Hasil untuk "Distribution or transmission of electric power"

Jongchan Choi, Yaosuo Xue, Hong Wang

The power grid is undergoing a significant transformation with the rapid increase in inverter-based resources (IBRs), including large-scale photovoltaic (PV) plants. Ensuring reliable and resilient grid operation in this new paradigm necessitates high-granularity electromagnetic transient (EMT) modeling that accurately captures the behavior of individual inverters and their interactions within IBR plants. Central to this approach is the detailed representation of both the IBR plant’s collector system and the dynamics of individual inverters. To achieve this, a high-granularity EMT model of a large-scale PV plant has been developed using advanced simulation algorithms, including matrix splitting and the Schur complement. These proposed techniques significantly enhance simulation speed, numerical stability, and accuracy while improving the modularity and efficiency of the collector system’s representation. The effectiveness of the proposed methods is validated through simulations of a representative large-scale PV plant consisting of 125 individual PV inverters, 25 IBR unit transformers, and a 52-bus collector system.

Fang Z. Peng, Hao Huang, Leon M. Tolbert et al.

Abstract The 50/60 Hz alternating current (AC) electric power has been the standard and most flexible energy source powering our modern societies for one and a half centuries since the war of the currents: AC versus direct current (DC). A reactive power concept that was introduced at the beginning of the AC power was very useful for circuit/system analysis, design, control, optimization, and ultimately for more efficient and stable generation, transmission, distribution, and consumption. The initial reactive power theory was based on single-phase sinusoidal AC power to capture inductive and capacitive power that yields to net-zero average power over one fundamental cycle. Soon it was expanded to non-sinusoidal AC power and finally to instantaneous three-phase AC power. However, these reactive power theories remain separate and limited to special cases and have never been consolidated and made valid to all cases. Today, more widespread adoption of power electronics and renewable energy is bringing back DC power into the electric grids. The reactive power concept has never been applied to DC power systems. There is no reactive power in DC power systems according to the existing reactive power theories. Do DC power systems really have no reactive power? Capacitors and inductors are widely used in DC just like in AC power systems. Are they not reactive power components? Why are they different from their AC counterparts? Furthermore, are batteries active or reactive power components? What about active devices like power converters (or inverters) with AC (or DC) on one side and DC (or AC) on the other? Do they generate or consume reactive power? Finally, what about AC and DC hybrid power systems? How to define reactive power in such a complex power system that has a multitude of loads, buses, and sources? Is there reactive power between any two loads, any two buses, or any two sources in a power system and what is the total reactive power in such a complex power system as a whole? As the motivation and goal of this paper to answer the above basic questions, to unify the existing AC reactive power theories and to ultimately provide theoretical and insightful guidance for system analysis, design, control, efficiency, optimization, and operation of complex power systems, a concept of spacetime (both spatial and temporal) active and reactive power (pq) theory—the spatiotemporal aspect of active and reactive power—is developed for both AC and DC power systems. The theoretical definitions and physical meanings of the spacetime reactive power will be developed, and real applications and thought experiments/cases/exercises will be explored and discussed. The developed mathematics to define the active (or real) and reactive (or imaginary) power—p and q respectively by dot (scalar) and cross (vector) products of multi-dimension spacetime vectors and time-space mapping principle/law can have some fundamental implications as well.

Sander Meland, Mojtaba Yousefi, Ahmad Hemmati et al.

Transmission system operators maintain grid stability using reserve markets; aggregators help small participants contribute by pooling their flexibility. Moreover, Reserve market prices and capacities are uncertain for the aggregator until the bidding deadline, and this underscores strategic approaches. This paper introduces a deep reinforcement learning framework tailored for aggregators that coordinate exclusively small-scale loads, participating in the Norwegian reserve markets. The proposed framework reflects a real-life bidding process, and multiple types of reinforcement learning models are used within the framework. The two datasets are hourly data from June and October, 2023, to evaluate how seasonal variations affect the models performance. First, the different models are trained on the data from the first three weeks of the given dataset and then tested on the last week of the dataset. For the testing of the models, they are tested against baseline values to give a good indication of whether the models are able to learn or not. From the test results, most models are performing better than the minimum baseline values and thus the models are able to learn, and the framework is feasible. Regarding the different type of reinforcement learning models trained and tested within this framework, the Deep Q-Network model performs most consistently on a higher level compared to the other models.

Chungfeng Zhang, Mingli Chen, Yongjun Zhang et al.

Abstract Recognition of partial discharge (PD) patterns is essential for insulation diagnosis of covered conductors in overhead lines. Current research has not sufficiently addressed the complex background noise in real environments, and most detection methods depend primarily on feature engineering or deep learning, suggesting potential for improvement in accuracy and efficiency. This has led the authors to propose a PD pattern recognition algorithm that integrates feature selection and deep learning. This algorithm incorporates the design of a discrete wavelet denoising function specifically tailored to the characteristics of PD for data preprocessing. It employs Bayesian optimization algorithms and light gradient boosting machines for characterizing corona discharge features. Furthermore, it develops multi‐scale clustering features and phase‐resolved features for feature fusion, and constructs insightful features based on the light gradient boosting machine. Finally, a novel deep learning model is formulated, demonstrating exceptional detection performance for early faults in covered conductors. Experimental results show that this algorithm attains an Matthews correlation coefficient score of 0.814, a 13.2% improvement over the baseline algorithm's 0.719, and a speed increase of 39.18%. The final accuracy amounts to 97.85%. This algorithm demonstrates exceptional performance in detecting early insulation faults in conductors.

Yutao Xu, Zhukui Tan, Jikai Li et al.

Abstract The lightweight of modular multilevel converter (MMC) and the DC faults ride‐through ability are main challenges for MMC‐high voltage direct current (HVDC) transmission systems. By introducing the concept of time‐division multiplexing, an arm multiplexing MMC (AM‐MMC) topology with high utilization of submodules is presented to reduce the weight and volume of MMC. In order to block the DC side fault current, this paper proposes a novel submodule in AM‐MMC, instead of using full‐bridge submodules. The proposed recombined half‐bridge submodules of AM‐MMC (RHAM‐MMC) contains four half‐bridge submodules and an IGBT with reverse parallel diodes. The topology and operating principle of RHAM‐MMC are introduced in detail. The time‐division multiplexing of middle arms between upper and lower arms is achieved by introducing arm selection switches. Thus, a new type of arm switch and switching method is designed based on the switch state. The DC faults ride‐through strategy is carried out based on its DC fault characteristic analysis. In addition, the economy analysis is conducted on the switching loss and operating loss of RHAM‐MMC. Compared with the fault ride‐through capability of other sub‐modules (SMs), RHAM‐MMC performs better in terms of investment cost and device losses. The simulation results based on MATLAB/Simulink reveal that RHAM‐MMC can achieve the DC side fault ride‐through and show effectiveness of the DC fault ride‐through control strategy.

Samar Fatima, Verner Püvi, Matti Lehtonen et al.

Abstract The electrification of the transport sector to control the carbon footprint has been gaining momentum over the last decade with electric vehicles (EVs) seen as the replacement for conventional internal combustion engines. Economic incentives, subsidies, and tax exemptions are also paving the way for rising EV penetration in the power distribution networks. However, the exponential EV adoption requires careful technical and regulatory analysis of traditional networks to satisfy the network reliability constraints. Therefore, it would be vital to find EV hosting capacity (HC) limits of networks from a multifaceted approach involving various market players, mainly distribution system operators and EV owners. This review provides a systematic categorization of EV hosting capacity evaluation and improvement methods, thus enabling researchers and industry personnel to navigate the advancing landscape of EVs. This novel framework extends beyond the theoretical implication of diverse objective functions and HC improvement methods to the actual numerical values of EV HC across varying geographical settings. Therefore, this unique synthesis of varying aspects of EV HC facilitates the in‐depth understanding of the integration of sustainable energy and transport sector.

Wenbo Wang, Jeremy Keen, Jason Bank et al.

The rapid growth of residential solar photovoltaics (PV) applications is a challenge for distribution utilities as they work to maintain grid standards and minimize customer interconnection times. A “screening process” is typically used by utilities to approve customer interconnection request. While conventional “fast-track screening” methods (e.g., limiting PV capacity to 15% of transformer capacity) can be done quickly, they are too restrictive for new PV interconnections. On the other hand, detailed studies often require power flow modeling and would increase customer interconnection times. This work uses a random forest (RF) model to screen residential solar applications without the need for power flow analysis. The proposed RF model is based on commonly available PV application information and network data as inputs, such as application size and solar penetration. The correlation and importance of these RF inputs are investigated so that utilities have flexible implementation options. Further advantages of this data-driven approach are transparency, i.e., utilities can show how different inputs affect a pass/fail decision, and a quantified probability associated with the screening decisions can be provided. Case studies show how a utility would use the proposed approach and benchmark the proposed approach with conventional screening methods. The proposed approach was found to be more accurate than the conventional fast-track screens. It was also found to be faster than detailed power flow studies and nearly as accurate.

Shiqi Cao, Ning Lin, Venkata Dinavahi

Enhanced environmental standards are leading to an increasing proportion of microgrids (MGs) being integrated with renewable energy resources in modern power systems, which brings new challenges to simulate such a complex system. In this work, comprehensive modeling of a grid of microgrids for faster-than-real-time (FTRT) emulation is proposed, which can be utilized in the energy control center for contingencies analysis and dynamic security assessment. Electromagnetic transient (EMT) modeling is applied to the microgrid in order to reflect the detailed device processes of the converter and renewable energy sources, while the AC grid utilizes the transient stability modeling to reduce the computational burden and obtain a high acceleration value over real-time execution. Consequently, a dynamic power injection interface is proposed for the coexistence of the two simulation types. The reconfigurability and parallelism of the field-programmable gate arrays (FPGAs) enable the whole system to be executed in FTRT mode with 51 times acceleration over real-time. Meanwhile, three case studies are emulated and the results are validated by the off-line simulation tool Matlab/Simulink®.

Mohammad Hossein Nazemi, Farhad Haghjoo, Sérgio Cruz et al.

This paper proposes a non-invasive negative sequence impedance-based technique to detect stator turn-to-turn faults (STTFs) and dentify the related faulty phase at early stages based on the tracking the magnitude and angle variations of the negative sequence current component generated due to STTFs. To extract these indicators, a simplified steady-state negative sequence equivalent circuit of the induction motor is used. To neutralize the effect of various produced disturbances by the inherent non-ideal construction of the machine and also unbalanced feed voltage to the STTF diagnosis, they will be estimated and removed from the main obtained component. It is shown experimentally that the introduced technique is independent of mechanical loading level (load variations) and is applicable for network or inverter-fed motors as well. Online fault detection and faulty phase identification, as the most important goals of the protection plan, are accessible by defining an appropriate threshold for the magnitude and allowable range of angle variation of the introduced criterion, respectively. The performance of the method is evaluated by simulation as well as multiple experimental tests. The experimental results have shown that from the sensitivity point of view, even weak faults are detectable by such a technique. Also, the obtained tests showed that such technique is robust, reliable and secure in the face of unbalanced voltage sources and load level variations. In addition, the performance of this method for the inverter-fed mode showed that the related sensitivity will be increased in such a condition.

Mostafa Gholami, Iraj Ahmadi, Mohammad Pouriani

Abstract Fault indicators (FI) and remotely controlled switches (RCS) can reduce the power outage time in distribution network (DN) by finding and isolating the faulty area. Therefore, they play an important role in reducing the power outage cost and increasing the reliability of the DN. In DN, there may be high‐priority loads. One of the goals of improving and updating the DN is to increase the reliability of all network buses, especially buses feeding such loads. Here, the placement of FI and RCS, as the distribution system automation devices, is designed and modelled to increase the reliability of the buses supplying high‐priority loads. For the placement problem, two goals of cost and reliability have been considered. But the problem is not defined as a multi‐objective optimization. Rather, it is modelled as a one‐objective optimization (i.e. network cost) and constrained to a certain level of reliability in predetermined locations and buses. The IEEE‐33bus network is used as the sample network and different scenarios are simulated. The number of FI and RCS and the optimization cost of simulated scenarios are compared to evaluate the efficiency of the proposed model. The obtained results show the adequacy of the modelling.

Travis Hagan, Dilan Senaratne, Rich Meier et al.

Real-time power system algorithms are necessary for grid advancement, but few practical applications have been demonstrated in a research usability context. The work in this paper consists of implementing a data correction algorithm, its deployment within realistic substation equipment, and the design of a testbed to demonstrate the overall framework and its usability. A digital simulator is used to generate Phasor Measurement Unit (PMU) data for the algorithm. The algorithm corrects data that has been perturbed by GPS spoofing attacks. Finally, the entire system is visualized on power-utility software, SEL Synchrowave Operations. Considerations and potential issues are discussed and are applicable to digital Hardware-in-the-Loop (HIL) systems as well as to field-deployed systems. The system is demonstrated with 11 simultaneously GPS-spoofing attacked PMUs in a 21 PMU system. The HIL testbed developed in this paper provides a valuable tool for easily testing a variety of real-time power system algorithms and the communications and control necessary for them operate successfully.

M. Ali, Syed Ali Abbas Kazmi, Z. Khan et al.

There are three main parts of an electric power system—power generation, transmission, and distribution. For electric companies, it is a tough challenge to reduce losses of the power system and deliver lossless and reliable power from the generating station to the consumer end. Nowadays, modern power systems are more complex due to gradually increasing loads. In the electrical power system, especially in transmission and distribution networks, there are power losses due to many reasons such as overloading of the line, long distribution lines, low power factors, corona losses, and unsuitable conductor size. The main performance factor of the power system is reliability. Reliability means continuity of the power supply without any interruptions from the generating station to the demand side. Thus, due to these power losses, there are voltage stability problems and economic losses in the electrical system. The voltage stability of the power system can be increased by improving the voltage profile. In this paper, different techniques are analyzed that include the integration of wind power, the integration of photovoltaic power, and reactive power injection by integrating FACTS devices. These techniques are applied to the IEEE 57 bus system with standard data using simulation models developed in MATLAB. Thus, the results of the analysis of these techniques have been compared with each other.

Baowei Li, Minghao Wen, Xin Shi et al.

Abstract This paper analyses the formation mechanism of the transmission distortion of electronic voltage transformer, and points out that the integrator will magnify the transient transfer error and superimpose the dynamic additional component on the output signal, which may cause the transfer distortion of voltage signal in serious cases. To restrict the electronic transformer transient variable error effect on distance relay, a distance relay method using instantaneous value after equal transfer processes is proposed. It directly uses output differential signals of the capacitor voltage divider and Rogowski coil. The capacitor voltage divider and Rogowski coil are decomposed into several typical variable link in series. The virtual digital transfer link, which is constructed by the digital filter, is used to compensate for the difference parts of the transfer link, so that the voltage and current signals pass through the same transfer link. It can mitigate the influence of voltage and current signal transfer difference on the calculation accuracy of distance relay. The simulation results show that the proposed distance relay method has fast operation speed and is less affected by abnormal voltage and current signal transfer, and its performance is better than existing distance relay methods.

Shoufeng Jin, Huidong Tian, Qingyu Wang et al.

Abstract For the structural characteristics of power transmission equipment such as bushings, the plug‐in structure is mostly used for current‐carrying connections owing to the large size and long distance at high voltage levels. The contact element strip is the key component of the current‐carrying structure, carrying the combined electrical–thermal effect. Its electrical current‐carrying performance is important. In recent years, discharge failures caused by the overheating failure of electrical connections have occurred from time to time. However, there have been relatively few studies on the failure mechanism of the electrical connection structures of high‐voltage power transmission equipment, such as bushings. In this study, from the perspective of corrosion reaction kinetics, a two‐dimensional phase‐field model of high‐temperature corrosion is established to obtain the carrier concentration distribution in the film. The effects of temperature, gas partial pressure, film thickness, and applied electric field on the growth rate of corrosion reaction film were calculated using the finite element method. At the same time, with the contact element strips used in the bushing as the test object, a corrosion test was carried out in SF6 atmosphere to simulate the high‐temperature corrosion caused by the uneven current carrying of the contacts in actual operating conditions. Combined with the effect of temperature on the film growth rate, the contact area was the most severely corroded location. The simulation can provide a qualitative analysis for the contact degradation test and a new method for studying the factors affecting the corrosion mechanism of contact element strips.

Davod Rezaei, Mehdi Gholipour, Farzad Parvaresh

Abstract This paper proposes a high‐speed and accurate method for extracting the arrival times (ATs) of traveling waves (TWs) in the power system that can be used for fault location applications and transmission line protection. The proposed method is based on the expression of the traveling wave as the exponentially damped component superimposed on the sinusoidal wave in a small time window. Also the sine component is removed by using approximation and consecutive differences of the input signal samples (the modal components of three‐phase voltages or currents) from the resulting wave. Due to the fact that the estimation of traveling wave arrival times (TWATs) is done applying basic mathematical operations in the time domain, the proposed method, in addition to the simplicity of implementation, has the appropriate accuracy and speed for applications such as online fault location and protection purposes. In order to evaluate the performance of the proposed approach in fault locating, a 230 kV transmission line is modelled in EMTP/ATP. Then, the fault location under various conditions of faults such as changes in location and type of fault, fault conditions as well as variations in the measurement noise level and sampling frequency are studied using MATLAB.

Yang Fu, Xiaoyan Guo, Yang Mi et al.

Abstract In order to solve the problems of inefficient, inflexible and insecure for traditional centralized algorithm in the process of optimization dispatch, and with the application of artificial intelligence technology to smart grids, the novel distributed solution is proposed by using the deep reinforcement learning and the consensus theory to optimize the economic dispatch. Firstly, the optimal commitment sequence of massive units is realized through constructing deep reinforcement learning model. Secondly, the optimal unit output and efficient economic dispatch can be obtained by utilizing the improved consensus algorithm together with Adam's algorithm. Finally, simulation results of IEEE‐14 and IEEE‐162 node systems may demonstrate the effectiveness of the proposed solution for the smart grids with complex network structures, which can not only solve the problem of massive data processing, but also it may reduce the dependence on the exact objective function when dealing with extremely complex load distribution scenes and distributed powers.

Jinfei Xiong, Fulin Zhou, Qunzhan Li

Abstract Cascaded H‐bridge inverter (CHBI) is widely used in the industry application for its outstanding features. However, CHBI needs a large number of isolated DC sources. If some of the DC sources are out of work, the DC voltage cannot maintain the desired value and even decreases to zero, thus degrading the quality of the output voltage of the CHBI. Thus, a soft‐switching modulation strategy based on the carrier phase shift SPWM is proposed in this paper to cope with the DC source failure. The strategy is proposed to achieve two goals: 1) one is to adjust the DC voltage of faulty cells back to the normal; 2) the other one is to make the pulse width modulation (PWM) pulses of each cell change without cell voltage level‐skip. The correction and efficiency are verified by a prototype of three‐cell CHBI built in the laboratory.

Kehan Xu, Zhe Zhang, Qinghua Lai et al.

Abstract Overhead transmission line faults are mostly single‐phase grounding faults, and to ensure the power supply reliability of photovoltaic power plants in the cases of tie line transient faults, a feasible solution is to employ the single‐phase reclosing. However, for the single‐phase reclosing of the tie line, photovoltaic power source may face the over‐voltage problem during the non‐full phase operation, which will seriously affect the success rate of the single‐phase reclosing. This paper, according to different non‐full phase operation control strategies of photovoltaic power source, establishes the corresponding sequence network analysis models, and proposes the theoretical calculation method of non‐full phase operation voltage, which takes account of different neutral point grounding modes of step‐up transformer and different load levels. Meanwhile, the closing impulse problem of the single‐phase reclosing is discussed. The correctness of the theoretical method is verified by digital simulation results. On this basis, the applicable scope and application suggestions of the single‐phase reclosing are given. The research conclusions can provide important guidance and reference for the application of single‐phase reclosing technology in tie line of renewable energy power plant.

Zhao Yang Dong, Yuchen Zhang

Global energy systems are transforming from fossil fuels to renewables, but the conventional electricity systems are so fragile that could lead to negative consequences such as soaring prices, rolling blackouts, security issues and delays to emission reductions. Confronting to these issues, electricity systems of the future will be vastly changed, dominated by new technologies and business models, increasingly digital and highly complex. Such transformation will be enabled by means to efficiently, stably and affordably distribute electrical power from many sources and storage points. Market design, policy, regulations, legislations, cyber security and politics are barely keeping up with advances in technologies, and energy technology choices have multi-generational implications for people and economies. These issues are global and to find a solution requires true systems thinking, informed by cutting-edge research. This paper envisages interdisciplinary digitalized future energy systems for emission reductions and proposes a 6-theme template to shape the future energy system. The six research themes have been designed such that the “whole is greater than the sum of the parts”. Each theme is informed by the others and the inter-linking of the six themes’ inputs and outputs will drive the outcomes and impacts of future energy systems.

Tianshi Cheng, Tong Duan, Venkata Dinavahi

Parallel-in-time methods are emerging to accelerate the solution of time-consuming problems in different research fields. However, the complexity of power system component models brings challenges to realize the parallel-in-time power system electromagnetic transient (EMT) simulation, including the traveling wave transmission lines. This paper proposes a system-level parallel-in-time EMT simulation method based on traditional nodal analysis and the Parareal algorithm. A new interpretation scheme is proposed to solve the transmission line convergence problem. To integrate different kinds of traditional EMT models, a component-based EMT system solver architecture is proposed to address the increasing model complexity. An object-oriented C++ implementation is proposed to realize the parallel-in-time Parareal algorithm based on the proposed architecture. The results on the IEEE-118 test system show 2.30x speed-up compared to the sequential algorithm under the same accuracy with 6 CPU threads, and a high parallel efficiency around 40%. The performance comparison of various IEEE test cases shows that the system's time-domain characteristics determine the speed-up of Parareal algorithm, and the delays in transmission lines significantly affect the performance of parallel-in-time power system EMT simulations.