Flux-Weakening Strategy to Extend the Operation of Brushless DC Motors

Brushless DC (BLDC) motors are widely used in various applications today. The two commonly used control methods include the maximum torque per ampere (MTPA) control and maximum torque per volt (MTPV) control, which can be easily implemented through different advances in firing angle. However, both of those methods also have their limitations and drawbacks. The MTPA may not produce enough torque to satisfy operation requirements, especially during high-speed operation. The MTPV method, while capable of delivering higher torque, results in higher losses. This paper proposes a novel flux-weakening (FW) control strategy to enable the BLDC motors to operate within a higher speed range, produce sufficient torque, and minimize the magnitude of stator current. The proposed method applies the MTPA at low speeds, and at higher speeds or when high torque is required, it smoothly transitions to the FW region. The proposed method is demonstrated to have improved dynamic response, a wider speed/torque operating range, and higher efficiency (compared to MTPV).