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In this paper, we study multiple interconnected smart microgrids, and develop an efficient strategy for their internal device scheduling and energy trading. This paper achieves the following objectives. First, each microgrid holistically manages its internal devices, such as local storage systems and reactive power compensation levels, and external active/reactive energy trading (with the external grid and other microgrids) simultaneously for real-time optimization. Scenarios of social cooperation and game in interconnected microgrids are formulated as distinct objectives of the microgrids, which aim to optimize their own performance and gain benefits through energy trading. Second, microgrids of different network topologies (radial and meshed) and nominal voltages are fully incorporated. Third, a fully distributed model-predictive and computational-intelligence-based algorithm is proposed, so that microgrids’ devices operate autonomously with minimum communication exchange, obviating the need for a central controller. Convergence properties of the proposed distributed algorithm are analyzed and benchmarked with a state-of-the-art distributed algorithm, and numerical simulations for different scenarios are performed demonstrating that the proposed distributed strategy can be feasibly applied to real-world microgrids. [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) system inverters have been frequently utilized for reactive power support in the literature. Although the benefits of PV reactive power for the grid have been quantified, the costs incurred by the PV owner have largely been ignored. This paper combines the findings from power electronics research and power system economics to formulate the cost of reactive power from PV inverters, considering the inverter degradation due to the reactive power provision. One-year simulations with real weather and load data for the case of Singapore for different levels of PV penetration have been conducted. Subsequently, the benefits of local reactive power provision to the system and its effect on the lifetime of PV inverters were analyzed. It was found that the cost of inverter lifetime reduction is a significant part of the reactive power cost (more than 50% at lower PV penetration), but decreases at higher PV penetration when the reactive power support is distributed over more PV systems. Through comprehensive analysis, the feasible range for monetary incentives for PV reactive power support has been identified. The results from this paper can, therefore, be used as a foundation for future research, formulating regulations, and for market analysis. [ABSTRACT FROM AUTHOR]

This work proposes an analytical approach for reactive power dispatch and energy arbitrage in grid-connected distribution systems with distributed energy resources. The comprehensive approach minimizes the operational cost of the system while incorporating the price of electricity, cost of reactive power, reactive power charge, line losses, and energy arbitrage. Mathematical programing and metaheuristic algorithms have been employed as benchmarks, and the efficacy of the analytical approach was validated on 69 and 119-bus radial distribution systems with real solar irradiance and electricity price data. The proposed approach removes the dependence on initial solutions and parameter tuning, shows superior results compared to the benchmark algorithms, and is up to 100 times faster compared to existing algorithms commonly used. It is therefore suitable for both day-ahead and real time power dispatch applications. [ABSTRACT FROM AUTHOR]

Abstract With the increasing adoption of photovoltaic systems (PVs) in distribution grid, many researchers and grid operators have proposed and started to utilise PV inverters for local reactive power compensation (RPC). The local RPC has been shown to reduce losses in the system, and to help maintain voltage within acceptable range. Moreover, RPC using PV is already competitive when compared with traditional reactive power devices. Nevertheless, the RPC using a PV inverter increases the current flowing through it, and hence the losses and the temperature of its components. As a result, the lifetime of the inverter will be reduced with increasing reactive power usage, incurring costs to the system owner and increases the PV levelised cost of electricity (LCOE). It is therefore imperative to consider the inverter degradation, as a rise in the LCOE may cause PV to be less competitive compared to other energy sources. Thus, in this work, the competitiveness of PV inverter as a reactive power compensator is reassessed, accounting for the inverter lifetime reduction. Case studies on test systems based on real distribution network are conducted to illustrate the importance of considering inverter lifetime reduction. The results from this work can be used by PV owners, power system operators and regulators in determining whether to utilise PV for RPC, and to what extent, based on their market situation. [ABSTRACT FROM AUTHOR]

Short-term and very short-term load forecasting are essential for power grid management operations such as automatic generation control, unit commitment scheduling, and transmission loss estimation. Most existing forecasting techniques require that the load data be available up to the current time step. In recent years, cyber attacks increasingly threaten the secure operation of power grids. One potential cyber threat is communication failure which will affect load forecasting. When communication failure happens and actual load data are not available, forecasting accuracy suffers. To overcome this problem, we propose a time-forward kriging based approach to forecast load with and without communication failure. This technique has the ability to forecast the load by utilizing load information from neighboring regions. The proposed method has been tested using NYISO and PJM load data with 5-min and 1-h intervals, respectively. Our results show that the proposed method is capable of forecasting load under communication failure with acceptable accuracy and improved accuracy when compared with other forecasting techniques. [ABSTRACT FROM AUTHOR]

This work analyses the economic and technical impact of local reactive power provision in grid-connected microgrids with distributed energy resources. Costs of reactive power provision by photovoltaic systems and battery energy storage systems are explicitly formulated and an objective function incorporating the costs is proposed. The advantage of the proposed objective function is validated by comparing it with other objective functions frequently employed in the literature. From various case studies, the extent of economic and technical benefits of local reactive power provision for the microgrid is established. Subsequently, the technical and economic competitiveness of reactive power provision using inverter-based distributed energy resources are compared against those using switched capacitors. Extensive sensitivity analyses are performed to determine the scenarios in which one technology is more competitive than the other. Inverter efficiency has been identified as the most important parameter for reactive power provision from distributed energy resources while electricity price is the most crucial factor for switched capacitors’ competitiveness in producing reactive power. [ABSTRACT FROM AUTHOR]

High and continuously increasing photovoltaic (PV) penetration in distribution network introduces many potential power system problems. One of the most important, and often the first to arise, is overvoltage issue. Although many measures have been proposed and implemented to solve the problem, a standardised metric to assess their economic viability is lacking. This paper introduces a PV levelised cost of integration (LCI) metric, which consists of all the capital and operational expenditures incurred when implementing the measures divided by the PV energy generated throughout its lifetime. The measures analysed are active power curtailment (APC), reactive power control (RPC), active-reactive power control (ARPC), as well as various battery energy storage (BES) measures. These measures were simulated on 69-bus and 119-bus distribution networks with real weather and electricity price data. Among the pertinent results are: (1) ARPC is the most cost-effective voltage mitigation measure, followed closely by RPC and APC, (2) BES cost needs to decrease by more than 80% for BES to be economically viable for overvoltage mitigation, and (3) change in reactive power charge, line losses, and BES roundtrip efficiency losses are all important components of LCI and need to be considered in assessing PV integration measures. The results and the LCI framework presented in this study can be used by policy makers, regulators, and researchers to evaluate renewable energy integration policies, methods, and algorithms. • PV Levelised Cost of Integration is proposed to evaluate PV integration measures. • PV active–reactive power control has the lowest levelised cost of integration cost. • Battery cost needs to decrease ¿80% before it becomes economical for PV integration. • The most suitable measure depends on the network's characteristics and priorities. [ABSTRACT FROM AUTHOR]

• Local optimization of global variables is proposed. • It does not require any communication with central controller or neighbors. • The approach is stable and performs as well as centralized optimization. • It does not need grid topology and removes privacy and latency issues. • The importance of solar forecasting and algorithm validation is highlighted. The number of distributed energy resources (DERs) deployed in distribution systems has been rapidly increasing in recent years. Consequently, many researchers have proposed to utilise the DERs for local reactive power support. Yet, the expansion of infrastructure necessary to allow communication among the DERs, and with a centralised controller, has not been as fast. This necessitates an independent local control method that is able to fulfil the objectives of a centralised controller. Therefore, this work proposes a data-driven local optimisation of global objectives (LOGO) algorithm to control the reactive power dispatch from DERs in distribution systems. The proposed method has been validated across different test systems with real topology, irradiance and load data, for steady-state undervoltage and overvoltage scenarios. The results have shown that LOGO performs almost as well as centralised optimisation without any communication and without any information regarding the grid topology. LOGO is able to satisfy the voltage constraints using only locally available information even when other algorithms fail to do so. Compared with distributed and other local reactive power controls, LOGO is much more stable and yields significantly better results. Moreover, LOGO's superiority over other control methods increases with system size and complexity. Hence, this work provides a viable alternative for real-life dispatch optimisation and opens up new possibilities to optimise global variables without any communication. Lastly, this paper also highlights the importance of accurate solar forecasting and validation of reactive power control. [ABSTRACT FROM AUTHOR]

With the shift in renewable portfolio standards, conventional fossil-fuel based generators are expected to be partially or fully replaced with renewable energy sources such as photovoltaics (PVs). However, replacing the conventional synchronous generators with PV generators may raise new stability concerns such as lack of inertia, insufficient reactive power and voltage fluctuations, which can jeopardize the reliability of the entire network. In this paper, various impacts of integrating utility-scale PVs and rooftop PVs and replacing the existing conventional generators on the stability of a power network are investigated. Detailed steady state, transient and small signal analyses are conducted on a large test system, namely Texas 2000-bus system for different PV penetration levels. System transients such as line faults, double-line faults, loss of generator, loss of PVs and cloud cover scenarios are simulated to study their impacts on the test system with different PV penetration levels. It is demonstrated from the impact analysis that the benefits of PVs are highly dependent on a spectrum of factors such as node criticality, type, location and penetration of PVs, and type of transients. Furthermore, the influence of battery energy storage system that are generally associated with PVs on the system stability is also discussed. • Modeling and analysis of power network with different solar penetration levels. • Voltage stability analysis of grid with solar determine the most sensitive buses. • Transient and small-signal stability analysis to analyze the impacts of solar. • Analysis with storage devices to determine their influence in network damping. [ABSTRACT FROM AUTHOR]