INDIRECT TORQUE CONTROL OF PMSM USING DISCRETE EVENT SYSTEM APPROACH

Abstract

In this paper, we consider permanent magnet synchronous motor drive (PMSM) as a discrete event system (DES), with discrete state and continuous dynamics at each state. This enables to express the voltage applied to the PMSM explicitly in terms of discrete and continuous parameter of the system. A new lookup table is established which gives the discrete parameter corresponding to the switching states. Further, by solving the dynamic equations involved, a closed form expressions for flux and torque are derived which show precisely the effect of discrete state and the continuous system variables. This model is then used in an indirect torque control scheme (IDTC) of PMSM. Indirect Torque Control being in the nature of a feed forward control scheme through simulation results in fast response than conventional Direct Torque control (DTC) scheme in terms of transient speed response, load disturbance rejection, robustness and in dealing with uncertainty in machine parameters. In the proposed scheme, the flux and torque are estimated through switching parameters instead of using current measurement as in DTC thus eliminating the effect of noise. Also, a hardware implementation of the proposed IDTC is shown to perform favorable compared to conventional DTC. Another novel feature of the proposed IDTC scheme is that the current is not measured for load rejection as in conventional DTC thus circumventing the effect of noise in the current. The results can be extended to other model based