Volume 19, Issue 3 -

Given an undirected graph representing the network, the optimization problem of finding the minimum number of phasor measurement units to place on the edges such that the graph is fully observed, is studied. The proposal addresses the issue of the optimization using a two-phase branch-and-bound algorithm based on combining both Depth-First Search and Breadth-First Search algorithms to attempt to find guaranteed global solutions for OPP. The problem in question is stated, outlining the underlying mathematical model in use formulated in terms of (pure) mixed-integer-linear-programming (MILP) and the branch-and-bound algorithm adopted to obtain efficient solutions in practice. A topology based on transformations considering pre-existing conventional and zero injection measurements in a power network is implemented. The (zero-one) (MILP) model is applied to IEEE systems. The numerical results indicate that the branch-and-bound ensures solution points at the optimal objective function value from a global-optimization point of view. The synchronized and conventional measurements are included in a (DC) linearized State Estimator (SE). The topological observability analysis is verified numerically based on observability criteria for achieving solvability of state estimation. Large-scale systems is also analyzed to exhibit the applicability of the proposed algorithm to practical power system cases.

In power system, utility engineers are often faced with the challenge of reinforcing weak power networks without adding any new infrastructures. This paper analyses the topological structure of a topologically weak network and then institutes a way of reinforcing the network through restructuring. The proposed scheme explores the concept of network structural characteristics of power networks in conjunction with the shortest electrical distance from graph theory. The branch impedances of new sets of candidate transmission lines that could possibly reinforce the existing structurally weak network are determined. The standard IEEE 5-bus and 30-bus test systems are used to illustrate the effectiveness of the proposed scheme. The results obtained show that the proposed approach is generally useful in power system network design, planning and efficient operation.

In consideration of the natural environment and depletion of energy resources, the widespread use of electric power system is expected in which the power is generated from sources of renewables such as wind and solar. When these plants are introduced in large scale, the use of broad land is required. Due to low transmission losses and small stability problems, multi-terminal high voltage direct current (MTDC) transmission becomes advantageous as long-distance power transmission system. Since DC current does not incorporate a zero cross point, therefore it’s blocking is difficult. This paper proposes a DC resonant semiconductor breaker which enables rapid fault clearance for self-excited HVDC transmission. This circuit breaker is connected as a semiconductor switch, in parallel with a group of capacitors, and resistors in the DC transmission line. The capacitor is charged to a higher voltage from the DC transmission line. For generating reverse current to allow the zero cross point in the transmission line, the semiconductor switch turns on to open the circuit breaker. After blocking, the inductance of the line is demagnetized by the resistor and fault clearing is achieved. The system except fault point can continue its normal operation.

This article proposes a new Karl Pearson’s coefficient of correlation (‘r’) based islanding detection scheme which utilizes negative sequence voltage and voltage unbalance signal. In order to check the legitimacy of the proposed technique, large numbers of non-islanding and islanding events are generated by modeling IEEE 34-bus network. This scheme detects islanding situation even under 0 % power mis-match condition and thus, reduces the non detection zone (NDZ). Furthermore, the proposed technique detects islanding situation quickly as well as remains stable during the critical non-islanding situation like faults on adjoining feeder having varying location and fault resistance. Moreover, the proposed technique remains immune to variation in external system condition and fundamental frequency. The performance of the proposed technique is comprehensively compared with the schemes currently reported in the literature. This comparison apparently demonstrates the benefits of the proposed technique over existing schemes.

This study presents a highly reliable 3-phase 4-wire, three dual-buck full-bridge shunt active power filter (3 DB FB APF) for distribution system. The proposed topology uses three single phase dual buck full bridge inverter sharing the same dc-link capacitor with high utilization of dc-bus voltage. The dual buck inverter circuit composed of one power switch and one diode leg instead of two power switches conventional inverter leg effectually eliminate the undesirable “shoot-through” phenomenon occurs in conventional inverter circuit. The fuzzy and adaptive hysteresis current controller based i d -i q control strategy has been adopted to generate optimized switching frequency. For validation, the proposed topology is implemented in the OPAL-RT LAB using OP5142-Spartan 3 FPGA. The dynamic performance of the proposed 3 DB FB APF is assessed for sinusoidal, unbalanced and non-sinusoidal voltage source condition with unbalanced non-linear load that is when both three-phase and single-phase loads are present in the system. Besides, the results with proportional-integral (PI) controller are compared with FLC in terms of harmonic compensation. Furthermore, a comparison has been made between split capacitor dual buck half bridge active power filter (2C DB HB APF) and proposed 3 DB FB APF based on switch power rating.

Despite the benefits of demand response in energy management, the non-existence of its key concepts; dynamic pricing and smart grid, in some countries makes its impracticable in these countries, therefore making energy management unattainable for their consumers. This paper proposed a Smart Distribution Board (SDB) using a priority model for energy management in non-smart grid network. An historical consumption signatures of user’s loads were used to develop a priority model for load units of the SDB. Performance comparison was carried out between the SDB and a conventional Distribution Board which has no level of intelligence. Results obtained indicated that the SDB correctly emulated the energy usage pattern of users, thereby ensuring load preference is maximally satisfied autonomously within a limited budgeted energy and period.

Aggregated loads play a significant role in maintaining the frequency of power system when the generation is not able to follow frequency deviations. An automatic Demand Dispatch (DD) enables the power system to employ the aggregated loads for balancing demand and supply. In this paper, a Demand Side Frequency Droop (DSFD) has been proposed which provides ancillary service to the grid and maintains the frequency of the power system when the generation system is not capable of following the demand. At the time of a frequency fall/rise, Balancing Authority (BA) can detect aggregated load or group of aggregated loads that have power consumption above or below their standard maximum/minimum consumption levels. Then, the BA issues a droop-based signal to the relevant aggregator. Afterwards, the DSFD will be implemented in the aggregator or the group of aggregators to specify the required power consumption amount for bringing the frequency back to its rated level. Subsequently, this signal will be sent to the Appliance Management Unit (AMU) at each participating house. The AMU sends the signal in the form of deferral or interruptible commands to the appliances depending on the priority, availability and the specification of the appliances. It will be demonstrated that the proposed DSFD control maintains the frequency of the power system within a specified range.

Abstract: Plug-in electrical vehicles (PEVs) can participate in frequency regulation (FR) in electric power systems under the framework of vehicle-to-grid (V2G) technology. With a growing number of electrical vehicles (EVs), a greater number of distributed electrical vehicle (EV) chargers may change charge or discharge power simultaneously to participate in FR, resulting in over response. In this paper, considering the over-response and equality issues, an asynchronous method for dispersed PEVs participation in FR is proposed. PEVs participate in FR with the same set of parameters. Over-response can be avoided during the process of FR. Equality enables the dispersed PEVs to participate in FR with the same probability. The presented method empowers PEVs to actively participate in FR without a control centre or a communication network. Simulation results demonstrate the validity of the presented method in different operational scenarios.

This paper presents a new protection algorithm for power transformers. The new algorithm is based on Discrete Wavelet Transform (DWT) and (ANFIS) Inference System. The simulation of power transformer is done using BCTRAN subroutine of ATP software to simulate the internal faults cases. The protection algorithm using DWT and ANFIS is implemented MATLAB Simulink software. The new Algorithm is tested on 40/40/15 MVA, 220/70/11.5 KV power transformer. The proposed algorithm satisfies high degree of accuracy and faster response time.

The modelling of Lithium-ion batteries is considered as a powerful tool for the introduction and testing of this technology in energy storage applications. In fact, new application domains for the battery technology have recently placed greater emphasis on their energy management, monitoring, and control strategies. Battery models have become an essential tool for the design of battery-powered systems; their usage includes battery state-of-charge (SoC), state-of-health (SoH) estimations, and battery management system design and battery characterization. This paper presents a method on how to estimate Lithium-Ion battery equivalent circuit model (ECM) parameters based on experimental characteristic measurements by charging and discharging the battery at different modes. The experiment is realized with a computer that realizes the control of charge and discharge via LabVIEW TM software. In this paper, tests are conducted on Lithium-Ion battery 18650 (nominal voltage of 3.7 V and nominal capacity of 2900 mAh) with the proposed method to evaluate the battery model parameters. The proposed method has the best dynamic performance and gives accurate parameter identification which enables the use of models to simulate the battery system performance.

Power distribution networks with distributed generations may experience faults. It is essential to promptly locate the fault for fast repair and restoration. This paper presents a novel method for identifying the faulted section and accurate location of faults that occur on power distribution grid. Appropriate matrices are set up to represent meter locations on the grid and the topology of the grid. The voltage and current measurements obtained are utilized to decide the fault sections. Then fault location is determined by solving equations that link measurements and fault locations through bus impedance matrix. The method is applicable to both single and simultaneous, multiple faults that may occur on unbalanced, meshed distribution networks with distributed generations.

As a necessary electrical equipment for the construction of power grid, the safety and reliability of the transformer is the focus that people have always paid attention to. In recent years, the DC bias of the transformer has a serious impact on the safe operation of the power system, which has attracted wide attention of scholars at home and abroad. In view of this phenomenon, combined with the basic principle of transformer excitation, the simulation of the DC bias phenomenon is carried out by using Simulink software in this paper. According to the simulation results, the distortion characteristics of excitation current under DC bias are summarized. Then, based on the variation characteristics of excitation current under over excitation and DC bias, the law of transformer core vibration is deduced, and the cause of transformer abnormal vibration under DC bias is revealed. Finally, by analyzing the data of a transformer substation running under DC bias, it is found that the measured data are basically the same with our simulation results, which provides a basis and reference for further research on the phenomenon of transformer DC bias.