Method for equalizing the charge state of an electrical energy storage device

Abstract

The present invention relates to a method for equalizing the state of charge of an electrical energy storage device having a plurality of battery cells of battery packs, comprising the steps of: detecting a voltage parameter which represents the voltage of the battery cells of the battery packs; determining the positive maximum charge of the battery cells of the battery packs with respect to a reference voltage level of all battery cells of the electrical energy storage device having an equalized state of charge; determining the negative maximum charge of the battery cells of the battery packs with respect to a reference voltage level of all battery cells of the electrical energy storage device having an equalized state of charge; determining the charge to be equalized of the battery cells of the battery packs; determining the charge error of the charge to be equalized; determining the charge to be equalized of the battery cells of the battery packs; if the charge to be equalized exceeds a pre-given threshold, calculating a duration for equalizing the state of charge of the battery cells of the battery packs based on the charge to be equalized; and equalizing the state of charge of the battery cells of the battery packs within the duration. Furthermore, the present invention relates to an electrical energy storage device, a computer program, a machine-readable storage medium and an application.

Description

Field of the Invention

[0001] The present invention relates to a method for equalizing the state of charge of an electrical energy storage device having a plurality of battery cells, an electrical energy storage device, a computer program, and an application of the method according to the preamble of the independent claim. Field of the Invention

[0003] In today's hybrid and electric vehicles, energy storage devices using lithium-ion technology are used, which are composed of a large number of electrochemically connected battery cells connected in series. The battery management system is used to monitor the energy storage device, and in addition to safety monitoring, it should ensure the highest possible service life.

[0004] To this end, it is necessary to ensure that the state of charge (Stage of Charge, "SOC") of the battery cells is coordinated with each other despite different self-discharges. This is achieved by means of charge state equalization ("Cell Balancing") through appropriate battery cell symmetrization, which is usually performed resistively. For this purpose, a resistor and a switching element are provided for each battery cell so that each battery cell can be discharged selectively via the ohmic resistor.

[0005] In addition to the different self-discharge rates of the individual battery cells, the capacities of the battery cells also differ from each other, for example due to production variations. This effect is negligibly small at the beginning of the life of the battery cells, but may increase during the service life of the battery cells due to differences in battery aging, and may lead to a capacity difference of several percent between the battery cells.

[0006] During the idle phase of the control device of the battery management system for controlling the energy storage device, charge state equalization is performed. For this purpose, an electronic unit for performing charge state equalization within a pre-given duration is activated. This pre-given is made during the shutdown of the control device. Therefore, it is not possible to adjust the programmed duration or the charge to be equalized or the charge to be equalized .

[0007] According to the current state of the art, the charge to be equalized and the duration of charge state equalization can be determined by means of the following relationship:

[0008] - Determine the charge of battery cell i in all battery cells of the battery pack relative to a reference state of charge of the charge :

[0009]

[0010] - Determine the charge to be equalized of battery cell i in all battery cells of the battery pack ("Balancing - Bedarf"):

[0011]

[0012] - Determine the duration of the equalization of the state of charge of battery cell i in all battery cells of the battery pack:

[0013]

[0014] The reference state of charge (Referenzladungszustand) is the state of charge taken by all battery cells having an equalized state of charge ("balanced state").

[0015] The charge is the minimum charge of all batteries relative to the reference state of charge of the charge.

[0016] Based on the measurement and calculation accuracy, the charge to be equalized and the associated duration .

[0017] Document CN103020445 discloses a method for predicting the SOC and SOH of a lithium iron phosphate battery pack installed in an electric vehicle. The prediction method includes the following steps: improving the Thevenin battery equivalent model; determining the state equation and output equation of the system; identifying the battery pack model parameters; using the Kalman filter algorithm to iterate the state variables of the system so that the predicted value of the SOC is closer to the actual value; and using a two - channel Kalman filter algorithm to perform an online prediction of the internal resistance and capacity of the lithium iron phosphate battery pack, and simultaneously predicting the SOH of the battery pack, i.e., the value of the battery pack in the current state and output state (Ausgangszustand), according to the changes in the internal resistance and capacity.

[0018] Document CN102231546 discloses a battery pack management system with balanced charging and discharging functions and its control method, which relates to a battery pack management system for dynamic battery packs. The battery pack management system is characterized in terms of its structure in that the control unit of the central unit is connected to the battery pack and the relay group in order to detect the operating states of the battery pack and the relay group. The control unit and the module for balanced discharging are successively connected to the battery pack and the relay group in order to control the balanced discharging of the battery pack and the relay group, wherein the control unit, the module for balanced charging are successively connected to the battery pack and the relay group in order to control the balanced charging of the battery pack and the relay group, wherein the supercapacitor is connected to the balanced discharging module in order to store the discharging energy of the battery pack and the relay group for supplying energy to the battery pack management system.

[0019] The object of the present invention is to further improve the prior art. This object is solved by the features of the independent claims. Summary of the Invention

[0020] Advantages of the Invention

[0021] The operating method according to the invention with the characteristic features of the independent claims, in contrast, has the following advantages: the calculation accuracy of the charge to be balanced is determined and taken into account in calculating the duration for balancing the state of charge. Thereby, the accuracy and efficiency of the state of charge balancing are improved, and thus the capacity and efficiency of the electrical energy storage are increased. For this purpose, the method for balancing the state of charge of an electrical energy storage with a plurality of battery pack cells has the following steps:

[0022] a) Detecting a voltage parameter , which represents the voltage of the battery pack cell i among a plurality of battery pack cells;

[0023] b) With respect to the reference voltage level of all battery pack cells of the electrical energy storage with a balanced state of charge , determining the positive maximum charge of the battery pack cell i according to the following :

[0024] ,

[0025] where represents the no-load voltage curve with a positive capacity estimation error, and represents the sensor tolerance of the detected voltage parameter and the modeled positive battery pack cell voltage error;

[0026] c) With respect to the reference voltage level of all battery pack cells of the electrical energy storage with a balanced state of charge , determining the negative maximum charge of the battery pack cell i among a plurality of battery pack cells according to the following :

[0027] ,

[0028] where represents an open-circuit voltage curve with a negative capacity estimation error, and represents the sensor tolerance of the detected voltage parameter and the modeled negative battery cell voltage error of the battery pack;

[0029] d) Determine the charge to be equalized for battery cell i in a plurality of battery cells of a battery pack according to the following :

[0030] ,

[0031] where represents the charge of battery cell i relative to a reference voltage level and represents the minimum charge of all battery cells in series relative to a reference voltage level ;

[0032] e) Determine the charge error of the charge to be equalized according to the following :

[0033] ,

[0034] where represents the charge of the battery cell with the minimum charge ; ;

[0035] f) Determine the charge to be equalized for the battery cell of the battery pack according to the following :

[0036] ,

[0037] where W represents a pre-given weighting factor;

[0038] g) If the charge to be equalized exceeds a pre-given threshold, calculate the duration for equalizing the state of charge of the battery cell based on the charge to be equalized according to the following

[0039] ,

[0040] where represents the ohmic resistance assigned to the battery cell;

[0041] h) Equalize the state of charge of the battery cells of the battery pack within a duration The method according to the invention is not limited to the order shown in this embodiment. More precisely, steps a to h can be carried out repeatedly, successively in time and / or simultaneously.

[0042] An electric energy storage device in the sense of the present invention should be understood as an energy storage device having a plurality of battery cells, from which electrical energy can be drawn or to which electrical energy can be supplied and drawn. The electric energy storage device is configured as a charge memory and / or a magnetic energy storage device and / or an electrochemical energy storage device. The electrochemical energy storage device is in particular a rechargeable battery pack or accumulator.

[0043] Other advantageous embodiments are the subject matter of the dependent claims.

[0044] If the weighting factor W takes the value 1, the entire charge error is subtracted from the charge to be equalized

[0045] and if the weighting factor W takes the value 0, the charge error is not taken into account .

[0046] The no-load voltage curve, sensor tolerance and / or capacity estimation error are determined statically and / or dynamically for determining the positive maximum charge and / or the negative maximum charge .

[0047] When determined statically, the positive charge with a fixed no-load voltage curve, sensor tolerance and / or capacity error and the negative maximum charge are determined as input error values, which are stored, for example, in a memory of the control device by means of a table.

[0048] When determined dynamically, the positive charge with a dynamic no-load voltage curve, sensor tolerance and / or capacity error and the negative maximum charge are determined as input error values, for example, the input parameters such as , and are determined dynamically, and the positive charge and the negative maximum charge are redetermined for each application case.

[0049] The reference voltage level of the battery cells of the electric energy storage device having an equalized state of charge of all battery cells is = 3.7 V. This corresponds to a state of charge of 50% of all battery cells of a 48 V energy storage device.

[0050] The capacity estimation error of the open-circuit voltage curve OCV is at most ±4%. From this, the uncertainty of charge determination can be reliably taken into account.

[0051] The electrical energy storage device advantageously includes a plurality of battery cells, at least one voltage sensor, and at least one device, in particular an electronic battery management control device, which is configured to perform the steps of the method according to the invention.

[0052] The electrical energy storage device has a discharge resistor for selectively discharging individual battery cells. In combination with a switching element, the individual battery cells can be discharged through this ohmic resistor in a targeted manner.

[0053] A computer program is advantageously provided, which includes instructions that cause: an electrical energy storage device according to the invention can implement the method steps of the method according to the invention.

[0054] A machine-readable storage medium is advantageously provided, on which a computer program is stored.

[0055] The method according to the invention is advantageously applied to an electrical energy storage device and a stationary memory, the electrical energy storage device being for an electric vehicle, a hybrid vehicle, a plug-in hybrid vehicle, an aircraft, an electric scooter or an electric bicycle, a portable device for telecommunications or data processing, an electric hand-held tool or an electric kitchen machine, and the stationary memory being for storing electrical energy obtained in particular in a regenerative manner. Description of the Drawings

[0056] Embodiments of the invention are shown in the drawings and are explained in more detail in the following description.

[0057] Figure 1 A schematic diagram showing the open-circuit voltage curve of the electrical energy storage device; and

[0058] Figure 2 A schematic diagram showing the computational uncertainty of charge determination for the charge to be balanced. Detailed Description of the Invention

[0059] In all the figures, the same reference numerals denote the same device components.

[0060] Figure 1 Showing the open-circuit voltage curve 100 ("OCV") of the electrical energy storage device in different states of health SOH C (beginning of life ("BOL") - end of life ("EOL")) of a schematic diagram.

[0061] Reference numeral Aging state [%] 101 95 102 90 103 85 104 80 105 75

[0062] These curves can be determined, for example, based on the battery type and chemistry of the battery pack through an aging test in the laboratory. All no-load voltage curves intersect at a 50% state of charge, which approximately corresponds to 3.7 in this case of battery type. This state of charge corresponds to a 48V energy storage system or accumulator with an equalized charge state of all battery pack cells.

[0063] In a battery management system, the no-load voltage curves are respectively used to determine the charge to be equalized, and the charge to be equalized substantially corresponds to the estimated capacity (OCV(SOH C )). The battery capacity can be determined by methods that are prior art. If the measured battery capacity is between two no-load voltage curves, the corresponding no-load voltage curve is interpolated.

[0064] If the currently estimated or maximum capacity estimation error is known, for example ±4%, then the enveloping no-load voltage curves with the maximum capacity estimation error can be determined. The actual no-load voltage curve of the battery pack cells lies within these enveloping no-load voltage curves.

[0065] The calculation accuracy of the charge to be equalized is related to the accuracy of the modeled no-load voltage, the measurement accuracy of the battery pack cell voltage measurement, and the accuracy of the modeled battery pack cell voltage. If the battery pack cells are completely relaxed, the error of the modeled battery pack cell voltage is equal to 0, otherwise this error is additively superimposed on the measurement accuracy of the battery voltage measurement.

[0066] If all battery pack cells should have a charge state of 3.7V in the equalized charge state, and for example, a battery voltage of 3.7V is measured, the capacity estimation error has no effect.

[0067] If the measured battery voltage deviates more and more from the reference voltage ( = 3.7V), the influence of the capacity estimation error increases. The voltage measurement error of the sensor and the error of the modeled battery pack cell voltage are additively superimposed on the no-load voltage error.

[0068] The accuracy of the state of charge equalization between the battery pack cells is improved by the method according to the present invention. The charge of the electrically serially connected battery pack cells is better equalized, and thus the capacity and efficiency of the accumulator are increased.

[0069] In the case of a 48V accumulator, the battery cells of the battery pack are balanced to a target state of charge of 50%. This means that the battery cells of the battery pack jointly experience a state of charge of 50%. By increasing the accuracy of the state of charge balancing, the minimum and maximum voltage limits are reached later, which results in an increase in the power of the electrical accumulator.

[0070] Furthermore, the number of unnecessary state of charge balancings ("Pseudobalancing") is minimized, which results in an increase in the discharge resistance and the service life of the accumulator.

[0071] Figure 2 Schematic illustration of the calculation unreliability of the charge determination for the charge to be balanced. Curve 201 shows Q Pos , and curve 202 shows Q Neg minus the specific charge Q to be balanced of the battery cells of the battery pack. For this calculation, a capacity estimation error of 3.5% is assumed with a voltage measurement accuracy of the voltage sensor of 3 mV.

Claims

1. A method for equalizing the state of charge of an electrical energy storage device having a plurality of battery cells, the method comprising the following steps: a) Detect the voltage parameter U mess，i , where the voltage parameter represents the voltage of the battery in the battery pack; b) Reference voltage level U of all battery cells of an electrical energy storage device with a balanced state of charge BalLevel , the positive maximum charge Q of the battery cells is determined according to the following i,Pos :[[]]END]] Q i,Pos = OCV PosErr (U mess,i + U PosErr ) - OCV PosErr (U BalLevel ), Among them, OCV PosErr represents an open-circuit voltage curve with a positive capacity estimation error, and U PosErr represents the sensor tolerance of the detected voltage parameter U mess,i and the modeled positive battery cell voltage error; c) Reference voltage level U of all battery cells of the electrical energy storage device with a balanced state of charge BalLevel , the negative maximum charge Q of the battery cells is determined according to the following i,Neg :[[]]END]] Q i,Neg = OCV NegErr (U mess,i - U NegErr ) - OCV NegErr (U BalLevel ), where OCV NegErr represents an open-circuit voltage curve with a negative capacity estimation error, and U NegErr represents the sensor tolerance of the detected voltage parameter U mess,i and the modeled negative battery cell voltage error; d) Determine the charge ΔQ to be equalized for the battery cells of the battery pack based on the following i : ΔQ i = Q i - Q min ,, where Q i represents the charge of the battery cells of the battery pack relative to the reference voltage level U BalLevel and Q min represents the minimum charge of all battery cells in series relative to the reference voltage level U BalLevel ; e) Determine the charge ΔQ to be equalized based on the following i charge error ΔQ i，Err : ΔQ i，Err = Q i，Pos - Q min，Neg , where Q min，Neg represents the charge Q min of a battery cell of the battery pack having the minimum charge Q i，Neg ; f) determining the charge ΔQ to be equalized for the battery pack cells according to the following i，use ΔQ i，use = ΔQ i - W * ΔQ i，err , where W represents a pre-givable weighting factor; g) If the charge ΔQ to be equalized i，use exceeds a pre-given threshold, then based on the charge ΔQ to be equalized i，use calculate the duration t for equalizing the state of charge of the battery cells of the battery pack i,bal : where R Bal represents the ohmic resistance assigned to the battery of the battery pack; h) Equalize the state of charge of the battery cells of the battery pack within the duration t i,bal ​ 2. The method according to claim 1, wherein if the weighting factor W takes the value 1, the entire charge error ΔQ is subtracted from the charge ΔQ to be equalized i and if the weighting factor W takes the value 0, the charge error ΔQ is not considered i，err . i，err .

3. The method according to claim 1 or 2, wherein the no-load voltage curve, the sensor tolerance and / or the capacity estimation error are determined statically and / or dynamically for determining the positive maximum charge Q i，Pos and / or the negative maximum charge Q i，Neg .

4. The method according to claim 1 or 2, wherein the reference voltage level U of the battery cells of the electrical energy storage having an equalized charge state of all battery cells of the battery pack is BalLevel U BalLevel = 3.7 V.

5. The method according to claim 1 or 2, wherein the capacity estimation error of the open-circuit voltage curve OCV is at most ±4%.

6. An electrical energy storage device, comprising a plurality of battery cells, at least one voltage sensor and at least one device configured to perform the steps of the method according to any one of claims 1 to 5.

7. The electrical energy storage device according to claim 6, wherein at least one device comprises an electronic battery management control device.

8. The electrical energy storage device according to claim 6 or 7, characterized in that the electrical energy storage device has a discharge resistor for selectively discharging individual battery cells.

9. A computer program product, comprising instructions that cause: the electrical energy storage device according to any one of claims 6 to 8 to perform the method steps according to any one of claims 1 to 5.

10. A machine-readable storage medium having stored thereon the computer program comprised in the computer program product according to claim 9.

11. An application of the method according to any one of claims 1 to 5 in the electrical energy storage device according to any one of claims 6 to 8 and in a stationary memory, the electrical energy storage device being for an electric vehicle, an aircraft, a portable device for telecommunication or data processing, an electric hand tool or a kitchen machine, the stationary memory being for storing electrical energy.

12. The application according to claim 11, wherein the electrical energy is obtained in a regenerative manner.

13. The application according to claim 11, wherein the electric vehicle comprises a hybrid vehicle, an electric scooter or an electric bicycle.

14. The application according to claim 13, wherein the hybrid vehicle comprises a plug-in hybrid vehicle.

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