Sliding Mode Driving Strategy for Four-switch Three-phase Brushless DC Motor

Reviewing the direct current control of four-switch three-phase brushless DC motor (BLDCM), to theoretically explore the system operating mechanism in more depth, the paper put forward a novel sliding mode driving strategy. The uniform mathematic description equations of four-switch three-phase BLDCM were represented and six kinds of operating modes (mode1-mode6) were divided up into two groups, mode2, mode3, mode4, and mode5 classified as the first one and mode1, mode4 as the second one. With mode2 and mode1 taken for the examples of the first group and the second group respectively, the fundamental description equation and the standard state space description in every mode were provided, whereas the sliding mode plane, the convergence conditions and the sub-mode division in each mode were discussed. The system analytic solution derived the qualitative conclusions that the convergence domain in any mode was not the whole state space but a small subclass including the reference stable value. Furthermore an engineering method to calculate the system convergence domain of the sliding mode plane based on the Taylor series expansion was also introduced. To verify the feasibility of the plan, a complete simulation system in Matlab6.5/Simulink was built and the system convergence domain was determined. The whole theoretical analysis and the simulation results revealed the validity and reliability of the strategy