Few industrial applications are capable of returning energy into the ac distribution system on a continuous basis. For example, mining companies usually transport their product downhill for few kilometers before processing it. In such cases, the drive maintains the transportation belt conveyor at constant speed and takes the kinetic energy. Due to the large amount of energy and the continuous operating mode, the drive should be capable of taking the kinetic energy, transforming it into electrical energy, and sending it into the ac distribution system. This would make the drive a generator that would compensate for the active power required by other loads connected to the electrical grid. The system we have considered up to now uses a sensor to measure position of the rotor. In many cases it is impossible to use sensors for speed measurement, perhaps because it is either technically impossible or extremely expensive. For example, we can mention the pumps used in oil rigs to pump out the oil. These have to work under the surface of the sea, sometimes at depths of 50 meters, and getting the speed measurement data up to the surface means extra cables, which is extremely expensive. Cutting down the number of sensors and measurement cables provides a major cost reduction. The two level inverters with levels 0 or have some limitations in operating at high frequency in high-powerand high-voltage applications due to switching losses and constraints of device ratings. The multilevel inverters can alleviate this problem. It is easier to produce a high- power, high- voltage inverter with multilevel structure because of the way in which device voltage stresses are controlled in the structure. Increasing the number of voltage levels in the inverter without requiring higher ratings on individual devices can increase the power rating. The unique structure of multilevel voltage source inverter's allows them to reach high voltages with low harmonics without the use of transformers or series connected synchronizing devices. As the number of voltage level increases, the harmonic content of the output voltage waveform decreases significantly. The behaviour of Induction motor during motoring and re-generating mode with accurate speed control without the aid of sensors, when fed by a multilevel inverterwith space vector pulse width modulation (SVM) is presented in this paper.

Keywords: Induction Motor Drives, Vector Control, Sensor less Control, Multilevel Inverter, Extended Kalman Filter, State Vector, Re-generation, Pulse Width Modulation, Rotor speed estimation, Space Vector Modulation.