Section: New Results

Observability analysis of AC electric machines

Participants : Mohamad Koteich [CentraleSupelec, L2S, Renault] , Guillaume Sandou [correspondent] , Gilles Duc [CentraleSupelec, L2S] , Abdelmalek Maloum [Renault] .

High-performance control of electric drives requires an accurate knowledge of the rotor position and/or speed. These mechanical variables are traditionally measured using sensors, which increases the cost and reduces both the robustness and the reliability of the system. This emphasizes the importance of electric drives control without shaft sensors, often referred to as sensorless control : it consists of replacing sensors with a state observer algorithm, that estimates the desired mechanical variables from currents and voltages sensing and based on the system’s model. Nevertheless, before designing a state observer, the observability of the system should be examined, that is, it should be checked whether the states to be estimated can be reconstructed, unambiguously, from the input/output signals of the system.

This work addresses the modeling and the observability analysis of electric drives in the view of mechanical sensors removal. Firstly, electrical machines models are elaborated, and it is shown that a unified modeling of alternating current machines is feasible, for the purpose of designing unified control and estimation strategies. The observability of the machines’ models is next studied in the view of sensorless control. The local instantaneous observability theory is applied, which enables us to formulate physically insightful analytic conditions that can be easily interpreted and tested in real time. The validity of the observability conditions is confirmed by numerical simulations and experimental data, using an extended Kalman observer. This work contributes to novel outlooks on the sensorless alternating current drives and to a deeper understanding of its properties, in order to develop higher performance estimation techniques in the critical operating conditions (mainly at standstill and/or zerostator-frequency). The concepts introduced throughout this work, such as the equivalent flux and the observability vector, with the obtained results, open new horizons in a domain that seems to become mature enough [48] , [76] , [46] , [49] , [45] , [15] , [16] , [91] , [92] , [47] .