In the case of adjustable drives systems with an induction motor (IM), a harmonic regime is manifested, whose knowledge and analysis are always necessary. However, most studies are focused on specific drive systems, the results of these works being valid only for drive systems of the same type. The objective of the present paper was to determine the harmonics consequences not only on the technical characteristics of the IM but also on the power supply as well as on the mechanical drive system. Thus, by initiating a methodology for estimating the consequences of each voltage harmonic separately, the aim was to substantiate a generally applicable method, which allows the evaluation, for any application, of the overall effects of the harmonics. The main feature of the method used in this paper was the consideration of the presence of voltage harmonics in the stator voltage of the IM, of certain frequencies and with certain levels, and the determination of all the electrical and mechanical consequences on the model of the drive system. It has been found that the harmonics of the IM affects the power quality (PQ) of the power supply, having significant influences also on the mechanical part of the drive system.

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The design methods of earthing from standards recommend the choice of electrode lengths and propose that the distances between electrodes to be 1-3 times larger than their length. The number of electrodes is determined from the condition of achieving the design earth resistance, while the design ends with the choice of one of the variants. This paper presents the methodology for calculating the earthing system with cylindrical, vertical electrodes arranged in a line. The main variables are the length and the number of earth electrodes, as well as the distance between adjacent ones. Firstly, a set of technologically advantageous values for the earth electrode length is established (e.g., 10 values). For each value of the electrode length and different numbers of electrodes (e.g., 11 values), the distance between adjacent electrodes is determined (e.g., for 110 cases), which leads to the design value resistance. Finally, optimal solutions are identified based on the five optimal applied criteria. The proposed optimal criteria for earthing design are the footprint area, the total earthing volume, the total dispersion surface, the total metal mass, and the investment costs. Comparing the optimal solutions with other technically possible solutions clearly highlights substantial savings concerning space, material, and cost.

The aim of this paper is to present a new speed control structure for induction motors (IM) by using fuzzy-logic based speed controllers. A fuzzy controller is designed to achieve fast dynamic response and robustness for low and high speeds. Different types of membership functions of the linguistic variables and output/input characteristics are analyzed. A simple but robust structure enables a wide range speed control of the driving system. The rotor flux field oriented control (FOC) is realized by using a flux observer based on the IM model with nonlinear parameters. The control is extended to operate also in the field weakening region with an optimal rotor flux regulation. The control structure was implemented on a computer system, based on a fixed point digital signal processor (DSP). To verify the performances of the proposed driving system, simulated and experimental results are presented