Control device of vehicle steering system

1 . A control device of a vehicle steering system comprising a turning motor that turns a turning wheel in accordance with a steering angle of a steering wheel, the control device comprising:

a turning angle controller configured to generate, based on a turning angle target value serving as a target value of a turning angle of the turning wheel, a motor current command value serving as a control target value of current to be supplied to the turning motor,

wherein the turning angle controller includes:

a feedforward compensator configured to improve followability of the turning angle with respect to the turning angle target value;

a feedback compensator configured to control the motor current command value based on a deviation between an output value of the feedforward compensator and an actual turning angle serving as an actual turning angle of the turning wheel; and

a disturbance observer configured to estimate a disturbance component acting on an inertial system including the turning motor and to remove the disturbance component from the motor current command value.

2 . The control device according to claim 1 , wherein

when Gm denotes a target transmission characteristic of a control system that receives the turning angle target value and outputs the actual turning angle, and Gref denotes a transmission characteristic of a control system that receives the output value of the feedforward compensator and outputs the actual turning angle,

the feedforward compensator is configured to output a value obtained by applying a transmission characteristic Gm/Gref to the turning angle target value.

3 . The control device according to claim 1 , wherein

when Gm denotes a target transmission characteristic of a control system that receives the turning angle target value and outputs the actual turning angle, Gref denotes a transmission characteristic of a control system that receives the output value of the feedforward compensator and outputs the actual turning angle, and P denotes a transmission characteristic of a control system that receives an output value of the feedback compensator and outputs the actual turning angle,

the feedforward compensator is configured to output a first value obtained by applying the target transmission characteristic Gm to the turning angle target value and output a second value obtained by applying a transmission characteristic Gm/P to the turning angle target value,

the feedback compensator is configured to control the motor current command value based on a deviation between the first value and the actual turning angle, and

the disturbance observer is configured to control the motor current command value based on a value obtained by adding the second value to the output value of the feedback compensator.

4 . The control device according to claim 1 , wherein

the disturbance observer is configured to:

include a filter having a predetermined high frequency attenuation characteristic;

generate an inverse model of the inertial system by applying the filter to an inverse characteristic of a plant model serving as a transmission characteristic of the inertial system;

calculate a torque estimation value of the disturbance component by subtracting a value obtained by converting an output value of the disturbance observer into torque and further applying the filter from a value obtained by multiplying the actual turning angle by the inverse model;

calculate a current estimation value of the disturbance component by converting the torque estimation value into current; and

remove a value obtained by multiplying the current estimation value by a compensation gain from the output value of the feedback compensator, and output a result value as the motor current command value.

5 . The control device according to claim 1 , wherein

the disturbance observer is configured to:

include a filter having a predetermined high frequency attenuation characteristic;

generate an inverse model of a plant model serving as a transmission characteristic of the inertial system;

calculate a torque estimation value of the disturbance component by subtracting a value obtained by converting an output value of the disturbance observer into torque from a value obtained by multiplying the actual turning angle by the inverse model and further applying the filter;

calculate a current estimation value of the disturbance component by converting the torque estimation value into current; and

remove a value obtained by multiplying the current estimation value by a compensation gain from the output value of the feedback compensator, and output a result value as the motor current command value.

6 . The control device according to claim 1 , wherein

the disturbance observer is configured to:

include a filter having a predetermined high frequency attenuation characteristic;

generate an inverse model of the inertial system by converting an inverse characteristic of a plant model serving as a transmission characteristic of the inertial system into current and further applying the filter;

calculate a current estimation value of the disturbance component by subtracting a value obtained by applying the filter to an output value of the disturbance observer from a value obtained by multiplying the actual turning angle by the inverse model; and

remove a value obtained by multiplying the current estimation value by a compensation gain from the output value of the feedback compensator, and output a result value as the motor current command value.

7 . The control device according to claim 1 , wherein

the disturbance observer is configured to:

include a filter having a predetermined high frequency attenuation characteristic;

generate an inverse model of the inertial system by converting an inverse characteristic of a plant model serving as a transmission characteristic of the inertial system into current;

calculate a current estimation value of the disturbance component by subtracting an output value of the disturbance observer from a value obtained by multiplying the actual turning angle by the inverse model and further applying the filter; and

remove a value obtained by multiplying the current estimation value by a compensation gain from the output value of the feedback compensator, and output a result value as the motor current command value.

8 . The control device according to claim 1 , wherein

the feedback compensator is formed of a PID controller.

9 . The control device according to claim 1 , wherein

the feedback compensator is formed of a PD controller.