The brushless doubly fed machine (BDFM) with multi harmonic combined starting changes the motor stator winding connection mode, so that the excitation current generates the fundamental magnetomotive force (MMF) in the air gap and the harmonic MMF of different pole pairs in the same direction as the fundamental wave. The fundamental MMF cooperates with these harmonic MMFs to interact with the composite coil winding on the rotor to reduce the starting current and increase the starting torque, thereby improving the starting performance of the motor. This article establishes the mathematic model of the MMF of the stator winding of the motor through detailed derivation, analyzes the MMF harmonic content of the motor when starting; and analyzes the air gap flux density of the motor when starting to study its starting performance. Simulation and test results show that the use of multi harmonic combined starting method reduces the starting current of the motor, increases the starting torque, and makes the motor have better starting performance.

Multi harmonic combined starting, Brushless doubly fed machine (BDFM), Composite coil, Magnetomotive force (MMF), Starting performance