Method and system for constructing simplified equivalent circuit model of battery energy storage system

Abstract

The invention discloses a method for constructing a simplified equivalent circuit model of a battery energy storage system. The method comprises the following steps: acquiring data information of a target battery energy storage system; the polarization capacitance in the target battery energy storage system is not considered, and a neglected capacitance equivalent circuit model of the target battery energy storage system is constructed; simplifying the target battery energy storage system into a circuit model comprising a resistor and a voltage source by adopting the Thevenin theorem; calculating the series current and the charge state of the model; and completing the construction of the simplified equivalent circuit model of the battery energy storage system according to the obtained result. The invention also discloses a system for realizing the construction method of the simplified equivalent circuit model of the battery energy storage system. According to the method, the capacitor-neglected equivalent circuit model of the target battery energy storage system is constructed, the circuit model is constructed, and the parameters are calculated, so that the simplified equivalent circuit model of the battery energy storage system is constructed, and the method is higher in reliability, better in accuracy and higher in modeling effect.

Description

Technical Field

[0001] The present invention belongs to the field of electrical automation, and in particular relates to a method and system for constructing a simplified equivalent circuit model of a battery energy storage system. Background Art

[0002] With the development of economy and technology and the improvement of people's living standards, electricity has become an indispensable secondary energy source in people's production and life, bringing endless convenience to people's production and life. Therefore, ensuring the stable and reliable supply of electricity has become one of the most important tasks of the power system.

[0003] At this stage, environmental problems are becoming more and more serious, so more and more renewable energy power generation systems are beginning to be integrated into the power system and generate electricity. However, the inherent intermittent and volatile problems of renewable energy have always been the key problem restricting its large-scale and stable access to the power grid. At the same time, traditional power sources such as thermal power generation are facing the situation of being shut down; and the withdrawal of thermal power generation systems will also make the problem of reduced grid inertia more prominent. When the power grid encounters severe disturbances, the frequency stability of the power grid will be difficult to maintain due to insufficient inertia, and the power system is prone to a series of chain reactions, resulting in more power outages, and may even trigger large-scale power outages, which will have a serious impact on the social economy and residents' lives.

[0004] Battery energy storage systems have flexible charging and discharging capabilities. They can store electricity when there is excess renewable energy generation, and release electricity when there is insufficient power generation or a power shortage in the grid, effectively smoothing power fluctuations and maintaining grid frequency stability. Therefore, at this stage, power systems are beginning to connect to energy storage systems in large numbers. Therefore, modeling energy storage systems for complete analysis and research is of great significance to power systems.

[0005] At present, traditional energy storage system modeling solutions include electrochemical solutions and data-driven solutions. However, the electrochemical modeling solution involves a large number of chemical reaction equations and complex parameter calculations, which requires a huge amount of calculations and an extremely complex model. The data-driven modeling solution is highly dependent on a large amount of battery experimental data; once the amount of data is insufficient, the reliability and accuracy of the data-driven model will be greatly reduced. Summary of the invention

[0006] One of the purposes of the present invention is to provide a method for constructing a simplified equivalent circuit model of a battery energy storage system with high reliability, good accuracy and high efficiency.

[0007] A second object of the present invention is to provide a system for realizing a method for constructing a simplified equivalent circuit model of the battery energy storage system.

[0008] The method for constructing a simplified equivalent circuit model of a battery energy storage system provided by the present invention comprises the following steps:

[0009] S1. Obtain the data information of the target battery energy storage system;

[0010] S2. According to the data information obtained in step S1, without considering the polarization capacitance in the target battery energy storage system, and construct an equivalent circuit model of the target battery energy storage system that ignores capacitance;

[0011] S3. According to the model constructed in step S2, using Thevenin's theorem, simplify the target battery energy storage system into a circuit model including a resistor and a voltage source;

[0012] S4. According to the model constructed in step S3, calculate the series current and state of charge of the model;

[0013] S5. According to the results obtained in steps S2 - S4, complete the construction of the simplified equivalent circuit model of the battery energy storage system.

[0014] The step of, according to the data information obtained in step S1, without considering the polarization capacitance in the target battery energy storage system, and constructing an equivalent circuit model of the target battery energy storage system that ignores capacitance, specifically includes the following steps:

[0015] According to the data information obtained in step S1, model the target battery energy storage system as an equivalent circuit model composed of a number of series - connected and parallel - connected Randles models;

[0016] In the Randles model, it includes a resistor, a polarization resistor, an internal resistance, and an open - circuit voltage, and the corresponding polarization capacitance is ignored;

[0017] Finally, construct an equivalent circuit model of the target battery energy storage system that ignores capacitance.

[0018] The step of, according to the model constructed in step S2, using Thevenin's theorem, simplifying the target battery energy storage system into a circuit model including a resistor and a voltage source, specifically includes the following steps:

[0019] Using Thevenin's theorem, simplify the series - connected and parallel - connected battery system of the target battery energy storage system into a circuit including a resistor R COMP and a voltage source OCV COMP ;

[0020] The sum of the resistances of the i - th branch is denoted as R series,i , and the sum of the voltage sources of the i - th branch is denoted as OCV series,i ;

[0021] Calculate R series,i using the following formula:

[0022]

[0023] where n is the number of resistors in the i-th branch; R ik is the resistor in the i-th branch, and R in = R W,kn + R P,kn + R I,kn , R W,kn is the wire resistance, R P,kn is the polarization resistance, R I,kn is the internal resistance;

[0024] The OCV is calculated using the following formula series,i :

[0025]

[0026] where m is the number of voltage sources in the i-th branch; OCV j is the open-circuit voltage of the i-th branch;

[0027] The combined resistance R comp,1..i of the first branch to the i-th branch is calculated using the following formula

[0028]

[0029] where R comp,1..(i-1) is the combined resistance of the first branch to the (i - 1)-th branch;

[0030] The circuit of the target battery energy storage system is disconnected, and the current I CC,i flowing through the i-th branch is calculated using the following formula

[0031]

[0032] where R CC,i is the sum of the resistances of the i-th branch and the (i - 1)-th branch, and R CC,i = R series,i + R series,i-1 ;

[0033] The calculated OCV series,i is OCV comp,i = OCV series,i-1 - (R series,i-1 ) I CC ;

[0034] Finally, the OCV series,nn and R series,nn of the last branch nn are calculated, so as to obtain OCV comp = OCV series,nn and R comp = R series,nn .

[0035] The series current of the calculation model in step S4 specifically includes the following steps:

[0036] The system voltage V is calculated using the following formula: system :

[0037] V system = OCV comp + R comp I system

[0038] where I system is the current passing through the battery system.

[0039] The series current I of the i-th branch is calculated as string,i being

[0040] The state of charge of the calculation model in step S4 specifically includes the following steps:

[0041] The state of charge SOC in (t) is calculated using the following formula:

[0042]

[0043] where SOC in (t - t step ) is the state of charge value of the system at the previous time step; t step is the time step; Q batt is the battery capacity of the target battery energy storage system.

[0044] The present invention also provides a system for implementing a method for constructing a simplified equivalent circuit model of the battery energy storage system, including a data acquisition module, a model equivalent module, a model simplification module, a parameter calculation module, and a model construction module; the data acquisition module, the model equivalent module, the model simplification module, the parameter calculation module, and the model construction module are connected in series in sequence; the data acquisition module is used to acquire data information of the target battery energy storage system and upload the data information to the model equivalent module; the model equivalent module is used to construct an equivalent circuit model of the target battery energy storage system without considering the polarization capacitance according to the received data information, and upload the data information to the model simplification module; the model simplification module is used to simplify the target battery energy storage system into a circuit model including a resistor and a voltage source according to the received data information and the constructed model by using Thevenin's theorem, and upload the data information to the parameter calculation module; the parameter calculation module is used to calculate the series current and state of charge of the model according to the received data information and the constructed model, and upload the data information to the model construction module; the model construction module is used to complete the construction of the simplified equivalent circuit model of the battery energy storage system according to the received data information and the obtained results.

[0045] The method and system for constructing a simplified equivalent circuit model of the battery energy storage system provided by the present invention, through the construction of an equivalent circuit model of the target battery energy storage system without considering capacitance and based on Thevenin's theorem for the construction of the circuit model and the calculation of parameters, not only realizes the construction of the simplified equivalent circuit model of the battery energy storage system, but also has higher reliability, better accuracy, and higher modeling effect. Brief Description of the Drawings

[0046] Figure 1 It is a schematic diagram of the method flow of the method of the present invention.

[0047] Figure 2 It is a schematic diagram of the SOC simulation result of the embodiment of the method of the present invention.

[0048] Figure 3 It is a schematic diagram of the functional modules of the system of the present invention. Detailed Embodiments

[0049] As Figure 1 shown is a schematic diagram of the method flow of the method of the present invention: The method for constructing a simplified equivalent circuit model of the battery energy storage system disclosed by the present invention includes the following steps:

[0050] S1. Acquire data information of the target battery energy storage system;

[0051] S2. Based on the data information obtained in step S1, without considering the polarization capacitance in the target battery energy storage system, and construct an equivalent circuit model of the target battery energy storage system that ignores capacitance; specifically including the following steps:

[0052] Based on the data information obtained in step S1, model the target battery energy storage system as an equivalent circuit model composed of several series and parallel Randles models;

[0053] In the Randles model, it includes resistance, polarization resistance, internal resistance, and open-circuit voltage, and the corresponding polarization capacitance is ignored; in the conventional Randles model, it includes resistance, polarization resistance, polarization capacitance, internal resistance, and open-circuit voltage. This model is intuitive and accurate, but it is extremely time-consuming in simulation calculations; and the method of the present invention is for the purpose of grid frequency regulation, assuming that the battery is in a steady-state operation state. Therefore, the polarization capacitance in the Randles model of the present invention can be ignored; the polarization capacitance is the main reason for the slow calculation. Ignoring it can greatly reduce the calculation burden, and it only has a certain impact on the dynamic performance of the model, while having a very small impact on the steady-state performance of the model;

[0054] Finally, construct an equivalent circuit model of the target battery energy storage system that ignores capacitance;

[0055] S3. According to the model constructed in step S2, using Thevenin's theorem, simplify the target battery energy storage system into a circuit model including a resistor and a voltage source; specifically including the following steps:

[0056] Using Thevenin's theorem, simplify the series and parallel battery systems of the target battery energy storage system into a circuit including a resistor R COMP and a voltage source OCV COMP ;

[0057] The sum of the resistances of the i-th branch is denoted as R series,i , and the sum of the voltage sources of the i-th branch is denoted as OCV series,i ;

[0058] Calculate R series,i using the following formula:

[0059]

[0060] In the formula, n is the number of resistors in the i-th branch; R ik is the resistance of the i-th branch, and R in =R W,kn +R P,kn +R I,kn , R W,kn is the wire resistance, R P,kn is the polarization resistance, R I,knis the internal resistance;

[0061] The OCV is calculated using the following formula series,i :

[0062]

[0063] where m is the number of voltage sources in the i-th branch; OCV j is the open-circuit voltage of the i-th branch;

[0064] The combined resistance R of the first branch to the i-th branch is calculated using the following formula comp,1..i :

[0065]

[0066] where R comp,1..(i-1) is the combined resistance of the first branch to the (i - 1)-th branch;

[0067] Disconnect the circuit of the target battery energy storage system, and the current I flowing through the i-th branch is calculated using the following formula CCi :

[0068]

[0069] where R CC,i is the sum of the resistances of the i-th branch and the (i - 1)-th branch, and R CC,i = R series,i + R series,i-1 ;

[0070] The calculated OCV series,i is OCV comp,i = OCV series,i-1 - (R series,i-1 )I CC ;

[0071] Finally, the OCV of the last branch nn series,nn and R series,nn are calculated, so as to obtain OCV comp = OCV series,nn and R comp = R series,nn ;

[0072] S4. According to the model constructed in step S3, calculate the series current and state of charge of the model;

[0073] During specific implementation, calculating the series current of the model specifically includes the following steps:

[0074] The system voltage V is calculated using the following formula system :

[0075] Vsystem =OCV comp +R comp I system

[0076] Where I system is the current passing through the battery system;

[0077] The series current I of the i-th branch is calculated string,i as

[0078] The state of charge of the calculation model, specifically including the following steps:

[0079] The state of charge SOC in (t) is calculated using the following formula:

[0080]

[0081] Where SOC in (t - t step ) is the state of charge value of the system at the previous time step; t step is the time step; Q batt is the battery capacity of the target battery energy storage system;

[0082] S5. According to the results obtained in steps S2 - S4, complete the construction of the simplified equivalent circuit model of the battery energy storage system.

[0083] The following further illustrates the method of the present invention in conjunction with an embodiment:

[0084] Set the detailed model as the reference model (i.e., the model considering the polarization capacitance), and use it to evaluate the performance of the model of the present invention. The evaluation index is accuracy, defined as the magnitude of the difference in the current calculation results between the current calculation result of the detailed model and i d and the current calculation result i neg of the model of the present invention, and the corresponding calculation formula is

[0085]

[0086] This error needs to be calculated for each simulation time step.

[0087] Meanwhile, this error is not limited to the evaluation of current, and other parameters such as the state of charge (SOC) are also applicable to this evaluation index.

[0088] For the evaluation of the running time, the simulation running time of each model can be recorded using the timing command in the MATLAB program for comparison with each other, and its time record refers to the real-time clock (RTC) of the computer used.

[0089] Considering that the battery energy storage system (BESS) is designed to achieve the function of grid frequency response, the dynamic containment (DC) load curve is used to explore the impact of ignoring capacitance on the model accuracy performance. This is because in various battery application scenarios, the response speed corresponding to the DC load curve may be the fastest. Assuming a DC operating state, the present invention applies the annual frequency data of a certain power grid to a single battery cell modeled by a detailed equivalent circuit model and the circuit model of the present invention. Among them, the load curve data is frequency data with a sampling time interval of 1 second.

[0090] Calculate the operating current of the battery model and the state of charge (SOC) of the battery. Using the data of operating with dynamic containment (DC) for a whole year, and calculate the error current data, the curve of which is as Figure 2 shown. Figure 2 The transient current waveform of a certain day is presented. At this moment, the error reaches the maximum value. However, 12 seconds after the maximum error appears, the error amplitude begins to decrease. This indicates that due to the absence of capacitance, there are certain differences in the calculation results, but this difference only has an impact during the transient process. The results show that when the model of the present invention is applied to frequency response, the absence of capacitance elements under transient conditions will not have a significant impact on the calculation results of battery current.

[0091] As Figure 3 shown in the schematic diagram of the functional modules of the system of the present invention: The system for implementing the construction method of the simplified equivalent circuit model of the battery energy storage system disclosed in the present invention includes a data acquisition module, a model equivalent module, a model simplification module, a parameter calculation module, and a model construction module; the data acquisition module, the model equivalent module, the model simplification module, the parameter calculation module, and the model construction module are connected in series in sequence; the data acquisition module is used to acquire the data information of the target battery energy storage system and upload the data information to the model equivalent module; the model equivalent module is used to construct an equivalent circuit model of the target battery energy storage system without considering the polarization capacitance in the target battery energy storage system according to the received data information, and upload the data information to the model simplification module; the model simplification module is used to simplify the target battery energy storage system into a circuit model including a resistor and a voltage source according to the received data information and the constructed model by using the Thevenin theorem, and upload the data information to the parameter calculation module; the parameter calculation module is used to calculate the series current and the state of charge of the model according to the received data information and the constructed model, and upload the data information to the model construction module; the model construction module is used to complete the construction of the simplified equivalent circuit model of the battery energy storage system according to the received data information and the obtained results.

Claims

1. A method for constructing a simplified equivalent circuit model of a battery energy storage system, comprising the following steps: S1. Obtain the data information of the target battery energy storage system; S2. According to the data information obtained in step S1, without considering the polarization capacitance in the target battery energy storage system, and construct an equivalent circuit model of the target battery energy storage system that ignores capacitance; S3. According to the model constructed in step S2, use Thevenin's theorem to simplify the target battery energy storage system into a circuit model containing a resistor and a voltage source; S4. According to the model constructed in step S3, calculate the series current and state of charge of the model; S5. According to the results obtained in steps S2 to S4, complete the construction of the simplified equivalent circuit model of the battery energy storage system.

2. The method for constructing a simplified equivalent circuit model of a battery energy storage system according to claim 1, wherein The step S2 of not considering the polarization capacitance in the target battery energy storage system according to the data information obtained in step S1 and constructing an equivalent circuit model of the target battery energy storage system that ignores capacitance specifically includes the following steps: According to the data information obtained in step S1, model the target battery energy storage system as an equivalent circuit model composed of several series and parallel Randles models; In the Randles model, it includes a resistor, a polarization resistor, an internal resistance, and an open-circuit voltage, and the corresponding polarization capacitance is ignored; Finally, construct an equivalent circuit model of the target battery energy storage system that ignores capacitance.

3. The method for constructing a simplified equivalent circuit model of a battery energy storage system according to claim 2, characterized in that The step S3 of using Thevenin's theorem to simplify the target battery energy storage system into a circuit model containing a resistor and a voltage source according to the model constructed in step S2 specifically includes the following steps: Using Thevenin's theorem, the series and parallel battery systems of the target battery energy storage system are simplified into a circuit including a resistor R COMP and a voltage source OCV COMP ; The sum of the resistances of the i-th branch is denoted as R series,i , and the sum of the voltage sources of the i-th branch is denoted as OCV series,i ; R is calculated using the following formula seriesi :[[-END]] where n is the number of resistors in the i-th branch; R ik is the resistor in the i-th branch, and R in = R W,kn + R P,kn + R I,kn , R W,kn is the wire resistance, R P,kn is the polarization resistance, R I,kn is the internal resistance; The OCV is calculated using the following formula seriesi :[[]]END]] where m is the number of voltage sources in the i-th branch; OCV j is the open-circuit voltage of the i-th branch; The combined resistance R of the 1st branch to the i-th branch is calculated using the following formula comp,1..i :[[]]END]] where R comp,1..(i-1) is the combined resistance of the 1st to (i - 1)th branches; Disconnect the circuit of the target battery energy storage system, and calculate the current I flowing through the i-th branch using the following formula CCi : where R CC,i is the sum of the resistances of the i-th branch and the (i - 1)-th branch, and R CC,i = R series,i + R series,i-1 ; Calculated OCV series,i is OCV comp,i = OCV series,i-1 -(R series,i-1 )I CC ; Finally, calculate the OCV of the last branch nn series,nn and R series,nn , thus obtaining the OCV comp = OCV series,nn and R comp = R series,nn .

4. The method for constructing a simplified equivalent circuit model of a battery energy storage system according to claim 3, wherein The specific steps of calculating the series current of the model in step S4 include the following steps: The system voltage V is calculated using the following formula system :[[]]END]] V system = OCV comp + R comp I system Where I system is the current passing through the battery system; Calculate the series current I of the i-th branch string,i is 5. The method for constructing a simplified equivalent circuit model of a battery energy storage system according to claim 4, wherein The specific steps of calculating the state of charge of the model in step S4 include the following steps: The state of charge SOC is calculated using the following formula in (t): where SOC in (t - t step ) is the state of charge value of the system at the previous time step; t step is the time step; Q batt is the battery capacity of the target battery energy storage system.

6. A system for implementing a method for constructing a simplified equivalent circuit model of the battery energy storage system according to any one of claims 1 to 5, characterized in that It includes a data acquisition module, a model equivalence module, a model simplification module, a parameter calculation module, and a model construction module; the data acquisition module, the model equivalence module, the model simplification module, the parameter calculation module, and the model construction module are connected in series in sequence; the data acquisition module is used to obtain the data information of the target battery energy storage system and upload the data information to the model equivalence module; the model equivalence module is used to, according to the received data information, without considering the polarization capacitance in the target battery energy storage system, and construct an equivalent circuit model of the target battery energy storage system that ignores capacitance, and upload the data information to the model simplification module; The model simplification module is used to, according to the received data information, use Thevenin's theorem to simplify the target battery energy storage system into a circuit model containing a resistor and a voltage source according to the constructed model, and upload the data information to the parameter calculation module; the parameter calculation module is used to, according to the received data information, calculate the series current and state of charge of the model according to the constructed model, and upload the data information to the model construction module; The model construction module is used to complete the construction of the simplified equivalent circuit model of the battery energy storage system according to the received data information and the obtained results.

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