Power systems proliferated by distributed generation sources are becoming increasingly prone to frequency and voltage disturbances. These problems are exacerbated in microgrids since they have fewer intrinsic disturbance-rejecting measures and features. To increase the reliability and stability of emerging power systems, the advanced control structures of the distributed generation sources based on power electronics devices must be deployed during suboptimal operating conditions. The aggravating circumstance is that both voltage and frequency excursion can be transient and long-lasting and consequently can occur simultaneously. The algorithm proposed in this paper integrates voltage support (nominal voltage restoration) and inertia emulation features with the comprehensive current references management scheme, thus securing improved grid operating conditions during several different faults and occurrences. The control algorithm is developed and tested in the context of a small microgrid, but it can be applied with minimal alterations in traditional grids, also. To prove that it is possible to decrease simultaneously voltage unbalances and frequency deviations, a test microgrid consisting of a synchronous generator, photovoltaic system, battery storage system, and controllable balanced and unbalanced loads was developed in a hardware-in-the-loop environment.

In this paper, an effective procedure for broken rotor bar (BRB) fault detection in a three-phase squirrel-cage induction machine (SCIM) is proposed. This approach relies on a motor current signature analysis (MCSA) by observing the specific fault-related current component generated by applying the DC injection braking method. Unlike the traditional MCSA, which is commonly focused on the detection of BRB sidebands around the fundamental current component, the proposed methodology introduces a new BRB feature in the current spectrum which makes it much easier for identification. The distinctive time-frequency evolution pattern of this feature provides the reliable identification of BRBs, even under no-load operating conditions, thus overcoming the major drawback of traditional MCSA-based methods. Fault severity classification is easily performed through the magnitude inspection of the BRB fault-related current component. In addition, the proposed approach does not require high-complexity signal processing algorithms to achieve reliable results. The proposed concept is presented theoretically, assisted by a magnetically coupled multiple circuit model of the SCIM, both with healthy and faulty rotor bars. Finally, the experimental tests validate the proposed methodology and demonstrate its effectiveness and usefulness.

Short‐circuit faults and asymmetrical power production and consumption result in the appearance of unbalanced voltages. The change in voltage profiles could result in grid‐connected converter's overcurrent protection triggering if power references are kept at the pre‐disturbance level. This study provides a framework for current references calculation that can result in virtually any active and reactive power profiles that are within the domain of the converter's physical capabilities. This is accomplished by introducing three references calculation algorithms, which are all based on the same underlying concept. The first algorithm gives the grid operator the option to choose to prioritise the production of either active or reactive power and to curtail the power production only to the extent that converter's current ratings are not surpassed. Simultaneously, the oscillations in one of the powers are managed. The second approach also provides power production prioritisation feature, but here power production is realised through adjustable ratio between positive and negative current components. The third scheme is an enhancement of the previous two schemes and allows for the constant power factor to be produced before and during the disturbances. Distribution network model emulated in the hardware‐in‐the‐loop environment was used for the validation of proposed solutions.

With the increase in power installed from distributed generation sources (DGS), many problems have appeared following the utilisation of novel topologies and structures. Higher-level controllers for the safe operation of power grids with a high penetration of DGS must be developed. This task becomes difficult as the size and complexity of modern power systems have increased. The development and testing of these systems under strict human supervision controlling each step of the testing procedure is no longer viable. This paper presents a comprehensive integrated platform based on an HIL emulator for the development and testing of electric power systems rich in DGS. Essentially, DGS is considered a controllable black-box system. A detailed calculation of the power references for an arbitrary DGS is shown. The paper also describes the utilisation of enhanced Python scripting which was designed to load all network-related data, start the emulation, collect the data, and generate reports. Furthermore, fully developed controller built-in oscilloscope functionality is introduced. The incorporated oscilloscope facilitates non-intrusive DGS controller data acquisition and analysis, reducing the need for external measurements. The proposed framework was verified by a case study in which a grid topology consisting of 26 nodes was emulated on parallel CHIL infrastructure. Four active and twenty-two passive nodes were instantiated and their reaction to a distribution network grid faults was examined. DGS converter control was executed in external controllers outside of the dedicated HIL environment. All DGSs were governed by different control strategies, regarding maximisation of active/reactive power production, minimisation of the active/reactive power oscillations, adjustable positive/negative components ratio, or without any limitations under voltage disturbances. Real-time experiments confirmed the usefulness and flexibility of the proposed framework concept.

Power electronics devices are highly dynamic and nonlinear systems governed by complex control algorithms. In addition, power electronics converters must demonstrate high reliability and must be safe to operate, although in some applications they condition dangerously high power levels. Therefore, the development, evaluation and deployment of these systems traditionally had to be meticulously conducted, using specialized tools and approaches. With the proliferation of power electronics devices into the domain of power systems, in form of distributed generation sources, the mentioned tools and approaches had to evolve further. Consequently, a wide range of representations of the addressed systems within various digital platforms is nowadays at disposal of researchers and engineers. These representations, designated as digital twins, facilitate, and sometimes simply make possible, expeditious development and comprehensive evaluation of increasingly complex power electronics-based systems. This chapter catalogues the most important digital twin types, explicates their advantages and disadvantages and addresses their applicability. Hence, it could be regarded as a set of guidelines on how to choose appropriate digital twin type and digital twinning platform for some particular research and engineering problem. Also, details on how digital twins of distributed generation sources will be created and utilized in near future are provided.