CN110909443A - High-precision battery pack charging remaining time estimation method and system - Google Patents
High-precision battery pack charging remaining time estimation method and system Download PDFInfo
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Abstract
The invention relates to a high-precision battery pack charging remaining time estimation method and system, which accurately estimate the remaining charging time aiming at different constant-current constant-voltage charging stages by carrying out stage processing on the battery pack charging process and setting a temperature threshold value and combining temperature prediction of a battery pack thermal model in the battery charging process, thereby improving the accuracy of battery pack charging time prediction.
Description
Technical Field
The invention relates to the technical field of electricity, in particular to a high-precision method and a system for estimating the charging remaining time of a battery pack.
Background
With the continuous development of battery technology, rechargeable batteries are being widely used, and are widely and massively used in the fields of mobile phones, wearable devices, automobiles and the like. The rechargeable battery brings great convenience to life and also necessarily brings the operation of charging the battery. In the charging process, the charging time is the most important influence on the use experience, and a user naturally wants to be able to accurately know the remaining charging time of the device so as to be able to schedule the charging time leisurely. However, there is no specific and reliable method for estimating the remaining charging time when the device to be charged is charged, and only a rough estimation can be made by dividing the remaining charging capacity by the charging current. The method of rough estimation can obtain closer charging time under ideal conditions, but in the actual charging process, as the temperature of the battery rises, the charging current will be reduced, so that the residual charging time calculated for multiple times does not linearly decrease along with the increase of the charging time as expected, and in the extreme case, the feedback is increased along with the residual charging time.
Even batteries of the same batch and the same model have differences in capacity, internal resistance and the like due to processes and the like in the manufacturing process, and continuous charge and discharge cycles lead to larger and larger differences among the batteries in the long-term use process, thereby causing inconsistency in charging of the battery pack. On the other hand, as the living standard is improved, more accurate time control is required in each field, so that the method has important significance for accurately estimating the residual time of the battery charging.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a high-precision battery pack charging remaining time estimation method and system.
In order to achieve the above purpose, the technical scheme adopted by the invention comprises the following steps:
a high-precision battery pack charging remaining time estimation method comprises the following steps:
A. establishing a battery pack charging and heating simulation model library file based on charging parameters in the charging process so as to obtain a battery pack charging and heat generating model, obtaining boundary conditions based on a Newton cooling law so as to obtain a battery pack charging and heat dissipating model, and establishing a battery pack thermal model by combining the battery pack charging and heat generating model and the battery pack charging and heat dissipating model;
B. estimating the state of charge of the battery pack when the battery pack starts to charge according to the historical condition of the use of the battery pack, wherein the historical condition comprises the discharge time, the current voltage, the open-circuit voltage and the discharge current of the battery pack;
C. calculating the number of hours to be charged of the battery pack according to the charge state when the battery pack starts to be charged and the total ampere-hour number of the battery pack;
D. dividing the charging process into a constant current stage and a constant voltage stage according to the voltage change of a battery cell of the battery pack; the constant current stage is a charging stage in which the voltage of the battery does not reach the maximum voltage when the single battery is fully charged; the constant voltage stage is a charging stage after the battery voltage reaches the maximum voltage when the battery monomer is fully charged;
E. b, predicting a temperature rise value of the battery pack during charging in the constant-current stage by combining the battery pack thermal model obtained in the step A so as to calculate the charging time in the constant-current stage;
F. calculating the charging time at the constant voltage stage by using a current reduction curve at the constant voltage stage;
G. and accumulating and calculating the residual charging time of the battery pack by adopting a sectional integration method according to the obtained charging time at the constant current stage and the charging time at the constant voltage stage.
Further, the step A comprises the following substeps:
a1, establishing a battery pack charging and heating simulation model library file according to the charging voltage, the charging current, the charging time and the temperature of each point in the battery pack in the actual charging test;
a2, establishing a battery pack charging and heat generating model by combining a battery monomer heat generating rate model established by the heat generating rates of unit volumes of positive and negative lugs through a battery pack charging thermal simulation model library file, wherein the battery pack charging and heat generating model calculates the temperature of a battery pack through the charging voltage, the charging current and the charging time of the battery pack;
a3, obtaining a battery pack charging and heat dissipation model through a boundary condition obtained through Newton's cooling law;
and A4, combining the simultaneous battery pack charging heat generation model and the battery pack charging heat dissipation model to obtain a battery pack thermal model.
Further, the step B comprises the step of calculating the optimal value of the state of charge of the battery pack at the beginning of charging by an iterative method by adopting linear discretization of a first-order RC equivalent circuit model.
Further, the step E comprises the following substeps:
e1, further dividing the constant current stage into a plurality of charging stages; setting a battery pack temperature threshold value of charging staging, and setting available charging current within each threshold value range according to the battery pack temperature threshold value;
e2, aiming at a certain charging stage, predicting a temperature rise value in the charging process of the battery pack in the stage by using the thermal model of the battery pack obtained in the step A and calculating the charging time of the charging stage; if the temperature rise of the battery pack in the charging process of the stage does not reach the temperature threshold of the battery pack, and the available charging current is not reduced in the charging process of the stage, directly using the charging ampere hours required by the charging stage and the available charging current to obtain the charging time prediction of the charging stage; if the temperature rise of the battery pack in the charging process at the stage is in contact with the temperature threshold of the battery pack, and the available charging current is reduced due to the temperature rise of the battery pack in the charging process at the stage, predicting the charging condition after the available charging current is reduced according to the temperature threshold of the battery pack, and calculating the charging time prediction under the condition; simultaneously calculating the remaining ampere hours to be charged after the charging is finished in stages;
e3, when the charging is finished in stages, judging whether the constant current stage is finished; if the constant current stage is judged to be finished, entering a constant voltage stage, if the constant current stage is not judged to be finished, entering the next charging stage and executing the step E2;
e4, when it is determined in substep E3 that the constant current phase has ended, indicating that substep E2 has been performed for all charging phases, then the charging time predictions for all charging phases are accumulated to obtain the constant current phase charging time.
Further, the substep a2 further comprises performing temperature correction using multi-channel temperature real-time acquisition.
Further, the step B further includes judging whether the state of charge of the battery pack when charging is started is too low; and if the charge state is judged to be too low, performing low-current pre-charging on the battery pack.
A high-precision battery pack charging remaining time estimation system comprises a data acquisition module, a battery pack thermal model establishment module and a battery pack remaining charging time calculation module which are in data connection with one another;
the data acquisition module comprises a voltage acquisition circuit and a current acquisition circuit;
the battery pack thermal model establishing module is used for establishing a battery pack charging thermal simulation model library file according to charging voltage, charging current, charging time and temperatures of all points in the battery pack in an actual charging test acquired by the data acquisition module, establishing a battery pack charging heat generation model by combining the battery pack charging thermal simulation model library file with a battery monomer heat generation rate model established by heat generation rates of unit volumes of positive and negative lugs, obtaining a battery pack charging heat dissipation model by obtaining boundary conditions according to a Newton cooling law, and obtaining a battery pack thermal model by combining a simultaneous battery pack charging heat generation model and a battery pack charging heat dissipation model;
the battery pack residual charging time calculation module estimates the charge state of the battery pack when the battery pack starts to charge according to the history situation of the use of the battery pack, calculates the ampere hours to be charged of the battery pack according to the charge state of the battery pack when the battery pack starts to charge and the total ampere-hour number of the battery pack, calculates the charging time of the battery pack in a constant current stage and the charging time of the battery pack in a constant voltage stage respectively based on the battery pack thermal model established by the battery pack thermal model establishment module and by using a constant voltage stage current descending curve, and then calculates the battery pack residual charging time.
Furthermore, the data acquisition module also comprises a temperature acquisition circuit, and the temperature acquisition circuit acquires the multichannel temperature of the battery pack in real time.
Further, the data acquisition module is a data acquisition device arranged on a battery management system originally possessed by the battery pack.
The invention has the beneficial effects that:
the method and the system for estimating the residual charging time of the high-precision battery pack are adopted to estimate the residual charging time of the battery pack, the charging process of the battery pack is processed in stages and a temperature threshold is set, the temperature prediction in the charging process of the battery pack is combined with the thermal model of the battery pack, the residual ampere hours are firstly obtained and the charging process is divided into a plurality of stages when the residual charging time is calculated, and then the ampere hours required to be charged in the current stage are determined; the charging current and the battery thermal model at different stages are used for estimating the time for charging the batteries at different stages, so that the charging time in each charging stage is respectively calculated according to the temperature rise condition of the battery pack, and the accuracy of charging time prediction is improved; according to the method, the temperature change in the battery charging process is considered, so that the size of the battery charging current can be predicted more accurately, the remaining time estimation method is optimized, and finally the remaining charging time of the battery pack can be calculated according to the charging time of different stages. For the constant-current charging stage, whether the temperature of the battery pack reaches a temperature threshold value is judged through the prediction of the temperature rise in the charging process of the battery pack in each charging stage, and whether the available charging current is reduced is further judged to correct the prediction of the charging time; and calculating the charging time required by the constant-voltage charging stage by using a fixed current descending curve, and adding the charging time required by the constant-current charging stage and the constant-voltage charging stage to obtain a predicted value of the residual charging time of the battery pack. The method avoids the charging time prediction deviation caused by the fluctuation of the charging current affected by the temperature in the prior art through the staged prediction, and can accurately indicate the residual charging time to a user at any charging stage; the thermal model of the battery pack and the segmentation principle of the charging process are simple and easy to understand, the calculation method is reliable, the obtained calculation result has enough accuracy and can meet the requirement of charging time prediction, the method can be applied to various charging battery use scenes, and the application range is wide. The high-precision battery pack charging remaining time estimation system is realized without using a complex circuit, can fully utilize the existing circuit devices of the battery pack and a management system, has low cost and good maintainability, and has sufficient market application prospect.
Drawings
Fig. 1 is a schematic flow chart of a high-precision battery pack charging remaining time estimation method according to the present invention.
Fig. 2 is a schematic diagram of a high-precision system for estimating the remaining charging time of a battery pack according to the present invention.
Fig. 3 is a charging current and voltage curve diagram of the constant current charging stage and the constant voltage charging stage according to the embodiment of the invention.
Detailed Description
For a clearer understanding of the contents of the present invention, reference will be made to the accompanying drawings and examples.
The invention aims at the problems that most of the charging process is divided into a plurality of sections when the battery is charged at present, and the design improvement is carried out according to different constant current and constant voltage conditions in the charging process. Before calculation, a heat generation model and a heat dissipation model are established for the heat generation and heat dissipation characteristics required by different batteries to be used so as to obtain a finally used battery thermal model.
Aiming at different constant-current constant-voltage charging stages, the method that the charging current is obtained only by looking up a table according to the current battery temperature and the residual charge (SOC) which are widely adopted at present is improved, the battery temperature rise in the charging process is predicted by utilizing a battery thermal model, so that the charging time is prolonged due to the reduction of the charging current caused by the battery temperature rise, and the accurate charging time can be estimated more accurately.
Then, in estimating the battery charging time, for different phases: calculating or looking up a table according to the current temperature and SOC to obtain a charging current, and predicting the temperature rise, wherein if the current can complete the current charging stage, the charging time prediction of the stage is directly obtained by using the charging electric quantity and the charging current; if the charging current is used and the current at the later charging stage is reduced due to the estimated temperature rise, predicting a reduction curve of the charging current by using a battery thermal model, wherein the charging time corresponding to the curve is the time of the stage; the same applies to the latter stages. And finally, adding the sum of all the stage time to obtain the charging remaining time of the battery pack.
That is, firstly, according to battery characteristics (cell voltage and capacity, total battery voltage and the like) and battery environment conditions, respectively establishing a battery pack charging heat generation model and a battery pack charging heat dissipation model (heat generation model and heat dissipation model for short), and establishing a battery pack thermal model by integrating the heat generation model and the heat dissipation model; when the charging remaining time is calculated, firstly, the remaining ampere hours are obtained, the charging process is divided into a plurality of stages, and then the ampere hours required to be charged in the current stage are determined; and estimating the time used for charging the batteries at different stages by using the charging current at different stages and the thermal model of the battery pack. The method considers the temperature change in the battery charging process, so that the system can more accurately predict the magnitude of the battery charging current so as to optimize the remaining time estimation method, and finally the remaining charging time of the battery pack can be calculated according to the charging time of different stages.
Fig. 1 is a schematic flow chart of the method for estimating the remaining charging time of the high-precision battery pack according to the present invention, which comprises the following steps:
A. establishing a thermal model of the battery pack, preferably, specifically comprising the following steps:
a1, establishing a battery pack charging and heating simulation model library file according to the charging voltage, the charging current, the charging time and the temperature of each point in the battery pack in the actual charging test, namely establishing a thermal simulation model library file in the battery cell charging process according to the charging voltage, the charging current, the charging time and the temperature of each point in the battery pack in the actual charging test, wherein the software can use comsol or ANSYS Workbench, and the library file comprises the simulation of the battery charging condition in different service conditions under different environmental conditions;
a2, establishing a battery pack charging and heat generating model by combining a battery monomer heat generating rate model established by the heat generating rates of unit volumes of positive and negative electrode ears through a battery pack charging heat simulation model library file, calculating the temperature of the battery pack through the charging voltage, the charging current and the charging time of the battery pack by the battery pack charging and heat generating model, and/or performing temperature correction by using multi-channel temperature real-time acquisition, wherein the battery pack charging and heat generating model is as follows:
in the formula, the left side of the equal sign is increment (unsteady state quantity) of the thermodynamic energy of the battery micro-element in unit time, the sum of the first three terms on the right side of the equal sign is the energy (diffusion quantity) increased by the heat transfer action of the battery micro-element in unit time, and the last term q on the right side is the heat generation rate (source term) of the battery. Rho is the average density of the battery, kg/m3(ii) a Cp is the average specific heat capacity of the battery, and the value is determined according to the circumstances (1050J/(kg · K) is used in the patent); t is the battery temperature, K; t is time, s; kx, ky and kz are thermal conductivities inside the battery along the directions of an x axis, a y axis and a z axis, and W/(m.K); q is the heat generation rate per unit volume of the battery, W/m3；
The heat generation rate model of the battery monomer is as follows:
wherein Vb is the volume of the battery, m3(ii) a I is the charging and discharging current of the battery, A is a negative value during charging and a positive value during discharging; u is the cell voltage, U0 is the cell open circuit voltage, V; t is the battery temperature, K; dU0/dT is a temperature coefficient, and 0.22mV/K is taken;
the heat generation rate model of the unit volume of the positive electrode lug and the negative electrode lug is as follows:
wherein qAl and qCu are the heat generation rate per unit volume of the anode tab and the cathode tab of the battery respectively, and W/m3(ii) a QAl and QCu are the heating values of the positive and negative electrode tabs of the battery respectively, W; RAl and RCu are the resistance of the positive and negative electrode tabs, omega, respectively; VAl, VCu are the volumes of the positive and negative electrode tabs, m3；
The battery monomer heat generation rate model q is obtained based on the heat generation rates of unit volumes of the positive electrode ear and the negative electrode ear in a simultaneous manner, so that a battery pack charging heat generation model can be obtained, a temperature calculation formula is used in the actual calculation in a simultaneous manner, and the used temperature calculation formula is similar to the following form:
wherein Δ T1Is the temperature rise value after a certain charging time, A is the calculated proportionality coefficient, B is the correction parameter,
and
the charging voltage and the charging current. Thus, the rising value of the battery temperature after a certain charging time can be obtained;
a heat generation model during battery charging can be established through the model library file obtained in the step A1, and the heat generation model participates in charging decision in actual use by calling a function fitting curve; in the function calculation formula, the battery temperature can be predicted by inputting the charging voltage, the charging current and the charging time; meanwhile, as an optimal scheme, a multi-channel temperature real-time acquisition can be used for correcting a temperature result for a battery heat generation model in actual charging, so that the calculation is more accurate;
a3, obtaining a battery pack charging and heat dissipation model through a boundary condition obtained through a Newton cooling law, wherein the boundary condition obtained through the Newton cooling law is as follows:
wherein h is the convective heat transfer coefficient of the cell and the surrounding fluid; t ∞ is the temperature of the fluid surrounding the battery; t is the surface temperature of the battery; lambda is the thermal conductivity of the nominal material of the cell; n is a vector direction vertical to the surface of the battery, can be in the directions of x, y and z axes, and can be used for calculating the temperature delta T after heat dissipation2；
When a battery heat dissipation model is established, the shape, the material and the environmental heat dissipation condition of the battery need to be comprehensively considered. For example, the shapes of the power batteries which are mainstream at present are cylindrical batteries, square aluminum shell batteries and soft package batteries. Different materials are different in different heat dissipation modes: at present, the lithium iron phosphate type square battery is mainly adopted in the domestic electric automobile power battery, and heat dissipation is realized in a mode of an aluminum plate and an additional fan or liquid cooling is realized; the 18650 electric core power battery module that Tesla adopted only adopts the liquid cooling structure, and the heat is transmitted to the liquid cooling pipe through the heat conduction silica gel gasket, and is taken away by the free circulation flow of expansion with heat and contraction with cold of the cooling liquid, so that the temperature of the whole battery pack is balanced and uniform; some enterprises begin to pay attention to the direct cooling method of the solid-liquid mixed cooling refrigerant as the battery cooling. Aiming at different heat dissipation layouts and different heat dissipation modes, working conditions are often complex in the use of an actual battery, but the lower simulation precision can meet the requirement of actual use under the simple working condition of vehicle static charging;
a4, combining the simultaneous battery pack charging heat generation model and the battery pack charging heat dissipation model to obtain a battery pack thermal model for predicting the battery temperature at each stage, wherein the specific formula is as follows:
Tn＝Tn-1+ΔT1+ΔT2
namely, the charging voltage, the current and the time at the moment are input, so that the temperature at the next moment can be calculated.
B. Estimating the state of charge of the battery pack when the battery pack starts to charge according to the historical condition of the use of the battery pack, judging whether the state of charge of the battery pack when the battery pack starts to charge is too low, and if the state of charge is judged to be too low, performing low-current pre-charging on the battery pack; the estimation comprises the steps of adopting linear discretization of a first-order RC equivalent circuit model, and calculating to obtain an optimal value of the state of charge when the battery pack starts to be charged by an iteration method, wherein the historical conditions comprise the discharge time, the current voltage, the open-circuit voltage and the discharge current of the battery pack; specifically, for example, using kalman filtering, the calculation formula uses a first-order RC equivalent circuit model (i.e., Thevenin model), and for this model, the state equation and the observation equation are as follows:
the linear discretization is carried out as follows:
wherein:
UD actual measurement terminal voltage V; RD is the battery internal resistance, Ω, given by the current SOC lookup table; ri is the internal resistance of the battery, omega, given by SOC lookup at the last moment; iL is the discharge current, A; u ∞ is the open circuit voltage, V; ut is the estimated terminal voltage, V; t is the discharge time, s; CD is the capacitance value in the external characteristics of the battery, F; wk is the process noise of the system, and is basically determined by the noise of the current, and Vk is the variance of the voltage measurement noise; input i using time k-1(k-1) and a matrix A, B, estimating the prior estimate and covariance matrix at time k in the filtering algorithm. And calculating an innovation error and Kalman gain by using the prior estimation value, the measurement value at the moment k and the matrix C to obtain the posterior estimation. And correcting the prior estimation value and the covariance matrix at the k moment according to the Kalman gain and the innovation to finally obtain the estimation value at the k moment, and performing repeated iteration to obtain the SOC optimal value.
C. Calculating the number of hours to be charged of the battery pack according to the charge state of the battery pack when the battery pack starts to be charged and the total ampere-hour number of the battery pack, wherein the calculation formula is Cnow＝SOC×CallIn which C isallThe total ampere hours of the current battery pack is determined by the characteristics of the battery pack.
D. Dividing the charging process into a constant current stage and a constant voltage stage according to the voltage change of a battery cell of the battery pack; the constant current stage is a charging stage in which the voltage of the battery does not reach the maximum voltage when the single battery is fully charged; the constant voltage stage is a charging stage after the battery voltage reaches the maximum voltage when the battery monomer is fully charged; as shown in fig. 3, the battery charging process is first a constant current phase, i.e. the current is constant while the voltage curve rises, and then a constant voltage phase, i.e. the voltage is constant while the current is decreasing in a curve;
the method divides a charging process into a plurality of stages, in a system with the existing battery management, the charging management is completed in a subsection mode, and when a platform without the charging management is used, a developer presets, for example: when the voltage of a battery monomer is 4.2V when full, the voltage is reduced to 3.8V after being placed for a period of time or slightly used, and when the voltage is used up to 2.8V, the battery voltage is set to be charged in a constant current before reaching 4.2V, 1C charging is carried out before the temperature does not exceed 55 ℃ (C is a method for representing the comparison current of the nominal capacity of the battery, such as the battery is 1000mAh capacity, 1C is charging current 1000mA), 0.8C charging is carried out at 55 ℃, 0.8C charging is carried out at 60 ℃, 0.5C charging is carried out at 60 ℃, the battery voltage reaches 4.2V, constant voltage charging is carried out, 4.5V voltage is used, the current is slowly reduced, and finally the charging process can be divided into a plurality of stages;
in designing the charging process of a battery, a charging strategy is often given certain guidance by a battery supplier. Common strategies include two: firstly, according to the setting of the charging temperature of the battery, the charging current of the battery under a certain temperature condition has a corresponding limit value, and the charging is only required to be carried out below the limit value; secondly, the charging current is determined according to the SOC of the battery, and when the corresponding SOC value reaches a certain threshold value, the corresponding charging current is generated. In practical use, manufacturers generally adopt a first charging strategy, and divide the battery charging strategy into a plurality of stages according to current levels corresponding to different temperatures, which are generally divided into two stages: the constant current stage charging is firstly carried out, and then the constant voltage stage charging is carried out. The constant current stage can be divided into many small stages, such as: when the voltage of the battery is lower, the corresponding residual capacity in the battery is also relatively lower, and at the moment, the battery needs to be subjected to large-current constant-current charging, and the battery is often charged at 1C of the capacity of the battery; when the temperature of the battery is detected to rise to a critical point in the charging process (a battery factory usually sets that 1C charging can be carried out before the critical point reaches 55 ℃, the charging needs to be carried out when the temperature reaches 55 ℃, and the like, and the charging is carried out when the temperature is reduced to 0.8C, the charging current is reduced, and the constant current charging at the next charging current value stage is carried out; the general charging process is: for a battery pack with specific capacity, the magnitude of charging current is firstly obtained by a certain coefficient so as to carry out constant current charging, and the power supply of a storage battery is continuously increased during charging, so that the charging can be accelerated at this stage; when the voltage of the battery pack monomer reaches a charging threshold value, constant voltage charging is carried out, the threshold value transferred in the stage is set differently according to different proportions, and the battery charging can be completed directly in the stage. However, there are many segmentation methods, such as detecting whether the battery capacity is too low before constant current charging and adding a pre-charging link (charging by using battery 0.1C), or adding a section of constant current charging or pulse charging after constant voltage charging, so that the battery can be charged better; in practice, the current and voltage levels can be subdivided in constant current charging and constant voltage charging.
E. And B, predicting a temperature rise value of the battery pack during constant-current stage charging by combining the battery pack thermal model obtained in the step A, and calculating the charging time of the constant-current stage, wherein the method specifically comprises the following steps:
e1, further dividing the constant current stage into a plurality of charging stages; setting a battery pack temperature threshold value of charging staging, and setting available charging current within each threshold value range according to the battery pack temperature threshold value;
e2, aiming at a certain charging stage, predicting a temperature rise value in the charging process of the battery pack in the stage by using the thermal model of the battery pack obtained in the step A and calculating the charging time of the charging stage; if the temperature rise of the battery pack in the charging process of the stage does not touch the temperature threshold of the battery pack, namely the available charging current is not reduced in the charging process of the stage, directly using the charging ampere hours required by the charging stage and the available charging current to obtain the charging time prediction ti of the charging stage; if the temperature rise of the battery pack in the charging process at the stage is in contact with the temperature threshold of the battery pack, namely the available charging current is reduced due to the temperature rise of the battery pack in the charging process at the stage, predicting the charging condition after the available charging current is reduced according to the temperature threshold of the battery pack and calculating the charging time prediction ti under the condition; while using formula Cn＝Call-Cnow-Cn-1Calculating the remaining number of hours to be charged after the charging is completed in stages, wherein Cn-1The number of hours of charge is the number of hours of charge;
e3, when the charging is finished in stages, judging whether the constant current stage is finished; if the constant current stage is judged to be finished, entering a constant voltage stage, if the constant current stage is not judged to be finished, entering the next charging stage and executing the step E2;
e4, when the constant current stage is judged to be finished in the substep E3, namely the substep E2 is executed for all the charging stages, and the charging time of all the charging stages is predicted and accumulated to obtain the charging time of the constant current stage;
F. calculating the charging time at the constant voltage stage, including calculating the charging time ti at the constant voltage stage by using a fixed current-dropping curve, where the constant voltage charging stage is usually the last charging stage of the battery and the current-dropping curve is fixed, as shown in fig. 3, the charging time corresponding to the curve can be directly used as the time t of the charging stagei；
G. Calculating the residual charging time of the battery pack by using a sectional integration method to accumulate the charging time in the constant current stage and the charging time in the constant voltage stage to obtain a predicted value of the residual charging time of the battery pack
Wherein t isiThe time taken for the different phases.
The invention also comprises a high-precision battery pack charging remaining time estimation system, which corresponds to the high-precision battery pack charging remaining time estimation method and can be understood as an estimation system for realizing the estimation method, and the estimation system has a structure shown in figure 2 and comprises a data acquisition module, a battery pack thermal model establishment module and a battery pack remaining charging time calculation module which are in data connection with each other; the data acquisition module comprises a voltage acquisition circuit, a current acquisition circuit and an optional temperature acquisition circuit, the temperature acquisition circuit acquires the temperature of the battery pack in real time in a multi-channel manner, each acquisition circuit can be a data acquisition device arranged on a battery management system originally arranged on the battery pack, for example, when the data acquisition device is used in a pure electric vehicle or a plug-in hybrid electric vehicle, no additional module or detector is needed to be added, the vehicle is integrated, and the segmented charging current are respectively transmitted to the battery management system on the existing battery management system; the battery pack thermal model establishing module establishes a battery pack charging thermal simulation model library file according to charging voltage, charging current, charging time and temperature of each point in the battery pack in an actual charging test acquired by the data acquisition module, establishes a battery pack charging heat generation model by combining the battery pack charging thermal simulation model library file with a battery monomer heat generation rate model established by heat generation rates of unit volumes of positive and negative lugs, obtains a battery pack charging heat dissipation model by obtaining boundary conditions according to a Newton's cooling law, obtains a battery pack thermal model by combining the battery pack charging heat generation model and the battery pack charging heat dissipation model in a simultaneous manner, and specifically refers to the establishing of the battery pack thermal model in the estimating method step A; the battery pack residual charging time calculation module estimates the charge state of the battery pack when the battery pack starts to charge according to the history situation of the use of the battery pack, calculates the number of ampere hours to be charged of the battery pack according to the charge state of the battery pack when the battery pack starts to charge and the total ampere-hour number of the battery pack, respectively calculates the charging time of the constant current stage and the charging time of the constant voltage stage of the battery pack, specifically refers to the estimation method, predicts the temperature rise value of the battery pack when the battery pack is charged in the constant current stage based on the established battery pack thermal model to further calculate the charging time of the constant current stage of the battery pack (step E), calculates the charging time of the constant voltage stage by using a current reduction curve of the constant voltage stage (step F), and further calculates the battery pack.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (9)
1. A high-precision battery pack charging remaining time estimation method comprises the following steps:
A. establishing a battery pack charging and heating simulation model library file based on charging parameters in the charging process so as to obtain a battery pack charging and heat generating model, obtaining boundary conditions based on a Newton cooling law so as to obtain a battery pack charging and heat dissipating model, and establishing a battery pack thermal model by combining the battery pack charging and heat generating model and the battery pack charging and heat dissipating model;
B. estimating the state of charge of the battery pack when the battery pack starts to charge according to the historical condition of the use of the battery pack, wherein the historical condition comprises the discharge time, the current voltage, the open-circuit voltage and the discharge current of the battery pack;
C. calculating the number of hours to be charged of the battery pack according to the charge state when the battery pack starts to be charged and the total ampere-hour number of the battery pack;
D. dividing the charging process into a constant current stage and a constant voltage stage according to the voltage change of a battery cell of the battery pack; the constant current stage is a charging stage in which the voltage of the battery does not reach the maximum voltage when the single battery is fully charged; the constant voltage stage is a charging stage after the battery voltage reaches the maximum voltage when the battery monomer is fully charged;
E. b, predicting a temperature rise value of the battery pack during charging in the constant-current stage by combining the battery pack thermal model obtained in the step A so as to calculate the charging time in the constant-current stage;
F. calculating the charging time at the constant voltage stage by using a current reduction curve at the constant voltage stage;
G. and accumulating and calculating the residual charging time of the battery pack by adopting a sectional integration method according to the obtained charging time at the constant current stage and the charging time at the constant voltage stage.
2. The method of claim 1, wherein step a comprises the substeps of:
a1, establishing a battery pack charging and heating simulation model library file according to the charging voltage, the charging current, the charging time and the temperature of each point in the battery pack in the actual charging test;
a2, establishing a battery pack charging and heat generating model by combining a battery monomer heat generating rate model established by the heat generating rates of unit volumes of positive and negative lugs through a battery pack charging thermal simulation model library file, wherein the battery pack charging and heat generating model calculates the temperature of a battery pack through the charging voltage, the charging current and the charging time of the battery pack;
a3, obtaining a battery pack charging and heat dissipation model through a boundary condition obtained through Newton's cooling law;
and A4, combining the simultaneous battery pack charging heat generation model and the battery pack charging heat dissipation model to obtain a battery pack thermal model.
3. The method of claim 1, wherein step B comprises calculating the state of charge optimum at the beginning of charging the battery pack by an iterative method using linear discretization of a first-order RC equivalent circuit model.
4. The method of claim 1, wherein step E comprises the substeps of:
e1, further dividing the constant current stage into a plurality of charging stages; setting a battery pack temperature threshold value of charging staging, and setting available charging current within each threshold value range according to the battery pack temperature threshold value;
e2, aiming at a certain charging stage, predicting a temperature rise value in the charging process of the battery pack in the stage by using the thermal model of the battery pack obtained in the step A and calculating the charging time of the charging stage; if the temperature rise of the battery pack in the charging process of the stage does not reach the temperature threshold of the battery pack, and the available charging current is not reduced in the charging process of the stage, directly using the charging ampere hours required by the charging stage and the available charging current to obtain the charging time prediction of the charging stage; if the temperature rise of the battery pack in the charging process at the stage is in contact with the temperature threshold of the battery pack, and the available charging current is reduced due to the temperature rise of the battery pack in the charging process at the stage, predicting the charging condition after the available charging current is reduced according to the temperature threshold of the battery pack, and calculating the charging time prediction under the condition; simultaneously calculating the remaining ampere hours to be charged after the charging is finished in stages;
e3, when the charging is finished in stages, judging whether the constant current stage is finished; if the constant current stage is judged to be finished, entering a constant voltage stage, if the constant current stage is not judged to be finished, entering the next charging stage and executing the step E2;
e4, when it is determined in substep E3 that the constant current phase has ended, indicating that substep E2 has been performed for all charging phases, then the charging time predictions for all charging phases are accumulated to obtain the constant current phase charging time.
5. The method of claim 2 wherein substep a2 further comprises temperature correction using a multi-channel real-time temperature acquisition.
6. The method of claim 1, wherein step B further comprises determining if the state of charge at which the battery pack begins to charge is too low; and if the charge state is judged to be too low, performing low-current pre-charging on the battery pack.
7. A high-precision battery pack charging remaining time estimation system comprises a data acquisition module, a battery pack thermal model establishment module and a battery pack remaining charging time calculation module which are in data connection with one another;
the data acquisition module comprises a voltage acquisition circuit and a current acquisition circuit;
the battery pack thermal model establishing module is used for establishing a battery pack charging thermal simulation model library file according to charging voltage, charging current, charging time and temperatures of all points in the battery pack in an actual charging test acquired by the data acquisition module, establishing a battery pack charging heat generation model by combining the battery pack charging thermal simulation model library file with a battery monomer heat generation rate model established by heat generation rates of unit volumes of positive and negative lugs, obtaining a battery pack charging heat dissipation model by obtaining boundary conditions according to a Newton cooling law, and obtaining a battery pack thermal model by combining a simultaneous battery pack charging heat generation model and a battery pack charging heat dissipation model;
the battery pack residual charging time calculation module estimates the charge state of the battery pack when the battery pack starts to charge according to the history situation of the use of the battery pack, calculates the ampere hours to be charged of the battery pack according to the charge state of the battery pack when the battery pack starts to charge and the total ampere-hour number of the battery pack, calculates the charging time of the battery pack in a constant current stage and the charging time of the battery pack in a constant voltage stage respectively based on the battery pack thermal model established by the battery pack thermal model establishment module and by using a constant voltage stage current descending curve, and then calculates the battery pack residual charging time.
8. The system of claim 7, wherein the data acquisition module further comprises a temperature acquisition circuit that performs multi-channel real-time temperature acquisition on the battery pack.
9. The system of claim 7 or 8, wherein the data acquisition module is a data acquisition device arranged on a battery management system originally provided in the battery pack.
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