Insulation resistance value detection method, detection circuit and battery management system

Abstract

The invention discloses an insulation resistance value detection method and detection circuit of an automobile battery and a battery management system, and belongs to the field of battery detection. Acquiring voltage sequences of the sampling points after a second switch of the insulation resistance detection circuit is switched from on to off and after the second switch is switched from off to on respectively; for each voltage sequence, whether the difference value of the last two voltages in the voltage sequence is smaller than a preset threshold value or not is judged, if yes, the last voltage serves as the steady-state voltage of the voltage sequence, and if not, curve fitting is conducted according to the voltage sequence, and the steady-state voltage of the voltage sequence is obtained according to the fitted curve; and calculating a positive-end insulation resistance value and a negative-end insulation resistance value according to the steady-state voltages of the two groups of voltage sequences. By acquiring the voltage data in a short time, the stable voltage is accurately predicted, and on the basis of ensuring the calculation precision of the insulation value, the rapid detection function of insulation is realized.

Description

Technical Field

[0001] The present application relates to the field of battery detection, and specifically to an insulation resistance detection method, a detection circuit and a battery management system for automobile batteries. Background Art

[0002] As one of the core components of electric vehicles and a high-voltage platform for electric vehicles, the power battery pack must ensure its safety, so insulation testing must be performed on electric vehicles. However, when the insulation value is large and the body capacitance is large, the voltage used to calculate the insulation value needs to wait for a long time to reach a stable state, which seriously affects the speed of insulation testing. If the insulation test is used as a high-voltage condition, it will seriously affect the user experience. Summary of the invention

[0003] The present application provides an insulation resistance detection method, a detection circuit and a battery management system, which can solve the technical problem of low efficiency of automobile battery insulation detection in the prior art.

[0004] In a first aspect, an embodiment of the present application provides an insulation resistance detection method, which is applied to an insulation resistance detection circuit of an automobile battery, wherein the insulation resistance detection circuit includes a sampling circuit connected in parallel between a positive electrode of a battery pack and a negative electrode of a battery pack, wherein the sampling circuit includes a first branch and a second branch connected in parallel, wherein first to fourth resistors are sequentially arranged on the first branch along a direction from the positive electrode of the battery pack to the negative electrode of the battery pack, wherein a connection point between the second resistor and the third resistor is electrically grounded, wherein a third branch is connected in parallel between a connection point between the first resistor and the second resistor and the negative electrode of the battery pack, wherein a second switch is arranged on the third branch, and a plurality of second branch resistors are arranged on the second branch, wherein the insulation resistance detection method includes:

[0005] Taking the connection point of the third resistor and the fourth resistor as the sampling point, respectively obtaining a voltage sequence of the sampling point within a first preset time period after the second switch is switched from on to off and after the second switch is switched from off to on; for each voltage sequence, determining whether the difference between the last two voltages in the voltage sequence is less than a preset threshold value, if so, taking the last voltage as the steady-state voltage of the voltage sequence, if not, performing curve fitting according to the voltage sequence, and obtaining the steady-state voltage of the voltage sequence according to the fitted curve;

[0006] The positive terminal insulation resistance and the negative terminal insulation resistance are calculated based on the steady-state voltages of the two voltage sequences.

[0007] In combination with the first aspect, in one implementation, performing curve fitting according to the voltage sequence and obtaining the steady-state voltage of the voltage sequence according to the fitted curve specifically includes the following steps:

[0008] Perform curve fitting according to the voltage sequence and determine whether the curve fitting goodness meets expectations;

[0009] If the goodness of fit reaches the expectation, the steady-state voltage of the voltage sequence is obtained according to the curve after this fitting;

[0010] If the goodness of fit does not meet expectations, the voltage values ​​are continuously collected to update the voltage sequence, and the curve is fitted again according to the updated voltage sequence until the goodness of fit meets expectations to obtain the corresponding steady-state voltage, or until the number of fitting times reaches a preset upper limit.

[0011] In combination with the first aspect, in one implementation, if the fitting number reaches a preset upper limit and the goodness of fit still does not meet expectations, then after waiting for a second preset time period, the voltage value is collected again and used as the steady-state voltage to calculate the positive end insulation resistance and the negative end insulation resistance.

[0012] In combination with the first aspect, in one implementation, the second preset time period is calculated using the following formula:

[0013] T=kRC

[0014] Among them, T represents the second preset time period, the unit is s; k is an integer not less than 5; R represents the designed insulation resistance of the battery pack, the unit is Ω; C represents the parasitic capacitance of the whole vehicle, the unit is F.

[0015] In combination with the first aspect, in one implementation, the preset threshold is obtained by the following steps:

[0016] Calculate a first difference between a first voltage and a second voltage in the voltage sequence, and a second difference between the second voltage and a third voltage;

[0017] Determine whether the first difference exceeds a first threshold value, and a third difference between the first difference and the second difference exceeds a second threshold value, if so, set the preset threshold value within a first preset range, if not, set the preset threshold value within a second preset range;

[0018] The upper limit value of the first preset range is smaller than the lower limit value of the second preset range.

[0019] In combination with the first aspect, in one implementation, the first preset range is (0, 0.001], and the second preset range is (0.001, 0.005].

[0020] In combination with the first aspect, in one implementation, performing fitting according to the voltage sequence and obtaining a steady-state voltage according to the fitted curve specifically includes the following steps:

[0021] Based on the following formula, the voltage series is curve-fitted using the nonlinear least squares method to obtain multiple parameters of the curve:

[0022]

[0023] Wherein, U represents the voltage in the voltage sequence; a1 represents the first parameter; a2 represents the second parameter; a3 represents the third parameter; t represents the sampling time of the voltage in the voltage sequence; e represents the natural constant;

[0024] The following formula is used to process multiple parameters to obtain the steady-state voltage:

[0025] U ′ =a1+a2

[0026] Among them, U ′ In a second aspect, an embodiment of the present application provides an insulation resistance detection circuit, the insulation resistance detection circuit comprising a positive terminal insulation resistance, a negative terminal insulation resistance, a sampling circuit connected in parallel between a positive electrode of a battery pack and a negative electrode of a battery pack, a memory, a processor, and a detection program stored in the memory and executable on the processor;

[0027] The sampling circuit comprises a first branch and a second branch connected in parallel, wherein the first branch is provided with first to fourth resistors in sequence along the direction from the positive electrode of the battery pack to the negative electrode of the battery pack, the connection point of the second resistor and the third resistor is connected to the electrical ground, a third branch is connected in parallel between the connection point of the first resistor and the second resistor and the negative electrode of the battery pack, a second switch is provided on the third branch, and a plurality of second branch resistors are provided on the second branch;

[0028] The positive terminal insulation resistance is connected between the positive pole of the battery pack and the electrical ground of the insulation resistance detection circuit, and the negative terminal insulation resistance is connected between the negative pole of the battery pack and the electrical ground of the insulation resistance detection circuit. When the processor executes the detection program, the insulation resistance detection method is implemented.

[0029] In combination with the second aspect, in one implementation, a difference between a sum of resistance values ​​of the first resistor and the second resistor and a sum of resistance values ​​of the third resistor and the fourth resistor does not exceed a set threshold;

[0030] The divided voltage of the fourth resistor does not exceed the measuring range of the sampling device.

[0031] In a third aspect, an embodiment of the present application provides a battery management system, including the insulation resistance detection circuit.

[0032] The beneficial effects brought by the technical solution provided in the embodiments of the present application include:

[0033] By acquiring voltage data in a short period of time, we first determine whether the difference between the last two voltages is small enough. If it is small enough, the voltage can be considered as the final steady-state voltage. Otherwise, the parameters in the preset function prototype are fitted based on the nonlinear least squares method to accurately predict the voltage at stable state. On the basis of ensuring the accuracy of insulation value calculation, the quick detection function of insulation is realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a circuit schematic diagram of an embodiment of an insulation resistance detection circuit of the present application;

[0035] Figure 2 This is a flow chart of an embodiment of an insulation resistance detection method of the present application. DETAILED DESCRIPTION

[0036] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0037] In order to make the objectives, technical solutions and advantages of the present application clearer, the implementation methods of the present application will be further described in detail below with reference to the accompanying drawings.

[0038] In a first aspect, an embodiment of the present application provides a method for detecting the insulation resistance of a vehicle battery.

[0039] In one embodiment, referring to Figure 1 and Figure 2 , Figure 1 This is a circuit diagram of an embodiment of an insulation resistance detection circuit for a car battery of the present application. Figure 2 This is a flow chart of an embodiment of the method for detecting the insulation resistance of a vehicle battery of the present application. Figure 1 and Figure 2As shown, the insulation resistance detection method of the automobile battery is applied to the insulation resistance detection circuit of the automobile battery, the insulation resistance detection circuit includes a sampling circuit connected in parallel between the positive electrode of the battery pack Vpack and the negative electrode of the battery pack Vpack, the sampling circuit includes a first branch and a second branch connected in parallel, the first branch is provided with first to fourth resistors in sequence along the direction from the positive electrode of the battery pack Vpack to the negative electrode of the battery pack Vpack, the connection point of the second resistor Rb and the third resistor Rc is connected to the electrical ground a, the third branch is connected in parallel between the connection point of the first resistor Ra and the second resistor Rb and the negative electrode of the battery pack Vpack, the third branch is provided with a second switch S2, and the second branch is provided with a plurality of second branch resistors, including a fifth resistor Re and a sixth resistor Rf. The above insulation resistance detection method includes:

[0040] Step S1, taking the connection point of the third resistor Rc and the fourth resistor Rd as the sampling point, respectively acquiring a voltage sequence of the sampling point within a first preset time period after the second switch S2 is switched from on to off and after the second switch S2 is switched from off to on.

[0041] Step S2: for each voltage sequence, determine whether the difference between the last two voltages in the voltage sequence is less than a preset threshold value. If so, take the last voltage as the steady-state voltage of the voltage sequence. If not, perform curve fitting according to the voltage sequence, and obtain the steady-state voltage of the voltage sequence according to the fitted curve.

[0042] Step S3, calculating the positive terminal insulation resistance Rp and the negative terminal insulation resistance Rn according to the steady-state voltages of the two voltage sequences.

[0043] In this embodiment, by obtaining voltage data in a short period of time, it is first determined whether the difference between the last two voltages is small enough. If it is small enough, the voltage can be considered as the final steady-state voltage. Otherwise, the parameters in the preset function prototype are fitted based on the nonlinear least squares method to accurately predict the voltage when stable, and the fast detection function of insulation is realized on the basis of ensuring the calculation accuracy of the insulation value.

[0044] For the sake of convenience, the voltage value within the preset time period is collected after the second switch S2 is switched from on to off to form a first voltage sequence. The voltage value within the first preset time period is collected after the second switch S2 is switched from off to on to form a second voltage sequence.

[0045] The first voltage sequence and the second voltage sequence each include at least three voltage values.

[0046] In this embodiment, reference Figure 2After the third switch S3 and the fourth switch S4 are closed to complete power-on, the first switch S1 is normally closed, and after the second switch S2 is opened, the Volt voltage value within X milliseconds, that is, the first preset time period, is recorded to obtain a first voltage sequence recorded as Volt_sequence1, and then the second switch S2 is closed and the Volt voltage division within X milliseconds is recorded to obtain a second voltage sequence recorded as Volt_sequence2, wherein the first preset time period of the first voltage sequence and the second voltage sequence can be determined according to the sampling period of the voltage and the number of voltage values ​​to be collected. For example, the value of X needs to ensure that the number of sampled voltage data is ≥3, if the sampling period is 100ms, then X should be ≥300ms, if the sampling period is 10ms, then X should be ≥30ms.

[0047] Preferably, the first preset time periods of the first voltage sequence and the second voltage sequence are consistent, which helps to simplify the processing logic of the voltage values ​​of the first voltage sequence and the second voltage sequence and improve the processing efficiency.

[0048] Furthermore, in one embodiment, the above-mentioned curve fitting is performed according to the voltage sequence, and the steady-state voltage of the voltage sequence is obtained according to the fitted curve, which specifically includes the following steps:

[0049] Perform curve fitting according to the voltage sequence and determine whether the curve fitting goodness meets expectations;

[0050] If the goodness of fit reaches the expectation, the steady-state voltage of the voltage sequence is obtained according to the curve after this fitting;

[0051] If the goodness of fit does not meet expectations, the voltage values ​​are continuously collected to update the voltage sequence, and the curve is fitted again according to the updated voltage sequence until the goodness of fit meets expectations to obtain the corresponding steady-state voltage, or until the number of fitting times reaches a preset upper limit.

[0052] Furthermore, in one embodiment, if the goodness of fit still does not reach expectations when the number of fitting times reaches a preset upper limit, the voltage value is collected again after waiting for a second preset time period and used as a steady-state voltage to calculate the positive terminal insulation resistance and the negative terminal insulation resistance.

[0053] In this embodiment, the first preset time period is the time period for quick inspection, and the second preset time period is the waiting time after the quick inspection fails, that is, the insulation value is calculated after the voltage stabilizes.

[0054] Furthermore, in one embodiment, the second preset time period is calculated using the following formula:

[0055] T=kRC

[0056] Wherein, T represents the second preset time period, in seconds. k is an integer not less than 5. R represents the designed insulation resistance of the battery pack Vpack, in Ω. C represents the parasitic capacitance of the vehicle, in F.

[0057] In this embodiment, the designed insulation resistance is generally equal to the larger value of the positive electrode insulation resistance Rp and the negative electrode insulation resistance Rn. The insulation resistance design standard of the automotive battery pack mainly depends on the circuit type and the operating voltage. For a DC circuit, the minimum insulation resistance requirement is 100Ω / V; and for an AC circuit, the minimum insulation resistance requirement is 500Ω / V.

[0058] In an RC (resistance-capacitance) circuit, the time constant τ describes the speed at which the capacitor charges or discharges, and is the product of resistance and capacitance (i.e., R*C). During the charging process, the capacitor voltage reaches approximately 99.33% of the final voltage within 5τ. During the discharging process, the capacitor voltage drops to approximately 0.67% of the initial voltage within 5τ, indicating that the voltage is close to a steady state. The closer the voltage is to the steady-state value, the higher the accuracy of the insulation resistance. Therefore, the value of k is greater than or equal to 5.

[0059] In the embodiment of the present application, by switching the state of the second switch S2 and waiting for 5RC (R is the insulation resistance determined by the battery system design, such as 2MΩ, C is the Y capacitor, then 5RC is 10s, both of which can be obtained in advance) time, the steady-state voltages in the two states are obtained for calculating the insulation value, which can improve the reliability of the steady-state voltage and thereby improve the accuracy of the insulation resistance calculation.

[0060] Furthermore, in one embodiment, the above-mentioned preset threshold is obtained by the following steps:

[0061] A first difference between a first voltage and a second voltage in the voltage sequence and a second difference between the second voltage and a third voltage are calculated.

[0062] Determine whether the first difference exceeds a first threshold value, and a third difference between the first difference and the second difference exceeds a second threshold value, if so, set the preset threshold value within a first preset range, if not, set the preset threshold value within a second preset range;

[0063] The upper limit value of the first preset range is smaller than the lower limit value of the second preset range.

[0064] In this embodiment, the first preset range and the second preset range are set to shorten the insulation detection time, that is, when the first difference and the second difference are very close, it indicates that the voltage has tended to a steady state. At this time, it is not necessary to set the preset threshold too small to improve the calculation efficiency, resulting in the insulation value cannot be calculated efficiently. If the difference between the first difference and the second difference is large, it indicates that the voltage has not tended to a steady state, and a smaller preset threshold needs to be set to ensure that the last voltage in the voltage sequence is a steady-state voltage, thereby ensuring the accuracy of the insulation resistance calculation.

[0065] Furthermore, in one embodiment, the first preset range is (0, 0.001], and the second preset range is (0.001, 0.005].

[0066] Exemplarily, when obtaining the steady-state voltages under two states, first determine whether the difference between the last two voltages in the voltage sequence recorded under the two states is less than a preset threshold VoltThresholds (for example, the value may be 0.001V, but is not limited to 0.001V, and the threshold may be adjusted according to the following two states: ① If the difference between the first voltage and the second voltage after the switching state is large and much larger than the difference between the second and third voltages, the preset threshold may be set to 0.001V; ② If the difference between the first voltage and the second voltage after the switching state is small and close to the difference between the second voltage and the third voltage, the preset threshold may be set to 0.005V).

[0067] Further, in one embodiment, if it is determined that the difference between the last two voltages in the voltage sequence is not less than a preset threshold, it means that the steady state has not yet been reached, and it is necessary to perform fitting according to the voltage sequence, and obtain the steady-state voltage according to the fitted curve, which specifically includes the following steps:

[0068] Based on the following formula, the voltage series is curve-fitted using the nonlinear least squares method to obtain multiple parameters of the curve:

[0069]

[0070] Wherein, U represents the voltage in the voltage sequence. a1 represents the first parameter. a2 represents the second parameter. a3 represents the third parameter. t represents the sampling time of the voltage in the voltage sequence. e represents the natural constant.

[0071] The following formula is used to process multiple parameters to obtain the steady-state voltage:

[0072] U ′ =a1+a2

[0073] Among them, U ′ Represents the steady-state voltage.

[0074] In this embodiment, if the difference between the last two voltages in the voltage sequence is less than a preset threshold, the last voltage is the steady-state voltage. Otherwise, based on the function prototype Using the nonlinear least squares method, Volt_sequence1 and Volt_sequence2 are fitted to obtain the parameters a1, a2 and a3 in the two states respectively, and then according to U ′ =a1+a2, the steady-state voltages under the two conditions can be calculated and are respectively denoted as U 1,steady and U 2,Steady If the difference between the last two voltages in one of the voltage sequences is less than a preset threshold, and the difference between the last two voltages in the other voltage sequence is not less than the preset threshold, then for the voltage sequence whose difference is less than the preset threshold, the last voltage value in the voltage sequence is used as the steady-state voltage, and for the voltage sequence whose difference is not less than the preset threshold, a curve fitting is performed on it to obtain the steady-state voltage, that is, the curve fitting is performed only for the voltage sequence whose steady-state voltage cannot be determined by the voltage difference.

[0075] After curve fitting according to the voltage series, first determine the goodness of fit R of the fitting curve. 2 Whether it meets expectations, the present application embodiment takes greater than 0.99 (but not limited to 0.99) as an example for exemplary explanation, wherein the calculation method of goodness of fit refers to the prior art. If it meets expectations, the fitting result U obtained by curve fitting is 1,steady and U 2,Steady It can be used to calculate the insulation resistance, because the goodness of fit determines the fitting effect. If the goodness of fit > 0.99, the fitting effect is good and the estimated steady-state voltage is more accurate, ensuring the calculation accuracy of the insulation resistance. Otherwise, the insulation resistance keeps the value of the previous moment, and records the current a1, a2 and a3, and uses the current a1, a2 and a3 as the initial value of the next iteration in the least squares fitting process.

[0076] Before the next fitting, it is necessary to collect another voltage value based on the original voltage sequence collected based on the first preset time period and add it to the voltage sequence. For example, the voltage sampling period is 100ms, the first preset time period X=300ms, and the number of voltage data in the first voltage sequence is 3. If the goodness of fit does not meet expectations after the curve fitting is performed according to the first voltage sequence, the first preset time period X is extended to 400ms to collect another voltage data. The number of voltage data in the first voltage sequence becomes 4. The curve fitting is performed again according to the updated first voltage sequence. If the goodness of fit meets expectations, the steady-state voltage is calculated based on the fitting data this time. If the goodness of fit still does not meet expectations, the first preset time period X is extended to 500ms, and voltage data is collected again to perform curve fitting and steady-state voltage calculation. Until the number of fitting times reaches the preset upper limit, for example, the upper limit of the number of fitting times is set to 3 times. If the goodness of fit R 2 If it is still less than 0.99 (but not limited to 0.99), then starting from the moment of the last voltage collection, wait for 5RC time and collect a voltage value, and use the voltage value collected this time directly as the steady-state voltage to calculate the insulation resistance.

[0077] Furthermore, in one embodiment, the positive terminal insulation resistance Rp is calculated using the following formula:

[0078]

[0079] Among them, R p Indicates the insulation resistance of the positive terminal. 1,steady It represents the first steady-state voltage after the second switch S2 switches from on to off. 2,Steady It represents the second steady-state voltage after the second switch S2 switches from off to on. V pack,1,Steady It represents the total voltage of the battery pack Vpack after the second switch S2 switches from on to off. pack,2,Steady It indicates the total voltage of the battery pack Vpack after the second switch S2 is switched from off to on.

[0080] Among them, R a Represents the first resistor, R b represents the second resistor. Among them, R c represents the third resistor.

[0081] R a , R b , R c and R d It is a resistor in an insulating circuit. Its resistance value is not limited to the resistance value shown in the circuit diagram.

[0082] Furthermore, in one embodiment, the negative terminal insulation resistance Rn is calculated using the following formula:

[0083]

[0084] Among them, R n Indicates the insulation resistance of the negative terminal. 2,Steady It represents the second steady-state voltage after the second switch S2 switches from off to on. V pack,2,Steady It indicates the total voltage of the battery pack Vpack after the second switch S2 is switched from off to on. Among them, R a Represents the first resistor, R b represents the second resistor.

[0085] Among them, R c Represents the third resistor. R p Indicates the insulation resistance of the positive terminal.

[0086] Among them, R d represents the fourth resistor.

[0087] In the second aspect, the embodiment of the present application also provides an insulation resistance detection circuit for an automobile battery, the insulation resistance detection circuit includes a positive terminal insulation resistance, a negative terminal insulation resistance, a sampling circuit connected in parallel between the positive electrode of the battery pack Vpack and the negative electrode of the battery pack Vpack, a memory, a processor, and a detection program stored in the memory and executable on the processor. There is a communication interface and a communication bus between the memory and the processor.

[0088] The sampling circuit includes a first branch and a second branch connected in parallel. The first branch is provided with first to fourth resistors in sequence along the direction from the positive electrode of the battery pack Vpack to the negative electrode of the battery pack Vpack. The connection point of the second resistor Rb and the third resistor Rc is connected to the electrical ground a. A third branch is connected in parallel between the connection point of the first resistor Ra and the second resistor Rb and the negative electrode of the battery pack Vpack. A second switch S2 is provided on the third branch, and a plurality of second branch resistors are provided on the second branch.

[0089] The above-mentioned positive end insulation resistance Rp is connected between the positive pole of the battery pack Vpack and the electrical ground a of the insulation resistance detection circuit, and the above-mentioned negative end insulation resistance Rn is connected between the negative pole of the battery pack Vpack and the electrical ground a of the insulation resistance detection circuit. When the above-mentioned processor executes the above-mentioned detection program, it is the insulation resistance detection method of the above-mentioned automobile battery.

[0090] In this embodiment, by obtaining voltage data in a short period of time, it is first determined whether the difference between the last two voltages is small enough. If it is small enough, the voltage can be considered as the final steady-state voltage. Otherwise, the parameters in the preset function prototype are fitted based on the nonlinear least squares method to accurately predict the voltage when stable, and the fast detection function of insulation is realized on the basis of ensuring the calculation accuracy of the insulation value.

[0091] The communication bus may be of any type and is used to interconnect the processor, the memory, and the communication interface.

[0092] The communication interface includes an input / output (I / O) interface, a physical interface, and a logical interface, etc., which are used to interconnect the components inside the insulation resistance detection device of the automobile battery, and an interface used to interconnect the insulation resistance detection device of the automobile battery with other devices (such as other computing devices or user devices). The physical interface can be an Ethernet interface, an optical fiber interface, an ATM interface, etc. The user device can be a display, a keyboard, etc.

[0093] The memory can be various types of storage media, such as random access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), flash memory, optical storage, hard disk, programmable ROM (PROM), erasable PROM (EPROM), electrically erasable PROM (EEPROM), etc.

[0094] The processor may be a general-purpose processor, which may call the insulation resistance detection program of the automobile battery stored in the memory and execute the insulation resistance detection method of the automobile battery provided in the embodiment of the present application. For example, the general-purpose processor may be a central processing unit (CPU). The method executed when the insulation resistance detection program of the automobile battery is called may refer to the various embodiments of the insulation resistance detection method of the automobile battery of the present application, which will not be described in detail here.

[0095] Furthermore, in one embodiment, the difference between the sum of the resistance values ​​of the first resistor Ra and the second resistor Rb and the sum of the resistance values ​​of the third resistor Rc and the fourth resistor Rd does not exceed a set threshold.

[0096] The divided voltage of the fourth resistor Rd does not exceed the measuring range of the sampling device.

[0097] In this embodiment, the value of each resistor is based on the premise that when S1 and S2 are in different on and off states, and the positive and negative insulation resistances are large and small, the voltage division of Rd should not exceed the maximum range of the voltage sampling device.

[0098] It should be noted that the serial numbers of the above-mentioned embodiments of the present application are only for description and do not represent the advantages or disadvantages of the embodiments.

[0099] The terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned drawings are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally includes steps or units that are not listed, or optionally includes other steps or units inherent to these processes, methods, products or devices. The terms "first", "second" and "third" are used to distinguish different objects, etc., and do not represent a sequence, nor do they limit "first", "second" and "third" to different types.

[0100] In the description of the embodiments of the present application, "exemplary", "for example" or "for example" are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "exemplary", "for example" or "for example" in the embodiments of the present application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary", "for example" or "for example" is intended to present related concepts in a specific way.

[0101] In the description of the embodiments of the present application, unless otherwise specified, " / " means or, for example, A / B can mean A or B. "And / or" in the text is only a description of the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. In addition, in the description of the embodiments of the present application, "multiple" means two or more than two.

[0102] In some processes described in the embodiments of the present application, multiple operations or steps that appear in a specific order are included, but it should be understood that these operations or steps may not be executed in the order in which they appear in the embodiments of the present application or in parallel, and the sequence number of the operation is only used to distinguish the different operations, and the sequence number itself does not represent any execution order. In addition, these processes may include more or fewer operations, and these operations or steps may be executed in sequence or in parallel, and these operations or steps may be combined.

[0103] Through the description of the above implementation methods, those skilled in the art can clearly understand that the above-mentioned embodiment methods can be implemented by means of software plus a necessary general hardware platform, and of course by hardware, but in many cases the former is a better implementation method. Based on such an understanding, the technical solution of the present application is essentially or the part that contributes to the prior art can be embodied in the form of a software product, which is stored in a storage medium (such as ROM / RAM, disk, CD) as described above, and includes a number of instructions for a terminal device to execute the methods described in each embodiment of the present application.

[0104] The above are only preferred embodiments of the present application, and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. An insulation resistance detection method, applied to an insulation resistance detection circuit of an automobile battery, the insulation resistance detection circuit comprising a sampling circuit connected in parallel between a positive electrode of a battery pack and a negative electrode of a battery pack, the sampling circuit comprising a first branch and a second branch connected in parallel, the first branch having first to fourth resistors sequentially arranged along a direction from the positive electrode of the battery pack to the negative electrode of the battery pack, the connection point of the second resistor and the third resistor being connected to electrical ground, a third branch being connected in parallel between a connection point of the first resistor and the second resistor and the negative electrode of the battery pack, a second switch being arranged on the third branch, and a plurality of second branch resistors being arranged on the second branch, characterized in that: The insulation resistance detection method comprises: Taking the connection point of the third resistor and the fourth resistor as the sampling point, respectively obtaining a voltage sequence of the sampling point within a first preset time period after the second switch is switched from on to off and after the second switch is switched from off to on; for each voltage sequence, determining whether the difference between the last two voltages in the voltage sequence is less than a preset threshold value, if so, taking the last voltage as the steady-state voltage of the voltage sequence, if not, performing curve fitting according to the voltage sequence, and obtaining the steady-state voltage of the voltage sequence according to the fitted curve; The positive terminal insulation resistance and the negative terminal insulation resistance are calculated based on the steady-state voltages of the two voltage sequences.

2. The insulation resistance detection method according to claim 1, characterized in that: The method of performing curve fitting according to the voltage sequence and obtaining the steady-state voltage of the voltage sequence according to the fitted curve specifically includes the following steps: Perform curve fitting according to the voltage sequence and determine whether the curve fitting goodness meets expectations; If the goodness of fit reaches the expectation, the steady-state voltage of the voltage sequence is obtained according to the curve after this fitting; If the goodness of fit does not meet expectations, the voltage values ​​are continuously collected to update the voltage sequence, and the curve is fitted again according to the updated voltage sequence until the goodness of fit meets expectations to obtain the corresponding steady-state voltage, or until the number of fitting times reaches a preset upper limit.

3. The insulation resistance detection method according to claim 2, characterized in that: If the goodness of fit still does not meet expectations when the number of fitting times reaches the preset upper limit, the voltage value is collected again after waiting for a second preset time period and is used as the steady-state voltage to calculate the positive terminal insulation resistance and the negative terminal insulation resistance.

4. The insulation resistance detection method according to claim 3, characterized in that: The second preset time period is calculated using the following formula: T=kRC Among them, T represents the second preset time period, the unit is s; k is an integer not less than 5; R represents the designed insulation resistance of the battery pack, the unit is Ω; C represents the parasitic capacitance of the whole vehicle, the unit is F.

5. The insulation resistance detection method according to claim 1, characterized in that: The preset threshold is obtained by the following steps: Calculate a first difference between a first voltage and a second voltage in the voltage sequence, and a second difference between the second voltage and a third voltage; Determine whether the first difference exceeds a first threshold value, and a third difference between the first difference and the second difference exceeds a second threshold value, if so, set the preset threshold value within a first preset range, if not, set the preset threshold value within a second preset range; The upper limit value of the first preset range is smaller than the lower limit value of the second preset range.

6. The insulation resistance detection method according to claim 5, characterized in that: The first preset range is (0, 0.001], and the second preset range is (0.001, 0.005].

7. The insulation resistance detection method according to claim 1, characterized in that: The step of fitting according to the voltage sequence and obtaining the steady-state voltage according to the fitted curve specifically includes the following steps: Based on the following formula, the voltage series is curve-fitted using the nonlinear least squares method to obtain multiple parameters of the curve: Wherein, U represents the voltage in the voltage sequence; a1 represents the first parameter; a2 represents the second parameter; a3 represents the third parameter; t represents the sampling time of the voltage in the voltage sequence; e represents the natural constant; The following formula is used to process multiple parameters to obtain the steady-state voltage: U'=a1+a2 Wherein, U′ represents the steady-state voltage.

8. An insulation resistance detection circuit, characterized in that: The insulation resistance detection circuit includes a positive terminal insulation resistance, a negative terminal insulation resistance, a sampling circuit connected in parallel between the positive electrode of the battery pack and the negative electrode of the battery pack, a memory, a processor, and a detection program stored in the memory and executable on the processor; The sampling circuit comprises a first branch and a second branch connected in parallel, wherein the first branch is provided with first to fourth resistors in sequence along the direction from the positive electrode of the battery pack to the negative electrode of the battery pack, the connection point of the second resistor and the third resistor is connected to the electrical ground, a third branch is connected in parallel between the connection point of the first resistor and the second resistor and the negative electrode of the battery pack, a second switch is provided on the third branch, and a plurality of second branch resistors are provided on the second branch; The positive terminal insulation resistance is connected between the positive pole of the battery pack and the electrical ground of the insulation resistance detection circuit, and the negative terminal insulation resistance is connected between the negative pole of the battery pack and the electrical ground of the insulation resistance detection circuit. When the processor executes the detection program, it implements the insulation resistance detection method of the automotive battery as described in any one of claims 1-7.

9. The insulation resistance detection circuit according to claim 8, characterized in that: The difference between the sum of the resistance values ​​of the first resistor and the second resistor and the sum of the resistance values ​​of the third resistor and the fourth resistor does not exceed a set threshold; The divided voltage of the fourth resistor does not exceed the measuring range of the sampling device.

10. A battery management system, characterized in that: It comprises the insulation resistance detection circuit as claimed in claim 8.

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