Method for determining resistance parameters in pre-charge circuit and pre-charge circuit

Abstract

The application provides a resistance parameter determination method in a pre-charging circuit and a pre-charging circuit, and relates to the field of circuit electronics. The resistance parameter determination method comprises the following steps: obtaining a plurality of circuit correlation parameters of the pre-charging circuit; calculating a time constant of the pre-charging circuit according to a pre-charging time length and a maximum impact current allowed by the pre-charging circuit; substituting a power supply voltage, the maximum impact current and the time constant into a solving formula of a pre-charging resistor to deduce a resistance value of the pre-charging resistor; performing power checking and single-impact maximum energy checking on the pre-charging resistor to obtain a checking result; and in the case that the checking result indicates that the pre-charging resistor meets the charging and discharging requirements of the pre-charging circuit, taking the deduced resistance value of the pre-charging resistor as a resistance parameter of the pre-charging circuit. The application solves the technical problem of a small applicable range and a low resistance value of the pre-charging resistor in related technologies, which causes pre-charging failure.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and more specifically, to a method for determining resistance parameters in a pre-charging circuit and a pre-charging circuit. Background Technology

[0002] In modern electrical systems such as electric vehicles, energy storage systems, and high-voltage power equipment, the high-voltage DC bus often generates a huge transient inrush current at the moment of power-on due to the initial zero voltage of the large-capacity capacitor on the load side. This current may exceed the tolerance limits of power devices, relays, and connecting wires, causing safety hazards such as device damage, arcing, fuse malfunction, and even system failure. To suppress such inrush currents, the industry generally adopts pre-charging circuit technology, which involves connecting a pre-charging resistor in series in the main circuit. In related technologies, the resistance value of the pre-charging resistor mainly relies on traditional methods: the empirical formula method based on experimental data. This method relies on fitting an empirical formula with a large amount of measured data, which can quickly estimate the resistance range of the pre-charging resistor. However, this method of determining the resistance value has obvious drawbacks: its applicability is highly limited to specific voltage levels, capacitor capacity, and pre-charging time windows. In different application scenarios (such as 48V mild hybrid systems and 800V high-voltage platforms) or under new battery pack structures, the empirical formula often loses accuracy, and may even lead to pre-charging failure or resistor overheating and burning. Summary of the Invention

[0003] The main objective of this invention is to provide a method for determining the resistance parameters in a pre-charging circuit and a pre-charging circuit in order to solve the technical problems in related technologies where the applicable range is limited, the resistance value is low, and pre-charging fails when solving for the pre-charging resistance.

[0004] To achieve the above objectives, according to one aspect of the present invention, a method for determining the resistance parameter in a pre-charging circuit is provided, comprising: acquiring a plurality of circuit-related parameters of the pre-charging circuit, wherein the plurality of circuit-related parameters include at least: power supply voltage and load capacitance value; calculating the time constant of the pre-charging circuit based on the pre-charging duration and the maximum allowable inrush current of the pre-charging circuit, wherein the pre-charging duration refers to the time required for the capacitor voltage to rise from 0V to the target voltage; substituting the power supply voltage, the maximum inrush current, and the time constant into the formula for calculating the pre-charging resistance to derive the resistance value of the pre-charging resistance; performing power verification and maximum single-inrush energy verification on the pre-charging resistance to obtain a verification result; and, if the verification result indicates that the pre-charging resistance meets the charging and discharging requirements of the pre-charging circuit, using the derived resistance value of the pre-charging resistance as the resistance parameter of the pre-charging circuit.

[0005] Optionally, the step of obtaining multiple circuit-related parameters of the pre-charging circuit includes: reading the system design specifications of the pre-charging circuit to obtain the power supply voltage; measuring the load capacitance and inductance values ​​in the pre-charging circuit using a tester; and combining the power supply voltage, the load capacitance value, and the inductance value to obtain the multiple circuit-related parameters.

[0006] Optionally, before calculating the time constant of the pre-charging circuit based on the pre-charging duration and the maximum allowable inrush current of the pre-charging circuit, the method further includes: obtaining the total resistance of the pre-charging circuit, the peak current borne by the relay after closing, and the maximum surge current borne by the capacitor, wherein the total resistance of the pre-charging circuit includes: the line resistance and the equivalent series resistance of the load capacitor; calculating the maximum allowable inrush current of the pre-charging circuit based on the power supply voltage and the total resistance of the pre-charging circuit; and confirming that the maximum allowable inrush current of the pre-charging circuit meets the requirements if the maximum inrush current is less than the peak current borne by the relay after closing and the maximum surge current borne by the capacitor.

[0007] Optionally, before substituting the power supply voltage, the maximum inrush current, and the time constant into the solution formula for the pre-charging resistor to derive the resistance value, the method further includes: establishing the differential equation of the pre-charging circuit according to Kirchhoff's voltage law; performing a Laplace transform on the differential equation of the pre-charging circuit, solving the Laplace-transformed differential equation to obtain the time-domain expression of the current; performing an inverse Laplace transform on the time-domain expression of the current to obtain the current expression in the time domain; and determining the derivation formula for the pre-charging resistor by combining the current expression in the time domain, the inductance value of the pre-charging circuit, and the angular frequency.

[0008] Optionally, the differential equations of the pre-charging circuit include: ;

[0009] Where i is the pre-charge current, t is the pre-charge duration, L is the inductance value, R is the resistance, and C is the capacitance value. This refers to the power supply voltage.

[0010] Performing a Laplace transform on the differential equation of the pre-charging circuit yields the following formula: ;

[0011] Solving the differential equation after the Laplace transform, we obtain the time-domain expression for the current: .

[0012] Optionally, the formula for calculating the pre-charge resistance is: ,

[0013] Where R is the resistance value of the pre-charge resistor to be solved. This is the power supply voltage. The maximum impact current, is the time constant, and t is the precharge duration.

[0014] Optionally, the step of performing power verification and single-impact maximum energy verification on the pre-charge resistor to obtain verification results includes: calculating the square of the maximum impact current; calculating the power value of the pre-charge resistor based on the square of the maximum impact current and the resistance value of the pre-charge resistor; determining the power level of the pre-charge resistor based on the power value of the pre-charge resistor; verifying whether the power value is greater than the rated power threshold and whether the power level is higher than the preset power level threshold, to obtain a first verification result.

[0015] Optionally, the step of performing power verification and single-impact maximum energy verification on the pre-charge resistor to obtain the verification result further includes: calculating the single-impact maximum energy of the pre-charge circuit based on the maximum voltage of the battery pack in the pre-charge circuit and the load capacitance value; calculating the maximum impact energy that the pre-charge resistor can withstand in a single impact based on the specific heat capacity of the conductive material in the pre-charge circuit, the mass of the pre-charge resistor, and the maximum withstand temperature of the material; and determining that the thermal safety performance of the pre-charge resistor meets the requirements based on the comparison result between the single-impact maximum energy of the pre-charge circuit and the maximum impact energy that the pre-charge resistor can withstand in a single impact, thereby obtaining the second verification result.

[0016] According to another aspect of the present invention, a pre-charging circuit is provided, comprising: a battery pack including N individual batteries, where N is a positive integer; a pre-charging relay and a pre-charging resistor, wherein the pre-charging relay is connected to the battery pack and the pre-charging resistor is directly connected to the pre-charging relay; a positive relay connected in parallel with the pre-charging relay; a capacitor and a target load, wherein the capacitor and the target load are respectively connected to the positive relay; a negative relay connected to the capacitor and the target load; a fuse connected to the negative relay; and a main control unit for controlling the charging and discharging processes of the battery pack and executing the resistance parameter determination method in the pre-charging circuit described in any one of the above embodiments.

[0017] Optionally, the power-on process of the pre-charging circuit includes: closing the negative relay, then closing the pre-charging relay, keeping the positive relay in the open state, and starting pre-charging; after the pre-charging time has elapsed and the external capacitor is fully charged, confirming that the pre-charging is complete; opening the pre-charging relay, closing the positive relay, and powering on.

[0018] By applying the technical solution of this invention, the resistance value of the pre-charging resistor can be accurately derived through multiple circuit-related parameters, pre-charging time, and maximum inrush current. This transforms the design of the pre-charging resistor from empirical estimation to theoretical derivation, improving the controllability and reliability of the pre-charging process. It fully considers the inherent dynamic characteristics of the circuit, so that the calculation of the pre-charging resistor value no longer relies on manual fitting of empirical data, but is adaptively solved based on physical models and measured parameters. Furthermore, it performs power verification and single-inrush maximum energy verification on the pre-charging resistor, introducing a second-order dynamic system modeling and energy-power dual-dimensional verification mechanism to ensure that the selected resistor has sufficient energy tolerance. This avoids excessive current, resistor overheating failure, or bypassing before pre-charging is completed due to excessively low resistance values, fundamentally solving the pre-charging failure problem caused by low resistance values. This addresses the technical problem in related technologies where the application range is limited and low resistance values ​​lead to pre-charging failure when solving for the pre-charging resistor. Attached Figure Description

[0019] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0020] Figure 1 This is a flowchart of an optional method for determining resistance parameters in a pre-charging circuit according to an embodiment of the present invention; and

[0021] Figure 2 This is a schematic diagram of an optional pre-charging circuit according to an embodiment of the present invention. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0024] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0025] To facilitate understanding of the present invention by those skilled in the art, some terms or nouns involved in the various embodiments of the present invention are explained below:

[0026] Load capacitance, or C for short, is used to store electrical energy and absorb initial inrush current during pre-charging, stabilize bus voltage, and prevent voltage surges from damaging downstream devices.

[0027] A pre-charge resistor, or R for short, is connected in series in a high-voltage circuit to limit the inrush current at the moment of power-on, enabling slow charging and protecting relays, fuses, and electronic devices from overcurrent damage.

[0028] Supply voltage is the DC power supply voltage that provides energy to the high-voltage system. It is the driving source of the pre-charging circuit and determines the target charging level of the capacitor.

[0029] Inductance, or L for short, is composed of the parasitic inductance of the line or the external filter inductance. It affects the rise rate and oscillation characteristics of the pre-charge current and is one of the key parameters of a second-order dynamic system.

[0030] Kirchhoff's Voltage Law (KVL) is a fundamental law describing circuits in a closed loop where the algebraic sum of the voltages across all components is zero. It is used to establish differential equation models for pre-charged circuits.

[0031] The Laplace transform is used to convert time-domain differential equations into complex frequency-domain algebraic equations, simplifying the solution process for second-order circuits and facilitating the analysis of the system's dynamic response characteristics.

[0032] The inverse Laplace transform converts the complex frequency domain solution back to a time domain expression, which is used to obtain the exact functional form of the precharge current as a function of time.

[0033] This invention is applicable to various technical scenarios, including high-voltage power distribution systems for new energy vehicles and pre-charging circuits for DC bus in energy storage power stations. For example, in scenarios involving 800V high-voltage platforms for electric vehicles, fast-charging systems for battery packs, and power-on scenarios for on-board DC-DC converters, this invention can accurately calculate the pre-charging resistance value, effectively suppressing inrush current and preventing faults such as relay sticking, fuse mis-blowout, and capacitor breakdown. By introducing second-order dynamic system modeling and a dual-dimensional energy-power verification mechanism, this invention transforms pre-charging resistance design from empirical estimation to theoretical derivation, improving the controllability and reliability of the pre-charging process, shortening the system development cycle, reducing component selection redundancy, and enhancing the overall safety margin and service life of the high-voltage system.

[0034] This invention aims to propose a more efficient and accurate pre-charge resistance solution strategy by introducing innovative circuit models and mathematical relationships. This strategy not only significantly improves solution accuracy but also has broader applicability, applicable to different types of circuits and complex operating conditions. Furthermore, the method for determining resistance parameters in pre-charge circuits is of great significance for improving the overall performance and safety of circuit systems, particularly in fields such as electric vehicles and power equipment, where it can effectively reduce the risk of failures caused by high-voltage surges.

[0035] Figure 1 This is a flowchart of an optional method for determining resistance parameters in a pre-charging circuit according to an embodiment of the present invention, such as... Figure 1 As shown, the method for determining the resistance parameters in the pre-charging circuit includes steps S101 to S104. The present invention will be described in detail below with reference to each implementation step.

[0036] Step S101: Obtain multiple circuit-related parameters of the pre-charging circuit, wherein the multiple circuit-related parameters include at least: power supply voltage and load capacitance value.

[0037] It should be noted that the key to solving the pre-charge resistor lies in accurately determining the relevant circuit parameters, including the power supply voltage. capacitance value Inductance value Time constant and the initial resistance value of the pre-charge resistor These parameters can be obtained through experimental measurement or theoretical calculation. For example, the power supply voltage. The capacitance value is usually given by the system design specifications. and inductance value Then it is necessary to perform accurate measurements using a testing instrument.

[0038] Optionally, the step of obtaining multiple circuit-related parameters of the pre-charging circuit includes: reading the system design specifications of the pre-charging circuit to obtain the power supply voltage; measuring the load capacitance and inductance values ​​in the pre-charging circuit using a tester; and combining the power supply voltage, load capacitance, and inductance values ​​to obtain multiple circuit-related parameters.

[0039] The system design specifications are derived from the architecture definition document of the high-voltage power distribution system, clearly specifying the maximum output voltage range of the battery pack. This voltage value serves as the driving source for the pre-charging circuit and is used as the input excitation for the subsequent dynamic model. Then, a tester is used to measure the load capacitance and inductance values ​​in the pre-charging circuit. For example, an LCR meter (an electronic measuring instrument used to accurately measure the inductance, capacitance, and resistance parameters of electronic components) is used to perform an impedance scan of the load capacitance under low excitation signal conditions to obtain its equivalent capacitance value within the operating frequency range. Simultaneously, a network analyzer or inductance testing module is used to independently measure the parasitic inductance and external filter inductance in the circuit. This measurement method effectively separates the actual component parameters from theoretical estimation errors, allowing for a closer approximation of the dynamic response characteristics of the actual circuit.

[0040] Substituting the measured and read parameters into the second-order differential equation model, intermediate variables such as time constant, damping coefficient, and characteristic frequency can be derived. These parameters together constitute the input set required for solving the pre-charge resistance, which helps to improve the physical consistency and numerical stability of subsequent resistance calculations.

[0041] It should be noted that before calculating the time constant of the pre-charging circuit, the pre-charging duration and the maximum current value need to be determined.

[0042] First, it explains how to calculate the maximum current. Optionally, before calculating the time constant of the pre-charging circuit based on the pre-charging time and the maximum allowable inrush current of the pre-charging circuit, it also includes: obtaining the total resistance of the pre-charging circuit, the peak current borne by the relay after closing, and the maximum surge current borne by the capacitor. The total resistance of the pre-charging circuit includes the line resistance and the equivalent series resistance of the load capacitor. The maximum allowable inrush current of the pre-charging circuit is calculated based on the power supply voltage and the total resistance of the pre-charging circuit. If the maximum inrush current is less than the peak current borne by the relay after closing and the maximum surge current borne by the capacitor, it is confirmed that the maximum allowable inrush current of the pre-charging circuit meets the requirements.

[0043] The line resistance is determined by the conductor material, cross-sectional area, and trace length, and can be measured using a DC resistance meter. The equivalent series resistance of the load capacitor is determined by the internal material and structural characteristics of the capacitor, and can be extracted using an impedance analyzer at the operating frequency. The sum of these two resistances forms the total series resistance of the pre-charge circuit, which helps to construct a more realistic current decay model. According to Ohm's law, at the instant the capacitor's initial voltage is zero, the maximum inrush current can be estimated by the ratio of the power supply voltage to the total resistance. This value serves as the upper limit benchmark for pre-charge resistance design, providing physical boundary conditions for subsequent parameter constraints and helping to avoid device stress risks caused by current exceeding limits.

[0044] For example, the maximum current can be calculated using the following formula:

[0045] ;

[0046] in: : Battery pack voltage (e.g., 400V or 800V); The total resistance of the pre-charge circuit is mainly composed of the line resistance and the equivalent series resistance of the capacitor, typically in the milliohm range.

[0047] If the maximum inrush current is less than the peak current that the relay can withstand after closing and the maximum surge current that the capacitor can withstand, the maximum allowable inrush current of the pre-charging circuit is confirmed to meet the requirements. The peak current withstand capability of the relay is defined by its contact material and arc-extinguishing structure. The maximum surge current limit of the capacitor comes from the thermomechanical withstand limit of its internal polarization layer and internal connections. When the calculated maximum inrush current is lower than the rated threshold of the above two devices, it indicates that the current pre-charging parameters are compatible in the current dimension and can be used as a prerequisite verification condition for entering the time constant calculation stage.

[0048] In addition, the precharge time refers to the time required for the capacitor voltage to rise from 0V to the target voltage (e.g., 90%-95% of the battery voltage). Under the premise of ensuring safety, the precharge time should be shortened as much as possible.

[0049] Alternatively, the time constant τ = R × C can be used for quick estimation: charging to 95% voltage requires approximately 3 times the time constant (τ ≈ 3RC); charging to 99% voltage requires approximately 5 times the time constant (τ ≈ 5RC). Here, τ is the time constant, R is the initial resistance value, and C is the capacitance value at the load terminal.

[0050] It should be noted that the pre-charge time limit needs to be balanced between protecting the hardware and the user experience. If it is too fast (t is too small): the resistance value R needs to be very small, resulting in a large maximum current, which may burn out the relay; if it is too slow (i.e., t is too large): the user has to wait too long, resulting in a poor experience.

[0051] Step S102: Calculate the time constant of the pre-charging circuit based on the pre-charging time and the maximum allowable inrush current of the pre-charging circuit. The pre-charging time refers to the time required for the capacitor voltage to rise from 0V to the target voltage.

[0052] Optionally, before substituting the power supply voltage, maximum inrush current, and time constant into the solution formula for the pre-charging resistor to derive its resistance value, the following steps are also included: establishing the differential equation of the pre-charging circuit based on Kirchhoff's voltage law; performing a Laplace transform on the differential equation of the pre-charging circuit, solving the transformed differential equation to obtain the time-domain expression of the current; performing an inverse Laplace transform on the time-domain expression of the current to obtain the current expression in the time domain; and combining the time-domain current expression, the inductance value of the pre-charging circuit, and the angular frequency to determine the derivation formula for the pre-charging resistor.

[0053] Step S103: Substitute the power supply voltage, maximum inrush current, and time constant into the formula for calculating the pre-charge resistor to derive the resistance value of the pre-charge resistor.

[0054] First, based on Kirchhoff's voltage law, establish the differential equation for the pre-charge circuit:

[0055] ;

[0056] in, For pre-charging current, Taking time as the time term, after performing a Laplace transform on the differential equation, we obtain:

[0057]

[0058] Solve for the current The expression is:

[0059] ;

[0060] The inverse Laplace transform yields the current expression in the time domain. Further analysis reveals that the pre-charge resistance... The following conditions must be met:

[0061] ;

[0062] in, It is the angular frequency, determined by the circuit characteristics. This is combined with the time constant. By defining the pre-charge resistance, we can finally obtain the formula for solving the pre-charge resistance:

[0063]

[0064] in, This is the maximum value of the pre-charge current. Pre-charge duration.

[0065] Using the formula derived above, the resistance value of the pre-charge resistor can be calculated step by step. First, determine the power supply voltage according to the system design specifications. and capacitance value The inductance value was obtained through experimental measurement. Secondly, based on the pre-charge time and maximum current Calculate the time constant Finally, substitute each parameter into the formula. The resistance value of the pre-charge resistor can then be obtained.

[0066] It should be noted that the theoretical basis of the method for determining the resistance parameters in the pre-charging circuit provided by this invention mainly comes from Kirchhoff's laws, Ohm's law, and the law of conservation of energy in circuit theory. Specifically, in the pre-charging circuit, Kirchhoff's voltage law (KVL) and current law (KCL) are used to analyze the dynamic behavior of the circuit, while Ohm's law provides the basic relationship between resistance, voltage, and current. The solution theory of second-order linear non-homogeneous differential equations is used to describe the dynamic response process of the pre-charging circuit. By defining and solving the circuit state variables, a set of mathematical expressions characterizing the pre-charging resistance properties can be derived.

[0067] Step S104: Perform power verification and single-impact maximum energy verification on the pre-charge resistor to obtain the verification results.

[0068] Optionally, the steps of performing power verification and single-impact maximum energy verification on the pre-charge resistor to obtain the verification results include: calculating the square of the maximum impact current; calculating the power value of the pre-charge resistor based on the square of the maximum impact current and the resistance value of the pre-charge resistor; determining the power level of the pre-charge resistor based on the power value of the pre-charge resistor; verifying whether the power value is greater than the rated power threshold and whether the power level is higher than the preset power level threshold, and obtaining the first verification result.

[0069] The maximum inrush current is derived from the ratio of the power supply voltage to the total impedance of the pre-charging circuit. Its square reflects the intensity of thermal stress borne by the resistor during the transient process, and this value can be used as the input basis for power calculation. Then, according to Joule's law, the power value is the product of the square of the current and the resistance. This calculation result characterizes the heat power instantaneously dissipated by the resistor during the pre-charging process, and can be used to evaluate the temperature rise trend of the resistor material under short-term high load, assisting in matching heat dissipation design and selection boundaries.

[0070] The power rating is determined by the nominal rated power parameter of the resistor. Based on the calculated instantaneous power value, a resistor model with a corresponding range can be selected. For example, a higher-than-calculated option can be chosen from standard ratings such as 1W, 2W, and 5W. This helps avoid material degradation or failure due to insufficient power matching. When the calculated power value is close to or exceeds the resistor's rated power threshold, it may cause localized overheating. If the selected power rating is not higher than the preset threshold, it may not be able to cover the accumulated heat buildup over multiple pre-charge cycles. This dual verification allows for an initial screening based on power rating.

[0071] In practical applications, the power rating of the pre-charge resistor must also be considered. To ensure the stability of the resistor under high power conditions, it is recommended to select a resistor with a rated power greater than the calculated value. The power rating of the pre-charge resistor... Through formula Calculated.

[0072] The following explains the maximum energy verification for a single impact.

[0073] Optionally, the steps of performing power verification and single-impact maximum energy verification on the pre-charge resistor to obtain the verification results further include: calculating the single-impact maximum energy of the pre-charge circuit based on the maximum voltage of the battery pack and the load capacitance value in the pre-charge circuit; calculating the maximum impact energy that the pre-charge resistor can withstand in a single impact based on the specific heat capacity of the conductive material in the pre-charge circuit, the mass of the pre-charge resistor, and the maximum withstand temperature of the material; and determining that the thermal safety performance of the pre-charge resistor meets the requirements based on the comparison between the single-impact maximum energy of the pre-charge circuit and the maximum impact energy that the pre-charge resistor can withstand in a single impact, thereby obtaining the second verification result.

[0074] For example, the formula for calculating the maximum energy of a single impact is:

[0075] ;

[0076] In the formula, The maximum energy of a single impact designed for this purpose. - Maximum battery pack voltage, C- Load capacitance value;

[0077] The formula for calculating the maximum impact energy that the selected pre-charge resistor can withstand in a single event is:

[0078]

[0079] In the formula: The maximum impact energy that can be withstood in a single event; c is the specific heat capacity of the conductive material (such as alloy wire); m is the mass. This is the highest temperature that the material can withstand.

[0080] In this embodiment, the maximum impact energy that the pre-charge resistor can withstand in a single pulse can be calculated based on the specific heat capacity of the conductive material in the pre-charge circuit, the mass of the pre-charge resistor, and the maximum withstand temperature of the material. Specific heat capacity characterizes the heat required for the material to heat up, mass determines the heat capacity, and the maximum withstand temperature reflects the thermal stability boundary of the material. These three factors together constitute the upper limit of the resistor's thermal absorption, which can be used to evaluate its temperature rise response capability under a single pulse energy. When the energy demand of the pre-charge circuit does not exceed the heat carrying capacity of the resistor material, it indicates that the resistor has the physical basis to withstand the impact at the thermodynamic level. This helps to form an independent verification of the energy dimension and assists in screening resistive components with sufficient thermal redundancy.

[0081] Step S105: If the verification result indicates that the pre-charging resistor meets the charging and discharging requirements of the pre-charging circuit, the derived resistance value of the pre-charging resistor is used as the resistance parameter of the pre-charging circuit.

[0082] By applying the technical solution of this invention, the resistance value of the pre-charging resistor can be accurately derived through multiple circuit-related parameters, pre-charging time, and maximum inrush current. This transforms the design of the pre-charging resistor from empirical estimation to theoretical derivation, improving the controllability and reliability of the pre-charging process. It fully considers the inherent dynamic characteristics of the circuit, so that the calculation of the pre-charging resistor value no longer relies on manual fitting of empirical data, but is adaptively solved based on physical models and measured parameters. Furthermore, it performs power verification and single-inrush maximum energy verification on the pre-charging resistor, introducing a second-order dynamic system modeling and energy-power dual-dimensional verification mechanism to ensure that the selected resistor has sufficient energy tolerance. This avoids excessive current, resistor overheating failure, or bypassing before pre-charging is completed due to excessively low resistance values, fundamentally solving the pre-charging failure problem caused by low resistance values. This addresses the technical problem in related technologies where the application range is limited and low resistance values ​​lead to pre-charging failure when solving for the pre-charging resistor.

[0083] According to another aspect of the present invention, a pre-charging circuit is also provided, comprising: a battery pack including N individual cells, where N is a positive integer; a pre-charging relay and a pre-charging resistor, wherein the pre-charging relay is connected to the battery pack and the pre-charging resistor is directly connected to the pre-charging relay; a positive relay connected in parallel with the pre-charging relay; a capacitor and a target load, wherein the capacitor and the target load are respectively connected to the positive relay; a negative relay connected to the capacitor and the target load; a fuse connected to the negative relay; and a main control unit for controlling the charging and discharging processes of the battery pack and executing the resistance parameter determination method in the pre-charging circuit of any of the above embodiments.

[0084] Figure 2 This is a schematic diagram of an optional pre-charging circuit according to an embodiment of the present invention, such as... Figure 2As shown, the pre-charging circuit includes: S1 - pre-charging relay; S2 - positive relay; S3 - negative relay; C - load capacitor; M - load; F1 - fuse; MCU - main control chip; AFE - BMS analog front-end chip (acquisition chip); R - pre-charging resistor.

[0085] Optionally, the power-on process of the pre-charging circuit includes: closing the negative relay, then closing the pre-charging relay, keeping the positive relay in the open state, and starting pre-charging; after the pre-charging time has elapsed and the external capacitor is fully charged, confirming that the pre-charging is complete; opening the pre-charging relay, closing the positive relay, and powering on.

[0086] like Figure 2 The high-voltage power-on procedure is as follows: First, close the negative relay S3, then close the pre-charge relay S1, and open the positive relay S2 to start pre-charging; after time t, the external capacitor is fully charged, and the pre-charging is completed. At this time, open the pre-charge relay S1 and close the positive relay S2 to start power-on.

[0087] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects: by constructing a second-order dynamic circuit model including power supply voltage, inductance, capacitance and time constant, and deriving the theoretical solution formula for the pre-charge resistor by combining Laplace transform and inverse transform, the transformation from empirical estimation to physical modeling-driven is realized, so that the calculation process of the pre-charge resistor value is coupled with the actual dynamic response characteristics of the circuit, which helps to improve the accuracy and consistency of the resistance value selection, no longer relying on empirical formulas for specific voltage levels or capacitance ranges, can adapt to more load capacitance ranges, and expand the applicable boundaries of pre-charge resistor design.

[0088] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects: By introducing a time constant calculation mechanism based on the maximum impact current and pre-charge time, and simultaneously performing dual verification of power and single-impact energy, the resistor selection simultaneously meets the constraints of instantaneous thermal power and cumulative thermal energy, helping to avoid current overruns due to excessively low resistance or material thermal failure due to insufficient energy tolerance. The power verification is based on Joule's law to calculate instantaneous dissipation power, while the energy verification is based on deriving the tolerance limit from the material's thermodynamic parameters. These two verifications complement each other, reducing device selection redundancy and improving design efficiency.

[0089] In the description of this invention, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is generally based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this invention; the directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0090] For ease of description, spatial relative terms such as "above," "on top of," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation beyond the orientation of the device as described in the figures. For example, if the device in the figures were inverted, a device described as "above" or "on top of" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0091] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0092] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for determining resistance parameters in a pre-charging circuit, characterized in that, include: Obtain multiple circuit-related parameters of the pre-charging circuit, wherein the multiple circuit-related parameters include at least: power supply voltage and load capacitance value; The time constant of the pre-charging circuit is calculated based on the pre-charging time and the maximum allowable inrush current of the pre-charging circuit. The pre-charging time refers to the time required for the capacitor voltage to rise from 0V to the target voltage. Substituting the power supply voltage, the maximum inrush current, and the time constant into the formula for calculating the pre-charging resistor, the resistance value of the pre-charging resistor is derived. The power and maximum energy of a single impact are checked on the pre-charge resistor to obtain the check results. If the verification result indicates that the pre-charging resistor meets the charging and discharging requirements of the pre-charging circuit, the derived resistance value of the pre-charging resistor shall be used as the resistance parameter of the pre-charging circuit.

2. The method for determining the resistance parameters in the pre-charging circuit according to claim 1, characterized in that, The step of obtaining multiple circuit-related parameters of the pre-charging circuit includes: The power supply voltage is obtained by reading the system design specifications of the pre-charging circuit; The load capacitance and inductance values ​​in the pre-charging circuit were measured using a tester. By combining the power supply voltage, the load capacitance value, and the inductance value, the multiple circuit-related parameters are obtained.

3. The method for determining the resistance parameters in the pre-charging circuit according to claim 1, characterized in that, Before calculating the time constant of the pre-charging circuit based on the pre-charging duration and the maximum allowable inrush current of the pre-charging circuit, the following steps are also included: The total resistance of the pre-charging circuit, the peak current borne by the relay after closing, and the maximum surge current borne by the capacitor are obtained. The total resistance of the pre-charging circuit includes the line resistance and the equivalent series resistance of the load capacitor. The maximum allowable inrush current of the pre-charging circuit is calculated based on the power supply voltage and the total resistance of the pre-charging circuit. If the maximum inrush current is less than the peak current that the relay withstands after closing and the maximum surge current that the capacitor withstands, then the maximum allowable inrush current of the pre-charging circuit is confirmed to meet the requirements.

4. The method for determining the resistance parameters in the pre-charging circuit according to claim 1, characterized in that, Before substituting the power supply voltage, the maximum inrush current, and the time constant into the formula for calculating the pre-charging resistor to derive its value, the following steps are also included: Based on Kirchhoff's voltage law, establish the differential equation for the pre-charge circuit; The differential equation of the pre-charging circuit is subjected to a Laplace transform, and the Laplace transform differential equation is solved to obtain the time-domain expression of the current. The time-domain expression of the current is subjected to an inverse Laplace transform to obtain the current expression in the time domain; By combining the current expression in the time domain, the inductance value of the pre-charging circuit, and the angular frequency, the derivation formula for the pre-charging resistance is determined.

5. The method for determining the resistance parameters in the pre-charging circuit according to claim 4, characterized in that, The differential equations of the pre-charge circuit include: ； Where i is the pre-charge current, t is the pre-charge duration, L is the inductance value, R is the resistance, and C is the capacitance value. This refers to the power supply voltage. Performing a Laplace transform on the differential equation of the pre-charging circuit yields the following formula: ； Solving the differential equation after the Laplace transform, we obtain the time-domain expression for the current: .

6. The method for determining the resistance parameters in the pre-charging circuit according to any one of claims 1 to 5, characterized in that, The formula for solving the pre-charge resistance is: Where R is the resistance value of the pre-charge resistor to be solved. This is the power supply voltage. The maximum impact current, is the time constant, and t is the precharge duration.

7. The method for determining the resistance parameters in the pre-charging circuit according to claim 1, characterized in that, The steps for performing power verification and single-impact maximum energy verification on the pre-charge resistor to obtain the verification results include: Calculate the square of the maximum impact current; The power value of the pre-charging resistor is calculated based on the square of the maximum inrush current and the resistance value of the pre-charging resistor. The power rating of the pre-charge resistor is determined based on its power value. The power value is verified to be greater than the rated power threshold, and the power level is higher than the preset power level threshold, to obtain the first verification result.

8. The method for determining the resistance parameters in the pre-charging circuit according to claim 1, characterized in that, The steps of performing power verification and single-impact maximum energy verification on the pre-charge resistor to obtain the verification results further include: The maximum single-impact energy of the pre-charging circuit is calculated based on the maximum voltage of the battery pack in the pre-charging circuit and the load capacitance value. Based on the specific heat capacity of the conductive material in the pre-charging circuit, the mass of the pre-charging resistor, and the highest withstand temperature of the material, calculate the maximum impact energy that the pre-charging resistor can withstand in a single event. Based on the comparison between the maximum single impact energy of the pre-charging circuit and the maximum single impact energy that the pre-charging resistor can withstand, it is determined that the thermal safety performance of the pre-charging resistor meets the requirements, and the second verification result is obtained.

9. A pre-charging circuit, characterized in that, include: A battery pack consists of N individual batteries, where N is a positive integer. A pre-charge relay and a pre-charge resistor, wherein the pre-charge relay is connected to the battery pack, and the pre-charge resistor is directly connected to the pre-charge relay; The positive relay is connected in parallel with the precharge relay; A capacitor and a target load are respectively connected to the positive relay; A negative relay is connected to the capacitor and the target load. A fuse is connected to the negative relay; The main control unit is used to control the charging and discharging processes of the battery pack and to execute the method for determining the resistance parameters in the pre-charging circuit as described in any one of claims 1 to 8.

10. The pre-charging circuit according to claim 9, characterized in that, The power-on process of the pre-charging circuit includes: Close the negative relay, then close the pre-charge relay, keeping the positive relay in the open state, and begin pre-charging; After the pre-charging time has elapsed and the external capacitor is fully charged, the pre-charging is confirmed to be complete. Disconnect the pre-charge relay and close the positive relay to power on.

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