V2G bidirectional charging and discharging control method of electric red-ong system based on battery state

Abstract

The invention relates to a battery state-based V2G bidirectional charging and discharging control method for an electric red-honed system, which comprises the following steps of: calculating SOC (State of Charge) and SOH (State of Health) according to current, voltage, temperature and residual electric quantity of a battery which are received in real time, and generating a charging and discharging instruction in combination with a preset charging and discharging strategy rule; the power output of charging equipment is adjusted, or the on-off of a discharging loop is controlled; in combination with a preset charging and discharging strategy rule, a charging and discharging instruction is generated, the state data of the battery is collected in real time through the electric red operation system, the state of charge and the state of health of the battery are calculated, the state of charge and the state of health of the battery are evaluated more scientifically and accurately, and the actual condition of the battery can be truly reflected. Meanwhile, differentiated charging and discharging strategies are formulated for the batteries in different health states, the technical problem of battery life loss caused by over-charging and over-discharging is avoided, automatic control over the charging and discharging process is achieved, manual intervention is reduced, and control accuracy and timeliness are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of charging and discharging technology, and particularly relates to a V2G bidirectional charging and discharging control method based on battery state. BACKGROUND

[0002] In the existing V2G bidirectional charging and discharging system based on the smart grid interactive platform, the vehicle-mounted intelligent terminal and the bidirectional charging and discharging machine acquire the power grid load and electricity price information in real time through wireless communication, and automatically charge at the low valley period of power grid electricity consumption and reversely discharge at the peak period by using the mobile characteristics of large-scale electric vehicles, so as to not only improve the power grid utilization rate by 'peak load shifting', but also enable users to obtain benefits through the electricity price difference. Such a system generally adopts an electricity price analysis module, a power grid load analysis module and a battery state management module, and issues a charging and discharging instruction through a touch screen or a mobile phone terminal, and controls the charging and discharging direction and current size of the bidirectional charging and discharging machine in combination with battery state data including state of charge (SOC), state of health (SOH), voltage (V), current (I) and temperature (T) and the like, so as to meet the power grid amplitude modulation, frequency modulation and user vehicle demand.

[0003] However, frequent bidirectional charging and discharging cycles, deep discharging and large current charging and discharging can accelerate the capacity attenuation and internal resistance growth of the power battery of the electric vehicle, which not only reduces the battery performance, but also shortens the service life of the battery, and finally increases the replacement cost of the user. In addition, for the charging and discharging device adopting a large-power bidirectional charging and discharging module, if the discharging rate is too large, the bidirectional module and the filter capacitor will bear the impact current, which affects the reliability and service life thereof; and if the discharging rate is too small, it is difficult to timely respond to the peak power demand of the power grid, which weakens the peak shaving effect of V2G. SUMMARY

[0004] In order to overcome the above-mentioned defects of the prior art, the purpose of the present application is to provide a V2G bidirectional charging and discharging control method based on battery state.

[0005] The technical scheme adopted by the present application to solve the technical problems is as follows: a V2G bidirectional charging and discharging control method based on battery state, comprising:

[0006] calculating SOC and SOH according to the current, voltage, temperature and residual capacity of the battery received in real time;

[0007] executing the charging and discharging strategy by adjusting the power output of the charging equipment or controlling the on-off of the discharging loop;

[0008] generating a charging and discharging instruction in combination with the preset charging and discharging strategy rule: determining that the battery is a normal healthy battery when SOH is greater than or equal to 80%, determining that the battery is a low healthy battery when SOH is less than 80%, and executing the corresponding charging and discharging strategy according to the battery health state.

[0009] As a further improvement of the present application: wherein the charging rules in the charging-discharging strategy rules include:

[0010] For normal healthy battery, when 20%≤SOC<80%, adopt constant current charging, the charging current I is according to the battery rated capacity C n , I=0.5C n ; when SOC≥80%, switch to constant voltage charging, the charging voltage V is set to the battery rated voltage Vn, at this time the charging current gradually decreases until the battery is fully charged.

[0011] As a further improvement of the present application: wherein, during the charging process, if the battery temperature T exceeds the range of 0-45℃, reduce the charging current I to protect the battery, the formula is:

[0012]

[0013] In the formula, T max is the maximum value of the normal temperature range, T is the current temperature, T opt is the best temperature for battery charging.

[0014] As a further improvement of the present application: wherein, for low-healthy batteries, adopt small current constant current charging throughout the process, the charging current I=0.2C n , slow down battery wear; when SOC≥70%, stop charging.

[0015] As a further improvement of the present application: wherein the discharging rules in the charging-discharging strategy rules include:

[0016] For normal healthy battery, when the grid has demand and SOC>30%, allow discharging, the discharging current is I dis ;

[0017] According to the grid demand power P grid and the battery voltage V, the formula is:

[0018] But not more than the maximum allowed discharging current of the battery I max .

[0019] As a further improvement of the present application: for low-healthy batteries, only when the grid has emergency demand and SOC>40%, discharge with small current, the discharging current I dis =0.1C n ; when SOC≤40%, prohibit discharging.

[0020] As a further improvement of the present application: also includes SOC calculation: through the ampere-hour integration method, combined with the battery charging and discharging current and time to calculate. The formula is:

[0021]

[0022] In the formula, SOC t-1 is the state of charge at the last collection time, I is the charging and discharging current, C n is the rated capacity of the battery.

[0023] As a further improvement of the application: also includes SOH evaluation: comprehensive consideration of battery capacity attenuation and internal resistance growth, the evaluation formula is:

[0024]

[0025] In the formula, C current is the current actual available capacity of the battery, C n is the rated capacity of the battery, R n is the initial content of the battery, R current is the current internal resistance of the battery; alpha is the weight of the battery capacity, beta is the weight of the battery internal resistance, alpha+beta=1, the battery health state value is obtained through the battery capacity and internal resistance weighting calculation.

[0026] Compared with the prior art, the beneficial effects of the application are:

[0027] Through real-time collection of battery voltage, current, temperature and charge capacity and other multi-dimensional parameters by the electric Hong operating system, and combined with the ampere-hour integral method and internal resistance weighting method to calculate SOC and SOH synchronously, the battery state evaluation is more dynamic and high-precision, and can truly reflect the battery health level under different working conditions.

[0028] The system seamlessly connects the power grid, battery and user terminal throughout the whole process, the charging and discharging instructions are automatically issued by the strategy decision module and executed in the power control module in a closed loop, which maximizes the reduction of manual intervention; different charging and discharging strategies are formulated for batteries with different health states, which avoids the technical problem of battery life loss caused by overcharging and overdischarging, and realizes the automatic control of the charging and discharging process, reduces manual intervention, and improves the accuracy and timeliness of control. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical scheme and advantages of the application clearer, the technical scheme of the application will be described clearly and completely below in combination with specific embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, not all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the application.

[0030] It should be noted that the terms "first", "second", and the like, herein do not necessarily have an ordinal or chronological significance, but are used for the purpose of differentiating between two or more objects or actions. It is to be understood that the data so used can be interchangeable, under appropriate circumstances, with one another, unless indicated otherwise. Furthermore, expressions such as "including", "containing", "comprising", "having", and the like are intended to be broad and encompass the case where nothing besides the specifically mentioned item is present. For example, a process, method, system, product, or apparatus that comprises a list of steps or units is not necessarily limited to those specifically mentioned steps or units, but can include additional steps or units that are not expressly listed or inherent to such process, method, system, product, or apparatus.

[0031] The functions described herein can be implemented in hardware, software executed by a processor, firmware, or any combination thereof. If implemented in software executed by a processor, the functions can be stored on or transferred over as one or more instructions or code on a computer-readable medium. Other examples and implementations are within the scope and spirit of the disclosure and appended claims. For example, due to the nature of software, functions described above can be implemented using software executed by a processor, hardware, firmware, hardwiring, or combinations of any of these. Features implementing functions can also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations. Also, as used herein, including in the claims, "or" as used in a list of items prefaced by "comprising," "including," "containing," "having," or "with" to specify items present in, for example, a manufacturing process, a composition of matter, a biological process, a mechanical process or process of or involving a machine or machine-readable medium is intended to mean an "inclusive or," rather than an "exclusive or." "But for" clauses are used to establish cause-and-effect relationships of actions by an entity, either a machine or a human or both, upon which an action of another entity depends. However, such clauses are used hereinafter only to provide context for the action of the dependent entity and establish a cause-and-effect relationship of actions by an entity, either a machine or a human or both, upon which an action of another entity depends. "But for" clauses are not used to establish cause-and-effect relationships of actions by an entity, either a machine or a human or both, upon which an action of another entity depends.

[0032] Electric Hong is an Internet of Things operating system that adapts to the characteristics of the power industry. It is based on open source Hong Meng and open source Euler, selects the most suitable technology capability set for the power scene, and adds a "characteristic application layer" for the power system. Through the Internet of Things communication protocol, it realizes a system covering different types and brands of power equipment, connects a large number of power equipment terminals from different manufacturers, exchanges and communicates information, realizes the rapid adaptation of Internet of Things equipment, and the data of different equipment can also be integrated. With the increase of the proportion of renewable energy and the increase of the demand for grid peak regulation, vehicle-to-grid (V2G) bi-directional charging and discharging technology has become an effective "peak load shifting" method. The existing V2G system based on the smart grid interaction platform is prone to cause battery capacity to decay rapidly, internal resistance to grow, and cycle life to be shortened due to frequent deep charging and discharging, large current charging and discharging, and reverse discharging cycles. There is a lack of special protection strategies for batteries in different health states, making it difficult to balance the contradiction between maximizing benefits and protecting battery life. When discharging at high power, the bi-directional module and its filter capacitor need to withstand impact current, which may cause excessive temperature rise or device overload, reducing system reliability. If the discharging rate is set too low, the system will be difficult to meet the peak power demand of the grid in time, weakening the peak regulation effect. The existing system relies on fixed price thresholds or simple load forecasting, and lacks dynamic feedback and strategy adjustment for real-time SOH, temperature and other states of the battery. It is difficult to provide reliable peak regulation services while protecting the battery in response to sudden conditions such as temperature abnormalities and SOH decline. Although basic data and benefits can be viewed, the explanation and suggestions for battery health indicators are not intuitive enough for users to understand or be aware of the risk of battery degradation. The degree of automation is limited, and more manual intervention is still needed to adjust strategy parameters, increasing the complexity of operation. The bi-directional charging hardware, communication protocols and platform interface standards of different manufacturers are not unified, limiting large-scale promotion and interconnection. When interfacing with distributed energy, microgrids or energy storage systems, there is a lack of unified open standards and flexible expansion mechanisms.

[0033] To solve the above problems, the application provides a battery state-based electric Hong system V2G bi-directional charging and discharging control method, comprising:

[0034] Calculate SOC and SOH based on the real-time received current, voltage, temperature and remaining power of the battery, and generate charging and discharging instructions in combination with the preset charging and discharging strategy rules;

[0035] Adjust the power output of the charging equipment or control the on-off of the discharging circuit;

[0036] In combination with the preset charging and discharging strategy rules, generate charging and discharging instructions: when SOH≥80%, determine that the battery is a normal healthy battery; when SOH<80%, determine that the battery is a low healthy battery.

[0037] By collecting current, voltage, temperature and remaining power in real time and calculating SOC and SOH, the state of charge and the state of health of the battery are quickly and dynamically evaluated, so that the system can accurately perceive the current working condition of the battery and provide a reliable basis for subsequent control decisions. By combining fine adjustment of the power output of the charging device with rapid switching of the discharge loop, high response and high precision control of the charging and discharging process can be achieved, and smooth switching and rapid response can be achieved under different working conditions. Based on the classification of SOH≥80% and SOH<80%, the battery is divided into "normal health" and "low health", so that the system can automatically generate differentiated charging and discharging instructions for batteries with different health states, ensuring grid peak shaving and user benefits, and effectively avoiding deep stress damage to low health batteries, thereby prolonging the service life of the overall battery pack.

[0038] As an embodiment of the present application, the charging rule in the charging and discharging strategy rule comprises:

[0039] For normal health batteries, when 20%≤SOC<80%, constant current charging is adopted, and the charging current I is determined according to the rated capacity C of the battery n , I=0.5C n ; when SOC≥80%, constant voltage charging is switched, and the charging voltage V is set to the rated voltage Vn of the battery, at which time the charging current gradually decreases until the battery is fully charged.

[0040] Further, during the charging process, if the battery temperature T exceeds the range of 0-45℃, the charging current I is reduced to protect the battery, and the formula is:

[0041]

[0042] In the formula, T max is the maximum value of the normal temperature range, T is the current temperature, and T opt is the optimal temperature for charging the battery.

[0043] Constant current charging (I=0.5·C) is adopted in the range of 20%≤SOC<80%, which can quickly and stably raise the battery power to a high level; when SOC≥80%, constant voltage charging is switched, and through parallel control of voltage maintenance and current natural attenuation, the battery is ensured to be fully charged without overcharging; the charging current is dynamically reduced to effectively inhibit the damage of high temperature to the chemical system of the battery, prevent thermal runaway and accelerate aging; the regular segmented charging and temperature protection logic are automatically executed by the electric Hong operating system without manual intervention; through fine power adjustment and closed-loop control, smooth switching and safety protection of the charging process are realized, and the overall reliability and user trust of the system are improved.

[0044] Further, for low health batteries, small current constant current charging is adopted throughout the process, and the charging current I=0.2Cn , slow down battery loss; when SOC≥70%, stop charging.

[0045] The constant and small charging current can significantly reduce the large-scale migration of lithium ions between electrodes and structural stress, thereby slowing down the pulverization and lithium precipitation of electrode materials and delaying capacity decay; the joule heat generated by small current charging is greatly reduced, effectively inhibiting the increase in battery temperature and avoiding the intensified side reactions caused by high temperature, thereby protecting the chemical stability of the battery interior. Automatic stop charging when SOC reaches 70% avoids damage to the electrode surface film layer caused by overcharging in the high SOC interval, reducing the risk of lithium dendrite growth and sudden increase in internal resistance. Through the double protection measures of small current constant current and limited SOC, the remaining available capacity of the low health battery can be maximally maintained, and the cycle life and service life can be significantly prolonged.

[0046] As an embodiment of the present application, the discharge rule in the charge and discharge strategy rule includes:

[0047] For a normal healthy battery, when the power grid has a demand and SOC>30%, discharge is allowed, and the discharge current is I dis ;

[0048] According to the power grid demand power P grid and the battery voltage V, the formula is:

[0049] But not more than the maximum allowable discharge current of the battery I max .

[0050] By limiting the calculated value and the maximum allowable discharge current of the battery I max , the impact of overcurrent discharge on the internal structure of the battery and the bidirectional power module is effectively prevented, and the system reliability and equipment life are improved; combined with the threshold constraint of SOC>30%, irreversible loss of battery capacity and internal resistance caused by deep discharge is avoided, the battery life is protected while meeting the power grid demand; on-demand discharge not only can peak shaving, but also can fully release the available energy of the battery under the premise of ensuring the minimum remaining power, realizing the win-win of user benefit and power grid peak shaving benefit; the discharge instruction is automatically generated and issued by the electric Hong operating system, combined with the closed-loop adjustment of the power control module, the smooth switching and precise execution of the discharge process are realized, reducing manual intervention and improving response speed.

[0051] Further, for a low health battery, only when the power grid has an emergency demand and SOC>40%, discharge at a small current, the discharge current I dis =0.1C n ; when SOC≤40%, discharge is prohibited.

[0052] Small current discharge can not only provide necessary support for the power grid in emergency, but also reduce the stress and thermal stress in the battery to the minimum to prevent the rapid deterioration of electrode materials; small current discharge reduces the lithium ion gradient effect and structural stress cycle in high-rate discharge, inhibits the generation and expansion of electrode micro-cracks, thereby slowing down the internal resistance growth and capacity decay; limited power release in emergency can help the power grid to quickly "first aid", and through the double constraints of SOC threshold and current limit, the system peak shaving efficiency and battery safety are maximized.

[0053] As an embodiment of the application, SOC calculation is also included: through ampere-hour integration method, the battery charging and discharging current and time are combined for calculation. The formula is:

[0054]

[0055] In the formula, SOC t-1 is the state of charge at the last collection time, I is the charging and discharging current, C n is the rated capacity of the battery.

[0056] As an embodiment of the application, SOH evaluation is also included: the battery capacity attenuation and internal resistance growth are comprehensively considered, and the evaluation formula is:

[0057]

[0058] In the formula, C current is the current actual available capacity of the battery, C n is the rated capacity of the battery, R n is the initial content of the battery, R current is the current internal resistance of the battery; α is the weight of the battery capacity, β is the weight of the battery internal resistance, α+β=1, and the battery health state value is obtained through the weighted calculation of the battery capacity and internal resistance.

[0059] Main functions of the application:

[0060] Through the electric Hong operating system, the power grid and the vehicle network are realized to be linked and controlled, and at the same time, the user terminal is communicated and connected, so that the user side can realize visual perception of the operation data of the power grid and the vehicle network. Based on the health classification (SOH≥80% and SOH<80%), the constant current-constant voltage, temperature self-adaptation and small current limiting charging rules, and the on-demand and emergency current limiting discharge rules are formulated, which not only can efficiently respond to the "valley charging peak discharging" price difference peak shaving demand and obtain economic benefits, but also can effectively inhibit the damage of deep charge and discharge and large current cycle to the battery, delay the capacity decay and internal resistance growth; the whole automatic closed loop control and PI algorithm ensure the smooth switching and system reliability of the charging and discharging process, and the real-time visual interaction of the user terminal enhances the use experience, and the method is compatible with multiple hardware platforms, has good expansibility and application value.

[0061] In view of the above, those skilled in the art, after reading the present application file, can make other various corresponding transformation schemes according to the technical solutions and technical concepts of the present application without creative mental labor, which all belong to the protection scope of the present application.

Claims

1. A battery state-based electric vehicle system V2G bidirectional charge and discharge control method, characterized by, Comprise: According to the real-time received current, voltage, temperature, remaining power of the battery to calculate SOC, SOH; By adjusting the power output of the charging device, or controlling the on-off of the discharge circuit, the charging and discharging strategy is executed; Combined with the preset charging and discharging strategy rule, the charging and discharging instruction is generated: when SOH≥80%, the battery is determined as a normal healthy battery; When SOH<80%, the battery is determined as a low healthy battery; and the corresponding charging and discharging strategy is executed according to the battery health state.

2. The battery state-based electric vehicle system V2G bidirectional charge and discharge control method according to claim 1, characterized in that, The charging rule in the charging and discharging strategy rule includes: for a normal healthy battery, when 20%≤SOC<80%, constant current charging is adopted, the charging current I is determined according to the battery rated capacity C n I=0.5C n .

3. The battery state-based electric vehicle system V2G bidirectional charge and discharge control method according to claim 2, characterized in that, Among them, the charging rule in the charging and discharging strategy rule includes: for a normal healthy battery, when SOC≥80%, switch to constant voltage charging, the charging voltage V is set to the rated voltage Vn of the battery, and the charging current gradually decreases until the battery is fully charged.

4. The battery state-based electric vehicle system V2G bidirectional charge and discharge control method according to claim 2 or 3, characterized in that, Among them, During the charging process, if the battery temperature T exceeds the range of 0-45℃, the charging current I is reduced, and the formula is: where T max is the maximum of the normal temperature range, T is the current temperature, T opt is the optimal temperature for charging the battery.

5. The battery state-based electric vehicle system V2G bidirectional charge and discharge control method according to claim 4, characterized in that, Among them, For low health battery, use small current constant current charging throughout the process, charging current I = 0.2C n ; when SOC ≥ 70%, stop charging.

6. The battery state-based electric vehicle system V2G bidirectional charge and discharge control method according to claim 1, characterized in that, Among them, the discharge rule in the charging and discharging strategy rule includes: for normal healthy batteries, when the power grid has demand and the SOC is greater than 30%, discharging is allowed, and the discharging current is I dis ; According to the grid demand power P grid and the battery voltage V, calculated as: but not exceeding the battery maximum allowed discharge current I max .

7. The battery state-based electric vehicle system V2G bidirectional charge and discharge control method according to claim 6, characterized in that, For low health battery, only discharge at small current when grid emergency demand and SOC > 40%, discharge current I dis = 0.1C n ; when SOC < 40%, discharge is prohibited.

8. The battery state-based electric vehicle system V2G bidirectional charge and discharge control method of claim 1, wherein, It also includes SOC calculation: through the ampere-hour integration method, combined with the battery charging and discharging current and time for calculation; The formula is: In the formula, SOC t-1 is the state of charge at the previous acquisition time, I is the charge and discharge current, C n is the battery rated capacity.

9. The battery state-based electric vehicle system V2G bidirectional charge and discharge control method of claim 1, wherein, It also includes SOH evaluation: comprehensively considering the capacity attenuation and internal resistance growth of the battery, the battery health state value is obtained through the weighted calculation of the battery capacity and internal resistance.

10. The battery state-based electric vehicle system V2G bidirectional charge and discharge control method of claim 9, wherein, The SOH evaluation formula is: In the formula, C current is the current battery actual available capacity, C n is the battery rated capacity, R n is the battery initial content, R current is the current battery internal resistance; α is the weight of the battery capacity, β is the weight of the battery internal resistance, α+β=1, and the battery health state value is obtained through the battery capacity and internal resistance weighting calculation.

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