Brushless doubly fed machine (BDFM) is a new type of adjustable-speed machine developed in recent years. It has broad application prospects in the field of variable frequency speed regulation and wind power generation. However, the traditional loss calculation method is no longer applicable due to the special structure and complex magnetic field distribution of BDFM. A novel hybrid rotor structure which has better coupling ability than the commonly used rotor structures such as cage rotor, wound rotor and reluctance rotor is presented but it also increases the difficulty of rotor loss calculation. In this paper, in order to calculate the rotor loss accurately, the time-stepping finite element mathematical models of rotor iron loss and copper loss of BDFM with hybrid rotor are established by considering the influence of skin effect, harmonic magnetic field and eddy-current loss. Based on the mathematical model of iron loss, the spatial distribution and time-variable value of magnetic flux linkage are obtained, and then the iron losses of rotor (hysteresis loss, eddy-current loss and added loss) is calculated. Based on the mathematical model of copper loss, the copper loss is determined by three main factors which is the bar conductor current, skin effect coefficient and DC resistance of bar conductor. In addition, the bar conductor current is calculated by magnetic vector potential, and the skin effect coefficient is identified by referring to the calculation method of induction machine cage winding. In order to verify the validity and feasibility of proposed mathematical model, the simulation model of BDFM with hybrid rotor is established and analyzed, and the results of simulation and calculation are consistent. Thus, this mathematical model provides a theoretical basis for the rotor losses research of BDFM with hybrid rotor.
This work is supported by the National Natural Science Foundation of China under Grant 51537007.