KR101893629B1 - Electronic control unit for controlling steering assist current, electric power steering system including the same, and method of steering assist current control - Google Patents

Abstract

The present invention relates to an electronic control apparatus for controlling a steering assist current, an electric power steering system including the same, and a steering assist current control method.
The present invention determines state variables including pinion angle information, pinion angular velocity information obtained by differentiating the pinion angle information, steering angle information, and steering angle velocity information obtained by differentiating the steering angle information, and the frequency response bandwidth of the electric power steering system, State feedback gain to the N-th state feedback gain to determine a state feedback torque and a state feedback current value using the state variable and the first state feedback gain to the N-th state feedback gain, part; And determining a basic control current value according to a vehicle speed and a steering torque of the vehicle through a steering assist current map and receiving the state feedback current value from the state feedback unit, And a steering assist controller for calculating a steering assist current value by subtracting the steering assist current from the steering assist current and generating a steering assist current corresponding to the steering assist current value to supply the steering assist current to the electric motor of the electric power steering system. Lt; / RTI >

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic control unit for controlling a steering assist current, an electric power steering system including the same, and a steering assist current control method.

The present invention relates to an electronic control apparatus for controlling a steering assist current, an electric power steering system including the same, and a steering assist current control method.

The electric power steering system generates an auxiliary steering force through an electric motor, so that the fuel consumption and pollutant discharge are small compared with the hydraulic power steering system which generates the auxiliary steering force by operating the oil pump by the power of the engine On the other hand, the frequency response band of the system itself is lower than that of the hydraulic power steering system, so that it is not possible to reflect the road surface information of the specific frequency region, which is useful information to the driver among the torque sensor signals, to the steering control.

Specifically, the frequency response characteristic of the electric power steering system is about 10 Hz, and the road surface information of 10 Hz or more among the torque sensor signals is blocked. For example, when the road surface information useful for the driver is included in the frequency range of 20 Hz to 30 Hz, the conventional electric power steering system fails to properly reflect the road surface information included in the frequency range of 20 Hz to 30 Hz at the time of steering control It is.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electronic control device that improves the frequency response characteristics of an electric power steering system through state feedback control based on a system model and reflects road surface information in a frequency range of 10 Hz or more in steering assist current control , An electric power steering system including the same, and a steering assist current control method.

In order to achieve the above-mentioned object, in one aspect, the present invention provides a steering control device for a steering control device, which determines a state variable including pinion angle information, pinion angular velocity information obtained by differentiating the pinion angle information, steering angle information, Determining a first state feedback gain to an Nth state feedback gain such that a frequency response bandwidth of the power steering system is a road surface information containing frequency region, and using the state variable and the first state feedback gain to Nth state feedback gain A state feedback unit for calculating a state feedback torque and a state feedback current value; And determining a basic control current value according to a vehicle speed and a steering torque of the vehicle through a steering assist current map and receiving the state feedback current value from the state feedback unit, And a steering assist controller for calculating a steering assist current value by subtracting the steering assist current from the steering assist current and generating a steering assist current corresponding to the steering assist current value to supply the steering assist current to the electric motor of the electric power steering system. Lt; / RTI >

In another aspect, the present invention provides a steering control system comprising: a steering-related sensor for sensing vehicle state information related to driving and steering of a vehicle, including a torque sensor, a steering angle sensor, a vehicle speed sensor, and a motor position sensor; A steering angle sensor for receiving steering angle information from the steering angle sensor, receiving pinion angle information from the steering angle sensor, pinion angular velocity information obtained by differentiating the pinion angle information, differential steering angle information, And determines a first state feedback gain to an Nth state feedback gain using the state variable, and calculates a state feedback gain using the state variable and the first state feedback gain to the Nth state feedback gain, Torque control, and steering feedback current value, determines a basic control current value based on the vehicle speed and the steering torque of the vehicle through the steering assist current map, subtracts the state feedback current value from the basic control current value, And generating a steering assist current corresponding to the steering assist current value, Device; And an electric motor for generating an auxiliary steering force for assisting a steering force of a driver by receiving steering assist current from the electronic control unit.

According to another aspect of the present invention, there is provided a method of controlling a steering assist current in an electronic control apparatus of an electric power steering system, the method comprising the steps of: calculating a steering assist current by using a steering assist angle signal obtained by differentiating the pinion angle information, the pinion angular speed information obtained by differentiating the pinion angle information, A state variable determining step of determining a state variable including the steering angle velocity information; A state feedback torque calculating step of determining a first state feedback gain to an Nth state feedback gain using the state variable and calculating a state feedback torque using the first state feedback gain to an Nth state feedback gain; Calculating a state feedback current value by dividing the state feedback torque by a motor torque constant of the electric motor of the electric power steering system; A steering assist current value calculating step of determining a basic control current value according to a vehicle speed and a steering torque of the vehicle through a steering assist current map and subtracting a state feedback current value from the basic control current value to calculate a steering assist current value; And a steering assist current supply step of generating a steering assist current corresponding to the steering assist current value and supplying the steering assist current to the electric motor.

As described above, according to the present invention, since the frequency response characteristic of the electric power steering system is changed to 10 Hz or more through the state feedback control in the electronic control unit, the road surface information included in the frequency range of 10 Hz or more is output to the steering assist current control There is an effect that can be reflected.

1 is a block diagram schematically illustrating a configuration of an electric power steering system according to an embodiment of the present invention;
2 is a block diagram schematically showing a configuration of an electronic control apparatus according to an embodiment of the present invention;
3 is a block diagram schematically showing an equivalence system equivalent to a system model and a system model of an electric power steering system,
4 is a board diagram comparing the frequency response of an electric power steering system according to an embodiment of the present invention and the frequency response of a conventional electric power steering system,
5 is a graph comparing the power spectral density of the torque sensor signal with the power spectrum density of the torque sensor signal when the state feedback control is not applied when the state feedback control is applied,
6 is a flowchart illustrating a process of controlling a steering assist current in an electronic control apparatus according to an embodiment of the present invention.

Hereinafter, some embodiments of the present invention will be described in detail with reference to exemplary drawings. In describing the components of the present invention, the terms first, second, A, B, (a), (b), and the like can be used. These terms are intended to distinguish the constituent elements from other constituent elements, and the terms do not limit the nature, order or order of the constituent elements. When a component is described as being "connected", "coupled", or "connected" to another component, the component may be directly connected to or connected to the other component, It should be understood that an element may be "connected," "coupled," or "connected."

1 is a block diagram schematically illustrating a configuration of an electric power steering system according to an embodiment of the present invention.

An electric power steering system according to an embodiment of the present invention includes a steering related sensor 100 including a torque sensor 110, a steering angle sensor 120, a vehicle speed sensor 130 and a motor position sensor 140, An electronic control unit (ECU) 200, and an electric motor 300.

The steering-related sensor 100 senses vehicle state information related to the running and steering of the vehicle. The steering-related sensor 100 includes a torque sensor 110, a steering angle sensor 120, a vehicle speed sensor 130, a motor position sensor 140, and the like.

The torque sensor 110 senses the relative rotational displacement of the column shaft which is the input shaft and the pinion shaft which is the output shaft according to the rotation of the steering wheel to measure the steering torque information and generates the torque sensor signal including the steering torque information, 200).

In the present invention, the torque sensor 110 transmits a torque sensor signal to the electronic control unit 200 and transmits the pinion angle information, which is the rotation angle of the pinion shaft, which is the output shaft, to the electronic control unit 200.

The steering angle sensor 120 generates a steering angle signal, which is a signal obtained by measuring the steering angle of the steering wheel rotated by the driver's operation, and transmits the steering angle signal to the electronic control unit 200. Here, it is a matter of course that the steering angle information is included in the steering angle signal.

In the present invention, the torque sensor 110 and the steering angle sensor 120 may be configured individually or integrally with each other, such as a torque angle sensor (TAS).

The vehicle speed sensor 130 senses the vehicle speed of the vehicle, generates a vehicle speed signal proportional to the sensed vehicle speed, and transmits the generated vehicle speed signal to the electronic control unit 200.

The motor position sensor 140 generates information on the motor shaft rotation angle, which is information on the motor shaft rotation angle of the electric motor 300, and transmits it to the electronic control unit 200.

The electronic control unit 200 receives information required for steering control from a plurality of sensors including a torque sensor 110, a steering angle sensor 120, a vehicle speed sensor 130 and a motor position sensor 140, The steering assist current to be supplied to the electric motor 300 is controlled.

In the present invention, the electronic control unit 200 receives the pinion angle information received from the torque sensor 110, the pinion angular velocity information obtained by differentiating the pinion angle information, the steering angle information received from the steering angle sensor 120, Determining a first state feedback gain to an Nth state feedback gain using a state variable, and determining a state feedback torque and an Nth state feedback gain using a state variable and a first state feedback gain to an Nth state feedback gain, Calculates a state feedback current value, determines a basic control current value according to the vehicle speed and the steering torque of the vehicle through a steering assist current map, calculates a steering assist current value by subtracting a state feedback current value from a basic control current value, Generates a steering assist current corresponding to the steering assist current value, and supplies the steering assist current to the electric motor (300). Here, the first state feedback gain to the N-th state feedback gain is a state feedback gain such that the frequency response characteristic of the electric power steering system is a road surface information containing frequency region in a frequency region of 10 Hz or more.

In an embodiment of the present invention, the Nth state feedback gain may be a fourth state feedback gain, and the road surface information containing frequency region may be 20 Hz to 30 Hz.

In other words, the frequency response characteristic of the electric power steering system can be made 20 Hz to 30 Hz through the first state feedback gain to the fourth state feedback gain.

)에 제 2 상태 궤환 이득(K2)을 곱한 값, 피니언각 정보(θ_p)에 제 3 상태 궤환 이득(K3)을 곱한 값 및 피니언각속도 정보(

)에 제 4 상태 궤환 이득(K4)을 곱한 값을 모두 더해서 상태 궤환 토크를 연산하고, 상태 궤환 토크를 전동 모터(300)의 모터 토크 상수로 나눠서 상태 궤환 전류값을 연산할 수 있다.In the embodiment of the present invention, the electronic control unit 200 calculates the steering angle information (? _C ) by multiplying the steering angle information? _C by the first state feedback gain (K1)

) Multiplied by the second state feedback gain K2, a value obtained by multiplying the pinion angle information? _P by the third state feedback gain K3, and a value obtained by multiplying the pinion angular velocity information

) Is multiplied by the fourth state feedback gain K4 to compute the state feedback torque and divide the state feedback torque by the motor torque constant of the electric motor 300 to calculate the state feedback current value.

A detailed description of the configuration for determining the first state feedback gain to the N-th state feedback gain in the present invention will be given in the description of the configuration of the electronic control device 200. [

The electric motor 300 receives the steering assist current from the electronic control unit 200 and generates an assist steering force assisting the steering force of the driver. Here, when the electric power steering system according to the embodiment of the present invention is a rack and pinion type electric power steering system, the electric motor 300 transmits the auxiliary steering force to the rack bar.

2 is a block diagram schematically showing a configuration of an electronic control apparatus according to an embodiment of the present invention.

The electronic control unit 200 according to the embodiment of the present invention includes a steering assist control unit 210 and a state feedback unit 220.

The steering assist controller 210 receives information required for steering control from the steering-related sensor 100 including the torque sensor 110 and the steering angle sensor 120, generates a steering assist current through the received information, (300).

In the present invention, the steering assist control unit 210 determines the basic control current value through the basic logic of the electric power steering system, that is, determines the basic control current value according to the vehicle speed and the steering torque of the vehicle through the steering assist current map, The state feedback current value is subtracted from the basic control current value to finally calculate the steering assist current value.

The steering assist controller 210, which has calculated the steering assist current value, generates a steering assist current corresponding to the steering assist current value and supplies it to the electric motor 300.

The state feedback unit 220 determines the state variable including the pinion angle information, the pinion angular velocity information obtained by differentiating the pinion angle information, the steering angle information, and the steering angle velocity information obtained by differentiating the steering angle information, and the frequency response bandwidth of the electric power steering system State feedback gain to the N-th state feedback gain to determine the state feedback torque and the state feedback current value using the state variable and the first state feedback gain to the N-th state feedback gain . Here, the state feedback unit 220 divides the state feedback torque by the motor torque constant of the electric motor 300 to calculate the state feedback current value.

The principle of determining the first state feedback gain to the Nth state feedback gain in the present invention is as follows.

First, in order to determine the first state feedback gain to the fourth state feedback gain when the Nth state feedback gain is the fourth state feedback gain, a system model expressed as 2A in FIG. 2 and a system model expressed as 2B in FIG. 2 The state equations and the output equations of the electric power steering system are established using the parameters of the equivalent system and the state variables.

Here, the moment of inertia of the equivalent system (J _peq ) is _calculated by the following equation (2): gear ratio G _p of the pinion gear, mass M _r of the rack bar, inertia moment J _p of the pinion gear, (G _bs ) of the ball screw, the inertia moment (J _bs ) of the ball screw, the reduction ratio (G _b ) between the ball nut ball screw and the electric motor 300 and the inertia moment J _m of the electric motor 300 And the damping coefficient B _peq of the equivalent system is _expressed by the following equation (3): gear ratio G _{p of the} pinion gear, damping coefficient B _r of the rack bar, damping coefficient B _p of the pinion gear, The gear ratio G _bs of the ball screw, the damping coefficient B _bs of the ball screw, the reduction ratio G _b between the ball nut and the electric motor 300 and the damping coefficient B _m of the electric motor 300 can do.

Also, the torsional stiffness (K _peq ) of the equivalent system is equal to the torsional stiffness (K _c ) of the torsion bar as shown in Equation (4).

The state equation and the output equation of the electric power steering system for determining the first state feedback gain to the fourth state feedback gain in the state feedback unit 220 are expressed by the following equations (5) and (6).

Where A is the state matrix, X is the state vector, B is the input matrix, U is the input vector, C in the output equation is the output matrix, and y is the output vector. In the present invention, the output vector y becomes the steering torque T _c , and the respective parameters of the matrix are as follows.

,

,

,

,

,

,

,

,

,

,

Among the above factors, T _d means driver's torque, T _m means motor torque, and F _t means rack thrust.

Torsional stiffness (K _c) of the present invention the column shaft moment of inertia (J _c), see the ball screw nut and the electric motor speed ratio (G _b), the rack mass (M _r), the torsion bar of the bar between 300 on, The damping coefficient B _c of the column shaft, the gear ratio G _p of the pinion gear, the gear ratio G _bs of the ball screw, the inertial moment J _p of the pinion gear, the moment of inertia J _bs of the ball screw, damping coefficient of the moment of inertia of 300 (J _m), the rack bar damping coefficient (B _r), the damping coefficient of the pinion gear (B _p), the damping coefficient of the ball screw (B _bs) and an electric motor 300 of the ( B _m ) can be calculated through a system identification method based on the test data of the electric power steering system. The calculated inertia moment (J _c ) of the column shaft, the ball nut ball screw and the electric motor 300 ) ratio (G _b), the torsional rigidity of the torsion bar (K _c), a damping coefficient of a column shaft _(c B), the gear ratio of the pinion gear (G _p) between, Mass of the bar (M _r), the gear ratio (G _bs), reduction gear ratio between the ball nut of the ball screw and an electric motor (300) (G _b), the moment of inertia of the pinion gear (J _p), the ball moment of inertia of the screw of the ball screw (J _bs), the damping coefficient of the moment of inertia (J _m), the rack bar of the electric motor (300) (B _r), the damping coefficient (B _p), the damping coefficient of the ball screw of the pinion gear (B _bs) and an electric motor The damping coefficient B _m of the electronic control unit 300 may be stored in the data storage unit (not shown) of the electronic control unit 200.

On the other hand, the frequency response characteristic of the electric power steering system is determined by the pole (Pole) of the transfer function [G (s)] derived from the state equation. Since the input of the transfer function G (s) in the present invention is the road surface information and the output is the steering torque sensed by the torque sensor 110, the transfer function {G (s) The rack torque F _t is substituted into the input U (s) and the steering torque T _c is substituted into the output Y (s). Here, the rack thrust F _t means the amount of external force including the road surface information transferred to the rack bar.

The state equation in the absence of the state feedback control is expressed by Equation 8 below, and the transfer function and the characteristic equation thereof are expressed by Equations (9) and (10). Here, B ₁ denotes the first column of the input matrix B, B ₂ denotes the second column of the input matrix B, and B ₃ denotes the third column of the input matrix B.

In the present invention, since there is the state feedback control, the motor torque T _m becomes a value obtained by subtracting the state feedback torque (K _fd X) from the reference input r according to the basic logic as shown in Equation (11). Here, the reference input r is a motor torque corresponding to the basic control current value calculated through the basic logic, _Kfd is a first state feedback gain K1, a second state feedback gain K2, The gain K3 and the fourth state feedback gain K4 as variables.

Equation (11) is substituted into the motor torque (T _m ) in Equation (8), the state equation in the present invention, that is, the state equation in the case of state feedback control, can be obtained as in Equation (12) The characteristic equations are as shown in equations (13) and (14).

As mentioned above, the frequency response characteristic of an electric power steering system is determined by the pole (Pole) of the transfer function {G (s)}.

In a conventional electric power steering system without state feedback control, the pole of the transfer function {G (s)}, that is, the solution of the characteristic equation, is determined by the state matrix A, and by the state matrix A The electric power steering system has a frequency response characteristic of about 10 Hz as shown by the bold line in FIG. 4 due to the solutions of the determined characteristic equations (p ₁₁ , p ₁₂ , p ₁₃ , p ₁₄ ) 16, the solution of the characteristic equation is determined by the state feedback gain matrix (K _fd ).

Thus, the solution of the characteristic equation for to indicate the frequency response characteristics of the road surface information comprising the frequency domain, such as electric power steering system of Figure 4 a thin line _{(p 21, p 22, p} 23, p 24) is to state feedback gain matrix out (K _fd ) can be determined. Here, the solutions (p ₂₁ , p ₂₂ , p ₂₃ , p ₂₄ ) of the characteristic equations that allow the electric power steering system to exhibit the frequency response characteristics in the road surface information-containing frequency region can be determined by the actual vehicle test.

이 p₂₁, p₂₂, p₂₃, p₂₄의 해를 갖도록 결정될 수 있고, 전동식 파워 스티어링 시스템의 주파수 응답 특성이 특성 방정식

의 해(p₂₁, p₂₂, p₂₃, p₂₄)에 의해 도 4의 굵은 선(10Hz 근처)에서 얇은 선(노면 정보 포함 주파수 영역, 20Hz 내지 30Hz)으로 변경될 수 있다.In other words, the state feedback gain matrix (K _fd )

P ₂₁ , p ₂₂ , p ₂₃ , p ₂₄ , and the frequency response characteristic of the electric power steering system can be determined to have the solution of the characteristic equation

(Frequency band including road surface information, 20 Hz to 30 Hz) at the bold line (near 10 Hz) in Fig. 4 by the solutions (p ₂₁ , p ₂₂ , p ₂₃ , p ₂₄ )

In the present invention, the state feedback unit 220 develops the characteristic equation of the present invention as shown in Equation 17 below, and then uses the Ackermann's formula as shown in Equation (18) to calculate the state feedback gain matrix K _fd The first state feedback gain to the fourth state feedback gain can be determined. Here,? ₁ ,? ₂ ,? ₃ ,? ₄ are coefficients obtained when the characteristic equation of the present invention is developed.

이 p₂₁, p₂₂, p₂₃, p₂₄의 해를 갖도록 제 1 상태 궤환 이득 내지 제 4 상태 궤환 이득을 결정하고, 피니언각 정보, 피니언각속도 정보, 조향각 정보 및 조향각속도 정보를 포함한 상태 변수를 곱하여 상태 궤환 토크를 연산하고, 상태 궤환 토크를 모터 토크로 나눠서 상태 궤환 전류값을 연산하며, 조향 보조 제어부(210)에서 기본 제어 전류값에서 상태 궤환 전류값을 차감하여 조향 보조 전류값을 최종적으로 연산하여 조향 보조 전류를 생성하고, 이를 전동 모터(300)에 공급하여 조향 제어를 수행하면 기존에 조향 제어에 반영하지 못했던 노면 정보 포함 주파수 영역에 포함된 노면 정보가 조향 제어에 반영된다.In this way, in the state feedback unit 220,

The first state feedback gain to the fourth state feedback gain are determined so as to have the solution of p ₂₁ , p ₂₂ , p ₂₃ , p ₂₄ , and the state variable including the pinion angle information, the pinion angular velocity information, the steering angle information, And the state feedback current value is calculated by dividing the state feedback torque by the motor torque. The steering assist controller 210 subtracts the state feedback current value from the basic control current value and outputs the steering assist current value as the final feedback current value And generates the steering assist current. When the steering assist control is performed by supplying the electric current to the electric motor 300, the road surface information included in the road surface information frequency region, which has not been reflected in the steering control, is reflected in the steering control.

When the road surface information included in the road surface information-containing frequency region is reflected in the steering control, as shown in FIG. 5, the power spectrum density in the road surface information-containing frequency region of the torque sensor signal is improved as compared with the conventional one, It can be seen that the information transfer function is improved as compared with the related art.

Hereinafter, a process of controlling the steering assist current in the electronic control unit 200 of the electric power steering system will be described.

6 is a flowchart illustrating a process of controlling a steering assist current in an electronic control apparatus according to an embodiment of the present invention.

In order to allow the electric power steering system to display the frequency response characteristics of the road surface information-containing frequency domain through the state feedback control, the electronic control unit 200 in the present invention controls the steering angle information, the pinion angular velocity information obtained by differentiating the pinion angle information, The state variable including the steering angle velocity information differentiated from the information and the steering angle information is determined (S610). It goes without saying that the pinion angle information is received from the torque sensor 110 and the steering angle information is received from the steering angle sensor 120. [

The electronic control apparatus 200 determines the first state feedback gain to the Nth state feedback gain using the state variable and the system model expressed as 2A in Fig. 2 and the equivalent system parameters expressed as 2B in Fig. 2 , State feedback torque is calculated using the first state feedback gain to the N-th state feedback gain (S620, S630). Here, the N state feedback gain of the fourth may be the state feedback gain, the electronic control device 200 to which to represent the frequency response characteristics of the included frequency domain road surface information as shown in Equation 17 (p _21, p _22, p ₂₃ , p ₂₄ ), the first state feedback gain to the fourth state feedback gain can be determined using the Ackerman's formula as shown in Equation (18).

Subsequently, the electronic control unit 200 divides the state feedback torque by the motor torque constant of the electric motor 300 to calculate a state feedback current value (S640).

The electronic control device 200 determines the basic control current value according to the vehicle speed and the steering torque of the vehicle through the steering assist current map, and subtracts the state feedback current value from the basic control current value to calculate the steering assist current value (S650 ).

The electronic control unit 200, which has calculated the steering assist current value, generates a steering assist current corresponding to the steering assist current value and supplies it to the electric motor 300 (S660).

While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. That is, within the scope of the present invention, all of the components may be selectively coupled to one or more of them. The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

Claims (10)

Determining a state variable including pinion angle information, pinion angular velocity information obtained by differentiating the pinion angle information, steering angle information, and steering angle speed information obtained by differentiating the steering angle information, and determining whether the frequency response bandwidth of the electric power steering system is in a road surface information- State feedback gain to the N-th state feedback gain to determine a state feedback torque and a state feedback current value using the state variable and the first state feedback gain to the N-th state feedback gain, ; And
A steering assist controller for calculating a steering assist current value by subtracting the state feedback current value from a basic control current value and generating a steering assist current corresponding to the steering assist current value and supplying the steering assist current to an electric motor of the electric power steering system,
Wherein the steering assist current is controlled based on the steering assist current. The method according to claim 1,
Wherein the road surface information-containing frequency region is 20 Hz to 30 Hz. The method according to claim 1,
And the N-th state feedback gain is a fourth state feedback gain. The method according to claim 1,
Wherein the state feedback unit divides the state feedback torque by a motor torque constant of the electric motor to calculate the state feedback current value. A steering-related sensor that detects vehicle state information related to the running and steering of the vehicle, including a torque sensor, a steering angle sensor, a vehicle speed sensor, and a motor position sensor;
A steering angle sensor for receiving steering angle information from the steering angle sensor, receiving pinion angle information from the steering angle sensor, pinion angular velocity information obtained by differentiating the pinion angle information, differential steering angle information, And determines a first state feedback gain to an Nth state feedback gain using the state variable, and calculates a state feedback gain using the state variable and the first state feedback gain to the Nth state feedback gain, An electronic control device for calculating a torque and a state feedback current value, calculating a steering assist current value by subtracting the state feedback current value from a basic control current value, and generating a steering assist current corresponding to the steering assist current value; And
An electric motor for generating an auxiliary steering force for assisting steering force of a driver by receiving a steering assist current from the electronic control unit;
And an electric power steering system. 6. The method of claim 5,
Wherein the electronic control unit calculates the state feedback current value by dividing the state feedback torque by a motor torque constant of the electric motor. 6. The method of claim 5,
And the N-th state feedback gain is a fourth state feedback gain. 8. The method of claim 7,
Wherein the first state feedback gain to the fourth state feedback gain is a state feedback gain such that the frequency response characteristic of the electric power steering system is 20 Hz to 30 Hz. A method of controlling a steering assist current in an electronic control unit of an electric power steering system,
A state variable determining step of determining a state variable including pinion angle information, pinion angular velocity information obtained by differentiating the pinion angle information, steering angle information, and steering angle speed information obtained by differentiating the steering angle information;
A state feedback torque calculating step of determining a first state feedback gain to an Nth state feedback gain using the state variable and calculating a state feedback torque using the first state feedback gain to an Nth state feedback gain;
Calculating a state feedback current value by dividing the state feedback torque by a motor torque constant of the electric motor of the electric power steering system;
A steering assist current value calculation step of calculating a steering assist current value by subtracting the state feedback current value from a basic control current value; And
Generating a steering assist current corresponding to the steering assist current value and supplying the steering assist current to the electric motor;
/ RTI > 10. The method of claim 9,
And the N-th state feedback gain is a fourth state feedback gain.

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