A Robust Over-modulation Scheme for Direct Torque and Flux Controlled Reluctance Synchronous Motors in Field-weakening Region

Direct torque and flux control (DTFC) is acknowledged as one of the most effective approaches for reluctance synchronous motor (RSM) drives due to its smooth torque response, low current harmonics and direct applicability to field-weakening (FW) operation. However, the conventional FW algorithm for RSM only provides constrained constant power speed region (CPSR) because of its limited usage of DC-link voltage. Furthermore, most of the existing over-modulation strategies for DTFC based FW operation are mathematically very complicated and highly model dependent, making them less attractive. To maximize the CPSR of direct torque and flux controlled RSM, this paper proposes a new robust over-modulation scheme. The proposed scheme is simple and robust since it does not require the knowledge of machine parameters. The effectiveness of the proposed over-modulation scheme is verified through simulations.