Control device, electric power steering device, and control method
A control device includes a reaction force controller to generate an input torque input to a control target and control a reaction force transmitted to a steering person and 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. The assist controller includes a high-pass filter with a first cutoff frequency, a low-pass filter with a second cutoff frequency higher than the first cutoff frequency, and a disturbance compensation value calculator. When a transfer function of the low-pass filter is Q(s) and a transfer function of the high-pass filter is HPF(s), a transfer function of a control target is constrained by a transfer function of the nominal model in a frequency band in which a gain in a gain characteristic of Q(s)·HPF(s) is 1.
1. A control device that controls a control target including at least a motor in a steering mechanism, the steering mechanism including an input shaft to which a steering wheel steered by a steering person is connected and an output shaft connected to the input shaft via a torsion bar, the motor being 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; and
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; 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
a disturbance compensation value calculator;
when a transfer function of the low-pass filter is Q(s) and a transfer function of the high-pass filter is HPF(s), 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 Q(s)·HPF(s) is 1;
the disturbance compensation value calculator is operable 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.
2. The control device according to claim 1 , 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.
3. The control device according to claim 1 , wherein the disturbance compensation value calculator is operable to calculate the disturbance compensation value based on a differential torque that is a difference between the input torque and a torque calculated using the nominal model based on the output of the control target.
4. The control device according to claim 3 , wherein 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.
5. The control device according to claim 3 , 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 the differential torque; and
the friction compensation value and the disturbance compensation value are added to the differential torque from which a frequency component lower than the first cutoff frequency is removed by the high-pass filter to generate the correction torque.
6. The control device according to claim 5 , 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.
7. The control device according to claim 1 , wherein the assist controller is operable to generate the correction torque based on a rotation angle of the input shaft.
8. The control device according to claim 1 , wherein an order of the low-pass filter is 3 or more.
9. An electric power steering device comprising:
the control device according to claim 1 ; and
the steering mechanism.
10. A control method for controlling a control target including at least a motor in a steering mechanism, the steering mechanism including an input shaft to which a steering wheel steered by a steering person is connected and an output shaft connected to the input shaft via a torsion bar, the motor being 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; and
generating a correction torque to correct the input torque based on an output of the control target and a nominal model; 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 Q(s)·HPF(s) is 1 when a transfer function of a high-pass filter having a first cutoff frequency is HPF(s) and a transfer function of a low-pass filter having a second cutoff frequency higher than the first cutoff frequency is Q(s); and
calculating a disturbance compensation value to compensate at least a portion of self-aligning torque generated in the control target; and
the correction torque includes the disturbance compensation value.