CN110816282A - Regenerative braking control method for electric automobile - Google Patents
Regenerative braking control method for electric automobile Download PDFInfo
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- B60—VEHICLES IN GENERAL
- B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
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Abstract
The invention discloses a regenerative braking control method of an electric automobile, which comprises the steps of establishing a road surface characteristic value calculation method based on an adhesion system, establishing a semi-empirical mathematical model of an adhesion coefficient and a slip rate, introducing a road surface state characteristic value, and identifying a road surface condition and an average adhesion coefficient corresponding to the road surface; judging the braking force of the front wheel and the rear wheel according to the height of the adhesion coefficient and the braking strength; taking the brake strength, the battery SOC and the vehicle speed as the input of a fuzzy controller, establishing an empirical fuzzy rule, outputting the proportion of the regenerative brake force to the front wheel brake force through the fuzzy controller, and comparing the proportion with the maximum torque which can be output by a motor to obtain the final regenerative brake force; and determining the maximum braking force which can be provided by the motor according to the final regenerative braking force to obtain the friction braking force of the front wheel. On the premise of ensuring the braking safety, the invention reasonably distributes the front and rear wheel braking force, the motor braking force and the friction braking force according to different adhesion coefficients, improves the recovery rate of braking energy and the driving range and increases the braking safety.
Description
Technical Field
The invention relates to the field of electric automobiles, in particular to a regenerative braking control method for an electric automobile.
Background
In the key technology of the electric automobile power system, whether the reasonability of a control strategy directly influences the performance level of the whole automobile or not, compared with a fuel automobile, the energy utilization rate of the pure electric automobile power system is relatively high, the braking energy recovery rate can be effectively improved through a reasonable regenerative braking control strategy, the whole automobile efficiency is further improved, the pollutant emission of the automobile is effectively reduced, and the petroleum is saved. Meanwhile, the reasonable control strategy can prolong the service life of the power battery, prolong the driving range of the electric automobile and reduce the risk of overhigh cost caused by early scrapping of the battery, so that the research on the regenerative braking control strategy is an important link for the whole automobile research and development and performance test of the pure electric automobile.
The electric automobile and the traditional fuel oil automobile are the biggest difference in braking, namely the electric automobile can generate energy through motor braking, and the power battery is charged in a motor power generation mode, so that the recycling of braking energy is realized, the energy is saved, and the cruising mileage of the electric automobile is increased. Most researchers only aim at improving the energy recovery rate as much as possible, and neglect the braking safety and stability to a certain extent. The actual regenerative braking control strategy needs to take the satisfaction of the intention or comfort of a driver as a control premise, simultaneously considers the road surface condition, takes the characteristics of the motor as a control basis, reasonably distributes the front and rear wheels, coordinates the proportional relation between regenerative braking and friction braking, judges the motor torque and the mechanical torque according to different working conditions of braking by the controller ECU, and can be repeatedly tested by simulation.
According to the analysis of the whole vehicle power system, the regenerative braking system mainly comprises a motor braking system and a traditional hydraulic braking system, and the motor braking system comprises a whole vehicle controller, a driving motor, a motor controller, a power battery and a battery management system. The motor controller is used for controlling the driving motor to work in a power generation state and applying feedback braking force; the battery management system controls electric energy to be recovered in the battery; conventional hydraulic brake systems include a hydraulic brake actuator and a brake controller for controlling the establishment and adjustment of friction braking forces. In the actual deceleration or braking process of the electric automobile, the vehicle control unit outputs a braking control distribution signal to the motor controller according to the braking intention of a driver to control the braking proportion of the motor, and the proportion of regenerative braking to braking is different due to different vehicle speeds, battery SOC, braking strength and the like.
Currently, typical regenerative braking control strategies mainly include an optimal feeling regenerative braking control strategy (ideal regenerative braking control strategy), a parallel regenerative braking control strategy, and the like. The optimal feel regenerative braking control strategy ensures braking stability and braking effectiveness, but has the disadvantage that in practical application, the braking system assistance is required, and strict curve distribution is difficult. In practical application, the brake system can be combined with ABS anti-lock technology, so that the brake safety is ensured. The braking system based on the parallel regenerative braking control strategy mainly uses friction braking and assists regenerative braking, has a simple structure and high practical application value, but has the defect that a driver feels poor in energy recovery effect. And the two control strategies do not consider the adhesion coefficient, and particularly when the road surface with low adhesion coefficient (accumulated water, ice and snow) is braked, the regenerative braking force is improved, so that the wheels are easily locked, and the braking safety is reduced.
Disclosure of Invention
The invention aims to provide a regenerative braking control method for an electric automobile, which can reasonably distribute front and rear wheel braking force, motor braking force and friction braking force according to different adhesion coefficients on the premise of ensuring braking safety, improve the recovery rate of braking energy and the driving range of the electric automobile, and increase the braking safety.
In order to realize the purpose of the invention, the invention adopts the following technical scheme: a regenerative braking control method for an electric vehicle comprises the following steps:
step 3, taking the brake strength, the battery SOC and the vehicle speed as the input of a fuzzy controller, establishing an experience fuzzy rule, outputting the proportion of the regenerative brake force to the front wheel brake force through the fuzzy controller, and comparing the proportion with the maximum torque which can be output by a motor to obtain the final participation value of the regenerative brake force;
and 4, determining the maximum braking force which can be provided by the motor according to the final regenerative braking force, and subtracting the maximum braking force from the front wheel braking force to obtain the front wheel friction braking force.
Preferably, in step 1, the method comprises the following steps: step a, establishing a wheel mathematical model according to a Burckhardt model and a Kiencke model, introducing a slip rate s to represent the proportion of slip components in the wheel motion process, and defining as follows:
in the formula, ωdIs the wheel angular velocity (rad/s); r isdIs the wheel rolling radius (m); vtireIs the longitudinal rolling speed (m/s) of the wheel;
b, establishing a mathematical model of the adhesion coefficient and the slip rate, and establishing a road surface characteristic value calculation method based on the adhesion coefficient, wherein the formula is as follows:
in the formula (I), the compound is shown in the specification,
represents
The slope of the curve, this coefficient for all roads is taken to be 30, P1、P2Constant values for different road surfaces;
c, defining the characteristic parameters for identifying the road surface state as follows:
in the formula (I), the compound is shown in the specification,
a braking force coefficient representing a braking process; s represents the slip rate of the braking process, and the mathematical model in step b is substituted into the formula in step c to make the slip rate s and the upper limit of integration s equal to the optimal slip rate spTo obtain the peak adhesion coefficientAnd different road surface characteristic value threshold values taup；
D, calculating the road surface characteristic value tau according to the formula in the step c, and distinguishing the road surface condition of the section where the characteristic value is located, so that the road surface condition at the moment and the average adhesion coefficient corresponding to the road surface can be identified.
Preferably, in step 2, the method comprises the following steps: step e, the formula of the braking force distribution curve I curve of the front wheel brake and the rear wheel brake is as follows:
step f, recording in various
On a road surface with the value that the front wheel is locked, but the braking force relation curve of the front wheel and the rear wheel is f line group when the rear wheel is not locked, the relation is as follows:
in the above formula, FbfFor front wheel brake braking force, FbrBraking force for a rear wheel brake; g is the vehicle weight; h isgThe height of the mass center of the whole vehicle is; l is the axle base of the whole vehicle; b is the distance from the center of mass of the whole vehicle to the rear axle;
step g. in the different
The relation curve of the braking force of the front wheel and the rear wheel when only the rear wheel is locked and the front wheel is not locked is a gamma line group, and the relation formula is
Step h, satisfying the relation expression of the braking force of the front wheel and the rear wheel of the ECE braking regulation:
in the above formula, FbfFor front wheel brake braking force, FbrBraking force for a rear wheel brake; g is the vehicle weight; h isgThe height of the mass center of the whole vehicle is; l is the axle base of the whole vehicle; b is the distance from the center of mass of the whole vehicle to the rear axle; a is the distance from the center of mass to the front axle;
determining a critical adhesion coefficient
Value of (2), critical adhesion coefficient
The corresponding f line is called fxCurve, point of intersection M of the ECE normal and the horizontal axis, according to formula MxFinding f as M/0.9xPoint of intersection M with the transverse axisxWill (M)xAnd 0) substituting the f line group formula in the step a to obtain fxCorresponding critical coefficient of adhesion
The value is obtained.
Preferably, in step a, when the wheel is rolling purely, Vtire＝ωdrdWhen the slip ratio s is 0; when the wheel is purely trailing, ω d0, when s is 100%; when the wheel rolls and slides, s is more than 0 and less than 100 percent.
Preferably, in step E, the improved braking force distribution strategy is as followsBased on CE regulations, combining the f line group with the I curve, and distributing through a braking force distribution strategy when the adhesion coefficient is
The maximum braking force participated by the front wheels is as follows:
in the formula, zA、zBBrake intensities corresponding to A, B points, respectively;
coefficient of adhesion
The maximum braking force participated by the front wheels is as follows:
in the formula, zD、zE、zFRespectively, D, E, F points for brake strength.
Preferably, when the motor is in the regenerative braking mode and the rotating speed of the motor exceeds the rated rotating speed, the maximum working power of the motor is 40kW, and the regenerative braking torque of the motor is reduced along with the increase of the rotating speed; when the rotating speed of the motor is too low, the counter electromotive force generated by the motor is too low, the battery is difficult to charge, and the regenerative braking torque determined by the working characteristics of the motor is TmComprises the following steps:
in the formula, TmA regenerative braking torque (Nm) with which the motor itself can participate; n ismThe motor speed (r/min); t ismax_rMaximum braking torque (Nm) of the motor; n is0Setting the speed of the vehicle to be 5km/h and the corresponding motor speed to be 141r/min for the critical speed (r/min) participating in regenerative braking; n isratedThe rated rotating speed of the motor is the basic speed (r/min) of the motor; pm_maxIs the maximum power (kW) of the motor)。
Preferably, the maximum braking force that the motor can provide under the constraint of the power generation capacity of the motor in the power transmission structure of the pure electric vehicle is as follows:
in the formula igIs a vehicle transmission gear ratio; i.e. i0η being the vehicle final drive gear ratioTIs the vehicle driveline efficiency.
Preferably, the regenerative braking capability is influenced by the charging capability of the power battery, the regenerative braking power of the battery for converting electric energy into chemical energy and storing the chemical energy is smaller than the charging power of the battery, the regenerative braking power of the battery and the charging power have a single-value increasing relationship, the charging capability of the battery can be improved by improving the charging power of the battery, when the SOC is greater than a certain limit, the battery is not charged by the regenerative braking, so that the service life of the battery is not influenced by overcharging, and the limit is set to be 0.9, so that the charging characteristic of the power battery is obtained as follows:
in the formula of UbCharging the power battery with a voltage (V); i.e. ib_maxThe maximum regenerative braking force of the power transmission structure of the pure electric vehicle under the constraint of the battery charging capacity is obtained for the maximum charging current (A) of the power battery:
preferably, the actual motor regenerative braking force is introduced into a vehicle speed and battery SOC interference factor function, and the specific function is expressed as:
in the formula, epsilon 1 and epsilon 2 are respectively a vehicle speed interference factor and an SOC interference factor.
Preferably, the actual regenerative braking force of the motor under the constraint of the generating capacity of the motor, the constraint of the charging capacity of the motor and the constraint of the interference factor is as follows:
Fre_max＝ε1ε2min(Fm_max,Fb_max)
compared with the prior art, the electric automobile regenerative braking control method adopting the technical scheme has the following beneficial effects: the regenerative braking control method of the electric automobile determines the braking strength according to the deceleration of the automobile and the stroke change rate of the brake pedal, takes the braking strength, the SOC of the power battery and the speed of the automobile as the input of the fuzzy controller, determines the participation proportion of the regenerative braking force, and finally determines the regenerative braking force of the front wheel motor, the friction braking force of the front wheels and the friction braking force of the rear wheels by combining the maximum torque which can be output by the motor in the current state, so that the energy recovery rate of the automobile can be improved under the road surfaces with different adhesion coefficients while the braking safety is improved, and the driving range is increased.
Drawings
FIG. 1 is a graph showing the distribution of braking forces of front and rear brakes according to an embodiment of the regenerative braking control method for an electric vehicle;
FIG. 2 is a schematic graph of a braking force distribution strategy when the adhesion coefficient is less than or equal to the critical adhesion coefficient in the present embodiment;
FIG. 3 is a graphical illustration of a braking force distribution strategy for embodiments of the present invention in which the adhesion coefficient is greater than the threshold adhesion coefficient;
FIG. 4 is a schematic flow chart illustrating the friction braking force of the front and rear wheels of the whole vehicle;
FIG. 5 is a schematic flow chart of a regenerative braking control of the entire vehicle in this embodiment;
FIG. 6 is a comparison diagram of SOC of the ADVISOR original control strategy and the control strategy under the CYC-UDDS cycle condition in the present embodiment.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
The regenerative braking control method of the electric automobile comprises the following steps: step 1, establishing a road surface characteristic value calculation method based on an adhesion system, establishing a semi-empirical mathematical model of an adhesion coefficient and a slip ratio, introducing a road surface state characteristic value, and identifying a road surface condition and an average adhesion coefficient corresponding to the road surface. The method specifically comprises the following steps: step a, establishing a wheel mathematical model according to a Burckhardt model and a Kiencke model, introducing a slip rate s to represent the proportion of slip components in the wheel motion process, and defining as follows:
in the formula, ωdIs the wheel angular velocity (rad/s); r isdIs the wheel rolling radius (m); vtireIs the longitudinal rolling speed (m/s) of the wheel;
when the wheel is rolling purely, Vtire＝ωdrdWhen the slip ratio s is 0; when the wheel is purely trailing, ω d0, when s is 100%; when the wheel rolls and slides, s is more than 0 and less than 100 percent.
B, establishing a mathematical model of the adhesion coefficient and the slip rate, and establishing a road surface characteristic value calculation method based on the adhesion coefficient, wherein the formula is as follows:
in the formula (I), the compound is shown in the specification,
represents
The slope of the curve, this coefficient for all roads is taken to be 30, P1、P2Constant values for different road surfaces;
c, introducing a road surface state characteristic value concept, and defining characteristic parameters for identifying the road surface state as follows:
in the formula (I), the compound is shown in the specification,
a braking force coefficient representing a braking process; s represents the slip rate of the braking process.
Substituting the mathematical model in step b into the formula in step c to make the slip rate s and the upper limit of integration s equal to the optimal slip rate spTo obtain the peak adhesion coefficient
And different road surface characteristic value threshold values taup(ii) a The characteristic value threshold of the typical pavement is segmented, and because the characteristic value threshold difference between the dry cement pavement and the dry asphalt pavement is very small, the two pavements are combined and considered, so that the characteristic value division intervals of various pavements are obtained as shown in the following table:
| road surface condition | Interval of characteristic value |
| Ice | [0，0.0015] |
| Snow (snow) | [0.0014，0.0098] |
| Wet cobble | [0.0098，0.047] |
| Wet asphalt | [0.047，0.0885] |
| Dry cement and dry asphalt | [0.0885，0.1572] |
| Dried cobble | [0.1572，0.4069] |
And d, estimating a slip rate stable value according to the formula in the step a, estimating a braking force coefficient at the moment according to the ratio of the ground braking force to the vertical load, calculating a road surface characteristic value tau according to the formula in the step c, and judging the road surface condition of the section where the characteristic value is located, so that the road surface condition at the moment and the average adhesion coefficient corresponding to the road surface can be identified.
And 2, judging the braking force of the front wheel and the rear wheel according to the height of the adhesion coefficient and the braking strength. And 3, taking the brake strength, the battery SOC and the vehicle speed as the input of a fuzzy controller, establishing an empirical fuzzy rule, outputting the proportion of the regenerative brake force to the front wheel brake force through the fuzzy controller, and comparing the proportion with the maximum torque which can be output by a motor to obtain the final participation value of the regenerative brake force. The method specifically comprises the following steps: step e, the formula of the braking force distribution curve I curve of the front wheel brake and the rear wheel brake is as follows:
step f, recording in various
On a road surface with the value that the front wheel is locked, but the braking force relation curve of the front wheel and the rear wheel is f line group when the rear wheel is not locked, the relation is as follows:
in the above formula, FbfFor front wheel brake braking force, FbrBraking force for a rear wheel brake; g is the vehicle weight; h isgIs the quality of the whole vehicleHeart height; l is the axle base of the whole vehicle; b is the distance from the center of mass of the whole vehicle to the rear axle;
step g. in the differentThe front and rear wheel braking force relation curve when only the rear wheel is locked and the front wheel is not locked is a gamma line group, and the relation formula is as follows:
step h, satisfying the relation expression of the braking force of the front wheel and the rear wheel of the ECE braking regulation:
in the above formula, FbfFor front wheel brake braking force, FbrBraking force for a rear wheel brake; g is the vehicle weight; h isgThe height of the mass center of the whole vehicle is; l is the axle base of the whole vehicle; b is the distance from the center of mass of the whole vehicle to the rear axle; a is the centroid to front axis distance. As shown in fig. 1, a distribution curve graph of braking forces of front and rear brakes in the electric vehicle regenerative braking control method is shown, in this embodiment, according to an advsor electric vehicle model, a vehicle parameter of the advsor electric vehicle model is substituted into a formula of steps e to h, so as to obtain a curve I, a curve f, a curve γ and a brake regulation curve S shown in fig. 1.
Determining a critical adhesion coefficient
Value of (2), critical adhesion coefficient
The corresponding f line is called fxCurve, point of intersection M of the ECE normal and the horizontal axis, according to formula MxFinding f as M/0.9xPoint of intersection M with the transverse axisxWill (M)xAnd 0) substituting the f line group formula in the step a to obtain fxCorresponding critical coefficient of adhesionThe value is obtained.
The control strategy distributes braking force as much as possible to the driving wheels on the premise of ensuring the braking safety, maintains the braking stability of the automobile, avoids the situation that the rear wheels are locked before the front wheels or only the rear wheels are locked, avoids the front wheels from being locked firstly as much as possible, ensures the braking efficiency and improves the energy recovery rate. The improved braking force distribution strategy is based on the ECE regulation, combines the f-line group and the I curve, and is divided into a control strategy under low adhesion coefficient and a control strategy under high adhesion coefficient according to different road adhesion conditions. In the braking or deceleration process, the road surface condition is firstly identified, so that the control strategy is switched according to the change of the road surface adhesion coefficient.
Coefficient of adhesion
Fig. 2 is a schematic diagram of a braking force distribution strategy when the adhesion coefficient is less than or equal to the critical adhesion coefficient, and specifically includes the following steps: step A, solving the front wheel braking force corresponding to the intersection point M of the ECE normal line and the horizontal axis as 2412.86N; step B, according to formula MxFinding f as M/0.9xPoint of intersection M with the transverse axisx2680.62N; step C. Point (M)x0) substitution of formula (5) to yield fxCoefficient of adhesion of
Is 0.37. The thickened OABC line shown in FIG. 2 is the brake force distribution control line, specifically A, B, depending on the real-time valueValue dependent, set in FIG. 2
Corresponding to line f as0.3Its A, B value is 0.9f0.3Corresponding brake strength values.
Brake strength in the OA region of the figure: in order to improve the energy recovery rate as much as possible, the regenerative braking force is borne as much as possible, and if the braking force provided by the motor is smaller than the total required braking force, the braking force is supplemented by the friction braking force of the front wheels; brake strength in the AB interval in the figure: the front wheel braking force and the rear wheel braking force are distributed according to an AB line, wherein the AB line is designed to be parallel to and on the left side of an f line under the current adhesion coefficient, and the front wheel braking force on the AB line is 90% of the f line, so that the front wheel is prevented from being locked first, the front wheel braking force is shared by the regenerative braking force and the friction braking force, and the regenerative braking force is determined by the maximum torque provided by a motor; brake strength in the BC interval in the figure: the braking force of the front wheel and the rear wheel is distributed according to the curve of the ideal curve I, the regenerative braking force is determined by the maximum torque which can be provided by the motor at the moment, and the regenerative braking force of the motor is set to be released when the braking intensity z is larger than 0.7. Therefore, according to the above distribution control strategy, the maximum braking force involved by the front wheels is:
in the formula, zA、zBRespectively, A, B points for brake strength.
Coefficient of adhesion
FIG. 3 is a graph illustrating a braking force distribution strategy when the adhesion coefficient is greater than the critical adhesion coefficient, the thickened ODEFG shown in FIG. 3 is a braking force distribution control line, and the setting in FIG. 3 is
Wherein the DE line segment is superposed with an ECE regulation line, the front wheel braking force is maximized as much as possible on the premise of meeting the regulation, and the specific braking force distribution strategy is as follows: braking strength in the OD interval in the figure: the regenerative braking force is borne as much as possible, and if the braking force provided by the motor is smaller than the total required braking force, the braking force is supplemented by the friction braking force of the front wheels; the braking strength is in the DE interval in the figure: the braking force of the front wheel and the rear wheel is distributed according to the ECE regulation boundary line, and when the maximum braking torque provided by the motor does not meet the total braking force of the front wheelWhen required, the friction braking force is used for supplementing; brake strength in the interval EF in the figure: the braking force of the front wheel and the rear wheel is distributed according to the parallel line of 90% of the f curve under the current adhesion coefficient, the regenerative braking force is determined by the maximum torque provided by the motor, and the residual braking force is supplemented by the friction braking force of the front wheel and the braking force of the rear wheel; brake strength in FG interval in the figure: the braking force of the front wheel and the braking force of the rear wheel are distributed according to an ideal I curve, the same is carried out, the maximum torque which can be provided by the motor determines the regenerative braking force, and the regenerative braking force of the motor is set to be released when the braking intensity z is larger than 0.7. Therefore, according to the above distribution control strategy, the maximum braking force involved by the front wheels is:
in the formula, zD、zE、zFRespectively, D, E, F points for brake strength.
Fig. 4 is a schematic flow chart of friction braking force of front and rear wheels of the whole vehicle, and fig. 5 is a schematic flow chart of regenerative braking control of the whole vehicle. When the rotating speed of the motor exceeds the rated rotating speed, the maximum working power of the motor is 40kW, and the regenerative braking torque of the motor is reduced along with the increase of the rotating speed; when the rotating speed of the motor is too low, the counter electromotive force generated by the motor is too low, the battery is difficult to charge, and the regenerative braking torque determined by the working characteristics of the motor is TmComprises the following steps:
in the formula, TmA regenerative braking torque (Nm) with which the motor itself can participate; n ismThe motor speed (r/min); t ismax_rMaximum braking torque (Nm) of the motor; n is0Setting the speed of the vehicle to be 5km/h and the corresponding motor speed to be 141r/min for the critical speed (r/min) participating in regenerative braking; n isratedThe rated rotating speed of the motor is the basic speed (r/min) of the motor; pm_maxIs the maximum power of the motor (kW)。
In this embodiment, according to the power transmission structure of the pure electric vehicle under the constraint of the power generation capability of the motor, the maximum braking force that can be provided by the motor is:
in the formula igIs a vehicle transmission gear ratio; i.e. i0η being the vehicle final drive gear ratioTIs the vehicle driveline efficiency.
The regenerative braking capability is also influenced by an energy storage device, namely the charging capability of the power battery, the regenerative braking power of the battery for converting electric energy into chemical energy and storing the chemical energy is smaller than the charging power of the battery, the regenerative braking power of the battery and the charging power have a single-value increasing relation, the charging capability of the battery can be improved by improving the charging power of the battery, and the maximum charging current is set to be not more than 5 ℃ for ensuring the charging safety. When the SOC is larger than a certain limit, the charging of the power battery is not received any more by regenerative braking so as to avoid the influence of overcharging on the service life of the battery, the limit value is set to be 0.9, so that the charging characteristics of the power battery are as follows:
in the formula of UbCharging the power battery with a voltage (V); i.e. ib_maxThe maximum charging current (A) of the power battery is obtained. Therefore, in the charging process, if the generated power of the motor is smaller than the maximum charging power of the battery, the charging current is reduced and adjusted accordingly.
According to the power transmission structure of the pure electric vehicle researched in the embodiment, the maximum regenerative braking force under the constraint of the battery charging capacity is as follows:
the actual motor regenerative braking force needs to consider the two situations at the same time, so a vehicle speed and battery SOC interference factor function is introduced, and the specific function is expressed as follows:
in the formula, epsilon 1 and epsilon 2 are respectively a vehicle speed interference factor and an SOC interference factor.
And 4, determining the maximum braking force which can be provided by the motor according to the final regenerative braking force, and subtracting the maximum braking force from the front wheel braking force to obtain the front wheel friction braking force. Under the constraint condition of the generating capacity of the motor, the constraint of the charging capacity of the motor and the constraint of the interference factor, the actual regenerative braking force of the motor is as follows:
Fre_max＝ε1ε2min(Fm_max,Fb_max)
as shown in fig. 6, which is a SOC comparison graph of an ADVISOR original control strategy and the control strategy under the CYC-UDDS circulation condition, the braking energy recovery effect of the ADVISOR electric vehicle model original control strategy and the control strategy under the circulation condition CYC-UDDS is compared, and the braking energy recovery effect is represented by small fluctuation of increase of a power battery SOC curve and change of the overall amplitude. The braking energy recovery data of the two control strategies under the CYC _ UDDS cycle condition are compared as shown in the following table:
| principal parameters | ADVISER Pro-CONTROL STRATEGY | Improved control strategy |
| Total braking energy (KJ) | 1697 | 1697 |
| Energy loss of vehicle (KJ) | 7060 | 7130 |
| Energy recovered from the battery (KJ) | 440 | 835 |
| Recovery ratio of braking energy (%) | 25.9 | 49.2 |
| Recovery of effective braking energy (%) | 6.23 | 11.7 |
By adopting the regenerative braking control method for the electric automobile, which is disclosed by the invention, the control method meets the ECE R13 braking regulation, and on the premise of ensuring the braking safety, the energy recovery rate of the automobile can be improved under the road surfaces with different adhesion coefficients, and the driving range is increased.
Although the present invention has been described with reference to a preferred embodiment, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (10)
1. A regenerative braking control method for an electric vehicle is characterized by comprising the following steps: the method comprises the following steps:
step 1, establishing a pavement characteristic value calculation method based on an adhesion system, establishing a semi-empirical mathematical model of an adhesion coefficient and a slip rate, introducing a pavement state characteristic value, and identifying a pavement condition and an average adhesion coefficient corresponding to the pavement;
step 2, judging the braking force of the front wheel and the rear wheel according to the height of the adhesion coefficient and the braking strength;
step 3, taking the brake strength, the battery SOC and the vehicle speed as the input of a fuzzy controller, establishing an experience fuzzy rule, outputting the proportion of the regenerative brake force to the front wheel brake force through the fuzzy controller, and comparing the proportion with the maximum torque which can be output by a motor to obtain the final participation value of the regenerative brake force;
and 4, determining the maximum braking force which can be provided by the motor according to the final regenerative braking force, and subtracting the maximum braking force from the front wheel braking force to obtain the front wheel friction braking force.
2. The electric vehicle regenerative braking control method according to claim 1, characterized in that: in step 1, the method comprises the following steps:
step a, establishing a wheel mathematical model according to a Burckhardt model and a Kiencke model, introducing a slip rate s to represent the proportion of slip components in the wheel motion process, and defining as follows:
in the formula, ωdIs the wheel angular velocity (rad/s); r isdIs the wheel rolling radius (m); vtireIs the longitudinal rolling speed (m/s) of the wheel;
b, establishing a mathematical model of the adhesion coefficient and the slip rate, and establishing a road surface characteristic value calculation method based on the adhesion coefficient, wherein the formula is as follows:
in the formula (I), the compound is shown in the specification,
representsThe slope of the curve, this coefficient for all roads is taken to be 30, P1、P2Constant values for different road surfaces;
c, defining the characteristic parameters for identifying the road surface state as follows:
in the formula (I), the compound is shown in the specification,
a braking force coefficient representing a braking process; s represents the slip rate of the braking process, and the mathematical model in step b is substituted into the formula in step c to make the slip rate s and the upper limit of integration s equal to the optimal slip rate spTo obtain the peak adhesion coefficient
And different road surface characteristic value threshold values taup；
D, calculating the road surface characteristic value tau according to the formula in the step c, and distinguishing the road surface condition of the section where the characteristic value is located, so that the road surface condition at the moment and the average adhesion coefficient corresponding to the road surface can be identified.
3. The electric vehicle regenerative braking control method according to claim 1, characterized in that: in step 2, the method comprises the following steps: step e, the formula of the braking force distribution curve I curve of the front wheel brake and the rear wheel brake is as follows:
step f, recording in various
On a road surface with the value that the front wheel is locked, but the braking force relation curve of the front wheel and the rear wheel is f line group when the rear wheel is not locked, the relation is as follows:
in the above formula, FbfFor front wheel brake braking force, FbrBraking force for a rear wheel brake; g is the vehicle weight; h isgThe height of the mass center of the whole vehicle is; l is the axle base of the whole vehicle; b is the distance from the center of mass of the whole vehicle to the rear axle;
step g. in the different
The relation curve of the braking force of the front wheel and the rear wheel when only the rear wheel is locked and the front wheel is not locked is a gamma line group, and the relation formula is
Step h, satisfying the relation expression of the braking force of the front wheel and the rear wheel of the ECE braking regulation:
in the above formula, FbfFor front wheel brake braking force, FbrBraking force for a rear wheel brake; g is the vehicle weight; h isgThe height of the mass center of the whole vehicle is; l is the axle base of the whole vehicle; b is the distance from the center of mass of the whole vehicle to the rear axle; a is the distance from the center of mass to the front axle;
determining a critical adhesion coefficientValue of (2), critical adhesion coefficient
The corresponding f line is called fxCurve, point of intersection M of the ECE normal and the horizontal axis, according to formula MxFinding f as M/0.9xPoint of intersection M with the transverse axisxWill (M)xAnd 0) substituting the f line group formula in the step a to obtain fxCorresponding critical coefficient of adhesionThe value is obtained.
4. The electric vehicle regenerative braking control method according to claim 2, characterized in that: in step a, when the wheel rolls purely, Vtire＝ωdrdWhen the slip ratio s is 0; when the wheel is purely trailing, ωd0, when s is 100%; when the wheel rolls and slides, s is more than 0 and less than 100 percent.
5. The electric vehicle regenerative braking control method according to claim 3, characterized in that: in step e, the improved braking force distribution strategy is based on ECE regulations and combined with the f-line set and the I-curve, and the distribution is carried out by the braking force distribution strategy when the adhesion coefficient is
The maximum braking force participated by the front wheels is as follows:
in the formula, zA、zBBrake intensities corresponding to A, B points, respectively;
coefficient of adhesion
The maximum braking force participated by the front wheels is as follows:
in the formula, zD、zE、zFRespectively, D, E, F points for brake strength.
6. The electric vehicle regenerative braking control method according to claim 3, characterized in that: when the motor is in a regenerative braking mode, when the rotating speed of the motor exceeds the rated rotating speed, the maximum working power of the motor is 40kW, and the regenerative braking torque of the motor is reduced along with the increase of the rotating speed; when the rotating speed of the motor is too low, the counter electromotive force generated by the motor is too low, the battery is difficult to charge, and the regenerative braking torque determined by the working characteristics of the motor is TmComprises the following steps:
in the formula, TmA regenerative braking torque (Nm) with which the motor itself can participate; n ismThe motor speed (r/min); t ismax_rMaximum braking torque (Nm) of the motor; n is0Setting the speed of the vehicle to be 5km/h and the corresponding motor speed to be 141r/min for the critical speed (r/min) participating in regenerative braking; n isratedThe rated rotating speed of the motor is the basic speed (r/min) of the motor; pm_maxThe maximum power (kW) of the motor.
7. The electric vehicle regenerative braking control method according to claim 6, characterized in that: the power transmission structure of the pure electric automobile is limited by the power generation capacity of the motor, and the maximum braking force provided by the motor is as follows:
in the formula igIs a vehicle transmission gear ratio; i.e. i0η being the vehicle final drive gear ratioTIs the vehicle driveline efficiency.
8. The electric vehicle regenerative braking control method according to claim 7, characterized in that: the regenerative braking capability is influenced by the charging capability of the power battery, the regenerative braking power of the battery for converting electric energy into chemical energy and storing is smaller than the charging power of the battery, the regenerative braking power of the battery and the charging power have a single-value increasing relationship, the charging power of the battery can be improved by improving the charging power of the battery, when the SOC is more than a certain limit, the battery is not charged by the regenerative braking, so that the service life of the battery is not influenced by overcharging, the limit value is set to be 0.9, and the charging characteristic of the power battery is obtained as follows:
in the formula of UbCharging the power battery with a voltage (V); i.e. ib_maxThe maximum regenerative braking force of the power transmission structure of the pure electric vehicle under the constraint of the battery charging capacity is obtained for the maximum charging current (A) of the power battery:
9. the electric vehicle regenerative braking control method according to claim 8, characterized in that: the actual motor regenerative braking force needs to be introduced into a vehicle speed and battery SOC interference factor function, and the specific function is expressed as:
in the formula, epsilon 1 and epsilon 2 are respectively a vehicle speed interference factor and an SOC interference factor.
10. The electric vehicle regenerative braking control method according to claim 9, characterized in that: under the constraint condition of the generating capacity of the motor, the constraint of the charging capacity of the motor and the constraint of the interference factor, the actual regenerative braking force of the motor is as follows:
Fre_max＝ε1ε2min(Fm_max,Fb_max)
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