Method for reasonably adjusting end-of-discharge voltage of lithium battery with attenuation of battery life

Abstract

The present invention provides a method for reasonably adjusting an end-of-discharge voltage of a lithium battery with attenuation of a battery life. The method includes: acquiring an end-of-charge voltage, an end-of-discharge voltage and a rated capacity based on a basic parameter table for a lithium battery, then setting a safety end-of-charge voltage and a safety end-of-discharge voltage to obtain an initial safety discharge capacity, and finally setting a preset discharge capacity of the battery; using an Ampere-hour integration method to estimate a discharged power, taking the preset discharge capacity as a discharge standard, and stopping discharge when the discharged power reaches the preset discharge capacity; and the safety discharge capacity being gradually less than the preset discharge capacity within a battery life cycle, and the battery stopping discharge when the voltage reaches the safety end-of-discharge voltage. By controlling the discharge capacity to be unchanged, the present invention ensures stably outputting power in the case that the battery capacity attenuates, so that a user feels that the endurance mileage of an electric vehicle is stably unchanged within a certain period. The method has the characteristics of simple adjusting control method and convenience in commercialization.

Claims

1. A method for reasonably adjusting an end-of-discharge voltage of a lithium battery with attenuation of a battery life, characterized by comprising: step I, acquiring an end-of-charge voltage, an end-of-discharge voltage and a rated capacity based on a basic parameter table for a lithium battery, then setting a safety end-of-charge voltage and a safety end-of-discharge voltage to obtain an initial safety discharge capacity, and finally setting a preset discharge capacity of the battery; step II, using an Ampere-hour integration method to estimate a discharged power, taking the preset discharge capacity as a discharge standard, and stopping discharge when the discharged power reaches the preset discharge capacity; and step III, the safety discharge capacity being gradually less than the preset discharge capacity within a battery life cycle, and the battery stopping discharge when the voltage reaches the safety end-of-discharge voltage.

2. The method for reasonably adjusting an end-of-discharge voltage of a lithium battery with attenuation of a battery life according to claim 1, characterized in that in the step I, the set safety end-of-charge voltage U.sub.S,C is less than the end-of-charge voltage U.sub.C,C, and the set safety end-of-discharge voltage U.sub.S,D is greater than the end-of-discharge voltage U.sub.C,D; wherein power released from the safety end-of-charge voltage U.sub.S,C to the safety end-of-discharge voltage U.sub.S,D is a safety discharge capacity C.sub.S; the safety discharge capacity C.sub.S is gradually decreased with the attenuation of the battery; when the battery does not attenuate, the safety discharge capacity C.sub.S is equal to the initial safety discharge capacity C.sub.S,O; the preset discharge capacity is selected to be C.sub.P=k.Math.C.sub.S,O.

3. The method for reasonably adjusting an end-of-discharge voltage of a lithium battery with attenuation of a battery life according to claim 1, characterized in that in the step II, the method for using the ampere-hour integration method to estimate the discharged power is as follows: discharged power C.sub.a=∫.sub.0.sup.t.sup.1I(t)dt; wherein in case of t=0, the voltage of the battery is the safety end-of-charge voltage U.sub.S,C; and at t.sub.1, the discharge capacity of the battery just reaches the preset discharge capacity C.sub.P; when the discharged power reaches the preset discharge capacity, discharge is stopped, and the end voltage at this time is a new end-of-discharge voltage U.sub.P,D; and when the battery does not attenuates, U.sub.P,D=U.sub.P,D,O, thereby obtaining U.sub.S,D≤U.sub.P,D≤U.sub.P,D,O.

4. The method for reasonably adjusting an end-of-discharge voltage of a lithium battery with attenuation of a battery life according to claim 1, characterized in that in the step 3, as the battery attenuates, the safety discharge capacity C.sub.S is gradually decreased; in order to ensure that the power discharged by the battery at each time may reach the preset discharge capacity C.sub.P, the U.sub.P,D, and the U.sub.P,D is selected to be gradually reduced from U.sub.P,D,O to U.sub.S,D; when the voltage of the battery reaches U.sub.S,D, the battery may stop the discharge, and the discharge capacity at the moment is less than or equal to the preset discharge capacity.

5. The method for reasonably adjusting an end-of-discharge voltage of a lithium battery with attenuation of a battery life according to claim 2, characterized in that a proportion coefficient k is greater than 0 and less than 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 is a flow chart of a method for reasonably adjusting an end-of-discharge voltage of a lithium battery with attenuation of the battery life in the embodiment of the present invention.

[0023] FIG. 2 is a basic parameter table of a battery in a battery attenuation experiment in the embodiment of the present invention.

[0024] FIG. 3 is a battery voltage-capacity diagram under different numbers of cycles of a battery attenuation experiment in the embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] The technical solution adopted by the present invention will be further described below in combination with schematic diagrams.

[0026] FIG. 1 is a flow chart of a method for reasonably adjusting an end-of-discharge voltage of a lithium battery with attenuation of the battery life. The present invention uses dynamic data of voltage and current of a lithium battery collected by a battery management system (BMS) to determine, according to an Ampere-hour integration method, a real-time discharge capacity of the battery, thereby determining a new end-of-discharge voltage. A detailed description is made below in combination with specific embodiments and corresponding lithium battery life cycle experiments.

[0027] The method for reasonably adjusting an end-of-discharge voltage of a lithium battery with attenuation of the battery life includes the following steps:

[0028] Step I, it is determined that an end-of-charge voltage U.sub.C,C is 4.2 V, an end-of-discharge voltage U.sub.C,D is 2.5 V, and a rated capacity C.sub.N is 3 Ah according to a basic parameter table for a lithium battery shown in FIG. 2. At this time, a safety end-of-charge voltage U.sub.S,C is set to be 4.15 V, and a safety end-of-discharge voltage U.sub.S,D is set to be 2.8 V. They obviously meet a quantitative relation. Power released from the safety end-of-charge voltage U.sub.S,C to the safety end-of-discharge voltage U.sub.S,D is called a safety discharge capacity C.sub.S. The safety discharge capacity C.sub.S would be gradually decreased with the attenuation of the battery. When the battery does not attenuate, the initial safety discharge capacity is C.sub.S=C.sub.S,O. It can be known from test data that C.sub.S,O is equal to 3105 mAh. K is 0.8454 according to a requirement, so the preset discharge capacity is C.sub.P=k.Math.C.sub.S,O=0.8454*3105=2625 mAh.

[0029] Step II, it can be known according to FIG. 3 that as the number of attenuations increases, the discharge capacity of the battery is gradually decreased when the end-of-discharge voltage appears. The discharged power can be calculated according to the Ampere-hour integration method. Discharge is stopped when the discharged power reaches the preset discharge capacity. It can be seen from S1 that C.sub.P is equal to 2625 mAh. An auxiliary line of C.sub.P=2625 mAh is made in FIG. 3. It can be apparently seen that when the discharge capacity reaches the preset discharge capacity, the voltage of the battery is gradually decreased as the number of cycles increases. After 20, 54, and 88 cycles, voltages corresponding to the preset discharge capacity are respectively 3.1287 V, 2.9383 V and 2.9048 V. Therefore, U.sub.P,D is reduced from 3.1287 V to 2.9383 V and further to 2.9048 V.

[0030] Step III, as the battery continues to attenuates, the battery will reach a critical value; when the discharged power reaches the preset discharge capacity C.sub.P=2625 mAh, the end voltage is just equal to the safety end-of-discharge voltage U.sub.S,D. The U.sub.S,D of the present embodiment is 2.8 V, and two end conditions are triggered at the same time. As the battery further attenuates, the battery will cross this critical value. Hereafter, the discharge capacity of the battery would not reach the preset discharge capacity. When the voltage reaches the safety end-of-discharge voltage U.sub.S,D, the battery stops discharge.

[0031] It can be found through the above content that the method and process for adjusting the end-of-discharge voltage of the present invention can be clearly understood, and are mainly divided into two stages as the battery attenuates. When the discharge capacity can meet the preset discharge capacity, the preset discharge capacity is used as an end condition to stop discharge; when the discharge capacity is less than the preset discharge capacity, it is apparent for the voltage to reach the safety end-of-discharge voltage at first, and the safety end-of-discharge voltage is used as an end condition to stop discharge.

[0032] The above is only a preferred embodiment of the present invention, and does not play any limitation role to the present invention. Equivalent replacement or modification and other changes in any form which are made by any person skilled in the art to the technical solution and technical content disclosed in the present invention without departing from the present invention shall not depart from the content of the technical solution of the present invention, and still fall within the protection scope of the present invention.