A novel method for dynamic voltage control, followed by a power loss reduction in a wide area scheme, is presented in this study. The proposed scheme is based on a combination of multi-agent system ...and cooperative game theory concepts and determines appropriate coordination of reactive power resources for maintaining voltage security as well as lowering post-disturbance power loss of power system. In addition, the algorithm takes the advantages of previously proposed mechanisms by the authors, i.e. a predictive mechanism in taking remedial actions according to the trends of voltage magnitudes and impending remedial actions and a preventive approach providing an effective number of changes of taps in on-load tap changers. The acquired results of simulations, performed in the Nordic 32 test system, show the effectiveness and robustness of the proposed scheme.
This study introduces a new approach for coordinating volt–var control (VVC) between sub-transmission and distribution systems through optimal reactive power dispatch of distributed energy resources ...(DERs) that are aggregated as virtual power plants (VPPs). At the sub-transmission level, shunt devices and the reactive power provided by the VPPs are coordinated and optimised using a VVC algorithm with weighted sum of multiple objects that include minimising voltage deviations from desirable levels at load buses, minimising loses, minimising solar curtailment, minimising demand response usage and minimising mechanical switching of shunt elements. The algorithm runs every 5 min and is solved using the AC optimal power flow technique. At the distribution level, each VPP runs a distribution VVC algorithm to dispatch reactive power from DERs. The goal of the VPP reactive power control is to meet sub-transmission service requirements while satisfying all the constraints at the distribution side. Each VPP updates its reactive power capability every 5 min to allow the sub-transmission controller to formulate the optimisation problem for the next dispatch interval. The proposed tool is simulated on a Duke Energy Carolina system to demonstrate the capability of providing voltage support by dispatching reactive power of DERs as a VPP.
The operation and economic profitability of modern energy systems is constrained by the availability of renewable energy and water resources. Lower water availability due to climate change, higher ...demand and increased water consumption for non-energy and energy needs may cause problems in Africa. In most African power systems, hydropower is a dominant renewable energy resource, and interconnection capacities are usually limited or unreliable. This paper describes a new modelling framework for analysing the water-energy nexus in the African Power Pools. This framework includes soft linking between two models: the LISFLOOD model is used to generate hydrological inputs and the Dispa-SET model is used for mid-term hydrothermal coordination and optimal unit commitment and power dispatch over the whole African continent. The results show a good agreement between the model outputs and the historical values, despite data-related limitations. Furthermore, the simulations provide hourly time series of electricity generation at the plant level in a robust way. It appears that some African power pools heavily rely on the availability of freshwater resources, while others are less dependent. In the long term, the dependence of the power system on water resources is likely to increase to meet the increasing electricity demand in Africa.
•Robust and highly detailed analysis of water-energy nexus in African power pools.•Open source soft-linking framework between LISFLOOD and Dispa-SET models.•First open-source unit commitment and power dispatch model of African power pools.•A compilation of diverse data sources used for the integrated water-energy modelling.•Examination of current and future electricity situation and potential of power trade.
An analytical method for placement and sizing of distributed generation on power distribution systems for loss reduction is introduced. The proposed analytical method is developed based on a new ...formulation for the power flow problem, which is non-iterative, direct, and involves no convergence issues even for systems with high R/X branch ratios. Further, this power flow solution is extremely useful whenever fast and repetitive power flow estimations are required. A priority list based on loss sensitivity factors is developed to determine the optimal locations of the candidate distributed generation units. Sensitivity analysis is performed to estimate the optimal size and power factor of the candidate distributed generation units. Various types of distributed generators (DGs) have been dealt with and viable solutions are proposed to reduce total system loss. The proposed method has been tested on 33-bus and 69-bus distribution systems, which are extensively used as examples in solving the placement and sizing problem of DGs. Exhaustive power flow routines are also performed to verify the sizes obtained by the analytical method. The test results show that the proposed analytical method could lead to optimal or near-optimal solution, while requiring lower computational effort.
This paper explores a new configuration for modular DC/DC converters, namely, series connection at the input, and parallel connection at the output, such that the converters share the input voltage ...and load current equally. This is an important step toward realizing a truly modular power system architecture, where low-power, low-voltage, building block modules can be connected in any series/parallel combination at input or at output, to realize any given system specifications. A three-loop control scheme, consisting of a common output voltage loop, individual inner current loops, and individual input voltage loops, is proposed to achieve input voltage and load current sharing. The output voltage loop provides the basic reference for inner current loops, which is modified by the respective input voltage loops. The average of converter input voltages, which is dynamically varying, is chosen as the reference for input voltage loops. This choice of reference eliminates interaction among different control loops. The input-series and output-parallel (ISOP) configuration is analyzed using the incremental negative resistance model of DC/DC converters. Based on the analysis, design methods for input voltage controller are developed. Analysis and proposed design methods are verified through simulation, and experimentally, on an ISOP system consisting of two forward converters.
In this study, a multi objective method for optimal network reconfiguration as well as reactive power dispatches of distributed generations (DGs) has been proposed to improve the network performances ...by using non-dominated sorting particle swarm optimisation. The various network performances in terms of multi objective function include minimisation of system power loss, voltage deviation and energy wastage from solar and wind generation system. The effectiveness of the proposed method has been tested on the IEEE 33-bus radial distribution system for different combinations of network reconfiguration and reactive power output of DGs or its varying power factor. The obtained results also compared and indicated that better network performances achieved with both network reconfiguration and power factor optimisation over other cases. In addition, this strategy also results in lesser energy wastage from distributed renewable generation over without network reconfiguration option; hence, this approach is also suitable for saving and utilising maximum capacity of available renewable sources.
New telecommunication towers are installed in remote/rural areas to facilitate the increasing connectivity worldwide. With concerns over environmental issues, such towers are to be environmentally ...friendly. Conventionally, diesel generator supply power to towers in remote/rural areas, which leads to carbon emission. Also, the operation of diesel generator entails considerable operating cost (fuel and maintenance costs). Thus, a wind-photovoltaic (PV) based DC microgrid is proposed for supplying power to telecommunication towers in remote/rural areas ensuring reliable, economical, and green power supply. Therefore, techno-economic analysis is carried out here to determine the feasibility and cost of electricity (COE) per unit of the proposed DC microgrid. A non-dominated sorting genetic algorithm II is implemented to solve the multi-objective optimal sizing problem to achieve a trade-off between the cost and the reliability. Hourly solar irradiation and wind speed data is used for long-term analysis equivalent to the lifespan of the battery. Further, de-rating factor and maximum power point tracking factor are considered while modelling the renewable resources. The loss of power supply probability, excess energy, and COE are calculated and different scenarios are studied to examine the techno-economic feasibility of the proposed DC microgrid.
This study proposes a power electronics interface (PEI) for photovoltaic (PV) applications with a wide range of ancillary services. As the penetration of distributed generation systems is booming, ...the PEI for renewable energy sources should be capable of providing ancillary services such as reactive power compensation and low-voltage ride through (LVRT). This study proposes a robust model predictive-based control strategy for grid-tied Z-source inverters (ZSIs) for PV applications with LVRT capability. The proposed system has two operation modes: normal grid condition and grid fault condition modes. In normal grid condition mode, the maximum available power from the PV panels is injected into the grid. In this mode, the system can provide reactive power compensation as a power conditioning unit for ancillary services from DG systems to main ac grid. In case of grid faults, the proposed system changes the behaviour of reactive power injection into the grid for LVRT operation according to the grid requirements. Thus, the proposed controller for ZSI is taking into account both the power quality issues and reactive power injection under abnormal grid conditions. The proposed system operation is verified experimentally, the results demonstrate fast dynamic response, small tracking error in steady-state, and simple control scheme.
Dynamic states in the power grid – deep voltage sags and swells, voltage fluctuation – can cause faults and defects in sensitive loads and in consequence financial losses. This study presents a ...voltage conditioner based on a direct PWM AC/AC converter with matrix chopper cooperating with a distribution transformer, called a hybrid distribution transformer (HDT). In comparison with other solutions of hybrid and smart distribution transformers, the proposed HDT is characterised by having a simple construction and small number of power electronic switches, a wide range and continuously variable voltage control character, and good dynamic properties, in combination with a high reliability. The study contains a detailed operational description and the experimental test results of a 1 kVA rated power laboratory model. The experimental tests were conducted in a closed control-loop with a peak detector unit in a feedback path, as well as with various types of voltage perturbation with linear and non-linear loads. In addition, some of the properties of the proposed HDT have been compared with other similar hybrid and smart distribution transformers described in the literature.
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