Design of a Medium-Voltage High-Power Brushless Doubly Fed Motor with a Low-Voltage Fractional Convertor for the Circulation Pump Adjustable Speed Drive

The brushless doubly fed motor (BDFM) shows great potential for use in large medium-voltage adjustable-speed drive (ASD) systems due to its high reliability and cost benefits of a partially rated low-voltage power electronics converter. However, undesired performance caused by rich useless space-harmonics restrict the application of the BDFM in medium-voltage high-power ASD systems. In this paper, a medium-voltage wound rotor BDFM consisting of specially designed stator and rotor windings is developed. Firstly, the wound rotor with unequal turns and unequal pitches is designed and then compared with a nested loop counterpart. In addition, a 10 kV single-layer winding with shifted slot number in the stator is proposed to further reduce the space-harmonics by equivalent pitched effect. The finite element model of the BDFM is established to analyze electromagnetic performance and the influence of magnetic slot wedges. A lumped parameter thermal model is developed to quickly evaluate the average temperature rise of the proposed prototype. Field tests of driving a circulation water pump in a steel rolling mill were conducted to validate the feasibility of the proposed scheme.