Field-Weakening Speed Extension of BLDCM Based on Instantaneous Power Theory

The excitation of BLDCM is provided by the permanent magnet, which has many advantages compared with the conventional DC motor. But for the drive, due to the limit of the bus voltage, the operation with speed higher than base speed needs the flux be reduced. The impossibility for regulating the flux of the permanent magnet has become the bottleneck of the speed extension of motor. A square wave current field-weakening control method based on theory of Instantaneous power is adopted in this paper, which effectively solves the operation difficulty of permanent magnet BLDCM when the speed is higher than the base speed. Compared with the other control modes, this method needs no change of the motor structure, no extra hardware or the complex vector transform. A wide-range speed extension ratio and good operation performance can be achieved by controlling the reactive component Se. The simulation results indicate that the speed range approximates 2:1 for this method, the current shows no distinct distortion and the expected purpose can be reached.