This study presents a technique to locate the source of faults in distribution systems, i.e. to pinpoint where the fault has occurred along the distribution system. More specifically, it localises the origin of short duration voltage variations (SDVVs) in a distribution system. Fault location (its origin) is estimated solely from the voltage waveforms during the fault. More specifically, the energies of the instantaneous symmetrical components corresponding to the voltage waveforms are used to estimate the fault location. The proposed localisation strategy considers that the signal records during a fault are captured at the feeder start node and at other nodes scattered along the distribution systems. Simulation results show the feasibility of the proposed technique to accurately localise the origin of faults in distribution systems.

Modern power system involves growing use of open channel communication in secondary frequency regulation which introduces time delay in the automatic generation control loop which may lead to system instability. This study proposes a novel power system frequency stabiliser (PSFS) which is a modified secondary controller in order to improve the system stability in the presence of large communication delays. An auxiliary signal is added to the secondary controller to provide additional damping. The gain of the controller is obtained by meta-heuristic methods. The proposed controller is first developed on a single area hydropower system and the same is then applied on the Western System Coordinating Council 3-machine, 9-bus power system. Furthermore, to show the effectiveness of the proposed PSFS in a large practical multi-area system; it is also applied to the IEEE 39-bus system. Results show that the proposed controller significantly improves the stability of a power system operating with large communication delay which is first considered as constant and then the stability improvement with the proposed PSFS in the presence of random communication delays is also shown. The PSFS performance is tested by the results obtained with MATLAB/Simulink simulations and further verified on a real-time simulator.

As a typical approach to demand response (DR), direct load control (DLC) enables a load service entity (LSE) to adjust the electricity usage of residential customers for peak shaving during a DLC event. Households are connected in low-voltage distribution networks, which are always three-phase unbalanced. However, existing work has not considered the detailed operational constraints of three-phase distribution networks, which may lead to decisions that deviate from reality or are even infeasible in practice. Moreover, centralised control may cause privacy and communication issues. This study proposes a distributed residential DLC method that considers the operational constraints of three-phase unbalanced distribution networks and privacy of residential customers. Numerical tests on IEEE benchmark systems demonstrate effectiveness of the method. The proposed distributed method can converge within 17 iterations in IEEE 123-bus distribution system, which demonstrates scalability of the proposed algorithm.

In some recent articles, the vulnerability of phasor measurement unit (PMU) to the time synchronisation attack by spoofing its global positioning system (GPS) has been highlighted as a threat to power grid protection, control and monitoring system. Having spoofed PMU GPS signals, one can manipulate the measurements and inject bad data to power grid protection and monitoring system. The existing anti-spoofing methods are all based on GPS signal analysis. The mentioned methods are just able to detect spoofing without any data refinement as the data of power grid has not been practically used in calculations. Furthermore, some of these methods lose their certainty in noisy and harsh environments due to low power of GPS signals. A novel anti-spoofing algorithm has been proposed based on power grid infrastructures which can join to any of the existing anti-spoofing algorithm to empower spoofing detection process. The proposed algorithm adopts phasor measurement analysis and state estimation methods to detect spoofing. The composite of this algorithm with any of the existing algorithms will not only cover the probable malfunctioning in spoofing detection but also be able to refine counterfeit measurements.

This study presents a two-stage planning framework of the battery energy storage system (BESS) and micro-turbine (MT) in a microgrid. In the first stage, the optimal allocation decisions are made before the actual realisation of the operational uncertainties. In the second stage, the optimal operation strategies are made for the microgrid by minimising the costs paid to the main grid, fuel cells, MTs, BESSs and controllable loads (CLs). The hot water system and interruptible load are considered as CLs. Their mathematical models are built to investigate their roles in smoothing renewable energy. In addition, efforts are made to keep the linearity of the formulated optimisation problem, and the backward scenario reduction method is adopted to further enhance the computational efficiency. The modified IEEE 33-bus radial system is used as a microgrid to verify the effectiveness of the proposed approach for both islanded and grid-connected microgrids. Sensitivity analysis has been conducted to compare the economics and robustness of the identified solutions.

This study presents an innovative approach where both sides of a back-to-back (BtB) system are controlled using the synchronverter approach, allowing to control the power transfer through the converters as it would be in a real motor–generator pair system. A novel way to transfer the DC voltage control loop in the BtB converter is proposed, letting to a softer and less noisy power transferring, as shown in simulation results. The modelling equations of the synchronverter and the traditional dq frame in a BtB converter are presented in this work. In addition, a comparison between these two control approaches using three different performance indexes is done, showing that the power transfer behaviour using the synchronverter approach is significantly improved. Finally, the ability of the BtB converter working as a power balancer system (PBS) to manage congestion between two distribution networks in a test bed case is tested. Results show that it is possible to obtain the PBS power quality benefits without the additional phase-locked loop units and the decoupling process, necessary with the dq frame, resulting in a simpler controller design.

Due to the limited generation and finite inertia, microgrids suffer from a large frequency and voltage deviation which can lead to system collapse. Thus, a reliable load shedding method is required to maintain frequency stability. A wireless network, benefiting from the high flexibility and low deployment cost, is considered as a promising technology for fine-grained management. In this study, a distributed load shedding solution via a wireless network is proposed for balancing the supply–demand and reducing the load-shedding amount. Firstly, the real-power coordination of different priority loads is formulated as an optimisation problem. To solve this problem, a distributed load shedding algorithm based on sub-gradient method is developed for gradually shedding loads. Using this method, power compensation can be utilised and has more time to decrease the power deficit, consequently reducing the load-shedding amount. Secondly, a multicast metropolis schedule based on time-division multiple access is developed. In this protocol, time slots are dedicatedly allocated to increase the response rate. A checking and retransmission mechanism is utilised to enhance the reliability of our method. Finally, the proposed solution is evaluated by using an NS3-Matlab co-simulator. The numerical results demonstrate the feasibility and effectiveness of our solution.

Plug-in electric bus (PEB) is an environmentally friendly mode of public transportation and PEB fast charging stations (PEBFCSs) play an essential role in the operation of PEBs. Under effective control, deploying an energy storage system (ESS) within a PEBFCS can reduce the peak charging loads and the electricity purchase costs. To deal with the (integrated) scheduling problem of (PEBs charging and) ESS charging and discharging, in this study, the authors propose an optimal real-time coordinated charging and discharging strategy for a PEBFCS with ESS to achieve maximum economic benefits. According to whether the PEB charging loads are controllable, the corresponding mathematical models are, respectively, established under two scenarios, i.e. coordinated PEB charging scenario and uncoordinated PEB charging scenario. The price and lifespan of ESS, the capacity charge of PEBFCS and the electricity price arbitrage are considered in the models. Further, under the coordinated PEB charging scenario, a heuristics-based method is developed to get the approximately optimal strategy with computation efficiency dramatically enhanced. Finally, the authors validate the effectiveness of the proposed strategies, interpret the effect of ESS prices on the usage of ESS and provide the sensitivity analysis of ESS capacity through the case studies.

This study presents a new fault location algorithm for multiple-circuit shared tower transmission lines with different voltages utilising synchronised measurements. The formulation of the proposed algorithm is based on overhead transmission lines theory and Taylor series expansion of distributed-parameter line model. The untransposition of the lines and the mutual coupling between the parallel lines are considered to achieve precise fault location. Kirchhoff's current law and fault location equation are used to identify the faulty section and obtain the location of all normal shunt faults and inter-circuit faults. The power system is simulated with DIgSILENT Power Factory software and all calculations are performed by MATLAB. Numerous fault cases are conducted to demonstrate the efficacy of the proposed algorithm considering different values of fault resistances, different fault locations and all fault types. In addition, the effects of synchrophasors errors, measurement errors and the soil resistivity variations are investigated. The results of simulation prove the efficacy of the proposed algorithm for all fault cases.

Local controls for harmonic distortion and voltage unbalance have become inapplicable due to the increasing penetration and decentralisation of disturbance sources. The complication and expansion of distribution networks cause difficulties in measuring certain system parameters, which reduce the practicability of global optimisation controls. Accordingly, this study introduces a partition control strategy driven by the disturbance data of nodes, which is used to allocate active power filters (APFs) to individually or simultaneously suppress harmonic distortion and voltage unbalance in distribution networks. A multidimensional piecewise linear representation based on local extreme points is proposed to extract the trend features of univariate disturbance time series (UDTS) and multivariate DTS (MDTS). Trend features, disturbance severities, and subsection lengths are used to establish a parameter matrix as the pattern representation of DTS. A feature distance (FD) method is developed to implement pattern matching on UDTS or MDTS to measure the coupling degrees of single or integrated disturbance among nodes. Area division and APF allocation are performed based on the coupling degrees. Case studies on a 14-bus distribution system are conducted to verify the rationality of the partition control strategy and the accuracy of the FD method.

This study presents a generic linearised modelling method and a virtual parallel resistor damping control for a voltage source converter-based high-voltage direct current (HVDC) system including a direct current (DC) grid. The generic modelling method is composed of DC network's equivalent node-admittance matrix and the Thévenin equivalent matrix of all converters. A simplified two-terminal HVDC system is used to identify the key factors influencing the stability of the DC grid easily. Those key factors are proved by two methods, namely, root locus and participation factors analysis. The parameters of the virtual parallel resistor damping control are designed using the simplified HVDC system. The performance of the proposed damping control is studied employing the linearised model of the DC grid. Time simulations such as instability suppressing, power-controlled station N − 1 fault, and DC system faults are carried out to validate the effectiveness of the damping control.

With the development of grid interconnections, the propagation phenomena of disturbance are more and more apparent. They take the form of electromechanical waves. These waves could contribute to cascading events and even large blackouts. To avoid this problem and to devise a prevention control strategy, the authors present further analysis of disturbance propagation. In this study, the disturbance propagation characteristic is studied to illuminate the influence of the network structure and the line reactance. The relationship function between generator inertia and impedance is derived. The model approach of power networks based on unsymmetrical inertia distribution is presented; the electromechanical wave model of power systems is built based on the network frame structure. The simulations are carried out to demonstrate the accuracy and effectiveness of the proposed disturbance propagation model.

Photovoltaic (PV) systems, as distributed energy resources, can adversely affect the coordination of the protection system in distribution circuits. Various approaches have been presented in the literature to solve this problem, but none of them has proposed a solution for the staircase current waveforms seen in PV-dominated distribution systems. As there is insufficient time to apply new settings to a protection device following a fault, the appropriate solution should be to adaptively modify the characteristic curves in advance of the fault. Accordingly, using the voltage profile as a pre-fault index for current waveform, this study suggests an adaptive approach to efficiently modify the protection settings before the fault occurrence. To this end, first, an offline technique is used to calculate the best appropriate group setting corresponding to each voltage profile. Second, in real time and according to the voltage profile, an online algorithm applies the predefined group settings to the corresponding protection devices. Simulation results demonstrate the effectiveness of the proposed method on a practical network such that by applying the proposed technique, settings on programmable protection devices can be readily modified to improve on their coordination.

This article deals with automatic generation control (AGC) of an unequal two-area system under deregulated environment. Area-1 comprises distribution generation (DG) and thermal units and area-2 has gas and thermal units. The DG unit comprises wind turbine system (WTS), dish-Stirling solar thermal system (DSTS), aqua electrolyser, fuel cell, diesel generator, and battery energy storage system. A maiden attempt has been made to apply a cascade controller called integer order proportional–integral–derivative with filter (PIDN) cascaded with fractional order integral–derivative (PIDN-FOID) controller and its performance is compared with I, PI, and PIDN controller. Investigation reveals that PIDN-FOID outperforms in terms of peak deviations, settling time, and oscillations in both constant and variable conditions of wind speed and solar insolation. The effect of using WTS, DSTS, both WTS and DSTS on system dynamics is also evaluated and explored that system dynamics improves with integration of these renewable sources. The gains and other parameters are optimised by whale optimisation algorithm. The effect of DC link, redox flow battery, and both on system dynamics is also evaluated in the presence of PIDN-FOID controller and explores that the use of these shows promising dynamic performance. The robustness of controller gains and parameters are tested with change in size of contract.

Achieving optimum coordination of directional overcurrent relays is a very complicated task in the large interconnected system including huge numbers of relays. In the literature, various objective functions (OFs) are reported to obtain minimum operating time of relays and minimum prescribed discrimination time between the operations of primary and backup (P/B) relays. In this paper, the performance of five well-established OFs is examined, and in addition, a new OF is proposed to improve the previously proposed OFs. The proposed OF (POF) minimises operating time of P/B relays together with discrimination time between their operations. Also, the coordination problem is formulated considering near and far-end faults and solved by using a genetic algorithm. In order to evaluate the effectiveness, the POF is implemented over the IEEE 14-bus and IEEE 30-bus distribution networks, and obtained results are compared with those obtained by using previously proposed OFs presented in the literature.

Undervoltage load shedding (UVLS) is the last resort against voltage instability in critical situations. Here, the UVLS scheme is formulated as a mixed integer programming (MIP) model. The aim of the proposed UVLS model is to provide a predetermined value of loading margin with minimum amount of load shed. The full non-linear AC power flow equations are linearised using a piecewise linear technique. The proposed linear AC power flow is then integrated into the UVLS problem. A ZIP load model is utilised to demonstrate the fulfilment of the MIP-based UVLS model under non-linear static loads. The efficacy of the developed linear AC power flow is verified under different operational conditions and contingencies. The results of the proposed MIP-based UVLS model are compared with the original non-linear programming UVLS formulation. To verify the performance of the developed load shedding strategy, the proposed MIP-based UVLS model is implemented in IEEE 14-bus and IEEE 118-bus test systems.

In this paper, a bi-objective robust model is proposed for network expansion planning (NEP) considering the integration of the microgrid aggregators. The objectives include minimization of both the expansion cost and transmission lines loading index. Forced outages of system components are taken into account as the system uncertainties. A hybrid method as the combination of gravitational search algorithm (GSA) and primal-dual interior point (PDIP) method is employed to solve the nonlinear programming (NLP) problem of the NEP. In the proposed hybrid method, the operation sub-problems are solved by the PDIP method under the worst-case single component contingencies, while the expansion plan is defined as scenario independent variables obtained by the GSA algorithm. To detect the worst-case single component contingencies with the severest effects on the system security, a subsidiary optimization problem is solved for each load level of the system. A realistic network of Qom as a part of Tehran Regional Electric Company, Iran, as well as IEEE 118-bus test system are analysed to evaluate the efficiency of the proposed method. A key conclusion is that the stochastic model may not provide sufficient security level, and a robust model is required to ensure the system security against the severe contingencies.

This study presents results on a dynamic anti-windup compensator (DAWC) for the flexible AC transmission system-based wide-area damping controller (WADC). A systematic design approach of the DAWC is proposed following a typical two-step design procedure. First, a third-order WADC is designed for a 10-machine, 39-bus power system reinforced with a static synchronous compensator to damp the critical inter-area modes by employing appropriate global signal measurements. The full-order DAWC design method is applied to improve the dynamic performance of the saturated WADC. The robustness of the DAWC can cover a wide range of the operating conditions. Comparative studies on static AW and DAWC have been carried out on both the numerical simulation and experimental platform. Both simulation and experimental results demonstrate the improved performances of the DAWC.

This study presents a new formulation for real-time active network management (ANM) control of distribution networks to maximise energy yield from distributed generation (DG). Coordinated scheduling of renewable DG and distribution network control assets can limit DG curtailment and significantly increase energy yield and economic performance of DG in weak or congested networks. Optimal power flow (OPF) has been employed in the literature for this purpose. However, single time frame snapshot formulations are limited by their narrow interpretation of temporal constraints. Here a formulation is presented for a new receding-horizon OPF technique to better control real-time ANM in distribution networks with high levels of temporally and spatially variable renewable DG. It is shown to improve the coordination between time sequences of system dispatch and improve voltage performance.

The objective of this study is to upgrade the lossy financial transmission right (FTR) mechanism through the introduction of lossy option FTRs. The lossy FTR mechanism retains the potential to deliver superior risk hedging performance compared with the traditionally deployed lossless FTR mechanism since the locational marginal price decomposition is unnecessary for the settlement of lossy FTRs. The existing lossy FTR theory is, however, based on only obligation FTRs. Although obligation FTRs are the primary risk hedging instruments under any FTR mechanism, option FTRs can improve market competition by allowing flexible hedge positions. Therefore, an investigation is carried out to explore a lossy version of option FTRs. The configuration template and the settlement rule for lossy option FTRs are established. A suitable auction model is prepared for the issuance of lossy option FTRs. The lossy FTR auction formulation is carried out based on a novel representation of power flow equations. Detailed case studies are presented to show the practical utility of the proposed lossy FTR instrument.

Robust and efficient state estimation (SE) is essential for power system operation and energy management. However, in modern large-scale power systems, the main existing SE algorithms lack either estimation reliability or computation efficiency with the increasing number of multiple gross errors. This study addresses such deficiencies and proposes a variant of the greedy pursuit algorithm. Deriving from compressed sensing, the proposed algorithm operates on the measurement set and exploits the sparsity of bad measurements. By updating the composed normalised measurement errors, it detects the overall reliability, eliminates the bad measurements, and restores the wrongly rejected measurements per iteration. Numerical tests on various benchmark power systems illustrate the superior performance of the proposed algorithm, compared to several representative SE algorithms.

The usage of medium-voltage switchgear is more and more common in high altitude areas. Few relative standards about the selection of switchgear air gap in low air pressure conditions are currently available for referring. In this study, four different types of switchgear air gaps, as well as a typical rod-plane gap, are taken as the samples, and their positive and negative lightning strike discharge characteristics under low air pressure are tested in the artificial climate chamber. The effects of the electrode structure, polarity, air pressure, humidity, and gap distance on the discharge performances are analysed as well. Research results indicate that the four switchgear air gaps and typical rod-plane gap differs greatly in lightning impulse discharge performances and polarity effects. In low air pressure conditions, the lightning impulse breakdown voltage of either positive or negative polarity can be corrected by U ₅₀ = U _50,0 × (P/P ₀) ⁿ . The discharge voltage under positive lightning impulse is more easily affected by air pressure than that under negative lightning impulse. Atmosphere humidity will cause dispersiveness of air-gap lightning impulse discharge voltage, which performs to be non-linear with a gap distance lower under 400 mm. Research results are referable for the design, selection and installation of medium-voltage switchgear in high altitude areas.

With the increasing installation of the high-voltage direct current device and flexible AC transmission system, the power transfer capability increases significantly. However, the risk of line overloads or even cascading failures caused by DC blocking or line outage also augments, which requires accurate and effective post-contingency corrective control (CC) actions. Traditional sensitivity-based methods are fast, but are less accurate and may suffer from the seesaw problem. Artificial intelligence optimisation-based methods usually exhibit better CC performance but are time-consuming. For fastly performing accurate CC actions, a second-order cone programming (SOCP)-based CC optimisation model for line overloads alleviation in meshed AC/DC power systems is proposed. Initially, to reduce the number of CC actions and optimisation variables (OVs), a heuristic search method is proposed to automatically select the most effective generators/loads for the overloaded lines. Subsequently, thyristor controlled series capacitor (TCSC) compensation levels and multi-terminal direct current (MTDC) power are treated as additional OVs to minimise load shedding/generation rescheduling. Additionally, to boost computational efficiency, SOCP format power flow equations for systems with MTDCs and TCSCs are proposed. Eventually, the effectiveness, accuracy, and superiority in computational efficiency of the proposed method are verified based on the modified IEEE 30-bus test system.

Virtual synchronous generator (VSG) possesses the advantage of friendly interaction with power grid by simulating synchronous generator characteristics. However, its low-voltage ride through (LVRT) capability is insufficient. The excessive output current of VSG easily causes wind turbines to break away from the power grid, which will exacerbate the negative impact of grid fault. Thus, a new LVRT control strategy is proposed based on the analysis of excitation state for VSG. The droop characteristic, reactive power loop and active power loop of the VSG are improved, respectively, by specifically analysing the response characteristics of VSG. Moreover, the additional current loop is redesigned to assist the system operating in the under excitation state and suppress unbalanced currents without changing the original VSG characteristics. Furthermore, a new orientation method is adopted to accelerate the transient process and achieve better transient performance. It is worth noting that the proposed control strategy does not need switch control algorithm with smooth handoff algorithm under grid fault, and it can deal with both symmetric and asymmetric grid voltage drop problems at the same time. The correctness and feasibility of proposed scheme are verified by rigorous theoretical deduction and complete simulation verification.

Keeping voltage quality in isolated microgrids while feeding non-linear and/or unbalanced loads is one of the major challenges in the control of these networks. This study proposes a new hierarchical control for enhancing voltage quality in sensitive load bus (SLB) of isolated microgrids considering non-SLBs (NSLBs (DG buses and local buses)) with voltage quality limitations. At the primary level of this hierarchical control, a droop controller is responsible for controlling voltage and frequency of microgrids. The duty of the secondary control level is that in the case of the reduction of voltage quality indices at SLB, it enhances them to their determined levels by sending proper control signals to the primary level to determine each DGs compensation effort. It is worth noting that improving the voltage quality indices at SLB can lead to a drop in NSLBs voltage quality indices. Although NSLBs do not have the strict voltage quality limitation of SLB, but keeping the voltage quality of these buses in their allowed limitation is necessary. The third level of the proposed hierarchical control is designed to guarantee the voltage quality indices limitation at NSLBs. Simulation results are given to demonstrate the effectiveness of the proposed control scheme.

Single-phase neutral reactors are used in shunt compensated transmission lines (TLs) to accelerate the extinction of the secondary arc through suppression of the arc current. Application of similar shunt reactors with the same capacities is prevalent in the transmission systems. Using the traditional method, however, for each TL, a specially designed neutral reactor is needed that could be in some cases extremely large and practically infeasible. This study investigates the feasibility of application of a properly designed neutral reactor, which is independent of the line length. This solution only depends on the ratio of positive- and zero-sequence capacitances of the line as well as the shunt reactor inductance. Accordingly, for all TLs at the same voltage level equipped with shunt reactors of the same capacities, the proposed neutral reactance would be almost identical which helps to minimise the cost and design complexity. Meanwhile, the required insulation level would be kept sufficiently small for any compensation degree. Based on the steady-state analysis and time-domain simulations conducted using the electromagnetic transient program, it is shown that for the majority of TLs, it is possible to extinguish the secondary arc within an acceptable short period of time by applying the proposed neutral reactor.

High impedance faults (HIFs) and the associated electric arc is a topic of public safety and concern because fault currents are generally too small to be detected in a reliable way by conventional over-current relays. This study proposes an analytical model for analysing HIFs in power distribution systems. The proposed analytical model considers the complex interaction between a time-varying fault impedance, the power distribution line and an equivalent source impedance at the substation bus. Hence, this approach requires the joint solution of a partial differential equation and a single non-linear equation. The proposed methodology calculates the transient conductance, voltage and current at the substation bus, considering several contact surfaces and short circuit levels. The analytical model was validated by means of comparisons with measurements in a real distribution system, results published by other authors and computer simulations in electromagnetic transient programs. The obtained results show good agreement between the analytical model, measurements and computer simulations. A sensitivity analysis of the interaction of all the parameters associated to HIFs is also presented.

The increasing interdependence between electric power and natural-gas systems requires integrated simulation tools applicable to the coupled system. Therefore, this study proposes steady-state and transient simulation tools for electricity-gas integrated energy systems (IESs) by using convex optimisation. Steady-state IES simulation is designed for long-term planning studies while transient IES simulation, which includes line-pack storage, is designed for real-time operational research. The proposed convex steady-state gas flow model introduces binary variables to represent gas flow directions, and employs the second-order cone (SOC) to relax non-convex pipeline gas flow equations. As a result, steady-state gas flow analysis is formulated as a mixed integer SOC programming problem. The proposed transient gas flow model employs the implicit finite difference method to transform partial differential equations into algebraic difference equations. Moreover, the short-term gas flow directions are specified and SOC relaxations are used. Simulation results on an integrated IEEE 24-node system and Belgian 20-node gas system verify the effectiveness of the proposed SOC models. The impacts of wind power forecast errors on multi-period gas network operations are also investigated.