Modified switching scheme-based explicit torque control of brush-less direct current motor drive

A modified explicit torque control (ETC) scheme for permanent magnet (PM) machine with non-sinusoidal back emf is investigated in this article. The conventional ETC scheme for the PM machines with non-sinusoidal back emf furnishes a wide band for the switching frequency and offers a faster response in the torque. In this article, a modified scheme for switching vector selection is proposed to reduce the switching frequency while maintaining the advantage of faster torque response. Other than the conventional two-phase excitation, which uses opposite vectors for switching to get the speedier response in torque, the modifications proposed for the ETC of PM machine are (i) a closer vector selection from the available two-phase vector plane and (ii) a combination of two phase and three phase excitation. Both these modifications gives a faster response in the torque as that of conventional ETC, while this offers a reduction in the switching frequency. Switching frequency variations are expressed mathematically, and experimental results are presented for the modified schemes of ETC and for the conventional ETC based to validate the proposed scheme.