Electric vehicle battery charging and discharging control method based on V2G technology

Abstract

The invention relates to the technical field of DC micro-grid DC / DC converter control equipment, in particular to an electric vehicle battery charging and discharging control method based on a V2G technology, and aims to solve the problem that unreasonable charging and discharging control may cause bad peak load. The control method comprises the steps that S1, the electric vehicle is connected into a power grid through a charging pile, whether users participate in peak regulation of the power grid or not is judged, and if not, the vehicle is charged normally; if yes, formally entering a charging and discharging control program; s2, setting a load upper limit PH-Limit and a load lower limit PL-Limit of the power grid; s3, detecting the actual load P of the power grid; s4, a battery charging judgment program; and S5, a battery discharging judgment program.

Description

Technical Field

[0001] The present invention relates to the technical field of electric vehicle battery charge and discharge control, and in particular to an electric vehicle battery charge and discharge control method based on V2G technology. Background Art

[0002] At present, the number of electric vehicles is growing rapidly, and the capacity of charging piles is also growing. When large-scale electric vehicles are connected to the power grid through charging piles, their charging and discharging behaviors will have adverse effects on power grid planning and safe and stable operation, such as voltage deviation, harmonic pollution, three-phase imbalance, increased network loss, increased peak-to-valley difference in power grid load, and shortened transformer life.

[0003] The two-way interactive technology of electric vehicles to the grid (Vehicle to Grid, V2G) can realize "two-way communication and two-way energy transmission" between electric vehicles and the grid. During the peak period of electricity consumption, electric vehicles can be used as energy storage units to discharge to the grid, and during the low period of electricity consumption, electric vehicles can be charged as loads. This expands the use of new energy.

[0004] The realization of V2G technology is inseparable from a reasonable charge and discharge control strategy. From the perspective of the power grid, electric vehicles cannot be connected to the power grid at will, and unreasonable charge and discharge control may lead to undesirable peak loads. Summary of the invention

[0005] In view of this, the purpose of the present invention is to propose a method for controlling the charging and discharging of electric vehicle batteries based on V2G technology, so as to solve the problem that unreasonable charging and discharging control may lead to undesirable peak loads.

[0006] A method for controlling battery charging and discharging of an electric vehicle based on V2G technology, comprising:

[0007] S1: Electric vehicles are connected to the grid through charging piles. Do users also participate in the peak load regulation of the grid? If so,

[0008] If not participating, the car will charge normally; if participating, it will formally enter the charging and discharging control program;

[0009] S2: Set the upper limit of the load of the power grid P H-Limit and load lower limit P L-Limit ;

[0010] S3: Detect the actual load P of the power grid;

[0011] S4: Battery charging judgment procedure:

[0012] S41: Determine the actual load P and the load lower limit P L-Limit The size relationship of

[0013] S42: If the actual load P is less than or equal to the load lower limit P L-Limit , enter S43; if the actual negative

[0014] Load P is greater than the load lower limit P L-Limit , end the charging procedure that has already started;

[0015] S43: Determine the battery's SOC. If the SOC is less than or equal to the upper limit, issue a charging command, the battery starts charging, and returns to S31. If the SOC is greater than the upper limit, end the charging process.

[0016] Start the charging procedure;

[0017] S5: Battery discharge judgment procedure:

[0018] S51: Determine the actual load P and the load upper limit P H-Limit The size relationship of

[0019] S52: If the actual load P is greater than or equal to the load upper limit P H-Limit , enter S53; if the actual load

[0020] P is less than the upper load limit P H-Limit , end the discharge procedure that has already started;

[0021] S53: Determine the battery's SOC. If the SOC is greater than the lower limit, issue a discharge command, the battery starts discharging, and return to S41. If the SOC is less than the lower limit, end the discharging procedure that has already started.

[0022] As a further improvement of the present application, the battery discharge judgment program also includes a user vehicle usage habit prediction module, which predicts the subsequent vehicle usage of the vehicle based on the vehicle usage habits. If the vehicle is needed within the set time, the battery of the vehicle does not participate in the battery discharge judgment program; if the vehicle is not needed within the set time, the battery of the vehicle participates in the battery discharge judgment program.

[0023] As a further improvement of the present application, the set time is divided into three levels: two hours, three hours, and four hours, and different levels are set according to needs.

[0024] Furthermore, the upper limit is 90%.

[0025] Furthermore, the lower limit is 20%.

[0026] As a further improvement of the present application, the control method also includes designing a main circuit structure, a front and rear two-stage design, the front stage adopts a bidirectional three-phase voltage-type PWM converter, and the rear stage realizes a half-bridge buck-boost circuit structure by adding a Buck-Boost converter.

[0027] As a further improvement of the present application, the bidirectional three-phase voltage-type PWM converter includes 6 power electronic fully-controlled devices IGBTs, namely T1-T6, two power electronic fully-controlled devices IGBTs are connected in series to form a group, three groups are connected in parallel, and each group of two power electronic fully-controlled devices IGBTs is connected to a line of the three-phase circuit.

[0028] As a further improvement of the present application, the latter stage adopts a bidirectional DC / DC converter control strategy, including two series-connected power electronic fully-controlled devices IGBT, namely T7 and T8.

[0029] The beneficial effect of the present invention is that by judging the actual load P and the load lower limit P L-Limit The relationship between the actual load P and the load upper limit P H-Limit The size relationship between the battery and the load can be determined by choosing the appropriate time to charge or discharge, thus effectively avoiding peak loads.

[0030] In addition, from the perspective of electric vehicle charging load calculation, full consideration is given to user habits and the characteristics of electric vehicles themselves, laying a good foundation for formulating reasonable, efficient and orderly charging and discharging strategies, thereby improving the interests of both the grid and user sides. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only for the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 This is a schematic diagram of the main circuit structure of a method for controlling battery charging and discharging of an electric vehicle based on V2G technology according to an embodiment of the present invention;

[0033] Figure 2 This is a structural schematic diagram of part of the current flow in the main circuit charging state of an electric vehicle battery charging and discharging control method based on V2G technology according to an embodiment of the present invention;

[0034] Figure 3 This is a structural schematic diagram of part of the current flow in the main circuit discharge state of an electric vehicle battery charge and discharge control method based on V2G technology according to an embodiment of the present invention;

[0035] Figure 4 This is a control block diagram of a main circuit converter of an electric vehicle battery charging and discharging control method based on V2G technology according to an embodiment of the present invention;

[0036] Figure 5The present invention is a flowchart of a method for controlling battery charging and discharging of an electric vehicle based on V2G technology. DETAILED DESCRIPTION

[0037] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments.

[0038] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0039] like Figure 1-3 As shown, a method for controlling battery charging and discharging of an electric vehicle based on V2G technology includes:

[0040] S1: Electric vehicles are connected to the grid through charging piles. Do users also participate in the peak load regulation of the grid? If so,

[0041] If not participating, the car will charge normally; if participating, it will formally enter the charging and discharging control program;

[0042] S2: Set the upper limit of the load of the power grid P H-Limit and load lower limit P L-Limit ;

[0043] S3: Detect the actual load P of the power grid;

[0044] S4: Battery charging judgment procedure:

[0045] S41: Determine the actual load P and the load lower limit P L-Limit The size relationship of

[0046] S42: If the actual load P is less than or equal to the load lower limit P L-Limit , enter S43; if the actual negative

[0047] Load P is greater than the load lower limit P L-Limit , end the charging procedure that has already started;

[0048] S43: Determine the battery's SOC. If the SOC is less than or equal to the upper limit, issue a charging command, the battery starts charging, and returns to S31. If the SOC is greater than the upper limit, end the charging process.

[0049] Start the charging procedure;

[0050] S5: Battery discharge judgment procedure:

[0051] S51: Determine the actual load P and the load upper limit P H-Limit The size relationship of

[0052] S52: If the actual load P is greater than or equal to the load upper limit P H-Limit , enter S53; if the actual load

[0053] P is less than the upper load limit P H-Limit , end the discharge procedure that has already started;

[0054] S53: Determine the battery's SOC. If the SOC is greater than the lower limit, issue a discharge command, the battery starts discharging, and return to S41. If the SOC is less than the lower limit, end the already started discharge procedure. Specifically, the upper limit is 90% and the lower limit is 20%.

[0055] SOC refers to the ratio of the remaining power of an electric vehicle's power battery to the rated capacity of the power battery under the same conditions, which is used to indicate the current power consumption status of the power battery. SOC cannot be obtained from the power battery itself, but needs to be calculated based on external parameters such as external voltage, current, and internal resistance. When the mileage of an electric vehicle is known, the SOC consumed by the electric vehicle can be calculated as:

[0056]

[0057] Where: SOC L To calculate the SOC consumed by electric vehicles, E L E is the amount of electricity consumed by electric vehicles during driving; cap E is the rated capacity of the electric vehicle power battery; 100 is the electric energy consumed by the electric vehicle’s power battery for every 100 kilometers traveled; d is the electric vehicle’s mileage.

[0058] The charge SOC is

[0059] The SOC of an electric vehicle after charging is:

[0060]

[0061] Where: SOC c After charging the electric vehicle, SOC, EC The amount of electricity used to charge an electric vehicle; η c is the charging efficiency; t c is the charging time; p c is the charging power.

[0062] The SOC after charging is (SOC c *E cap +Previous SOC*E cap ) / E cap .

[0063] The battery discharge judgment program also includes a user vehicle usage habit prediction module, which predicts the subsequent vehicle usage of the vehicle based on the vehicle usage habits. If the vehicle needs to be used within a set time, the battery of the vehicle does not participate in the battery discharge judgment program. If the vehicle does not need to be used within the set time, the battery of the vehicle participates in the battery discharge judgment program.

[0064] The set time has three levels: two hours, three hours, and four hours, and different levels can be set according to needs.

[0065] For different users, their daily car-using habits, daily driving distances, and when to charge are all different, and there are large differences. The factors that most affect the amount of electric vehicle charging power are the user's daily driving distance and the time when the user starts charging the electric vehicle. The farther an electric car travels in a day, the more electricity it consumes, and the longer it takes to charge the power battery. The closer the charging times chosen by users are to each other, the greater the charging load will be during these time periods. According to current domestic and foreign surveys and studies on electric vehicle travel data, the current starting charging time of electric vehicles roughly conforms to the normal distribution after fitting using the maximum likelihood estimation method, while the daily driving distance of electric vehicles roughly conforms to the log-normal distribution after fitting. The daily mileage probability density function is as follows:

[0066]

[0067] Where: L is the daily mileage of the electric vehicle, in km; μ L is the expected value of the logarithm of the driving distance, μ L =3.20;σ L is the standard deviation of the logarithm of the driving distance, σ L =0.88.

[0068] The driving range of most electric vehicles is about 20km. After a simple estimation based on the SOC calculation formula consumed by electric vehicles, it can be found that the remaining power of most electric vehicles is enough to be connected to the microgrid for discharge every day, and then used as mobile energy storage for electric energy feedback.

[0069] The probability density function of the time when an electric vehicle is connected to the microgrid after completing the last driving mileage is as follows:

[0070]

[0071] Where: expected value μ c =17.6, standard deviation σ c =3.4.

[0072] The control method also includes designing a main circuit structure, a front and rear two-stage design, the front stage adopts a bidirectional three-phase voltage-type PWM converter, considering that the battery voltage of the electric vehicle is low and the DC bus voltage is high, in order to achieve voltage level matching and safe and effective energy interaction, it is necessary to add a Buck-Boost converter between the battery side of the electric vehicle and the DC bus to achieve the voltage level matching requirement between the two, and the back stage realizes a half-bridge buck-boost circuit structure by adding a Buck-Boost converter.

[0073] The bidirectional three-phase voltage-type PWM converter includes six power electronic fully-controlled devices IGBT, which are T1-T6. Two power electronic fully-controlled devices IGBT are connected in series to form a group, and three groups are connected in parallel. Each group of two power electronic fully-controlled devices IGBT is connected to a line of the three-phase circuit. The power electronic fully-controlled device IGBT has the advantages of light weight, less harmonic components, and fast response speed, so it can achieve controllable current conversion in four quadrants. However, if you want to change the working state of the converter, you can change the period or duty cycle of the pulse in PWM through an appropriate control method to control the on-off time of the switch, thereby controlling the output voltage and current.

[0074] The latter stage adopts a bidirectional DC / DC converter control strategy, including two series-connected power electronic fully controlled devices IGBT, namely T7 and T8. If T7 is turned on and T8 is turned off, the battery is in a charging state, and the energy is mainly provided by the AC / DC converter and the DC side capacitor. Figure 2 As shown in Figure 2, if T7 is disconnected and T8 is disconnected, the three-phase converter only charges the DC side capacitor. Figure 3 The battery shown is in a discharge state and charges the inductor at the same time; if T7 is disconnected and T8 is disconnected, both the battery and the inductor are in a discharge state.

[0075] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention (including the claims) is limited to these examples. Under the concept of the present invention, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.

[0076] The present invention is intended to cover all such substitutions, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for controlling battery charge and discharge of an electric vehicle based on V2G technology, characterized in that: The method includes S1: The electric vehicle is connected to the power grid through the charging pile. Does the user participate in the peak load regulation of the power grid? If not, the car is charged normally; if yes, the charging and discharging control program is officially entered; S2: Set the upper limit of the load of the power grid P H-Limit and load lower limit P L-Limit ; S3: Detect the actual load P of the power grid; S4: Battery charging judgment procedure: S41: Determine the actual load P and the load lower limit P L-Limit The size relationship of S42: If the actual load P is less than or equal to the load lower limit P L-Limit , enter S43; If the actual load P is greater than the load lower limit P L-Limit , end the charging procedure that has already started; S43: Determine the battery's SOC. If the SOC is less than or equal to the upper limit, issue a charging instruction, the battery starts charging, and return to S31; if the SOC is greater than the upper limit, end the charging procedure that has already started. S5: Battery discharge judgment procedure: S51: Determine the actual load P and the load upper limit P H-Limit The size relationship of S52: If the actual load P is greater than or equal to the upper load limit P H-Limit , enter S53; If the actual load P is less than the upper load limit P H-Limit , end the discharge procedure that has already started; S53: Determine the battery's SOC. If the SOC is greater than the lower limit, issue a discharge command, the battery starts discharging, and return to S41. If the SOC is less than the lower limit, end the discharging procedure that has already started.

2. The electric vehicle battery charge and discharge control method based on V2G technology according to claim 1, characterized in that: The battery discharge judgment program also includes a user vehicle usage habit prediction module, which predicts the subsequent vehicle usage of the vehicle based on the vehicle usage habits. If the vehicle needs to be used within a set time, the battery of the vehicle does not participate in the battery discharge judgment program. If the vehicle does not need to be used within the set time, the battery of the vehicle participates in the battery discharge judgment program.

3. The electric vehicle battery charge and discharge control method based on V2G technology according to claim 2 is characterized in that: The set time has three levels: two hours, three hours, and four hours, and different levels can be set according to needs.

4. The electric vehicle battery charge and discharge control method based on V2G technology according to claim 1, characterized in that: The upper limit value is 90%.

5. The electric vehicle battery charge and discharge control method based on V2G technology according to claim 1, characterized in that: The lower limit is 20%.

6. The electric vehicle battery charge and discharge control method based on V2G technology according to claim 1, characterized in that: The control method also includes designing a main circuit structure, a front and rear two-stage design, the front stage adopts a bidirectional three-phase voltage type PWM converter, and the rear stage realizes a half-bridge buck-boost circuit structure by adding a Buck-Boost converter.

7. The electric vehicle battery charge and discharge control method based on V2G technology according to claim 6 is characterized in that: The bidirectional three-phase voltage-type PWM converter includes six power electronic fully-controlled devices IGBTs, namely T1-T6. Two power electronic fully-controlled devices IGBTs are connected in series to form a group, and three groups are connected in parallel. Two power electronic fully-controlled devices IGBTs in each group are connected to a line of the three-phase circuit.

8. The electric vehicle battery charge and discharge control method based on V2G technology according to claim 6 is characterized in that: The latter stage adopts a bidirectional DC / DC converter control strategy, including two series-connected power electronic fully-controlled devices IGBT, namely T7 and T8.

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