Method for determining the current peaks supported by an electrical energy storage device at various states of charge

Abstract

The application discloses a kind of determination methods of supporting current peak of electric storage device at each state of charge, comprising the following steps: step one, computer terminal constructs the data model of electric storage device and simulates the current value I of single battery in electric storage device in 10% to 90% state of charge output by the data model i I (i=1,2,…,n) to obtain the current waveform corresponding to each state of charge in 10% to 90% state of charge;Step two, discharge the battery to the lower limit cutoff voltage of the battery;Step three, charge the battery to any state of charge in 10% to 90% state of charge;Step four, stimulate the battery with any current value in the current waveform corresponding to the any state of charge;Step five, repeat steps three and four for each charge value in 10% to 90% state of charge to determine the current value in the current waveform corresponding to each charge value.

Description

Technical Field

[0001] This invention relates to the field of measurement technology, and in particular to a method for measuring the peak value of the supporting current of an energy storage device under various charging states. Background Technology

[0002] Currently, as more and more thermal power units are being replaced by new energy power plants, the overall rotational inertia of the system is decreasing, which seriously affects the stability of the power system. Energy storage devices have received widespread attention for providing ancillary services to the power grid due to their fast response speed, precise control, and ability to compensate for unbalanced power in the system. By utilizing the advantages of energy storage devices to serve power grid frequency events, on the one hand, energy storage can smooth out the fluctuations in grid-connected power caused by wind and solar power fluctuations, and keep the grid-connected power within a reasonable range. On the other hand, the fast response of energy storage devices can also resist power imbalances caused by load disturbances.

[0003] However, due to limitations such as the capacity, aging level, and power status of energy storage devices, the maximum output power of energy storage devices varies with frequency changes. In other words, the peak power of energy storage devices is affected by many factors. Therefore, if a method can be provided to determine the peak power of energy storage devices under a certain state, the maximum supporting power that energy storage devices can provide to the power grid can be known, which is of great significance to the stability of the power system. Summary of the Invention

[0004] Based on this, and to address the aforementioned problems, this invention proposes a method for determining the peak current supporting the energy output of an energy storage device under various states of charge. The method utilizes a data model to simulate and obtain the current waveform output by the battery. By setting rules, the peak current supporting the energy output is determined in the current waveform corresponding to each state of charge (SOC) of the battery between 10% and 90%, thereby providing strong data support for the stability of the power system.

[0005] The technical solution of the present invention is: a method for measuring the peak value of the supporting current of an energy storage device under various states of charge, comprising the following steps:

[0006] Step 1: The computer terminal constructs a data model of the energy storage device and uses this data model to simulate the current value I output by a single battery in the energy storage device under a state of charge of 10%-90%. i =e; i = 1, 2, ..., n, thus obtaining the current waveform corresponding to each charging state in the 10%-90% charging state;

[0007] Step 2: Discharge the battery to its lower limit cutoff voltage;

[0008] Step 3: Charge the battery to any one of its 10%-90% state of charge.

[0009] Step 4: Excite the battery with any current value from the current waveform corresponding to any state of charge.

[0010] Step 5: Repeat steps 3 and 4 for each charge value of the battery in its 10%-90% state of charge to determine the current value in the current waveform corresponding to each charge value;

[0011] The current value in the current waveform corresponding to each charge value of the battery during its 10%-90% state of charge is determined according to the following rules:

[0012] a. When the battery discharge ends, if the battery voltage value just reaches its lower limit cutoff voltage value, then any current value is considered to be the peak current that supports the output of electrical energy when the battery is in any state of charge.

[0013] b. When the battery discharge ends, if the battery voltage fails to reach its lower cutoff voltage or reaches the lower cutoff voltage prematurely, select any other current value in the current waveform and repeat steps two to four until the current value that meets rule a is obtained.

[0014] In a further technical solution, the formula for the power-frequency relationship in the data model of the energy storage device is as follows:

[0015] In a further technical solution, the simulation formula for the electrical energy output of the energy storage device is as follows:

[0016]

[0017] In a further technical solution, if the battery voltage fails to reach its lower cutoff voltage, the larger current value in the current waveform is selected.

[0018] In a further technical solution, if the battery voltage reaches the lower cutoff voltage value ahead of time, the smaller current value in the current waveform is selected.

[0019] In a further technical solution, a step for determining the battery capacity value is included between step one and step two:

[0020] Place the battery in an environment of about 25°C for about 1 hour, then fully charge it using a constant current and constant voltage method and let it stand until the polarization and other chemical reactions disappear. Then discharge it using a constant current method to the lower limit cutoff voltage value and let it stand until the polarization and other chemical reactions disappear. Repeat the above steps three times. If the difference between the charging capacity and the discharging capacity of the battery in the three tests is within 2%, then it is a valid result of the battery's maximum usable capacity test. The average of the three valid results is the battery's maximum usable capacity.

[0021] The beneficial effects of this invention are:

[0022] 1. This measurement method achieves the technical effect of measuring the peak value of the supporting current in the energy storage device under various charging states;

[0023] 2. This formula achieves the technical effect of constructing a data model for energy storage devices;

[0024] 3. This formula achieves the technical effect of constructing a data model for energy storage devices;

[0025] 4. By using the sample selection method, the current value that meets rule a can be found more efficiently;

[0026] 5. By using the sample selection method, the current value that meets rule a can be found more efficiently;

[0027] 6. By measuring the maximum usable capacity of the battery, the charge value in the 10%-90% state of charge (SOC) range can be determined more accurately, thus making the measurement results more accurate. Attached Figure Description

[0028] Figure 1 This is a flowchart illustrating steps 1 and 2 as described in Embodiment 1 of the present invention;

[0029] Figure 2 This is a schematic diagram of the experimental measurement results of the 20% state of charge (SOC) described in Embodiment 1 of the present invention. Detailed Implementation

[0030] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0031] A method for determining the peak value of the supporting current of an energy storage device under various states of charge includes the following steps:

[0032] Step 1: The computer terminal constructs a data model of the energy storage device and uses this data model to simulate the current value I output by a single battery in the energy storage device under a state of charge of 10%-90%. i =e(i=1,2,…,n) to obtain the current waveform corresponding to each charging state in the 10%-90% charging state;

[0033] Step 2: Discharge the battery to its lower limit cutoff voltage;

[0034] Step 3: Charge the battery to any one of its 10%-90% state of charge.

[0035] Step 4: Excite the battery with any current value from the current waveform corresponding to any state of charge.

[0036] Step 5: Repeat steps 3 and 4 for each charge value of the battery in its 10%-90% state of charge to determine the current value in the current waveform corresponding to each charge value;

[0037] The current value in the current waveform corresponding to each charge value of the battery during its 10%-90% state of charge is determined according to the following rules:

[0038] a. When the battery discharge ends, if the battery voltage value just reaches its lower limit cutoff voltage value, then any current value is considered to be the peak current that supports the output of electrical energy when the battery is in any state of charge.

[0039] b. When the battery discharge ends, if the battery voltage fails to reach its lower cutoff voltage or reaches the lower cutoff voltage prematurely, select any other current value in the current waveform and repeat steps two to four until the current value that meets rule a is obtained.

[0040] The following describes, in detail, the method for measuring the peak value of the supporting current of the above-mentioned energy storage device under various charging states, with reference to Example 1.

[0041] It includes simulation steps and measurement steps.

[0042] Step one, regarding the simulation step, involves constructing a data model of the energy storage device's battery peak power based on the power-frequency relationship formula in the power grid. The power-frequency relationship formula in the power grid is shown in Formula 1:

[0043] Formula 1:

[0044]

[0045] In Formula 1, ΔP e ΔP represents the power supplied by the generator in the system. L Indicates load power; ΔP bes ΔP represents the power provided by the energy storage device. When the energy storage device outputs power, ΔP bes A positive value indicates a positive value; conversely, a negative value indicates a negative value. H and D represent the generator's inertial time constant and damping coefficient, respectively.

[0046] Since the frequency response of the energy storage device is affected by various factors such as the grid generator parameters and the magnitude of load disturbances, different grids respond differently to loads. Therefore, this embodiment 1 is based on known grid parameters to obtain the maximum frequency support capability provided by the energy storage device to the grid under a given load disturbance. The simulation formula for the energy output of the energy storage device is Formula 2, as follows:

[0047] Formula 2:

[0048]

[0049] In Formula 2, H bes and D bes These represent the inertial time constant and damping coefficient of the energy storage device, respectively. In this embodiment 1, the focus is on the support provided by the energy storage device during the inertial response, so the ability of the energy storage device to provide frequency recovery is not considered. Therefore, the damping coefficient is set to 0.

[0050] After the data model of the energy storage device is completed, the terminal of the energy storage device prevents overcharging / discharging by setting the state of charge (SOC) interval of the batteries in the energy storage device to 10%. The SOC range of the batteries is selected as 10%-90%. By setting the initial SOC value of the energy storage device model, a 10% disturbance is added to the load, and the H value is changed. bes The magnitude of the value is used to obtain the output current of the energy storage device model at different peak values. The terminal of the energy storage device analyzes the output current I at different peak values. i The series and parallel connection of d (i = 1, 2, ..., n) is used to obtain the current waveform corresponding to each state of charge of a single battery in the energy storage device in its 10%-90% state of charge.

[0051] Step 2: Regarding the determination of the peak value of the energy support force of the energy storage device, the obtained single cell output current waveform is used in an actual battery for measurement. The battery standard sample selected in this embodiment 1 is an 18650 lithium-ion battery with a rated capacity of 1.5Ah, a rated voltage of 3.6V, and a voltage range of 2.5-4.2V.

[0052] It is worth noting that although the data model of the energy storage device is constructed using the terminal of the energy storage device in this embodiment 1, the focus of this step is on constructing the data model of the energy storage device. Therefore, any method that can construct the data model of the energy storage device is within the protection scope of this invention.

[0053] like Figure 1 As shown, the determination of the battery's maximum power support capacity includes the following steps:

[0054] 1. Discharge the battery at a current of 0.3A to the lower cutoff voltage and leave it for about 1 hour;

[0055] 2. Charge the battery with a current of 0.75A until it reaches a state of charge between 10% and 90%, and leave it for about 1 hour.

[0056] 3. Excite the battery with a current value from the current waveform corresponding to the state of charge simulated in step 1, and then place the battery again for about 1 hour.

[0057] 4. Repeat steps 2 and 3 of the maximum energy support capacity test of the battery to measure each charge value of the battery from 10% to 90% state of charge, so as to obtain the peak value of the maximum energy support capacity provided by the battery at each charge value and its corresponding current value.

[0058] The current value in the current waveform corresponding to each charge value of the battery between 10% and 90% state of charge is determined according to the following rules:

[0059] a. When the battery finishes discharging, if the battery voltage reaches its lower limit cutoff voltage, then the current value is considered to be the peak value of the battery's energy output capability at that charge value.

[0060] b. When the battery discharges to the end, if the battery voltage fails to reach its lower cutoff voltage or reaches the lower cutoff voltage prematurely, select any other current value in the current waveform and repeat steps 1-3 until the current value that meets rule a is obtained.

[0061] Preferably, if the battery voltage fails to reach its lower cutoff voltage, the larger current value in the current waveform is selected; and if the battery voltage reaches the lower cutoff voltage ahead of time, the smaller current value in the current waveform is selected. This selection method can more efficiently find the current value that meets rule a.

[0062] like Figure 2 As shown, experimental results for 20% state of charge (SOC) were selected from the range of 10%-90%. The experimental results indicate that when H... bes The current corresponding to 30V causes the battery's terminal voltage to drop to near the lower cutoff voltage of 2.5V, thus proving that the inertia at this time is the maximum support capacity that a single battery cell can provide, thereby achieving the technical objective of providing data support for the stability of the power system.

[0063] Preferably, the battery capacity test is performed before the peak value of the supporting force of the energy output of the energy storage device, which can provide an accurate battery capacity value for the subsequent state of charge (SOC).

[0064] The current and voltage values ​​and the constant current discharge current values ​​in the capacity test of this battery are the data values ​​in the battery's instruction manual. The specific capacity test method for this battery is to place the battery in an environment of about 25°C for about 1 hour.

[0065] The battery was then fully charged using a constant current constant voltage (CCCV) method, with a charging current of 0.75A and a voltage of 4.2V. After the battery was fully charged, it was left to stand for about 1 hour.

[0066] Then discharge the battery to the lower cutoff voltage using a constant current method. The discharge current is 0.3A. After the battery is discharged, place it for about 1 hour. Repeat this step three times. If the difference between the charging capacity and the discharging capacity of the three tests is within 2%, then the result of this maximum usable capacity test is valid.

[0067] By repeating the capacity test steps of the battery three times, three valid values ​​of the maximum usable capacity of the battery are obtained, and the average of these three values ​​is taken as the accurate battery capacity value of state of charge (SOC).

[0068] By measuring the battery's maximum usable capacity, the charge value at 10%-90% state of charge (SOC) can be determined more accurately, thus making the measurement results more accurate.

[0069] The embodiments described above are merely illustrative of specific implementations of the present invention, and while the descriptions are detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for determining the peak value of the supporting current of an energy storage device under various states of charge, characterized in that, Includes the following steps: Step 1: The computer terminal constructs a data model of the energy storage device and uses this data model to simulate the current value I output by a single battery in the energy storage device under a state of charge of 10%-90%. i =e, i = 1, 2, ..., n, thereby obtaining the current waveform corresponding to each charging state in the 10%-90% charging state; Step 2: Discharge the battery to its lower limit cutoff voltage; Step 3: Charge the battery to any one of its 10%-90% state of charge. Step 4: Excite the battery with any current value from the current waveform corresponding to any state of charge; Step 5: Repeat steps 3 and 4 for each charge value of the battery in its 10%-90% state of charge to determine the current value in the current waveform corresponding to each charge value; The current value in the current waveform corresponding to each charge value of the battery during its 10%-90% state of charge is determined according to the following rules: a. When the battery discharge ends, if the voltage value of the battery reaches its lower limit cutoff voltage value, then the arbitrary current value is considered to be the peak current of the battery supporting the output of electrical energy in the arbitrary state of charge. b. When the battery discharge ends, if the battery voltage fails to reach its lower cutoff voltage or reaches the lower cutoff voltage prematurely, select any other current value in the current waveform and repeat steps two to four until a current value that meets rule a is obtained. The power-frequency relationship formula for the data model of the energy storage device is as follows: ΔP e This indicates the power supplied by the generator in the system; ΔP L Indicates load power; ΔP bes ΔP represents the power provided by the energy storage device. When the energy storage device outputs power, ΔP bes A positive value indicates a positive value; conversely, a negative value indicates a negative value. H and D represent the generator's inertial time constant and damping coefficient, respectively. The simulation formula for the electrical energy output of the energy storage device is as follows: H bes and D bes These represent the inertial time constant and damping coefficient of the energy storage device, respectively.

2. The method for determining the peak value of the supporting current of an energy storage device under various states of charge, as described in claim 1, is characterized in that... If the voltage of the battery fails to reach its lower cutoff voltage, the larger current value in the current waveform is selected.

3. The method for determining the peak value of the supporting current of an energy storage device under various states of charge, as described in claim 1, is characterized in that... If the battery voltage reaches the lower cutoff voltage value ahead of schedule, then the smaller current value in the current waveform is selected.

4. The method for determining the peak value of the supporting current of an energy storage device under various states of charge, as described in claim 1, is characterized in that... Between step one and step two, there is also a step for determining the battery capacity value: The battery is placed in an environment of about 25°C for 1 hour, then fully charged using a constant current and constant voltage method and left to allow the polarization chemical reaction to disappear. Then, it is discharged using a constant current method to the lower limit cutoff voltage value and left to allow the polarization chemical reaction to disappear. The above steps are repeated three times. If the difference between the charging capacity and the discharging capacity of the battery in the three tests is within 2%, it is a valid result of the maximum usable capacity test of the battery. The average of the three valid results is the maximum usable capacity of the battery.

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