Energy storage (ES) has become increasingly important in modern power system, whereas no single type of ES element can satisfy all diverse demands simultaneously. This study proposes a hybrid energy storage system (HESS) based on superconducting magnetic energy storage (SMES) and battery because of their complementary characteristics for the grid integration of wind power generations (WPG). This study investigates the mathematical model and the topology of the proposed HESS, which is equipped with a grid-side DC/AC converter, a battery buck/boost converter and a SMES DC chopper. The advanced control strategies comprised of device level and system level are designed. The control strategy for the converters which can be considered as device level is briefly discussed. The significant contribution of this study is proposing a novel system-level control strategy for reasonable and effective power allocation between SMES and battery. According to the control objectives, a fuzzy logic controller optimised with genetic algorithm is adopted. The detailed controller designs are described, meanwhile system stability and HESS operation performance are evaluated. MATLAB simulations are presented to demonstrate the effectiveness of the proposed strategies.

Back-to-back starting is a widely accepted starting method for pumped storage units. A back-to-back starting model of pumped storage units was built using the ElectroMagnetic Transients Program including DC (EMTDC) software package. The short-circuit fault during back-to-back starting was investigated for the first time. The starting process was simulated and compared with real data from a pumped storage power plant in northeast China. The rotor speed and the effect of resistance during fault period were also discussed. The results showed that the fault current has significant magnitude and low-frequency characteristic. Recommendations were provided to realise secure and reliable fault clearance during back-to-back starting based on the fault characteristics and real de-excitation test results of the pumped storage power plant.

A mode switching doubly fed induction generator (MSDFIG) scheme is proposed for the purpose of achieving low-voltage ride-through for wind turbines. The MSDFIG operates as a doubly fed induction generator (DFIG) under normal condition but upon the detection of a low-voltage incident, the generator is to smoothly transfer to operate under the induction generator mode through the switching in of a set of stator-side crowbar. The MSDFIG automatically reverts back to the DFIG mode when network voltage recovers. A new strategy on the control of the crowbar resistance is included. Analysis shows that the proposed MSDFIG scheme can ride through the complete low-voltage and voltage recovery stages. Effectiveness of the scheme is demonstrated through simulation and experiment studies.

Growing share of concentrating solar power (CSP) plants in power systems creates the need for including these renewable sources in power system reliability studies. As such studies analyse the grid on a global scale and start to be performed increasingly by Monte Carlo simulations, modelling of CSP production has to be reasonably simplified in order to reduce the calculation time. The model simplification also concerns the minimisation of the required specific knowledge and input data which enables power system engineers to evaluate the impact of CSP without substantial expertise in its underlying physics and by focusing on the key design parameters. There is a large variety of accurate CSP simulation programs and models, and yet neither of them offers the required simplicity. This study addresses this gap by proposing reduced models for predicting energy output of parabolic trough and central receiver systems. The calculation procedure and its underlying assumptions are presented. The adequacy of the models is demonstrated by comparing their predictions with that of the System Advisor Model for different case scenarios.

This study considers generation and demand challenges of a 100% renewable UK electricity grid and how this could be addressed with interconnection or energy storage. Hourly demand and electricity generation profiles for a year have been constructed: Business as Usual (BAU) with a yearly demand of 540 TWh and Green Plus (GP) with a demand of 390 TWh, Two further scenarios based on the above have been considered with electrification of heating (ASHP) and electric vehicle transportation (EV). The resultant hourly imbalances have been used to calculate the interconnection and energy storage requirements. This paper discusses the findings of the BAU scenario. The calculated interconnector capacity required was found to be 60 GW and cost £58 billion. Energy storage capacity requirements vary depending on the selected technology. Rated capacity was estimated to be 14 GW with storage capacity of 3 TWh for pumped storage, 11 GW and 2.3 TWh for liquid air, and 65 GW and 13.6 TWh for hydrogen storage, at a cost of £65, £76 and £45 billion respectively. This paper indicates that storing hydrogen in underground caverns would offer the cheapest solution. However, whilst these technological solutions can address generation and demand imbalance in a fully renewable electricity grid, there clearly remain barriers to each technology.

Many recent works on wave energy conversion use a form of model predictive control (MPC) to maximise energy harvest. This active control strategy is generally used because it permits the inclusion of constraints that represent the physical limits of wave energy conversion devices in the optimisation algorithm. In this study, the authors present a centralised MPC design for an array configuration of wave energy converters. Its performance is evaluated via computer simulation and is compared against that of decentralised MPC and linear damping controller for several values of damping in both regular and irregular waves.

ln recent years, the concept of decentralising power generation through the deployment of distributed generators (DGs) has been widely accepted and applied, driven by the growing market of renewable energy sources. These DGs are normally equipped with a switching power interface, acting as front end with the grid. This paper proposes a multi-task control strategy for distributed generation systems that simultaneously allows the DG to inject the available energy, as well as to work as a voltage drop compensator or as an active power filter, mitigating load current disturbances and improving power quality of the grid. The main contribution of the proposed system, with respect to other solutions in the literature, is that the proposed control loops are based on the Conservative Power Theory decompositions. This choice provides decoupled power and current references for the inverter control, offering a very flexible, selective and powerful control strategy for the DG. The paper also discusses the choice of the current waveform for injecting/absorbing active power into/from the grid, and both sinusoidal and resistive references have been compared in terms of damping capability. Finally, simulation and experimental results are provided in order to validate the proposed functionalities of the DG control system.

This study proposes a single-objective optimal sizing approach for an islanded microgrid (IMG). The approach determines the optimal component sizes for the IMG, such that the life-cycle cost is minimised while a low loss of power supply probability (LPSP) is ensured. As wind speed and solar irradiation exhibit both diurnal and seasonal variations, the proposed algorithm takes advantages of the typical meteorological year-based chronological simulation and enumeration-based iterative techniques. The mathematical models presented in this study for the IMG components consider the non-linear characteristics as well as the reactive power. The LPSP is also formulated based on the supply-demand balances of both real and reactive powers, and an economic evaluation model is presented. The proposed sizing approach identifies the global minimum, and simultaneously provides the optimal component sizes as well as the power management strategies. This study also presents a number of sensitivity analyses as well as comparisons with a commercial software package.

Price signals have been suggested to bring about greater demand side flexibility and thus support the integration of variable sources of energy, such as wind. A conflict exists between keeping these signals simple for consumers, while making responses appropriate for increasingly complex supply–demand balancing dynamics in future. This study reviews some of the demand responses observed in time-of-use (ToU) tariff trials and assesses their effectiveness in scenarios with higher levels of wind. The authors simulate wholesale real-time prices for high-wind scenarios as a benchmark tariff. Simple tariff structures are compared against real-time prices for the extent to which they can ‘nudge’ demand in the ‘right direction’. They present results which suggest that even in high-wind scenarios, simple ToU tariffs could have a beneficial effect on overall system costs. The load shifting and reduction behaviour observed under ToU trials could lower energy costs by between 4 and 6% without the need for complex price signals.

A new quantitative assessment of transient stability for power systems integrated with doubly fed induction generator (DFIG) wind farms is proposed by evaluating the transient energy margin (TEM) through the formulation of the transient energy function (TEF) for multimachine systems. To achieve an accurate TEM, the TEF is modified to account for the separation of the critical machines from the system and an unstable equilibrium point is calculated on the basis of post-fault trajectory reaching the potential energy boundary surface. Simulation results show that such power systems integrated with DFIG wind farms are more sensitive to transient events of higher voltage sag, longer fault clearing time, lower load operation and higher wind power penetration level. It is also observed that machines located far from the fault are also exposed to inferior transient stability because of fault with geographical dispersion of wind farms. As a result, advanced switchgear, faster isolators, more efficient power reserve systems and advanced reactive power compensating devices must be equipped to ensure reliable operation of power systems integrated with the DFIG wind farms during transient events.