Design and Starting Performance Study of a Soft-Start Brushless Doubly Fed Machine

Traditional brushless doubly fed machine(BDFM) are difficult to take into account both high starting characteristics and high operating efficiency, which limits the range of industrial application. In order to solve this problem, with the composite coil structure adopted by the rotor winding of BDFM and based on the magnetomotive force(MMF) harmonic theory of stator winding, this paper presents a soft starting method. This method enables the motor to automatically increase the starting resistance when starting, which reduces the starting current and the impact on the grid. And the mechanical characteristics become hard. When running, the starting resistance returns to normal, which makes the running efficiency high. First, this paper introduces the working principle of soft-start BDFM, and gives several designs of stator winding and rotor winding(RW) for comparative analysis. Then, the two-dimensional transient magnetic field analysis method is used to analyze the magnetic field changes. Finally, a test prototype was developed and an experimental platform was built. Under soft starting and asynchronous starting, the no-load and load starting performance of the soft-start BDFM is studied through simulation and experiment. The results confirmed the feasibility of the design.