CN110481343B - Combined second-order sliding mode control method for moment compensation of four-wheel hub motor-driven automobile - Google Patents
Combined second-order sliding mode control method for moment compensation of four-wheel hub motor-driven automobile Download PDFInfo
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- CN110481343B CN110481343B CN201910814242.7A CN201910814242A CN110481343B CN 110481343 B CN110481343 B CN 110481343B CN 201910814242 A CN201910814242 A CN 201910814242A CN 110481343 B CN110481343 B CN 110481343B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
- B60L15/00—Methods, circuits, or devices for controlling the traction-motor speed of electrically-propelled vehicles
- B60L15/20—Methods, circuits, or devices for controlling the traction-motor speed of electrically-propelled vehicles for control of the vehicle or its driving motor to achieve a desired performance, e.g. speed, torque, programmed variation of speed
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
- B60L2220/00—Electrical machine types; Structures or applications thereof
- B60L2220/40—Electrical machine applications
- B60L2220/44—Wheel Hub motors, i.e. integrated in the wheel hub
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
- B60L2240/00—Control parameters of input or output; Target parameters
- B60L2240/10—Vehicle control parameters
- B60L2240/12—Speed
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
- B60L2240/00—Control parameters of input or output; Target parameters
- B60L2240/10—Vehicle control parameters
- B60L2240/14—Acceleration
- B60L2240/16—Acceleration longitudinal
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
- B60L2240/00—Control parameters of input or output; Target parameters
- B60L2240/10—Vehicle control parameters
- B60L2240/24—Steering angle
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
- B60L2240/00—Control parameters of input or output; Target parameters
- B60L2240/40—Drive Train control parameters
- B60L2240/42—Drive Train control parameters related to electric machines
- B60L2240/423—Torque
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
- B60L2240/00—Control parameters of input or output; Target parameters
- B60L2240/40—Drive Train control parameters
- B60L2240/48—Drive Train control parameters related to transmissions
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
- B60L2250/00—Driver interactions
- B60L2250/26—Driver interactions by pedal actuation
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/60—Other road transportation technologies with climate change mitigation effect
- Y02T10/72—Electric energy management in electromobility
Abstract
The invention discloses a combined second-order sliding mode control method for moment compensation of a four-wheel hub motor-driven automobile, which comprises the following steps of: step 1: acquiring an ideal yaw rate of the vehicle by combining a two-degree-of-freedom model of the vehicle through basic parameters of the overall dimension of the vehicle and the mass of the whole vehicle, vehicle attitude data and road surface state data, wherein the ideal yaw rate of the vehicle is used as a real-time yaw rate following control target; step 2: acquiring an initial control torque of a four-wheel hub motor through driving intention information and current vehicle speed information; and step 3: the method comprises the steps of designing a sliding mode control model taking the vehicle yaw velocity and the vehicle mass center side slip angle as control variables in real time, applying an additional yaw moment to the vehicle instability state through the sliding mode control model, and compensating the additional yaw moment on the initial control moment of the four-wheel hub motor. The invention can compensate the four-wheel-drive yaw moment of the hub, thereby more effectively improving the operation stability of the vehicle and increasing the steering sensitivity of the vehicle.
Description
Technical Field
The invention relates to the technical field of pure electric vehicle control, in particular to a combined second-order sliding mode control method for torque compensation of a four-wheel hub motor-driven vehicle.
Background
The hub motor technology and application change the traditional automobile transmission system through subversive innovation, are widely paid attention to in the new energy automobile industry in a prospective mode, are regarded as the main development trend of the new energy automobile driving technology in the future, have huge industrialization development prospects, and are integrated into a hub by adopting distributed driving compared with a traditional centralized driving internal combustion engine or motor, and driving, transmission and braking devices are integrated into the hub, so that transmission parts such as a clutch, a transmission shaft, a differential mechanism, a transfer case and the like are omitted. The hub motor drives the driving actuator of the vehicle, namely the hub motor is arranged in the independent wheel, and the control freedom degree and the accuracy are greatly improved.
The torque vector control mainly aims to improve the vehicle control performance, increase the steering response speed, reduce the instability of steering, improve the over-bending speed and the like. The traditional centralized driving internal combustion engine or electric motor car needs to realize torque vector control by means of a torque vector distribution differential, and has a complex structure and low degree of freedom. Compared with the traditional mechanical transmission automobile, the hub four-wheel-drive pure electric automobile can be independently controlled due to the wheel power, and the four-wheel differential torque vector control is more flexible. The four-wheel differential torque vector control method is a core module for controlling the four-wheel drive differential torque vector of the hub, and differential torque yaw moment control is a vehicle active safety control technology, so that the transverse stability of a vehicle is improved, the tendency of over-steering or serious under-steering of an automobile is inhibited, and the control stability under the limit working condition of the vehicle is improved.
The existing wheel hub four-wheel drive pure electric vehicle torque compensation mode generally adopts a PID control algorithm, the PID control is a pure mathematical algorithm, a whole vehicle dynamics model is not considered, and self-adaptive control cannot be realized; although some controls adopt independent first-order sliding mode or independent second-order sliding mode control, in the sliding mode movement, serious buffeting is generated, or the approaching speed of the sliding mode is slow, and the response efficiency of the system is low.
Disclosure of Invention
The invention aims to provide a combined second-order sliding mode control method for moment compensation of a four-wheel hub motor-driven automobile. The invention can compensate the four-wheel-drive yaw moment of the wheel hub, thereby more effectively improving the operation stability of the vehicle and increasing the steering sensitivity of the vehicle.
In order to achieve the aim, the invention provides a combined second-order sliding mode control method for torque compensation of a four-wheel hub motor-driven automobile, which is characterized by comprising the following steps of:
step 1: establishing a vehicle two-degree-of-freedom model through the overall dimension of the vehicle, basic parameters of the mass of the whole vehicle, vehicle attitude data and road surface state data, and acquiring an ideal yaw rate of the vehicle through the vehicle two-degree-of-freedom model, wherein the ideal yaw rate of the vehicle is used as a real-time yaw rate following control target;
step 2: acquiring an initial control torque of a four-wheel hub motor through driving intention information and current vehicle speed information;
and step 3: the method comprises the steps of designing a sliding mode control model taking the vehicle yaw velocity and the vehicle mass center side slip angle as control variables in real time, applying an additional yaw moment to the vehicle instability state through the sliding mode control model, and compensating the additional yaw moment on the initial control moment of the four-wheel hub motor.
Compared with the prior art, the invention has the advantages that:
in the existing scheme, the number of independent PID control, first-order sliding mode control and second-order sliding mode control is more, the invention adopts second-order sliding mode + self-adaptive control + PID control + exponential and hyperbolic tangent segment approach law design + yaw angular velocity and compensation moment first-order inertia filtering, and various control methods and means are combined for use. The traditional PID control only has mathematical model control and does not accord with the whole vehicle dynamics operation rule, so the control effect is poor; the first-order sliding mode control has better effect than PID control, but the first-order sliding mode control can generate severe buffeting; although the problem of buffeting is relieved to a certain extent by considering the first derivative of the slip form surface of the system response change rate, the second-order slip form control has no solution means for determining the upper and lower boundaries of the additional compensation moment change rate integral and can only provide an estimated maximum value, so that the approach speed of the slip form is low; the combined second-order sliding mode control method solves the problems of upper and lower bounds of the additional compensation moment change rate integral through an adaptive control strategy, and the index approach rate and hyperbolic tangent approach law are designed in two sections, so that the approach speed of the sliding mode is improved in adaptability, and the buffeting problem is relieved.
Drawings
FIG. 1 is a flow chart of a differential torque moment compensation control frame of a four-wheel drive vehicle driven by a hub motor;
Detailed Description
The invention is described in further detail below with reference to the following figures and specific examples:
the combined second-order sliding mode control method for the torque compensation of the four-wheel hub motor-driven automobile shown in fig. 1 comprises the following steps:
step 1: establishing a vehicle two-degree-of-freedom model through the overall dimension of the vehicle, basic parameters of the mass of the whole vehicle, vehicle attitude data and road surface state data, and acquiring an ideal yaw rate of the vehicle through the vehicle two-degree-of-freedom model, wherein the ideal yaw rate of the vehicle is used as a real-time yaw rate following control target;
step 2: acquiring an initial control torque of a four-wheel hub motor through driving intention information and current vehicle speed information;
and step 3: and designing a sliding mode control model taking the vehicle yaw angular velocity (provided by measurement of a vehicle-mounted gyroscope) and the vehicle mass center side slip angle (provided by measurement of the vehicle-mounted gyroscope) as control variables, applying an additional yaw moment to the vehicle instability state through the sliding mode control model, and compensating the additional yaw moment on the initial control moment of the four-wheel hub motor.
In the technical scheme, the yaw velocity and the centroid slip angle are two most basic reference characteristic quantities which reflect the driving stability of the automobile, the yaw velocity and the centroid slip angle mainly emphasize the basic characteristic quantity of the stability problem of the automobile, reflect the speed of change of a course angle in the driving process of the automobile and determine the steering characteristic of the automobile; the latter emphasizes the basic characteristic quantity of the automobile track keeping problem and reflects the deviation degree of the automobile from the preset track in the steering process. The sliding mode control is based on two control variables of yaw velocity and mass center side slip angle, the ideal yaw velocity of the vehicle is obtained on the basis of a linear two-degree-of-freedom model of the whole vehicle, the ideal yaw velocity is used as a vehicle control following target to obtain a compensation yaw moment, an additional yaw moment is applied to the instability state of the whole vehicle, the compensation yaw moment is compensated on the initial control moment of four wheels of a hub, and the stability of the whole vehicle is further improved.
The slip form surface is defined according to the error and the error change rate of the ideal yaw velocity and the real-time yaw velocity; designing a sliding mode approaching rule approaching sliding mode surface by adopting a hyperbolic tangent function; obtaining an additional yaw moment change rate through a sliding mode surface, a sliding mode surface change rate and the whole vehicle dynamic relation of the whole vehicle rotational inertia; finally, the additional yaw moment to be compensated is obtained by integrating the yaw moment change rate.
In the sliding mode control, due to the existence of the sign function sgn(s), the system has the characteristic of discontinuous switch, buffeting is easy to generate, the boundedness and the parity of the hyperbolic tangent function tanh (x) in the saturation function sat (x) are adopted, the graph of the hyperbolic tangent function tanh (x) is clamped between a horizontal straight line y which is 1 and a horizontal straight line y which is-1, and when the absolute value of x is large, the graph of the hyperbolic tangent function tanh (x) is close to the straight line y which is 1 in a first quadrant and is close to the straight line y which is-1 in a third quadrant. The hyperbolic tangent function tanh (x) replaces the sign function sgn (x) to design an approach law, so that buffeting generated in limited areas on two sides of the system when the system state approaches a switching surface and passes through the switching surface back and forth is inhibited, and smooth continuity of control input near the switching surface is ensured.
In the technical scheme, in the step 1, a two-degree-of-freedom model in a combined second-order sliding mode control strategy is established according to the overall dimension of the vehicle, basic parameters of the mass of the whole vehicle, vehicle attitude data and road surface state data, a complete vehicle kinematic equilibrium equation is established according to the two-degree-of-freedom model, the complete vehicle kinematic equilibrium equation is subjected to Laplace transform solution, and finally the ideal yaw angular velocity of the vehicle is obtained. The real-time yaw rate and the ideal yaw rate have better following performance by combining a second-order sliding mode control strategy;
in the technical scheme, the driving intention information comprises gear information of a gear shifter, accelerator pedal information, brake pedal information and steering wheel angle information, and the initial control torque on the four wheels of the hub is obtained by identifying and controlling an algorithm according to the driving intention of a driver by using the gear information of the gear shifter, the accelerator pedal information, the brake pedal information, the steering wheel angle information and the current vehicle speed information.
In the step 3 of the technical scheme, a sliding mode surface of the sliding mode control model is defined according to the error and the error change rate of the ideal yaw rate of the vehicle and the real-time yaw rate of the vehicle; designing a sliding mode approaching rule approaching sliding mode surface by adopting a hyperbolic tangent function; obtaining an additional yaw moment change rate through the sliding mode surface, the sliding mode surface change rate and the finished automobile rotational inertia; finally, the additional yaw moment is obtained by integrating the change rate of the additional yaw moment. The sliding mode control is a control which simplifies the complex vehicle dynamics control problem into an approach process from a state to an ideal state, and has the advantage that the control is independent of a plurality of parameters and disturbances, and the additional yaw moment change rate is obtained firstly through the control, and then the additional yaw moment is obtained through integration.
In step 3 of the technical scheme, a two-degree-of-freedom model is used for calculating to obtain an ideal yaw rate of the vehicle, a real-time yaw rate of the vehicle is obtained through an on-board gyroscope, and an error between the ideal yaw rate of the vehicle and the real-time yaw rate of the vehicle, an error change rate between the ideal yaw rate of the vehicle and the real-time yaw rate of the vehicle, an error weight between the ideal yaw rate of the vehicle and the real-time yaw rate of the vehicle, and an error change rate weight between the ideal yaw rate of the vehicle and the real-time yaw rate of the vehicle are obtained according to the ideal yaw rate of the vehicle and the real-time yaw rate of the vehicle; then defining a sliding mode surface of the sliding mode control model according to an error between the ideal yaw rate of the vehicle and the real-time yaw rate of the vehicle, an error change rate between the ideal yaw rate of the vehicle and the real-time yaw rate of the vehicle, an error weight between the ideal yaw rate of the vehicle and the real-time yaw rate of the vehicle, and an error change rate weight between the ideal yaw rate of the vehicle and the real-time yaw rate of the vehicle; then, designing a sliding mode sectional approach rule approach sliding mode surface by adopting an exponential approach and a hyperbolic tangent function according to a sliding mode surface, a sliding mode surface change rate, a sliding mode surface sign function and an approach rate parameter of a vehicle yaw velocity of the sliding mode control model; obtaining an additional yaw moment change rate through the sliding mode surface, the sliding mode surface change rate and the finished automobile rotational inertia; finally, the additional yaw moment is obtained by integrating the change rate of the additional yaw moment.
In step 3 of the above technical solution, when obtaining the additional yaw moment change rate, the following adaptive control needs to be performed, and the control process is:
the steady state oscillation amplitude h of the sliding mode motion is a function of approaching the speed of a switching surface, the coefficient q of the sliding mode surface and the sampling period T, the convergence degree of the sliding mode surface s (k) is influenced by the speed of the switching surface and the sampling period T, a designed control system is subjected to stability analysis according to a second stability criterion of the vehicle Lyapunov, a steady state oscillation amplitude h function comprising an exponential approach section of the sliding mode surface s (k) and a hyperbolic tangent approach section is constructed, and when the vehicle starts to move, the motion state of the vehicle is controlled by adopting the exponential approach law of the sliding mode surface s (k) so that the yaw angular velocity of the vehicle reaches the ideal yaw angular velocity of the vehicle; after the switching point of the exponential approximation law control and the hyperbolic tangent function approximation law control of the sliding mode surface s (k) is reached, the hyperbolic tangent function approximation law is used for controlling the motion state of the vehicle so that the yaw angular speed of the vehicle reaches the ideal yaw angular speed of the vehicle; obtaining the upper and lower bounds of the approximation law of the sliding mode compensation moment variation rate integral of the exponential approximation section and the hyperbolic tangent approximation section, and adaptively improving the approximation speed of the sliding mode;
when s (k) converges to 0 and s (k) approaches to zero (when s (k) is equal to 0, sliding is carried out at the zero to ensure smooth sliding), a value corresponding to s (k)/2 is calculated, and a sampling time point corresponding to the value is a switching point of exponential approximation law control and hyperbolic tangent function approximation law control of the sliding mode surface s (k).
The value of the sliding mode surface s (k) is within the range of [ -h, h ] of the exponential approximation law and [ -h, h ] of the hyperbolic tangent function approximation law.
In the technical scheme, the value is reduced, the buffeting of the system can be reduced, but the value is too small, the approaching speed of the system to the switching surface is influenced, and meanwhile, T cannot be very small, so that the ideal value is divided into two sections, when the system starts to move, the value is larger, and an exponential approaching law is adopted; as time increases, the values should decrease gradually, using the hyperbolic tangent function approximation law. The appropriate T is set empirically.
The invention relates to an effective control method for solving the problem of uncertain parameter or time-varying parameter system control, which is an effective control method for solving the problem of uncertain parameter or time-varying parameter system control.
In step 3 of the above technical scheme, in order to obtain a smoother control variable curve, interference and noise are filtered through first-order inertial filtering, that is, random interference signals when the yaw rate and the sliding mode compensation torque initial value change are filtered out, which is helpful for improving the smoothness degree of output signals and filtering singular points;
performing inertial filtering on the real-time yaw velocity and the additional yaw moment respectively by using first-order inertial filtering control twice;
in the inertial filtering aiming at the real-time yaw rate, the input of the inertial filtering is the real-time yaw rate in a sampling period, the real-time yaw rate in the previous sampling period, a preset filtering coefficient, a time constant and the time of each period, and real-time yaw rate interference signals and singular points are respectively filtered according to a first-order inertial filtering algorithm;
in the inertial filtering aiming at the real-time additional yaw moment, the input of the inertial filtering is the additional yaw moment in a sampling period, the additional yaw moment in the previous sampling period, the preset filtering coefficient, the time constant and the time of each period, and the additional yaw moment interference signals and singular points are respectively filtered according to a first-order inertial filtering algorithm.
The results of the two filtering processes are used to obtain a curve formed by the real-time yaw rate or the decided initial value of the compensation moment, and the curve becomes smoother.
In step 3 of the above technical solution, the PID residual moment compensation control method for the additional yaw moment is to set P, I, D values and the difference between the ideal yaw rate and the real-time yaw rate empirically, and obtain the PID residual moment compensation value through the PID control algorithm, P-ratio, I-integration, and D-differential accumulation, and finally calculate.
In the technical scheme, the basic parameters of the overall dimension and the overall mass of the vehicle comprise the height of the mass center of the vehicle, the distance from the front axle of the vehicle to the center of the vehicle, the distance from the rear axle of the vehicle to the center of the vehicle, the track of the front wheel of the vehicle, the track of the rear wheel of the vehicle, the equivalent lateral deflection rigidity of the front axle of the vehicle, the equivalent lateral deflection rigidity of the rear axle of the vehicle, the overall mass of the whole vehicle, the half-load mass of the whole vehicle and the full.
In the technical scheme, the vehicle attitude data comprises vehicle motion information, tire parameter information and vehicle power part state information;
the vehicle motion information comprises longitudinal vehicle speed, lateral vehicle speed and mass center slip angle;
the tire parameter information includes longitudinal tire force and lateral tire force;
the vehicle power part state information comprises wheel rotating speed, longitudinal acceleration, yaw angular speed and lateral acceleration;
the road surface condition data is a road surface adhesion coefficient.
All the control strategies are combined to form complete closed-loop control, and influence factors in torque compensation control are considered by adopting a scientific method. The actual running working condition of the automobile is complex, the requirement of the actual variable working condition is difficult to meet by adopting simple PID and other control methods, the sliding mode control is used as a special variable-structure nonlinear control method, the robustness is strong, the control system is not influenced by the parameter change and external disturbance of a controlled object, and therefore the sliding mode control is very suitable for controlling the yaw stability of the automobile.
In the invention, a vehicle control strategy framework is that a hub four-wheel-drive pure electric vehicle is taken as a controlled object, and four-wheel driving torque decided by a TVC control algorithm of a controller is received for response; the vehicle feeds back vehicle state parameters such as vehicle speed, acceleration, yaw angular velocity and the like to a control algorithm, and the equivalent lateral deflection rigidity and vertical load distribution of front and rear shafts are obtained through parameter and variable calculation; through the design of steering characteristics, setting an ideal value of the yaw rate as a TVC following control target; and finally, carrying out control decision on the ideal yaw rate and an actual value to obtain a required total additional yaw moment, and carrying out moment distribution decision to obtain driving moments on four wheels.
In the invention, after the initial moment analyzed by the driving intention of a driver, the compensation moment obtained by the second-order sliding mode control and the self-adaptive control and the PID residual moment are compensated, the total distributed moment acting on the four wheels is as follows:
Mztot＝Mz(initial value for analysis of Driving intention)+Mz(sliding mode + self-adaptation)+Mz(PID)
Wherein M isztotRepresenting the total compensation torque; mz(initial value for analysis of Driving intention)Representing the initial value of the required torque analyzed by the driving intention; mz(sliding mode + self-adaptation)The additional yaw moment obtained by second-order sliding mode control and self-adaptive control is represented; mz(PID)And the residual compensation torque after the second-order sliding mode and the self-adaptive control are obtained through PID control is shown.
The yaw moment distribution needs to satisfy the constraint: the total torque requirement is unchanged and the torque output capacity of the motor is improved. Under the general condition, the whole control process faces the driving process under the conventional working condition, the control aims at improving the automobile maneuverability during steering, and the control is not the stability control under the limit working condition, so the total torque requirement is required to be ensured to be unchanged in the whole control process, and the speed control process of a driver is not interfered; the motor can only send out fixed maximum torque under a certain rotating speed limited by external characteristics. Therefore, during differential torque distribution, the differential torque distribution needs to be dynamically adjusted according to the working point of the motor.
Details not described in this specification are within the skill of the art that are well known to those skilled in the art.
Claims (9)
1. A combined second-order sliding mode control method for four-wheel hub motor-driven automobile torque compensation is characterized by comprising the following steps:
step 1: establishing a vehicle two-degree-of-freedom model through the overall dimension of the vehicle, basic parameters of the mass of the whole vehicle, vehicle attitude data and road surface state data, and acquiring an ideal yaw rate of the vehicle through the vehicle two-degree-of-freedom model, wherein the ideal yaw rate of the vehicle is used as a real-time yaw rate following control target;
step 2: acquiring an initial control torque of a four-wheel hub motor through driving intention information and current vehicle speed information;
and step 3: designing a sliding mode control model taking the vehicle yaw velocity and the vehicle mass center side slip angle as control variables in real time, applying an additional yaw moment to the vehicle instability state through the sliding mode control model, and compensating the additional yaw moment on the initial control moment of the four-wheel hub motor;
in the step 3, calculating by using a two-degree-of-freedom model to obtain an ideal yaw rate of the vehicle, obtaining a real-time yaw rate of the vehicle by using an on-board gyroscope, obtaining an error between the ideal yaw rate of the vehicle and the real-time yaw rate of the vehicle, an error change rate between the ideal yaw rate of the vehicle and the real-time yaw rate of the vehicle, an error weight between the ideal yaw rate of the vehicle and the real-time yaw rate of the vehicle, and an error change rate weight between the ideal yaw rate of the vehicle and the real-time yaw rate of the vehicle; then defining a sliding mode surface of the sliding mode control model according to an error between the ideal yaw rate of the vehicle and the real-time yaw rate of the vehicle, an error change rate between the ideal yaw rate of the vehicle and the real-time yaw rate of the vehicle, an error weight between the ideal yaw rate of the vehicle and the real-time yaw rate of the vehicle, and an error change rate weight between the ideal yaw rate of the vehicle and the real-time yaw rate of the vehicle; then, according to the sliding mode surface, the sliding mode surface change rate, the sliding mode surface sign function and the approach rate parameter of the vehicle yaw angular velocity in the sliding mode control model, designing a sliding mode approach rule to approach the sliding mode surface by adopting a hyperbolic tangent function; obtaining an additional yaw moment change rate through the sliding mode surface, the sliding mode surface change rate and the finished automobile rotational inertia; finally, the additional yaw moment is obtained by integrating the change rate of the additional yaw moment.
2. The combined second-order sliding-mode control method for moment compensation of the four-wheel hub motor-driven automobile according to claim 1, characterized in that: in the step 1, a two-degree-of-freedom model in a combined second-order sliding mode control strategy is established according to the overall dimension of the vehicle, basic parameters of the mass of the whole vehicle, vehicle attitude data and road surface state data, a complete vehicle kinematic equilibrium equation is established according to the two-degree-of-freedom model, Laplace transformation solving is carried out on the complete vehicle kinematic equilibrium equation, and finally the ideal yaw angular velocity of the vehicle is obtained.
3. The combined second-order sliding-mode control method for moment compensation of the four-wheel hub motor-driven automobile according to claim 1, characterized in that: the driving intention information comprises gear information of a gear shifter, accelerator pedal information, brake pedal information and steering wheel angle information, and the initial control torque on the four wheels of the hub is obtained by identifying and controlling an algorithm according to the driving intention of a driver according to the gear information of the gear shifter, the accelerator pedal information, the brake pedal information, the steering wheel angle information and the current vehicle speed information.
4. The combined second-order sliding-mode control method for moment compensation of the four-wheel hub motor-driven automobile according to claim 1, characterized in that: in the step 3, a sliding mode surface of the sliding mode control model is defined according to the error and the error change rate of the ideal yaw velocity of the vehicle and the real-time yaw velocity of the vehicle; designing a sliding mode approaching rule approaching sliding mode surface by adopting a hyperbolic tangent function; obtaining an additional yaw moment change rate through the sliding mode surface, the sliding mode surface change rate and the finished automobile rotational inertia; finally, the additional yaw moment is obtained by integrating the change rate of the additional yaw moment.
5. The combined second-order sliding-mode control method for moment compensation of the four-wheel hub motor-driven automobile according to claim 1, characterized in that: in step 3, when the additional yaw moment change rate is obtained, the following adaptive control needs to be performed, and the control process is as follows:
the steady state oscillation amplitude h of the sliding mode motion is a function of approaching the speed of a switching surface, the coefficient q of the sliding mode surface and the sampling period T, the convergence degree of the sliding mode surface s (k) is influenced by the speed of the switching surface and the sampling period T, a designed control system is subjected to stability analysis according to a second stability criterion of the vehicle Lyapunov, a steady state oscillation amplitude h function comprising an exponential approach section of the sliding mode surface s (k) and a hyperbolic tangent approach section is constructed, and when the vehicle starts to move, the motion state of the vehicle is controlled by adopting the exponential approach law of the sliding mode surface s (k) so that the yaw angular velocity of the vehicle reaches the ideal yaw angular velocity of the vehicle; after the switching point of the exponential approximation law control and the hyperbolic tangent function approximation law control of the sliding mode surface s (k) is reached, the hyperbolic tangent function approximation law is used for controlling the motion state of the vehicle so that the yaw angular speed of the vehicle reaches the ideal yaw angular speed of the vehicle; obtaining the upper and lower bounds of the approximation law of the sliding mode compensation moment change rate integral of the exponential approximation section and the hyperbolic tangent approximation section;
when s (k) converges to 0 and s (k) approaches to the equilibrium point zero, a value corresponding to s (k)/2 is calculated, and a sampling time point corresponding to the value is a switching point of exponential approximation law control and hyperbolic tangent function approximation law control of the sliding mode surface s (k).
6. The combined second-order sliding-mode control method for moment compensation of the four-wheel hub motor-driven automobile according to claim 1, characterized in that:
in the step 3, first-order inertial filtering control is used twice, and inertial filtering is respectively carried out on the real-time yaw velocity and the additional yaw moment;
in the inertial filtering aiming at the real-time yaw rate, the input of the inertial filtering is the real-time yaw rate in a sampling period, the real-time yaw rate in the previous sampling period, a preset filtering coefficient, a time constant and the time of each period, and real-time yaw rate interference signals and singular points are respectively filtered according to a first-order inertial filtering algorithm;
in the inertial filtering aiming at the real-time additional yaw moment, the input of the inertial filtering is the additional yaw moment in a sampling period, the additional yaw moment in the previous sampling period, the preset filtering coefficient, the time constant and the time of each period, and the additional yaw moment interference signals and singular points are respectively filtered according to a first-order inertial filtering algorithm.
7. The combined second-order sliding-mode control method for moment compensation of the four-wheel hub motor-driven automobile according to claim 1, characterized in that: in the step 3, the method for performing PID residual moment compensation control on the additional yaw moment is to set P, I, D values according to experience, and the difference between the ideal yaw rate and the real-time yaw rate, and finally calculate to obtain a PID residual moment compensation value through a PID control algorithm, P proportion, I integral, D differential accumulation.
8. The combined second-order sliding-mode control method for moment compensation of the four-wheel hub motor-driven automobile according to claim 1, characterized in that: the basic parameters of the overall dimension and the whole vehicle mass of the vehicle comprise the height of the mass center of the vehicle, the distance from the front shaft of the vehicle to the center of the vehicle, the distance from the rear shaft of the vehicle to the center of the vehicle, the track of the front wheel of the vehicle, the track of the rear wheel of the vehicle, the equivalent lateral deflection rigidity of the front shaft of the vehicle, the equivalent lateral deflection rigidity of the rear shaft of the vehicle, the whole vehicle servicing mass, the whole vehicle half-load mass and the whole vehicle full-.
9. The combined second-order sliding-mode control method for moment compensation of the four-wheel hub motor-driven automobile according to claim 1, characterized in that: the vehicle attitude data comprises vehicle motion information, tire parameter information and vehicle power part state information;
the vehicle motion information comprises longitudinal vehicle speed, lateral vehicle speed and mass center slip angle;
the tire parameter information includes longitudinal tire force and lateral tire force;
the vehicle power part state information comprises wheel rotating speed, longitudinal acceleration, yaw angular speed and lateral acceleration;
the road surface condition data is a road surface adhesion coefficient.
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