Automatic flux-weakening control of permanent magnet synchronous motors using a reduced-order controller

This study presents a novel means of designing a simple and effective position and velocity controller for permanent magnet synchronous motors (PMSM). In contrast to the conventional two-loop control methods with full-state feedback, the proposed controller does not need current information of the motor for feedback purposes. However, under normal operation the steady-state d-axis current can still be controlled to zero to minimize power dissipation. In addition, implementing a simple overmodulation strategy allows the controller to automatically generate a flux-weakening control to expand the range of operating speed when voltage saturation occurs. In addition to not depending on system parameters used by the controller, the automatically generated demagnetizing current is also optimal in the sense of minimum power dissipation that differs from the maximum output torque design or the constant power design of the general flux-weakening control methods. Simulation and experimental results show that the controller can achieve an effective speed and position control with near-minimum power dissipation, even when voltage saturation occurs.