A new four-level dual inverter fed open-end winding induction motor drive

It is known that Four-level inversion can be achieved with two two-level inverters feeding an open-end winding induction motor from both ends with unequal DC link voltages in the ratio of 2:1. It is also known that this power circuit configuration could result in the overcharging of the DC-link capacitor corresponding to the inverter operating with the lower voltage. In this paper, a new power circuit topology is proposed, wherein, a rectifier-inverter combination is nested, or embedded, in the conventional two-level inverter configuration. The output of the conventional two-level inverter feeds one end of the open-end winding induction motor, while the output of the nested rectifier-inverter combination feeds the other end. By a judicious choice of the DC-link voltage of the embedded rectifier, it is possible to obtain a four-level drive, while avoiding the overcharging of the DC-link capacitor corresponding to the inverter operating with the lower DC input voltage. Also, the problem of zero-sequence currents, commonly encountered in Open-end winding induction motor drives, is avoided by resorting to a carrier based PWM scheme. This PWM scheme automatically ensures that the inverter connected to the higher DC-link voltage is switched with a lower frequency, compared to its low voltage counterpart.