IMPERFECTION OF THE PWM INVERTER AND ITS EFFECTS ON THE OUTPUT VOLTAGE VALUE.

Abstract

During the control of the induction machine, the speed or magnetic flux sensors are often replaced by the software ones. The Vds and Vqs desired voltage, generated at the controllers outputs, are supposed known with precision. That is to say, they are the truth image of the real voltage applied to the machine phases. In this paper, we will justify by experiment that it is not valid. Especially at the very low speeds, as the imperfections of the converter due to the dead time, connecting wire and the transistors drop voltage can introduce a considerable error on the real voltages. Initially, we give a theoretical formulation of these two types of voltage drops. Then, we solved the problem by compensating them at the entry of the inverter control block. Lastly, we give experiment results highlighting the two types of voltage drops before and after their corrections. More than, experimental results concerning an induction machine field-oriented control, functioning at low speeds, is given. The influence of the imperfections is highlighted by observing the evolution of the Park voltage components Vds and Vqs applied really to the machine and those, theoretical, generated by the control.