A Step Response Identification Method for the Characteristic Parameters of a Supercapacitor

Abstract

The present invention discloses a step response identification method for characteristic parameters of a supercapacitor, comprising the following steps: collecting the current of the supercapacitor with a current acquisition system, initializing the supercapacitor to be measured to a zero state, applying a DC voltage source with a constant amplitude to the supercapacitor to be measured, sampling its current and saving the samples, calculating the basic coefficient and the average basic coefficient, calculating the estimation coefficient, the estimation factor and the average estimation coefficient, and calculating the resistance value and the capacitance value of the supercapacitor; The present invention takes the supercapacitor as the monitoring object, monitors the working state of its internal components in real time, verifies by experiments and analyzes the results, and confirms that the identification method proposed by the present invention can identify the feasibility and accuracy of the method for characteristic parameters of the internal components of the supercapacitor by real-time monitoring of the output current of the supercapacitor, and has the outstanding characteristics of strong timeliness of obtaining data, high accuracy of obtaining data, and no damage to the supercapacitor.

Description

Technical Field

[0001] The present invention relates to the technical field of supercapacitors, and in particular, to a step response identification method for characteristic parameters of a supercapacitor. Background Art

[0002] In order for humans to have an increasingly green and environmentally friendly living and working environment, people have accelerated the process of utilizing renewable new energy such as wind energy and solar energy. Among them, as an important electric energy storage device, the supercapacitor energy storage system is favored in electric vehicles, buses, subways, rail trains, new energy power generation and other applications due to its high power density, large instantaneous charge and discharge current, long cycle service life and other advantages, and is playing an increasingly important role.

[0003] The performance of a supercapacitor in aspects such as electric energy storage, charging, and discharging depends on its basic components, namely the resistance R and capacitance C. Changes in these characteristic parameters R and C will affect the electric energy storage ability of the supercapacitor, relate to its reliability and safety, and affect its power loss and efficiency during the charge and discharge process. Therefore, it is very crucial to accurately obtain these characteristic parameters. However, as a product, the supercapacitor is usually well encapsulated, and it is very difficult to directly test these characteristic parameters. Therefore, people have carried out research on monitoring the characteristic parameters of supercapacitors.

[0004] The performance of a supercapacitor actually depends on its internal basic components, namely the resistance R and capacitance C. The sizes of these components determine its performance in specific applications. The charging speed of a supercapacitor is related to the time constant, and the time constant is related to its characteristic parameters R and C. For example, the smaller R is, the faster its charge and discharge. The larger C is, the more electric energy is stored and the stronger the storage ability. Therefore, changes in these characteristic parameters will affect its electric energy storage ability and charge and discharge performance, and also involve the reliability and safety of the capacitor in a specific circuit. The equivalent circuit model of a traditional supercapacitor is as Figure 1 shown. The supercapacitor consists of two components, a resistance R and a capacitance C. Let the input voltage of the supercapacitor be u i (t), the capacitor voltage be u c (t), and the current be i1(t). Then there is:

[0005]

[0006] Taking the input step voltage signal u i (t) to analyze the internal characteristic parameters of the supercapacitor, that is:

[0007]

[0008] Before working, the u of the supercapacitor is grounded or otherwise i(t) and i1(t) are both zero, that is, the supercapacitor to be measured is in a zero state. By combining equations (1.1), (1.2), and (1.3) and considering the zero state, u can be obtained. c (t) and the step response of i1(t), both of which are closely related to the characteristic parameters R and C. In engineering, it is very difficult to measure u of a well-packaged supercapacitor without disassembly and damage. c (t).

[0009] In the prior art, most of the identification methods for the characteristic parameters of supercapacitors have problems such as complex processes and poor anti-interference capabilities. Moreover, some identification methods can only estimate the parameter information of the capacitance value, and its equivalent resistance will also have an impact during actual operation and will change with temperature, etc., resulting in inaccurate measurement of supercapacitors. In addition, some identification methods do not consider the influence of resistance, resulting in inaccurate measured capacitance values. Therefore, the present invention proposes a step response identification method for the characteristic parameters of supercapacitors to solve the problems existing in the prior art. Summary of the Invention

[0010] Aiming at the above problems, the purpose of the present invention is to propose a step response identification method for the characteristic parameters of supercapacitors to solve the problems that most of the existing identification methods for the characteristic parameters of supercapacitors have complex processes, poor anti-interference capabilities, and low accuracy.

[0011] To achieve the purpose of the present invention, the present invention is realized through the following technical solutions: A step response identification method for the characteristic parameters of a supercapacitor, comprising the following steps:

[0012] Step 1: Prepare a current acquisition system and a constant voltage DC voltage source with an amplitude of U a volts in advance, then initialize the supercapacitor to be measured to a zero state, and use the current acquisition system to collect the current of the capacitor.

[0013] Step 2: Connect the constant voltage DC voltage source prepared in Step 1 to the input end of the supercapacitor to be measured. At the same time, use the current acquisition system prepared in Step 1 to sample the current of the supercapacitor to be measured, and save the collected samples. Denote SCU(j) as the jth sample, representing the current collected in the jth sampling period, j = 1, 2, 3,..., N, N is the number of samples, and the sampling period is T.

[0014] Step 3: According to the samples SCU(j) saved in Step 2, calculate the basic coefficient FirstPara(j) respectively, and then calculate the average basic coefficient MulParaAv according to the basic coefficient FirstPara(j), where j = 1, 2, 3,..., m, 1 < m ≤ N.

[0015] Step 4: Calculate the estimation coefficient SecondPara(j) based on the average base coefficient MulParaAv calculated in Step 3. Then calculate the average estimation coefficient SecondParaAv based on the estimation coefficient SecondPara(j). Next, calculate the estimation factor ThirdPara based on the average base coefficient MulParaAv, where j = 1, 2, 3, ……, m, and 1 < m ≤ N + 1;

[0016] Step 5: Calculate the resistance value R of the supercapacitor based on the average estimation coefficient SecondParaAv calculated in Step 4;

[0017] Step 6: Calculate the capacitance value C of the supercapacitor based on the average estimation coefficient SecondParaAv and the estimation factor ThirdPara calculated in Step 4.

[0018] A further improvement lies in that: in Step 1, the method of grounding the input and output ports of the supercapacitor to be measured is adopted to initialize the supercapacitor to be measured to the zero state. When the current remains zero for a preset time, the supercapacitor to be measured is initialized to the zero state.

[0019] A further improvement lies in that: in Step 3, the calculation formula for the base coefficient FirstPara(j) is:

[0020]

[0021] A further improvement lies in that: in Step 3, the calculation formula for the average base coefficient MulParaAv is:

[0022]

[0023] A further improvement lies in that: in Step 4, the calculation formula for the estimation coefficient SecondPara(j) is:

[0024]

[0025] A further improvement lies in that: in Step 4, the calculation formula for the average estimation coefficient SecondParaAv is:

[0026]

[0027] A further improvement lies in that: in Step 4, the calculation formula for the estimation factor ThirdPara is:

[0028] ThirdPara = ln(MulParaAv).

[0029] A further improvement lies in that: in the fifth step, the calculation formula for the resistance value R of the supercapacitor is:

[0030]

[0031] A further improvement lies in that: in the sixth step, the calculation formula for the capacitance value C of the supercapacitor is:

[0032]

[0033] The beneficial effects of the present invention are as follows: The present invention takes the supercapacitor as the monitoring object, and monitors the working state of its internal components in real time. Based on the MATALB / Simulink platform, the circuit model of the supercapacitor and the identification method of the characteristic parameters of the internal components of the supercapacitor are verified by experiments and the results are analyzed. It is confirmed that the identification method proposed by the present invention can identify the characteristic parameters of the internal components of the supercapacitor by real-time monitoring of the output current of the supercapacitor without disassembling or damaging the supercapacitor device, and has the outstanding characteristics of strong timeliness of obtaining data, high accuracy of obtaining data, and no damage to the supercapacitor, which lays a foundation for more timely and accurate dynamic monitoring of the working state of the supercapacitor. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention, and those of ordinary skill in the art can also obtain other drawings based on these drawings without creative efforts.

[0035] Figure 1 It is a schematic diagram of the equivalent circuit model of the traditional supercapacitor in the background art of the present invention;

[0036] Figure 2 It is a schematic diagram of the step response identification method process of the characteristic parameters of the supercapacitor of the present invention;

[0037] Figure 3 It is a schematic diagram of the supercapacitor circuit model in the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments of the present invention belong to the scope of protection of the present invention.

[0039] See also Figure 2 , Figure 3 In this embodiment, a circuit model of a supercapacitor is established in Simulink under the Matlab environment, and an experiment is carried out on the circuit model for verification. The specific steps are as follows:

[0040] Step 1: First, establish a supercapacitor circuit model, such as Figure 3 As shown, the capacitor C = 10.3125F, the resistor R = 0.1008Ω, the gain of the white noise is 0, that is, there is no noise interference input, and the step signal with an amplitude of 768 controls the controlled voltage source to generate U a =768V step voltage source u i (t) is for the supercapacitor, the current sensor collects the supercapacitor current i1(t), and the voltage across the capacitor is initialized to 0V, that is, the supercapacitor is initialized to zero state;

[0041] Step 2: Set the sampling period T = 2.5 × 10 -3 seconds, the sampling time is 1s (through a lot of experimental research, it is found that supercapacitors can eliminate oscillations in a very short time. In order to maximize the experimental accuracy and reduce the simulation time, the sampling time is determined to be 1s), start the simulation, u i (t) is connected to the input terminal of the supercapacitor. At the same time, the current sensor collects i1(t) and saves it. SCU(j) = i1(jT) represents the jth sampling value, j = 1, 2, 3, ..., N, when N = 4 × 10 2 When SCU(j) changes very little, the experiment ends, the sampling ends, and the following Table 1 shows the sample information collected;

[0042] Table 1 Current samples collected

[0043] Sampling time t <![CDATA[Output current value i1(t)]]> 0 0 0.0025 7604.81044256058 0.0050 7586.54283077621 0.0075 7568.31909985420 …… …… 0.9925 2934.09790151373 0.9950 2927.04986766633 0.9975 2920.01876399059 1 2913.00454981831

[0044] Step 3: Calculate the basic coefficient based on the sample SCU(j) saved in step 2 Its FirstPara(j) value is shown in Table 2 below;

[0045] Table 2: FirstPara(j) value table analyzed

[0046] Serial number FirstPara(j) 1 0.99759788729 2 0.99759788729 3 0.99759788729 4 0.99759788729 …… …… 396 0.99759788729 397 0.99759788729 398 0.99759788729 399 0.99759788729

[0047] The average basic coefficient MulParaAv is calculated from the above table as follows:

[0048]

[0049] Step 4: Calculate the estimation coefficient SecondPara(j) based on the average base coefficient MulParaAv calculated in Step 3 as follows:

[0050]

[0051] where j = 1, 2, 3, ……, 399, and the values of SecondPara(j) are shown in Table 3 below;

[0052] Table 3 Values of SecondPara(j)

[0053]

[0054] The average estimation coefficient SecondParaAv can be calculated from the above table as follows:

[0055]

[0056] Calculate the estimation factor ThirdPara based on the average base coefficient MulParaAv as follows:

[0057] ThirdPara = ln(MulParaAv) = ln(0.99759788729) = -0.002405002;

[0058] Step 5: Calculate the resistance value R of the supercapacitor based on the average estimation coefficient SecondParaAv calculated in Step 4 as follows:

[0059]

[0060] Step 6: Calculate the capacitance value C of the supercapacitor based on the average estimation coefficient SecondParaAv and the estimation factor ThirdPara calculated in Step 4 as follows:

[0061]

[0062] From the calculation results of Steps 5 and 6 above, it can be seen that when there is no interference, the capacitance C = 10.3180148 F and the resistance R = 0.1007461 Ω identified by the method proposed in the present invention, and their relative errors are 0.053% and 0.053% respectively. It can be seen that in the absence of interference, the identification error is small and very close to the true values of the characteristic parameters C and R.

[0063] The above is the identification of the characteristic parameters of the supercapacitor without interference signals. However, in actual operation, the interference signal i d (t) is mixed into the current i1(t) of the energy storage capacitor, that is, SCu(j) = i1(jT) + i d (jT). id (t) generally appears as white noise. Therefore, in order to verify the anti-interference performance of the method described in the present invention, the above experimental steps from Step 1 to Step 6 are repeated. The difference lies in that in Step 1, the parameters of the random white noise module and the gain module need to be set to simulate the interference in the project. The variance of the white noise is 0.1, and the gains are taken as six groups of 5, 10, 15, 20, 25, and 30 respectively. Multiple experiments are carried out, and the experimental results are shown in Table 4 below.

[0064] Table 4 Identification of characteristic parameters under interference

[0065]

[0066] As can be seen from Table 4 above, when using the identification method proposed in the present invention to estimate the characteristic parameters R and C of the supercapacitor, the estimation error of R is less than that of C. For example, when the signal-to-noise ratio is 2.6%, the relative estimation errors of R and C are 3.720% and 4.292% respectively. As the interference increases, the estimation errors of the parameters increase. For example, when the noise-to-signal ratio is 0.65%, the relative estimation errors of R and C are 0.211% and 0.292% respectively; when the signal-to-noise ratio is 3.9%, the relative estimation errors of R and C reach 8.441% and 10.962% respectively. These results show that the identification method proposed in the present invention can effectively and reliably identify the characteristic parameters of the supercapacitor, has strong anti-interference ability and high identification accuracy.

[0067] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A step response identification method for the characteristic parameters of a supercapacitor, characterized in that, Including the following steps: Step 1: Prepare a current acquisition system and a constant-voltage DC voltage source with an amplitude of U a volts in advance. Then initialize the supercapacitor to be measured to the zero state, and use the current acquisition system to collect the current of this capacitor; Step 2: Connect the constant-voltage DC voltage source prepared in Step 1 to the input terminal of the supercapacitor under test. At the same time, use the current acquisition system prepared in Step 1 to sample the current of the supercapacitor under test, and save the collected samples. Denote SCU(j) as the j-th sample, representing the current collected in the j-th sampling period, j = 1, 2, 3, ……, N, where N is the number of samples and the sampling period is T; Step 3: According to the samples SCU(j) saved in Step 2, calculate the basic coefficient FirstPara(j) respectively, and then calculate the average basic coefficient MulParaAv based on the basic coefficient FirstPara(j), where j = 1, 2, 3, ……, m, 1 < m ≤ N. The calculation formula of the basic coefficient FirstPara(j) is: Step 4: According to the average basic coefficient MulParaAv calculated in Step 3, calculate the estimation coefficient SecondPara(j), then calculate the average estimation coefficient SecondParaAv based on the estimation coefficient SecondPara(j), and then calculate the estimation factor ThirdPara based on the average basic coefficient MulParaAv, where j = 1, 2, 3, ……, m, 1 < m ≤ N + 1. The calculation formula of the estimation coefficient SecondPara(j) is: The calculation formula of the estimation factor ThirdPara is: ThirdPara = ln(MulParaAv); Step 5: According to the average estimation coefficient SecondParaAv calculated in Step 4, calculate the resistance value R of the supercapacitor. The calculation formula of the resistance value R of the supercapacitor is: Step 6: According to the average estimation coefficient SecondParaAv and the estimation factor ThirdPara calculated in Step 4, calculate the capacitance value C of the supercapacitor. The calculation formula of the capacitance value C of the supercapacitor is:

2. The step - response identification method for the characteristic parameters of a supercapacitor according to claim 1, wherein: In Step 1, the supercapacitor under test is initialized to the zero state by grounding the input and output ports of the supercapacitor under test. When the current remains zero for a preset time, the supercapacitor under test is initialized to the zero state.

3. A step response identification method for the characteristic parameters of a supercapacitor according to claim 1, characterized in that: In Step 3, the calculation formula of the average basic coefficient MulParaAv is:

4. The step response identification method for the characteristic parameters of a supercapacitor according to claim 1, characterized in that: In Step 4, the calculation formula of the average estimation coefficient SecondParaAv is:

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