CN107102551B - Damping force constraint-based damping adjustable semi-active suspension hybrid model prediction control method - Google Patents

Damping force constraint-based damping adjustable semi-active suspension hybrid model prediction control method Download PDF

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CN107102551B
CN107102551B CN201710437023.2A CN201710437023A CN107102551B CN 107102551 B CN107102551 B CN 107102551B CN 201710437023 A CN201710437023 A CN 201710437023A CN 107102551 B CN107102551 B CN 107102551B
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active suspension
control
damping
time domain
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CN107102551A (en
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吴光强
张亮修
陈洁
王宇
郭炯珉
金杰
鞠丽娟
马畅
窦传威
孙安宁
魏宏
熊云亮
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SAIC Volkswagen Automotive Co Ltd
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Tongji University
SAIC Volkswagen Automotive Co Ltd
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    • G05B13/02Adaptive control systems, i.e. systems automatically adjusting themselves to have a performance which is optimum according to some preassigned criterion electric
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Abstract

The invention discloses a damping force constraint-based damping adjustable semi-active suspension hybrid model predictive control method, which comprises the steps of establishing a semi-active suspension hybrid system model, carrying out finite time domain optimization control on a semi-active suspension hybrid system based on a model predictive control theory, converting the finite time domain optimization control into a mixed integer quadratic programming problem containing a real-valued variable and a binary variable, and realizing hybrid model predictive control on a damping continuously adjustable semi-active suspension. The invention has the advantages that the contradiction between comfort and operation stability is solved; the nonlinear constraint condition existing in the semi-active suspension optimization method is solved; converting the semi-active suspension control problem into an optimization control problem with limited time domain constraint; the problem of rolling time domain optimization with nonlinear constraints is effectively solved.

Description

Damping force constraint-based damping adjustable semi-active suspension hybrid model prediction control method
Technical Field
The invention relates to the technical field of automobile suspension control, in particular to a damping force constraint-based damping adjustable semi-active suspension hybrid model prediction control method.
Background
Suspension systems are important to improve the ride and handling stability of a vehicle. The semi-active suspension system overcomes the technical defects that the rigidity and the damping of a passive suspension are not adjustable, and the cost of the semi-active suspension system is far lower than that of an active suspension, and represents the main direction of the development of an automobile suspension. The damping-adjustable semi-active suspension can independently track a damping force demand signal, the damping force can be continuously adjusted to any point of a damping working area, and the vehicle performance requirements under different road conditions and working conditions can be met. At present, damping-adjustable semi-active suspensions are mainly divided into magnetorheological (or electrorheological) suspensions and electromagnetic valve type suspensions, wherein the electromagnetic valve type damping-adjustable semi-active suspensions have the advantages of simple structure, quick response, reliable performance, easiness in engineering realization and the like.
At present, the logical relationship between the working range of the damping force and the control force demand signal and the relative speed of the suspension is not directly considered in the semi-active suspension control process, and the optimal control damping force is solved and then limited or restrained according to the output force range of the actual shock absorber and the relative speed of the suspension, so that the suspension cannot obtain the optimal control effect. Giorgetti N et al, based on model predictive Control theory, convert a constrained semi-active suspension Control system into a piecewise affine system and solve it by mixed integer quadratic programming, but do not consider the nonlinear boundary constraints of the damper damping forces (Giorgetti N, Bemporad A, Tsengz H E, et al. Hybrid model predictive Control application damping [ J ]. International Journal of Control, 2006, 79(5):391 398).
The patent document (CN 105974821A) proposes a hybrid control method for a semi-active suspension of a vehicle based on a damping multi-mode switching shock absorber, which determines the recovery damping coefficient and the compression damping coefficient of the shock absorber in different damping modes through simulation analysis, and designs a hybrid model predictive controller for the semi-active suspension based on a hybrid logic dynamic modeling method.
The main difficulty in semi-active suspension control is how to deal with the various nonlinear constraints that the damper damping force must satisfy. The invention provides a hybrid model predictive control method for comprehensively balancing comfortableness and operation stability and considering damping force constraint of a semi-active suspension aiming at a solenoid valve type damping continuously adjustable semi-active suspension system, a semi-active suspension hybrid system model is established, limited time domain optimization control of the semi-active suspension hybrid system is carried out based on a model predictive control theory, the limited time domain optimization control is converted into mixed integer quadratic programming comprising a real value variable and a binary value variable, and hybrid model predictive control of the damping continuously adjustable semi-active suspension is realized.
Disclosure of Invention
The invention aims to provide a damping adjustable semi-active suspension hybrid model predictive control method which comprehensively balances comfort and operation stability and is based on damping force constraint.
In order to solve the technical problems, the invention provides a damping force constraint-based damping adjustable semi-active suspension hybrid model predictive control method, which comprises the following steps of establishing a semi-active suspension hybrid system model, carrying out finite time domain optimization control on a semi-active suspension hybrid system based on a model predictive control theory, converting the finite time domain optimization control into a mixed integer quadratic programming containing a real-valued variable and a binary variable, and realizing hybrid model predictive control on a damping continuously adjustable semi-active suspension, wherein the finite time domain optimization control comprises the following steps:
step 1: dynamic modeling of a damping-adjustable semi-active suspension hybrid system;
step 2: optimizing nonlinear constraint of the damping adjustable semi-active suspension;
and step 3: semi-active suspension hybrid model predictive control;
and 4, step 4: and (3) solving the rolling time domain optimization of the semi-active suspension hybrid system.
The dynamic modeling of the damping-adjustable semi-active suspension hybrid system in the step 1 comprises the following steps: a) introducing auxiliary variables, and converting logical and nonlinear constraint conditions into a group of threshold values and logical conditions; b) and establishing a hybrid system model containing system equations and constraint conditions by using a hybrid system description language, and converting the hybrid system model into an MLD model by using a self-contained HYSDEL compiler.
The logical constraint condition refers to a passive constraint condition of the semi-active suspension, namely when the sign of the damping force demand is the same as the relative speed of the suspension, the required control force is equal to the optimal control force.
The nonlinear constraint condition means that the damping force of the shock absorber must meet a certain boundary condition, namely the optimized damping force is located in the force action range of the actual shock absorber.
The semi-active suspension hybrid model predictive control of the step 3 comprises the following steps: a) in the prediction time domain
Figure DEST_PATH_IMAGE001
Keeping the function type and weight function of the objective function unchanged to the firstkThe predicted input and output of the point are independent variables, the first one is establishedkThe discrete target function of the points, and then the linear weighting of the target function of each point is carried out to obtain the target function in the prediction time domain; b) expanding the constraint condition to the whole prediction time domain, namely constraining each prediction point to obtain a state space equation and the constraint condition in the prediction time domain; c) and constructing model predictive control of the semi-active suspension hybrid system based on an objective function and a constraint condition in a prediction time domain, solving the optimization through a rolling time domain at each sampling moment, taking a first element of an optimal control sequence as control input of the current moment, and repeating the optimization process at the next sampling moment.
The rolling time domain optimization solution of the semi-active suspension hybrid system in the step 4 comprises the following steps: a) loosening the integral constraint limit of part or all of the binary variables in the optimized variables to generate a series of quadratic plans corresponding to the original MIQP; b) and solving the series of quadratic programming to obtain a suboptimal solution or a global optimal solution of the MIQP which meets the integer constraint condition.
The invention has the following advantages:
1) the invention solves the contradiction between comfort and operation stability by constructing a multi-objective optimization method;
2) the invention solves the nonlinear constraint condition existing in the optimization problem of the semi-active suspension by a hybrid logic dynamic modeling method;
3) the invention adopts a hybrid model predictive control method to convert the semi-active suspension control problem into an optimization control method with constraint in a limited time domain;
4) the invention converts the optimization problem with nonlinear constraint into mixed integer quadratic programming containing real-valued variables and binary variables, and solves the problem by means of a branch-and-bound algorithm, thereby effectively solving the rolling time domain optimization problem with nonlinear constraint.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:
FIG. 1a is a passive suspension of a model single-wheeled vehicle according to an embodiment of the present invention;
FIG. 1b is a semi-active suspension with adjustable damping shock absorbers for a model single wheel vehicle according to an embodiment of the present invention;
FIG. 2 is a damping characteristic curve obtained from an actual shock absorber characteristic test according to an embodiment of the present invention;
FIG. 3 is a table of main parameters for simulation verification in Matlab \ Simulink environment according to the present embodiment of the present invention;
FIGS. 4-6 show the RMS curves of vibration responses at different speeds under random road conditions;
FIGS. 7-10 illustrate sinusoidal wave raised road surface shapes and corresponding vibration response time history curves;
FIG. 11 is a root mean square table of the system for three different road surface grades in accordance with an embodiment A, B, C of the present invention.
Detailed Description
The invention is described in detail below with reference to the accompanying drawings, taking a model of a semi-active suspension single-wheel vehicle as an example, but it can be implemented in many different ways, as defined and covered by the claims.
The suspension optimization control objective function comprehensively balancing comfort and operation stability at least comprises two parts of contents: a) the vertical vibration acceleration of the vehicle body and the two-norm of the dynamic stroke of the suspension are used as comfort performance indexes; b) the two-norm of the tire dynamic displacement is used as an operation stability performance index.
The invention provides a damping force constraint-based damping adjustable semi-active suspension hybrid model predictive control method, which comprises the following steps of establishing a semi-active suspension hybrid system model, carrying out finite time domain optimization control on a semi-active suspension hybrid system based on a model predictive control theory, converting the finite time domain optimization control into mixed integer quadratic programming containing real-valued variables and binary variables, and realizing hybrid model predictive control on a damping continuously adjustable semi-active suspension, wherein the mixed integer quadratic programming comprises the following real-valued variables and binary variables:
step 1: dynamic modeling of a damping-adjustable semi-active suspension hybrid system;
step 2: optimizing nonlinear constraint of the damping adjustable semi-active suspension;
and step 3: semi-active suspension hybrid model predictive control;
and 4, step 4: and (3) solving the rolling time domain optimization of the semi-active suspension hybrid system.
The dynamic modeling of the damping-adjustable semi-active suspension hybrid system in the step 1 comprises the following steps: a) introducing auxiliary variables, and converting logical and nonlinear constraint conditions into a group of threshold values and logical conditions; b) and establishing a hybrid system model containing system equations and constraint conditions by using a hybrid system description language, and converting the hybrid system model into an MLD model by using a self-contained HYSDEL compiler.
The logical constraint condition refers to a passive constraint condition of the semi-active suspension, namely when the sign of the damping force demand is the same as the relative speed of the suspension, the required control force is equal to the optimal control force.
The nonlinear constraint condition means that the damping force of the shock absorber must meet a certain boundary condition, namely the optimized damping force is located in the force action range of the actual shock absorber.
Step 1: dynamic modeling of a damping-adjustable semi-active suspension single-wheel vehicle:
fig. 1a shows a passive suspension of a model of a single wheel vehicle, and fig. 1b shows a semi-active suspension of a model of a single wheel vehicle equipped with a damper adjustable shock absorber, wherein:
Figure 100002_DEST_PATH_IMAGE002
in order to obtain a sprung mass,
Figure DEST_PATH_IMAGE003
is the unsprung mass of the spring,
Figure 100002_DEST_PATH_IMAGE004
in order to be the spring rate, the spring,
Figure DEST_PATH_IMAGE005
in order to provide a passive suspension damping coefficient,
Figure 100002_DEST_PATH_IMAGE006
in order to be the rigidity of the tire,
Figure DEST_PATH_IMAGE007
Figure 100002_DEST_PATH_IMAGE008
and
Figure DEST_PATH_IMAGE009
respectively the sprung mass, the unsprung mass and the vertical displacement of the road surface. Suspension stiffness in FIG. 1a
Figure 100002_DEST_PATH_IMAGE010
And damping
Figure DEST_PATH_IMAGE011
Is a constant value; the damping force of fig. 1b can be continuously adjustable according to the actual driving road conditions.
For the damping continuously adjustable semi-active suspension, the dynamic equation is
Figure 100002_DEST_PATH_IMAGE012
(1)
Figure DEST_PATH_IMAGE013
(2)
In the formula:
Figure 100002_DEST_PATH_IMAGE014
Figure DEST_PATH_IMAGE015
the vertical acceleration of the sprung and unsprung masses respectively,
Figure 100002_DEST_PATH_IMAGE016
a control damping force is applied to damp the shock absorber.
Selection state variable
Figure DEST_PATH_IMAGE017
Output variable
Figure 100002_DEST_PATH_IMAGE018
Control quantity of
Figure DEST_PATH_IMAGE019
Obtaining a system state equation of
Figure 100002_DEST_PATH_IMAGE020
(3)
Figure DEST_PATH_IMAGE021
(4)
Wherein the content of the first and second substances,
Figure 100002_DEST_PATH_IMAGE022
Figure DEST_PATH_IMAGE023
Figure 100002_DEST_PATH_IMAGE024
Figure DEST_PATH_IMAGE025
Figure 100002_DEST_PATH_IMAGE026
step 2: optimizing nonlinear constraint of the damping adjustable semi-active suspension:
comprehensively considering the requirements of the semi-active suspension on the smoothness and the operation stability of the vehicle, defining performance indexes as follows:
Figure DEST_PATH_IMAGE027
(5)
wherein the content of the first and second substances,
Figure 100002_DEST_PATH_IMAGE028
Figure DEST_PATH_IMAGE029
and
Figure 100002_DEST_PATH_IMAGE030
weighting coefficients of the vertical vibration acceleration of the vehicle body, the dynamic stroke of the suspension and the dynamic displacement of the tire are selected according to the relative importance of the smoothness and the operation stability;
Figure DEST_PATH_IMAGE031
weighting coefficients are input for control.
According to the formulas (3) and (4), the objective function (5) can be expressed as
Figure 100002_DEST_PATH_IMAGE032
(6)
Wherein the content of the first and second substances,
Figure DEST_PATH_IMAGE033
Figure 100002_DEST_PATH_IMAGE034
the required control force of the semi-active suspension is subject to certain constraints, i.e.
Figure DEST_PATH_IMAGE035
(7)
Figure 100002_DEST_PATH_IMAGE036
(8)
(7) The equation gives the passive constraint condition of the semi-active suspension that the required control force is equal to the optimal control force when the damping force demand sign is the same as the relative velocity of the suspension. (8) The formula gives the boundary condition that the damping force of the shock absorber must satisfy, namely the optimized damping force is located in the force action range of the actual shock absorber. Fig. 2 is a damping characteristic curve obtained by a characteristic test of an actual shock absorber, and the characteristic curve of the present embodiment is drawn only under partial current, and the actual current action range of the shock absorber is 0.29-1.6A. The damping force at the maximum current (1.6A) and the minimum current (0.29A) are taken as control quantity boundaries, which are related to the relative speed of the suspension and exhibit strong nonlinearity.
For the purpose of description of optimization, the boundary of the expression (8) is expressed by a set of linear inequalities of the control quantity and the state quantity, that is
Figure DEST_PATH_IMAGE037
(9)
Wherein the content of the first and second substances,
Figure 100002_DEST_PATH_IMAGE038
Figure DEST_PATH_IMAGE039
and
Figure 100002_DEST_PATH_IMAGE040
in order to be a coefficient of fit,
Figure DEST_PATH_IMAGE041
combining equations (6) - (9), the optimal control of the semi-active suspension can be regarded as hybrid system optimal control under the nonlinear constraint condition.
And step 3: semi-active suspension hybrid model predictive control:
1) dynamic modeling of a semi-active suspension hybrid system:
for the nonlinear constraint problem of the semi-active suspension, in this embodiment, a Mixed Logical Dynamic (MLD) modeling method proposed by Bemporad a is adopted, and a system equation and constraint conditions are described under a unified model framework in consideration of logic, dynamics, constraints and the like of the system.
Introducing binary auxiliary variables
Figure 100002_DEST_PATH_IMAGE042
And
Figure DEST_PATH_IMAGE043
the constraint (7) is converted into a set of thresholds and logic conditions, i.e.
Figure 100002_DEST_PATH_IMAGE044
(10)
In the formula: "
Figure DEST_PATH_IMAGE045
"(equivalent) and"
Figure 100002_DEST_PATH_IMAGE046
"(implication) is a logical operator.
Introducing binary auxiliary variables
Figure DEST_PATH_IMAGE047
And
Figure DEST_PATH_IMAGE049
continuous auxiliary variable
Figure 100002_DEST_PATH_IMAGE050
Figure DEST_PATH_IMAGE051
Figure 100002_DEST_PATH_IMAGE052
Figure DEST_PATH_IMAGE053
Figure 100002_DEST_PATH_IMAGE054
Figure DEST_PATH_IMAGE055
Figure 100002_DEST_PATH_IMAGE056
Figure DEST_PATH_IMAGE057
The constraints (8) (9) are converted into a set of thresholds and logic conditions, i.e.
Figure 100002_DEST_PATH_IMAGE058
(11)
Figure DEST_PATH_IMAGE059
(12)
Figure 100002_DEST_PATH_IMAGE060
(13)
Figure DEST_PATH_IMAGE061
(14)
Establishing a Hybrid System model containing System equations (3) (4) and constraints (10) (11) (12) (13) (14) by using Hybrid System Description Language (HYSDEL), and converting the Hybrid System model into an MLD model by using an own HYSDEL compiler, namely converting the Hybrid System model into the MLD model
Figure 100002_DEST_PATH_IMAGE062
(15)
Figure DEST_PATH_IMAGE063
(16)
Wherein the content of the first and second substances,
Figure 100002_DEST_PATH_IMAGE064
Figure DEST_PATH_IMAGE065
Figure DEST_PATH_IMAGE066
Figure DEST_PATH_IMAGE067
Figure 100002_DEST_PATH_IMAGE068
Figure DEST_PATH_IMAGE069
Figure 100002_DEST_PATH_IMAGE070
2) semi-active suspension hybrid system model predictive control
The present embodiment is based on Hybrid Model Predictive Control (HMPC) theory, and researches the finite time domain optimization Control of the semi-active suspension Hybrid system. In the prediction time domain
Figure DEST_PATH_IMAGE071
Keeping the function type and weight function of the objective function (6) unchanged, andkthe predicted input and output of the point are independent variables, the first one is establishedkA discrete objective function of points; then linearly weighting the objective function of each point to obtain the objective function in the prediction time domain, namely
Figure 100002_DEST_PATH_IMAGE072
(17)
Similarly, the two types of (15) and (16) are maintained, and are extended to the whole prediction time domain
Figure DEST_PATH_IMAGE073
I.e. constraining each predicted point, obtaining the state space equation and constraint condition in the prediction time domain
Figure 100002_DEST_PATH_IMAGE074
(18)
Figure DEST_PATH_IMAGE075
(19)
Wherein the content of the first and second substances,
Figure 100002_DEST_PATH_IMAGE076
Figure DEST_PATH_IMAGE077
Figure 100002_DEST_PATH_IMAGE078
Figure DEST_PATH_IMAGE079
Figure 100002_DEST_PATH_IMAGE080
in thattAt the moment of time, the time of day,
Figure DEST_PATH_IMAGE081
for the state values of the MLD system, model predictive control of the semi-active suspension hybrid system is regarded as solving the following optimization problem:
Figure DEST_PATH_IMAGE082
(20)
wherein the variables are optimized
Figure DEST_PATH_IMAGE083
At each sampling instanttSolving the above optimization by rolling time domain, from the optimal control sequence
Figure DEST_PATH_IMAGE084
First element of (1)
Figure DEST_PATH_IMAGE085
As control input for the current time, i.e.
Figure DEST_PATH_IMAGE086
At the next sampling instantt+1, repeating the optimization process. It can be concluded that the optimized variables of the quadratic program (20) include real-valued variables and binary variables, which can be further converted into a Mixed Integer Quadratic Program (MIQP) solution.
The rolling time domain optimization solution of the semi-active suspension hybrid system in the step 4 comprises the following steps: a) loosening the integral constraint limit of part or all of the binary variables in the optimized variables to generate a series of quadratic plans corresponding to the original MIQP; b) and solving the series of quadratic programming to obtain a suboptimal solution or a global optimal solution of the MIQP which meets the integer constraint condition.
And 4, step 4: and (3) solving the rolling time domain optimization of the semi-active suspension hybrid system:
the optimization solution is convenient, and the output vector in the prediction time domain is defined
Figure DEST_PATH_IMAGE087
Controlling the input vector
Figure DEST_PATH_IMAGE088
Weighting matrix
Figure DEST_PATH_IMAGE089
And
Figure DEST_PATH_IMAGE090
namely:
Figure DEST_PATH_IMAGE091
Figure DEST_PATH_IMAGE092
Figure DEST_PATH_IMAGE093
Figure DEST_PATH_IMAGE094
the objective function (17) is written in the form:
Figure DEST_PATH_IMAGE095
(21)
meanwhile, equation of state space (18) is written in the form:
Figure DEST_PATH_IMAGE096
(22)
wherein the content of the first and second substances,
Figure DEST_PATH_IMAGE097
Figure DEST_PATH_IMAGE098
Figure DEST_PATH_IMAGE099
Figure DEST_PATH_IMAGE100
Figure DEST_PATH_IMAGE101
Figure DEST_PATH_IMAGE102
the formula (22) is substituted into the formula of the objective function (21) to obtain
Figure DEST_PATH_IMAGE103
(23)
Order to
Figure DEST_PATH_IMAGE104
Figure DEST_PATH_IMAGE105
Figure DEST_PATH_IMAGE106
Figure DEST_PATH_IMAGE107
The objective function (23) is expressed as
Figure DEST_PATH_IMAGE108
(24)
The constraint (19) is written as follows:
Figure DEST_PATH_IMAGE109
(25)
wherein
Figure DEST_PATH_IMAGE110
Figure DEST_PATH_IMAGE111
Figure DEST_PATH_IMAGE112
Figure DEST_PATH_IMAGE113
Figure DEST_PATH_IMAGE114
Is further written as
Figure DEST_PATH_IMAGE115
(26)
Wherein
Figure DEST_PATH_IMAGE116
Figure DEST_PATH_IMAGE117
Figure DEST_PATH_IMAGE118
To this end, a mixed integer quadratic programming MIQP of the semi-active suspension system is obtained according to an objective function (24) formula and a constraint condition (26) formula, namely
Figure DEST_PATH_IMAGE119
(27)
In the formula:
Figure DEST_PATH_IMAGE120
in order to optimize the vector, the vector is optimized,
Figure DEST_PATH_IMAGE121
i.e. by
Figure DEST_PATH_IMAGE122
Both real and binary variables.
For the problem posed by equation (27), Branch-and-bound (Branch) is based on&Bound) algorithm, first relaxing the optimization variables
Figure 279491DEST_PATH_IMAGE122
Medium two-value variable
Figure DEST_PATH_IMAGE123
Generating a series of quadratic plans corresponding to the original MIQP by limiting part or all of the integer constraints; and then solving the series of quadratic programming to obtain a suboptimal solution or a global optimal solution of the MIQP which meets the integer constraint condition, wherein the solving of the quadratic programming is completed by means of a Matlab optimization tool box.
In this embodiment, simulation verification is performed in a Matlab \ Simulink environment, and main parameters are shown in fig. 3.
Two simulation working conditions are set: 1) inputting working conditions on a random road surface; 2) and inputting the working condition of the road surface with the sine wave protrusions. The control effect is compared with a passive suspension and an LQR control semi-active suspension, wherein the LQR control parameter is selected to be the same as the hybrid model predictive control algorithm of the invention, and the optimal control law is
Figure DEST_PATH_IMAGE124
(28)
In the formula:
Figure DEST_PATH_IMAGE125
the gain is feedback controlled for LQR.
Derived from LQR control algorithms due to nonlinear constraints of semi-active suspensions
Figure DEST_PATH_IMAGE126
Cannot be completely realized, and additional control laws are required
Figure DEST_PATH_IMAGE127
(29)
For the convenience of later simulation comparison, a Passive suspension simulation result is represented by 'Pasive', an LQR algorithm control result is represented by 'LQR', and a hybrid model predictive control algorithm for research is represented by 'HMPC'. Fig. 4 to 10 show simulation effect diagrams of the present embodiment.
Random road input conditions are widely used to test vehicle comfort and handling stability. A, B, C three-level road surfaces are respectively adopted, the vehicle speeds are 40km/h, 60km/h, 80km/h and 100km/h in sequence, and the simulation time is 20 s. Fig. 11 shows the root mean square values of A, B, C systems at three different road surface levels, and it can be seen that the root mean square values of the evaluation indexes (vehicle body vertical acceleration, suspension dynamic stroke and tire dynamic load) of the Passive suspension, the LQR suspension and the HMPC suspension all show an ascending trend from level a to level C, while on the road surface at different levels, the HMPC suspension can effectively reduce the numerical values of the indexes relative to the Passive suspension and the LQR suspension, and improve the comprehensive performance of the suspension. In order to test the vibration response at different vehicle speeds, the root mean square values of the vibration response quantity at different vehicle speeds are shown in fig. 4 to 6, and it can be seen that the root mean square values of various evaluation indexes of the Passive suspension, the LQR suspension and the HMPC suspension, such as the vehicle body vertical acceleration, the suspension dynamic stroke and the tire dynamic load, all show an increasing trend along with the increase of the vehicle speed. Under different vehicle speeds, the LQR suspension and the HMPC suspension can effectively reduce each evaluation index value, and the control effect of the HMPC suspension is better than that of the LQR suspension.
The sine wave protrusion road surface input is used for testing the suspension bounce performance, in order to simulate the suspension performance more clearly, the amplitude and the width of the sine wave protrusion are respectively set to be 0.05m and 6m, the amplitude and the width exceed the actual vehicle wheelbase, the vehicle speed is 30km/h, 60km/h and 90km/h in sequence, and the simulation time is 10 s.
FIGS. 7-10 show sinusoidal wave raised road surface shapes and corresponding vibration response time history curves, wherein the vehicle speed is
Figure DEST_PATH_IMAGE128
And only intercepting the simulation result when 2-5 s is given. As seen from fig. 8, the HMPC suspension can effectively control the vertical acceleration of the vehicle body, and can rapidly attenuate the vibration acceleration of the vehicle body after the wheel passes the sinusoidal bump, as compared to the Passive suspension and the LQR suspension. As can be seen from fig. 9 and 10, the Passive suspension and the LQR semi-active suspension both fluctuate to different degrees at the later stage of the sine wave bulge, while the HMPC suspension can rapidly attenuate the dynamic stroke of the suspension and the dynamic load of the tire at the later stage of the sine wave bulge, and has a better vibration attenuation effect.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (1)

1. A damping force constraint-based damping adjustable semi-active suspension hybrid model prediction control method is characterized by comprising the following steps: establishing a semi-active suspension hybrid system model, performing finite time domain optimization control on the semi-active suspension hybrid system based on a model prediction control theory, converting the finite time domain optimization control into a mixed integer quadratic programming containing a real-valued variable and a binary variable, and realizing hybrid model prediction control on the damping continuously adjustable semi-active suspension, wherein the method comprises the following steps:
step 1: dynamic modeling of a damping-adjustable semi-active suspension single-wheel vehicle:
for the damping continuously adjustable semi-active suspension, the dynamic equation is
Figure 876507DEST_PATH_IMAGE001
In the formula:
Figure DEST_PATH_IMAGE002
Figure 299705DEST_PATH_IMAGE003
the vertical acceleration of the sprung and unsprung masses respectively,
Figure DEST_PATH_IMAGE004
a control damping force applied to the damping vibration absorber;
Figure 328710DEST_PATH_IMAGE005
in order to obtain a sprung mass,
Figure DEST_PATH_IMAGE006
is the unsprung mass of the spring,
Figure 22122DEST_PATH_IMAGE007
in order to be the spring rate, the spring,
Figure DEST_PATH_IMAGE008
in order to provide a passive suspension damping coefficient,
Figure 88691DEST_PATH_IMAGE009
in order to be the rigidity of the tire,
Figure DEST_PATH_IMAGE010
and
Figure 957159DEST_PATH_IMAGE011
the vertical displacement of the sprung mass, the unsprung mass and the road surface respectively;
selection state variable
Figure DEST_PATH_IMAGE012
Output variable
Figure 210810DEST_PATH_IMAGE013
Control quantity of
Figure DEST_PATH_IMAGE014
Obtaining a system state equation of
Figure 924557DEST_PATH_IMAGE015
Wherein the content of the first and second substances,
Figure DEST_PATH_IMAGE016
Figure 857352DEST_PATH_IMAGE017
step 2: optimizing nonlinear constraint of the damping adjustable semi-active suspension;
comprehensively considering the requirements of the semi-active suspension on the smoothness and the operation stability of the vehicle, defining performance indexes as follows:
Figure DEST_PATH_IMAGE018
(5)
wherein the content of the first and second substances,
Figure 834404DEST_PATH_IMAGE019
Figure DEST_PATH_IMAGE020
and
Figure 903248DEST_PATH_IMAGE021
weighting coefficients of the vertical vibration acceleration of the vehicle body, the dynamic stroke of the suspension and the dynamic displacement of the tire are selected according to the relative importance of the smoothness and the operation stability;
Figure DEST_PATH_IMAGE022
inputting a weighting factor for the control;
according to the formulas (3) and (4), the objective function (5) is expressed as
Figure 358369DEST_PATH_IMAGE023
Wherein the content of the first and second substances,
Figure DEST_PATH_IMAGE024
Figure 478159DEST_PATH_IMAGE025
the required control force of the semi-active suspension is subject to certain constraints, i.e.
Figure DEST_PATH_IMAGE026
(7) The formula gives a passive constraint condition of the semi-active suspension, and the formula (8) gives a boundary condition which must be met by the damping force of the shock absorber;
the boundary of the expression (8) is expressed by a set of linear inequalities of the control quantity and the state quantity, i.e.
Figure 157271DEST_PATH_IMAGE027
Wherein the content of the first and second substances,
Figure DEST_PATH_IMAGE028
Figure 759416DEST_PATH_IMAGE029
and
Figure DEST_PATH_IMAGE030
in order to be a coefficient of fit,
Figure 415963DEST_PATH_IMAGE031
combining the formulas (6) to (9), wherein the optimization control of the semi-active suspension is regarded as hybrid system optimization control under the nonlinear constraint condition;
and step 3: semi-active suspension hybrid model predictive control;
dynamic modeling of a semi-active suspension hybrid system:
introducing binary auxiliary variables
Figure DEST_PATH_IMAGE032
And
Figure 777543DEST_PATH_IMAGE033
the constraint (7) is converted into a set of thresholds and logic conditions, i.e.
Figure DEST_PATH_IMAGE034
In the formula: "
Figure 958382DEST_PATH_IMAGE035
"and"
Figure DEST_PATH_IMAGE036
"is a logical operator;
introducing binary auxiliary variables
Figure 936571DEST_PATH_IMAGE037
And
Figure DEST_PATH_IMAGE038
continuous auxiliary variable
Figure 674825DEST_PATH_IMAGE039
Figure DEST_PATH_IMAGE040
The constraints (8) (9) are converted into a set of thresholds and logic conditions, i.e.
Figure 159420DEST_PATH_IMAGE041
(11)
Figure DEST_PATH_IMAGE042
Figure 445914DEST_PATH_IMAGE043
Figure DEST_PATH_IMAGE044
Establishing a hybrid system model containing system equations (3) (4) and constraints (10) (11) (12) (13) (14), and converting the hybrid system model into an MLD model by using an own HYSDEL compiler thereof, namely
Figure 637031DEST_PATH_IMAGE045
Wherein the content of the first and second substances,
Figure DEST_PATH_IMAGE046
Figure 237646DEST_PATH_IMAGE047
2) semi-active suspension hybrid system model predictive control:
in the prediction time domain
Figure DEST_PATH_IMAGE048
Keeping the function type and weight function of the objective function (6) unchanged, andkthe predicted input and output of the point are independent variables, the first one is establishedkA discrete objective function of points; then linearly weighting the objective function of each point to obtain the objective function in the prediction time domain, namely
Figure 842327DEST_PATH_IMAGE049
The two types of (15) and (16) are maintained and are extended to the whole prediction time domain
Figure DEST_PATH_IMAGE050
I.e. constraining each predicted point, obtaining the state space equation and constraint condition in the prediction time domain
Figure 879815DEST_PATH_IMAGE051
Figure DEST_PATH_IMAGE052
Wherein the content of the first and second substances,
Figure 380067DEST_PATH_IMAGE053
in thattAt the moment of time, the time of day,
Figure DEST_PATH_IMAGE054
for the state values of the MLD system, model predictive control of the semi-active suspension hybrid system is regarded as solving the following optimization problem:
Figure 256143DEST_PATH_IMAGE055
wherein the variables are optimized
Figure DEST_PATH_IMAGE056
At each sampling time t, the optimization is solved through a rolling time domain, and an optimal control sequence is used
Figure 774718DEST_PATH_IMAGE057
First element of (1)
Figure DEST_PATH_IMAGE058
The optimized variables of the quadratic programming (20) comprise real-valued variables and binary variables and are further converted into mixed integer quadratic programming MIQP solution;
and 4, step 4: and (3) solving the rolling time domain optimization of the semi-active suspension hybrid system:
defining an output vector in the prediction time domain
Figure 542297DEST_PATH_IMAGE059
Controlling the input vector
Figure DEST_PATH_IMAGE060
Weighting matrix
Figure 61003DEST_PATH_IMAGE061
And
Figure DEST_PATH_IMAGE062
namely:
Figure 6350DEST_PATH_IMAGE063
the objective function (17) is written in the form:
Figure DEST_PATH_IMAGE064
meanwhile, equation of state space (18) is written in the form:
Figure 379431DEST_PATH_IMAGE065
wherein the content of the first and second substances,
Figure 40613DEST_PATH_IMAGE067
the formula (22) is substituted into the formula of the objective function (21) to obtain
Figure DEST_PATH_IMAGE068
Order to
Figure 46615DEST_PATH_IMAGE069
Figure DEST_PATH_IMAGE070
The objective function (23) is expressed as
Figure 248183DEST_PATH_IMAGE071
The constraint (19) is written as follows:
Figure DEST_PATH_IMAGE072
wherein:
Figure 226503DEST_PATH_IMAGE073
Figure DEST_PATH_IMAGE074
is further written as
Figure 922233DEST_PATH_IMAGE075
Wherein:
Figure DEST_PATH_IMAGE076
to this end, a mixed integer quadratic programming MIQP of the semi-active suspension system is obtained according to an objective function (24) formula and a constraint condition (26) formula, namely
Figure 71324DEST_PATH_IMAGE077
In the formula:
Figure DEST_PATH_IMAGE078
in order to optimize the vector, the vector is optimized,
Figure 483107DEST_PATH_IMAGE079
i.e. by
Figure DEST_PATH_IMAGE080
Both real and binary variables.
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