A Sensorless DTC Scheme for 60-Pulse AC-DC Converter Fed 5-Level Six-Leg NPC Inverter Based Medium Voltage Induction Motor Drive

A new approach to improve the power quality of medium voltage induction motor drive (MVIMD) at both utility and drive end is presented. Here, 3-multi-winding transformers (MWT) (T
₁
, T
₂
, T
₃
) are utilized and each MWT converts 3-phase input AC-supply into two isolated 5-phase AC-supplies with unique (18°) phase-shift among them. Moreover, due to unique (±6° and 0°) angle in the primary sides of these MWTs, the line current drawn from the grid has 60-pulses. By applying this technology, the input current harmonics are decreased to well below the requirement of the IEEE 519 standard. This 60-pulse AC-DC converter gives 6-isolated DC-supplies, which are input of a 5-level six-leg neutral point clamped (NPC) inverter feeding an induction motor. A modified direct torque control (DTC) strategy is used in this study for 5-level six-leg NPC inverter fed induction motor drive (IMD). Because of it, this IMD has better performance than the existing IMD. The system performance is evaluated using MATLAB-Simulink software and is then experimentally verified on a prototype developed in the laboratory under all required operation of IMD to validate the performance of the system.