Steer-by-wire system self-adaptive steering angle tracking strategy based on high-order all-drive theory

Abstract

The invention discloses a steer-by-wire system self-adaptive steering angle tracking strategy based on a high-order all-drive theory, which comprises the following steps of: 1, establishing a kinetic model of a steer-by-wire system according to the steer-by-wire system of a passenger vehicle, and determining a state variable and a control variable; 2, designing an extended disturbance observer according to the kinetic model established in the step 1, and observing the internal and external uncertainty and disturbance of the system, and compensating the uncertainty and disturbance to a controller; 3, converting the steering-by-wire system dynamics model in the step 1 into an all-wheel-drive system model, and designing a self-adaptive high-order all-wheel-drive controller; and 4, verifying the stability of the high-order all-wheel-drive controller designed in the step 3 according to a Lyapunov stability method. According to the method, uncertainty interferences inside and outside the system are considered in the built steer-by-wire system model, the interferences are lumped, the extended disturbance observer is used for observation and compensation to the controller, and the accuracy and robustness of the control system are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of steer-by-wire for passenger vehicles, and in particular to an adaptive corner tracking strategy of a steer-by-wire system based on a high-order all-wheel drive theory. Background Art

[0002] The mainstream steering system of passenger vehicles at this stage is the electric power steering system. Compared with the pure mechanical steering system, this system applies the motor drive torque, which saves the driver's manpower, but there is still mechanical coupling between the steering wheel and the lower steering gear. The wire-controlled steering system replaces the mechanical coupling with wires and electronic control units, and realizes the collection, processing and transmission of angle sensors through electrical signals, truly realizing mechanical decoupling. The wire-controlled steering system provides important support for the implementation of unmanned driving technology and promotes the development of intelligent networking of vehicles. At the same time, due to the elimination of the mechanical connection between the steering wheel and the lower steering gear, the design of automotive parts is saved to a certain extent, the activity space is expanded for passengers, and the driving experience and comfort are improved.

[0003] Aiming at the problem of the angle tracking of the lower steering gear, many researchers at home and abroad have conducted in-depth exploration and research on its tracking control strategy. At present, most researchers use PID controllers, sliding mode controllers or variations of the two, such as adaptive PID controllers, sliding mode predictive controllers, etc. The above methods are based on the improvement and supplement of conventional methods and fail to jump out of the existing control strategies. The present invention adopts a new control method, namely high-order all-wheel drive angle tracking control. This method is an important innovation beyond the existing methods. Based on the high-order all-wheel drive method, we have made a lot of attempts and explorations and achieved ideal control effects, which has potential application space in engineering practice. Summary of the invention

[0004] The purpose of the present invention is to provide an adaptive corner tracking strategy for a wire-controlled steering system based on high-order all-wheel drive theory to solve the corner tracking problem for the lower steering mechanism proposed in the above background technology. Many researchers at home and abroad have conducted in-depth exploration and research on its tracking control strategy. At present, most researchers use PID controllers, sliding mode controllers or their variations, such as adaptive PID controllers, sliding mode predictive controllers, etc. The above methods are based on the improvement and supplement of conventional methods, and fail to escape the existing control strategy problems.

[0005] To achieve the above object, the present invention provides the following technical solution: comprising the following steps:

[0006] Step 1: According to the steer-by-wire system of a passenger vehicle, a dynamic model of the steer-by-wire system is established, and the state variables and control variables are determined;

[0007] Step 2: Based on the dynamic model established in step 1, an extended disturbance observer is designed to observe the internal and external uncertainties and disturbances of the system and compensate them to the controller;

[0008] Step 3: Convert the steer-by-wire system dynamics model of step 1 into an all-wheel drive system model and design an adaptive high-order all-wheel drive controller;

[0009] Step 4: Verify the stability of the high-order all-wheel drive controller designed in step 3 according to the Lyapunov stability method.

[0010] Preferably, according to Newton's law and in combination with the characteristics of the steer-by-wire system, a dynamic model of the steer-by-wire system is established, and the model expression is:

[0011]

[0012] In the formula, J e is the moment of inertia equivalent to the pinion column, B e is the damping coefficient equivalent to the pinion column, Angular displacement, angular velocity and angular acceleration of the pinion column, d(δ p ,δ p ,t) is the observable disturbance inside and outside the system, i m is the motor reduction ratio, T m is the motor torque;

[0013] The equivalent parameter expansion of the above formula is as follows:

[0014]

[0015] J c ,J gear ,J m are the moments of inertia of the steering column, reduction gear and motor, M rack is the mass of the tie rod, i gc ,i mc ,i rc are the reduction ratios from the gearbox to the steering column, from the motor shaft to the steering column, and from the tie rod to the steering column, respectively. c ,B gear ,B m ,B rack They are the damping coefficients of the steering column, reduction gear, motor and tie rod;

[0016] The internal and external disturbances of the system are expanded as:

[0017]

[0018] T f is the system friction, F rack f is the gear applied to the steering tie rod is the system uncertain disturbance;

[0019] Continue to simplify to:

[0020]

[0021] In the formula

[0022]

[0023] Preferably, an extended disturbance observer is designed based on the dynamic model established in step 1 to observe the internal and external uncertainties and disturbances of the system and compensate them to the controller;

[0024] The specific design method of the extended disturbance observer is as follows:

[0025] Don't of Therefore, the extended disturbance observer design differential equation expression is:

[0026]

[0027] In the formula

[0028] k1=3ω

[0029] k2=3ω 2

[0030] K3=ω 3

[0031] ω represents the regulation bandwidth.

[0032] Preferably, the steer-by-wire system dynamics model of step 1 is converted into an all-wheel drive system model, and an adaptive high-order all-wheel drive controller is designed. The specific design method is as follows:

[0033] The high-order all-wheel drive control method proposed by Academician Duan Guangren has the following tracking control formula: (n) =H T (z (0～n-1) , t)θ+L[z (0～n-1) ,t]u+q[z (0～n-1) , t]-(x * ) (n)

[0034] The error z is the tracking error, and the nth-order derivative of z is

[0035] z (n) =x (n) =(x * ) (n)

[0036] The high-order formula for the controller output is then:

[0037] u=L -1 [z (0～n-1) , t][A (0～n-1) z (0～n-1) +q[z (0～n-1) , t]-(x * ) (n) ]

[0038] Substituting into the second-order steer-by-wire system model formula, the order n = 2, the following controller output is obtained:

[0039]

[0040] Preferably, the stability of the high-order all-wheel drive controller designed in step 3 is verified according to the Lyapunov stability method;

[0041] Substituting the controller equation into the system dynamics equation yields:

[0042]

[0043] In order to make

[0044] z (0～1) →0

[0045] prove:

[0046] The closed loop part can be written in the following state space form:

[0047]

[0048] Φ T (A 0～n-1 )P(A 0～n-1 )+P(A 0～n-1 )Φ(A 0～n-1 )≤-Q

[0049] The following preparations need to be made to meet the requirements of controller design:

[0050] For any μ>0,A∈R r×r satisfy:

[0051]

[0052] Among them, μ>0, P>0 has the following relationship

[0053] Φ T (A 0～n-1 )P(A 0～n-1 )+P(A 0～n-1 )Φ(A 0～n-1 )≤-μP(A 0～n-1)Therefore, we can construct the Lyapunov function V = (z (0～1) ) T Pz (0～1)

[0054] Derivation of it

[0055]

[0056] in

[0057]

[0058] When t approaches infinity

[0059]

[0060] In summary, V≤0, proving that the designed high-order all-wheel drive controller is stable.

[0061] Compared with the prior art, the present invention has the following beneficial effects:

[0062] 1. The present invention takes into account the uncertainty interference inside and outside the system in the constructed wire-controlled steering system model, aggregates these interferences, observes them with an extended disturbance observer and compensates them in the controller, thereby improving the accuracy and robustness of the control system;

[0063] 2. The present invention also uses the concept of high-order full-drive control, which does not require the "order reduction" processing of the state space method. It is a method that truly considers "control" itself rather than "state". At the same time, the high-order full-drive system method allows the replacement of all open-loop system characteristics to obtain a linear steady-state closed-loop system, which is difficult to achieve in the first-order system method;

[0064] 3. The high-order all-wheel drive method proposed in the present invention has a high degree of design freedom in design, which can be effectively used to realize the multi-objective comprehensive optimization design of the system, and has good control flexibility. For some nonlinear terms that meet specific conditions, the stability and robustness of the closed-loop linear part can be improved in the design, thereby achieving the effect of simplifying the controller;

[0065] 4. The embodiments of the present invention are well verified in the experimental platform test. Taking the general sinusoidal working condition and double lane-changing working condition as examples, the proportional integral differential controller (PID), sliding mode controller (SMC) and high-order all-wheel drive controller (HOFA) are compared. The test results show that the high-order all-wheel drive control method designed by the present invention has the advantages of fast response speed, small tracking error and strong robustness. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 A schematic diagram of the design process of the high-order all-wheel drive method proposed in an embodiment of the present invention;

[0067] Figure 2 It is a structural schematic diagram of a lower steering machine experimental platform of a steer-by-wire system for a passenger vehicle in an embodiment of the present invention;

[0068] Figure 3 A schematic diagram of system model control of a high-order all-wheel drive method proposed in an embodiment of the present invention;

[0069] Figure 4 This is a comparison chart of the sinusoidal tracking effect obtained from the experimental platform;

[0070] Figure 5 This is a comparison chart of the sinusoidal tracking error obtained from the experimental platform;

[0071] Figure 6 This is a comparison chart of the tracking effect of double lane-shifting conditions obtained from the experimental platform;

[0072] Figure 7 This is a comparison chart of tracking errors in double lane-changing conditions obtained from the experimental platform. DETAILED DESCRIPTION

[0073] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0074] See also Figure 1-7 The embodiment proposes a novel steering angle tracking control method for a steer-by-wire system based on a high-order all-wheel drive system according to the present invention to achieve effective steering angle tracking of the steering machine under the steer-by-wire technology, and verifies and explains it through an experimental platform.

[0075] The implementation example verification mainly includes the following parts:

[0076] 1. Establish a mathematical model of the steer-by-wire system;

[0077] 2. In order to reduce the impact of internal and external disturbances, an extended disturbance observer is designed to compensate the high-order all-wheel drive controller;

[0078] 3. Design a high-level all-wheel drive controller based on the steer-by-wire system model;

[0079] 4. All-wheel drive system stability proof and control gain parameter design;

[0080] 5. Add a low-pass filter to the controller output to eliminate the interference of high-frequency noise;

[0081] 6. Use Lyapunov method to prove the stability of the controller.

[0082] (1) Model establishment

[0083] According to Newton's law and the characteristics of the steer-by-wire system, the dynamic model of the steer-by-wire system is established:

[0084]

[0085] In the formula, J e is the moment of inertia equivalent to the pinion column, B e is the damping coefficient equivalent to the pinion column, Angular displacement, angular velocity and angular acceleration of the pinion column, d(δ p ,δ p ,t) is the observable disturbance inside and outside the system, i m is the motor reduction ratio, T m is the motor torque.

[0086] The equivalent parameter expansion of the above formula is as follows:

[0087]

[0088] J c ,J gear ,J m are the moments of inertia of the steering column, reduction gear and motor, M rack is the mass of the tie rod, i gc ,i mc ,i rc are the reduction ratios from the gearbox to the steering column, from the motor shaft to the steering column, and from the tie rod to the steering column, respectively. c ,B gear ,B m ,B rack They are the damping coefficients of the steering column, reduction gear, motor and tie rod.

[0089] The internal and external disturbances of the system are expanded as:

[0090]

[0091] T f is the system friction, F rack It is the rack applied to the steering tie rod. is the system uncertain disturbance.

[0092] The system model is organized into the following formula:

[0093]

[0094] Continue to simplify to:

[0095]

[0096] In the formula

[0097]

[0098] Let x1 = δ p , Then the system can be transformed into the following state space equation:

[0099]

[0100] (2) Extended disturbance observer design

[0101] In order to reduce the impact of internal and external disturbances on the system, the present invention designs an extended disturbance observer, and the specific design ideas are as follows:

[0102] Let the state estimate be

[0103]

[0104] Don't The estimated value of , so the extended disturbance observer design differential equation expression is:

[0105]

[0106] In the formula

[0107] κ1=3ω

[0108] κ2=3ω 2

[0109] κ3=ω 3

[0110] ω represents the regulation bandwidth.

[0111] (3) Controller design

[0112] By formula It can be seen that the simplified model of the system is as follows:

[0113]

[0114] Based on the above system dynamics model, the design of the high-order all-wheel drive controller is as follows: The high-order all-wheel drive control method proposed by Academician Duan Guangren has the following formula: (n) =H T (x (0～n-1) θ+L[x (0～n-1) ]u+q[x (0～n-1) ]

[0115] In the formula

[0116] HT (x (0～-1) )=0

[0117] L[x (0～n-1) ]=a1

[0118]

[0119] Let the tracking error be

[0120] z=xx *

[0121] Then the nth-order derivative of the error z is

[0122] z (n) =x (n) -(x * ) (n)

[0123] Then, it can be transformed into the following high-order error formula:

[0124] Z (n) =H T (z (0～n-1) , t)θ+L[z (0～n-1) ,t]u+q[z (0～n-1) , t]-(x * ) (n)

[0125] The high-order formula for the controller output is then:

[0126] u=-L -1 [z (0～n-1) , t)[A (0～n-1) z (0～n-1) +q[z (0～n-1) , t]-(x * ) (n) ]

[0127] Substituting into the second-order steer-by-wire system model formula, the order n = 2, the following controller output is obtained:

[0128]

[0129] (4) Parameter design

[0130] In order to make the high-order all-wheel drive controller system stable and reliable, the pole configuration method is used in the parameter selection process. The parameter matrix is ​​designed as follows:

[0131] A 0～1 =-ZF 2 V -1

[0132] To find the controller gain parameters,

[0133]

[0134] Z = [1 1]

[0135]

[0136] By adjusting parameters a and b, the controller can make the control effect of the model respond quickly and be stable.

[0137] (5) Filter design

[0138] In order to eliminate the high-frequency noise output by the controller, the following discrete first-order low-pass filter is designed:

[0139] y[j]=k·u[k]+(1-k)·y[k-1]

[0140] Where u[k] is the input of the filter, y[k-1] is the output at the previous moment, and y[k] is the output at the current moment.

[0141] (6) Stability analysis Substituting the controller equation into the system dynamics equation yields:

[0142]

[0143] In order to make

[0144] z (0～1) →0

[0145] prove:

[0146] The closed loop part can be written in the following state space form:

[0147]

[0148] Φ T (A 0～n-1 )P(A 0～n-1 )+P(A 0～n-1 )Φ(A 0～n-1 )≤-Q

[0149] in

[0150] P(A 0～n-1 )=[P1 P2 … P n ], P i ∈R nr×r

[0151] The following preparations need to be made to meet the requirements of controller design:

[0152] For any μ>0,A∈R r×r satisfy:

[0153]

[0154] Among them, μ>0, P>0 has the following relationship

[0155] Φ T (A 0~n-1 )P(A 0~n-1 )+P(A 0~n-1 )Φ(A 0~n-1 )≤-μP(A 0~n-1 )

[0156] Therefore, we can construct the Lyapunov function V = (z (0~1)T Pz (0~1)

[0157] Derivation of it

[0158]

[0159] in

[0160]

[0161] When t approaches infinity

[0162]

[0163] In summary, It is proved that the designed high-order all-wheel drive controller is stable.

[0164] like Figure 4 , Figure 6 As shown in the figure, there are comparison diagrams of the tracking effects of the sinusoidal working condition and the double lane-changing working condition obtained by the experimental platform. From the result diagrams of the two working conditions, it can be observed that the high-order all-wheel drive method (HOFA) proposed in the present invention has a fast response speed and excellent tracking effect, and can also maintain the best tracking effect when the reference curve is reversed.

[0165] At the same time, if Figure 5 , Figure 7 As shown, it is a comparison diagram of tracking errors under sinusoidal working condition and double lane-shifting working condition. It can be observed that under the same conditions and working condition, the high-order all-wheel drive method proposed in the present invention has the smallest tracking error.

[0166] The results obtained from the examples show that the high-order all-wheel drive method proposed in the present invention has good robustness and fast response performance, and has potential application space in engineering practice and production.

[0167] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0168] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An adaptive corner tracking strategy for a steer-by-wire system based on high-order all-wheel drive theory, characterized by: The following steps are involved: Step 1: According to the steer-by-wire system of a passenger vehicle, a dynamic model of the steer-by-wire system is established, and the state variables and control variables are determined; Step 2: Based on the dynamic model established in step 1, an extended disturbance observer is designed to observe the internal and external uncertainties and disturbances of the system and compensate them to the controller; Step 3: Convert the steer-by-wire system dynamics model of step 1 into an all-wheel drive system model and design an adaptive high-order all-wheel drive controller; Step 4: Verify the stability of the high-order all-wheel drive controller designed in step 3 according to the Lyapunov stability method.

2. The adaptive corner tracking strategy of the steer-by-wire system based on high-order all-wheel drive theory according to claim 1, characterized in that: According to Newton's law and the characteristics of the steer-by-wire system, a dynamic model of the steer-by-wire system is established. The model expression is: In the formula, J e is the moment of inertia equivalent to the pinion column, B e is the damping coefficient equivalent to the pinion column, are the angular displacement, angular velocity and angular acceleration of the pinion column, respectively. is the observable disturbance inside and outside the system, i m is the motor reduction ratio, T m is the motor torque; J c ,J gear ,J m are the moments of inertia of the steering column, reduction gear and motor, M rack is the mass of the tie rod, i gc ,i mc ,i rc are the reduction ratios from the gearbox to the steering column, from the motor shaft to the steering column, and from the tie rod to the steering column, respectively. c ,B gear ,B m ,B rack They are the damping coefficients of the steering column, reduction gear, motor and tie rod; The internal and external disturbances of the system are expanded as: T f is the system friction, F rack f is the rack force applied to the steering tie rod, is the system uncertain disturbance; Continue to simplify to: In the formula 3. The second step of the adaptive corner tracking strategy of the steer-by-wire system based on high-order all-wheel drive theory according to claim 1 is characterized in that: According to the dynamic model established in step 1, an extended disturbance observer is designed to observe the internal and external uncertainties and disturbances of the system and compensate them to the controller; The specific design method of the extended disturbance observer is as follows: They are The estimated value of , so the extended disturbance observer design differential equation expression is: In the formula κ1=3ω k2=3h 2 k3=ω 3 ω represents the regulation bandwidth.

4. The third step of the adaptive corner tracking strategy of the steer-by-wire system based on high-order all-wheel drive theory according to claim 1 is characterized in that: The steer-by-wire system dynamics model in step 1 is converted into an all-wheel drive system model, and an adaptive high-order all-wheel drive controller is designed. The specific design method is as follows: The high-order all-wheel drive control method proposed by Academician Duan Guangren has the following tracking control formula z (n) =H T (z (0～n-1) ,t)θ+L[z (0～n-1) ,t]u+q[z (0～n-1) ,t]-(x * ) (n) The error z is the tracking error, and the nth-order derivative of z is z (n) =x (n) -(x * ) (n) The high-order formula for the controller output is then: u=-L -1 [z (0～n-1) ,t][A (0～n-1) z (0～n-1) +q[z (0～n-1) ,t]-(x * ) (n) ] Substituting into the second-order steer-by-wire system model formula, the order n = 2, the following controller output is obtained:

5. The step 4 of the adaptive corner tracking strategy of the steer-by-wire system based on high-order all-wheel drive theory according to claim 1 is characterized in that: According to the Lyapunov stability method, verify the stability of the high-order all-wheel drive controller designed in step 3; Substituting the controller equation into the system dynamics equation yields: In order to make z (0～1) →0 prove: The closed loop part can be written in the following state space form: F T (A 0～n-1 )P(A 0～n-1 )+P(A 0～n-1 )Φ(A 0～n-1 )≤-Q The following preparations need to be made to meet the requirements of controller design: For any μ>0, A∈R r×r satisfy: Among them, μ>0, P>0 has the following relationship Φ T (And 0～n-1 )P(A 0～n-1 )+P(A 0～n-1 )Φ(A 0～n- 1)≤-μP(A 0～n-1 ) Therefore, we can construct the Lyapunov function V=(z (0～1) ) T Pz (0～1) Derivation of it in When t approaches infinity In summary, V≤0, proving that the designed high-order all-wheel drive controller is stable.

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