Numerical Average-Value Modeling of the Brushless DC Motor 120-Degree Inverter System

Average-value modeling is indispensable for large and small-signal analysis of electromechanical systems with power electronic drives. Development of accurate analytical average-value models for the brushless DC motor with 120-degree inverter systems is particularly challenging due to the complicated commutation-conduction patterns of the stator currents. This paper extends a recently proposed approach for numerical averaging of power electronic converters to constructing average-value model for the brushless DC motor with a 120-degree inverter system. In the proposed model, a proper qd model of the permanent magnet synchronous machine is used, and the inverter dynamics are represented using nonlinear algebraic functions that are obtained numerically using the detailed model. The new model is compared to a hardware prototype and detailed simulation, and is shown to be accurate in predicting the large-signal time-domain transients.