Improved Controller Design for Torque Control Characteristics in Direct Torque Control System of PMSM

This paper proposes a novel torque controller in a direct torque control (DTC) system for permanent magnet synchronous motors (PMSM). A reference flux vector calculation (RFVC) DTC uses a PI controller for torque control and can be applied with a PWM voltage-fed inverter. The RFVC DTC's controller can be designed using classical control theory with a linear transfer function by analyzing the relationship between the torque, torque angle, rotor speed, and angular frequency of the stator flux-linkage vector. In contrast, the conventional equivalent modeling method is only applicable with high control gain. At a lower control gain, the convergence performance degrades in the conventional model. Therefore, the torque control characteristics are improved by the proposed system, which is based on the decoupling rotor speed in the torque control system. Simulation and experimental results confirm the validity of the proposed system.