Unipolar PWM predictive current-mode control of a variable-speed low inductance BLDC motor drive

This study presents the design and implementation steps of a digital predictive controller to regulate a low-inductance, three-phase, three-wire permanent magnet brushless DC motor currents. These types of motors are usually driven by multi-stage converters, switched at high frequencies, or use additional inductances to limit the current ripple. The motor's trapezoidal back electromotive force and rectangular currents waveforms make the design and the tuning process of linear controllers difficult. This task complexity increases when a wide speed range is considered. Digital predictive controllers are easily implemented in digital signal processors (DSPs), being successfully used to regulate currents of different types of power electronic converters. A unipolar pulse width modulation predictive controller is proposed here to regulate the rectangular currents of a brushless DC motor, without the need for any additional filter or converter. Experimental and simulation results using a 5 kW/48 V three-phase brushless DC (BLDC) motor are presented to demonstrate the feasibility of this proposal. It will be presented a methodology to compensate the conditioning and sampling circuits delays as well as the inverter's semiconductors voltage drop. The control algorithm was implemented in a TMS320F28335 DSP.