ℋ∞ tuning technique for PMSM cascade PI control structure

In this paper the nonsmooth optimization technique is proposed for parameter tuning of a set of PI controllers. PI controllers connected in a cascade structure are controlling the stator currents and the rotor speed of PMSM (permanent magnet synchronous motor). Performance criteria are specified with weighting functions for each PI controller. Important aspects of weight design and its impact on cascade control of PMSM are presented. Nonlinear nature of PMSM is resolved by sampling LPV (linear parameter varying) model at key values of the rotor speed and creating set of design points. Tuning of cascaded PI controllers is performed as a two step procedure. In the first step the inner current loop is tuned for all the design points. As a second step to the procedure, the inner loop PI controller parameters are locked and outer speed PI controller is tuned around the q-axis current loop.