Effects of Stator Winding Configuration on the Voltage Balancing of DC-Link Capacitor of Six-Phase Three-Level NPC Inverters

A six-phase machine can be classified according to the distribution of the magnetic axes of its stator phases, which may follow either a symmetrical or asymmetrical arrangement. These two stator configurations result in different degrees of freedom for the system, which in turn affect design criteria, control strategies, and fault management of the machine. When a six-phase machine is connected to a three-level NPC inverter, the stator configuration plays a significant role in balancing the DC bus capacitors. This paper investigates the impact of the stator layout on the low-frequency oscillations of the voltage across the capacitor. The analysis encompasses the control systems of electric machines and modulation strategies for both symmetrical and asymmetrical stator configurations. The experimental validation is carried out using a 12-phase induction machine that can be reconfigured as a six-phase machine with either symmetric or asymmetric stator winding.