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1. Introduction
To meet the need of reducing the cost of industrial systems, sensorless control applications on electrical machines are increasing day by day. In variable speed control systems, the induction motors are more preferred to DC motors because of its low-cost, requiring less maintenance, robust construction and smaller size per kW output power. Although their many advantages, they also have disadvantages such as complex driver structures and controller algorithms (Demirtas et al., 2018). The driver circuit is simply combined of six semiconductor switches (metal oxide semiconductor field effect transistor or insulated gate bipolar transistor). To generate gate signals, vector control or voltage/frequency (V/f) control methods are commonly used in industrial systems. Nowadays, the vector control method is more preferred for the gate controller algorithm to the V/f method because of its better performance at low speeds.
The most important way to reduce the cost of variable speed control systems is to get rid of the optic or magnetic-based position sensors. The angular velocity of the motor can be calculated without using a sensor. The mathematical model of the motor is used to achieve this. First of all, the mathematical model is established. Then, phase currents and voltages are obtained from current and voltage transducers which are quite cheap compared to the position sensors. The obtained current and voltage data are used in the model to estimate the motor position. This process is called model reference adaptive system (MRAS)-based position observer.
Many methods can be applied for motor position observer such as Luenberger (Orlowska-Kowalska, 1989; Kwon et al., 2005), kalman filter (Bolognani et al., 2003), sliding mode (Qiao et al., 2013; Foo and Rahman, 2010; Benchaib et al., 1999; Jiacai et al., 2012), artificial neural network (Gadoue et al., 2009; Hussain and Bazaz, 2016), fuzzy logic (Karanayil et al., 2005; Gadoue et al., 2010) and robust control (Mohamed, 2007; Yao et al., 2014). There are many studies in the literature about observer, sliding mode control and fractional control used in electric motors. Di Gennaro et al. (2014) presented a sensorless control scheme for induction motor with core loss. In this study, two sensorless control schemes (high order sliding mode twisting algorithm and super-twisting...