Energy storage system lithium battery pack charging control method and device
Technical Field
The invention relates to the technical field of lithium battery application, in particular to a method and a device for controlling charging of a lithium battery pack of an energy storage system.
Background
The application range of power batteries is very wide, and packaged batteries PACK are often connected in series and parallel to achieve the required system voltage and system capacity. After series-parallel connection, due to the fact that a plurality of sections of batteries are used in series, each section of battery is inconsistent, overcharge and overdischarge of a part of battery cells can occur when two ends of each battery are charged and discharged, potential hazards of overcharge and overdischarge are caused, and battery cell failure or fire explosion can be generated in serious cases. Therefore, the application system of the lithium battery pack needs to add a BMS (battery management system) to manage charging and discharging of the battery, but the battery pack under BMS management cannot communicate with the charger in a user scene, and technical feasibility of real-time current reduction according to BMS requirements does not exist. Therefore often trigger overcharge protection at the end of charging, treat that charging current removes the back, the lithium cell voltage fall of standing and then the BMS removes overcharge protection, and the charger restarts to charge, triggers the protection again when the electric current risees to a definite value, and the repeated charging and protection of so doing is a very harsh technical challenge to the BMS board, arouses easily that the BMS board damages and then leads to the lithium cell to overcharge and even arouse the conflagration. Especially as the capacity of lithium batteries decreases, the constant current ratio decreases, the inconsistency is exacerbated, and the problem is further magnified. The existing charging technology mainly adopts the following steps:
1. the design of a common three-section charger aiming at the lead-acid battery is directly adopted, wherein the constant voltage stage is easy to trigger repeated protection, and the probability of bad occurrence is improved. In addition, in the partial charging technology, three-stage charging is optimized to be changed into two-stage charging and constant-current and constant-voltage charging for reducing the repeated charging times, the repeated protection of the BMS board in the floating charging stage is reduced, but the repeated charging problem in the constant-voltage stage cannot be reduced.
2. Part of charging technologies are based on an optimized charging strategy considering charging temperature rise, for example, the invention disclosed in patent No. 201911311092.4 can solve the problem of temperature rise caused by high power, and the three-stage charging method for the lithium ion battery disclosed in patent No. 201911309713.5 fully exploits the advantages of rapid charging rate and shortens charging time on the premise of ensuring temperature safety by utilizing the characteristics of the lithium ion battery. Both of the above inventions emphasize the rapidity of charging, and do not consider the safety problem caused by repeated charging.
3. The other technology requires the lithium battery to be communicated with a charger, and the charging and discharging voltage and current are adjusted in real time according to the SOC state calculated by the BMS after the communication is established, so that efficient charging is realized. The communication reading status as described in patent No. 201910094576.1 defines priority, but this technique is not feasible for wide spread in the household energy storage industry.
In summary, to solve the above potential safety hazard of lithium battery pack charging, currently, no practical household charging control method on the battery pack level exists.
Disclosure of Invention
The invention aims to provide a method and a device for controlling charging of a lithium battery pack of an energy storage system, so as to overcome the defects in the prior art.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a charging control method for a lithium battery pack of an energy storage system is provided, wherein the lithium battery pack of the energy storage system has a constant-current charging mode and a variable-value constant-voltage charging mode, and the charging control method comprises the following steps:
s1, judging whether charging is needed, if so, triggering the constant current charging mode, wherein the constant current charging mode adopts the maximum current of an energy storage system to charge the lithium battery pack, and otherwise, stopping;
and S2, judging whether BMS overvoltage protection is started or not, if so, performing a variable constant voltage charging mode, wherein the variable constant voltage charging mode performs charging by dynamically adjusting a constant voltage value, and otherwise, continuing to perform a constant current charging mode.
Further, in step S1, it is determined whether charging is required or not by the charging flag, if the charging flag is 1, charging is required, otherwise, the charging is suspended, and in the constant current charging mode, the constant voltage limiting value is UC1=UMAX, UMAX=3.65V × N, wherein UC1To not trigger the protection voltage value.
Further, the step S2 includes the following steps:
s20, judging whether the constant voltage flag bit is 1, if so, entering BMS protection and executing a variable value constant voltage charging mode, otherwise, continuing executing a constant current charging mode;
s21, setting the charging voltage U in the variable value constant voltage charging modeC=MIN[Us ,UMAX]-0.5V, wherein UsFor total pressure value before protection, UMAX=3.65V*N;
S22, charging voltage UCAnd carrying out constant voltage charging on the control target until the charging current is less than a preset value, marking the constant voltage as 0, and finishing the charging.
Further, in the step S20, if the BMS enters the single-node or multi-node overvoltage protection, the constant voltage flag is 1.
Further, the preset value is 0.05C.
The invention also provides a device of the method for controlling the charging of the energy storage system lithium battery pack, wherein the energy storage system lithium battery pack has a constant current charging mode and a variable value constant voltage charging mode, and the device comprises:
the first judgment module is used for judging whether charging is needed or not, if so, the constant current charging mode is triggered, the lithium battery pack is charged by adopting the maximum current of the energy storage system in the constant current charging mode, and if not, the charging is stopped;
and the second judgment module is used for judging whether BMS overvoltage protection is started or not, if so, a variable value constant voltage charging mode is carried out, the variable value constant voltage charging mode carries out charging by dynamically adjusting a constant voltage value, and otherwise, the constant current charging mode is continuously executed.
Compared with the prior art, the invention has the advantages that: the invention can successfully and thoroughly solve the problem of repeated switching after the lithium battery is fully charged, and the charging efficiency and the conversion efficiency of the variable value constant current charging mode are far higher than those of the pulse charging mode without adopting the control method.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a flowchart of a method for controlling charging of a lithium battery pack of an energy storage system according to the present invention.
Fig. 2 is a voltage-current waveform diagram in the present invention.
Fig. 3 is a schematic diagram of the charging control device for the lithium battery pack of the energy storage system.
Detailed Description
The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings so that the advantages and features of the present invention can be more easily understood by those skilled in the art, and the scope of the present invention will be more clearly and clearly defined.
Referring to fig. 1, the invention discloses a charging control method for a lithium battery pack of an energy storage system, wherein the lithium battery pack of the energy storage system has a constant current charging mode and a variable value constant voltage charging mode, and the charging control method comprises the following steps:
and step S1, judging whether charging is needed, if so, triggering the constant current charging mode, wherein the constant current charging mode adopts the maximum current of the energy storage system to charge the lithium battery pack, and if not, stopping the charging.
Specifically, in the step, whether charging is needed or not is judged through a charging flag bit, if the charging flag bit is 1, charging is needed, otherwise, the charging is stopped, and in a constant-current charging mode, a constant-voltage amplitude limit value is UC1=UMAX, UMAX=3.65V × N, wherein UC1To not trigger the protection voltage value.
And detecting the charging voltage and the charging current in real time in the charging process in the constant current charging mode, changing the charging setting when the overcharge protection of the BMS board is judged, and entering the step S2.
And step S2, judging whether BMS overvoltage protection is entered, if so, performing a variable value constant voltage charging mode, wherein the variable value constant voltage charging mode performs charging by dynamically adjusting a constant voltage value, and otherwise, continuing to perform a constant current charging mode.
Specifically, the method comprises the following steps:
and step S20, judging whether the constant voltage flag bit is 1, if so, entering BMS protection and executing a variable value constant voltage charging mode, otherwise, continuing executing a constant current charging mode, and specifically, if the BMS enters single-section or multi-section overvoltage protection, the constant voltage flag bit is 1.
Step S21, setting the charging voltage U in the variable value constant voltage charging modeC=MIN[Us ,UMAX]-0.5V, i.e. the charging voltage is set to the total voltage value U before protectionsAnd UMAXIs reduced by 0.5V, wherein UsFor total pressure value before protection, UMAX=3.65V*N。
Step S22, charging voltage UCAnd performing constant-voltage charging for the control target until the charging current is less than a preset value, wherein the charging current is selected to be 0.05C, marking the constant voltage as 0, and ending the charging.
Specifically, after the BMS resumes charging, the lithium battery enters into UCIn a constant-voltage charging mode of charging voltage, the charging current gradually rises, and due to internal resistance of an internal resistance loop and other reasons, the BMS does not trigger single-section or multi-section overvoltage protection any more until the charging current is reduced to a charging end threshold value, and the charging is ended.
Referring to fig. 2, a voltage-current waveform diagram of an embodiment of the invention is shown, wherein the period T0-T1 is a constant current charging period, and the voltage gradually increases as the charging progresses; and T1-T2 is a constant current and constant voltage switching stage, when the voltage is detected to rise rapidly and the charging current drops to 0A, the BMS charging protection is judged, and the constant voltage charging is marked at the position 1. And assigning a value to the constant voltage charging voltage, wherein the specific value is-0.5V at the time of T1, and the value is smaller than the amplitude limiting voltage value. T2-T3 is the constant voltage charging phase until the end of charging. It is necessary to point out that necessary protection limiting conditions need to be added to constant current to constant voltage identification according to hardware parameters of the charger in practical engineering application, so as to prevent mode misjudgment.
Referring to fig. 3, the present invention further provides an apparatus for controlling charging of an energy storage system lithium battery pack according to the above method, where the energy storage system lithium battery pack has a constant current charging mode and a variable value constant voltage charging mode, and the apparatus includes: the first judgment module 1 is used for judging whether charging is needed or not, if so, triggering the constant current charging mode, and the constant current charging mode adopts the maximum current of an energy storage system to charge the lithium battery pack, otherwise, stopping the charging; and the second judgment module 2 is used for judging whether BMS protection is started or not, if so, performing a variable value constant voltage charging mode, and if not, continuously performing a constant current charging mode, wherein the variable value constant voltage charging mode performs charging by dynamically adjusting a constant voltage value.
The invention has the advantages that: 1. by adopting the lithium battery charging control method, the problems of repeated protection of the BMS system and repeated charging of the charger can be fundamentally solved, the reliability and the safety of the system can be improved, and the service life of the lithium battery pack can be prolonged; 2. compared with the pulse charging similar to the repeated protection caused by the conventional charger in the constant voltage stage, the control algorithm provided by the invention can realize continuous current charging, and the charging efficiency and the conversion efficiency are obviously higher than those of the conventional control method.
Although the embodiments of the present invention have been described with reference to the drawings, the owner of the patent may make various changes or modifications within the scope of the appended claims, such as exchanging data representing flag bits, etc., within the scope of the present invention as long as the scope of the present invention is not exceeded by the claims.