## 1 Introduction
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline
**Techniques** & **Types** & **Benefits** & **Drawbacks** \\ \hline \multirow{4}{*}{Open Loop} & Direct calculation [4] & Fast, dynamic, and Simple & Parametric variation error \\  & Determination of stator & & Inaccurate at high stator \\  & inductance [5] & Zero speed estimation & current, valid for salient motors \\  & & Back EMF integration [7] & Fast, Robust, and accurate at high frequency & Difficult to calculate back \\  & & & high frequency & EMF, not accurate at low speeds \\ \hline \multirow{4}{*}{Closed Loop} & EKF [9] & Reduced computation time and noise rejection & Low speed, poor performance \\  & MRAS [10] & Adaptation at high speed, machine model not required & Parametric surface \\  & SMO [11] & Robust, parametric invariance and no steady state error & Stand still or zero speed \\ \hline \multirow{4}{*}{Non-ideal property-based} & Low Frequency injection [12] & Applicable even for non-salient motors & Dynamic performance is poor, saturation problem \\  & & & Not applicable for higher \\ \cline{1-1}  & & & not required & inertia motor, slow dynamic \\ \cline{1-1}  & & & response \\ \cline{1-1}  & INFORM [14] & Parameter invariance & Flux distortion and current \\ \cline{1-1}  & & & ripples cause estimation error \\ \hline \end{tabular}
\end{table} 
Table 1: Comparative Literature Survey on State-of-the-Art Techniques. considered and controlled by the Finite Control Set-Model Predictive Control (FCS-MPC). Inverters switching states are used to optimize the observer states of the motors and the FCS-MPC can efficiently handle the discrete nature of the switching states in the microprocessor [17]. In modern state estimation techniques of the motors, hybrid methodologies are employed by combining any of the two previous matured techniques. [PERSON] et al. described the application of UKF and Fuzzy UKF (FUKF) with an elastic connection for the estimation of parameters and mechanical state variables of the AC drives [18]. A suitable adaptation mechanism with IP controller reinforced by two supplementary feedbacks in the form of a cascade control structure is inspected [18]. However, the control structure performance degrades by the existing estimation error. Introduced hybrid modification improves the quality of the estimation. A fuzzy system has been designed based on linguistic rules. The authors reported better performance of the FUKF compared to the UKF; however, the former one requires pre-feed data of motors' nonlinear behavior. [PERSON] et al. introduced a novel technique for the surface-mounted type of PMSM drives called Hybrid Dual-Mode Control (HDMC) that contains two control modes to find appropriate performances of the steady-state and transient response [19]. The HDMC is a hybrid combination of two techniques, which inherits the excellent steady-state routines of the Field Oriented Control (FOC) and the quick responsibility of the Deadbeat Predictive Control (DBPC). The combination of MPC-EKF has been tested previously; however, [PERSON] et al. suggested that UKF has a remarkable advantage over EKF [7]. The PMSM model is highly nonlinear, and states' estimation without sensors involves complexity in implementation due to noisy signals of the PWM [20]. The MPC handles the selection of the proper sequence of states for the inverter; therefore, the MPC increases efficiency and reduces time compared to the FOC method. Moreover, the MPC has many advantages, such as easy modeling, simple principle, constraints handling, and strong robustness [21]. Similarly, the UKF is very robust against parametric variation and handles the measurement noise and system noise. Optimal estimation of the states in Kalman filters is based on least-squares techniques. In sensorless motor drive control, there is a significant impact of parametric variation, inverter nonlinearities, and zero/low-speed operation on the stability of the control system. Moreover, in a high-speed region, a high observer's bandwidth is required.