Massive deployment of distributed energy resources (DERs) along with innovations in information and communication technologies have changed the power system from a hierarchical structure to a more deregulated model by introducing new generations at lower levels. This change raises operational and market challenges. Local energy trading provides opportunities to manage these DERs by encouraging localised trading. The concept of local energy trading at the distribution level is widely broadcasted for implementation in the power system. In the design of electricity markets for local energy trading, a clear definition of market participants, their objective, and purpose of market clearing should be established. This design depends on the changing needs of the power system and can be performed from different viewpoints. Classification and organisation of the literature on potential designs for local energy trading can help researchers to develop their future steps properly. This study presents a comprehensive review on this topic and provides a systematic classification of the market players, market clearing objectives, and approaches. Several research works are analysed against different criteria, including scalability, overheads requirements, and network constraints management.

This study proposes a new application and a novel control scheme for utilising Smart PV and Smart Park inverters to mitigate temporary overvoltage (TOV) phenomenon in distribution systems. As more number of the inverter-based distributed generators such as PV are connected to a medium- and low-voltage distribution systems, TOV phenomenon becomes more prevalent during single line to ground fault. Currently, the IEEE 142 ‘Effective grounding’ technique has been the reference for various grounding schemes to prevent TOV. This study explores the potential of low-cost and a novel solution for the first time that utilises a specialised controller associated with PV/SmartPark inverters (Smart inverters) as a TOV suppressor. The efficacy of the aforementioned novel application has been demonstrated on a simplified benchmark system of the IEEE Standard 399-1997 with few modifications. A 4 MW conventional PV plant is considered along with 10 MVAR Smart inverter connected to the point of common coupling. During normal operation of the distribution systems, the Smart inverter controller acts in a voltage regulation mode to curtail the voltage rise due to reverse power flow from the 4 MW PV plant. During a fault condition, the TOV sensor enables the TOV control to suppress the violated limits of voltages in the healthy phases to an acceptable value.

The complicated response of inverter-interfaced distributed generators (IIDG) to faults has been reported, which severely affects all parts of relaying, i.e. fault sensing and polarisation, and faulted phase selection. Given this, the root causes of difficulties in dealing with the protection of inverter-based microgrids are explained. Then, the study describes a directional element using unique features of zero-sequence components that retains satisfactory performance even in IIDG-based microgrids. The zero-sequence component is the only sequence component that can be calculated in the time domain without time delay and thus can cause less delay in the outcome of protective schemes compared with the other two sequences. With this, instantaneous zero-sequence power is defined and one term derived from it, zero-sequence reactive power, is utilised to polarise ground faults. It is proven that the zero-sequence reactive power is negative for forwarding ground faults and positive for reverse ground faults. An interesting feature is that the zero-sequence reactive power is calculated by averaging a new quantity in the time domain over half a power cycle. Hence, the time delay is half that of the conventional phasor-based methods. A sample microgrid is simulated in MATLAB/SIMULINK to evaluate the directional element and the results demonstrate the improvements.

Nowadays the fast-decoupled state estimation (FDSE) is widely used in almost every power system control centre. FDSE is effective and efficient for most transmission systems but it may not converge for systems with a large ratio of branch resistance to reactance (R/X); meanwhile the branch current magnitude measurements (BCMMs) cannot be reliably used in FDSE, thereby limiting its applications especially for the distribution systems where BCMMs abound. In this study, the above two problems have been addressed by transforming all measurements so that they can be classified as quasi-real power measurements and quasi-reactive power measurements, leading to a generalised FDSE (GFDSE) with a solid theoretical foundation. The formulation of GFDSE is based on only the assumption, rather than three assumptions used in FDSE. As a result, GFDSE has good adaptability to transmission systems as well as distribution systems; additionally, BCMMs can be reliably used in GFDSE. Case studies based on IEEE benchmark systems and a real grid of China demonstrate that the proposed GFDSE has very good convergence properties for transmission systems and distribution systems; and at the same time, the proposed GFDSE is also superior to FDSE in terms of computational efficiency under almost all cases.

The data is not always shared among sub-networks due to concerns about information privacy or difficulties in synchronous information exchange. It is difficult or even impossible to obtain the probabilistic power flow (PPF) by the centralised analysis. In this paper, an equivalent model considering static power–frequency characteristics (SPFCs) and renewable uncertainties is proposed. In this model, SPFCs of equivalent loads and generators are derived to retain SPFCs of original external loads and generators, respectively. In addition, probabilistic characteristics and correlations of equivalent loads are formulated based on Cholesky decomposition to preserve original external renewable uncertainties. The proposed model is further applied to PPF and then PPF can be solved via Monte Carlo simulation method, which makes that the PPF results can be obtained when the detailed data of the original external network cannot be shared. Owing to efficiently preserving the external SPFCs and renewable uncertainties in the proposed equivalent model, the accuracy of PPF results can be guaranteed. Simulation results of IEEE 14-bus and IEEE-118 bus systems demonstrate the effectiveness and superiority of the proposed equivalent model and its applications to PPF, compared with existing well known equivalent models and their applications to PPF.

This study introduces a grid planning approach for reactive power management at the transmission–distribution interface with the support of distributed generators (DGs). The main research question is: can reactive power management with DGs provide controllable reactive power with a very high availability and can this reduce or avoid the demand for additional reactive power compensators in a distribution grid section (e.g. mechanically switched compensators)? Therefore, an availability analysis of reactive power support is performed for different generation types at the distribution level, like hydro, thermal, wind and photovoltaic power plants. For the investigated case study of a real German distribution grid, reactive power management with the support of DGs could relevantly reduce the demand for additional reactive power compensation devices. However, the effectivity of DGs for reactive power support strongly depends on the applied grid planning rules and requirements at the transmission–distribution interface.

This study develops a new robust hierarchical predictive sliding mode controller to damp the wide-area electromechanical oscillations in an uncertain wide-area power system. The coefficient matrices of wide-area systems are often sparse matrices which cause the inverse calculation of them very complex or impossible. In the suggested approach, first the entire system is divided into several small subsystems with non-sparse matrices and lower order; then a new predictive sliding mode controller with robust reaching law is designed to provide the optimal performance and robustness to uncertainties and external disturbances. Also, the gradient of interaction errors is employed for coordination of overall wide-area system. The capability and efficiency of the developed control framework is verified through numerical simulations on an uncertain power grid with interconnected multi-areas, for various cases of perturbations and parameters’ uncertainties. Simulation studies illustrate the effectiveness of the suggested method to improve the wide-area power grid damping in terms of acceptable robustness to external disturbances and system's parameter variations, in comparison with two other methods which are adopted from the literature.

Power transformer protection has a high sensitivity due to its important role in power systems. Various factors such as inrush and sympathetic inrush currents may result in the inappropriate performance of protective relays and cause problems such as power outage or blocking of sensitive loads. Until now, several studies have been performed on the detection and reduction of inrush current, however, the effect of sympathetic inrush current on transformer protection has not been addressed. In this study, the operation of the protection system during the sympathetic inrush current is comprehensively analysed. Furthermore, the use of a fault current limiter is proposed to reduce the undesirable effects of the phenomena. The effects of the limiter on the saturation of power and current transformers are investigated. A real transmission station is simulated using DIgSILENT Power Factory Software to perform these studies by considering the resistive and impedance fault current limiter.‏ Results show that protective relays do not have an improper operation during the phenomena with limiters. Moreover, with the resistive fault current limiter, sympathetic inrush and inrush currents are decreased by 5 and 15% more than the impedance fault current limiter, respectively. Saturation of power and current transformers is significantly reduced with limiters, especially with a resistive fault current limiter.

In order to provide reasonable economic signals for distribution companies (DISCOs) and further compensate for distributed generators (DGs) integrated in distribution networks equitably, the contributions of DGs to loss and emission reduction in distribution networks should be allocated according to their own responsibilities. Generally, the loss and emission reduction of the network can be allocated based on traditional cooperative-game-based allocation methods such as nucleolus method and Shapley value method. However, traditional cooperative-game-based allocation methods will result in the combinational explosion problem with the integration of a large number of DGs. In order to tackle this problem, minimum costs-remaining savings (MCRS) method and Aumann–Shapley value method are employed for loss and emission reduction allocation. Simulation results of two cases show that compared with the allocation results of traditional cooperative-game-based allocation methods, the proposed MCRS method and Aumann–Shapley value method both have the characteristics of individual rationality, coalition rationality, and global rationality. Furthermore, neither MCRS method nor Aumann–Shapley value method has the problem of combinational explosion, which can reduce computational burden with regard to the integration of a large number of DGs.

To quantify the non-linear variation of top-oil temperature with load current, and further investigate the key parameters in the thermal model, a model for calculating the oil exponent is proposed in this study. First, a global oil momentum model was established based on the fluid resistance characteristic. Then, based on the heat transfer coupling relationship between the winding, the oil flow, and the radiator (outside air), a set of control equations describing the oil temperature and the oil flow rate was established by using energy conservation. Simultaneously, the top-oil temperature was recorded from a field traction transformer to verify the physical part of the proposed model. The regression model parameters were identified with the ordinary least-square estimation so the oil exponent can be calculated naturally. The calculated oil exponent of the traction transformer at a wide range of load was 0.7308, so the accuracy was improved by 9.47% compared with the IEEE/IEC recommended value. Newly updated oil exponent was also verified through a dynamic overload heat run test. It is expected that the proposed oil exponent model can help in estimating top-oil temperature with more convenience and accuracy, especially in frequent overload conditions.

This work presents a cooperative demand-side management (DSM) scenario in a low-voltage network considering a context of liberalised electricity markets. The authors show that introducing an additional inter-supplier cooperation mechanism among consumers enhances a better use of the flexibility consented by each individual, hence aiming at reaching a global optimum instead of optimising the costs of a few ones. To that end, a real-time pricing (RTP) scheme is explored based on cost functions differentiated in both time and consumption level that should reflect the true energy cost. The authors apply to each consumer a commodity cost function shared among the set of cooperative users of its respective supplier as well as one common network cost function shared by all cooperative users of all suppliers in the considered network. Each individual runs, through its smart meter (SM), a decentralised optimisation algorithm defining an energy consumption schedule for a set of flexible appliances (FAs). The mechanism the authors propose ensures that a fair cost distribution between all users is achieved by reaching the Nash equilibrium. To assess their proposition, they confront it to intermediate consumption strategies through a benchmark. The results confirm that their inter-supplier cooperation mechanism always leads to the minimum total cost.

Industrial automation has been widely used in electric power substations. In this context, the IEC 61850 standard provides for the utilisation of redundancy in the data link layer to increase frame reception probability. This study aims to evaluate the availability of two power substation automation architectures based on the IEC 62439-3 standard, which describes two redundancy protocols named parallel redundancy protocol (PRP) and high-availability seamless redundancy (HSR). The authors evaluate both architectures using either PRP or HSR protocol against using no redundancy protocols. The reliability block diagram method has been used, and afterwards, the mean time to failure and availability have been calculated. Results show that the utilisation of redundancy protocols allied to the repair during the mission allows classifying the architectures in the higher availability class according to CEI IEC 870-4.

A battery storage can diversify its portfolio by participating in the energy market, regulation market, and point-to-point (PTP) obligation market. In order for a battery storage to maximise profits and hedge risks, a portfolio management model that co-optimises a storage's bids in these three markets is proposed. The proposed model is trained and validated by real market data. The performance of the proposed portfolio is compared with the portfolio without consideration of PTP obligation, indicating that the proposed method is effective in risk hedging. Numerical results also show the trade-off between storage's expected profits and risks, which can be useful for a battery storage owner with a certain degree of risk aversion.

The existing transmission charging methods like long-run incremental cost give forward-looking charges which reflect the impact of system congestion on required network investment, but the flexibility of demand is not considered. This study proposes a novel transmission charging method which takes into consideration the demand response (DR). The proposed method could reflect: (1) how DR influences the short-run congestion management cost and long-run investment cost; (2) how DR influences the transmission charges. To promote the effect of DR, an approach is proposed to determine the optimal nodes for the implementation of DR based on the available transfer capability and congestion cost. Through the approach, different plans for the implementation of DR will be produced in different demand levels. The optimal node determination approach not only makes DR more targeted for the system congestion but also improves the effect of the proposed transmission charging method. The proposed method is applied to the IEEE 14-bus system and a practical system in Western China. The results indicate that the proposed charging method can offer consumers with economic incentives to alleviate congestion, especially when the DR implemented on the optimal nodes, and thus delay the network reinforcement investment.

The mismatched feeder impedance of the voltage-sourced converter (VSC) units may result in reactive power sharing error in the islanded microgrids. This study presents a reactive power sharing strategy for single-phase inverter-based microgrids that eliminates the circulating currents and reduces the coupling between real and reactive powers. The proposed controller is based on an adaptive complex virtual impedance that aims to equalise the characteristic output of VSCs. The resistive term regulates the virtual voltage drop using the proposed droop characteristic, while the inductive one controls the phase angle of VSC current and increases the ratio of the microgrid. The proposed strategy does not require a central controller and knowledge of the microgrid lines and loads data and is applicable for the various microgrid topologies. Furthermore, it employs the unidirectional low bandwidth communication link and is robust against the delay and failure of communication channels. The proposed method is implemented using the conventional droop control scheme and presents the medium plug and play capability. Both simulation and experimental case studies using various microgrid topologies are conducted to demonstrate the merits of the proposed scheme.

This study proposes a power flow methodology focused on the need for reconfiguration analysis in modern distribution networks. The proposal is based on the extended fast decoupled Newton–Raphson method, which uses the information of the network switching equipment status (open or closed). To deal with eventual islanding during a reconfiguration procedure, a numerical observability technique used in state estimation analysis has been adapted for topological processing when network segments are disconnected from voltage references. A complex per unit normalisation technique is employed so that the power flow calculation by the fast decoupled approach is viable, even for networks having high R/X ratio lines. Simulation results considering two distribution feeders, one of large size, with different topological conditions are presented. The performance of the proposed methodology qualifies it as a relevant computational tool to support network reconfiguration studies involving emergent distribution systems.

Integration of distributed generation (DG) at large scale with high penetration challenges the radial structure of the traditional distribution networks and the effectiveness of the conventional voltage regulation methods. In this study, the clusters partitioning and voltage regulation are researched. The modified electrical distance is introduced. An effective method, based on spectral clustering algorithm, is proposed for the partitioning of the DG network via the judgement of critical load buses. Two-stage voltage regulation optimisation is realised in each sub-community. The optimal objects are the minimal voltage fluctuation and the network loss of the distributed network. The independent variables are reactive-power absorption and active-power curtailment for each controllable photovoltaic node. An advanced particle swarm optimisation algorithm is applied to the voltage regulation for the sub-communities. After a case study of the IEEE 33-bus system, a regional distribution network in Anhui province of China is analysed. Simulation results indicate that the node voltages are stabilised with the improvement of power quality employing the proposed clusters partitioning method and zonal power control scheme.