A microgrid (MG) is a cyber-physical system that facilitates integration of several distributed renewable energy resources. In the last decade, several efforts were made to standardise the framework of a cyber-physical MG network and its control structure. In this perspective, various studies discussing the different control techniques are reported in the literature. However, a comprehensive and systematic review of a cyber-physical MG is discussed rarely. In this study, a comprehensive review of a MG architecture and hierarchical control structure in both islanded and grid-connected modes are presented. The hierarchical control of the MG includes primary, secondary, and tertiary control. Recent studies provide significant opportunities in dividing the control task among various layers resulting in a distributed framework. This study analyses the cyber and physical networks separately while discussing the primary, centralised, and distributed secondary control levels with their merits, demerits, and typical applications. A Venn diagram analysis is also presented that clearly distinguishes the primary control scheme in different research sub-areas. Furthermore, the MG communication structure, protocols, design, constraints, and cyber security are also reviewed systematically. Finally, future trends are summarised based on the state-of-the-art MG research.

For series-compensated line, the distance relay finds its limitations during voltage inversion, current inversion, load encroachment, power swing and balanced fault during the power swing. These limitations can be overcome by wide-area backup protection schemes. This study proposes a novel fault detection technique utilising the synchrophasor data of voltage and current signals at system protection centre. The algorithm compares the phase angle difference between positive-sequence voltage phasor under system intact condition and real-time positive- or negative-sequence current phasor, which is computed from the synchronised data obtained from phasor data concentrator after identifying the possible critical buses to which the faulted line is connected. Different cases of fault type, distance and resistance have been considered to validate the proposed scheme with 3-generator, 9-bus western system coordinating council using MATLAB/Simulink platform. The results justify the suitability of the proposed scheme to be deployed for achieving more reliable performance.

The frequency control is the mandatory task in a modern power system because of load demand variation and the integration of renewable energy sources (RESs). The main objective of automatic generation control (AGC) scheme is to maintain the balance between generation and load demand. This study proposes a graphical robust characteristic ratio assignment (RCRA) approach for PIDA controller tuning based on maximum sensitivity () for AGC. The basic feature of this graphical approach is that characteristic ratios () in RCRA scheme are calculated in terms of . The important part of this design is that the analytical expressions for coefficient gains of PIDA controller are derived in terms of and system parameters. Here, the non-reheat steam-turbine and hydro-turbine based single and multi-area power systems are considered for validation of the proposed control scheme. The critical issue in controller design for a hydro-turbine based power system is the non-minimum phase behaviour. The robustness and performance of RCRA-PIDA controller are examined under system non-linearities, parametric uncertainty and disturbances. Further, the performance of proposed approach is evaluated in the presence of RESs. Finally, it is observed that the proposed control approach performs better in comparison to the recently published control schemes.

The controlled islanding problem is typically considered only for pure ac power systems, with the ultimate objective of either minimising power imbalance or power-flow among islands. However, as ac/dc hybrid power systems are becoming popular worldwide, current controlled islanding schemes should be redesigned to take into account the presence of high-voltage dc (HVDC) links, possibly connecting different islands. Accordingly, in this study, the authors solve the classic islanding problem combining HVDC power modulation with the conventional ac cutset search. The flexibility of the HVDC allows the authors' strategy to jointly capture the previously mentioned objectives, and provides even lower power imbalances than the minimum imbalance strategy, at a relatively small cost of increasing power-flow impact. Then, the optimisation problem is formulated as a mixed-integer linear programming problem, which can be conveniently solved with existing commercial solvers. Finally, they validate their proposed strategy in two case studies, corresponding to a modified IEEE-118 system and to the China Southern Power Grid system. In both cases, dynamic simulations show that their proposed approach outperforms classic algorithms where the presence of HVDC power modulation is not explicitly taken into account.

This study describes the research and design of a novel and compact very low frequency cosine-rectangular (VLF-CR) and damped alternating current (DAC) voltage generator that can be used to test the insulation condition of the medium-voltage power cables. Further, a complete system based on a voltage multiplier (VM), which can be cascaded to increase the output voltage, is proposed to simultaneously realise VLF-CR and DAC voltages for the withstand voltage and offline partial discharge (PD) tests, enabling the test system to be lightweight and efficient. The system principle and operating characteristics associated with the generation of two different voltages are analysed in detail according to the new circuit topology of the proposed generator. Furthermore, oscillation suppression and multiple output units are considered to improve the voltage waveform and provide power supply to the VM module, respectively. A laboratory prototype is also developed and tested. Finally, the integrated generator is used for the PD testing on cables with artificial defects, verifying the practicability of the proposed system.