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The small area of the United Kingdom relative to weather systems makes renewable energy sources variable on short time scales. Short term variability is therefore a growing concern with increasing amounts of renewable energy integration. In this work, we address how tidal energy can contribute to reducing medium-term variability in the future UK energy mix. Two tidal integration scenarios are defined for 2050: for each scenario, a 5-min interval generation profile is calculated using an oceanographic model of UK tides, and the medium-term variability is assessed. Here we show that tidal power shows a lower level of variability compared to other resources. During spring tides, a national network of tidal power stations can produce continuous, although variable, electricity. It is then shown that tidal energy and storage can provide year-round continuous and constant power output, i.e. baseload generation. Therefore, we conclude that tidal energy can provide positive contributions and complement other renewable energy sources.

Due to the interaction converter control, pre-existing distortion and grid impedance, the harmonic levels caused by renewable energy sources (RESs) are continuously changing, and their assessment requires the use of dedicated computer models. Several time-domain models have been proposed to carry out this analysis, however, they fall short of at least one requirement: either they do not provide accurate results, or they require an excessively long simulation time. This paper presents a novel time-domain model to address the gap described above: the proposed model employs average functions and a novel switching emulator. Therefore, it is referred to as ‘average model with switching emulator’ (AMSE). The proposed model is compared with existing models, and the results indicate that the AMSE meet both requirements stated above, as it accurately represents harmonic distortion while reducing significantly the simulation time. The second part of the paper discusses mitigating solutions to harmonic amplification in systems with a high penetration of VSCs, and shows the effectiveness of using an Active Filter to reduce harmonic levels in system experiencing resonance conditions.

The growing adoption of decentralised renewable energy generation (such as solar photovoltaic panels and wind turbines) and low-carbon technologies will increase the strain experienced by the distribution networks in the near future. In such a scenario, energy storage is becoming a key alternative to traditional expensive reinforcements to network infrastructure, due to its flexibility, decreasing costs and fast deployment capabilities. In this work, an end-to-end data-driven solution to optimally design the control of a battery unit with the aim of reducing the peak electricity demand is presented. The proposed solution uses state-of-the-art machine learning methods for forecasting electricity demand and PV generation, combined with an optimisation strategy to maximise the use of photovoltaic energy to charge the energy storage unit. To this end, historical demand, weather, and solar energy generation data collected at the Stentaway Primary substation near Plymouth, UK, and at other six locations were employed.

With increasing penetration of distributed generators (DGs), existing distribution grids are becoming weaker. As a result, voltage regulation in distribution grids impose a significant challenge and can be improved by introducing additional control apparatuses. In this paper, a transformerless static synchronous series compensator (T-SSSC) is adopted to maximise the power transfer between DGs and a weak grid by improving grid voltage stability. A new control strategy is introduced to reduce the number of switching events during the operation of a T-SSSC, thus limiting the switching losses. Furthermore, a new droop based control scheme is proposed to minimise the voltage unbalance between phases. A medium voltage distribution grid with embedded T-SSSCs modelled in Simulink has been used to verify the effectiveness of the proposed control schemes. For completeness, the performance a T-SSSC is investigated following a sudden change in grid short circuit level.

This paper presents a stand-alone dc-bus Electric Vehicle (EV) charging station system using a photovoltaic (PV) source. The proposed topology includes a PV panel, an energy storage unit (ESU), and two EVs. Each unit is controlled independently; a voltage regulation scheme is implemented within the ESU converter to ensure the dcbus voltage is maintained at the nominal level under varying operating conditions. Two different operating scenarios are studied, and the results confirm that the algorithm developed allows regulating the dcbus voltage either with varying solar irradiance or when EV s are connected and disconnected from the dc grid. The proposed design offers lower energy conversion losses compared to the ac configuration and reduces energy demand on the existing ac distribution grid. It also finds applications in remote areas where parking facilities are provided for recreational purpose.

Temporal variability in renewable energy presents a major challenge for electrical grid systems. Tides are considered predictable due to their regular periodicity; however, the persistence and quality of tidal-stream generated electricity is unknown. This paper is the first study that attempts to address this knowledge gap through direct measurements of rotor-shaft power and shore-side voltage from a 1 MW, rated at grid-connection, tidal turbine (Orkney Islands, UK). Tidal asymmetry in turbulence parameters, flow speed and power variability were observed. Variability in the power at 0.5 Hz, associated with the 10-min running mean, was low (standard deviation 10–12% of rated power), with lower variability associated with higher flow speed and reduced turbulence intensity. Variability of shore-side measured voltage was well within acceptable levels (∼0.3% at 0.5 Hz). Variability in turbine power had 2 = 85% and ∼14% error). Therefore, the predictability and quality of tidal-stream energy was high and may be undervalued in a future, high-penetration renewable energy, electricity grid.

The DMAIC (Define, Measure, Analyze, Implement and Control) approach is a well-established approach used to improve industrial processes and products. The DMAIC approach is mostly used as part of quality assurance processes, but this paper will show that it can be applied to investigation of root cause analysis of equipment failure. Specifically, the piece of equipment under investigation is a circuit breaker used in a distribution system. A second contribution of this paper is to provide suggestions on approaches to overcome modeling challenges related to lack of data, both in terms of measurements and in terms of system parameters.

Due to the high number of photovoltaic (PV) inverters installed, in some regions of the UK the power generated under peak conditions exceeds the transmission system capacity limits. With the aim to mitigate this condition and operate the grid within its design limits, utilities curtail PV output power, thus causing financial loss for the PV system owners and limiting the use of the installed components. The control system proposed in this paper allows using the PV inverter as an Active Filter (AF), when the output power is curtailed, thus improving the system power quality and exploiting the installed MVA. A novel contribution is the description of a harmonic derating coefficient which limits harmonic current injection based on the fundamental current generated by the inverter. The proposed application fits within the scope of the smart grid, where multi-functional inverters can be controlled by utilities to improve grid operating conditions.

This chapter is intended to discuss the most general approach to harmonic studies, which can be applied to shunt FACT devices and to all devices regulated by means of power electronic switches, such as wind power plants. This approach is supported by international standards. Some specific installations may require special considerations that are not addressed in detail in this chapter; however, specific references are provided for further reading whenever these special conditions are identified.

This paper details the transient operation of a wind energy conversion system (WECS) used simultaneously as an active filter and power generator. This study is intended to address the system response to two types of transient phenomena: voltage dips (fast transients) and wind speed variations (slow transients). The system response to voltage dips is governed by the electrical system dynamics and control method and results in the evaluation of the WECS low-voltage ride through capability. The study of the system response to wind speed variations requires a complete mechanical model to be included. Simulation results are presented for a typical WECS, and a discussion is carried out dealing with the generalization of the present work to other configurations.

A three-phase distributed constants model for high-voltage windings of a transformer is presented. The mutual couplings between phase coils are considered introducing some approximations. Applying the Clarke transformation to the proposed model, the voltage and current surge waves are provided by a simple numerical method. In this way, the model can be used to design the insulation between the turns of a single coil and between the windings and the iron core. A comparison of the numeric results obtained by applying the proposed method with the results obtained by other authors confirms the validity of the model. Moreover, further results are obtained: the proposed approach allows also finding the voltage and current waveforms for asymmetric faults.

The number of distributed resources for renewable energy installed worldwide has been increasing rapidly in the last decade, and the great majority of these installations consist of solar panels and wind turbines. Other renewable sources of energy are not exploited to the same level: for instance, tidal energy is still a minute portion of the global energy capacity, in spite of the large amount of potential energy stored in tidal waves, and of the successful experience of the few existing plants. The world’s second largest tidal range occurs in the UK but at the moment tidal installations in this country are limited to a few prototypes. More recently, there has been a renewed interest in harnessing tidal energy in the UK, and a few tidal lagoon projects have been evaluated by the UK government. This paper provides an overview of the historical and current developments of tidal plants, a description of operation of tidal lagoons, challenges and opportunities for their integration within the UK energy systems and solutions to improve the dispatchability of tidal energy. The concepts described in the paper are applied to a tidal project proposed for South Wales.

The subject of this paper is telephone interference caused by harmonics in distribution systems. The first part of the paper presents a theoretical analysis of the phenomenon with a detailed discussion of the role of ground currents and harmonic sequence order. Applicable standards, acceptable interference levels and mitigating solutions are also summarized. The second part of the paper describes modeling and simulations of a typical distribution system. Simulation results show the importance of controlling harmonics on the feeder to limit telephone interference concerns.

This paper presents a preliminary study meant to determine the economic feasibility of partially using distributed generators (DGs) as active filters (AFs) meant to sink current harmonics injected by nonlinear loads (NLs) connected at the same feeder as the DG. Such approach may avoid the installation of dedicated AFs, nevertheless it may cause exceeding thermal stressing of insulation and solid state switches.

This paper describes a novel control method for a WECS (Wind Energy Conversion System) meant to partially operate as an AF (Active Filter). The control is defined in an equivalent reference frame obtained by applying the Park Transformation to the three-phase quantities. The zero-sequence component is includd in the control system; this feature enables the compensation of zero-sequence harmonics. The effectiveness of the proposed methodology is quantified in terms of current spectra and reduction of the voltage and current THD at the Point of Common Coupling (PCC). The proposed application results in higher power loss in the power converters that connects the generator rotor to the PCC with respect to sinusoidal operation. Nevertheless, it is proved that the WECS derating enables the reduction of the power converters' power loss. Voltage distortion at the windings terminals and power converters' terminals is a second consequence of the proposed application, and the peak stator and rotor voltage is an important design parameter in the choice of the solid state devices.

This study explains how a Steinmetz compensator works. Past explanations are based on phasor diagrams and do not address the basic physical phenomena of electromagnetic energy flow. This paper uses the Poynting vector to detect and understand the process of compensation and restoration of symmetry in an unbalanced system.

This work deals with the steady-state operation of wind energy conversion systems (WECSs) used simultaneously as active filters (AFs) and power generators. This application is motivated by the increasing number of non-linear loads (NLLs) on the power grid and by the possibility to offer an economical alternative to the installation of dedicated filters that sink the harmonic currents injected by such loads. The main contributions of this paper are as follows: (i) three different control systems that allow the simultaneous use of the WECS as AF and power generator are presented; (ii) compensation of triplen harmonics is addressed; (iii) additional power losses due to AF operation, leading to the derating of the WECS, are quantified; (iv) results based on numerical simulations are provided.

The problem of identifying the sources injecting periodic disturbances in the electric systems is a critical point in the assessment of the electric Power Quality. The available methods, based on a deterministic approach, do not always provide correct results under the different possible operating conditions. This paper proposes an innovative method, based on a Fuzzy inference and shows significant simulation results.