Several smart grid applications have recently been devised in order to timely perform supervisory functions along with self-healing and adaptive countermeasures based on system-wide analysis, with the ultimate goal of reducing the risks associated with potentially insecure operating conditions. Real-time transient stability assessment (TSA) belongs to this type of applications, which allows deciding and coordinating pertinent corrective control actions depending on the evolution of post-fault rotor-angle deviations. This study presents a novel approach for carrying out real-time TSA based on prediction of area-based centre-of-inertia (COI) referred rotor angles from phasor measurement unit (PMU) measurements. Monte Carlo-based procedures are performed to iteratively evaluate the system transient stability response, considering the operational statistics related to loading condition changes and fault occurrence rates, in order to build a knowledge database for PMU and COI-referred rotor-angles as well as to screen those relevant PMU signals that allows ensuring high observability of slow and fast dynamic phenomena. The database is employed for structuring and training an intelligent COI-referred rotor-angle regressor based on support vector machines [support vector regressor (SVR)] to be used for real-time TSA from selected PMUs. Besides, the SVR is optimally tuned by using the swarm variant of the mean-variance mapping optimisation. The proposal is tested on the IEEE New England 39-bus system. Results demonstrate the feasibility of the methodology in estimating the COI-referred rotor angles, which enables alerting about real-time transient stability threats per system areas, for which a transient stability index is also computed.

This study proposes a quasi-bridge-type fault current limiter (QBT-FCL) for reducing the fault current level and the magnitude of voltage sag. Before a fault occurs, because of the voltage-compensation effect, the equivalent impedance of the QBT-FCL is very low, and hence it has almost no influence on the circuit. Therefore, the load seems to directly connect to the voltage source, and there is almost no distortion to the load voltage and current waveforms. When the fault occurs, the limiter automatically inserts the impedance into the circuit, and thus the magnitude of the fault current and voltage sag can be effectively reduced. After the fault is cleared, the limiter starts to freewheel and recovers to the normal operation state. As a result, the QBT-FCL still has a negligible effect on the circuit and is ready for the next fault occurrence. Theoretical analysis for the proposed QBT-FCL has been fully developed in this study. Finally, the feasibility and performance of the proposed limiter have been verified by the simulated and experimental results.

A solution to the problem of transient stabilisation for multi-machine power systems, with transfer conductances different from zero, is given. The 3n-dimensional (aggregated) model of the n-generator system, with lossy transmission lines, non-linear loads and excitation control, is considered. A non-linear dynamic state-feedback control law that ensures, under some conditions on the physical parameters, global asymptotic stability of the operating point is constructed. To the best of the authors’ knowledge only existence results – with the restrictive assumption of uniform inertia generators – are available to date for this problem. Simulation results on the New England benchmark system illustrate the performance of the proposed controller.

In this study, a practical method is proposed for determining the distance and the section of fault in power distribution system (PDS). In the suggested method, at first the possible fault points are determined using a novel impedance-based fault location method. Since the number of these points may be more than one, thus two methods are proposed for determining the real location of fault. In the first method, the measured and recorded samples of voltages at the beginning of feeder for actual fault are compared with the stored samples of voltages which are obtained from simulating of fault at the possible fault points. The one with highest matching is the real location of fault. In the second method, frequency spectrum (FS) of voltage is defined as a suitable criterion for this purpose. Therefore the real fault point is determined by comparing and matching the FS of voltages obtained from the simulated faults and the recorded voltage for actual fault. The performance of the proposed method is evaluated in a real feeder in distribution network of Iran considering different types of faults, fault resistances, fault inception angles, real instrument transformer models and X/R ratio changes of upstream PDS network. The obtained results show that the performance of the proposed method is quite satisfactory and its accuracy is very high.

This paper presents an investigative study on unified power quality conditioner (UPQC) allocation for reactive power compensation of radial distribution networks. An UPQC consists of a series and a shunt inverter. The UPQC model based on phase angle control (UPQC-PAC) is used. In UPQC-PAC, the series inverter injects a voltage with controllable phase angle in such a way that the voltage magnitude at load end remains unchanged. Owing to the phase angle shift, the series inverter participates in load reactive power compensation along with the shunt inverter during healthy operating condition. The UPQC-PAC model is suitably modified so as to provide the reactive power compensation of a distribution network. The impact of the UPQC-PAC allocation is studied by placing it at each bus of a network, except the substation bus, one at a time. A load flow algorithm including the UPQC-PAC model is devised and used in the determination of its optimal location in a network. The simulation study shows that the optimal allocation of UPQC-PAC results in significant amount of power loss reduction, under voltage mitigation, and enhancement of voltage stability margin. Better power loss and bus voltage are obtained with UPQC-PAC compared with some existing reactive power compensation approaches.

Using wide area monitoring systems (WAMS) offers a possibility for an integrated measurement-based and model-based control, which suits to the operation of large electric power system (EPS), along with online analysis. This study presents studies on fixed-order controller design through model identification approach with use of synchronous measurement data. Firstly, in the study, the coherent generator in each area of large EPS is determined by the mutual information theory. Then, state-space two-input two-output model is identified for the generator that has highest participation factor and thus referred as coherent generator. The model identification algorithms; least-square, instrumental variable and subspace state-space based generalised Poisson moment function are used. Next, WAMS level model is identified between the input controllable variable and speed deviation difference of coherent generator of each area. Finally, a local controller (decentralised) in each coherent area and a centralised controller at WAMS level between two coherent areas are designed by optimisation of the several design functions; H^∞ norm, H ² norm, spectral abscissa and complex stability radius, as much as possible. These controllers feed supplementary control signal in addition to one fed by local conventionally tuned power system stabiliser. The centralised controller at WAMS level is demonstrated to stabilise the speed deviations of each generator between any two areas in the large EPS. The study is investigated with different input signal variables; ΔV _ref, ΔP_m excited by different pattern of disturbances.

Flexible AC transmission system devices provide the opportunity to improve the usage of the current transmission facilities by controlling network flows and nodal voltages. The optimal steady-state settings of these devices can be determined using optimal power flow calculations. However, this requires knowledge of the system parameters, generation settings and loads. A two-stage regression-based control scheme is proposed to determine the optimal settings of thyristor-controlled series compensators (TCSCs) with the objective to optimally utilise the current transmission system in the presence of renewable energy resources. A regression function describing the relationship between a set of key measurements and the optimal device settings is determined in the offline simulation. This function is then used to calculate the optimal device settings by only receiving the information from a limited number of key measurements without solving the OPF problem in the online operation. Studies are carried out with TCSCs in three-test systems, the IEEE 14-bus system, a 28-bus system and the IEEE 118-bus system. The simulation results with one, two and four TCSCs are presented, illustrating the performance of the proposed regression-based control scheme.

Owing to the increasing demand in the urban areas for new technologies such as heat pumps and electric vehicles (EVs), greater power capacity in low voltage (LV) distribution networks is becoming increasingly important. This study will investigate how to improve the power capacity through the implementation of point of use voltage regulation (PUVR). PUVR relies on a power electronics converter at each end-user. Most LV network cabling has a voltage limit of 1 kV, PUVR exploits this voltage rating to increase the network capacity. This study will describe and discuss the results from a viability study using data from a utility company, which shows that the capacity in the LV network could be increased by an additional 500 kVA. However, it was also found that PUVR using present off-the-shelf converters is not as cost-effective as replacing the LV network cables. Two power electronics topologies have been investigated in the simulation studies to date: the AC chopper circuit and the back-to-back inverter circuit. These two topologies were compared and the AC chopper was found to be a cheaper, more efficient topology. Therefore the AC chopper is more suitable for this application and may increase the viability of the PUVR.

Wind is one of the fast growing renewable resources that can significantly contribute in achieving emission-free electricity generation system. Since wind resources are distributed across geographical locations, wind resource sharing among different geographical locations is essential to facilitate wind energy penetration and its full utilisation. A wind resource sharing strategy, for interconnected electricity networks, to achieve the national and regional renewable energy target is presented in this study. A multi-objective decision making problem has been formulated to optimally share the installed wind generation capacity in a multi-area power systems. Computational models have been developed for wind generation adequacy, emission reduction from wind energy and capacity upgrade requirements for tie-line interconnections. Trade-off analysis has been used to select the best wind resource sharing options. The proposed wind resource sharing strategy has been applied to the interconnected power systems operated within the National Electricity Market (NEM) framework of Southeast Australia to share the available wind resources within the geographical areas of the participating states in the NEM.

In view of the potential problems in the system such as sustained oscillation and low damping ratio, which are not considered in traditional small-signal stability region (SSSR), an improved SSSR (ISSSR) calculation method based on the guardian map is proposed. First, according to the map theory, the system is mapped from the ISSSR to the negative half-plane. Then by direct sum operation the guardian map is constituted. Finally, the guardian map approach, which is able to solve the exact stability region of the Hurwitz matrix, is used for fast and accurate calculation of the boundary of ISSSR. Simulation tests on the IEEE 4-machine 11-node system and 16-machine 68-node system verify the correctness and effectiveness of the proposed method. Besides, the influence of the generator excitation system parameters on the ISSSR is also analysed, which is highly valuable in system dispatching instruction and small disturbance instability prevention.

Increasing use of heat pumps, micro-generation, electric vehicles and energy-saving technologies is expected to cause severe voltage imbalance on low-voltage (LV) radial feeders and deteriorate the power quality seen by single-phase (1Φ) and three-phase (3Φ) LV connected consumers. To solve this problem, a Scott transformer-based balancing technique is used to convert an unbalanced 3Φ supply into a balanced 3Φ supply at either one point on an LV radial feeder or a 3Φ load supply point. Moreover, by replacing the traditional methods of increasing LV cable cross-sections to solve voltage imbalance; or future solutions such as automatic network reconfiguration, the economic cost of operating and upgrading a ‘stressed’ LV feeder can be minimised. A computer simulation study, in which the proposed method is used to balance a typical UK LV network, with varying levels of imbalance, was carried out. Furthermore, a ‘small-scale’ physical voltage balancing system based on the proposed method was constructed and tested in the laboratory. The results obtained from various simulation and experimental scenarios demonstrated that the proposed method can continuously maintain a balanced 3Φ supply by compensating for phase-related voltage dips and surges resulting from variations in 1Φ connected loads.

An algorithm for controlling the voltage profile in a power distribution network with dispersed energy resources (DER) is described. The algorithm is based on predictions and fast communication links between the feeders remotely controlled switches, power lines, substations, end users and DERs. The advantages of using the algorithm are in establishing a reliable power distribution network, with a proper voltage profile, appropriate communications and strong interdependences between the components of the power distribution network. A special benefit of this concept is the possibility of having it included in the existing IEC61850 standard.