DTC of Three-Level NPC Inverter Fed Five-Phase Induction Motor Drive With Novel Neutral Point Voltage Balancing Scheme

In this paper, direct torque control (DTC) of fivephase induction motor (FPIM) is implemented using three-level neutral point clamped (TL-NPC) inverter. One of the advantages of three-level inverter over two-level one for DTC operation is the low torque ripple. Also TL-NPC inverter through space vector modulation technique gives low dv/dt transition with better voltage waveform. By applying conventional lookup table for DTC, the TL-NPC inverter does not ensures lower dv/dt transition. In this paper, a novel switching scheme for DTC of FPIM using TL-NPC inverter is proposed that ensures the low dv/dt transition and balancing of dc-link capacitor voltages of TL-NPC inverter. To form the lookup table for DTC operation, instead of using voltage vectors directly, virtual vectors (VVs) are utilized. Two switching states are used in one sample time to generate a VV in αβ plane, which gives zero resultant voltage in xy plane. The switching strategy ensures low number of transitions to reduce the switching losses. The switching state redundancies are used in a novel way to balance the dc-link capacitor voltages without using any additional hardware. The proposed technique to balance the dc-link capacitor voltage gives lower switching frequency. The MATLAB/Simulink environment is used for the simulation and the results are validated through experiments.