Dual voltage source inverter topology extending machine operating range

Field weakening operation of an electrical machine is a conventional method to extend the angular velocity range of a system above the peak output voltage of the inverter. A downside, however, is that an increased reactive current is required that creates losses but no output torque. A dual voltage source inverter topology is proposed, capable of driving an electrical machine without weakening its field in an extended speed range. For this purpose, a second inverter fed by a capacitor only is connected to the open-end side of the machine windings. Charging the floating capacitors is realized by adding an AC zero sequence current to the regular machine currents. The operating principles of the presented topology are demonstrated, showing their possible advantages when driving an electrical machine. Simulation results confirm the proposed ideas.