Electric power steering system

Abstract

An electric power steering system includes: a band-stop filterhaving a transfer function G(s) for suppressing resonance, and a phase compensatorhaving a transfer function G(s). The above function G(s) is represented by an expression G(s)=(s+2ζω+ω)/(s+2ζω+ω), where s is a Laplace operator, ζis a damping coefficient, ζis a damping coefficient, and ωis an angular frequency. On the other hand, the above function G(s) is represented by an expression G(s)=(s+2ζω+ω)/(s+2ζω+ω),where s is a Laplace operator, ζis a damping coefficient, ζis a damping coefficient, and ωis an angular frequency. Furthermore, the above damping coefficients ζ, ζsatisfy an expression ζ24 ζThus, a filter such as a phase compensator may attain a design freedom while preventing the increase of arithmetic load, whereby both the suppression of resonance and a good assist response in a normal steering speed region, for example, may be achieved.