CN116512934A - Torque distribution control method for realizing energy consumption optimization of three-motor four-drive electric automobile - Google Patents

Torque distribution control method for realizing energy consumption optimization of three-motor four-drive electric automobile Download PDF

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Publication number
CN116512934A
CN116512934A CN202310543478.8A CN202310543478A CN116512934A CN 116512934 A CN116512934 A CN 116512934A CN 202310543478 A CN202310543478 A CN 202310543478A CN 116512934 A CN116512934 A CN 116512934A
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China
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motor
torque
wheel
driving
vehicle
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王萍
任俏
林佳眉
胡云峰
陈虹
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Jilin University
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Jilin University
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • 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
    • B60L15/00—Methods, circuits, or devices for controlling the traction-motor speed of electrically-propelled vehicles
    • B60L15/20—Methods, circuits, or devices for controlling the traction-motor speed of electrically-propelled vehicles for control of the vehicle or its driving motor to achieve a desired performance, e.g. speed, torque, programmed variation of speed
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • 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
    • B60L15/00—Methods, circuits, or devices for controlling the traction-motor speed of electrically-propelled vehicles
    • B60L15/20—Methods, circuits, or devices for controlling the traction-motor speed of electrically-propelled vehicles for control of the vehicle or its driving motor to achieve a desired performance, e.g. speed, torque, programmed variation of speed
    • B60L15/2009—Methods, circuits, or devices for controlling the traction-motor speed of electrically-propelled vehicles for control of the vehicle or its driving motor to achieve a desired performance, e.g. speed, torque, programmed variation of speed for braking
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • 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
    • B60L15/00—Methods, circuits, or devices for controlling the traction-motor speed of electrically-propelled vehicles
    • B60L15/20—Methods, circuits, or devices for controlling the traction-motor speed of electrically-propelled vehicles for control of the vehicle or its driving motor to achieve a desired performance, e.g. speed, torque, programmed variation of speed
    • B60L15/2045—Methods, circuits, or devices for controlling the traction-motor speed of electrically-propelled vehicles for control of the vehicle or its driving motor to achieve a desired performance, e.g. speed, torque, programmed variation of speed for optimising the use of energy
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • 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
    • B60L15/00—Methods, circuits, or devices for controlling the traction-motor speed of electrically-propelled vehicles
    • B60L15/32—Control or regulation of multiple-unit electrically-propelled vehicles
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/60—Other road transportation technologies with climate change mitigation effect
    • Y02T10/72—Electric energy management in electromobility

Abstract

A torque distribution control method for realizing energy consumption optimization of a three-motor four-drive electric automobile belongs to the technical field of torque distribution control of electric automobiles. The invention aims to obtain a prediction model of an MPC controller by utilizing a dynamic model of a tire longitudinal slip rate and wheel driving torque, design a plurality of cost functions and adjusting weights to distribute total driving torque to three driving motors, design driving torque constraints of a front shaft motor and two rear shaft driving motors, ensure driving safety, and finally design a torque distribution control method of a performance evaluation index function for realizing energy consumption optimization of a three-motor four-drive electric automobile. In order to realize better stability and economical coordinated control, the cost function is designed to enable each power source to generate reasonable yaw moment in the torque distribution process so as to ensure stability, and simultaneously enable the front axle motor and the two rear wheel hub motors to work in a high-efficiency area as much as possible, so that the energy-saving aim of the vehicle is realized to the greatest extent on the premise of not influencing the operation stability.

Description

Torque distribution control method for realizing energy consumption optimization of three-motor four-drive electric automobile
Technical Field
The invention belongs to the technical field of torque distribution control of electric automobiles.
Background
In order to alleviate the problems of global energy shortage, environmental pollution and the like, the field of the electric automobile which is more environment-friendly and energy-saving is developed faster and faster. Compared with the traditional automobile, the electric automobile can improve the efficiency of the whole electric automobile system through light design and efficient electric drive system configuration, and particularly the distributed four-wheel drive electric automobile, because the transmission system is omitted, the whole automobile structure is simplified, the design is more flexible, and the operability of control is optimized. When the vehicle is in the running process, under the constraint of the power performance of the whole vehicle, the torque distribution among the power sources can be more freely realized, and the running economy of the vehicle is improved. The torque distribution control of the distributed driving electric vehicle mainly takes four-motor full-drive as a research object at present, the four-motor full-drive vehicle is high in configuration cost, and four motors work simultaneously to easily cause power redundancy so as to increase energy loss, so that an ideal energy-saving effect is difficult to achieve.
The following problems still exist at present:
1. at present, research on energy conservation of a three-motor four-drive electric automobile focuses on how to distribute total required torque to a front axle motor and two rear wheel hub motors so as to reduce motor efficiency loss, the method mainly surrounds global optimization and instantaneous optimization, the global optimization is mainly used under relatively fixed linear working conditions, and a basis is provided for the establishment of torque distribution ratio among driving motors on the basis of global optimization results; the real-time optimization based on the minimum system power loss can achieve the optimal instantaneous energy consumption, but can possibly cause abrupt change of the output driving torque of the power source, so that the state change of each motor is not smooth enough to generate more energy loss, and the optimal effect is difficult to realize.
2. The research of the distributed driving stability control which is carried out at present always strictly ensures the stability of the vehicle through yaw moment control, which limits the torque distribution ratio of the left motor and the right motor, and does not consider whether the side torque distribution can cause energy loss of the motors or not, thereby influencing the economical efficiency of the vehicle. In addition, dynamic coordination of stability and economy cannot be achieved because stability is severely constrained.
3. When the vehicle runs under dynamic working conditions such as acceleration and deceleration, the problem of energy dissipation of longitudinal sliding of the tire caused by driving force saturation due to load change of front and rear axles is not considered in the current research; at the same time, safety problems which occur in this operating mode due to the possibility of wheel locking due to an unreasonable torque distribution are not considered.
Disclosure of Invention
The invention aims to obtain a prediction model of an MPC controller by utilizing a dynamic model of a tire longitudinal slip rate and wheel driving torque, design a plurality of cost functions and adjusting weights to distribute total driving torque to three driving motors, design driving torque constraints of a front shaft motor and two rear shaft driving motors, ensure driving safety, and finally design a torque distribution control method of a performance evaluation index function for realizing energy consumption optimization of a three-motor four-drive electric automobile.
The method comprises the following steps:
s1, a prediction model based on energy consumption optimization MPC controller is obtained by utilizing a dynamic model of tire slip rate and wheel driving torque, wherein state variables of the prediction model consist of four wheel slip rates, and the control quantity is driving wheel torque;
(1) calculating a total torque demand command for the driver based on the desired longitudinal vehicle speed：
（1）
Wherein, the liquid crystal display device comprises a liquid crystal display device,，/>for PI controller parameters, +.>，/>Tracking reference longitudinal speed and vehicle longitudinal speed respectively;
(2) solving for yaw moment for stabilizing vehicle driving by tracking expected values of vehicle centroid slip angle and yaw rate；
S2, obtaining a prediction model of the energy consumption optimized MPC controller
(1) The steady state tire slip ratio is defined as:
（2）
wherein, the liquid crystal display device comprises a liquid crystal display device,for the rotational speed of the tire>Is the wheel slip ratio, wherein->Respectively represent a left front wheel, a right front left rear wheel and a right rear wheel, < >>The effective radius of the tire;
the longitudinal force is positively correlated with the tire slip ratio, and the linearity of the longitudinal force is expressed as:
（3）
in the middle of、/>Respectively the firstiLongitudinal and vertical forces of the individual tires, +.>Is the moment of inertia;
to obtain the slip ratio of the wheelsTorque of wheel->The kinetic model of the relationship is as follows:
（4）
taking into account thatThe above formula is written as:
（5）；
(2) and (3) designing a controller: the state variable of the prediction model consists of four wheel slip rates, the control quantity is the driving wheel torque, and the prediction model is as follows:
（6）
wherein the method comprises the steps of，/>The state vector of the system is defined as:
control amount->Torque is output for four drive wheels: />Wherein->Output driving torque for front axle motor, +.>The distribution coefficient of the driving torque from the front axle motor to the wheels on the left side and the right side is used for distributing the driving torque from the front axle motor to the wheels on the left side and the right side;
the prediction model is discretized according to Euler equation, and is setFor sampling time, the discrete prediction model is obtained as follows:
（7）
wherein the method comprises the steps of，/>；
Distributing the total driving torque to each wheel to enable each wheel to rotateMinimum, satisfy total driving force +.>The method comprises the steps of carrying out a first treatment on the surface of the The difference between the driving forces on the left and right sides satisfies the required yaw moment +.>Driving force of each wheel +.>And total driving torque->And->The relationship of (2) is as follows:
（8）；
s3, designing 4 cost functions, wherein the cost functions are as follows:
first objective function:
（9）
wherein, the liquid crystal display device comprises a liquid crystal display device,for left and right wheel track->，/>Is a weight coefficient;
second objective function:
（10）
minimizing tire slip power loss, the designed objective function is as follows:
（11）
third objective function:
（12）
wherein the method comprises the steps of，/>Boundary constraint values for longitudinal slip,、/>is a weight factor;
fourth objective function:
and (3) writing the motor efficiency as a function of torque, fitting motor Map data by using a sixth-order polynomial, and writing the sixth-order polynomial into:
（13）
wherein, the liquid crystal display device comprises a liquid crystal display device,for the fitted motor efficiency, +.>For fitting coefficients +.>Is motor torque;
the objective function when the motor is in drive mode is:
（14）
the objective function when the motor is in the braking energy recovery mode is:
（15）
the upper and lower limits of the output driving torque of the three motors are constrained by the load of the motors as follows:
（16）
the control amount constraint can be obtained:
（17）
the objective function is obtained as follows:
（18）
s4, when the driving torque of the front shaft and the rear shaft is distributed, the driving torque of the front shaft is not larger than that of the rear shaftShaft drive torque, design controller constraintsThe method comprises the following steps:
（19）
the front axle single motor provides power for the left wheel and the right wheel of the front axle, and the control quantity of the front axle is restrained to output driving force or braking force simultaneously, namely:
（20）
preventing rear wheels from locking through torque distributionIn order to avoid causing the sideslip of the vehicle and threatening the safety of a driver, the controller is constrained as follows:
（21）
the braking force of the front axle and the rear axle is restrained between an ideal I curve and the lower limit of ECE regulations, so that the stability of the braking process is ensured:
（22）
i.e.
（23）
Wherein, the liquid crystal display device comprises a liquid crystal display device,Las the distance from the front axle to the rear axle,is the height of the centroid,Gis the acceleration of gravity;
the solved band constraint problem is as follows:
（24）
optimizing and solving the objective function to obtain a control quantity which is the driving torque of the wheels;
s5, designing performance index evaluation functions from four aspects of steering stability, motor energy-saving performance, tire slip energy loss and longitudinal vehicle speed tracking;
(1) steering stability:
（25）
(2) energy-saving performance of the motor:
（26）
(3) tire slip energy loss:
（27）
(4) longitudinal vehicle speed tracking performance:
（28）。
the beneficial effects of the invention are as follows:
1. according to the invention, an energy management strategy is designed based on model predictive control, a six-degree polynomial is utilized to fit a motor energy efficiency Map graph, the motor driving state change fed back in real time is considered through rolling optimization, the high-efficiency working points of each motor are solved on line, the torque is distributed to enable the front axle motor and the two rear wheel hub motors to operate in the optimal efficiency area as far as possible, the strategy is not limited by working conditions, the energy loss of the motors can be minimized, and the real-time performance and the economical efficiency are considered;
2. according to the invention, various dynamic working conditions are considered, the excessive wheel sliding phenomenon caused by the load transfer change of the front axle and the rear axle under the conditions of turning and acceleration and deceleration of the vehicle is designed, a wheel sliding power loss matrix and a punishment matrix are designed, the energy loss caused by the wheel sliding is restrained, meanwhile, the potential safety hazard of the vehicle caused by the change of the axle load under the conditions of acceleration and braking is avoided, and corresponding constraint is set for limiting;
3. in order to realize better stability and economical coordinated control, under the condition of meeting the requirement of total driving torque, the invention does not strictly distribute additional yaw moment in yaw stability control, but designs a cost function to ensure stability by generating reasonable yaw moment in the torque distribution process by each power source, simultaneously, the front axle motor and the two rear wheel hub motors work in a high-efficiency area as much as possible, and the energy-saving aim of the vehicle is realized to the greatest extent on the premise of not influencing steering stability.
Drawings
Fig. 1 is a flow chart of a torque distribution control method based on energy consumption optimization of a three-motor four-drive electric automobile;
fig. 2 is a Map diagram of a PD18 motor according to the present invention;
FIG. 3 is a Map 6 th order polynomial fitting diagram of the motor according to the invention;
FIG. 4 is a block diagram of a flow chart of on-line optimization after Map fitting of a motor;
FIG. 5 is an ECE brake regulation range map;
FIG. 6 is a schematic diagram of simulation of motor output torque, tire slip ratio, yaw rate and centroid slip angle under static allocation for a dual lane-change condition, road attachment coefficient, vehicle speed kept around 60 km/h;
FIG. 7 is a schematic diagram of simulation of motor output torque, tire slip ratio, yaw rate and centroid slip angle under torque distribution control of energy consumption optimization of a three-motor four-drive electric vehicle under a dual lane-change condition, road adhesion coefficient, vehicle speed kept around 60 km/h;
FIG. 8 is a schematic diagram of simulation of the output torque, tire slip ratio, yaw rate and centroid slip angle of a motor under the torque distribution control of a four-motor four-drive electric vehicle under the dual lane-shifting condition, road surface attachment coefficient, vehicle speed kept around 60 km/h;
FIG. 9 is a simulation diagram of motor output torque, tire slip ratio, yaw rate and centroid slip angle under torque distribution control of energy consumption optimization of a three-motor four-drive electric vehicle under double lane shifting conditions, road adhesion coefficients and vehicle speeds of 50km/h to 70km/h acceleration;
FIG. 10 is a schematic diagram of simulation of motor output torque, tire slip ratio, yaw rate and centroid slip angle under torque distribution control of energy consumption optimization of a three-motor four-drive electric vehicle under double lane-shifting working conditions, road adhesion coefficient and vehicle speed of 70 km/h-50 km/h.
Detailed Description
The invention designs an energy management control strategy for a three-motor four-wheel drive electric automobile from the angle of energy consumption optimization. Firstly, a dynamic model of the longitudinal slip rate of the tire and the driving torque of the wheel is utilized to obtain a prediction model of the MPC controller; secondly, in order to dynamically coordinate the stability and economy of the three-motor four-wheel drive vehicle and realize the maximum reduction of the comprehensive energy consumption of the whole vehicle, the total driving torque is distributed to three driving motors through designing a plurality of cost functions and adjusting weights, so that the purposes of generating reasonable yaw moment among driving wheels to ensure the stable operation of the vehicle, enabling the motors to operate in a high-efficiency area and reducing the slip power loss of tires are achieved; thirdly, considering the wheel locking condition possibly caused by the load change of the front axle and the rear axle under the dynamic working condition, the driving torque constraint of the front axle motor and the two rear axle driving motors is designed, and the driving safety is ensured; finally, designing a performance evaluation index function, and verifying the energy conservation of the torque distribution control method for realizing the energy consumption optimization of the three-motor four-wheel drive electric automobile.
A torque distribution control method for realizing energy consumption optimization of a three-motor four-wheel drive electric automobile is realized by the following steps:
step one, designing and obtaining a three-motor four-wheel drive electric automobile model by using simulation software CarSim, and providing all state information of a vehicle in real time; in order to meet the driving force requirements under different driving conditions, the front axle motor is configured as a continental concentrated motor, and the two rear wheel hub motors are configured as PD18 motors; calculating a total torque demand command for the driver based on the desired longitudinal vehicle speedThe method comprises the steps of carrying out a first treatment on the surface of the Solving for yaw moment for stabilizing driving of vehicle by tracking desired value of centroid slip angle and yaw rate of vehicle>。
And secondly, obtaining a prediction model based on the energy consumption optimization MPC controller by utilizing a dynamic model of the tire slip rate and the wheel driving torque, wherein state variables of the prediction model consist of four wheel slip rates, and the control quantity is the driving wheel torque.
Step three, the invention distributes the total driving torque to the front axle motor and the two rear wheel hub motors to realize the control targets of improving the energy conservation of the whole vehicle and guaranteeing the driving safety of the vehicle, designs 4 cost functions, and respectively comprises the following steps: firstly, 6 times of polynomial fitting motor energy Map is utilized to solve the optimal point of motor efficiency on line, and each motor is enabled to work in a high-efficiency area under a driving mode and a braking mode so as to reduce motor energy loss and improve braking energy recovery efficiency; secondly, introducing a longitudinal sliding power loss matrix, and reducing the dynamic sliding energy dissipation of the tire; re-designing a penalty matrix to limit the slip amount beyond the boundary, and further inhibiting excessive slip of the tire; finally, it is ensured that the required yaw moment can be generated between the motors to control the steering stability of the vehicle.
And step four, considering the wheel locking condition of the vehicle possibly caused by the change of the load of the front axle and the rear axle under the acceleration and deceleration working condition, designing constraint on the driving torque of the front axle concentrated motor and the rear axle motor, and limiting the output braking force of the front axle and the rear axle based on ECE regulation and an I curve braking strategy under the deceleration condition, so as to ensure the driving safety.
Step five, designing performance index evaluation functions from four aspects of operation stability, motor energy-saving performance, tire slip energy loss and longitudinal vehicle speed tracking, and testing the performance of the torque distribution control method for realizing the energy consumption optimization of the three-motor four-wheel drive electric vehicle; proved by the energy conservation of the control method.
The invention discloses a torque distribution method for optimizing energy consumption of a three-motor electric vehicle, which takes a three-motor distributed four-drive electric vehicle consisting of a front shaft single motor and a rear shaft two hub motors as a research object.
For a detailed description of the technical content, construction features, implementation purposes, etc., of the present invention, the present invention is fully explained below with reference to the accompanying drawings:
the flow of the torque distribution control method for realizing the energy consumption optimization of the three-motor four-wheel drive electric automobile is shown in the figure 1, and the required total traction torque and the yaw moment required to be generated by each driving wheel are obtained from a driver model and stability control; in the MPC energy consumption optimization controller, the input is the longitudinal slip rate of four tires and the output measured value of the controlled object, and the output is the traction force of each motor respectively; the dynamic relation between the tire slip and the wheel driving torque is utilized, and the total driving torque is distributed to three driving motors through multi-objective function optimization; the MPC controller module is built in MATLAB/Simulink; the controlled object is a three-motor four-wheel drive electric automobile model constructed by using CarSim.
The control objective of the invention is that the control system obtains the required total traction torque from the driver model and the stability control according to the real-time feedback signal, and the controller solves the problem of distributing the total driving torque to three driving motors so as to achieve the purposes of generating reasonable yaw moment among driving wheels to ensure the stable operation of the vehicle, reducing the power loss of the motors and inhibiting the longitudinal sliding of the tires.
The invention provides a set of joint simulation model based on the operation principle and the operation process, and the construction and operation processes are as follows:
1. software selection
The simulation models of the controller and the controlled object of the control system are respectively built through software MATLAB/Simulink and CarSim, the software versions are MATLAB R2022a and CarSim 2019.1, and the simulation step length is 0.001s. The system mainly aims at providing a high-fidelity vehicle dynamics model, replaces a real three-motor four-wheel drive electric vehicle in a simulation experiment as an implementation object of a control method, and provides a simulation environment with low attachment limit working conditions; MATLAB/Simulink is used for building a simulation model of the controller, namely, the operation of the controller in the control system is completed through Simulink programming.
2. Joint simulation setup
To realize the joint simulation of MATLAB/Simulink and CarSim, the working path of CarSim is firstly set as a designated Simulink Model, then the set vehicle Model is added into Simulink in CarSim, and Simulink is operated to realize the joint simulation and communication of both. Retransmission is required if the model structure or parameter settings in CarSim are modified.
3. Three-motor four-wheel drive electric automobile model building in joint simulation software
The whole car model of the CarSim electric car mainly comprises a car body, a transmission system, a steering system, a braking system, tires, a suspension, aerodynamics, working condition configuration and other systems. The four-wheel drive vehicle is selected, and the wheel torque input of the four-wheel drive vehicle is selected from IMP_MUSM_L1, IMP_MUSM_L2, IMP_MUSM_R1 and IMP_MUSM_R2, and the parameters of the electric vehicle are shown in table 1.
Table 1 electric automobile parameter table
4. The invention relates to a torque distribution control principle based on energy consumption optimization of a three-motor four-drive electric automobile
The controlled object of the invention is a three-motor four-drive electric automobile, and the control aim is to optimize the working efficiency of the motor and the slip loss of the tire on the premise of ensuring the driving safety.
The following describes the specific steps of the control method of the present invention:
the method comprises the following steps of firstly, designing a three-motor four-wheel drive electric automobile model by using simulation software CarSim, wherein the model is used for simulating a real controlled object, and mainly has the effects of providing all state information of a vehicle in real time and changing the motion state of the vehicle by taking motor torque as an input quantity. To meet different driving conditionsLower driving force demand, the front axle motor is configured as a continental concentrated motor, and the two rear wheel hub motors are configured as PD18 motors in the present invention. To achieve torque distribution and steering stability requirements for the subsequent three electric machines, the total torque demand command for the driver needs to be calculated based on the desired longitudinal vehicle speedAnd solving for a yaw moment for stabilizing the driving of the vehicle by tracking the centroid slip angle and the yaw rate expectation value of the vehicle>。
(1) The three-motor four-wheel drive electric automobile model is characterized by comprising a front axle driving motor and two rear wheel hub motors. Compared with the traditional electric drive vehicle, the three-motor drive structure has the following advantages:
a. compared with the traditional single-motor all-wheel drive configuration
The configuration of the three motors can more easily realize independent control of each driving wheel, and greatly simplifies a mechanical transmission system, thereby reducing mechanical loss and whole vehicle quality.
b. Compared with four-wheel independent motor configuration
The hub motor positioned on the rear wheel in the three-motor driving configuration inherits the advantages of a common wheel type distributed electric drive automobile, the motor torque response is accurate and rapid, the control freedom degree is high, and a front wheel hub motor is reduced on the basis, and the three-motor configuration is superior to the four-wheel independent motor configuration in the aspects of cost, space requirement and control complexity.
According to the invention, the front shaft and the rear shaft are configured into different motors, so that driving requirements under different working conditions can be met, the total torque requirement of the vehicle can be met, the loss increase caused by energy surplus can be effectively reduced, and the three motors can all operate at the maximum efficiency as much as possible by controlling the motor driving area.
(2) Calculating a total torque demand command for the driver based on the desired longitudinal vehicle speed：
（1）
Wherein, the liquid crystal display device comprises a liquid crystal display device,，/>for PI controller parameters, +.>，/>The tracking reference longitudinal speed and the vehicle longitudinal speed, respectively.
(3) To meet stability requirements, solving for yaw moment to stabilize the vehicle by tracking the vehicle centroid slip angle and yaw rate expectation。
And step two, obtaining a dynamic model of the wheel slip rate and the wheel driving torque based on the wheel steady-state slip rate, and obtaining a prediction model of the MPC based on energy consumption optimization based on the dynamic model.
(1) To reduce tire slip energy loss, the steady state tire slip rate may be defined as:
（2）
wherein, the liquid crystal display device comprises a liquid crystal display device,for the rotational speed of the tire>Is the wheel slip ratio, wherein->Respectively represent a left front wheel, a right front left rear wheel and a right rear wheel, < >>Effective radius of the tire.
When the tire is operated in the longitudinal linear region, the longitudinal force of the tire satisfies a small slip ratio model, wherein the longitudinal force is positively correlated with the tire slip ratio.
Thus, a linear approximation of the longitudinal force can be expressed as:
（3）
in the middle of、/>Respectively the firstiLongitudinal and vertical forces of the individual tires, +.>Is the moment of inertia. />
The slip ratio of the wheels can be deduced from the equationTorque of wheel->The kinetic model of the relationship is as follows:
（4）
taking into account thatThe above can be written as
（5）。
(2) And (3) designing a controller: the state variable of the prediction model consists of four wheel slip rates, the control quantity is the driving wheel torque, and the prediction model is as follows:
（6）
wherein the method comprises the steps of，/>。
The state vector of the system can be defined as:control amount->Torque is output for four drive wheels: />Wherein->Output driving torque for front axle motor, +.>The distribution coefficient of the driving torque from the front axle motor to the wheels on the left side and the right side is used for the distribution coefficient of the driving torque from the front axle motor to the wheels on the left side and the right side.
The prediction model is discretized according to the Euler equation, and is set as sampling time, and the obtained discrete prediction model is as follows:
（7）
wherein the method comprises the steps of，/>。
In the present invention, the division for four-wheel driving forceCloth, explained as follows. On low traction road surface, when the wheel slip rate is lowThe wheel driving force is reduced due to saturation. To avoid this decrease +_ for each wheel>It needs to be small enough to prevent saturation.
Therefore, the invention determines that the total driving torque is distributed to each wheel so that each wheelMeeting the total driving force +.>The method comprises the steps of carrying out a first treatment on the surface of the The difference between the driving forces on the left and right sides satisfies the required yaw moment +.>Driving force of each wheelAnd total driving torque->And->The relationship of (2) is as follows: />
（8）。
And thirdly, the invention distributes total driving torque to the front axle motor and the two rear wheel hub motors so as to achieve the control objective of dynamically coordinating the stability and economy of the three-motor four-wheel drive and reducing the comprehensive energy consumption of the whole vehicle, and designs 4 cost functions, which are specifically described as follows.
The first objective function is designed to distribute the total required traction torque to the drive motors and to cause the drive wheels to generate a yaw moment to ensure steering stability:
（9）
wherein, the liquid crystal display device comprises a liquid crystal display device,for left and right wheel track->，/>Is a weight coefficient.
The second objective function is to reduce tire dynamic slip energy dissipation by introducing a longitudinal slip power loss matrix:
（10）。
minimizing tire slip power loss, the designed objective function is as follows:
（11）。
the third objective function is to design a penalty matrix for the excessive slip phenomenon of the tire, and obtain better stability while inhibiting the longitudinal slip of the tire:
（12）/>
wherein the method comprises the steps of，/>Boundary constraint value of longitudinal slip +_>、/>Is a weight factor.
And the fourth objective function is to reduce the energy efficiency loss of the motor, respectively carry out 6 times of polynomial fitting according to the efficiency Map diagrams of the front shaft motor and the rear shaft motor, and solve the high-efficiency working point of the motor based on MPC rolling optimization on-line optimizing under the condition of meeting the total driving force requirement. Under different working conditions, the front axle motor and the two rear wheel hub motors are enabled to work in a high-efficiency area as much as possible through a reasonable torque distribution scheme, so that the energy loss of the motor is reduced.
When the motor is in the driving mode, taking a map of the PD18 motor as an example, as shown in fig. 2, a corresponding efficiency value can be obtained from the motor efficiency map by calculating the motor rotation speed and the motor torque. Thus, motor efficiency can be described as a function of motor current time speed and torque, but it is difficult to construct a mathematical function to fit the curved surface of the motor efficiency map. In the invention, at each instant, the rotation speed is assumed to be constant, as shown by a dotted line in fig. 2, the motor efficiency can be written into a function of the torque, so that the motor efficiency can be represented, the energy consumption of the motor can be solved and optimized on line later, and a solving flow chart is shown in fig. 4. Firstly judging a driving mode of a motor, secondly determining a fitting function according to the current rotating speed range of the motor, and finally solving the optimal efficiency point of the function.
In order to write motor efficiency as a function of torque, motor Map data is fitted using a 6 th order polynomial in the present invention. The sixth order polynomial may be written as:
（13）
wherein, the liquid crystal display device comprises a liquid crystal display device,for the fitted motor efficiency, +.>For fitting coefficients +.>Is the motor torque. The motor efficiency fit curve is shown in fig. 3.
When the motors are in a driving mode, the driving torque of the three motors is reasonably distributed by taking the highest total driving efficiency of the power system as a target, and the objective function is as follows:
（14）。
when the motor is in a braking energy recovery mode, on the premise of meeting the braking stability requirement, the braking energy is recovered as much as possible, and the objective function is as follows:
（15）。
the upper and lower limits of the output driving torque of the three motors are constrained by the load of the motors as follows:
（16）。
the control amount constraint can be obtained:
（17）。
the objective function is obtained as follows:
（18）。
and step four, considering the wheel locking condition possibly caused by the change of the front and rear axle load of the vehicle under the acceleration and deceleration dynamic working condition, designing the controller constraint, and limiting the front and rear axle output braking force under the deceleration condition based on ECE regulation and I curve braking strategy.
Because the vehicle can generate backward movement of axle load during acceleration, the vertical load of the rear axle is increased, and the usable road surface of the rear wheel is attachedThe force is increased, so that the front axle driving torque is not larger than the rear axle driving torque when the front and rear axle driving torque is distributed, the controller constraint is designedThe method comprises the following steps:
（19）。
the front axle single motor provides power for the left wheel and the right wheel of the front axle, and the control quantity of the front axle is restrained to output driving force or braking force simultaneously, namely:
（20）。
the brake force distribution of a motor vehicle requires consideration of its energy consumption optimization while ensuring the stability of the vehicle. Studies have shown that if the front axle wheel locks during braking of the vehicle, the vehicle will not be able to turn; if the rear axle wheels lock, the vehicle may slip and roll over, both of which are dangerous.
The expected braking power distribution is that no locking occurs as much as possible, and if the locking occurs, the rear wheel is prevented from locking by torque distribution, so thatIn order to avoid causing the sideslip of the vehicle and threatening the safety of a driver, the controller is constrained as follows:
（21）。
under the deceleration condition, the braking strategy based on the ECE rule and the I curve is shown in fig. 5, the front and rear axle braking force is constrained between an ideal I curve and the lower limit of the ECE rule, and the stability of the braking process is ensured:
（22）
i.e.
（23）
Wherein, the liquid crystal display device comprises a liquid crystal display device,Las the distance from the front axle to the rear axle,is the height of the centroid,Gis the gravitational acceleration.
In summary, the problem with constraint to be solved in the present invention is as follows:
（24）
and optimizing and solving the objective function to obtain the control quantity which is the driving torque of the wheels.
Step five, designing a performance evaluation index function, and testing the performance of the proposed torque distribution control method for realizing the energy consumption optimization of the three-motor four-wheel drive electric automobile; the energy saving of the control method studied by the invention is demonstrated.
Performance index evaluation functions are designed from four aspects of steering stability, motor energy-saving performance, tire slip energy loss and longitudinal vehicle speed tracking, and are shown as follows:
(1) steering stability:
（25）。
energy-saving performance of the motor:
（26）。
tire slip energy loss:
（27）。
longitudinal vehicle speed tracking performance:
（28）。
the effectiveness of the torque distribution control method is verified by the following example simulation experiment:
in order to verify the performance of the torque distribution control method disclosed by the invention, a simulation experiment is designed in a CarSim and MATLAB/Simulink joint simulation environment. The simulation test working condition is set to be a double-lane working condition, the road surface adhesion coefficient is set, the vehicle speed is kept near 60km/h, the sampling time is set to be 0.001s, the time domain is predicted, under the working condition, the static distribution (shown in figure 6), the torque distribution (shown in figure 8) of the four-motor four-drive electric vehicle and the torque distribution control method (shown in figure 7) for optimizing the energy consumption of the three-motor four-drive electric vehicle are respectively subjected to simulation verification, and the energy conservation performance and stability evaluation results under the three schemes are shown in table 2.
Table 2 Performance evaluation table under the working condition of double lane change speed 60km/h
From fig. 6, fig. 7 and fig. 8, and by combining with table 2, it can be seen that, compared with a system without optimization targets and constraints and driven by four motors and four wheels, the torque distribution control method for optimizing energy consumption of a three-motor four-wheel drive electric vehicle provided by the invention has the advantages that on the premise of no loss of operation stability, the efficiency of the whole motor is greatly improved, the wheel slip loss is sufficiently restrained, and better stability and economical coordinated control are realized.
In order to further verify the effect of the torque distribution control method in the acceleration and deceleration working conditions, a simulation experiment is designed in a CarSim and MATLAB/Simulink joint simulation environment. Setting the simulation test working condition as a double-lane-shift working condition and the road adhesion coefficientSimulation verification is performed when the vehicle speed is accelerated at 50 km/h-70 km/h and the vehicle speed is decelerated at 70 km/h-50 km/h. By simulation (as shown in fig. 9, 10), andthe performance evaluation results in the table 3 fully prove that the torque distribution control method for optimizing the energy consumption of the three-motor four-drive electric automobile provided by the invention has stronger adaptability under the acceleration and deceleration dynamic working conditions, and realizes the large reduction of the comprehensive energy consumption of the whole automobile.
Table 3 Performance evaluation Table for double lane change speed of 50km/h to 70km/h under acceleration condition and 70km/h to 50km/h under deceleration condition
。/>

Claims (1)

1. A torque distribution control method for realizing energy consumption optimization of a three-motor four-drive electric automobile is characterized by comprising the following steps of: the method comprises the following steps:
s1, a prediction model based on energy consumption optimization MPC controller is obtained by utilizing a dynamic model of tire slip rate and wheel driving torque, wherein state variables of the prediction model consist of four wheel slip rates, and the control quantity is driving wheel torque;
(1) calculating a total torque demand command for the driver based on the desired longitudinal vehicle speed：
（1）
Wherein, the liquid crystal display device comprises a liquid crystal display device,，/>for PI controller parameters, +.>，/>Respectively, tracking reference longitudinal speed and vehicle longitudinal directionA speed;
(2) solving for yaw moment for stabilizing vehicle driving by tracking expected values of vehicle centroid slip angle and yaw rate；
S2, obtaining a prediction model of the energy consumption optimized MPC controller
（2）
Wherein, the liquid crystal display device comprises a liquid crystal display device,for the rotational speed of the tire>Is the wheel slip ratio, wherein->Respectively represent a left front wheel, a right front left rear wheel and a right rear wheel, < >>The effective radius of the tire;
the longitudinal force is positively correlated with the tire slip ratio, and the linearity of the longitudinal force is expressed as:
（3）
in the middle of、/>Respectively the firstiLongitudinal and vertical forces of the individual tires, +.>Is the moment of inertia;
to obtain the slip ratio of the wheelsTorque of wheel->The kinetic model of the relationship is as follows:
（4）
taking into account thatThe above formula is written as:
（5）；
(2) and (3) designing a controller: the state variable of the prediction model consists of four wheel slip rates, the control quantity is the driving wheel torque, and the prediction model is as follows:
（6）
wherein the method comprises the steps of，/>The state vector of the system is defined as:control amount->Torque is output for four drive wheels:wherein->Output driving torque for front axle motor, +.>The distribution coefficient of the driving torque from the front axle motor to the wheels on the left side and the right side is used for distributing the driving torque from the front axle motor to the wheels on the left side and the right side;
the prediction model is discretized according to Euler equation, and is setFor sampling time, the discrete prediction model is obtained as follows:
（7）
wherein the method comprises the steps of，/>；
Distributing the total driving torque to each wheel to enable each wheel to rotateMinimum, satisfy total driving force +.>The method comprises the steps of carrying out a first treatment on the surface of the The difference between the driving forces on the left and right sides satisfies the required yaw moment +.>Driving force of each wheel +.>And total driving torque->And (b)The relationship of (2) is as follows:
（8）；
s3, designing 4 cost functions, wherein the cost functions are as follows:
first objective function:
（9）
wherein, the liquid crystal display device comprises a liquid crystal display device,for left and right wheel track->，/>Is a weight coefficient;
second objective function:
（10）
minimizing tire slip power loss, the designed objective function is as follows:
（11）；
third objective function:
（12）
wherein the method comprises the steps of，/>Boundary constraint value of longitudinal slip +_>、Is a weight factor;
fourth objective function:
and (3) writing the motor efficiency as a function of torque, fitting motor Map data by using a sixth-order polynomial, and writing the sixth-order polynomial into:
（13）
wherein, the liquid crystal display device comprises a liquid crystal display device,for the fitted motor efficiency, +.>In order to fit the coefficients of the coefficients,is motor torque;
the objective function when the motor is in drive mode is:
（14）；
the objective function when the motor is in the braking energy recovery mode is:
（15）；
the upper and lower limits of the output driving torque of the three motors are constrained by the load of the motors as follows:
（16）
the control amount constraint can be obtained:
（17）
the objective function is obtained as follows:
（18）；
s4, when the driving torque of the front shaft and the rear shaft is distributed, the driving torque of the front shaft is not larger than the driving torque of the rear shaft, and the controller is designed to restrictThe method comprises the following steps:
（19）
the front axle single motor provides power for the left wheel and the right wheel of the front axle, and the control quantity of the front axle is restrained to output driving force or braking force simultaneously, namely:
（20）；
preventing rear wheels from locking through torque distributionIn order to avoid causing the sideslip of the vehicle and threatening the safety of a driver, the controller is constrained as follows:
（21）
the braking force of the front axle and the rear axle is restrained between an ideal I curve and the lower limit of ECE regulations, so that the stability of the braking process is ensured:
（22）
i.e.
（23）
Wherein, the liquid crystal display device comprises a liquid crystal display device,Las the distance from the front axle to the rear axle,is the height of the centroid,Gis the acceleration of gravity;
the solved band constraint problem is as follows:
（24）
optimizing and solving the objective function to obtain a control quantity which is the driving torque of the wheels;
s5, designing performance index evaluation functions from four aspects of steering stability, motor energy-saving performance, tire slip energy loss and longitudinal vehicle speed tracking;
(1) steering stability:
（25）
(2) energy-saving performance of the motor:
（26）
(3) tire slip energy loss:
（27）
(4) longitudinal vehicle speed tracking performance:
（28）。
CN202310543478.8A 2023-05-15 2023-05-15 Torque distribution control method for realizing energy consumption optimization of three-motor four-drive electric automobile Pending CN116512934A (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117141615A (en) * 2023-10-27 2023-12-01 天津所托瑞安汽车科技有限公司 Distributed power car train
CN117445698A (en) * 2023-12-13 2024-01-26 广西大学 Electric automobile torque distribution layered control system and method driven by hub motor

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117141615A (en) * 2023-10-27 2023-12-01 天津所托瑞安汽车科技有限公司 Distributed power car train
CN117141615B (en) * 2023-10-27 2024-02-13 天津所托瑞安汽车科技有限公司 Distributed power car train
CN117445698A (en) * 2023-12-13 2024-01-26 广西大学 Electric automobile torque distribution layered control system and method driven by hub motor
CN117445698B (en) * 2023-12-13 2024-04-23 广西大学 Layered control method for torque distribution of electric automobile driven by hub motor

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