Closed-loop compensating sensors versus new current derivative sensors for shaftsensorless control of inverter fed induction machines

The technology of shaft-sensorless control of ac machine has been developed through the past decade. Some improvements have been made on the evaluation of position information out of so-called nonmodel based methods, which do not have the drawback of the mathematical models. However, the improvement in the field of the current sensors was not focused on mechanical sensorless control and, thus, has not brought that much enhancement for this particular topic. With the introduction of the current derivative sensor (CDI) a new concept specialized for sensorless control has been proposed. The quality of the control signals can be increased, and the drawbacks with the measurement sequences needed for the detection cycles are reduced with the help of inexpensive and easy-to-use derivative current sensors.