Volume 26, Issue 4

In an integrated distribution system incorporating distributed generation (DG), various technical challenges must be addressed when the grid becomes disconnected and transforms into an islanded system. The main focus in such circumstances revolves around ensuring the stability of the islanded network. This study presents an advanced decision-making framework for supporting islanded networks by integrating metaheuristic Black Widow Optimization (BWO) and the rate of change of the voltage stability index (RoCVSI). The Rate of Change of the Voltage Stability Index (RoCVSI) detects instability in islanded networks by continuously monitoring rapid changes in the voltage stability margin. Upon identifying potential instability, an advanced decision-making strategy utilizing the Black Widow Optimization (BWO) algorithm is deployed. BWO generates multiple load-shedding scenarios and evaluates their impact on system stability, iteratively refining the solutions through processes similar to selection and cannibalism in black widow spiders. The optimal load-shedding strategy is then implemented to selectively shed specific loads, thereby reducing demand and enhancing island stability. The proposed scheme’s effectiveness for islanded network stability is assessed by extensively analyzing the IEEE 33-bus system. The efficiency of the proposed approach is confirmed through a comparative analysis, with results indicating the better efficiency of the proposed method in the islanded network.

The conventional adaptive full-order observer-based speed sensorless control method for induction motor is prone to instability at low-speed region as improper feedback gain matrix and imprecise speed adaptive law are often used. To address these problems, a new feedback gain matrix design approach as well as a new speed adaptive law design technique are proposed in this paper. Firstly, considering that the d-axis current estimation error in the traditional feedback gain matrix design method has a great influence on the stability of the speed estimation algorithm, especially at low speeds, a new feedback gain matrix design method is proposed to minimize the d -axis current estimation error. Secondly, a new speed adaptive law design technique is studied based on the conventional method, which only requires the d -axis and q -axis current estimation error with a weight coefficient to be designed, simplifying the conventional speed adaptive law. Thirdly, the transfer function from the speed observation error to the proposed adaptive error is analyzed by Routh stability criterion theory, and the weight coefficient suitable for full range stable operation is determined by MATLAB software. Fourthly, the stability of the proposed method in this paper is analyzed using the poles distribution maps. Finally, the proposed method is experimentally verified based on a 2.2 kW induction motor experimental platform. The experimental results show that the proposed method can make the induction motor operate steadily at low-speed and zero-speed region with rated load. In addition, the proposed method has better anti-disturbance performance than the existing method.

The three-level (3-L) neutral-point-clamped (NPC) converter has found widespread applications in various fields, due to its simple structure, low failure rate and high efficiency. However, the 3-L NPC converter suffers the issue of unbalanced neutral-point (NP) voltage due to the divided two dc-side capacitors. The large NP voltage ripple and offset Based on the detailed analysis of the effects of vectors and clamping patterns on the NP voltage, a discontinuous optimized modulation method for NPC grid-connected inverter with both low switching loss and ability to balance NP voltage is presented. By measuring NP voltage and utilizing the property that superfluous clamping patterns have opposing effects on the NP voltage, the modulation method adjusts the NP voltage with the injection of various zero sequence voltages (ZSV) into the original sinusoidal waves. The results of this study demonstrate that the CB-DPWM can control the NP voltage balanced and decrease switching loss compared to conventional DPWM and SVPWM strategies. Moreover, the CB-DPWM strategy does not need to identify sectors and subsectors or calculate dwelling times. This modulation strategy effectively suppresses low-frequency fluctuations and deviations of the NP voltage with the injection of a simple ZSV, and improves the power quality of the output voltages and currents. Compared to the traditional SVPWM scheme, the suggested CB-DPWM has a 27 % lower overall IGBT loss. Moreover, this method is implemented through carrier waves, which is simpler than modulation schemes based on space vector, greatly shortens the program running time, and is conducive to engineering implementation.

Three-terminal hybrid DC transmission technology has the advantages of long-distance and large capacity, and there is no phase change failure and other problems, which is an effective means of sending out new energy bases. Correspondingly, the reliability of the existing single-ended traveling wave protection is further degraded by the unknown fault characteristics introduced by the greater variety and combination of converters and add-ons in the three-terminal hybrid DC transmission system. Therefore, a single-ended protection scheme based on the refractive coefficient is proposed. First, an expression for the refraction coefficient of a three-terminal hybrid DC system is derived. Subsequently, the variability of the refraction coefficients for different faults is analyzed. Finally, a single-ended protection scheme using the fault characteristics of the refraction coefficients is proposed and validated by simulation. The program has the advantages of theoretical clarity, reliability, and the ability to recognize near-end faults.

The existing long-distance transmission line perception mainly focuses on the measurement and analysis of electrical parameters. When the line is subject to wind vibration, icing or galloping, the changes of electrical parameters are not obvious and difficult to capture, resulting in poor performance of long-distance transmission line fault state perception. In this regard, the long-distance transmission line condition sensing based on distributed optical fiber sensing technology is studied. This method designs corresponding sensing methods for four working conditions: using the back Brillouin scattering sensor and phase sensitive Rayleigh scattering sensor in the optical fiber sensing technology to form a multi parameter distributed optical fiber sensing device, which is used to sense the surface temperature, vibration, strain and other data of the long-distance transmission line; By analyzing the linear relationship between fiber Brillouin frequency shift and Brillouin power and fiber strain and temperature, the sensing results of icing thickness of long-distance transmission lines are obtained; By calculating the amplitude and phase information of the detection signal, the sensing results of long-distance transmission line vibration are obtained; By calculating the time difference of polarization mutation signal at both ends of long-distance transmission line, combined with the propagation speed of optical signal and the length of long-distance transmission line, the perception result of lightning fault location of long-distance transmission line can be obtained. The experimental results show that this method can more accurately collect the real-time operation data of long-distance transmission lines, and can effectively perceive the galloping, wind vibration and lightning fault location of long-distance transmission lines.

Hybrid power systems are the contemporary solution to meet the stiff climate change targets and also hold future for implementing distributed generation and microgrids. These systems have renewable sources as their key elements which in turn have high level of intermittency due to weather conditions and other reasons. At the same time, these hybrid power systems are also vulnerable to cyber threats owing to the intense adoption of various IoT Technologies (Internet of Things). Load frequency control (LFC) is a formidable task for the system operators under such scenario and robust control strategies are required to achieve the load frequency within tolerable limits. In this work Linear quadratic controller (LQR) has been proposed to address the challenges of hybrid power systems. Two area interconnected power systems are considered in this work with each one having different configuration with respect to source of power generation. Solar, wind, geo-thermal, electric vehicle charging infrastructure and pumped storage power plant are integrated together with conventional thermal power plant for showcasing the LQR based controller under data integrity cyber-attack scenario. The frequency response of the hybrid power system is demonstrated through MATLAB simulations.

Voltage breakdown in sub-transmission networks resulting from an increase in load demand can be addressed by incorporating distributed generation (DG) units such as hydro, wind, photovoltaic, and geothermal in some buses. This approach can lower power losses and the price of the primary generated energy while increasing network dependability and efficiency. Feasibility of dispersed generation integration & its effect on sub-transmission system operation were investigated using Ben Walied 66 kV sub-transmission network in Libya as a state. This study presents modified particle swarm optimization (MOPSO) technique to select the best option with dispersed generation units under various operating conditions. The Ben Walied 66 kV sub-transmission network has been subject of effects research on both normal operation and load growth scenarios. The goal of this study was to find best way to adjust penetration level of the three DGs in response to changes in the network loading. Three DG units have been refitted to study the effects on test networks for sub-transmission, which consist of 30 and 51 buses. A comparison analysis shows that while the ideal locations of DG units remain constant with load expansion, the optimal solution for the penetration level percentage of three DG units was boosted by new optimal sizes. Research has been done on how the power factor of distributed generators (DGs) affects the practical performance of 66 kV networks in steady-state conditions. The integration of DG units in regulating these losses and voltage variations is demonstrated by the results, which indicate that the ideal solution for DG unit’s power factor was at a value of 0.87 lagging.

In this paper, the effect of Solar Photovoltaic (SPV) penetration on the damping of critical and inter area modes arising from different penetration level of SPV into the Nigeria national grid has been studied. Also, the possible effects of SPV penetration on Critical Clearing Time (CCT) when a three-phase fault occurs on the grid are studied. The Nigeria 56-bus system was used for the investigation. Sensitivity analyses are carried out to obtain insight into how certain change in parameters affects both the transient and small signal stabilities of the Nigerian power systems. DigSILENT Power Factory was used for the simulation while the analysis was performed in MATLAB. Some of the important findings show that the grid developed increasing amplitude of oscillation from 20 % SPV penetration. There is no steady increase or decrease of CCT with penetration levels. The effect of changes in load on small signal conducted shows that both the real and imaginary load at Kano and Birnin kebbi bus should not exceed 257 MW, 176 MVAR and 171 MW, 134 MVAR, respectively so as to avoid system collapse.

The demand for the integration of renewable energy sources (RESs) with the existing distribution grid is increasing rapidly because of the growing power requirement. The variable power generation from RESs and changing power demand make it necessary to integrate energy storage units. To get stable and trouble-free operation in both transient state and steady state, a combination of battery and supercapacitor storage devices are considered in this work as hybrid energy storage devices (HESDs). But to ensure the power balance in the grid-connected microgrid is a critical aspect nowadays. Hence, a real power management algorithm is proposed in this work to ensure a balance between energy production and demand and provide stability in the microgrid. Both simulation and experimental implementation of the proposed scheme confirm the efficacy and smooth operation of the hybrid microgrid.

In recent days, ester-based alternatives like natural and synthetic oils are preferred as an alternative to mineral oil by the power industry due to its higher bio-degradability, superior thermal conductivity, and fire resistance than mineral oil. In addition to this, blended oils are quite attractive because of its low dielectric loss and a low ratio of degradation. The present research deals with the experimental studies on different insulating oils like mineral oil, synthetic ester oil, coconut oil, blended oils, and nanofluids, which are developed from ZnO and TiO 2 nanoparticle doped at 0.01 vol% in different insulating oils through ultrasonication process. In this experiment, the critical properties like electrical and physicochemical properties are examined according to International Electrotechnical Commission and American Society for Testing and Materials standards. Results show that ZnO and TiO 2 nano-powder enhances the AC breakdown voltage (BDV), dielectric permittivity, and DC resistivity properties of different insulating oils with improved flash and fire resistance. Remarkably, it is found that mineral oil-based TiO 2 nanofluid shows an enhancement of 55.8 % in AC BDV, 9.1 % in permittivity, and 15 % in flash resistance. Moreover, mineral oil based ZnO and TiO 2 nanofluid results exhibit remarkable decrement in loss tangent with increased DC resistance property. Finally, it is observed that the influence of TiO 2 nano-powder at 0.01 vol% remarkably enhances the electrical and physicochemical properties in different insulating oils compared to ZnO nanofluids. Hence, mineral oil and green insulating based synthetic ester oil (which is based on TiO 2 nanofluids) have been considered as a potential candidate to make alternatives to traditional insulating oil for power transformer applications. The findings offer critical insights for the future of transformer insulation systems, guiding industry standards and fostering innovation in material science.

A powerful and efficient program for restoring the electrical distribution system by effectively utilizing the maximum capabilities within the system, including soft open points, distributed generation resources, and network configuration changes, can significantly reduce both the quantity and duration of lost loads caused by permanent faults. In this research study, we address the issue of distribution network restoration with a focus on soft open points (SOPs) and intentional islanding using distributed generations. This problem is formulated as a constrained optimization problem in order to determine the optimal distribution network configuration, quality of intentional islanding through DGs, control function of SOPs, and amount of load shedding. The objective is to minimize lost load while minimizing switching operations and preferably minimal islanding. Given that this problem involves multiple complexities such as combinatorial nature, mixed-integer variables, non-linearity, non-convexity along with numerous variables and constraints; we employ an evolutionary method known as simulated annealing (SA) algorithm to solve it without any simplifications or assumptions about convexity. To enhance efficiency during implementation of SA algorithm, Kruskal’s algorithm is utilized for generating radial solutions which restricts search space to feasible solutions resulting in quicker attainment of high-quality optimal solutions. Finally, the outcomes of implementing the suggested approach on the 69-bus IEEE distribution system are presented and examined. It is demonstrated that by leveraging the potential of soft open points in load transfer control and network voltage regulation, along with utilizing intentional islanding capability provided by distributed generation resources, the restoration capability of the distribution system can be greatly enhanced.

Microgrids are a growing segment of the energy industry, representing a paradigm shift from remote central station power plants toward more localized, distributed generation. An efficient energy management structure is essential for a DC Microgrid with a PV system combined with a Hybrid Energy Storage System (HESS) of Battery and Supercapacitor. The combined supercapacitor and battery storage system provides a quick control for the DC-link voltage. It stabilizes the system and helps achieve smooth PV power delivery to loads. The boost converter used for the PV system is controlled by a Maximum Power Point Tracking (MPPT) method to extract maximum power and maintain a constant voltage at the DC bus despite the daily change in solar power. The boost-buck converter is used to control the charging and discharging processes of the BESS to maintain a constant voltage at the DC bus. To achieve the seamless operation of DC Microgrid with HESS during the power fluctuations, this work proposes power coordination and control scheme has been proposed. To analyse the performance and efficacy of the proposed DC Microgrid with HESS are implemented in MATLAB/SIMULINK.

Nowadays, Indian power distribution companies (PDCs) are implementing smart distribution networks. Older cities are becoming smarter as per the recent government’s policy. Existing overhead distribution lines are being replaced by underground cables as an essential criterion of a smart city. One of the main problems arising in this process is the overheating of the neutral grounding resistor (NGR) in 11 kV distribution systems, even in normal conditions. NGRs, placed inside the substations, are overloading the air conditioning and exhaust systems of the substation. Sometimes failure of the NGR occurs due to overheating. In this paper, a comprehensive investigation has been carried out to reach the roots of this problem. It is observed that long underground cables have a higher ground capacitance than overhead distribution lines. Due to the higher cable capacitance, the third harmonic current circulates through neutral, which overheats the NGR even in normal conditions. The situation becomes worse when the substation runs on diesel generators (DGs) in an isolated state under main grid failure, as a higher amount of third-harmonic current circulates depending on the type of winding and pitch factor of the DGs. Different solutions are proposed, and their advantages and disadvantages are analyzed. Finally, the rating of the NGR is modified, and louvers-cooling fan arrangement is preferred for the running substation.