Initial rotor position detection in synchronous machines using low frequency pulses

It is well-known that in the area of encoderless control methods for AC-drives a single approach is not capable to cover all speed ranges and all types of machines. Therefore, a combination of several methods is necessary. Especially in the case of electrically excited synchronous machines, the methods proposed for the low speed region and for the detection of the initial rotor position fail for many types of machines and demand for new solutions. In this paper, a method for the identification of the initial rotor position by injecting low frequency pulses is proposed. After the identification of the initial position, the drive is directly started with the help of a conventional high-speed method and rides through the critical speed region without any difficulties. The new method is designed for a reliable operation in a large group of electrically excited synchronous machines. Measurement results as well as a concept for the parameterization of the model are included in this paper.