A vehicle height control method based on a permanent magnet synchronous linear motor type active suspension

Abstract

The application discloses a vehicle height control method based on a permanent magnet synchronous linear motor type active suspension, which adopts a permanent magnet synchronous linear motor as an actuator of vehicle height control, and realizes the lifting of a vehicle body through the control of the permanent magnet synchronous linear motor. The method can adjust the vehicle height and attitude for a short time under specific working conditions of the vehicle, greatly improving the safety, maneuverability and passing capacity of the vehicle. The motor type suspension system has the characteristics of fast response and large energy density, can rapidly adjust the attitude of the vehicle body, and controls the smoothness in a reasonable range. The proposed scheme can also be used in similar other fields.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of automobile design, and particularly relates to a control method for height adjustment of an automobile body based on a permanent magnet synchronous linear motor. BACKGROUND

[0002] Automobile electrification is one of the new trends in the development of the automobile industry. Many scholars and companies have researched motor type active suspensions. Some scholars have proposed a rotary actuator automobile electromagnetic suspension system. However, the rotary actuator needs a gearbox to convert rotary motion into linear motion, and the structure is complex. Linear electromagnetic actuators are simple and compact because they do not have intermediate transmission mechanisms, and therefore have attracted attention. However, so far, the research on motor type active suspension systems has focused on vehicle ride comfort and energy recovery, and there is no relevant report on vehicle body posture adjustment, which is one of the important functions of active suspension.

[0003] Currently, vehicle height adjustment generally uses air suspensions and hydraulic suspensions. However, air suspensions need to open and close electromagnetic valves to realize the inflation and deflation of air bags, and have the disadvantages of slow inflation and deflation process and complex structure. Hydraulic suspensions have high sealing requirements for components, need to be installed with supporting devices, have high costs, and consume a large amount of energy. Although the reaction time of the hydraulic system is slightly faster than that of the air bag inflation and deflation, the hydraulic suspension system cannot quickly adjust the vehicle posture, especially in high-speed turning, emergency obstacle avoidance, and obstacle crossing.

[0004] From the current research situation, linear motors can better control ride comfort and energy recovery. Long-time adjustment of the vehicle body posture will increase energy consumption and reduce ride comfort. However, short-time adjustment of the vehicle body posture in specific situations will greatly improve the safety, maneuverability, and passing ability of the automobile. Motor type suspension systems have the characteristics of fast response and high energy density, can quickly adjust the vehicle body posture, and control the ride comfort within a reasonable range.

[0005] Based on the above analysis and consideration, the present application proposes a vehicle height control method based on a permanent magnet synchronous linear motor type active suspension, which can be used for short-time height and posture adjustment of the vehicle in specific working conditions. SUMMARY

[0006] In view of the deficiencies and defects of the current vehicle height control technology, the present application proposes a vehicle body height adjustment control method based on a permanent magnet synchronous linear motor type active suspension.

[0007] The technical scheme adopted by the present application is a vehicle body height adjustment control method based on a permanent magnet synchronous linear motor type active suspension, which specifically comprises the following steps:

[0008] Step 1: establishing a mathematical model of the permanent magnet synchronous linear motor in the d-q coordinate system;

[0009] Step 2, determine the electromagnetic thrust constant of the permanent magnet synchronous linear motor;

[0010] Step 3, carry out finite set model predictive current control on the permanent magnet synchronous linear motor;

[0011] Step 4, establish an active suspension model, and adopt a hierarchical control strategy to control the vehicle body height and the permanent magnet synchronous linear motor.

[0012] The application is also characterized in that,

[0013] The specific process of step 1 is as follows:

[0014] Step 1.1, establish the voltage equation of the permanent magnet synchronous linear motor in the d-q coordinate system:

[0015]

[0016] In formula (1), U d , U q is the voltage vector, R s is the armature resistance, i d , i q is the direct-axis and quadrature-axis current, φ d , φ q is the flux linkage vector, is the magnetic field electric angular velocity, n p is the number of pole pairs, τ is the pole pitch, and v is the equivalent linear speed of the linear motor.

[0017] Step 1.2, establish the flux linkage equation of the permanent magnet synchronous linear motor in the d-q coordinate system:

[0018]

[0019] In formula (2), L d is the direct-axis reactance, L q is the quadrature-axis reactance, and φ f is the permanent magnet flux linkage.

[0020] Step 1.3, establish the electromagnetic thrust equation of the permanent magnet synchronous linear motor in the d-q coordinate system:

[0021]

[0022] By using i d =0 vector control, the electromagnetic thrust equation of the linear motor becomes:

[0023]

[0024] The mechanical equilibrium equation of the permanent magnet synchronous linear motor is expressed as follows:

[0025]

[0026] In equation (5), M is the mass of the linear motor, v is the speed of the linear motor, B is the viscosity coefficient, and F is the velocity of the linear motor. l This represents the load resistance.

[0027] The specific process of step 2 is as follows:

[0028] Based on the required lifting height of the vehicle body, the design parameters of the cylindrical permanent magnet synchronous linear motor were determined. A model of the cylindrical permanent magnet synchronous linear motor was built in Ansoft / Maxwell software for parametric modeling. A current source was selected for excitation, and different primary winding phase current amplitudes were set. The electromagnetic thrust output of the permanent magnet synchronous linear motor at different current amplitudes was calculated, and the electromagnetic thrust constant K was obtained from the calculation. T .

[0029] The specific process of step 3 is as follows:

[0030] Step 3.1: Establish the mathematical model of the three-phase two-level inverter. There are a total of 8 inverter switching combination states. The relationship between the AC phase voltage and the switching function is expressed as follows:

[0031]

[0032] In equation (6), V AN V BN V CN For phase voltage, S a S b S c For the switching state of the three-phase bridge arm, U dc This is the DC bus voltage.

[0033] Step 3.2, construct the value function. Using the minimum tracking error between the reference current and the predicted current as the evaluation criterion, the value function is constructed as follows:

[0034]

[0035] In equation (7), These are the reference values ​​for the direct and quadrature axis currents, i. d (k+1),i q (k+1) are the predicted values ​​of the AC and DC axis currents at the next time step.

[0036] Step 3.3: Establish a prediction model for the permanent magnet synchronous linear motor. Select the d-axis and q-axis currents of the permanent magnet synchronous linear motor as state variables, and discretize them using the forward Euler discretization method to obtain the discrete state current prediction model of the permanent magnet synchronous linear motor.

[0037]

[0038] In formula (8), T s is sampling time.

[0039] The specific process of step 4 is as follows:

[0040] Step 4.1, a mathematical model of the active suspension is established, and the differential motion equation is as follows:

[0041]

[0042] In formula (9), z2 is the sprung mass displacement, z1 is the unsprung mass displacement, m2 is the sprung mass, m1 is the unsprung mass, k2 is the suspension spring stiffness, k1 is the tire stiffness, c is the suspension damping, q is the input caused by the uneven road, F d is the actuator active force. Wherein the active force F d generates the actuator force to lift the vehicle body, and the direction is the same as the direction of the vehicle body lifting;

[0043] Step 4.2, a hierarchical control strategy is used to design the vehicle height controller, the upper controller calculates the required actuator force of the active suspension according to the difference between the sprung mass displacement and the required lifting height of the vehicle body, and the lower controller makes the permanent magnet synchronous linear motor generate electromagnetic thrust to track the actuator force calculated by the upper layer.

[0044] The permanent magnet synchronous linear motor type active suspension has the characteristics of fast response and high energy density, and when the vehicle is in a specific situation for a short time of vehicle body posture adjustment, the vehicle body posture can be quickly adjusted, and the smoothness is controlled in a reasonable range, greatly improving the safety, maneuverability and passing ability of the vehicle. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 is the vehicle height lifting control system structure.

[0046] Figure 2 is the permanent magnet synchronous linear motor block diagram.

[0047] Figure 3 is the inverter circuit schematic diagram.

[0048] Figure 4 is the 1 / 4 vehicle suspension model.

[0049] Figure 5 is the sprung mass displacement of 0.12m lifting.

[0050] Figure 6 is the electromagnetic thrust of 0.12m lifting.

[0051] Figure 7 is the vehicle body acceleration of 0.12m lifting.

[0052] Figure 8 is the sprung mass displacement for a 0.12m drop.

[0053] Figure 9 is the electromagnetic force for a 0.12m drop.

[0054] Figure 10 is the vehicle body acceleration for a 0.12m drop. DETAILED DESCRIPTION

[0055] The present application will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0056] The present application adopts a vehicle height adjustment control method based on a permanent magnet synchronous linear motor type active suspension. When the vehicle is in a specific working condition and the vehicle height or attitude is adjusted for a short time, the expected height of the required lift is calculated according to the expected roll angle of the vehicle. After the permanent magnet synchronous linear motor is input with a three-phase sinusoidal voltage, the traveling wave magnetic field generated by the air gap between the primary and secondary interacts with the excitation magnetic field of the permanent magnet, generating an electromagnetic force as the input of the active suspension to realize the lifting of the vehicle height. The vehicle height controller adopts a hierarchical control strategy, the upper layer adopts a PI controller, and the lower layer adopts a finite set model predictive controller, and the controller principle is as shown in Figure 1 The reference quadrature axis current output by the upper layer PI controller is input to the lower layer finite set model predictive current control, a value function is established to minimize the tracking error between the reference current and the predicted current, a forward Euler discretization method is used to obtain a discrete state current prediction model of the permanent magnet synchronous linear motor, and a three-phase voltage is output to provide alternating current for the permanent magnet synchronous linear motor. The expected active force obtained by converting the reference quadrature axis current of the upper layer through the electromagnetic force constant is used as the reference force, and the three-phase voltage obtained by the lower layer finite set model predictive current is input to the permanent magnet synchronous linear motor to generate a corresponding electromagnetic force acting on the active suspension, thereby realizing the lifting of the vehicle height.

[0057] Based on the above considerations, a vehicle height adjustment control method based on a permanent magnet synchronous linear motor type active suspension is provided, and the control method comprises the following steps:

[0058] Step 1, a mathematical model of the permanent magnet synchronous linear motor in the d-q coordinate system is established:

[0059] Step 1.1, a voltage equation of the permanent magnet synchronous linear motor in the d-q coordinate system is established:

[0060]

[0061] In formula (1), U d , U q is the voltage vector, R s is the armature resistance, i d , i q is the quadrature axis current, and φd , φ q is the flux linkage vector, is the electrical angular velocity of magnetic field, n p is the number of pole pairs, τ is the pole pitch, v is the equivalent linear velocity of the linear motor.

[0062] Step 1.2, the flux linkage equation of the permanent magnet synchronous linear motor in the d-q coordinate system is established:

[0063]

[0064] In formula (2), L d is the direct-axis reactance, L q is the quadrature-axis reactance, φ f is the permanent magnet flux linkage.

[0065] Due to the symmetry of the three-phase winding of the linear motor, the traveling wave magnetic field is uniformly distributed, and it can be considered that the direct-axis reactance and the quadrature-axis reactance are the same, so that the flux linkage and the current are decoupled in the d-q coordinate system.

[0066] Step 1.3, the electromagnetic thrust equation of the permanent magnet synchronous linear motor in the d-q coordinate system is established:

[0067]

[0068] Using i d =0 vector control, the electromagnetic thrust equation of the linear motor becomes:

[0069]

[0070] The mechanical equilibrium equation of the permanent magnet synchronous linear motor is as follows:

[0071]

[0072] In formula (5), M is the mass of the linear motor, v is the linear motor movement speed, B is the viscous coefficient, F l is the load resistance.

[0073] According to formulas (1)-(5), the block diagram of the permanent magnet synchronous linear motor is obtained as Figure 2 shown.

[0074] Step 2, determine the electromagnetic thrust constant of the permanent magnet synchronous linear motor:

[0075] According to the required lifting height of the vehicle body, the design parameters of the cylindrical permanent magnet synchronous linear motor are determined. The model of the cylindrical permanent magnet synchronous linear motor is established in Ansoft / Maxwell software, parameterized modeling is performed, the current source is selected as the excitation, different primary winding phase current amplitudes are set, the electromagnetic thrust output by the permanent magnet synchronous linear motor with different current amplitudes is calculated, and the electromagnetic thrust constant KT .

[0076] Step 3, Finite set model predictive current control for permanent magnet synchronous linear motor:

[0077] Step 3.1, establish a mathematical model of three-phase two-level inverter, the circuit schematic diagram is shown in Figure 3 . The inverter switch combination state is a total of 8 kinds, the relationship between the AC side phase voltage and the switch function is expressed as follows:

[0078]

[0079] In formula (6), V AN , V BN , V CN are phase voltages, S a , S b , S c are the switch states of three-phase bridge arms, and U dc is the DC bus voltage.

[0080] Step 3.2, construct the value function, directly select the optimal switch state for the inverter, and construct the value function to ensure the minimum error between the current reference value and the predicted value, which reflects the performance of the designed predictive controller. The tracking error between the reference current and the predicted current is taken as the evaluation criterion, and the value function is constructed as:

[0081]

[0082] In formula (7), i , i are the reference values of the cross-axis and direct-axis currents respectively, i d (k+1), i q (k+1) are the predicted values of the cross-axis and direct-axis currents at the next moment respectively. The closer the reference current and the predicted current, the smaller the value function value, and the smaller the tracking error;

[0083] Step 3.3, establish the predictive model of the permanent magnet synchronous linear motor, select the d, q axis currents of the permanent magnet synchronous linear motor as the state variables, and use the forward Euler discretization method for discretization to obtain the discrete state current predictive model of the permanent magnet synchronous linear motor:

[0084]

[0085] In formula (8), T s is the sampling time.

[0086] The inverter's eight switching states correspond to eight basic space voltage vectors, resulting in seven different sets of predicted current values. Two of these zero vectors have the same effect. Based on the established value function, the seven predicted values ​​are substituted into the function to solve for the minimum voltage vector, which is the optimal voltage vector. This optimal voltage vector, along with the corresponding switching signal, is directly applied to the inverter to control the permanent magnet synchronous linear motor.

[0087] Step 4: Establish an active suspension model and use a layered control strategy to control the vehicle height and the permanent magnet synchronous linear motor;

[0088] Step 4.1, establish the mathematical model of the active suspension; the 1 / 4 vehicle suspension model is as follows: Figure 4 As shown by the solid line, the differential equation of motion is as follows:

[0089]

[0090] In equation (9), z2 is the sprung mass displacement, z1 is the unsprung mass displacement, m2 is the sprung mass, m1 is the unsprung mass, k2 is the suspension spring stiffness, k1 is the tire stiffness, c is the suspension damping, q is the input caused by uneven road surface, and F d The driving force of the actuator is F. d The force that generates the lifting and lowering of the vehicle body is in the same direction as the lifting and lowering of the vehicle body;

[0091] Step 4.2: Design a vehicle height controller using a hierarchical control strategy. The upper layer of the hierarchical control strategy uses a PI controller, and the lower layer uses a finite set model predictive controller. The upper layer controller calculates the required operating force of the active suspension based on the difference between the sprung mass displacement and the required lifting height of the vehicle body. The lower layer controller causes the permanent magnet synchronous linear motor to generate electromagnetic thrust to track the operating force calculated by the upper layer.

[0092] Here is an example to illustrate the feasibility of this method:

[0093] Condition 1: Vehicle body lifting control. The target vehicle height is set to 0.12m, the vehicle speed is 20m / s, the road surface is Class B, the simulation time is 30s, lifting control is initiated at 10s, and the vehicle falls back at 20s. The simulation results are as follows. Figures 5 to 7 As shown.

[0094] from Figures 5 to 7It can be seen that when the vehicle body height control is not performed, the vehicle body fluctuates around the equilibrium position, and when the vehicle body height adjustment is performed at the 10th second, the vehicle body height reaches the target height in about 0.56s, and falls rapidly in about 0.46s at the 20th second, the displacement fluctuation is stable during the vehicle body height adjustment, and the controller responds rapidly to the target vehicle height. When the vehicle body is in the equilibrium position, the electromagnetic thrust fluctuates around the equilibrium position. At the 10th second, the average electromagnetic thrust is about 4000N when the target height is 0.12m, and the electromagnetic thrust tracks the target value in about 0.96s. At the 20th second, the electromagnetic thrust falls rapidly in about 0.92s. It is shown that the actual output electromagnetic thrust of the linear motor can rapidly provide the actuating force for the linear motor type active suspension, and the response is rapid during lifting. In addition, the vehicle body acceleration does not change significantly with the sudden change of the vehicle body lifting height, which shows that the lifting control has little effect on the smoothness of the vehicle.

[0095] Working condition 2: vehicle body lowering control is performed. The target height of the vehicle body is set to -0.12m, the vehicle speed is 20m / s, the B-level road excitation is used, the simulation time is 30s, the lowering control is performed at the 10th second, and the falling is performed at the 20th second. The simulation result is shown in Figures 8 to 10 .

[0096] It can be seen from Figures 8 to 10 that the response conditions of the spring mass displacement, the electromagnetic thrust and the vehicle body acceleration are very similar to Figures 5 to 7 , except that the vehicle body lifting and falling is replaced by lowering and recovery, and the control force and the acceleration are basically the same. It can be seen that the vehicle body lowering control and the lifting control can rapidly reach the expected vehicle height, and the control force required is related to the lifting height.

[0097] The above shows and describes the basic principles, main features and advantages of the present application. It should be understood by those skilled in the art that the above examples do not limit the protection scope of the present application in any form, and any technical solutions obtained by equivalent replacement or the like fall within the protection scope of the present application.

Claims

1. A vehicle height control method based on a permanent magnet synchronous linear motor type active suspension, characterized by, The application discloses a vehicle height control method based on a permanent magnet synchronous linear motor. Step 1, a mathematical model of the permanent magnet synchronous linear motor in a d-q coordinate system is established; Step 2, an electromagnetic thrust constant of the permanent magnet synchronous linear motor is determined; Step 3, finite set model predictive current control is performed on the permanent magnet synchronous linear motor; Step 4, an active suspension model is established, and a layered control strategy is adopted to control the vehicle height and the permanent magnet synchronous linear motor. The specific process of step 4 is as follows: Step 4.1, an active suspension mathematical model is established, and a differential motion equation is as follows: （9） In formula (9), is a sprung mass displacement, is an unsprung mass displacement, is a sprung mass, is an unsprung mass, is a suspension spring rate, is a tire stiffness, is a suspension damping, is an input due to road irregularities, is an actuator active force, wherein the actuator active force generates a body lift, the direction of which is the same as the direction of the body lift. Step 4.2, a layered control strategy is adopted to design a vehicle height controller, an actuating force required by the active suspension is calculated according to a difference between a spring mass displacement and a required vehicle lifting height by an upper controller, and an electromagnetic thrust of the permanent magnet synchronous linear motor is caused to track the actuating force calculated by a lower controller.

2. The vehicle height control method based on the permanent magnet synchronous linear motor type active suspension according to claim 1, characterized by, The specific process of step 1 is as follows: Step 1.1, a voltage equation of the permanent magnet synchronous linear motor in the d-q coordinate system is established; （1） In formula (1), , is a voltage vector, is an armature resistance, , is a direct and quadrature axis current, , is a flux linkage vector, is a magnetic field electrical angular velocity, is a pole pair number, is a pole pitch, is a linear motor motion velocity; Step 1.2, a flux linkage equation of the permanent magnet synchronous linear motor in the d-q coordinate system is established; （2） In formula (2), is direct-axis reactance, is quadrature-axis reactance, is permanent magnet flux linkage; Step 1.3, an electromagnetic thrust equation of the permanent magnet synchronous linear motor in the d-q coordinate system is established; （3） Using The electromagnetic thrust equation of the linear motor becomes: （4） A mechanical balance equation of the permanent magnet synchronous linear motor is as follows: （5） In formula (5), is the mass of the linear motor, is the velocity of the linear motor, is the viscous coefficient, is the load resistance.

3. The vehicle height control method based on the permanent magnet synchronous linear motor type active suspension according to claim 2, characterized by, The specific process of step 2 is as follows: Firstly, according to the required lifting height of the vehicle body, the design parameters of the cylindrical permanent magnet synchronous linear motor are determined, then the model of the cylindrical permanent magnet synchronous linear motor is established in Ansoft / Maxwell software, parameterized modeling is carried out, current source is selected as the excitation, different primary winding phase current amplitudes are set, the electromagnetic thrust output by the permanent magnet synchronous linear motor with different current amplitudes is calculated, and the electromagnetic thrust constant is obtained according to the calculation .

4. The vehicle height control method based on the permanent magnet synchronous linear motor type active suspension according to claim 3, characterized by, The specific process of step 3 is as follows: Step 3.1, a mathematical model of a three-phase two-level inverter is established, there are totally 8 kinds of inverter switch combination states, and a relationship between an alternating current side phase voltage and a switch function is as follows: （6） In formula (6), , , is a phase voltage, , , is a switching state of a three-phase bridge arm, is a DC link voltage; Step 3.2, a value function is constructed, a tracking error between a reference current and a predicted current is taken as a judgment standard, and the value function is constructed as follows: （7） In formula (7), , are respectively reference values of the direct and quadrature axis currents, , are respectively predicted values of the direct and quadrature axis currents at the next moment. Step 3.3, a prediction model of the permanent magnet synchronous linear motor is established, d and q axis currents of the permanent magnet synchronous linear motor are selected as state variables, a forward Euler discretization method is adopted to perform discretization, and a discrete state current prediction model of the permanent magnet synchronous linear motor is obtained. （8） In formula (8), is the sampling time.

5. The vehicle height control method based on the permanent magnet synchronous linear motor type active suspension according to claim 1 or 4, characterized by, The upper layer of the layered control strategy adopts a PI controller, and the lower layer adopts a finite set model predictive controller.

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