## 1 Introduction  
A significant share of industrial mechanisms, including pumps, fans, air blowers, and compressors, are driven by electric motors, which are connected directly to a power grid without intermediate power converters and are launched using a direct start [1; 2; 3]. The vast majority of these motors are induction motors (IMs) [1; 2; 3]. Despite all the well-known induction motors' advantages, they expose significant losses during the rotor winding, which diminishes their energy efficiency class [4]. Line-start permanent magnet synchronous motors (LSPMSMs) do not have noticeable rotor winding losses at steady state, which increases their energy efficiency class in comparison to induction motors. LSPMSMs are available on the market and mostly are employed in pump and fan units [5; 6; 7]. Figure 1 shows a comparison of IM and LSPMSM designs. LSPMSMs are of great interest to researchers because of their high energy efficiency due to the growing interest of manufacturers in energy-efficient units [8; 9; 10; 11]. The LSPMSM model's performance can be improved by using computer-aided design optimization procedures [12; 13; 14]. There are studies investigating LSPMSM performance at unbalanced voltage [15]. In [16], the LSPMSM steady-state torque was evaluated by transient analysis using a neural network. Article [17] is devoted to LSPMSM modelling, using a bond graph model [18]. Article [19] discusses the latest LSPMSM design techniques. Article [20] presents an experimental comparison of a 4-pole 5.5 kW LSPMSM with axial and radial fluxes. There are also studies on the effect of LSPMSM rotor design on additional losses [21]. LSPMSMs face some difficulties in starting and synchronization processes, especially with loads with a high moment of inertia [22; 23; 24]. An LSPMSM lumped parameter model [25] was applied to estimate the successfulness of starting and further synchronization, which has been extremely beneficial for the experimental verification of LSPMSM characteristics. However, experimental parameter identification is related to significant obstacles. Evaluation of electrical parameters can be done using a finite element model (FEM) based on known motor constructive parameters [26]. However, this approach requires knowledge of the geometrical details of the motor core, winding data, and the materials it is composed of. This requires access to motor design documentation or irreversible disassembly of motor parts for study purposes, which is not always possible. In the case that the motor constructive parameters are unknown, there are several approaches for determining equivalent circuits parameters applicable for IMs [27; 28; 29; 30; 31; 32; 33] and LSPMSMs [25; 26; 34; 35]: (1) steady-state experiments, such as no-load tests, locked rotor tests, etc., allow individual motor parameters to be determined [25]; (2) computer-aided identification algorithms make it possible to use the transient response to estimate multiple motor parameters, as explained in [34]. Measurement techniques of individual LSPMSM parameters using steady-state experiments include: the stator winding DC resistance estimation; the leakage inductance estimation on sinusoidal voltage operation with rotor extraction; the locked rotor test for rotor resistance and inductance estimation; the DC step-voltage test to estimate the LSPMSM total inductances; and the open-circuit test used for the permanent magnet flux linkage estimation [25]. However, such an approach demands a very high measurement accuracy and relies on many assumptions. The presence of the mutual inductance of the stator winding and the rotor squirrel cage makes it impossible to measure the total inductances at a locked rotor. Further, the total inductances measurement using the DC step-voltage test has low accuracy because of the nonlinear nature of the motor total inductances, which is the result of the presence of main-path saturation and cross saturation in the motor magnetic circuit.