Based on previous investigations it is shown that the accuracy of online stator resistance monitoring of AC-machines fed by PWM inverters when using the superposition method suffers from dead time effects. A new and simple correction procedure is proposed to achieve high measurement accuracy without using temperature sensors. No additional hardware is required for this method. Experimental results are presented.

In this study, power quality coefficients that determine the distortion of electrical systems are established. The power factor is chosen as a universal criterion for electromagnetic and electro-energetic compatibility of distorted sources and distorting loads. Mathematical expressions are obtained for its calculation in various cases of electrical systems distortion. As an application example, power balances and power factors of a variable frequency asynchronous drive system are considered. The criterion: the power factor not only determines the energy and electromagnetic compatibility of the drive with power supply, but it also evaluates drive efficiency. Experimental studies were carried out under usage of inexpensive, commonly used measuring devices both on the grid side of the frequency converter and on the asynchronous motor side. The studied coefficients were determined in two ways: measuring instruments and analysis of oscillograms. The second method for determining the above coefficients from oscillograms of currents and voltages also requires finding the total harmonic distortion (THD) of currents and voltages for the corresponding load adjusting points. The similarity of the obtained results shows that both of these methods can be applied. According to the operating mode of the load, the criterion is calculated as an average range in a certain range of speed control, or it is determined by considering a given tachogram of speed changes. The results of experimental studies confirm the correctness of the theoretical provisions.

A possible reason for a low power quality at the output of a 132 MW wind farm is investigated. A resonant circuit formed by the wind farm components is found to be responsible for a high level of the dominating 7th current harmonic. Various compensation strategies are proposed and analyzed.

The article argues that the search for effective tools to ensure the economically secure future of energy companies and their development in the context of green transformation is necessary due to the speed of global transformations, the priority of reducing dependence on fuel and energy imports, the development of renewable energy sources, the instability of the environment for the functioning of energy companies (as a result of russia’s full-scale invasion of Ukraine) and their position both on the Ukrainian and European energy markets. The reality of the energy sector in the country and the steps for the recovery of the energy companies determined by the Economic Recovery Plan of Ukraine were analyzed. The evidence shows that the legislative amendments aimed at stabilizing the energy sector and solving key issues lack efficiency and cannot ensure the vital activity of energy enterprises and their development in the conditions of climate-neutral transformation. A methodology was proposed to assess the progress of the carbon-neutral development of energy companies, which should become the basis for attracting ESG investing. The vectors for creating a favorable environment for environmental, social, and governance (ESG) investing were identified as a unique opportunity to ensure the economically secure future of energy companies and their development in the context of green transformation.

A new source for the DC current offset in the PWM inverter-fed loads is found. A significant irregularity in dead time voltage compensation due to a very small offset in phase current measurement is the cause for it. In the phase currents and voltages, high DC offsets appear at low current magnitudes, which lead to a first torque harmonic in the drive. Recommendations how to avoid or compensate this effect are given in the paper.

Current harmonic production of a 5 MW offshore wind turbine prototype is investigated on an onshore test site. On the PCC an atypical high level of the sixth harmonic current was measured. The evaluation of the existing configuration for future extensions with other wind turbines requires the investigation of this effect. Therefore the existing technical structure with medium voltage cable connection and parallel double-tuned harmonic filter is analyzed. The sixth harmonic generation through asymmetrical loads is shortly introduced. It is shown, that the reason for the high level of sixth current harmonic is not a series-resonance, but an undesired additional effect caused by the double-tuned filter, which damps the uneven harmonics. Measurements confirm the theoretical approach.