Because of the more and more importance given to electrical energy as a
primary source of energy for the economic and social development, electrical drives are nowadays the heart of most industrial processes and strongly contribute to the evolution of the industrial civilization. These drives are indeed able to provide the needed energy both for low power applications, such as household appliances, and high power systems in transportations or manufacturing machines. Due to their rising importance an efficient and reliable control system for electrical machines has become of extreme importance both to improve the performance and to reduce the energy consumption. In the last years more advanced technical solutions able to obtain the same performance of traditional systems, without using any sensor (sensorless), have been introduced into the market. Only the methods exploiting the injection of additional signals into the motor supply can be used with low and zero speed operations,