An online calibration method for parallel branch current of a dynamically reconfigurable battery energy storage system

Abstract

A method for online calibration of parallel branch currents in a dynamically reconfigurable battery energy storage system relates to the field of energy storage in new energy power systems. To address the static and dynamic errors inherent in current calibration in existing parallel branch calibration methods, the present invention first obtains the original current sampling values ​​of the main circuit and each branch, then calculates the static error of the current based on the original current sampling values. Static error elimination is then performed on the original current sampling values ​​of each branch, and the current values ​​of each branch are calibrated based on the sum of the branch currents. The present invention is primarily used for online calibration of the parallel branch currents in a dynamically reconfigurable battery energy storage system.

Description

Technical Field

[0001] The present invention relates to the field of energy storage of new energy power systems, and in particular to an online calibration method for parallel branch currents of a dynamically reconfigurable battery energy storage system. Background Art

[0002] In a dynamically reconfigurable battery energy storage system, multiple cells or modules are connected in parallel. Due to the parallel connection, the currents in each parallel branch can be unequal due to inconsistent parameters such as the internal resistance of each cell or module. Due to cost and technical factors, the current sampling sensors used to measure the current in each parallel branch have limited sampling accuracy and do not necessarily achieve accurate current measurement, resulting in large measurement errors. Battery or battery system charge estimation and remaining capacity estimation both require high-precision current as a basis. Large current errors can lead to large charge estimation errors, resulting in power anomalies or even sudden shutdowns in the energy storage system, which can have unpredictable impacts on the energy storage system and the power grid.

[0003] In a dynamically reconfigurable battery energy storage system, current sampling is primarily divided into main circuit current sampling and branch current sampling. Main circuit current sampling involves installing current sensors on the main circuit busbar. These sensors are highly accurate, enabling high-precision measurement of the main circuit current with negligible measurement error. Branch current sampling, on the other hand, involves installing current sensors on each parallel branch. However, these sensors are less accurate and subject to significant static and dynamic errors. Static error refers to the false current value generated by the branch current sensor when no current is flowing (the actual current is zero), which can be considered a zero-state bias and is considered a static error. Dynamic error refers to the dynamic current deviation added to the static error when current is flowing. Furthermore, these static and dynamic errors in current sampling can fluctuate depending on the current magnitude and temperature. This means that the current sampling error varies with current and temperature, making it unsuitable for offline calibration and more suitable for online, real-time calibration.

[0004] During charging and discharging, the cells or modules in each branch of a dynamically reconfigurable battery energy storage system dynamically switch in and out of the main circuit. When switched out of the main circuit, static current calibration is achieved, while when switched in, dynamic current calibration is achieved. This combination allows for current calibration throughout the entire charging and discharging process. However, due to static and dynamic errors, branch current sampling can result in significant errors.

[0005] Therefore, an online calibration method for parallel branch current is needed to calibrate the collected current, eliminate current errors, and achieve accurate acquisition of the current in each branch. Summary of the Invention

[0006] In order to solve the defects of static error and dynamic error in current calibration of existing parallel branch calibration methods, the present invention provides an online current calibration method for parallel branches of a dynamic reconfigurable battery energy storage system, which can realize real-time error correction of current acquisition values, eliminate deviations, and achieve reliable current correction when the dynamic reconfigurable battery energy storage system is working.

[0007] The method for online calibration of parallel branch currents of a dynamically reconfigurable battery energy storage system according to the present invention comprises the following steps:

[0008] S1. Real-time acquisition of the original current sampling value of the main circuit current sensor and the original sampling value of the branch current sensor ;

[0009] S2. When the parallel branch exits the main circuit, the state of the switch corresponding to the branch is SwitchState=0. When the parallel branch is connected to the main circuit, the state of the switch corresponding to the branch is SwitchState=1.

[0010] When the parallel branch exits the main circuit, that is, when the state of the switch corresponding to the branch is SwitchState=0, the original current value collected As the current static error;

[0011] When the parallel branch is connected to the main circuit, that is, when the state of the switch corresponding to the branch is SwitchState=1, the original current value collected by the current sensor of each branch at each moment is , to eliminate static errors.

[0012] Furthermore, when the branch exits the main circuit, that is, when SwitchState=0, the static error of the current at each moment is:

[0013] ;

[0014] The static error of the current of the parallel branch at each moment when it exits the main circuit is calculated. The average value is used as the static error of the branch current :

[0015] ;

[0016] in, is the current static error, is the original current value.

[0017] Furthermore, when the branch is connected to the main circuit, that is, when SwitchState=1, the formula for eliminating the static error is:

[0018] ;

[0019] in, is the original current value of the branch The current value after eliminating the static error, is the current static error.

[0020] Furthermore: the current static error The calculation process used for current calibration is performed when the main circuit is reconnected, and it must be recalculated each time the parallel branch is removed from the main circuit.

[0021] Furthermore: on the basis of eliminating the static error, the sum of the currents of each branch at each moment is calculated:

[0022] ;

[0023] Where, is the sum of the currents in the j-th branch, N is the number of parallel branches, and j is the j-th branch;

[0024] Calculate the proportional relationship between the current value of each branch and the total current at each moment:

[0025] ;

[0026] in, is the proportional relationship between the current of the jth branch at time k that eliminates the static error and the sum of the currents of all branches;

[0027] Calculate the final corrected current value:

[0028] ;

[0029] in, is the corrected current value in the j-th branch, It is the main circuit current sensor at time K.

[0030] The beneficial effects of the present invention are:

[0031] The present invention can effectively eliminate the inherent static deviation and online dynamic deviation of the original measured current, significantly improve the current detection accuracy of each parallel branch in the battery system, and provide a basis for battery system power estimation and life estimation. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Flowchart of a method for online calibration of parallel branch current;

[0033] Figure 2 Schematic diagram of a dynamically reconfigurable battery system;

[0034] Figure 3 It is a schematic diagram of the total current curve of the battery;

[0035] Figure 4 It is the overall schematic diagram of the current curves of the three branches;

[0036] Figure 5 for Figure 4 A partial enlarged view of part A;

[0037] Figure 6 is the static current error waveform of the branch;

[0038] Figure 7 This is an overall schematic diagram comparing the calibrated branch current and the original current;

[0039] Figure 8 for Figure 7 A partial enlarged view of part B. DETAILED DESCRIPTION

[0040] The following are only preferred specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or replacements that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the scope of protection of the present invention. The embodiments described below are only used to explain the present invention and cannot be interpreted as limiting the present invention. The scope of protection of the present invention should be based on the scope of protection of the claims. The embodiments of the present invention are described in detail below. In order to facilitate the description of the present invention and simplify the description, the technical terms used in the description of the present invention should be interpreted broadly, including but not limited to conventional replacement schemes not mentioned in this application, and also including direct implementation and indirect implementation.

[0041] Example 1

[0042] Combine Figures 1-8 This embodiment describes a method for online calibration of parallel branch currents of a dynamically reconfigurable battery energy storage system, including the following steps:

[0043] S1, real-time acquisition of main circuit current sensor and the original sampling value of the branch current sensor The original sampling value of the current of the main circuit is used as a constraint condition, as shown in Table 1.

[0044] Table 1 shows the current sampling values ​​at different times;

[0045]

[0046] S2. When the parallel branch exits the main circuit, the state of the switch corresponding to the branch is SwitchState=0. When the parallel branch is connected to the main circuit, the state of the switch corresponding to the branch is SwitchState=1.

[0047] So when SwitchState=0, the actual current of the branch should be 0, and the original current value collected is It is not 0, at this time That is the current static error. When the branch exits the main circuit, the current static error at each moment is: The static current error of the parallel branch at each moment when it exits the main circuit is calculated. The average value is used as the static error of the branch current :

[0048] ;

[0049] The above current static error , which is used for the calculation process of current calibration when it is subsequently reconnected to the main circuit, and it must be recalculated each time the parallel branch exits the main circuit;

[0050] S3. When the parallel branch is reconnected to the main circuit, that is, when SwitchState=1, the original current value collected by the current sensor of each branch at each moment , static error elimination is performed, and static error elimination is performed every time the main circuit is connected, that is:

[0051] ;

[0052] On the basis of eliminating the static error, the sum of the currents of each branch at each moment is calculated:

[0053] ;

[0054] Where N is the number of parallel branches, j is the jth branch;

[0055] Calculate the proportional relationship between the current of each branch and the sum of the currents at each moment:

[0056] ;

[0057] Calculate the final corrected current:

[0058] ;

[0059] During the reconfiguration process, the three battery modules will be reconfigured based on the voltage. For example, during the charging process, the 3-choose-2 mode is executed, that is, in each reconfiguration cycle, the two battery modules with the lowest voltage will be selected for charging. After each reconfiguration cycle, the two battery modules connected to the main circuit in the next cycle will be re-determined based on the voltage. Figure 2 In the figure, Q1,1...Qn,1, Q1,2...Qn,2 and Q1,3...Qn,3 all represent power switching devices, such as IGBT / Mosfet. The first number represents the number of batteries in series in the dynamically reconfigurable system, and the second number represents the number of batteries in parallel in the dynamically reconfigurable system. Figure 2 In the example, the dynamically reconfigurable system is n series and 3 parallel. For example, Qn,3 represents the power electronic switch device corresponding to the third battery module in the nth string.

[0060] Figure 3 is the total current of the dynamically reconfigurable battery energy storage system when it is working;

[0061] Figure 4 It is the original sampling value of the branch current of the three parallel modules when the dynamic reconfigurable battery energy storage system is working; Figure 5 yes Figure 4 A partial enlargement from 11 o'clock to 12 o'clock;

[0062] from Figure 4 and Figure 5 As can be seen from the figure, when a branch exits the main circuit, the original sampling value of its current If it is not 0, the current raw sampling value This is the static error of the branch current. ,Right now .

[0063] The static current error at each moment when the parallel branch exits the main circuit is calculated. The average value is used as the static current error of the branch current :

[0064] ;

[0065] When the parallel branch is reconnected to the main circuit, that is, when SwitchState=1, the original current value collected by the current sensor of each branch at each moment is , to eliminate static errors, namely:

[0066] ;

[0067] After calculation, Figure 6 The static error of one branch during the entire operation is shown in Figure 2. Calculate the corresponding current static error for each of the three parallel branches.

[0068] Calculate the proportional relationship between the current of each branch and the sum of the currents at each moment:

[0069] ;

[0070] Calculate the final corrected current:

[0071] ;

[0072] Figure 7 What is shown is the comparison between the corrected current and the original current of one branch. Figure 8 yes Figure 7 A local enlarged view; and the battery module capacity is calculated using the original current and the calibrated current respectively. The calculation formula is:

[0073] ;

[0074] Where Ah is the unit of battery capacity, is the starting time corresponding to the working current, is the end time corresponding to the working current, I is the current, and dt is the time interval.

[0075] The calculation results are shown in Table 2.

[0076] Table 2 Current calculation comparison table

[0077]

[0078] From the above results, it can be seen that after current calibration, the current error is effectively eliminated. The battery module capacity calculated using the calibrated current is closer to the actual capacity of the battery module, and the calculation accuracy of the battery module capacity is greatly improved.

Claims

1. A method for online calibration of parallel branch currents of a dynamically reconfigurable battery energy storage system, characterized in that: The steps include: S1. Real-time acquisition of the original current sampling value of the main circuit current sensor and the raw current value of the branch current sensor ; S2. When the parallel branch exits the main circuit, the state of the switch corresponding to the branch is SwitchState=0. When the parallel branch is connected to the main circuit, the state of the switch corresponding to the branch is SwitchState=1. When the parallel branch exits the main circuit, that is, when the state of the switch corresponding to the branch is SwitchState=0, the original current value collected As the current static error; When the parallel branch is connected to the main circuit, that is, when the state of the switch corresponding to the branch is SwitchState=1, the original current value collected by the current sensor of each branch at each moment is , to eliminate static errors; When the branch exits the main loop, that is, when SwitchState=0, the current static error at each moment is: ； The static error of the current of the parallel branch at each moment when it exits the main circuit is calculated. The average value is used as the static error of the branch current : k is the sampling time; ； in, is the current static error, is the original current value; When the branch is connected to the main circuit, that is, when SwitchState=1, the formula for eliminating the static error is: ； in, is the original current value of the branch The current value after eliminating the static error, is the current static error; On the basis of eliminating the static error, the sum of the currents of each branch at each moment is calculated: ； Where, is the sum of the currents in the j-th branch, N is the number of parallel branches, and j is the j-th branch; Calculate the proportional relationship between the current value of each branch and the total current at each moment: ； in, is the proportional relationship between the current of the jth branch at time k that eliminates the static error and the sum of the currents of all branches; Calculate the final corrected current value: ； in, is the corrected current value in the j-th branch, It is the main circuit current sensor at time k.

2. The online calibration method for parallel branch current of a dynamically reconfigurable battery energy storage system according to claim 1 is characterized in that: The current static error The calculation process used for current calibration is performed when the main circuit is reconnected, and it must be recalculated each time the parallel branch is removed from the main circuit.

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