Future electricity network must be flexible, accessible, reliable and economically viable to realise the aims of the smart grid initiative. In order to achieve these objectives and to reduce ...greenhouse gas (GHG) emissions, research on various configurations or architectures of microgrid (µGrid) systems is gaining greater attention. This is occurring in step with increasing penetration of Renewable Energy Sources (RES) such as solar, wind and other micro-sources. Energy storage can also be a part of the µGrid architecture to ensure more stable and sustainable operation. The techno-economic viability of the µGrid system is also a point of concern. Again, the variable and uncontrollable behaviour of RES can also introduce power quality problems. To improve the systems reliability, efficiency and power quality, different µGrid architectures are introduced. Complex control of the µGrid controller is helping to overcome these conditions. In that case, integration of Custom Power Devices is also playing an important role. Therefore, µGrid policies should also deal with these issues in the light of future trends towards the Smart Grid. This paper presents a literature review, based on various existing and/or simulated µGrid architectures. In relation to the reliability, efficiency and power quality issues, different distribution systems have been introduced. The advantages and disadvantages of these configurations are discussed here. The benefits of RES and its associated power quality problems have been identified. The benefits of energy storage systems and the development of communication systems towards the stable, flexible and efficient operation of smart grids are also reviewed. Findings have been outlined and then the policies with future trends of µGrid are also discussed.
The aim of this paper is to perform a probabilistic risk assessment of power quality variations and events that may arise due to high photovoltaic distributed generation (PVDG) integration in a ...low-voltage distribution network (LVDN). Due to the spatial and temporal behavior of PV generation and load demand, such an assessment is vital before integrating PVDG at the existing load buses. Two power quality (PQ) variations such as voltage magnitude variation and phase unbalance together with one PQ abnormal event are considered as the PQ impact metrics. These PQ impact metrics are assessed in terms of two PQ indices, namely site and system indices. A Monte Carlo based simulation is applied for the probabilistic risk assessment. From the results, site overvoltage shows a likely impact to observe as the PVDG integration increases. The probability of 20% of customers violating 1.1 p.u. at 100% penetration level is 0.5. Integration of PVDG reduces the voltage unbalance as compared with no or low PVDG penetration. There is a higher probability of observing deep sag at the site as PVDG integration increases. This probabilistic approach can be used as a tool to assess the likely impacts due to PVDG integration against the worst-case scenarios.
The transformation of passive to energy-active consumers in smart homes has been enabled by the proliferation of distributed energy resources (DERs) and demand-side management technologies. Building ...a smart community-based electricity market (SCEM) centred around a local energy community has the potential to expedite this transformation by tapping the flexibility associated with peer-to-peer energy transactions inside the community. The article presents a systematic approach to quantifying the benefits of smart homes, starting from the energy-passive to energy-active homes under SCEM with intermediate stages identifying smart homes with DERs. The investigation also includes the impact of seasonal variations with contrasting characteristics. Smart homes with solar PV and energy storage under SCEM achieve maximum savings of 50% and 36.6% for the summer and winter months, respectively, and SCEM boosts consumption of localized green energy by a further 31% in the summer month. ES leverages the smart homes gain significantly through self-consumption and energy arbitrage. However, the operation of ES under SCEM in the winter month reduces the network's voltage stability. The article is conducted based on real-life measurements from an energy community in Ireland. Recommendations are made further to boost the transition of smart homes toward the decarburization of smart grid networks.
In order to obtain maximum power output of a Wind Energy Conversion System (WECS), the rotor speed needs to be optimised for a particular wind speed. However, due to inherent inertia, the rotor of a ...WECS cannot react instantaneously according to wind speed variations. As a consequence, the performance of the system and consequently the wind energy conversion capability of the rotor are negatively affected. This study considers the use of a time series Adaptive Linear Prediction (ALP) technique as a means to improve the performance and conversion efficiency of wind turbines. The ALP technique is introduced as a real time control reference to improve optimal control of wind turbines. In this study, a wind turbine emulator is developed to evaluate the performance of the predictive control strategy. In this regard, the ALP reference control method was applied as a means to control the torque/speed of the emulator. The results show that the employment of a predictive technique increases energy yield by almost 5%.
•A representation of the performance of a real wind turbine subjected to variable wind.•Adaptive Linear Prediction to improve performance and conversion efficiencies of WECS.•Wind turbine emulator as a means to evaluate time series linear prediction.•Wind sensor method offers an optimal power mapping technique.
The proliferation of rooftop solar PV distributed generator (PVDG) installation in a low-voltage distribution network (LVDN) imposes voltage fluctuation challenges that are a threat to distribution ...system operators. Reactive power control (RPC) methods are insufficient in isolation to combat the overvoltage fluctuations manifested in an LVDN with a significant number of grid-tied PVDG installations, whereas active power curtailment (APC) control can alleviate the voltage fluctuation in such situations and it is achieved at the cost of reduced active power injection. This paper explores how deficiencies in both RPC and APC as separate approaches can be mitigated by suitably combining RPC and APC algorithms. Strategies combining two RPCs and one RPC in conjunction with APC are proposed as two coordinating algorithms by means of an instantaneous measurement of node voltage and active power. These coordinating algorithms are embedded in all the rooftop PVDG grid-tied inverters (GTIs), where the GTI coordinates among them for voltage support without exceeding individual inverter volt-ampere rating. The result of the combined approach shows a significant improvement in managing and stabilizing the voltage and allows the penetration of PVDG to be increased from 35.65% to 66.7% of distribution transformer kilovolt-ampere rating.
Environmental contaminants and disease may synergistically contribute to amphibian population declines. Sub-lethal levels of contaminants can suppress amphibian immune defenses and, thereby, may ...facilitate disease outbreaks. We conducted laboratory experiments on newly metamorphosed foothill yellow-legged frogs (Rana boylii) to determine whether sublethal exposure to the pesticide carbaryl would increase susceptibility to the pathogenic chytrid fungus Batrachochytrium dendrobatidis that is widely associated with amphibian declines. We examined the effect of carbaryl alone, chytrid alone, and interactions of the two on individual survival, growth, and antimicrobial skin defenses. We found no effect of chytrid, carbaryl, or their interaction on survival. However, chytrid infection reduced growth by approximately one-half. This is the first report of suppressed growth in post-metamorphic amphibians due to infection with chytrid. Rana boylii skin peptides strongly inhibited chytrid growth in vitro, which may explain why chytrid exposure did not result in significant mortality. Skin peptide defenses were significantly reduced after exposure to carbaryl suggesting that pesticides may inhibit this innate immune defense and increase susceptibility to disease.
National targets for increased renewable energy are common-place internationally and small/micro-generation may help achieve such goals. Energy yields from such technologies however, are very ...location and site specific. In rural environments, the average wind speed is relatively high and the homogeneous landscape promotes laminar air flow and stable (relatively) wind direction. In urban environments however, the wind resource has lower mean wind speeds and increased levels of atmospheric turbulence due to heterogeneous surface forms. This paper discusses the associated costs per unit of electricity generated by micro wind energy conversion systems from the perspective of both urban and rural locations, with three case studies that consider the potential and financial viability for such systems. The case studies ascertain the cost of energy associated with a standard HAWT (horizontal axis wind turbine), in terms of exemplar rural and urban locations. Sri Lanka, Ireland and the UK, are prioritised as countries that have progressive, conservative and ambitious goals respectively towards the integration of micro-generation. LCOE (Levelized cost of energy) analyses in this regard, offers a contextualised viability assessment that is applicable in decision making relating to economic incentive application or in the determination of suitable feed-in tariff rates.
•Levelized cost of energy analysis of rural/urban wind energy systems is presented.•Progressive, conservative and ambitious wind energy case studies are compared.•Design of Experiments analysis (DOE) considers LCOE parameter intra-dependencies.•Urban wind energy harvesting for each case proved to be a cost preclusive option.
A new proposal for the placement, integration, and control of unified power quality conditioner (UPQC) in distributed generation (DG)-based grid connected/autonomous microgrid/microgeneration (μG) ...system has been presented here. The DG converters (with storage) and the shunt part of the UPQC Active Power Filter (APF sh ) is placed at the Point of Common Coupling (PCC). The series part of the UPQC (APF se ) is connected before the PCC and in series with the grid. The dc link can also be integrated with the storage system. An intelligent islanding detection and reconnection technique (IR) are introduced in the UPQC as a secondary control. Hence, it is termed as UPQC μG-IR . The advantages of the proposed UPQC μG-IR over the normal UPQC are to compensate voltage interruption in addition to voltage sag/swell, harmonic, and reactive power compensation in the interconnected mode. During the interconnected and islanded mode, DG converter with storage will supply the active power only and the shunt part of the UPQC will compensate the reactive and harmonic power of the load. It also offers the DG converter to remain connected during the voltage disturbance including phase jump.
In this study, the equation for the reactive and harmonic power compensation of a shunt active power filter (APF) system has been derived by studying the power exchange mechanism and power ...tetrahedron phasor diagram. The switching dynamics of a voltage source inverter (VSI)-based three-phase, three-wire (three-leg /half-bridge) shunt APF system with hysteresis band current control has been studied and verified by simulation. The relation between the design parameters and their effects on the active losses has also been identified. Detailed calculation and extensive simulation have been performed for a three-phase, three-wire shunt APF implemented in a 400VL–L distribution system, as an example, to study the effects of design parameter selection and their role in active power loss calculation. Simulated and calculated results are presented for the important design parameters for different switching frequencies together with their associated losses and kVA ratings. The procedure can be followed to design the parameters for other topologies, such as three-phase, four-wire or single-phase systems.
This paper reports the development of a laboratory prototype of a fully digital DSP-controlled 12-kVA unified power quality conditioner (UPQC), capable of compensating for both the supply voltage and ...the load current imperfections. A fully digital controller based on the TMS320F2812 DSP platform is implemented for the reference generation as well as control purposes. The delay problem in the digital controller is overcome by application of a fast DSP, a compact control technique and proper flow of control steps in the DSP software. A phase-locked loop-less software grid synchronization method has been implemented for the effective operation of the UPQC under conditions of grid frequency variation. A sequence-based compensation strategy has been developed to compensate for balanced and unbalanced sags while accommodating the fact that the voltage injection capability of the UPQC is limited. The prototype UPQC power circuit, control features, and control algorithm along with experimental results are presented in this paper.
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