Motor-driven Power Steering Control Method and System

Abstract

The present invention relates to a motor-driven power steering control method and system. The method may include: setting a virtual steering system model, the virtual steering system model including a column connecting a steering wheel to a rack, using a torsional displacement of the column in the set virtual steering system model to determine a column stiffness torque, and determining a target steering torque based on the determined column stiffness torque.

Description

Technical Field

[0001] The present invention relates to a motor-driven power steering control method and system including a virtual steering system model. Background Art

[0002] The disadvantage of traditional open-loop-based motor-driven power steering (MDPS) control is that its performance varies according to the dispersion of hardware and requires repeated adjustment to ensure the desired target steering performance.

[0003] However, the current open-loop-based control can overcome the above disadvantages through closed-loop feedback control.

[0004] That is, the feedback control generates a target steering torque to be controlled through a look-up table. Therefore, compared with the open-loop-based control method, the advantage of the feedback control is that it improves the robustness and adjustment efficiency of the control.

[0005] In the case of feedback control, it is difficult to predict the performance of the control logic at the initial stage of designing the feedback controller. Therefore, in order to improve the development efficiency, a steering system using a virtual steering system model is used.

[0006] However, in the traditional steering system using a virtual steering system model, it is difficult to change the target steering torque according to the change of the steering angle in the region with a relatively large steering angle (i.e., the eccentric region).

[0007] The information included in the background art section of the present invention is only used to enhance the understanding of the overall background art of the present invention and cannot be considered as an admission or any form of implication that this information constitutes the prior art known to those skilled in the art. Summary of the Invention

[0008] Various aspects of the present invention aim to provide a virtual steering system model in which various design requirements can be reflected in the target steering torque according to the change of the steering angle in the region with a relatively large steering angle.

[0009] According to one aspect of the present invention, the above and other objects can be achieved by providing a motor-driven power steering control method including setting a virtual steering system model including a column connecting a steering wheel to a rack gear, determining a column stiffness torque using a torsional displacement of the column as a variable in the set virtual steering system model, and determining a target steering torque based on the determined column stiffness torque.

[0010] When setting up the virtual steering system model, the column of the virtual steering system model connected to the steering wheel can be connected to the rack through a pinion, and the torsional displacement of the column is generated due to the rotation of the steering wheel.

[0011] When determining the column stiffness torque, the column stiffness torque can be determined based on the torsional displacement of the column, and the rate of change of the column stiffness torque with respect to the torsional displacement of the column can be set to be different at different amplitudes of the torsional displacement of the column.

[0012] The column stiffness torque can be a continuous function of the column torsional displacement.

[0013] When determining the column stiffness torque, the column stiffness torque can be determined based on the torsional displacement of the column, and the rate of change of the column stiffness torque with respect to the torsional displacement of the column in a plurality of sections can be set to be different, and the plurality of sections are divided from each other based on the amplitude of the torsional displacement of the column.

[0014] When determining the target steering torque, the target steering torque can be determined to be proportional to the sum of the determined column stiffness torque and the column damping torque determined using the rate of change of the torsional displacement of the column as a variable.

[0015] When determining the target steering torque, the auxiliary gain set using the vehicle speed as a variable can be reflected in the target steering torque.

[0016] The motor-driven power steering control method can further include, after determining the target steering torque, performing feedback control of the steering motor to track the determined target steering torque.

[0017] According to another aspect of the present invention, there is provided a motor-driven power steering control system, which includes a stiffness torque determination unit and a target steering torque determination unit. The stiffness torque determination unit is configured to use the torsional displacement of the column as a variable to determine the column stiffness torque in a virtual steering system model including a column connecting the steering wheel to the rack, and the target steering torque determination unit is configured to determine the target steering torque based on the determined column stiffness torque.

[0018] The stiffness torque determination unit can determine the column stiffness torque based on the torsional displacement of the column, and can set the rate of change of the column stiffness torque with respect to the torsional displacement of the column in a plurality of sections to be different, and the plurality of sections are divided from each other based on the amplitude of the torsional displacement of the column.

[0019] The motor-driven power steering control system may further include a damping torque determination unit configured to determine a column damping torque using a rate of change of a torsional displacement of a column as a variable, and a target steering torque determination unit may determine a target steering torque to be proportional to a sum of the determined column stiffness torque and the determined column damping torque.

[0020] The motor-driven power steering control system may further include a gain setting unit configured to set an assist gain using a speed of a vehicle as a variable, and the target steering torque determination unit may determine the target steering torque by reflecting the assist gain set by the gain setting unit.

[0021] The motor-driven power steering control system may further include a motor controller configured to control a steering motor using the target steering torque determined by the target steering torque determination unit.

[0022] The method and apparatus of the present invention have other features and advantages that will be apparent from or will be more particularly set forth in the accompanying drawings and the following detailed description, which are incorporated herein to explain certain principles of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a block diagram showing a configuration of a motor-driven power steering control system according to an exemplary embodiment of the present invention;

[0024] Figure 2 is a flowchart showing a motor-driven power steering control method according to an exemplary embodiment of the present invention;

[0025] Figure 3 is a view exemplarily showing a virtual steering system model according to an exemplary embodiment of the present invention;

[0026] Figure 4 is a graph showing a function between a torsional displacement and a stiffness torque of a conventional column;

[0027] Figure 5 is a graph showing a function between a torsional displacement and a stiffness torque of a column according to an exemplary embodiment of the present invention;

[0028] Figure 6 and Figure 7 is a graph showing a model analysis result and actual measurement data of a motor-driven power steering control system according to an exemplary embodiment of the present invention;

[0029] Figure 8is a graph showing the actual vehicle test data of a vehicle equipped with a power steering control system driven by a conventional motor;

[0030] Figure 9 is a graph showing the actual vehicle test data of a vehicle equipped with a power steering control system driven by a motor according to an exemplary embodiment of the present invention.

[0031] It will be understood that the drawings are not necessarily to scale, presenting a somewhat simplified representation of the various features illustrating the basic principles of the present invention. The specific design features of the present invention included herein (e.g., including specific dimensions, orientations, positions, and shapes) will be determined in part by the particular intended application and use environment.

[0032] In the drawings, reference numerals refer to the same or equivalent parts of the present invention throughout several views of the drawings. Detailed Embodiments

[0033] Reference will now be made in detail to various embodiments of the present invention, examples of which are illustrated in the drawings and will be described below. Although the present invention will be described in conjunction with the exemplary embodiments of the present invention, it should be understood that this description is not intended to limit the present invention to those exemplary embodiments. On the other hand, the present invention is intended to cover not only the exemplary embodiments of the present invention, but also various alternatives, modifications, equivalents, and other embodiments that may be included within the spirit and scope of the present invention as defined by the appended claims.

[0034] Specific structural or functional descriptions of the embodiments of the present invention set forth in the following description will be provided by way of example to describe the exemplary embodiments of the present invention. However, the present invention may be implemented in many alternative forms and should not be construed as limited to the exemplary embodiments set forth herein.

[0035] Various modifications and variations can be made to the exemplary embodiments of the present invention, and thus, the specific embodiments of the present invention will be illustrated in the drawings and will be described in detail in the following description of the exemplary embodiments of the present invention. However, the exemplary embodiments of the present invention are provided only to fully include the present invention and fully inform those skilled in the art of the scope of the present invention.

[0036] In the following description of the embodiments, it should be understood that when terms such as "first", "second", etc. are used to describe various elements, these terms are not used to limit these elements. That is, these terms are only used to distinguish the same or similar elements. Therefore, unless otherwise stated, within the technical scope of the present invention, the first element may be named the second element, and similarly, the second element may be named the first element.

[0037] In the following description of the embodiments, it should be understood that when an element is "connected to", "coupled to", etc. another element, the two elements can be directly connected or coupled, or one or more other elements can be inserted between the two elements. On the other hand, it should be understood that when an element is "directly connected to", "directly coupled to", etc. another element, no element can be inserted between the two elements. In the following description of the embodiments, other terms indicating the relationship between elements, such as "between" and "directly between" or "adjacent to" and "directly adjacent to", will be interpreted in the same way.

[0038] It should be understood that the terms used in the following description of the exemplary embodiments are only for describing specific embodiments and are not intended to limit the present invention, and unless otherwise specified, the expression of the singular form of an element includes the expression of the plural form of the element. In the following description of the embodiments, the terms "comprising", "having", etc. will be interpreted as indicating the presence of the features, numbers, steps, operations, elements or components or combinations thereof stated in the specification, and do not exclude the presence of one or more features, numbers, steps, operations, elements, components or combinations thereof, or the possibility of adding them.

[0039] It should be understood that unless otherwise defined, all terms (including technical or scientific terms) used in the following description of the exemplary embodiments have the same meaning as those commonly understood by those skilled in the art. In addition, it should be interpreted that the terms defined in a commonly used dictionary generally have a meaning consistent with the context meaning, and unless explicitly defined, do not have an ideal or overly formal meaning.

[0040] Hereinafter, exemplary embodiments of the present invention will be referred to in detail, and examples of the exemplary embodiments are shown in the drawings. In the following description of the exemplary embodiments and the drawings, even when the same or similar elements are depicted in different drawings, the elements are denoted by the same reference numerals.

[0041] An electric power steering system applicable to the exemplary embodiments of the present invention is a steering system that uses an electric motor to generate or supplement steering force, and can be a motor-driven power steering (MDPS) system or a steer-by-wire (SBW) system.

[0042] Various embodiments of the present invention relate to a method and a system that set a target steering torque to control a motor-driven power steering system including an electric motor, and then control the motor-driven power steering system based on the set target steering torque.

[0043] Figure 1is a block diagram showing the configuration of a motor-driven power steering control system according to an exemplary embodiment of the present invention. Figure 2 is a flowchart showing a motor-driven power steering control method according to an exemplary embodiment of the present invention, and Figure 3 is a view exemplarily showing a virtual steering system model 10 according to an exemplary embodiment of the present invention.

[0044] Referring to Figure 1 、 Figure 2 and Figure 3 , a motor-driven power steering control method according to an exemplary embodiment of the present invention includes: setting a virtual steering system model 10 including a column connecting a steering wheel to a rack (operation S100), determining a column stiffness torque using a torsional displacement of the column as a variable in the set virtual steering system model 10 (operation S200), and determining a target steering torque based on the determined column stiffness torque (operation S300).

[0045] The virtual steering system model 10 according to an exemplary embodiment of the present invention may be a rack-type motor-driven power steering (R-MDPS) system using a rack, and when setting the virtual steering system model 10 (operation S100), the column may be set between the steering wheel and the rack, and a pinion gear provided on the column may be connected to the rack.

[0046] More specifically, as Figure 3 shown, when setting the virtual steering system model 10 (operation S100), the column of the virtual steering system model 10 connected to the steering wheel may be connected to the rack through a pinion gear, and torsional displacement of the column may occur due to rotation of the steering wheel.

[0047] By determining a target steering torque T based on the virtual steering system model 10 q_ref , steering performance can be predicted and thus the development efficiency of steering control technology can be improved, and the characteristics of the steering system can be freely changed and thus various types of steering feelings can be generated and the adjustment efficiency can be improved.

[0048] When applying this virtual steering system model 10 to an SBW system in which the mechanical connection structure between the steering wheel and the steering gearbox is eliminated, a steering wheel reaction force and steering feeling similar to those of a mechanically installed steering system can be achieved.

[0049] In the virtual steering system model 10, a steering angular velocity ω sw and a rack force F rack can be used as input variables, an inertia J of the steering wheel sw , a stiffness K of the column serving as a reaction devicet 、The damping coefficient B of the column t 、The frictional torque T of the column fric_c 、The radius R of the pinion p and the weight M of the rack r can be used as system characteristic parameters, and the target steering torque T q_ref can be used as an output variable that depends on the relationship between the input variables and the system characteristic parameters. Additionally, W c is the angular velocity of the column, and V r is the velocity of the rack.

[0050] The bond graph for the virtual steering system model 10 can be used to derive the state equations, and the bond graph will be presented below.

[0051]

[0052] The state equations can be derived by setting the torsional displacement of the column, the momentum of the rack, the momentum of the steering wheel, and the transfer displacement of the rack as state variables.

[0053] Specifically, the bond graph can be used to derive the state equations, and in this example, the state equations can be derived by setting the torsional displacement q5 of the column, the momentum P 10 、the momentum P2 of the steering wheel, and the transfer displacement q 13 of the rack as state variables, as described below.

[0054]

[0055] Here, T in is the steering torque input through the steering wheel, and T fric_sw is the frictional torque applied to the steering wheel.

[0056] In an exemplary embodiment of the present invention, the target steering torque T applied to the column can be determined by numerical integration of the state equations, and the target steering torque T can be determined by Equation 1 below q_ref . q_ref .

[0057]

[0058] T q_ref : Target steering torque

[0059] K t : Stiffness of the column

[0060] q5: Torsional displacement of the column

[0061] B t : Damping coefficient of the column

[0062] Rate of change of torsional displacement of the torsion bar

[0063] The torsional displacement q5 of the column as a compliance value can be a rotational displacement (angle), and due to the rotation of the steering wheel, the torsional displacement q5 of the column changes in response to the torsional stiffness of the column. It should be understood that the torsional displacement θ of the column and the torsional angle of the torsion bar are the same, which will be described below.

[0064] That is, as described above, the target steering torque can be determined as the sum of the column stiffness torque and the column damping torque.

[0065] Figure 4 is a graph showing the function between the torsional displacement and the stiffness torque of a conventional column, and Figure 5 is a graph showing the function between the torsional displacement and the stiffness torque of a column according to an exemplary embodiment of the present invention.

[0066] Reference Figure 4 and Figure 5 , when determining the column stiffness torque (operation S200), the column stiffness torque can be determined based on the torsional displacement of the column.

[0067] As Figure 4 shown, conventionally, a linear model of the column stiffness torque τ K with respect to the torsional displacement of the column has been assumed. However, if a linear model of the column stiffness torque τ K is assumed, it is difficult to change the rate of change of the target steering torque according to the steering angle in a region with a relatively large steering angle (eccentric region).

[0068] As Figure 5 shown, when determining the column stiffness torque (operation S200) according to an exemplary embodiment of the present invention, a non-linear model of the column stiffness torque τ K with respect to the torsional displacement of the column can be set.

[0069] More specifically, the rate of change of the column stiffness torque τ K with respect to the torsional displacement of the column at different amplitudes of the torsional displacement of the column can be set to be different.

[0070] Conventionally, the column stiffness K t is set to a constant, and thus the column stiffness K t is used as a proportionality constant for the torsional displacement of the column. However, in an exemplary embodiment of the present invention, the column stiffness corresponding to the rate of change of the torsional displacement of the column can be set to change according to the amplitude of the torsional displacement of the column.

[0071] According to an exemplary embodiment of the present invention, asFigure 5 As shown, when the amplitude of the torsional displacement θ of the column is less than a predetermined angle θ0, the column stiffness torque τ K can be determined to be proportional to the predetermined column stiffness, as shown in the following equation.

[0072] τ k = K t θ

[0073] In addition, when the amplitude of the torsional displacement θ of the column is not less than the predetermined angle θ0, the column stiffness torque τ K can have a different rate of change from the predetermined column stiffness, as shown in the following equation.

[0074] τ k = K tnon (θ - θ0)+K t θ0

[0075] That is, at different amplitudes of the torsional displacement θ of the column, the column stiffness torque τ K can be set to have a different rate of change with respect to the torsional displacement θ of the column, and the amplitude of the torsional displacement θ of the column is different based on the predetermined angle θ0.

[0076] In addition, when determining the column stiffness torque (operation S200) according to an exemplary embodiment of the present invention, the column stiffness torque τ K can be set to have a different rate of change with respect to the torsional displacement θ of the column in a plurality of sections, and the plurality of sections are divided from each other based on the amplitude of the torsional displacement θ of the column.

[0077] That is, in the section where the amplitude of the torsional displacement θ of the column is less than the predetermined angle θ0 and in the section where the amplitude of the torsional displacement θ of the column is not less than the predetermined angle θ0, the column stiffness torque τ K can be set to have a different rate of change with respect to the torsional displacement of the column.

[0078] Therefore, in an eccentric region with a relatively large steering angle, a non-linear characteristic of the target steering torque can be achieved. Therefore, it is possible for the driver to adjust to improve the steering performance of the vehicle.

[0079] The column stiffness torque τ K can be a continuous function of the torsional displacement of the column.

[0080] Therefore, even if the torsional displacement of the column changes, the column stiffness torque τ K also changes continuously, and there is no sense of difference in the steering torque.

[0081] According to another exemplary embodiment of the present invention, the column stiffness torque τ KThe rate of change can vary according to the torsional displacement of the column and can be set to be distinguishable in all sections.

[0082] When determining the target steering torque (operation S300), the target steering torque can be determined to be proportional to the sum of the determined column stiffness torque τ K and the column damping torque τ B . The column damping torque is determined using the rate of change of the torsional displacement of the column as a variable.

[0083] The rate of change of the torsional displacement of the column can be used as a variable to determine the column damping torque τ B . The column damping torque τ B can be determined to be linearly proportional to the rate of change of the torsional displacement of the column .

[0084] According to an exemplary embodiment of the present invention, the target steering torque can be determined as the sum of the column stiffness torque τ K and the column damping torque τ B .

[0085] According to another exemplary embodiment of the present invention, when determining the target steering torque (operation S300), an auxiliary gain K a set using the speed of the vehicle as a variable can be reflected in the target steering torque.

[0086] The gain setting unit 50 can receive the speed V s of the vehicle and then set the auxiliary gain K a .

[0087] More specifically, the target steering torque T K can be determined by multiplying the sum of the column stiffness torque τ B and the column damping torque τ a by the auxiliary gain K q_ref . Thus, the target steering torque T q_ref is configured to vary according to the auxiliary gain K a . It can be expressed by the following formula.

[0088] T q_ref = K a (τ k + τ B )

[0089] Here, 0 < auxiliary gain Ka ≤ 1.

[0090] That is, if the target steering torque T q_ref might be determined to be too high a value, then by applying the auxiliary gain K ato reduce the target steering torque T q_ref .

[0091] The assist gain K a can be a value that varies according to the steering angle and driving speed of the vehicle. According to an exemplary embodiment of the present invention, the assist gain K a can be pre-mapped to decrease as the steering angle increases and can be pre-mapped to decrease as the driving speed of the vehicle increases.

[0092] After determining the target steering torque T q_ref (operation S300), the motor-driven power steering control method may further include performing feedback control of the steering motor 70 to track the determined target steering torque T q_ref (operation S400).

[0093] That is, the motor controller 60 may perform feedback control of the control amount of the steering motor 70 such that the actual steering torque input to the steering motor 70 is consistent with the target steering torque T q_ref .

[0094] Referring again to Figure 1 , the motor-driven power steering control system according to an exemplary embodiment of the present invention includes a stiffness torque determination unit 20 and a target steering torque determination unit 40. The stiffness torque determination unit 20 is configured to determine a column stiffness torque using the torsional displacement of the column as a variable in a virtual steering system model including a column that connects a steering wheel to a rack, and the target steering torque determination unit 40 is configured to determine a target steering torque based on the determined column stiffness torque.

[0095] The stiffness torque determination unit 20 may determine the column stiffness torque based on the torsional displacement of the column and may set different rates of change of the column stiffness torque with respect to the torsional displacement of the column in a plurality of sections that are divided from each other based on the magnitude of the torsional displacement of the column.

[0096] The motor-driven power steering control system may further include a damping torque determination unit configured to determine a column damping torque using the rate of change of the torsional displacement of the column as a variable, and the target steering torque determination unit 40 may determine the target steering torque to be proportional to the sum of the column stiffness torque and the column damping torque.

[0097] The motor-driven power steering control system may further include a gain setting unit 50 configured to set an assist gain using the speed of the vehicle as a variable, and the target steering torque determination unit 40 may determine the target steering torque in which the assist gain set by the gain setting unit 50 is reflected.

[0098] The motor-driven power steering control system may further include a motor controller 60 configured to control the steering motor 70 using the determined target steering torque.

[0099] The stiffness torque determination unit 20, damping torque determination unit 30, target steering torque determination unit 40, gain setting unit 50, and motor controller 60 according to an exemplary embodiment of the present invention may correspond to multiple parts of a controller, and the controller may be implemented by a non-volatile memory and a processor. The non-volatile memory is configured to store data related to an algorithm for controlling operations of various elements or software instructions implementing the algorithm, and the processor uses the data stored in the corresponding memory to perform operations, which will be described below.

[0100] Here, the memory and the processor may be implemented as separate chips. Alternatively, the memory and the processor may be implemented as a single integrated chip. Here, one or more processors may be provided.

[0101] Figure 6 and Figure 7 are graphs showing model analysis results and actual measurement data of a motor-driven power steering control system according to an exemplary embodiment of the present invention.

[0102] Referring to Figure 6 and Figure 7 , it can be confirmed that, compared with the conventional linear function of the column stiffness torque, if a non-linear function according to an exemplary embodiment of the present invention is set, in which the rate of change changes according to the torsional displacement of the column, the steering torque in the eccentric region changes.

[0103] It can be confirmed that the non-linear characteristic of the steering torque can be achieved in the eccentric region, and thus, the steering performance can be improved.

[0104] Figure 8 is a graph showing actual vehicle test data of a vehicle to which a conventional motor-driven power steering control system is applied, and Figure 9 is a graph showing actual vehicle test data of a vehicle to which a motor-driven power steering control system according to an exemplary embodiment of the present invention is applied.

[0105] Referring to Figure 8 and Figure 9 , it can be demonstrated that when measuring the steering torque according to the steering angle at each driving speed of the vehicle, the non-linear characteristic of the steering torque can be achieved in the eccentric region at each driving speed of the vehicle.

[0106] As is obvious from the above, the motor-driven power steering control method and system according to various aspects of the present invention can achieve various non-linear characteristics of a target steering torque in an eccentric region having a relatively large steering angle.

[0107] Therefore, it is possible for a driver to make adjustments to improve the steering performance of the vehicle.

[0108] For the purposes of facilitating explanation and for a precise definition in the appended claims, the terms "above", "below", "inner", "outer", "upward", "downward", "upwardly", "downwardly", "front", "rear", "rearward", "inside", "outside", "inwardly", "outwardly", "inner", "outer", "forward" and "backward" are used to describe the features of the exemplary embodiments shown in the figures with reference to the positions of those features. It will be further understood that the term "connected" or its derivatives refer to both direct and indirect connection.

[0109] For purposes of illustration and description, the foregoing description of specific exemplary embodiments of the invention has been given. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously, many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and its practical application to enable others skilled in the art to make and utilize the various exemplary embodiments of the invention and various alternatives and modifications thereof. The scope of the invention is intended to be defined by the appended claims and their equivalents.

Claims

1. A motor-driven power steering control method, comprising: Setting a virtual steering system model by a controller, the virtual steering system model including a model of a column connecting a steering wheel to a rack; Determining a column stiffness torque by the controller using a torsional displacement of the column as a variable in the set virtual steering system model; and Determining a target steering torque by the controller based on the determined column stiffness torque; Wherein, when determining the column stiffness torque, the column stiffness torque is determined based on the torsional displacement of the column, and a change rate of the column stiffness torque with respect to the torsional displacement of the column in a plurality of sections is set to be different, and the plurality of sections are divided from each other based on an amplitude of the torsional displacement of the column.

2. The motor-driven power steering control method according to claim 1, Among them, When setting the virtual steering system model, the column of the virtual steering system model connected to the steering wheel is connected to the rack through a pinion, and the torsional displacement of the column is generated due to rotation of the steering wheel.

3. The motor-driven power steering control method according to claim 1, Among them, When determining the column stiffness torque, the column stiffness torque is determined based on the torsional displacement of the column, and at different amplitudes of the torsional displacement of the column, a change rate of the column stiffness torque with respect to the torsional displacement of the column is set to be different.

4. The motor-driven power steering control method according to claim 3, wherein, The column stiffness torque is a continuous function of the torsional displacement of the column.

5. The motor-driven power steering control method according to claim 1, Among them, When determining the target steering torque, the target steering torque is determined to be proportional to a sum of the determined column stiffness torque and a column damping torque determined using a change rate of the torsional displacement of the column as a variable.

6. The motor-driven power steering control method according to claim 1, Among them, When determining the target steering torque, an assist gain set using a vehicle speed as a variable is reflected in the target steering torque.

7. The motor-driven power steering control method according to claim 1, further comprising: After determining the target steering torque, performing feedback control of a steering motor to track the determined target steering torque.

8. A motor-driven power steering control system, comprising: A stiffness torque determination unit configured to determine a column stiffness torque using a torsional displacement of a column as a variable in a virtual steering system model including a model of a column connecting a steering wheel to a rack; And A target steering torque determination unit configured to determine a target steering torque based on the determined column stiffness torque; Wherein, the stiffness torque determination unit is configured to determine the column stiffness torque based on the torsional displacement of the column, and a change rate of the column stiffness torque with respect to the torsional displacement of the column in a plurality of sections is set to be different, and the plurality of sections are divided from each other based on an amplitude of the torsional displacement of the column.

9. The motor-driven power steering control system according to claim 8 further includes a damping torque determination unit configured to determine a column damping torque using a rate of change of the torsional displacement of the column as a variable. Among them, The target steering torque determination unit is configured to determine the target steering torque to be proportional to the sum of the determined column stiffness torque and the determined column damping torque.

10. The motor-driven power steering control system according to claim 8 further includes a gain setting unit configured to set an assist gain using the speed of the vehicle as a variable. Among them, The target steering torque determination unit is configured to determine the target steering torque by reflecting the assist gain set by the gain setting unit.

11. The motor-driven power steering control system according to claim 8 further includes a motor controller configured to control a steering motor using the target steering torque determined by the target steering torque determination unit.

12. A motor-driven power steering control system including a controller configured to: In a virtual steering system model including a model of a column connecting a steering wheel to a rack, determine a column stiffness torque using the torsional displacement of the column as a variable; and Determine a target steering torque based on the determined column stiffness torque; The column stiffness torque is determined based on the torsional displacement of the column, and a rate of change of the column stiffness torque with respect to the torsional displacement of the column in a plurality of sections is set to be different, and the plurality of sections are divided from each other based on the magnitude of the torsional displacement of the column.

13. The motor-driven power steering control system according to claim 12, wherein, The controller is further configured to determine a column damping torque using a rate of change of the torsional displacement of the column as a variable. Wherein, the target steering torque is determined to be proportional to the sum of the determined column stiffness torque and the determined column damping torque.

14. The motor-driven power steering control system according to claim 12, Among them, The controller is further configured to set an assist gain using the speed of the vehicle as a variable, and Wherein, the controller is further configured to determine the target steering torque by reflecting the assist gain.

15. The motor-driven power steering control system according to claim 12, wherein, The controller is further configured to control a steering motor using the target steering torque.

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