Sliding mode brushless DC motor current and torque control algorithms

The unique attributes of the brushless DC motor make sliding mode control suitable and favored by many control designers. The essence of controller design for brushless DC motors is in fact the switching logic for the three-phase input voltages. Starting from the idea of sliding mode, three algorithms for current and torque control are developed from different approaches to the same problem. The first takes an analytical approach that computes the equivalent controls for each phase voltage and converts them to suitable DC values. The second deals with physical phenomena and generates a proper switching sequence directly without the need of a conversion process. The third further assumes no knowledge about the system parameters; by using current feedback and rotor position information, a lookup table is constructed to achieve the desired performance. The proposed algorithms are well suited for microprocessor control applications