The loss of excitation (LOE) is one of the main faults of the synchronous generator, which may cause serious damages to generator and makes the power system unstable. The main problem to distinguish between LOE and stable power swing (SPS) is a time delay, which is a main part of the detection time in all recent protection methods. This study presents a new method for LOE detection in the synchronous generator, which reduces time delay by half. The proposed method exploits a new index which is based on the variation of the generator output reactive power. It is a combination of the first- and second-order derivative of the generator output reactive power. In this method, after the generator losses its excitation, the proposed index will become and remain negative for a while. To prevent mal-operating under slowest power swing condition, the time delay of 0.85 s is used. The performance of the proposed method is evaluated under different conditions. The simulation results and experimental tests confirm the accuracy and fast operation of the proposed method.

Arc interruption of high voltage direct current (HVDC) circuit breakers (CBs) is one of the main challenging factors for using HVDC grids. To evaluate the arc interrupting capability in HVDC CBs, black box arc models are used to represent the nonlinear arc conductance depending on Cassie and Mayr dynamic arc equations. Extensive simulation studies are carried out to investigate the effect of controlled and uncontrolled parameters on the CB arcing time. A real line represents a part of 500 kV electrical connection systems between Egypt and the Kingdom of Saudi Arabia is simulated to be a faulty load. It is found that the arcing time of the HVDC CB can be reduced by increasing the value of cooling power coefficient (p) and decreasing the value of arc time constant (τ). It is also deduced that the arcing time is reduced by the increase of the commutation capacitance value (C) and decreasing the commutation inductance (L) value and vice versa. Moreover, it is concluded that the arcing time is greatly affected by the fault location and the fault arc resistance () according to fault conditions.

This study presents a model for the activities of the price-maker microgrid aggregator (MGA). In this model, an MGA is considered to aggregate several microgrids (MGs) and be in charge of obtaining an optimal bidding strategy for MGs as well as scheduling their resources and demand. Two price-maker strategies (the marginal and non-marginal strategies for players) are proposed and the robust scheduling and optimal transactions of a price-taker MGA are also obtained in order to analyse different bidding behaviour of MGA. A robust optimisation is used in this model in order to capture uncertainties associated with renewable generation in the worst-case situation. Accordingly, the robust solution is obtained for the optimal scheduling of an MGA participating in the pool-based day-ahead electricity market. The proposed robust bidding strategies and scheduling of a price-maker MGA are obtained considering a hypothetical test system and the results are compared with the bidding strategy and robust scheduling of a price-taker MGA. The results show that the robust scheduling and also the market prices are completely changed for different strategies of the MGA. Also, using the proposed model for the price-maker MGA increases the profits of MGs.

The objective of this study is to identify and eliminate unnecessary iteration loops in the load flow analysis of an active distribution network so as to improve its overall computational efficiency. The number of iteration loops is minimised through the integrated modelling of a distributed generator (DG) and the associated coupling transformer. The DG bus is not preserved in the load flow calculation and the aforementioned DG-transformer assembly is represented in the form of a voltage-dependent negative load at the point of connection to the main distribution network. Thus, the iteration stage that is involved in indirectly preserving the DG in the form of a voltage source or negative constant power load can be eliminated. This, in turn, eliminates the need for multiple rounds of forward–backward sweeps (FBS) iterations to determine the bus voltages. The power characteristics of the DG-transformer assembly are thoroughly investigated through a carefully performed case study so as to assess the general convergence performance of the proposed load flow algorithm. Furthermore, extensive comparative studies are carried out to verify the computational efficiency attained via the proposed DG modelling in the load flow analysis of an active distribution network.

The connection of distributed generation sources to the distribution network has negative effects on the network protection such as; a false trip of non-directional overcurrent relays. In this study, an offline method is proposed to overcome the false trip issue. In this method, the false trip is modelled as a new set of coordination constraints in the optimal coordination problem. For establishing false trip constraints, pickup current setting and characteristic type of relays are selected in addition to the time multiplier setting. Considering false trip constraints in the coordination problem increases the operating time of relays. Therefore, the optimisation is applied to obtain the settings of non-directional overcurrent relays in order to reduce their operating times in addition to resolving the false trip. Also, three new approaches are defined for pickup current selection based on pickup current range. A combination of genetic algorithm and linear programming technique is used to access optimised responses. Finally, the proposed method is implemented on a sample radial distribution network and the results demonstrated that the occurrence of the false trip was prevented and also the operating time of the relays was reduced to an acceptable level.

This study introduces a bidirectional power sharing scheme between an ac electric utility and a dc microgrid. These two are connected together through an interlinking converter (IC) and a dual active bridge (DAB). The proposed control scheme allows predefined amount of power to be supplied from the ac to dc side or the other way around. The DAB is connected at the dc side of the IC and it controls the bidirectional power flow. The dc microgrid contains dc–dc converters, where boost converters are used with the sources and buck converters are used to supply loads. These dc–dc converters and the DAB are controlled by state feedback with integral control in a linearised discrete domain. The DAB linearisation and control law are presented in detail. The dc microgrid is controlled by conventional V-P droop where the power from/to the ac side is considered as negative/positive load. Detailed simulation results are presented to validate the proposal. Also some hardware results are included that support the findings.

Due to prominent attenuation of travelling waves, double-end fault location method produces considerable errors when applied to ultra-high voltage AC half-wavelength transmission (UAHT) lines. In order to address this problem, this study presents a novel fault location scheme based on the attenuation, refraction and reflection principles of aerial-mode voltage travelling waves (AVTWs). In the scheme, the faulted section of an UAHT line is first determined according to the accumulated amplitude ratio of the pre-determined frequency components of AVTWs asynchronously sampled at both terminals of the line. Then, the Teager energy of the first two wavefronts of the AVTW – measured at the terminal in the faulted section – is used to define two factors for selecting the appropriate accurate fault location method. Finally, the single-end travelling wave method is adopted for locating the faults near the line terminal. The presented double-end method utilises the amplitude ratio of AVTWs to locate the faults far from the line terminal. A 1000 kV UAHT line model is considered with various fault conditions in PSCAD/EMTDC simulations. The simulation results and analysis demonstrate that the proposed fault location scheme is accurate and immune to fault distances, fault types, fault impedances and fault inception angles.

Considering increasing distributed energy resources and responsive loads in smart grid paradigm, this study proposes a new approach for robust hourly energy scheduling of distribution systems at the presence of severe uncertain renewable energy sources (RES). Wind and photovoltaic power generations are considered as the RESs. The aim is to minimise the total energy procurement cost, while considering the participation of RESs, by their optimal allocation in the network. The inherent uncertainty of RESs is handled via information gap decision theory. One of the features of the proposed model is to consider the impact of demand response and energy storage system as the effective tools to reduce unintended costs due to uncertainty of RESs. Also, the proposed model handles the uncertainty of multiple RESs in a way that maximum tolerable uncertainty of RESs is achieved for a given worsening of total energy procurement cost. The proposed model is formulated as a mixed integer nonlinear optimisation problem and is implemented in general algebraic modelling system environment. The model is applied on the IEEE standard 33-bus radial test system, and the obtained results substantiate that the utilisation of ESS and DR can reduce the impact of RESs' uncertainty on the energy cost.

The application of droop control in the voltage-source converter-based multi-terminal direct current (VSC-MTDC) system has been previously proposed in the literature. However, how to determine the droop coefficients to stabilise the DC voltage is still the key issue to concern and research. This study presents a novel calculation methodology for droop coefficients in the case of outage or power step disturbance on any converter station. The overall design objective is to minimise the DC voltage deviation between pre- and post-disturbance, depicted with a quadratic programming model. In addition, the selection method of the optimal DC voltage signal for droop controllers is developed in both cases of communication failure and communication normal. Based on the calculated droop coefficients and selected DC voltage signal, the power coordinated control among the converter stations is implemented to stabilise the DC voltage of the post-disturbance system quickly. Case studies are conducted on the Nordic 32 and New England system, respectively. The simulation results show that the proposed methodology for droop coefficients can significantly reduce the steady-state DC voltage deviations without the limitation of preassigning the maximum allowable DC voltage deviation, compared to the methodologies existing in the literature.

Considering continuous power supply conditions, there is currently no effective method for preventing ice disaster, and also some deficiencies of the existing completed short-circuit ice melting method has been found. Here, taking typical bundled and expanded conductors as the sample, its icing performance was tested and the combined ice-wind load of tested lines was analysed. Then, a new method of substituting expanded conductors with the same conductive cross-sectional area for bundled conductors to prevent ice disasters is proposed. Research results showed that: from stagnation point to both sides of crescent-shaped conductors, local collision rate gradually reduce to 0; under various meteorological factors, there is still a power function relationship between ice thickness of conductors (D_c ) and the diameter of conductors (D); the ice amount of six tested conductors gradually increases with the increase of ice thickness of Rotating Single-Cylinder Ice Collector (D_r ), while the ice amount reduction rate reduces first and then increases with D_r ; the combined ice-wind load ratio of bundled and expanded conductors increases with the increase of wind speed and D_r . Therefore, it is a low-cost method for improving the anti-icing capacity of transmission lines and preventing icing disaster once and for all.

One of the recently arisen issues for transformerless grid-connected photovoltaic (PV) systems is high-frequency leakage current, which flows through the parasitic capacitance of PV system and the neutral grounding resistor (NGR) of the grid. This paper deals with a systemic analysis on the capacitance of large PV systems considering the interconnecting conductors. A new Y-bus model is proposed to analyse the leakage current of PV strings/arrays of any size in high-frequency domain. In the model, different capacitances of PV panels and the inductance and capacitance of interconnecting cables are considered. Subsequently, a two-port circuit is derived by its admittance parameters, which is useful in leakage current studies. In the second step, a novel model for the common mode (CM) analysis of voltage-source inverters is derived based on which, a new leakage current mitigation technique is proposed which provides capacitive CM paths for both the negative and positive legs of the inverter. The model is assessed using different simulations in various conditions. The results confirm the usefulness of the proposed model.

This study presents a novel secondary control strategy for a radial microgrid with end-to-end distributed energy resource (DER) interconnections, operating under islanded conditions. The control strategy utilises sparse communication and precludes the presence of a centralised controller. The distributed algorithm has a twofold objective. The first task is to determine the desired power injection at each DER bus for a load change occurring anywhere in the microgrid. The remaining task includes obtaining the bus angle set points at all the DER units such that the actual power injections converge to the desired power injections at each DER bus. The algorithm enables accurate system wide power injection in proportion to the respective DER base ratings. The control strategy is tested on a three-bus, three-DER system with local loads. The controller is shown to work for two different sets of microgrid ratings. The bounds are evaluated for each design parameter specified according to the system nominal ratings to maintain the stability of the distributed algorithm. Proofs are stated to show the convergence of algorithms to the correct power injection solution for all the nodes. Real-time simulation results are presented to corroborate accurate power sharing through the algorithm.

Linearised model for frequency control of an islanding system comprising an equivalent synchronous generator and an equivalent doubly fed induction generator (DFIG) is derived. Small signal stability analysis is performed to determine the stable regions for DFIG supplementary droop controller under various wind velocities. In order to achieve better dynamic frequency response under different system parameters, the DFIG droop gain is adapted in real-time using a self-tuning controller designed based on particle swarm optimisation technique. In order to validate the results from small signal analysis and to demonstrate the effectiveness of the proposed self-tuning frequency controller, digital simulations using MATLAB/SIMULINK are performed on a local power system in central Taiwan. It is concluded from the simulation results that the proposed self-tuning frequency controller offer better dynamic frequency response than the fixed-gain droop controller.

Renewable energy is a rapidly growing environmental-friendly alternative for electricity generation, which will supersede using fossil fuels in the near future. Renewable-based generation is usually located at remote areas, and the large-scale generated power is required to be transmitted to the main load centres; thus, the main challenge facing the bulk power transmission is the precise determination of the most appropriate transmission option. This study presents a comprehensive techno-economic study for the selection of the adequate transmission option for large-scale power transmission. The proposed work aims to study different transmission alternatives to transfer 10,000 MW of renewable generated power to the load centres in the central region of Saudi Arabia. Different high-voltage AC (HVAC) voltage levels such as 725 and 500 kV, and high-voltage DC (HVDC) technologies are considered as alternatives, and a techno-economic evaluation of each option is presented. Moreover, detailed comparisons between different HVAC and HVDC technologies are introduced from technical, economic, and environmental perspective. The presented study, comparisons, and the subsequent recommendations are helpful for the network planner to evaluate different extra high-voltage (EHV) and AC/DC transmission options in terms of accessibility, load-carrying capability, efficiency, reliability, stability, environmental impact, and economics.