MTPA Strategy for Direct Torque Control of Brushless DC Motor Drive

In this article, a high-performance maximum torque per Ampere (MTPA) control strategy is proposed for surface-mounted brushless dc (BLDC) motor drive. Most of published works in the literature have not considered the effect of iron loss branch. As will be demonstrated analytically, underestimating the iron loss in the control system of BLDC motor has two undesirable effects. First, it causes torque errors. Second, the MTPA fails to track the true minimum current for a desired torque. Therefore, the control system should compensate the effect of iron loss. This compensation is proposed to achieve by a direct torque control scheme to prevent internal current loops and feedforward compensations. In addition, the Lagrange's theorem is employed to derive an MTPA criterion. It is proven that forcing the criterion to zero guarantees realization of MTPA strategy. In order to reach these control objectives, a nonlinear control method is designed with two new output, corresponding to electromagnetic torque and the MTPA criterion. Performance of the proposed controller in realization of MTPA and minimization of torque ripple is justified in real-time through simulations and experiments on a 200 W outer rotor prototype.