Abstract
The subject of this paper is gains selection of an extended induction machine speed observer. A high number of gains makes manual gains selection difficult and due to nonlinear equations of the observer, well-known methods of gains selection for linear systems cannot be applied. A method based on genetic algorithms has been proposed instead. Such an approach requires multiple fitness function calls; therefore, using a quality index based on simulations makes gains selection a time-consuming process. To find a fitness function that evaluates, in a short time, quality indices based on poles placement have been proposed. As the observer is nonlinear, equations describing the observer dynamics have been linearized. The relationship between poles placement and real dynamic properties has been shown. A series of studies has been performed to investigate the influence of the operating point of the machine on the dynamics of the observer. It has been proven that rotor speed has a significant impact on the placement of the poles and the observer may lose stability after a rotation direction change. A method of gains modification to maintain symmetrical properties of the observer for both directions has been presented. Experimental studies of the observer during machine reverse in the open and closed-loop control system have been performed. The results show that the observer can be implemented in a sensorless drive, using the proposed gains selection method.
Highlights
The availability and low price of digital signal processors and microcontrollers have increased interest in the development of controlled electric drives over recent decades
Rotor speed and external torque can change in a wide range, during gains selection, it must be taken into account and the conditions of the stability of the observer must be satisfied for all possible values of the rotor speed and load torque
Speed observer based on the extended model of an induction machine requires a selection of 12
Summary
The availability and low price of digital signal processors and microcontrollers have increased interest in the development of controlled electric drives over recent decades. Induction machines are commonly used as generators in wind turbines and micro hydro installations or as motors (that operate as generators during energy recovery) in electric vehicles Such applications require advanced control systems where state estimation is necessary. Model parameter robustness as well as good properties at a wide rotor speed range, including low speed, are the main benefits of the Luenberger based observers. Their complexity is low such observers can be implemented on modern microcontrollers, compared to e.g., Extended Kalman Filter which requires matrix product and inverse [24,25]. A lack of symmetry of the observer after rotation direction change has been proven as well as a method of gains modification to maintain that symmetry has been explained
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