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.