Three level rectifier versus three level inverter with DTC controlled induction motor

A three level NPC-rectifier versus three level NPC-inverter with direct torque controlled asynchronous motor is examined. Three level inverters have the problem of the DC-link voltage balance, especially if DTC control is considered. To reduce the problem both DC voltage and the potential of its middle point are controlled through a three level V.S.R. An appropriate feedback control is proposed to make the V.S.R. able to impose in the network nearly sinusoidal currents with unity power factor. The proposed control scheme is verified by means of simulations under significant conditions; the results are presented and discussed.