Modelica-based electrochemical energy storage system modeling simulation method

Abstract

The invention belongs to the technical field of electrochemical energy storage simulation, and particularly relates to an electrochemical energy storage system modeling simulation method based on Modelica. Comprising the following steps of 1, splitting a model; 2, establishing a primary battery element model; 3, establishing a battery module assembly model; 4, establishing an energy storage converter model; and 5, establishing an electrochemical energy storage model. The method has the beneficial effects that aiming at modeling of the energy storage battery, the characteristics of the Modelica language are fully utilized, and an object-oriented modeling method is adopted for the single battery, so that the reusability, the universality and the expandability of the model are improved, and the modeling efficiency is further improved; multi-field unified modeling is adopted for the battery module, electric and thermal coupling simulation is achieved, and a preliminary thought is provided for multi-physical-field simulation of the electrochemical energy storage system.

Description

Technical Field

[0001] The invention belongs to the technical field of electrochemical energy storage simulation, and in particular relates to a modeling and simulation method for an electrochemical energy storage system based on Modelica. Background Art

[0002] The electrochemical energy storage system is a kind of energy storage system with flexible configuration, simple structure, fast response time, high energy density, and the ability to meet various energy storage needs. It is used in rail transit on-board energy storage, DC power systems, energy storage power stations and other fields.

[0003] In the process of electrochemical energy storage system design simulation analysis, the current main method is to use equation-based causal modeling (i.e., procedural modeling) to develop models, such as the model in the simscape battary in Matlab. The energy storage model obtained based on causal modeling has strong coupling, low reusability, versatility, and scalability. At the same time, it is difficult to achieve unified modeling of interdisciplinary models when used in dynamic system analysis models.

[0004] Conventional electrochemical energy storage system simulation modeling is generally based only on electrical models, without achieving real-time coupled calculation of electrical and thermal quantities. For example, the RC equivalent circuit model commonly used in electrochemical energy storage can only be used for battery electrodynamic design simulation, and cannot take into account the thermal design of the battery. Although relevant researchers have modeled and simulated electrochemical energy storage batteries based on the multi-domain modeling language characteristics of Modelica, the electrochemical energy storage model itself is still an electrical model. Summary of the invention

[0005] The purpose of the present invention is to provide a modeling and simulation method for an electrochemical energy storage system based on Modelica, which can solve the problems of low reusability, versatility and scalability of electrochemical energy storage models and realize unified modeling of multiple fields of electrochemical energy storage systems.

[0006] The technical solution of the present invention is as follows: A modeling and simulation method for an electrochemical energy storage system based on Modelica, comprising the following steps:

[0007] Step 1: Split the model;

[0008] Step 2: Establish the original battery component model;

[0009] Step 3: Establish a battery module component model;

[0010] Step 4: Establish the energy storage converter model;

[0011] Step 5: Establish an electrochemical energy storage model.

[0012] The step 1 includes splitting the electrochemical energy storage model into a battery module component model and an energy storage converter component model.

[0013] The step 2 includes the battery cell model including the following battery data of the packaged battery cell: nominal capacity A, nominal voltage U n , charging cut-off voltage U c , discharge cut-off voltage U d , internal resistance R Ω (ohm), polarization resistance R ρ , the discharge curve of the actual battery at normal temperature and pressure stored in a spreadsheet offline data.

[0014] In step 2, the original battery component model encapsulates the equivalent circuit model into the original battery class, and the equivalent circuit model is established using a first-order RC circuit or a second-order RC circuit.

[0015] The main parameters in the first-order RC circuit include: U OC Open circuit voltage, R Ω Battery internal resistance, R ρ Polarization resistance, C ρ Polarization capacitance, Ibattery current;

[0016] The main parameters in the second-order RC circuit include:

[0017] U OC Open circuit voltage, R Ω Battery internal resistance, R ρ1 Polarization resistance, C ρ1 Polarization capacitance, R ρ2 Polarization resistance, C ρ2 Polarization capacitance, Ibattery current;

[0018] The second-order RC circuit has two RC circuits corresponding to battery polarization, which are used to characterize the electrochemical polarization and concentration polarization of the battery respectively.

[0019] The constraint equations of the original battery element model established in step 2 are:

[0020] (1) The port constraints that characterize the energy flow satisfy:

[0021] Potential variable: V = av - bv

[0022] Flow variable: I = ai

[0023] Energy flow: P = VI

[0024] Where V is voltage and I is current;

[0025] (2) The constraints that characterize the battery properties are satisfied:

[0026] Ud ≤v≤U c

[0027] (3) The constitutive equation that characterizes the physical properties of the battery is constrained by the equivalent circuit of the actual primary battery. Taking the first-order RC equivalent circuit as an example, the establishment of the transient polarization time of the battery is not considered. In steady state:

[0028] Potential variable: v = U oc +(R Ω +R ρ )i.

[0029] The battery module assembly model described in step 3 is obtained based on the connection method of the single cell in the module and is established using an equivalent circuit model. As the basic parameters representing the connection method of the single cell model, the number of series cells s and the number of parallel branches p in the module are necessary parameters to characterize the connection method of the original cell. The equivalent circuit model parameters of the battery module can be obtained by correcting the equivalent circuit of the single cell using s and p.

[0030] The battery module component model in step 3 includes:

[0031] (1) The equivalent circuit model of the module component model obtained by characterizing the series-parallel relationship of single cells and its corresponding interface in Modelica;

[0032] (2) The mathematical relationship between the electrical and thermal interfaces is established based on the characteristics of the Modelica language to characterize the electrical and thermal coupling effects.

[0033] The energy storage converter component model described in step 4 is used to describe the actual physical model of the energy storage converter. According to the actual physical model of the energy storage converter, it is established as a passive two-port network model in Modelica. The established energy storage converter model includes 2 potential variables and 2 flow variables, namely:

[0034] Port 1: Potential variable U 1 , flow variable i 1 , energy flow U 1 i 1

[0035] Port 2: Potential variable U 2 , flow variable i 2 , energy flow U 2 i 2

[0036] Based on the physical characteristics of the energy storage converter, the above model should satisfy the constitutive equation:

[0037] Energy flow: U 1 i 1 +U 2 i2 =0.

[0038] The step 5 includes:

[0039] Battery module series model:

[0040] The flow variables of the ports connected in series are the same, and the final model potential variable is the sum of the potential variables of each battery module connected in series. The flow variables are the same as the battery module model;

[0041] Battery module parallel model:

[0042] The potential variables of the parallel ports are the same, the potential variables of the final model are the same as the original battery module model, and the flow variable is the sum of the flow variables of each parallel module.

[0043] The beneficial effects of the present invention are as follows: for the modeling of energy storage batteries, the characteristics of the Modelica language are fully utilized, and an object-oriented modeling method is adopted for battery cells, thereby improving the reusability, versatility and scalability of the model, thereby improving the modeling efficiency; a multi-domain unified modeling is adopted for the battery module to realize electrical and thermal coupling simulation, which provides a preliminary idea for the multi-physical field simulation of the electrochemical energy storage system. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 A schematic diagram of a modeling and simulation system for an electrochemical energy storage system based on Modelica provided by the present invention;

[0045] Figure 2 It is a model of a galvanic cell component;

[0046] Figure 3 It is a battery module component model;

[0047] Figure 4 It is the energy storage converter component model;

[0048] Figure 5 It is an electrochemical energy storage model. DETAILED DESCRIPTION

[0049] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0050] A modeling and simulation method for an electrochemical energy storage system based on Modelica comprises the following steps:

[0051] Step 1: Split the model

[0052] According to the physical model of the actual electrochemical energy storage system, the modeled energy storage model is split. Figure 1As shown, the electrochemical energy storage model is split into a battery module component model and an energy storage converter component model, wherein the battery module component model is split into a primary battery component model which is derived from the primary battery model based on the series-parallel connection of the circuit.

[0053] Step 2: Model the galvanic cell components

[0054] The galvanic cell component model is a unified modeling that comprehensively considers different types of electrochemical energy storage systems. The modeling of the galvanic cell adopts an object-oriented modeling method to improve the reusability of the model. After the properties of many types of electrochemical cells are abstracted, they are encapsulated as galvanic cell classes. When a specific electrochemical energy storage system is established, the basic parameters of its actual galvanic cell model are obtained by instantiating the galvanic cell class.

[0055] The galvanic cell component model includes the following battery data for packaged galvanic cells: nominal capacity A (Ah), nominal voltage U n (V), charging cut-off voltage U c (V), discharge cut-off voltage U d (V), internal resistance R Ω (ohm), polarization resistance R ρ (ohm), the discharge curve (open circuit voltage-battery capacity curve) of the actual battery at room temperature and pressure stored in a spreadsheet offline data.

[0056] The galvanic cell component model encapsulates the equivalent circuit model into the galvanic cell class.

[0057] The equivalent circuit model is established using a first-order RC circuit or a second-order RC circuit, where the main parameters of the first-order RC circuit include: U OC Open circuit voltage, R Ω Battery internal resistance, R ρ Polarization resistance, C ρ Polarization capacitance, Ibattery current;

[0058] The main parameters in the second-order RC circuit include:

[0059] U OC Open circuit voltage, R Ω Battery internal resistance, R ρ1 Polarization resistance, C ρ1 Polarization capacitance, R ρ2 Polarization resistance, C ρ2 Polarization capacitance, Ibattery current;

[0060] The second-order RC circuit has two RC circuits corresponding to battery polarization, which are used to characterize the electrochemical polarization and concentration polarization of the battery respectively.

[0061] The above parameters are encapsulated as class attributes. When modeling the energy storage battery, the simulator selects the corresponding equivalent circuit according to the battery type used and inputs the corresponding parameters to instantiate the model.

[0062] The primary battery component module is based on basic battery parameters and component mathematical modules. The primary battery component module is as follows: Figure 2 shown.

[0063] To facilitate the reusability of the model in multi-physics modeling, the primary battery class is established as a component module with two ports based on the Modelica language, and the constitutive equation of the model is constrained by the actual equivalent circuit model.

[0064] The following are the constraint equations of the established primary battery component model:

[0065] (1) The port constraints that characterize the energy flow satisfy:

[0066] Potential variable: V = av - bv

[0067] Flow variable: I = ai

[0068] Energy flow: P = VI

[0069] Where V is voltage, I is current, a and b are port codes; v represents potential; i represents current.

[0070] (2) The constraints that characterize the battery properties are satisfied:

[0071] U d ≤v≤U c

[0072] Among them U d is the battery discharge cut-off voltage; U c It is the battery charging cut-off voltage.

[0073] (3) The constitutive equation that characterizes the physical properties of the battery is constrained by the equivalent circuit of the actual primary battery. Taking the first-order RC equivalent circuit as an example, the establishment of the transient polarization time of the battery is not considered. In steady state:

[0074] Potential variable: v = U oc +(R Ω +R ρ )i

[0075] If a more special telephone battery or a battery based on other principles is used, the primary battery modeling can be performed by customizing the basic physical quantities and the mathematical equations that describe their physical relationships, but this model should not be included in the primary battery category.

[0076] Step 3: Build a battery module component model

[0077] The battery module component model reflects the electrical composition of the primary battery on the one hand, and the main heat dissipation method of the primary battery inside it on the other hand. In order to comprehensively consider the coupling of electricity and heat, the battery module model is implemented based on Modelica using a multi-domain unified modeling method. The key lies in establishing an interface module between the battery module electrical module and the thermodynamic module.

[0078] The battery module component model is obtained based on the connection mode of the single cell in the module, and is still established using the equivalent circuit model. As the basic parameters representing the connection mode of the single cell original battery model, the number of series cells s and the number of parallel branches p in the module are necessary parameters to characterize the connection mode of the original battery. The equivalent circuit model parameters of the battery module can be obtained by correcting the equivalent circuit of the single cell using s and p, which will not be repeated here.

[0079] In order to realize the electrical and thermal coupling simulation of the battery module, it is necessary to modify the battery module model based on the original battery component model. Taking the first-order RC equivalent circuit model as an example, the established battery module component model is as follows: Figure 3 shown.

[0080] Battery module component model, including

[0081] (1) The equivalent circuit model of the module component model obtained by characterizing the series-parallel relationship of single cells and its corresponding interface in Modelica;

[0082] (2) The mathematical relationship between the electrical and thermal interfaces is established based on the characteristics of the Modelica language to characterize the electrical and thermal coupling effects.

[0083] like Figure 3 As shown in the figure, the model of the reaction battery kinetic characteristics refers to the original battery component model. For the heat dissipation model of the reaction battery module, the energy flow port is modified as follows:

[0084] Electric energy flow: P e =spVI

[0085] Thermal energy flow: P t =sI 2 (R Ω +R ρ ) / p

[0086] Among them, s is the number of primary cells in a series branch in the battery module; p is the number of parallel branches in the battery module; V and I are the potential variable and flow variable in a single primary cell model, respectively.

[0087] Modelica supports one-dimensional thermodynamic modeling calculations. In this case, the xy port (such as Figure 3) and add boundary conditions to solve. For complex thermodynamic models, a general interface is established between the xy ports through the heat energy flow port and the dedicated thermodynamic analysis model (such as the CFD numerical calculation model). After solving the thermodynamic problem between the xy ports using professional analysis software, the heat energy flow is returned to the component model in Modelica through the xy port. Therefore, the established xy port model is as follows:

[0088] Potential variable: H = xh-yh;

[0089] Flow variable: G = xg

[0090] Energy flow: P = HG

[0091] Among them, x and y are port codes, h represents enthalpy, and g represents mass flow

[0092] Where H is enthalpy and G is mass flow. Energy conservation between xy ports means that the sum of the energy flow and thermal energy flow at the port is zero.

[0093] Step 4: Build the energy storage converter model

[0094] The energy storage converter component model is used to describe the actual physical model of the energy storage converter. The energy storage converter component module of the present invention will ignore the energy loss of the converter itself.

[0095] In actual electrochemical energy storage, the battery is usually connected to the system through an inverter. The inverter is usually a DC / DC converter based on power electronics technology to match the battery voltage with the corresponding system voltage.

[0096] In the present invention, the energy storage converter model is established as an ideal, energy-conserving interface model.

[0097] Therefore, according to the actual physical model of the energy storage converter, it is established as a passive two-port network model in Modelica, such as Figure 4 shown.

[0098] The established energy storage converter model contains two potential variables and two flow variables, which are determined by the actual physical model of the energy storage converter. That is:

[0099] Port 1: Potential variable U 1 , flow variable i 1 , energy flow U 1 i 1

[0100] Port 2: Potential variable U 2 , flow variable i 2 , energy flow U 2 i 2

[0101] Based on the physical characteristics of the energy storage converter, the above model should satisfy the constitutive equation:

[0102] Energy flow: U 1 i 1 +U 2 i 2 =0.

[0103] The actual flow direction of energy between the two ports and the port voltage relationship should be determined by the actual conversion circuit model and its corresponding control method. This part is not modeled in the present invention.

[0104] Step 5: Build an electrochemical energy storage model

[0105] The actual electrochemical energy storage system consists of a battery system and an energy storage converter system. The battery system is generally composed of several battery modules connected in series and in parallel. Each battery module is generally placed symmetrically in a battery box and receives the same cooling effect. Therefore, the actual battery system model is obtained based on the battery module model. The electrical model of the battery system can be obtained according to the connection method of its battery modules, as described below:

[0106] Battery module series model:

[0107] The flow variables of the ports connected in series are the same, and the final model potential variable is the sum of the potential variables of each battery module connected in series. The flow variables are the same as the battery module model.

[0108] Battery module parallel model:

[0109] The potential variables of the parallel ports are the same, the potential variables of the final model are the same as the original battery module model, and the flow variable is the sum of the flow variables of each parallel module.

[0110] In addition, based on the design and simulation purpose of the electrochemical energy storage system, the simulation of the electrodynamics and heat dissipation performance of the battery module is often the focus of engineering design. Therefore, this patent uses the battery module as the basic unit to model the electrical and thermal models, and the connection method of the battery module in the battery pack constitutes the final electrochemical energy storage model.

[0111] The final battery system model is obtained by connecting the specified number of battery module models in the actual energy storage system according to the corresponding ports, and then the two ports of the battery system model after lumping are connected to one of the ports of the energy storage converter component model to obtain the electrochemical energy storage system model, such as Figure 5 shown.

[0112] The specific contents of the electrochemical energy storage model include:

[0113] (1) In order to distinguish the primary battery component models obtained by using different types of batteries, this model fully utilizes the characteristics of the Modelica language, expands the extensibility and reusability of the model, and adopts an object-oriented modeling method. The primary battery component model is encapsulated as a class, and the physical model of each parameter in the class is mathematically modeled using an equivalent circuit.

[0114] (2) In order to characterize the electrical and thermal coupling of the system, the electrical and thermal mathematical models and corresponding interfaces of the battery module model are established by combining the advantages of the Modelica language in modeling in multiple physical fields.

[0115] (3) In order to enable the established model to be simulated in the system, an ideal energy storage conversion model is used to establish an interface model that represents the energy storage system and the upstream system, namely the energy storage conversion model.

[0116] Figure 5 The left side of the port is the battery system model, which is composed of a specific number of battery module component models connected in series and parallel. The heat dissipation effect of the battery pack is evenly distributed to each battery module, that is, the constraint equations and solutions of the xy ports of each battery module component are the same. The port of the battery pack is connected to the 1 port of the energy storage converter component. The potential variables, flow variables and energy flows of the connected ports are the same, which is used as the condition for solving the equation.

Claims

1. A modeling and simulation method for an electrochemical energy storage system based on Modelica, characterized in that: The steps include: Step 1: Split the model; Step 2: Establish the original battery component model; Step 3: Establish a battery module component model; Step 4: Establish the energy storage converter model; Step 5: Establish an electrochemical energy storage model.

2. The electrochemical energy storage system modeling and simulation method based on Modelica according to claim 1, characterized in that: The step 1 includes splitting the electrochemical energy storage model into a battery module component model and an energy storage converter component model.

3. The electrochemical energy storage system modeling and simulation method based on Modelica according to claim 1, characterized in that: The step 2 includes the battery cell model including the following battery data of the packaged battery cell: nominal capacity A, nominal voltage U n , charging cut-off voltage U c , discharge cut-off voltage U d , internal resistance R Ω , polarization resistance R ρ , the discharge curve of the actual battery at normal temperature and pressure stored in a spreadsheet offline data.

4. The electrochemical energy storage system modeling and simulation method based on Modelica as claimed in claim 3, characterized in that: In step 2, the original battery component model encapsulates the equivalent circuit model into the original battery class, and the equivalent circuit model is established using a first-order RC circuit or a second-order RC circuit. The main parameters in the first-order RC circuit include: U OC Open circuit voltage, R Ω Battery internal resistance, R ρ Polarization resistance, C ρ Polarization capacitance, I battery current; The main parameters in the second-order RC circuit include: U OC Open circuit voltage, R Ω Battery internal resistance, R ρ1 Polarization resistance, C ρ1 Polarization capacitance, R ρ2 Polarization resistance, C ρ2 Polarization capacitance, I battery current; The second-order RC circuit has two RC circuits corresponding to battery polarization, which are used to characterize the electrochemical polarization and concentration polarization of the battery respectively.

5. The electrochemical energy storage system modeling and simulation method based on Modelica according to claim 4, characterized in that: The constraint equations of the original battery element model established in step 2 are: (1) The port constraints that characterize the energy flow satisfy: Potential variable: V = av - bv Flow variable: I = ai Energy flow: P = VI Where V is voltage and I is current; (2) The constraints that characterize the battery properties are satisfied: IN d ≤v≤U c (3) The constitutive equation that characterizes the physical properties of the battery is constrained by the equivalent circuit of the actual primary battery. Taking the first-order RC equivalent circuit as an example, the establishment of the transient polarization time of the battery is not considered. In steady state: Amount of change: v=U oc +(R Ω +R ρ )i.

6. The electrochemical energy storage system modeling and simulation method based on Modelica according to claim 1, characterized in that: The battery module assembly model described in step 3 is obtained based on the connection method of the single cell in the module and is established using an equivalent circuit model. As the basic parameters representing the connection method of the single cell model, the number of series cells s and the number of parallel branches p in the module are necessary parameters to characterize the connection method of the original cell. The equivalent circuit model parameters of the battery module can be obtained by correcting the equivalent circuit of the single cell using s and p.

7. A method for modeling and simulating an electrochemical energy storage system based on Modelica as claimed in claim 6, characterized in that: The battery module component model in step 3 includes: (1) The equivalent circuit model of the module component model obtained by characterizing the series-parallel relationship of single cells and its corresponding interface in Modelica; (2) The mathematical relationship between the electrical and thermal interfaces is established based on the characteristics of the Modelica language to characterize the electrical and thermal coupling effects.

8. The electrochemical energy storage system modeling and simulation method based on Modelica according to claim 1, characterized in that: The energy storage converter component model described in step 4 is used to describe the actual physical model of the energy storage converter. According to the actual physical model of the energy storage converter, it is established as a passive two-port network model in Modelica. The established energy storage converter model includes 2 potential variables and 2 flow variables, namely: Port 1: potential variable U1, flow variable i1, energy flow U1i1 Port 2: potential variable U2, flow variable i2, energy flow U2i2 Based on the physical characteristics of the energy storage converter, the above model should satisfy the constitutive equation: Energy flow: U1i1+U2i2=0.

9. The electrochemical energy storage system modeling and simulation method based on Modelica according to claim 1, characterized in that: The step 5 includes: Battery module series model: The flow variables of the ports connected in series are the same, and the final model potential variable is the sum of the potential variables of each battery module connected in series. The flow variables are the same as the battery module model; Battery module parallel model: The potential variables of the parallel ports are the same, the potential variables of the final model are the same as the original battery module model, and the flow variable is the sum of the flow variables of each parallel module.

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