CN102761141B - Electric quantity correction and control method of lithium ion power storage battery - Google Patents

Abstract

The invention provides a power correction and control method for a lithium-ion power storage battery. First, charge the lithium-ion battery with the standard charging system, periodically measure the terminal voltage of the battery, use the difference voltage DELTA-VH in the measured voltage to determine the power parameter of the battery, correct the battery power, and use the terminal voltage to judge the cycle of the battery at this time Rep Equivalence, Aging Level, or Health Status. These information are then displayed to the user of the battery so that the user of the battery knows the current status of the battery (such as the current maximum charging capacity of the battery and the state of health of the battery). Then the battery goes through a controlled discharge process to make the battery or battery pack work in the optimal SOC range and reach the specified remaining capacity range. The invention is suitable for power management of pure electric vehicles (EV) and hybrid electric vehicles (HEV), and can prolong the service life of batteries.

Description

A method for power correction and control of a lithium-ion power storage battery

technical field

The invention relates to a method for correcting and controlling the electric quantity (SOC) of a lithium-ion power storage battery, which is suitable for estimating and correcting the SOC of a power storage battery for a hybrid electric vehicle (HEV), so as to control the SOC within the optimum use range and avoid battery overcharge or overdischarge phenomenon. Belongs to the technical field of rechargeable lithium-ion power batteries

Background technique

The development of batteries for electric vehicles (EV) and hybrid electric vehicles (HEV) has made people pay more attention to high-energy and high-power battery systems. Factors restricting the practical application of high-energy and high-power batteries include single battery performance consistency, high-temperature performance, SOC estimation, actual operating life and price, among which SOC estimation is related to the correct use of the battery pack and affects the actual operation of the battery pack. Lifetime is therefore a very important parameter.

Many methods of measuring SOC have been proposed at home and abroad, but in actual battery application, due to the variability of the use environment (discharge rate, temperature, etc.) and the change of the chemical characteristics of the battery itself (aging, self-discharge, etc.), the estimation of SOC become very complicated. Some devices attempt to estimate the remaining charge by measuring the current drawn from the battery and how long it has been used (ampere-hour integration). However, this method fails to take into account the natural discharge of the battery and a battery that has been used for a long time cannot be charged to 100% of its rated capacity. Therefore, a method for estimating SOC with a modified method based on the ampere-hour integration method has emerged. An example is given to illustrate commonly used methods for assisting in estimating SOC, and then its limitations are pointed out.

The auxiliary correction methods used on the basis of the ampere-hour integral method generally fall into the following two categories.

1. Discharge condition look-up table method

The SOC relationship table of the battery at different discharge voltages, currents and temperatures is obtained by the experimental method. When the actual system uses the battery as the power supply, the remaining capacity can be obtained according to the discharge voltage, current and temperature of the battery. The disadvantage is that a lot of experiments are required, and the impact of battery cycle times and self-discharge on SOC is not considered.

2. Internal resistance correction method

The relationship between battery internal resistance, temperature and remaining capacity is measured experimentally, and the system can correct SOC according to the measured battery internal resistance. Since the internal resistance reflects the factors of battery aging, the relative estimation result is more accurate. However, it is not easy to accurately measure the internal resistance, and it is easy to interfere with the charging and discharging procedure.

For lithium-ion batteries, the open-circuit voltage method can be used to directly obtain the corresponding SOC from the measured open-circuit voltage according to the open-circuit voltage-SOC curve of the battery, but there are three problems in this method.

(1) Due to the consistency of the single battery, the discharge curve of each battery is slightly different, especially for the battery with poor power characteristics in the battery pack, it is easy to cause overcharge and overdischarge by using this method to estimate SOC.

(2) For batteries with particularly flat discharge curves, such as lithium-ion batteries made of certain electrode materials, open-circuit voltage measurement errors can lead to large SOC estimation errors.

(3) Obtaining the open-circuit voltage of the battery requires the battery to stand for a long time. If the standing time is too long, the battery cannot be used normally, and if the standing time is too short, the battery cannot reach a stable open-circuit state, resulting in a large estimation result deviation.

In addition, since HEV power batteries are often used in the environment of frequent charge and discharge, the SOC of the battery should have a margin for charge and discharge to avoid overcharge and overdischarge; Battery Life.

To sum up, aiming at the various deficiencies in the SOC power calibration and control methods reported in the prior art, the present invention intends to provide a calibration and control method to overcome the deficiencies in the prior art.

Contents of the invention

The invention provides a method for correcting and controlling the electric quantity of a lithium-ion power storage battery, which is characterized in that it is a correction and control method for correcting the upper limit of the electric quantity of the battery (SOC) by using the charging cut-off difference voltage DELTA-VH, and using the charging and discharging current, time, The battery temperature and the differential voltage of the battery terminal voltage determine the power parameters of the battery. When the charging cut-off differential voltage reaches a certain limit value, that is, the differential cut-off voltage DELTA-VH, check the differential voltage database to determine the battery power at this time. Thereby correcting the current capacity of the battery. According to the battery terminal voltage, check the cut-off voltage database to judge the equivalent number of cycles or the degree of aging or health status of the battery at this time. The charging cut-off differential voltage DELTA-VH refers to applying a specified charging current to the battery, collecting the terminal voltage of the battery periodically, collecting the first terminal voltage in the first cycle, and collecting the second terminal voltage in the second cycle, from the second The differential voltage determined by subtracting the first terminal voltage from the terminal voltage. The period refers to a sampling period of data, or multiple sampling periods. The charge cut-off differential voltage is used as an index of the look-up table (differential voltage database), and the electric quantity parameter is obtained therefrom. The voltage at the second terminal is used as the index of the look-up table (cut-off voltage database), from which the cycle number equivalent or aging degree or health state is obtained. The electric power parameter is the operating curve of the battery and the points on the operating curve, wherein the equivalent number of cycles refers to the equivalent value of the number of charge and discharge cycles used by the battery or battery pack, and is related to the second terminal voltage at which the battery is charged. This information is then displayed to the user so that the user knows the maximum capacity and current charge of the battery. The user makes an informed judgment as to whether the battery is adequate for its intended project. It is also possible to adjust the SOC to the optimum operating range of the HEV battery through a controlled discharge process. The power parameter can also be output to another process such as SOC estimation for capacity control.

The specific implementation steps of applying the second terminal voltage to determine the cycle number equivalent, aging degree or health state of the battery or battery pack are as follows:

1) First charge the battery with the standard charging system, the control circuit periodically measures the terminal voltage of the battery, select the battery terminal voltage measured in one cycle as the first terminal voltage, and record the battery terminal voltage measured in the second cycle as the second terminal voltage Two-terminal voltage, remove the value of the first terminal voltage from the second terminal voltage to obtain the differential voltage DELTA-L, until the differential voltage DELTA-L reaches the charging cut-off differential voltage DELTA-VH, record the second terminal at this time The voltage is V _H . The period refers to a sampling period of data, or multiple sampling periods. The standard charging system is a certain charging system determined according to the specific use conditions. It consists of a temperature value and a charging rate value. Generally, it can be set at 25°C and charged at the XC rate (X is 1, 2, 3...). The specific value of the charging cut-off differential voltage DELTA-VH is determined by the characteristics of the battery or battery pack and provided by the battery manufacturer.

2) According to the second terminal voltage, obtain the capacity Q of the battery or the battery pack under the standard charging system and the _number of cycles n or the number of cycles equivalent n' of the battery or the battery pack at this time in the cut-off voltage database by the method of looking up the table, and Corrected the current SOC to be 100%. The standard charging system is a certain charging system determined according to the specific use conditions, consisting of a temperature value and a charging rate value, generally set at 25°C, and charge at the XC rate (X takes 1, 2, 3...). The cycle number equivalent n' refers to the equivalent value of the number of charge and discharge cycles used by the battery or battery pack, which is related to the second terminal voltage V _H of the battery charge cut-off, and the relationship is determined by experiments in advance or provided by the battery manufacturer. obtained and stored in the cut-off voltage database. The capacity Q0 is only related to the _number of cycles n or equivalent n' of the number of cycles and the charging system, and the relationship is determined in advance by experiments or obtained from data provided by battery manufacturers.

3) Discharge in a standard discharge system to discharge an electric quantity Q such that SOC _H > SOC > SOC _L . The standard discharge system is a certain discharge system determined according to the specific use conditions, which consists of a temperature value and a discharge rate value. Generally, 25°C is used to discharge at a rate of 1C. The electric quantity Q is calculated by the formula Q=∫Idt. The SOC is defined as SOC=(1-Q/Q ₀ )*100%. The _SOCH and _SOCL are respectively the upper limit and the lower limit of the optimal working range of the power battery for HEV, and it is generally desirable that SOCH = 70% and _{SOCL =} 30%. The specific value of SOC can generally be taken as (SOCH _{+ SOCL} )/2.

4) Steps 1) to 3) constitute a complete SOC correction and control process.

5) During the driving process, the SOC under the standard charging and discharging system can be known at any time through the ampere-hour integral method. The discharge lower limit is controlled by the discharge cut-off voltage V _L . The specific value of the discharge cut-off voltage V _L is determined by the characteristics of the battery or battery pack, and is generally provided by the battery manufacturer.

6) If the driver finds that the SOC often reaches the upper and lower limits of charge and discharge during driving, it means that after a period of use, the average SOC has deviated from the optimal working range. At this time, the SOC correction process can be started to correct and adjust .

There are several different embodiments of the invention. These embodiments include applying a prescribed charging current to the battery and periodically sampling the terminal voltage of the battery. The first terminal voltage is collected in the first cycle, the second terminal voltage is collected in the second cycle, the first terminal voltage is subtracted from the second terminal voltage to determine the differential voltage, and the differential voltage is used to check the differential voltage database to determine The power parameter of the battery, and outputting the power parameter. Another embodiment is to measure the voltage at the first terminal in the first period, measure the voltage at the second terminal in the second period, apply the voltage difference between the voltage at the second terminal and the voltage at the second terminal minus the voltage at the first terminal, and apply the difference The value voltage checks the differential voltage database to determine the power parameter of the battery, and outputs the power parameter.

Another type of embodiment is to apply a specified charging current to the battery, and periodically collect the terminal voltage of the battery. Select one of the sampling periods to measure the first terminal voltage of the battery, and select one of the next sampling periods to measure the second terminal voltage of the battery. Subtracting the voltage at the first terminal from the voltage at the second terminal to determine a differential voltage, using the differential voltage to search a database of differential voltages to determine a power parameter of the battery, and outputting the power parameter. Another embodiment is to select one of the sampling periods to measure the first terminal voltage of the battery, select one of the next sampling periods to measure the second terminal voltage of the battery, and apply the second terminal voltage and the second The differential voltage obtained by subtracting the first terminal voltage from the terminal voltage, determining the power parameter of the battery by checking the differential voltage database, and outputting the power parameter.

To sum up, the present invention provides a power calibration and control method for a lithium-ion traction battery. First, charge the lithium-ion battery with the standard charging system, periodically measure the terminal voltage of the battery, use the difference voltage DELTA-VH in the measured voltage to determine the battery power parameter, correct the battery power, and use the terminal voltage to judge the battery cycle at this time Rep Equivalence, Aging Level, or Health Status. These information are then displayed to the user of the battery so that the user of the battery knows the current status of the battery (such as the current maximum charging capacity of the battery and the state of health of the battery). Then the battery goes through a controlled discharge process to make the battery or battery pack work in the optimal SOC range and reach the specified remaining capacity range. The invention is suitable for power management of pure electric vehicles (EV) and hybrid electric vehicles (HEV), and can prolong the service life of batteries.

Description of drawings

Figure 1 shows a preferred embodiment of a circuit for implementing the invention.

Figure 2 shows how to use battery current, terminal voltage, temperature and other parameters to determine the power parameters.

Figure 3 is the charging curve (a) of a 55Ah lithium-ion battery at 55°C and the charging curve (b) at room temperature (25°C).

detailed description

In order to fully demonstrate the advantages and effects of the present invention, the substantive features and remarkable progress of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Example 1

Figure 1 shows a preferred embodiment of a circuit for implementing the invention. The circuit 17 includes a display 12, a charging and discharging circuit 16, a voltage monitoring circuit 13, a current monitoring circuit 15, a temperature monitoring circuit 14 and a main controller circuit with a microprocessor, a memory, a timer, a counter and the like. The specific implementation method is as follows:

1) Connect the battery 18 and the charging and discharging circuit 16 in a conventional way;

2) connect the control circuit 11 comprising a single-chip microcomputer or a similar chip and the charge-discharge circuit 16 in a conventional manner;

3) The conventional connection between the battery 18 and the control circuit 11 includes the voltage monitoring circuit 13, the current detection circuit 15 and other parameter devices, and the conventional connection of the parameter circuit 14 for monitoring temperature and the like and the device 12 for displaying the SOC value can also be added;

4) Use the voltage, current and other parameters detected during battery charging to calculate and correct the upper limit SOC of the battery or battery pack with a single-chip computer, and adjust the SOC to the best working range of the HEV battery through a controlled discharge process .

Example 2

Figure 2 shows how to use battery current, terminal voltage, temperature and other parameters to determine the power parameters. The specific implementation method is as follows:

1) The difference voltage calculation device 205 receives the first terminal voltage measured by the voltage detection device 202 in the first cycle, and receives the second terminal voltage measured by the voltage detection device 202 in the second cycle, during which the timing device 203 records two measurements Periodic time intervals, the current detection device 204 measures and records the magnitude of the charging current;

2) remove the value of the first terminal voltage from the second terminal voltage to obtain the differential voltage DELTA-L;

3) Compare the differential voltage DELTA-L with the cut-off differential voltage DELTA-VH recorded or preset in the threshold limiting device 201, if DELTA-L≥DELTA-VH, then the threshold voltage recording device 209 records The voltage at the second terminal of the battery is V _H , and the SOC correction device 208 corrects the SOC value of the battery at this time to 100%;

4) The cycle number calculation device 207 calculates the cycle number n or the cycle number equivalent n' according to the V _H recorded in the cut-off voltage database 206 and 209;

5) The cut-off differential voltage DELTA-VH in the threshold limiting device 201 is obtained by checking the differential voltage database 211 according to the cycle time interval and the charging current;

6) Discharge the battery in a standard system, 203 and 204 record the discharge time and current, and the power meter 210 calculates the battery discharge power to correct the battery SOC to the optimal working range.

Example 3

Figure 3(a) and (b) list the charging curves of 55Ah lithium-ion batteries at 55°C and normal temperature at 25°C. The differential voltages of these curves are provided by manufacturers of lithium-ion batteries.

The biggest advantage of the present invention is that the battery can always work within the optimal SOC range, and the correction process can be started at any time if there is a slight deviation, which can prolong the service life of the power battery, and is especially suitable for power management of HEV power batteries.

Claims (10)

1. A power calibration method for a lithium-ion traction battery, characterized in that: determine the power parameter of the battery with the difference voltage of charge and discharge current, time, battery temperature and battery terminal voltage, when the charge difference voltage reaches the charge cut-off difference When the voltage is DELTA-VH, check the differential voltage database to determine the battery power at this time, so as to correct the current power of the battery; the charging cut-off differential voltage DELTA-VH refers to applying a specified charging current to the battery, periodically collecting The terminal voltage of the battery, the first terminal voltage is collected in the first cycle, the second terminal voltage is collected in the second cycle, and the difference voltage determined by subtracting the first terminal voltage from the second terminal voltage; the cycle refers to the data A sampling period of , or multiple sampling periods; Charge the battery with the standard charging system, control the circuit to periodically measure the terminal voltage of the battery, select the battery terminal voltage measured in one cycle as the first terminal voltage, and record the battery terminal voltage measured in the second cycle as the second terminal voltage , subtracting the value of the voltage at the first terminal from the voltage at the second terminal to obtain the difference voltage. 2. The correction method as claimed in claim 1, characterized in that: ① The differential voltage database refers to the database of the differential voltage at the end of charging when the SOC reaches a certain value at a specified charging current and temperature; ② The differential voltage is used as a look-up table to obtain the electric quantity parameter from the index of the differential voltage database. 3. The correction method according to claim 1, characterized in that the period refers to a sampling period of data, or a plurality of sampling periods. 4. The calibration method as claimed in claim 1, wherein said electric quantity parameter further comprises said operating curve of said battery; and an operating point on said operating curve of said battery. 5. A power control method for a lithium-ion traction battery, characterized in that the second terminal voltage corresponding to the charge cut-off voltage difference voltage DELTA-VH is used to judge the battery cycle equivalent or the degree of aging or the state of health, and control the battery or battery pack The method of working in the optimal SOC range includes: a) According to the second terminal voltage of the charge cut-off, the capacity _Q0 of the battery or battery pack and the cycle number n or cycle number equivalent n of the battery or battery pack at this time are obtained in the cut-off voltage database by the method of looking up the table ’, and correct the current SOC to be 100%; b) Discharge with a standard discharge system to discharge the electric quantity Q, so that SOC _H > SOC > SOC _L , and the SOC _H and SOC _L are respectively the upper limit and the lower limit of the best working range of the power battery for HEV; The cycle number equivalent refers to the equivalent value of the number of charge and discharge cycles used by the battery or battery pack, which is related to the second terminal voltage VH of the battery charge cut-off, and is determined in advance by experiments or obtained from data provided by the battery manufacturer, and Stored in the cutoff voltage database. 6. The method according to claim 5, characterized in that the standard charging system is a certain charging system determined according to the specific use conditions, which is composed of a temperature value and an XC charging rate value, usually the temperature is 25°C , X takes 1, 2, 3... in rate charging. 7. The method of claim 5, wherein: ① The cycle number equivalent n' refers to the equivalent value of the number of charge and discharge cycles used by the battery or battery pack, which is related to the second terminal voltage V _H of the battery charge cut-off. This relationship is determined by experiments in advance or provided by the battery manufacturer. The data is obtained and stored in the cut-off voltage database; ② The capacity Q ₀ is only related to the number of cycles n or equivalent n' of the number of cycles and the charging system, which is obtained from the data provided by the battery manufacturer in advance. 8. The method of claim 5, wherein the SOC is defined as SOC=(1-Q/Q ₀ )*100%. 9. The method according to claim 6, characterized in that SOCH=70%, _{SOCL =} 30%, and the specific value of SOC is (SOCH _{+ SOCL} )/2. 10. The method according to claim 1 or 5, characterized in that the driver initiates a correction process according to the usage of the battery to correct the battery SOC which deviates from the optimum working range.