Control device, electric power steering device, and control method

1. A control device that controls, as a control target, at least a portion including a motor in a steering mechanism including an input shaft to which a steering wheel steered by a steering person is connected, an output shaft connected to the input shaft via a torsion bar, and the motor connected to the output shaft, the control device comprising:

a reaction force controller to generate an input torque input to the control target based on a torsion bar torque generated in the torsion bar and control a reaction force transmitted from the steering wheel to the steering person;

an assist controller to generate a correction torque to correct the input torque based on an output of the control target and a nominal model; and

a state feedback circuit to feed back a state compensation value to the input torque based on the output of the control target; wherein

the assist controller is configured or programmed such that a transfer function of the control target is constrained by a transfer function of the nominal model in a frequency band where a gain in a gain characteristic of a complementary sensitivity function with respect to a modeling error between the control target and the nominal model is approximately 1; and

the state feedback circuit is operable to feed back the state compensation value so that an apparent transfer function of the control target approaches a transfer function of the nominal model based on the output of the control target.

2. The control device according to claim 1 , wherein the state feedback circuit is operable to feed back the state compensation value to the input torque after the state compensation value is corrected by the correction torque and before the state compensation value is input to the control target.

3. The control device according to claim 1 , wherein the state compensation value includes a compensation value that compensates at least a portion of an inertial force generated in the control target, a viscous force generated in the control target, and a frictional force generated in the control target.

4. The control device according to claim 1 , wherein

the assist controller includes:

a high-pass filter with a first cutoff frequency; and

a low-pass filter with a second cutoff frequency higher than the first cutoff frequency; and

when a transfer function of the low-pass filter is Q(s) and a transfer function of the high-pass filter is HPF(s), the complementary sensitivity function is expressed by Q(s)·HPF(s).

5. The control device according to claim 4 , wherein an order of the low-pass filter is 3 or more.

6. The control device according to claim 1 , wherein the state compensation value includes a compensation value to compensate at least a portion of an inertial force generated in the motor, a viscous force generated in the motor, and a frictional force generated in the motor.

7. The control device according to claim 1 , wherein the assist controller is operable to generate the correction torque based on a difference between a torque calculated using the nominal model based on an output of the control target and the input torque before the state compensation value is fed back after being corrected by the correction torque.

8. The control device according to claim 1 , wherein the assist controller is configured or programmed to generate the correction torque based on a rotation angle of the input shaft.

9. The control device according to claim 1 , wherein

the assist controller includes a disturbance compensation value calculator to calculate a disturbance compensation value to compensate at least a portion of a self-aligning torque generated in the control target; and

the correction torque includes the disturbance compensation value.

10. The control device according to claim 9 , wherein the disturbance compensation value includes a compensation value to compensate at least a portion of a frictional force generated in the control target, a disturbance torque caused by backlash generated in the control target, and a torque ripple generated in the control target.

11. The control device according to claim 9 , wherein

the assist controller is configured or programmed to:

include a friction compensation value calculator to calculate a friction compensation value to compensate at least a portion of a frictional force generated in the control target based on a differential torque that is a difference between the input torque and a torque calculated using the nominal model based on an output of the control target; and

generate the correction torque by adding the friction compensation value and the disturbance compensation value to the differential torque from which a frequency component lower than a first cutoff frequency has been removed by a high-pass filter having the first cutoff frequency.

12. The control device according to claim 11 , wherein

the friction compensation value calculator is operable to calculate the friction compensation value based on a component of a frequency lower than the first cutoff frequency in the differential torque; and

the disturbance compensation value calculator is operable to calculate the disturbance compensation value based on a component of the differential torque having a frequency lower than the first cutoff frequency.

13. An electric power steering device comprising:

the control device according to claim 1 ; and

the steering mechanism.

14. A control device that controls, as a control target, at least a portion including a motor in a steering mechanism including an input shaft to which a steering wheel steered by a steering person is connected, an output shaft connected to the input shaft via a torsion bar, and the motor connected to the output shaft, the control device comprising:

a reaction force controller to generate an input torque input to the control target based on a torsion bar torque generated in the torsion bar and control a reaction force transmitted from the steering wheel to the steering person;

an assist controller to generate a correction torque to correct the input torque based on an output of the control target and a nominal model; and

a state feedback circuit to feed back a state compensation value to the input torque, the state compensation value compensating at least a portion of an inertial force generated in the control target, a viscous force generated in the control target, and a frictional force generated in the control target; wherein

the assist controller is configured or programmed such that a transfer function of the control target is constrained by a transfer function of the nominal model in a frequency band where a gain in a gain characteristic of a complementary sensitivity function with respect to a modeling error between the control target and the nominal model is approximately 1; and

the state feedback circuit is operable to feed back the state compensation value to the input torque after the input torque is corrected by the correction torque and before the input torque is input to the control target.

15. A control method for controlling, as a control target, at least a portion including a motor in a steering mechanism including an input shaft to which a steering wheel steered by a steering person is connected, an output shaft connected to the input shaft via a torsion bar, and the motor connected to the output shaft, the control method comprising:

generating an input torque input to the control target based on a torsion bar torque generated in the torsion bar and controls a reaction force transmitted from the steering wheel to the steering person;

generating a correction torque to correct the input torque based on an output of the control target and a nominal model; and

feeding back a state compensation value to the input torque based on the output of the control target; wherein

the generating of the correction torque includes constraining a transfer function of the control target to a transfer function of the nominal model in a frequency band where a gain in a gain characteristic of a complementary sensitivity function with respect to a modeling error between the control target and the nominal model is approximately 1; and

the feeding-back of the state compensation value to the input torque includes feeding back the state compensation value so that an apparent transfer function of the control target approaches a transfer function of the nominal model based on an output of the control target.

16. A control method for controlling, as a control target, at least a portion including a motor in a steering mechanism provided with an input shaft to which a steering wheel steered by a steering person is connected, an output shaft connected to the input shaft via a torsion bar, and the motor connected to the output shaft, the control method comprising:

generating an input torque input to the control target based on a torsion bar torque generated in the torsion bar, and controlling a reaction force transmitted from the steering wheel to the steering person;

generating a correction torque to correct the input torque based on an output of the control target and a nominal model; and

feeding back, to the input torque, a state compensation value to compensate at least a portion of an inertial force generated in the control target, a viscous force generated in the control target, and a frictional force generated in the control target; wherein

the generating of the correction torque includes constraining a transfer function of the control target to a transfer function of the nominal model in a frequency band where a gain in a gain characteristic of a complementary sensitivity function with respect to a modeling error between the control target and the nominal model is approximately 1; and

the feeding-back of the state compensation value to the input torque includes feeding back the state compensation value to the input torque after the input torque is corrected by the correction torque and before the input torque is input to the control target.