CN111717278B - Fault-tolerant control method and system for electric vehicle steering failure - Google Patents

Fault-tolerant control method and system for electric vehicle steering failure Download PDF

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CN111717278B
CN111717278B CN202010608193.4A CN202010608193A CN111717278B CN 111717278 B CN111717278 B CN 111717278B CN 202010608193 A CN202010608193 A CN 202010608193A CN 111717278 B CN111717278 B CN 111717278B
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torque
front wheel
wheel
current
electric automobile
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CN111717278A (en
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王震坡
张雷
王子浩
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Beijing Bitnei Corp ltd
Beijing Institute of Technology BIT
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Beijing Bitnei Corp ltd
Beijing Institute of Technology BIT
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
    • B62D—MOTOR VEHICLES; TRAILERS
    • B62D6/00—Arrangements for automatically controlling steering depending on driving conditions sensed and responded to, e.g. control circuits
    • B62D6/001—Arrangements for automatically controlling steering depending on driving conditions sensed and responded to, e.g. control circuits the torque NOT being among the input parameters
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W50/00—Details of control systems for road vehicle drive control not related to the control of a particular sub-unit, e.g. process diagnostic or vehicle driver interfaces
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
    • B62D—MOTOR VEHICLES; TRAILERS
    • B62D5/00—Power-assisted or power-driven steering
    • B62D5/04—Power-assisted or power-driven steering electrical, e.g. using an electric servo-motor connected to, or forming part of, the steering gear
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W50/00—Details of control systems for road vehicle drive control not related to the control of a particular sub-unit, e.g. process diagnostic or vehicle driver interfaces
    • B60W2050/0001—Details of the control system
    • B60W2050/0019—Control system elements or transfer functions
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W50/00—Details of control systems for road vehicle drive control not related to the control of a particular sub-unit, e.g. process diagnostic or vehicle driver interfaces
    • B60W2050/0001—Details of the control system
    • B60W2050/0019—Control system elements or transfer functions
    • B60W2050/0028—Mathematical models, e.g. for simulation

Abstract

The invention relates to a fault-tolerant control method and a fault-tolerant control system for electric automobile steering failure, wherein the method comprises the following steps: acquiring a reference track of the electric automobile; determining an expected front wheel rotation angle by adopting an MPC (MPC) trajectory tracking method according to the reference trajectory; acquiring an actual front wheel corner of the electric automobile at the previous moment; determining the current differential moment by adopting a sliding mode front wheel angle tracking method according to the expected front wheel corner and the actual front wheel corner; determining the current torque of each wheel of the electric automobile according to a torque optimal distribution method of the current differential torque based on the tire load rate to obtain a wheel torque set; and controlling the current steering of the electric automobile according to the current torque of each wheel in the wheel torque set. The method of the invention realizes fault-tolerant control by using the execution mechanism with redundant functions, and improves the safety and reliability of vehicle running.

Description

Fault-tolerant control method and system for electric vehicle steering failure
Technical Field
The invention relates to the technical field of automobile steering control, in particular to a fault-tolerant control method and a fault-tolerant control system for steering failure of an electric automobile.
Background
The drive-by-wire four-wheel hub motor driven electric automobile is an ideal carrier of an intelligent internet automobile, the drive-by-wire steering system realizes active steering by controlling the motor, and has the advantages of short response time, high control precision and the like, but meanwhile, due to the introduction of electronic components such as a sensor, a controller, a motor and the like, the reliability of the system is reduced. For an intelligent automobile, when a steer-by-wire system breaks down, the automobile can only be decelerated and stopped, the upper-layer planned track cannot be tracked, and traffic accidents are easily caused under the working conditions of high-speed over-bending and the like. Therefore, fault tolerant control of a wire controlled steering system is of great importance. Most of the existing fault-tolerant control methods of the steer-by-wire system adopt a double-steering motor redundancy mode, and one backup steering motor is added, so that the steering of the original motor can be realized by the other motor when the original motor fails, but the complexity and the manufacturing cost of the system are increased by the method.
The application numbers are: 201511024464.7, title of the invention: in the patent of a steer-by-wire system with a sensor signal fault tolerance function and a control method thereof, the steer-by-wire system with the signal fault tolerance function and the control method thereof are provided, joint fault diagnosis is carried out by collecting signals of a front wheel corner, a yaw angular velocity, a lateral acceleration, a steering motor current and the like in the running process of a vehicle, the fault condition of each sensor is detected, if the sensor has a fault, the fault signal can be estimated and reconstructed on line through other sensor signals, and the fault signal is compensated, so that the reliability of the steer-by-wire system and the running stability and safety of the vehicle are improved. The scheme aims at the local sensor fault of the steering system, and carries out local fault tolerance through an observer or a state estimation redundancy substitution mode, but cannot deal with the fault tolerance control of the unrecoverable faults such as the function loss of the whole steering subsystem caused by the local fault.
The application numbers are: 201810340702.2, title of the invention: the patent of a fault-tolerant control system and a control method thereof of a wire-controlled four-wheel independent steering system provides the fault-tolerant control system and the control method thereof of the wire-controlled four-wheel independent steering system, which can effectively solve the problem of poor reliability of the wire-controlled four-wheel independent steering system by acquiring steering intention information and vehicle state information of a driver in real time, calculating the expected turning angle of each wheel in a four-wheel steering mode, and judging the adopted steering mode including a four-wheel independent steering mode, a transition mode 1, a front wheel steering mode, a transition mode 2 and a rear wheel steering mode by comparing with the actual turning angle of each wheel. The scheme is only suitable for the electric automobile with four-wheel independent steering function, and is not suitable for the front-wheel steering automobile.
The application numbers are: 201110171716.4, title of the invention: the fault diagnosis program in the central controller detects the fault state of the corner motor and the auxiliary motor, judges whether the fault exists, and if the fault does not exist, under the combined action of the corner motor and the auxiliary motor, the accurate control of the corner of the pinion is achieved, and the final driving intention of a driver is realized; if the corner motor fails, the power supply of the corner motor is cut off, the corner motor is shielded to idle, and the auxiliary motor undertakes all steering tasks. The scheme realizes fault-tolerant control by backing up the steering motor, increases the complexity of a space structure of a system in the vehicle, and has higher cost and poor economy.
The application numbers are: 201910057136.9, title of the invention: in the patent of a line-controlled four-wheel active steering electric wheel system and a steering fault-tolerant control method thereof, a steering fault-tolerant control method based on multi-controller switching is provided, a whole vehicle electronic control unit comprises a stability control module and a fault-tolerant control module, the controller switching is carried out according to a signal sent to the whole vehicle electronic control unit by a motor fault detection device, when a front wheel steering motor fails, a stability control strategy is implemented, and when the front wheel steering motor fails, a fault-tolerant control strategy is implemented. The scheme considers the problems of emergency reaction and path tracking of a driver after the failure of the steer-by-wire system occurs, but the method has low robustness under emergency working conditions such as high-speed bending and the like, and is only suitable for the steer-by-wire four-wheel active steering electric wheel system.
In summary, most of the existing fault-tolerant control methods for the steer-by-wire system aim at the problem of steering failure of a manned automobile, and the problem of trajectory tracking after the steering failure of an intelligent automobile is not considered. And most rely on the fault diagnosis module, under the urgent operating mode such as high-speed bending, fault diagnosis and switching control strategy also need certain time, and the real-time is difficult to guarantee.
Disclosure of Invention
The invention aims to provide a fault-tolerant control method and a fault-tolerant control system for electric vehicle steering failure, which utilize an actuating mechanism with a redundancy function to realize fault-tolerant control and improve the safety and reliability of vehicle running.
In order to achieve the purpose, the invention provides the following scheme:
a fault-tolerant control method for electric vehicle steering failure comprises the following steps:
acquiring a reference track of the electric automobile;
determining an expected front wheel rotation angle by adopting an MPC (MPC) trajectory tracking method according to the reference trajectory;
acquiring an actual front wheel corner of the electric automobile at the last moment;
determining the current differential torque by adopting a sliding mode front wheel angle tracking method according to the expected front wheel corner and the actual front wheel corner at the previous moment;
determining the current torque of each wheel of the electric automobile according to the torque optimal distribution method of the current differential torque based on the tire load rate to obtain a wheel torque set; including a current torque for each of the wheels in the set of wheel torques;
and controlling the current steering of the electric automobile according to the current torque of each wheel in the wheel torque set.
Optionally, the determining an expected front wheel turning angle by using an MPC trajectory tracking method according to the reference trajectory specifically includes:
constructing an MPC (multi-media control) track tracking optimization objective function according to the reference track of the electric automobile;
converting the MPC trajectory tracking optimization objective function into a standard quadratic function;
and solving the standard quadratic function by adopting a quadratic programming method to obtain the expected front wheel rotation angle.
Optionally, the determining the current differential torque by using a sliding-mode front wheel angle tracking method according to the expected front wheel turning angle and the actual front wheel turning angle at the previous moment specifically includes:
according to the formula
Figure BDA0002559919810000031
Determining a current differential torque;
wherein M isf' is the current differential torque, beffFor an equivalent damping of the steering actuator,
Figure BDA0002559919810000032
to obtain a first derivative of the desired front wheel angle, s ═ δfd-δf，δfdTo expect the front wheel turning angle, deltafFor actual front wheel turning angle, tauaThe aligning moment of the tire is k is 1/delta, delta is the boundary layer thickness of the sliding mode surface, sat (·) is a saturation function, and epsilon is a relaxation factor.
Optionally, the determining the current torque of each wheel of the electric vehicle according to the torque optimal distribution method based on the tire load rate of the current differential torque to obtain a wheel torque set specifically includes:
acquiring the current required longitudinal force of the electric automobile;
constructing a longitudinal force constraint objective function of the electric automobile based on the maximum output torque of the hub motor of the electric automobile and the road adhesion condition according to the current required longitudinal force and the current differential torque;
and solving the longitudinal force constraint objective function of the electric automobile by adopting an active set method, determining the current torque of each wheel of the electric automobile, and obtaining a wheel torque set.
A fault-tolerant control system for electric vehicle steering failure, comprising:
the reference track acquisition module is used for acquiring a reference track of the electric automobile;
the expected front wheel steering angle determining module is used for determining an expected front wheel steering angle by adopting an MPC (multi-control loop) trajectory tracking method according to the reference trajectory;
the actual front wheel steering angle acquisition module is used for acquiring the actual front wheel steering angle of the electric automobile at the previous moment;
a current differential torque determining module, configured to determine a current differential torque by using a sliding mode front wheel angle tracking method according to the expected front wheel turning angle and the actual front wheel turning angle at the previous time;
a wheel torque set obtaining module, configured to determine a current torque of each wheel of the electric vehicle according to a torque optimal distribution method of the current differential torque based on a tire load rate, so as to obtain a wheel torque set; including a current torque for each of the wheels in the set of wheel torques;
and the control module is used for controlling the current steering of the electric automobile according to the current torque of each wheel in the wheel torque set.
Optionally, the desired front wheel steering angle determining module specifically includes:
the MPC track tracking optimization target function building unit is used for building an MPC track tracking optimization target function according to the reference track of the electric automobile;
the conversion unit is used for converting the MPC trajectory tracking optimization target function into a standard quadratic function;
and the solving unit is used for solving the standard quadratic function by adopting a quadratic programming method to obtain the expected front wheel rotation angle.
Optionally, the current differential torque determination module specifically includes:
a current differential torque determination unit for determining the current differential torque according to a formula
Figure BDA0002559919810000041
Determining a current differential torque;
wherein M isf' is the current differential torque, beffFor an equivalent damping of the steering actuator,
Figure BDA0002559919810000042
to obtain a first derivative of the desired front wheel angle, s ═ δfd-δf，δfdTo expect the front wheel turning angle, deltafFor actual front wheel turning angle, tauaThe aligning moment of the tire is k is 1/delta, delta is the boundary layer thickness of the sliding mode surface, sat (·) is a saturation function, and epsilon is a relaxation factor.
Optionally, the wheel torque set obtaining module specifically includes:
the current demand longitudinal force acquisition unit is used for acquiring the current demand longitudinal force of the electric automobile;
the electric vehicle longitudinal force constraint objective function construction unit is used for constructing an electric vehicle longitudinal force constraint objective function based on the maximum output torque of the electric vehicle hub motor and the road adhesion condition according to the current required longitudinal force and the current differential torque;
and the wheel torque set obtaining unit is used for solving the longitudinal force constraint objective function of the electric automobile by adopting an active set method, determining the current torque of each wheel of the electric automobile and obtaining a wheel torque set.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
the invention provides a fault-tolerant control method and a fault-tolerant control system for electric vehicle steering failure, wherein when a steering system works normally, an expected front wheel turning angle is determined by adopting an MPC (multi-control computer) trajectory tracking method according to a reference trajectory; when a steering system fails, determining the current differential torque by adopting a sliding mode front wheel angle tracking method according to an expected front wheel corner and an actual front wheel corner, and determining the current torque of each wheel of the electric automobile according to the current differential torque based on a tire load rate torque optimal distribution method to obtain a wheel torque set; and controlling the current steering of the electric automobile according to the current torque of each wheel in the wheel torque set so as to ensure the track following capability of the automobile. The method of the invention realizes fault-tolerant control by using the execution mechanism with redundant functions, and improves the safety and reliability of vehicle running.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
Fig. 1 is a flowchart of a fault-tolerant control method for steering failure of an electric vehicle according to an embodiment of the present invention;
FIG. 2 is a three-degree-of-freedom vehicle model diagram provided by an embodiment of the invention;
FIG. 3 is a schematic diagram of a differential steering system according to an embodiment of the present invention;
fig. 4 is a schematic structural diagram of a fault-tolerant control system for electric vehicle steering failure according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention aims to provide a fault-tolerant control method and a fault-tolerant control system for electric vehicle steering failure, which utilize an actuating mechanism with a redundancy function to realize fault-tolerant control and improve the safety and reliability of vehicle running.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
Fig. 1 is a flowchart of a fault-tolerant control method for steering failure of an electric vehicle according to an embodiment of the present invention, and as shown in fig. 1, the fault-tolerant control method for steering failure of an electric vehicle according to the present invention includes:
and S101, acquiring a reference track of the electric automobile.
And S102, determining an expected front wheel rotation angle by adopting an MPC (MPC) trajectory tracking method according to the reference trajectory.
S102 specifically comprises the following steps:
and step 201, constructing an MPC trajectory tracking optimization objective function according to the reference trajectory of the electric automobile.
And 202, converting the MPC trajectory tracking optimization objective function into a standard quadratic function.
And 203, solving the standard quadratic function by adopting a quadratic programming method to obtain the expected front wheel rotation angle.
Tracking a reference trajectory (Y) planned by an upper layer using a Model Predictive Control (MPC) trajectory tracking methodref,ψref) The desired front wheel turning angle is obtained, and the specific processes of S101 and S102 are as follows:
the MPC trajectory tracking method can be divided into three basic steps: model prediction, roll optimization, and error feedback correction. Firstly, an MPC prediction model is established, and the vertical acting force of a suspension can be ignored in the modeling process aiming at the problem of track tracking when a drive-by-wire four-wheel hub motor-driven intelligent electric automobile is in steering failure. In order to improve the real-time performance of a control algorithm, a vehicle dynamic model is appropriately simplified, the translation of the electric vehicle in the vertical direction, the pitching around the y-axis and the rolling around the x-axis are ignored, and only the longitudinal motion, the transverse motion and the yawing motion of the electric vehicle are considered. The three-degree-of-freedom vehicle model is built as shown in fig. 2.
The vehicle dynamic balance equation is:
Figure BDA0002559919810000071
wherein m is the mass of the electric automobile, x is the longitudinal displacement,
Figure BDA0002559919810000072
is the first order differential of x and,
Figure BDA0002559919810000073
is the second differential of x, y is the lateral displacement,
Figure BDA0002559919810000074
is the first order differential of y and,
Figure BDA0002559919810000075
is the second differential of y, psi is the electric vehicle yaw angle,
Figure BDA0002559919810000076
is a first order differential of psi and,
Figure BDA0002559919810000077
is a second order differential of psi, FxfLongitudinal forces acting on the front tyre, FxrLongitudinal forces to which the rear tyre is subjected, FyfLateral forces acting on the front wheels, FyrThe side force, delta, acting on the rear wheelsfFor the front wheel corner of an electric vehicle, IzIs the rotational inertia of the electric automobile around the z-axisfIs the distance of the center of mass to the front axis,/rIs the distance of the center of mass to the rear axis, Δ MfAn additional yaw moment generated by the front axle two-wheel moment difference.
When the tire slip angle is small, the tire lateral force can be approximated to a linear expression, and the accuracy of the tire model is ensured by increasing the tire slip angle constraint. The tire longitudinal and lateral forces are expressed as:
Figure BDA0002559919810000078
Figure BDA0002559919810000079
wherein, ClfFor front axle single wheel longitudinal stiffness, ClrFor rear axle single wheel longitudinal stiffness, CcfFor front axle single wheel cornering stiffness, CcrRear axle single wheel cornering stiffness, s'fIs the slip ratio of the front axle single wheel, s'rSlip ratio of single wheel of rear axle, alphafIs the front axle single wheel slip angle, alpharIs the rear axle single wheel slip angle.
The tire slip angle small angle assumption can be approximated as:
Figure BDA00025599198100000710
the tire slip ratio s' is expressed as:
Figure BDA00025599198100000711
where r is the rolling radius of the vehicle, ω is the angular velocity of the vehicle, vxIs the speed of the vehicle.
The additional yaw moment can be expressed as:
Figure BDA0002559919810000081
wherein, BfFor front wheel track, Fx1And Fx2Both are longitudinal forces to which the front tire is subjected.
Converting the vehicle coordinate system and the geodetic coordinate system:
Figure BDA0002559919810000082
in summary, the vehicle dynamics model can be simplified as follows:
Figure BDA0002559919810000083
written as the state space expression:
Figure BDA0002559919810000084
selecting
Figure BDA0002559919810000085
The state quantity of the whole vehicle system respectively represents the longitudinal speed, the transverse speed, the yaw rate and the yaw angle under a vehicle coordinate system and the longitudinal displacement and the transverse displacement under a geodetic coordinate system; selecting u as deltafSelecting Y ═ psi, Y as the desired front wheel steering angle for the system virtual control quantity]Representing the actual trajectory of the vehicle for the system output byThe yaw angle and lateral displacement of the vehicle.
The linearized approximation of the nonlinear model (9) using a taylor series expansion and ignoring higher order terms is:
Figure BDA0002559919810000086
the linear error model in incremental form is expressed as
Figure BDA0002559919810000087
Wherein:
Figure BDA0002559919810000088
a forward Euler method is adopted, and a discrete state space expression is obtained by replacing differential with first-order difference quotient:
Figure BDA0002559919810000091
wherein: a (k) ═ I + ta (T), b (k) ═ tb (T), I is the identity matrix, T is the MPC sampling period, and k is the discrete step size.
Order to
Figure BDA0002559919810000092
The system state space expression is:
Figure BDA0002559919810000093
wherein:
Figure BDA0002559919810000094
Figure BDA0002559919810000095
η (k | t) is the system output, which is the output quantity coefficient matrix.
The prediction time domain of the model predictive controller is NpControl time domain as NcAnd has Nc≤NpFrom the state quantity x (k | t) at the present time and the control increment Δ u (k | t) in the control time domain, a predicted time-domain output quantity can be derived as
Figure BDA0002559919810000096
Written in matrix form:
Y(k)＝Ψ(k)x(k)+Θ(k)ΔU(k) (16)
wherein:
Figure BDA0002559919810000101
Figure BDA0002559919810000102
Figure BDA0002559919810000103
Figure BDA0002559919810000104
after the output quantity Y (k) of the whole vehicle system in the prediction time domain is obtained, the control increment delta U (k) of the system at the current moment can be obtained by solving an optimization objective function with constraint.
In order to track the expected track in real time, the control increment delta U (k) is required to be as small as possible by taking the minimum error between the system output and the expected value as an optimization target, considering the mechanical structure limitation of a vehicle steering actuating mechanism and the risk of vehicle runaway caused by overlarge change of a front wheel steering angle. Therefore, an optimized objective function of the MPC, i.e., an MPC trajectory tracking optimized objective function, is defined as:
Figure BDA0002559919810000111
wherein: etaref(t+i|t)＝[ψref(t+i|t),Yref(t+i|t)]TAnd (3) a reference track vector is planned for the upper layer, Q is output tracking precision, and R is a weight matrix of control increment. To prevent the occurrence of a situation where no feasible solution is available, a relaxation factor epsilon (epsilon) is added>0) (ii) a ρ is a weight coefficient of ε.
The above formula is converted to a standard quadratic, i.e. the standard quadratic function is:
Figure BDA0002559919810000112
wherein: delta UtFor controlling the variable increment, UtIn order to control the amount of the liquid,
Figure BDA0002559919810000113
Gt＝[2E(t)TQΘt 0]；E(t)＝ψtx(t|t)-Yref(t)。
in order to satisfy the constraints of mechanical structure and motion conditions, constraint conditions are applied to an optimization objective function and the state of a system part so as to achieve the optimal control effect.
Setting the control increment constraint and the control quantity constraint as follows:
Figure BDA0002559919810000114
the system output constraints are:
ymin≤y≤ymax (20)
to satisfy the approximately linear relationship of tire force to tire slip angle, the tire slip angle is limited to:
-2.5°≤αf≤2.5°,-5°≤αr≤5° (21)
considering the stability of the vehicle during driving, the centroid slip angle and lateral acceleration are limited as follows:
Figure BDA0002559919810000115
solving the optimization problem with the constraint by utilizing Quadratic Programming (QP), and obtaining the optimal control increment sequence in the control time domain as follows:
ΔUt＝[Δu(t),Δu(t+1),…,Δu(t+Nc-1)]T (23)
the optimal control quantity at the current moment is obtained by using the first element in the sequence as follows:
Figure BDA0002559919810000121
the optimum control amount u (t) obtained by using quadratic programming optimization solving equation (18) is used as the desired front wheel steering angle deltafd。
Under the normal driving condition of the intelligent automobile, the steer-by-wire system does not break down, the expected front wheel corner can be directly acted on a steering execution motor to execute the expected front wheel corner, and therefore the track tracking is achieved. And when the vehicle steering system is in failure, determining the current differential torque according to the expected front wheel steering angle by using the sliding mode front wheel steering angle tracking control strategy in S103 and S104.
And S103, acquiring the actual front wheel rotation angle of the electric automobile at the previous moment.
And S104, determining the current differential torque by adopting a sliding mode front wheel angle tracking method according to the expected front wheel corner and the actual front wheel corner at the previous moment.
In particular, according to the formula
Figure BDA0002559919810000122
Determining a current differential torque; wherein M isf' is the current differential torque, beffFor an equivalent damping of the steering actuator,
Figure BDA0002559919810000123
to obtain a first derivative of the desired front wheel angle, s ═ δfd-δf，δfdTo expect the front wheel turning angle, deltafFor actual front wheel turning angle, tauaThe aligning moment of the tire is k is 1/delta, delta is the boundary layer thickness of the sliding mode surface, sat (·) is a saturation function, and epsilon is a relaxation factor.
The current differential torque is determined according to the expected front wheel steering angle by using a sliding mode front wheel steering angle tracking strategy, and the specific processes of S103 and S104 are as follows:
the basic principle of differential steering is shown in FIG. 3, due to the kingpin offset rσThe longitudinal driving force of the left and right wheels of the front axle can generate a moment tau around the main pindirAnd τdifThe differential torque can be generated by controlling the driving torque of the left and the right wheels, and the torque can generate the corner of the front wheel due to the existence of the steering trapezoid.
Differential moment Mf' the moment difference generated by the longitudinal force of the wheels on two sides of the front axle around the respective kingpin can be expressed as:
Mf′＝(Fxfr-Fxfl)rσ (25)
wherein, FxfrAnd FxflAre respectively longitudinal forces r of two wheels at two sides of the front axleσIs the kingpin offset.
The dynamic model of the steering actuating mechanism is
Figure BDA0002559919810000131
Wherein, JeffAnd beffEquivalent moment of inertia and equivalent damping, τ, of the steering actuator, respectivelyaIs the aligning moment of the tire; tau isfIs the steering actuator frictional drag torque. Aligning moment tau of tyre when front wheel side deflection angle is smallaCan be approximately expressed as taua＝l2ClfαfAnd/3, wherein l is the ground contact half width of the tire.
The second derivative of the front wheel angle and the frictional drag torque of the steering actuator are generally small and can be considered as bounded disturbances to be ignored. The simplified model is:
Figure BDA0002559919810000132
obtaining an expected nose wheel steering angle delta for efficient tracking model predictive control solutionfdEstablishing a sliding mode surface switching function as follows:
s＝δfd-δf (28)
differentiating the slip form surface to obtain:
Figure BDA0002559919810000133
by using an exponential approximation law, there are
Figure BDA0002559919810000134
Can be obtained by combining formula (29)
Figure BDA0002559919810000135
The sliding mode control rate is:
Figure BDA0002559919810000136
the control rate is the differential torque required to track the desired front wheel steering angle.
In order to suppress buffeting caused by model uncertainty and external interference, a saturation function sat(s) is adopted to replace a sign function sgn(s), namely:
Figure BDA0002559919810000137
where Δ is the boundary layer thickness of the slip-form face.
S105, determining the current torque of each wheel of the electric automobile according to the torque optimal distribution method of the current differential torque based on the tire load rate to obtain a wheel torque set; the current torque of each of the wheels is included in the set of wheel torques.
S105 specifically comprises the following steps:
step 501, acquiring the currently required longitudinal force of the electric automobile. Specifically, a PID control method is adopted to track the reference vehicle speed v planned by the upper layerrefThe total longitudinal force demand of the four wheels of the vehicle is obtained.
And 502, constructing a longitudinal force constraint objective function of the electric automobile based on the maximum output torque of the hub motor of the electric automobile and the road adhesion condition according to the current required longitudinal force and the current differential torque.
Step 503, solving the electric vehicle longitudinal force constraint objective function by using an active set method, and determining the current torque of each wheel of the electric vehicle to obtain a wheel torque set.
Designing a lower-layer torque optimization distribution controller, wherein the specific process of S105 is as follows:
the lower layer torque optimal distribution controller realizes the required differential torque M obtained by solving the upper layer by optimally distributing the driving torques of four wheelsf' following a required longitudinal driving force F with a vehicle speedx_expThe stability of the vehicle is maintained while the tracking precision of the upper track is ensured. In order to increase the four-wheel tire stability margin as much as possible, the optimization objective function is designed to:
Figure BDA0002559919810000141
wherein, Fxi、FziAnd mui(i ═ 1, 2, 3, 4) are the longitudinal force, vertical load, and road adhesion coefficient at the four wheels, respectively.
The method has the advantages that the requirements of upper-layer differential torque and longitudinal force are met, meanwhile, the limitation of the maximum output torque of a hub motor and the road adhesion condition is considered, and the longitudinal force constraint condition, namely the longitudinal force constraint objective function of the electric vehicle is expressed as follows:
Figure BDA0002559919810000142
wherein, TmaxThe maximum output torque of the hub motor is obtained.
The optimization problem is expressed as L2The norm form is expressed as:
Figure BDA0002559919810000151
wherein u ═ Fx1,Fx2,Fx3,Fx4]T；v＝[Fexp,M′f,0]T；
Figure BDA0002559919810000152
A diagonal weighting matrix for determining a priority of a target control force (moment);
Figure BDA0002559919810000153
is a diagonal weighting matrix, where ciThe weight coefficient is used for adjusting the longitudinal force of the wheel in the optimization objective function; gamma is a weight coefficient.
When the weight coefficient is larger, the pre-determined distance satisfies | | Bu-v | | luminance under the constraint condition2The maximum torque that the in-wheel motor can output is as follows:
Fxi,max＝min(μiFzi,Tmax/r) (37)
thus, the boundary conditions of the control variables can be expressed as:
Figure BDA0002559919810000154
and converting the optimization problem into a convex quadratic programming problem and solving by using an active set method to obtain the driving torque of the four wheels.
And S106, controlling the current steering of the electric automobile according to the current torque of each wheel in the wheel torque set.
The invention also provides a fault-tolerant control system for electric vehicle steering failure, as shown in fig. 4, the fault-tolerant control system of the invention comprises:
the reference track acquiring module 1 is used for acquiring a reference track of the electric automobile.
And the expected front wheel steering angle determining module 2 is used for determining an expected front wheel steering angle by adopting an MPC (MPC) trajectory tracking method according to the reference trajectory.
And the actual front wheel steering angle obtaining module 3 is used for obtaining the actual front wheel steering angle of the electric automobile at the previous moment.
And the current differential torque determining module 4 is used for determining the current differential torque by adopting a sliding mode front wheel angle tracking method according to the expected front wheel corner and the actual front wheel corner.
A wheel torque set obtaining module 5, configured to determine a current torque of each wheel of the electric vehicle according to a torque optimal distribution method of the current differential torque based on a tire load rate, so as to obtain a wheel torque set; the current torque of each of the wheels is included in the set of wheel torques.
And the control module 6 is used for controlling the current steering of the electric automobile according to the current torque of each wheel in the wheel torque set.
Preferably, the desired front wheel steering angle determining module 2 specifically includes:
and the MPC trajectory tracking optimization target function building unit is used for building an MPC trajectory tracking optimization target function according to the reference trajectory of the electric automobile.
And the conversion unit is used for converting the MPC trajectory tracking optimization objective function into a standard quadratic function.
And the solving unit is used for solving the standard quadratic function by adopting a quadratic programming method to obtain the expected front wheel rotation angle.
Preferably, the current differential torque determination module 4 specifically includes:
a current differential torque determination unit for determining the current differential torque according to a formula
Figure BDA0002559919810000161
Determining a current differential torque; wherein M isf' is the current differential torque, beffFor an equivalent damping of the steering actuator,
Figure BDA0002559919810000162
to obtain a first derivative of the desired front wheel angle, s ═ δfd-δf，δfdTo expect the front wheel turning angle, deltafFor actual front wheel turning angle, tauaThe aligning moment of the tire is k is 1/delta, delta is the boundary layer thickness of the sliding mode surface, sat (·) is a saturation function, and epsilon is a relaxation factor.
Preferably, the wheel torque set obtaining module 5 specifically includes:
the current demand longitudinal force acquisition unit is used for acquiring the current demand longitudinal force of the electric automobile;
the electric vehicle longitudinal force constraint objective function construction unit is used for constructing an electric vehicle longitudinal force constraint objective function based on the maximum output torque of the electric vehicle hub motor and the road adhesion condition according to the current required longitudinal force and the current differential torque;
and the wheel torque set obtaining unit is used for solving the longitudinal force constraint objective function of the electric automobile by adopting an active set method, determining the current torque of each wheel of the electric automobile and obtaining a wheel torque set.
The invention provides a fault-tolerant control method and a fault-tolerant control system for steering failure of an electric automobile, which aim at the problems of track tracking and stability control when a steer-by-wire system fails, and do not depend on a fault diagnosis module; when a steering system fails, the sliding mode front wheel steering angle tracking control strategy can generate differential torque through driving torque distribution to realize front wheel steering so as to ensure the track tracking capability of the vehicle. The invention aims at the problem of trajectory tracking after the steering failure of the intelligent automobile based on the functional redundancy of the overdrive system, and achieves the purpose of fault-tolerant control by controlling the torque distribution of the driving system of the automobile, so that the intelligent automobile still keeps the trajectory tracking capability and the stability of the automobile when the steering failure occurs.
The invention has the advantages that:
1. the differential steering fault-tolerant control method applicable to the intelligent automobile after steering failure is provided, the functional redundancy of an overdrive system is fully utilized, and the problem of trajectory tracking of the intelligent automobile after steering failure is considered.
2. The control performance of the steering failure fault-tolerant control method under emergency conditions such as high-speed bending and the like is improved. And the robustness is good.
3. Real-time fault information is provided without depending on fault diagnosis, and time required by fault diagnosis and control strategy switching is reduced. The real-time performance of the control method is improved.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. For the system disclosed by the embodiment, the description is relatively simple because the system corresponds to the method disclosed by the embodiment, and the relevant points can be referred to the method part for description.
The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.

Claims (6)

1. A fault-tolerant control method for electric vehicle steering failure is characterized by comprising the following steps:
acquiring a reference track of the electric automobile;
determining an expected front wheel rotation angle by adopting an MPC (MPC) trajectory tracking method according to the reference trajectory;
acquiring an actual front wheel corner of the electric automobile at the last moment;
determining the current differential torque by adopting a sliding mode front wheel angle tracking method according to the expected front wheel corner and the actual front wheel corner at the previous moment;
determining the current torque of each wheel of the electric automobile according to the torque optimal distribution method of the current differential torque based on the tire load rate to obtain a wheel torque set; including a current torque for each of the wheels in the set of wheel torques;
determining the current torque of each wheel of the electric vehicle according to the torque optimal distribution method of the current differential torque based on the tire load rate to obtain a wheel torque set, wherein the method specifically comprises the following steps:
acquiring the current required longitudinal force of the electric automobile;
constructing a longitudinal force constraint objective function of the electric automobile based on the maximum output torque of the hub motor of the electric automobile and the road adhesion condition according to the current required longitudinal force and the current differential torque;
solving the longitudinal force constraint objective function of the electric automobile by adopting an active set method, determining the current torque of each wheel of the electric automobile, and obtaining a wheel torque set;
controlling the current steering of the electric vehicle according to the current torque of each wheel in the wheel torque set;
when the rotating system works normally, controlling the current steering of the electric automobile according to the expected front wheel steering angle; when a rotating system has a fault, determining the current differential torque by adopting a sliding mode front wheel angle tracking method according to the expected front wheel rotating angle and the actual front wheel rotating angle at the previous moment, determining the current torque of each wheel of the electric automobile according to the current differential torque based on a tire load rate torque optimal distribution method, obtaining a wheel torque set, and controlling the current steering of the electric automobile according to the current torque of each wheel in the wheel torque set.
2. The fault-tolerant control method for the steering failure of the electric vehicle according to claim 1, wherein the determining the expected front wheel turning angle by using an MPC (MPC) trajectory tracking method according to the reference trajectory specifically comprises:
constructing an MPC (multi-media control) track tracking optimization objective function according to the reference track of the electric automobile;
converting the MPC trajectory tracking optimization objective function into a standard quadratic function;
and solving the standard quadratic function by adopting a quadratic programming method to obtain the expected front wheel rotation angle.
3. The fault-tolerant control method for the electric vehicle steering failure according to claim 1, wherein the determining the current differential torque by using a sliding mode front wheel angle tracking method according to the expected front wheel turning angle and the actual front wheel turning angle at the previous moment specifically comprises:
according to the formula
Figure FDA0003409687810000021
Determining a current differential torque;
wherein M isf' is the current differential torque, beffFor an equivalent damping of the steering actuator,
Figure FDA0003409687810000022
to obtain a first derivative of the desired front wheel angle, s ═ δfd-δf，δfdTo expect the front wheel turning angle, deltafFor actual front wheel turning angle, tauaThe aligning moment of the tire is k is 1/delta, delta is the boundary layer thickness of the sliding mode surface, sat (·) is a saturation function, and epsilon is a relaxation factor.
4. A fault-tolerant control system for electric vehicle steering failure is characterized by comprising:
the reference track acquisition module is used for acquiring a reference track of the electric automobile;
the expected front wheel steering angle determining module is used for determining an expected front wheel steering angle by adopting an MPC (multi-control loop) trajectory tracking method according to the reference trajectory;
the actual front wheel steering angle acquisition module is used for acquiring the actual front wheel steering angle of the electric automobile at the previous moment;
a current differential torque determining module, configured to determine a current differential torque by using a sliding mode front wheel angle tracking method according to the expected front wheel turning angle and the actual front wheel turning angle at the previous time;
a wheel torque set obtaining module, configured to determine a current torque of each wheel of the electric vehicle according to a torque optimal distribution method of the current differential torque based on a tire load rate, so as to obtain a wheel torque set; including a current torque for each of the wheels in the set of wheel torques;
the wheel torque set obtaining module specifically includes:
the current demand longitudinal force acquisition unit is used for acquiring the current demand longitudinal force of the electric automobile;
the electric vehicle longitudinal force constraint objective function construction unit is used for constructing an electric vehicle longitudinal force constraint objective function based on the maximum output torque of the electric vehicle hub motor and the road adhesion condition according to the current required longitudinal force and the current differential torque;
the wheel torque set obtaining unit is used for solving the longitudinal force constraint objective function of the electric automobile by adopting an active set method, determining the current torque of each wheel of the electric automobile and obtaining a wheel torque set;
the control module is used for controlling the current steering of the electric automobile according to the current torque of each wheel in the wheel torque set;
when the rotating system works normally, determining the current steering of the electric automobile according to the expected front wheel steering angle determining module; when a rotating system has a fault, determining the current steering of the electric automobile according to the actual front wheel steering angle obtaining module, the current differential torque determining module, the wheel torque set obtaining module and the control module.
5. The fault-tolerant control system for electric vehicle steering failure according to claim 4, wherein the expected front wheel steering angle determining module specifically comprises:
the MPC track tracking optimization target function building unit is used for building an MPC track tracking optimization target function according to the reference track of the electric automobile;
the conversion unit is used for converting the MPC trajectory tracking optimization target function into a standard quadratic function;
and the solving unit is used for solving the standard quadratic function by adopting a quadratic programming method to obtain the expected front wheel rotation angle.
6. The fault-tolerant control system for electric vehicle steering failure according to claim 4, wherein the current differential torque determination module specifically comprises:
a current differential torque determination unit for determining the current differential torque according to a formula
Figure FDA0003409687810000031
Determining a current differential torque;
wherein M isf' is the current differential torque, beffFor an equivalent damping of the steering actuator,
Figure FDA0003409687810000032
to obtain a first derivative of the desired front wheel angle, s ═ δfd-δf，δfdTo expect the front wheel turning angle, deltafFor actual front wheel turning angle, tauaThe aligning moment of the tire is k is 1/delta, delta is the boundary layer thickness of the sliding mode surface, sat (·) is a saturation function, and epsilon is a relaxation factor.
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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN108454623A (en) * 2018-01-22 2018-08-28 大连理工大学 A kind of unmanned electric vehicle Trajectory Tracking Control method of four motorized wheels
CN109733205A (en) * 2018-12-10 2019-05-10 江苏大学 A kind of wheel hub electric car direct yaw moment control method with fault tolerance

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8660754B2 (en) * 2007-08-17 2014-02-25 Sauer-Danfoss Aps Steer by wire control system
KR101571629B1 (en) * 2014-07-01 2015-11-24 경북대학교 산학협력단 Fault tolerant apparatus for an independent controlled steering in a four wheel system

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN108454623A (en) * 2018-01-22 2018-08-28 大连理工大学 A kind of unmanned electric vehicle Trajectory Tracking Control method of four motorized wheels
CN109733205A (en) * 2018-12-10 2019-05-10 江苏大学 A kind of wheel hub electric car direct yaw moment control method with fault tolerance

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
基于自适应MPC的无人驾驶车辆轨迹跟踪控制;梁忠超等;《东北大学学报》;20200628;第835-840页 *

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