Method for calculating health degree of lead-acid storage battery

Abstract

The invention provides a health degree calculation method of a lead-acid storage battery. S1, constructing an equivalent circuit model of the lead-acid storage battery; s2, ohm internal resistance, polarization internal resistance and polarization capacitance of the equivalent circuit model are obtained; s3, determining an open-circuit voltage value of the lead-acid storage battery in real time according to the ohmic internal resistance, the polarization internal resistance and the polarization capacitance; s4, determining the state of charge of the lead-acid storage battery according to the open-circuit voltage value; s5, determining the health degree of the lead-acid storage battery according to the charge state; according to the method, the accuracy of the obtained open-circuit voltage value can be improved, and then the accuracy of the calculated state of charge and the accuracy of health degree calculation are improved.

Description

Technical Field

[0001] The present invention relates to the field of health estimation of a lead-acid battery, and in particular to a method for calculating the health of a lead-acid battery. Background Art

[0002] An important test item in the lead-acid battery health status detection system is the battery SOC, and SOC is also the basis for calculating the lead-acid battery SOH. The open circuit voltage method is a more practical SOC estimation algorithm; although the open circuit voltage method can obtain the battery SOC, this method requires the battery to be left at rest before measuring the voltage value. If the rest time is too long, the presence of self-discharge will cause the measured open circuit voltage value to be less than the voltage value at the stop time, resulting in inaccurate SOC estimation, and then inaccurate SOH estimation.

[0003] Therefore, in order to solve the above technical problems, it is urgent to propose a new technical means. Summary of the invention

[0004] In view of this, in order to obtain a more accurate open circuit voltage value and improve the accuracy of the calculated SOC and SOH, the present invention proposes a method for calculating the health of a lead-acid battery.

[0005] A method for calculating the health of a lead-acid battery proposed by the present invention comprises the following steps:

[0006] S1. Construct an equivalent circuit model of a lead-acid battery;

[0007] S2. Obtaining the ohmic internal resistance, polarization internal resistance and polarization capacitance of the equivalent circuit model;

[0008] S3. Determine the open circuit voltage value of the lead-acid battery in real time according to the ohmic internal resistance, polarization internal resistance and polarization capacitance;

[0009] S4. Determine the state of charge of the lead-acid battery according to the open circuit voltage value;

[0010] S5. Determine the health of the lead-acid battery according to the state of charge.

[0011] Further, the state of charge of the lead-acid battery is determined by the following method:

[0012]

[0013] Wherein, SOC represents the state of charge of the lead-acid battery, a represents the minimum open circuit voltage value of the lead-acid battery after it is fully discharged, b represents the proportionality coefficient, and U oc Indicates the open circuit voltage value of the lead-acid battery.

[0014] Furthermore, the open circuit voltage value U of the lead-acid battery oc Determined by:

[0015]

[0016] Among them, U oc (k), U(k) and I(k) represent the open circuit voltage, terminal voltage and current at time k respectively, U(k-1), U oc (k-1) and I(k-1) represent the terminal voltage value, open circuit voltage value and current value at time k-1 respectively, e represents a natural constant, T represents a sampling period, R0 represents an ohmic internal resistance, R1 represents a polarization internal resistance, and C1 represents a polarization capacitance.

[0017] Furthermore, in step S1, the equivalent circuit model adopts the Thevenin model.

[0018] Furthermore, the health of the lead-acid battery is calculated by the following formula:

[0019]

[0020] Among them, SOH represents the health of the lead-acid battery, Q 放 Indicates the amount of electricity released by a lead-acid battery at a standard discharge current in the standard discharge mode, Q 额 The rated capacity of the lead-acid battery, SOC 初 Indicates the state of charge of the lead-acid battery when it starts to discharge, SOC 末 Indicates the charge state of the lead-acid battery after discharge.

[0021] Beneficial effects of the present invention: The present invention can avoid the actual open circuit voltage value caused by self-discharge being greater than the measured open circuit voltage value by obtaining the open circuit voltage value in real time. In addition, there is a stable linear relationship between the open circuit voltage value and the state of charge. Determining the state of charge by the open circuit voltage value can improve the accuracy of the calculated state of charge, thereby improving the accuracy of the health calculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0023] Figure 1 It is a flow chart of the present invention.

[0024] Figure 2 It is the equivalent circuit model of lead-acid battery. DETAILED DESCRIPTION

[0025] The present invention is further described below in conjunction with the accompanying drawings:

[0026] A method for calculating the health of a lead-acid battery proposed by the present invention comprises the following steps:

[0027] S1. Construct an equivalent circuit model of a lead-acid battery;

[0028] S2. Obtaining the ohmic internal resistance, polarization internal resistance and polarization capacitance of the equivalent circuit model;

[0029] S3. Determine the open circuit voltage value of the lead-acid battery in real time according to the ohmic internal resistance, polarization internal resistance and polarization capacitance;

[0030] S4. Determine the state of charge of the lead-acid battery according to the open circuit voltage value;

[0031] S5. Determine the health of the lead-acid battery according to the state of charge. The above method can improve the accuracy of the determined health of the lead-acid battery.

[0032] In this embodiment, in step S1, an equivalent circuit model of a lead-acid battery is constructed;

[0033] The equivalent circuit model is a circuit model established based on the discharge characteristics of the battery. Compared with the chemical model, the equivalent circuit model has the characteristics of small calculation amount, easy parameter identification, high accuracy, etc. It is also easy to implement and integrate with embedded systems. The main equivalent circuit models include Rint (internal resistance) model, Thevenin (Thevenin) model, PNGV model and GNL model.

[0034] The Rint (internal resistance) model is an elementary model of the battery and is also the most idealized circuit model. It has only two electronic devices, the ideal voltage source E0 and the internal resistance R0. The model has a simple structure and can reflect the instantaneous change of the terminal voltage when the battery is loaded and unloaded. This model is easy to implement when modeling and simulating, and has strong versatility. However, the shortcomings of this model are also obvious. First, the polarization process of the battery in actual work is not taken into account. Therefore, in the initial period when the battery discharge current changes, the model has a large error. Secondly, the constant resistance value cannot reflect the changes in the battery internal resistance caused by factors such as the battery's SOC and temperature.

[0035] In the PNGV model, during the battery charging and discharging process, the capacitor C changes with the charge. The change in the charge in the battery causes the change in SOC. Each parameter will change with the change in the battery's SOC and temperature. The parameter identification is complex, not suitable for real-time estimation of SOC, and has poor practicality.

[0036] The GNL models can well reflect the dynamic characteristics of the battery with high accuracy, but their parameter identification process is complicated and is not suitable for this application.

[0037] Thevenin model circuit is as follows Figure 2 As shown, the model includes a polarization link composed of RC parallel connection. Due to the existence of polarization capacitor, it can simulate the dynamic characteristics of the battery. The model can better simulate the charging and discharging process of the battery; therefore, the equivalent circuit model of the lead-acid battery adopts the Thevenin model.

[0038] In this embodiment, in step S2, the ohmic internal resistance, polarization internal resistance and polarization capacitance of the equivalent circuit model are obtained; although there are many methods to obtain these three parameters, these three parameters are not constant in a complete charge and discharge cycle of the battery, and the parameters change with the change of the battery charge state. Therefore, the three parameters should be analyzed at different charge states respectively; the experimental scheme should be reasonably designed to fully reflect all the performance of the lead-acid battery, so as to obtain the parameters required for the battery model; therefore, it is preferred to use hybrid pulse power characteristics (Hybrid Pulse Power Characterization, HPPC) for parameter identification; the method of using the hybrid pulse power characteristics method to identify the ohmic internal resistance, polarization internal resistance and polarization capacitance is a prior art, and the specific acquisition process will not be repeated here; the three parameters can also be obtained by recursive least squares method and dynamic simulation method, which are not limited here.

[0039] In this embodiment, in step S3, the open circuit voltage value of the lead-acid battery is determined in real time according to the ohmic internal resistance, polarization internal resistance and polarization capacitance;

[0040] The open circuit voltage value U of the lead-acid battery oc Determined by:

[0041]

[0042] Among them, U oc (k), U(k) and I(k) represent the open circuit voltage, terminal voltage and current at time k respectively, U(k-1), U oc (k-1) and I(k-1) represent the terminal voltage value, open circuit voltage value and current value at time k-1 respectively, e represents a natural constant, T represents a sampling period, R0 represents an ohmic internal resistance, R1 represents a polarization internal resistance, and C1 represents a polarization capacitance.

[0043] Both the terminal voltage value and the current value can be measured by the sensor. Therefore, as long as the initial value of the open circuit voltage, as well as the ohmic internal resistance, polarization internal resistance and polarization capacitance are known, the open circuit voltage value can be predicted in real time. The traditional method of measuring the open circuit voltage requires the battery to be left to stand before measuring the voltage value. If the standing time is too long, the presence of self-discharge will cause the measured open circuit voltage value to be less than the voltage value at the stop time, making the measurement inaccurate. The above method can be used to measure the open circuit voltage in real time and improve the accuracy of the open circuit voltage value.

[0044] In this embodiment, in step S4, the state of charge of the lead-acid battery is determined according to the open circuit voltage value;

[0045] The open circuit voltage values ​​at different states of charge are measured by the static method, and the state of charge data and the open circuit voltage value are fitted to obtain the state of charge calculation formula of the lead-acid battery:

[0046]

[0047] Wherein, SOC represents the state of charge of the lead-acid battery, a represents the minimum open circuit voltage value of the lead-acid battery after it is fully discharged, b represents the proportionality coefficient, and U oc Indicates the open circuit voltage value of the lead-acid battery.

[0048] The steps to obtain the charge state calculation formula of the lead-acid battery by the static method are as follows:

[0049] SC1. At room temperature, fully charge the lead-acid battery and let it stand for half an hour. Measure the terminal voltage of the battery at this time. The voltage value obtained is the open circuit voltage value when SOC = 100%;

[0050] SC2. Use 15A (0.1C) current to discharge the battery at a constant current for 1h, and the amount of electricity discharged is 15Ah. At this moment, SOC = 90%. Same as in step 1, let the battery stand for half an hour and measure the voltage across it;

[0051] SC3. Fully charge the battery using the method in step 1, discharge at a constant current of 15A for 2 hours, and let it stand for half an hour. Measure the open circuit voltage value when the SOC is 80%;

[0052] SC4. Repeat the above steps to measure the open circuit voltage values ​​when SOC is 70% to 0%.

[0053] Take the average value of multiple measurements at each point;

[0054] SC5. Use the data fitting tool to fit the open circuit voltage value and the state of charge data, and obtain the state of charge calculation formula of the lead-acid battery:

[0055]

[0056] Among them, 11.3502 is the minimum open circuit voltage value of the lead-acid battery after it is fully discharged, and 0.0158 is the proportional coefficient.

[0057] There is a stable linear relationship between the open circuit voltage and the state of charge. If the battery is not frequently deeply discharged, the relationship between its open circuit voltage and SOC will not change for a long time; therefore, the state of charge determined based on the open circuit voltage is more accurate.

[0058] In this embodiment, in step S5, the health of the lead-acid battery is determined according to the state of charge;

[0059] The health of the lead-acid battery is calculated by the following formula:

[0060]

[0061] Among them, SOH represents the health of the lead-acid battery, Q 放 Indicates the amount of electricity released by a lead-acid battery at a standard discharge current in the standard discharge mode, Q 额 The rated capacity of the lead-acid battery, SOC 初 Indicates the state of charge of the lead-acid battery when it starts to discharge, SOC 末 Indicates the state of charge of the lead-acid battery after discharge, SOC 初 and SOC 末 It can be calculated based on the open circuit voltage value at different times. 放 It can be determined through the efficiency ratio model, because the efficiency ratio model can restore the discharge amount within a period of time to the discharge amount under the standard state; it can also calculate the actual capacity under the standard state. This is a prior art and will not be described in detail here.

[0062] The above method can evaluate the health of the battery more intuitively and accurately by comparing the current performance of the battery with the initial performance.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for calculating the health of a lead-acid battery, characterized in that: The steps include: S1. Construct an equivalent circuit model of a lead-acid battery; S2. Obtaining the ohmic internal resistance, polarization internal resistance and polarization capacitance of the equivalent circuit model; S3. Determine the open circuit voltage value of the lead-acid battery in real time according to the ohmic internal resistance, polarization internal resistance and polarization capacitance; S4. Determine the state of charge of the lead-acid battery according to the open circuit voltage value; S5. Determine the health of the lead-acid battery according to the state of charge.

2. The method for calculating the health of a lead-acid battery according to claim 1, characterized in that: The state of charge of the lead-acid battery is determined by the following method: Wherein, SOC represents the state of charge of the lead-acid battery, a represents the minimum open circuit voltage value of the lead-acid battery after it is fully discharged, b represents the proportionality coefficient, and U oc Indicates the open circuit voltage value of the lead-acid battery.

3. The method for calculating the health of a lead-acid battery according to claim 2, characterized in that: The open circuit voltage value U of the lead-acid battery oc Determined by: Among them, U oc (k), U(k) and I(k) represent the open circuit voltage, terminal voltage and current at time k respectively, U(k-1), U oc (k-1) and I(k-1) represent the terminal voltage value, open circuit voltage value and current value at time k-1 respectively, e represents a natural constant, T represents a sampling period, R0 represents an ohmic internal resistance, R1 represents a polarization internal resistance, and C1 represents a polarization capacitance.

4. The method for calculating the health of a lead-acid battery according to claim 3, characterized in that: In step S1, the equivalent circuit model adopts the Thevenin model.

5. The method for calculating the health of a lead-acid battery according to claim 2, characterized in that: The health of the lead-acid battery is calculated by the following formula: Wherein, SOH represents the health of the lead-acid battery, Q 放 Indicates the amount of electricity released by a lead-acid battery at a standard discharge current under standard discharge mode, Q 额 The rated capacity of the lead-acid battery, SOC 初 Indicates the state of charge of the lead-acid battery when it starts to discharge, SOC 末 Indicates the charge state of the lead-acid battery after discharge.

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