the third relay based on a resistance switching measurement method to determine a first capacitance of a first equivalent capacitance between a positive electrode of the power battery and a ground terminal and a second capacitance of a second equivalent capacitance between a negative electrode of the power battery and the ground terminal; controlling the first relay to close, and alternately closing the second relay and the third relay to determine a first stable time duration during which a first insulation detection voltage is in a stable state within the closed time duration of the second relay, and determining a second stable time duration during which a second insulation detection voltage is in a stable state within the closed time duration of the third relay, wherein the first insulation detection voltage is a voltage between the positive electrode of the power battery and the ground terminal, and the second insulation detection voltage is a voltage between the negative electrode of the power battery and the ground terminal; Calculating a target resistance value of a first insulation resistance between the positive electrode of the power battery and the ground terminal and a target resistance value of a second insulation resistance between the negative electrode of the power battery and the ground terminal based on the first stable time period, the second stable time period, the first capacitance, and the second capacitance; The first insulation detection voltage is determined to be in a stable state by: Determining that the first insulation detection voltage is stable when a ratio of a difference between the first insulation detection voltage at a current moment and the first insulation detection voltage at a previous moment to the first insulation detection voltage at the current moment is less than a set value; Determine whether the second insulation detection voltage is in a stable state by the following method: When it is determined that the ratio of the difference between the second insulation detection voltage at the current moment and the second insulation detection voltage at the previous moment to the second insulation detection voltage at the current moment is less than a set value, the second insulation detection voltage is stable.

4. The method according to claim 3, wherein The controlling the switching states of the first relay, the second relay, and the third relay based on the resistance switching measurement method to determine a first capacitance of a first equivalent capacitor between the positive electrode of the power battery and the ground terminal and a second capacitance of a second equivalent capacitor between the negative electrode of the power battery and the ground terminal includes: Controlling the first relay to close, determining that the first insulation detection voltage or the second insulation detection voltage is in a stable state, obtaining a first voltage of the first insulation detection voltage and a second voltage of the second insulation detection voltage, controlling the second relay to close, and starting timing, determining that the first insulation detection voltage or the second insulation detection voltage is in a stable state, obtaining a third voltage of the second insulation detection voltage, and stopping timing to determine a third stabilization time; controlling the second relay to open, and after determining that the first insulation detection voltage or the second insulation detection voltage is in a stable state, controlling the third relay to close and start timing, and after determining that the first insulation detection voltage or the second insulation detection voltage is stable, obtaining a fourth voltage of the first insulation detection voltage, and stopping timing to determine a fourth stabilization time; determining an initial resistance value of the first insulation resistor and an initial resistance value of the second insulation resistor based on the first voltage, the second voltage, the third voltage, the fourth voltage, the first resistance, the second resistance, the third resistance, and the fourth resistance; The first capacitance and the second capacitance are determined based on the initial resistance of the first insulation resistor, the initial resistance of the second insulation resistor, the third stabilization time, and the fourth stabilization time.

5. The method according to claim 4, wherein The determining the first capacitance and the second capacitance based on the initial resistance of the first insulation resistor, the initial resistance of the second insulation resistor, the third stabilization time, and the fourth stabilization time includes: A first product of a preset value and an initial resistance value of the first insulation resistor is calculated, and a ratio of the third stabilization time to the first product is determined as the first capacitance; and a second product of the preset value and the initial resistance value of the second insulation resistor is calculated, and a ratio of the fourth stabilization time to the second product is determined as the second capacitance.

6. The method according to claim 5, wherein The calculating, based on the first stable time period, the second stable time period, the first capacitance, and the second capacitance, a target insulation resistance value of a first insulation resistance between the positive electrode of the power battery and the ground terminal and a target insulation resistance value of a second insulation resistance between the negative electrode of the power battery and the ground terminal includes: A third product of the preset value and the first capacitance is calculated, and a ratio of the first stabilization time to the third product is determined as a target resistance of the first insulation resistor; and a fourth product of the preset value and the second capacitance is calculated, and a ratio of the second stabilization time to the fourth product is determined as a target resistance of the second insulation resistor.

7. The method according to claim 4, wherein The determining an initial resistance value of the first insulation resistor and an initial resistance value of the second insulation resistor based on the first voltage, the second voltage, the third voltage, the fourth voltage, the first resistor, the second resistor, the third resistor, and the fourth resistor includes: determining an uncorrected resistance value of the first insulation resistor based on the first voltage, the second voltage, the third voltage, and the fourth resistance; determining an initial resistance value of the first insulation resistor based on the uncorrected resistance value of the first insulation resistor and the first resistor; and determining an uncorrected resistance value of the second insulation resistor based on the first voltage, the second voltage, the fourth voltage, and the third resistance; An initial resistance value of the second insulation resistor is determined based on the uncorrected resistance value of the second insulation resistor and the second resistance.

8. The method according to claim 3, wherein Before controlling the switch states of the first relay, the second relay, and the third relay based on the resistance switching measurement method to determine a first capacitance of a first equivalent capacitor between the positive electrode of the power battery and the ground terminal and a second capacitance of a second equivalent capacitor between the negative electrode of the power battery and the ground terminal, the method further includes: A change in the operating mode of the electric vehicle is detected.

9. An electric vehicle, characterized in that: The device comprises an insulation resistance detection circuit as described in any one of claims 1 or 2.

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