Research On Field-weakening Control Technology Of BLDCM Based On Instantaneous Power Theory

Brushless DC motor(BLDCM) has lots of advantages, such as high power density, high reliability and high efficiency. It has been widely used in all areas of the national economy. However, the speed of BLDCM is difficult to rise after the rated speed has been achieved. This disadvantage limits its applications and hinders its promotion to some extent. Therefore, how to expand the speed range of BLDCM turns to be an important issue in the BLDCM study field, and attracts more and more attention of scholars.This paper designs the field-weakening control system based on instantaneous power theory to solve this problem. The field-weakening control is to generate a reverse magnet field to counteract the permanent magnet field through the armature reactions, hence the permanent magnet flux linkage of the stator winding decreases, and then the permanent magnetic field is reduced equivalently. In this way, the motor could run over the rated speed, therefore, the range of the motor speed can be expanded.This paper introduces the working principle of BLDCM, magnetic field inside the motor and the basic field-weakening theory at first, then introduces the instantaneous power theory, which is an natural extension of phase difference, effective value, active power and reactive power of the traditional power theory to the instantaneous value, which is not only for sinusoidal wave, but also for the transient process and any non-sinusoidal situations. Therefore, the instantaneous power theory can be seen as the promotion and extension of traditional power theory. Then based on the mathematical model of the BLDCM,the instantaneous power theory is applied to field-weakening control, and the relationship among the direct axis current, the quadrature axis current, the instantaneous active current and the reactive current is derived. The basic control principle is explained, a given torque can be gotten by changing the quadrature axis current coefficient, then the direct axis current coefficient of the motor is changed to increase the speed. On this basis, a new flux-weakening control algorithm is proposed, and the comprehensive and systematic description of the algorithm is also given in the paper. In this paper, the hardware and software of the field-weakening control system are designed based on the TMS320F28335 DSP, with the help of which the normal operation and boosting speed operation based on field-weakening control are realized. Finally the experiments are conducted to verify the effectiveness and feasibility of the proposed method.