  This paper is concerned with the robust design for a class of switching
systems from a fractional order control (FOC) perspective. In particular, the
tuning of the robust fractional order PI (RFPI) controller is proposed based on
phase margin and cross over frequency specifications, ensuring the quadratic
stability of the system, i.e., the third design specification is given by the
stability condition. The quadratic stability is analyzed using a
frequency-domain method equivalent to the common Lyapunov one. Two examples are
given to show the effectiveness of the proposed controller.
