In western China, large-scale wind power is generally bundled with thermal power, and transmitted to eastern China by high-voltage direct current (HVDC) systems. This constitutes the wind–thermal bundled system transmitted by HVDC (WTBH). In this study, a typical studied system of WTBH is presented, and its models for eigenvalue analysis are introduced. To improve the efficiency of eigenvalue analysis, an improved block modelling method is proposed for building the state-space model of WTBH. By eigenvalue analysis and electromagnetic transient (EMT) simulation, the impact of doubly-fed induction generator (DFIG)-based wind farm integration on sub-synchronous torsional interaction (SSTI) between thermal generators (TGs) and HVDC was investigated. The sensitivity of the operating parameters of DFIG-based wind farms was analysed, including wind speed, wind farm scale, and distance between the wind farm and HVDC rectifier station. The obtained results show that the integration of DFIG-based wind farms can mitigate the SSTI between the TG and HVDC. The system becomes more stable as the wind speed and wind farm scale increase or the distance between the wind farm and HVDC rectifier station decreases. The conclusions of this study are validated through EMT simulations in PSCAD/EMTDC, and provide theoretical reference for practical WTBH projects.

Large-scale electric vehicle (EV) charging will bring new challenges to coordination of grid and transportation. To facilitate large-scale EV applications, optimal locating and sizing of charging stations have become essential. For the investors of a charging station, economic benefit is the primary and the only objective. In this context, this work studies the siting and sizing of EV stations based on the optimal economic benefit. Benefit changes with time, location and capacity. A planning model method considering net present value (NPV) and life cycle cost (LCC) is proposed to determine the site and the size of the charging stations. The model has integrated distribution network constraint, the user constraint and the traffic flow captured constraint. Origin–destination lines and voronoi diagram are selected to calculate the traffic flow and the service region of each charging station, respectively. The quantum genetic algorithm was adopted for a better convergence of the planning model. Finally, a coupled 33-node distribution system and a 36-node transportation system are used to simulate various scenarios in the coupled networks of grid and transportation. The simulation results show that by introducing a planning model method considering NPV and LCC, the charging station economical benefits can be further improved.

This study proposes a novel method based on data mining for islanding detection of synchronous distributed generators. The method uses a new technique called data mining of code repositories (DAMICORE), which is a powerful data mining tool for detecting patterns and similarities in various kinds of datasets. In addition, a trip logic was developed in this proposal in order to detect islanding and disconnect the distributed generator. One of the most relevant features of the proposed method is its capability to generalise, which reduces the need of big datasets for training purposes. This approach has been tested with islanding, load switching and fault simulations, presenting promising results concerning performance, as well as detection time. General results showed a better performance of the method if compared to traditional anti-islanding protection schemes, such as frequency-based relays.

The conventional hierarchical control in an islanded microgrid (MG) does not consider the long time-span dynamics of distributed storages (DSs). The main challenge in control of battery energy storage systems (BESSs) is different levels of stored energy in terms of state of charge (SoC). In power droop control, the energy of the BESSs with lower initial SoC is drained earlier, and their capacities become unachievable. Moreover, using droop control to balance the SoC of BESSs, deviates the steady state frequency and voltage from the nominal values. However, restoration of the MG frequency employing the conventional distributed secondary controllers disturbs SoC-balancing, since SoC of BESSs are ignored. In this paper, a new distributed storage secondary controller (DSSC) scheme is designed for restoration of the voltage and frequency of a stand-alone MG, and to provide power-sharing and SoC-balancing, using a distributed cooperative architecture. The cooperative DSs are controllable and exchange the information with neighbor DSs through a communication network. The unknown output power of the uncooperative renewable distributed generation (DG) is considered as external disturbance to the DSSC. The designed DSSC is robust against the variation of the communication configuration, and eliminates the necessity to communicate with uncontrollable DGs and loads.

The performance of the excitation system plays a very important role in the voltage stability of the power grid. The brushless excitation system with a brushless alternating current exciter offers a lower failure rate and thus higher reliability in comparison with the static system with high-rated power electronics converters, brushes, and slip rings. However, its dynamic response is impaired due to the exciter lag in producing the required field current. In this study, the optimal design of an exciter for the large-scale power-plant synchronous generator based on the magnetic equivalent circuit method is pursued. The design goals are reducing the overall volume, minimising the magnitudes of the cogging torque and the field current ripples while satisfying the grid code requirements such as the ceiling values of available field voltage and current, rise time and settling time of the rectified output voltage under dynamic conditions. In addition, the other electrical, magnetic, thermal and mechanical constraints are included in the design algorithm. The proposed design method is used for obtaining the optimal specifications of an exciter for a 25 MW, 11 kV power-plant generator in order to attain superior characteristics than the existing one. The analytical results are validated using two-dimensional finite-element studies and experimental measurements.