Electric power steering apparatus, control method thereof and computer readable medium

摘要

The electric power steering apparatus is provided with: a steering torque detector that detects steering torque of a steering wheel; an electric motor that applies steering assist force to the steering wheel; a current detector that detects an actual current actually supplied to the electric motor; a target current setting unit that sets a target current to be supplied to the electric motor, on the basis of the steering torque detected by the steering torque detector; a feedback controller that performs feedback control so that the target current and the actual current coincide with each other; and a feedforward controller that performs feedforward control for increasing the actual current detected by the current detector if the target current increases, the feedforward controller including a frequency compensator that provides a smaller amount of increase in the actual current as a frequency of a variation in the target current is lower.

主权项

1. An electric power steering apparatus, comprising:
a first rotary shaft connected to a steering wheel; a rack shaft configured to effect turning of a wheel to be turned, by a rectilinear motion; a second rotary shaft configured to effect the rectilinear motion of the rack shaft; a torsion bar configured to provide a connection between the first rotary shaft and the second rotary shaft, and configured to be twisted by operation of the steering wheel; an electric motor configured to apply assist force for the operation of the steering wheel; a steering torque detector configured to detect steering torque of the steering wheel; and a target current setting unit configured to set a target current to be supplied to the electric motor, on the basis of the steering torque detected by the steering torque detector, a feedback controller configured to perform feedback control on the target current set by the target current setting unit, the target current setting unit comprising:
a target current determination unit configured to determine the target current; anda resonance compensator provided on an output side of the steering torque detector that is also an input side of the target, current determination unit, the resonance compensator being configured to suppress a resonance frequency component of a control system including the torsion bar as a spring element, and the electric motor, the second rotary shaft, and the rack shaft as inertial elements, andthe target current setting unit being further configured to set the target current in accordance with the steering torque subjected to the suppression of the resonance frequency component by the resonance compensator, wherein a transfer function H(s) of the resonance compensator is defined as:
H(s)=a·((2πfc1)·(2πfc2))/((s+2πfc1)·(s+2πfc2)); wherein:a=(4⁢⁢π2·γ12·J1+4⁢⁢π2·J2+m·γ22)·s2+4⁢⁢π2·ktb4⁢⁢π2·γ1,⁢ora=(4⁢⁢π2·γ12·J1+4⁢⁢π2·γ12·J2+m·γ12·γ22)·s2+4⁢⁢π2·γ12·ktb4⁢⁢π2·γ1·γ2;⁢and wherein:
s donates an operator for the Laplace transform,fc12 and fc2 represent cut-off frequencies of low-pass filters,γ1=θ1/θ2, where θ1 represents an angle of rotation of the electric motor, and θ2 represents an angle of rotation of the second rotary shaft,γ2=2·π·r, where r represents a radius of rotation of the second rotary shaft,J1 represents inertia of a motor shaft of the electric motor,J2 represents inertia of the second rotary shaft,m represents mass of the rack shaft, andktb represents a spring constant of the torsion bar.