Multiple Single-phase Research Articles

An enhanced CNN-LSTM based multi-stage framework for PV and load short-term forecasting: DSO scenarios

The importance of accurate forecasting in the electric sector has grown due to the increasing demand and adoption of high volume of Renewable Energy Sources (RES). Short-term forecasting (STF) using deep learning methods has shown potential for improving forecasting accuracy. However, the accuracy of these methods can be further enhanced by combining them to generate a hybrid model, selecting appropriate input features, generating new features, and optimizing model parameters. This paper proposes a novel multi-stage framework for PV and load STF that employs feature generation, feature selection, and optimal hyperparameter tuning preprocessing techniques. An enhanced hybrid CNN-LSTM deep learning model architecture is developed in the final stage of the proposed framework. The framework is assessed and compared to other leading-edge approaches across different DSO scenarios, including multiple single-phase residential loads, three-phase feeders, and secondary substation, demonstrating a significant reduction in forecasting errors.

An adaptive protection scheme for multiple single-phase grounding faults in radial distribution networks with inverter-interfaced distributed generators

Conventional zero-sequence current (ZSC) protection relays for low-resistance grounded systems (LGSs) are confronting challenges due to the risk of multiple single-phase grounding faults (MSGFs) and the ongoing increase in the penetration of inverter-interfaced distributed generators (IIDGs). Such issues concerning false or failure tripping require a reconsideration of traditional solutions. This paper presents a novel adaptive ZSC protection scheme using the current-compensation method for LGSs with IIDGs. The mechanism for in-phase MSGFs and out-of-phase MSGFs in LGSs with IIDGs is formulated. The ZSC calculation method for LGSs with IIDGs is introduced via the zero-sequence compensation factor, where the feeder ZSC generated by MSGFs is converted to its counterpart during a single fault. With the manufacturing message specification (MMS) protocol in IEC 61850 that is selected to help share IIDG information, the adaptive ZSC protection philosophy is implemented, which automatically amends the ZSC and sets the protection settings of all relays in real-time. The validity of theoretical analyses and the performance of the protection scheme have been demonstrated by using the PSCAD/EMTDC simulation under various scenarios.

AMI Data-Driven Strategy for Hierarchical Estimation of Distribution Line Impedances

Monitoring, operation, and protection of distribution power grids fundamentally rely on the accurate estimation of line impedances. However, line impedance estimation is challenging due to the difficulties in modeling the dependence on line temperature and aging. This paper proposes a new data-driven strategy to estimate low-voltage (LV) and medium-voltage (MV) line impedances using an advanced metering infrastructure (AMI). In the proposed strategy, two-level optimization problems are formulated using generalized equations for voltage drops along LV and MV lines and then extended based on AMI data collected over time. Hierarchical estimation is achieved using the local and global references to the LV and MV root buses, respectively, enabling parallel estimation for individual LV grids and thus reduced computation time. Reinforcement learning is also integrated to compensate for possible measurement errors in the AMI data, ensuring robust estimation of LV and MV line impedances. The proposed strategy is tested on a three-phase unbalanced MV grid with multiple single-phase LV grids under various conditions characterized by measurement samples and errors. The results of case studies and sensitivity analyses confirm that the proposed strategy improves the accuracy and robustness of line impedance estimation at both LV and MV levels.

An Appropriate Index to Assess the Global Cancellation Level of the Harmonic Currents Consumed by a Set of Single-Phase Uncontrolled Rectifiers and a Set of Fluorescent Lamps

An in-depth study of harmonic current reduction in European commercial buildings due to the harmonic cancellation effect when a set of single-phase uncontrolled rectifiers and a set of fluorescent lamps are connected at the same voltage level is essential, since both types of non-linear loads are very present in commercial and residential sectors. This paper provides an appropriate index to assess the global cancellation level of the harmonic currents for this study. The equivalent circuit per phase of the typical three-phase power system of European commercial installations is presented and simplified for the cancellation analysis of the harmonic currents consumed by a set of multiple identical single-phase uncontrolled rectifiers and a set of multiple identical fluorescent lamps connected at the same voltage level. The suitability and usefulness of the proposed index are shown by applying it to that analysis, which leads to some results of practical interest. This index can be generalized to any number of sets of multiple identical non-linear loads and can be applied in graphical and optimization studies that will allow a greater benefit from the harmonic cancellation effect to be obtained given the global nature of the index.

Three-Phase and Single-Phase Measurement of Overhead Power Line Impedance Evaluation

Calculation and measurement of the overhead power lines electrical parameters is common practice in today’s electrical engineering industry; however, there is very little data to actually compare these two approaches because measured data in such detail are mostly unavailable for academic purposes. Based on the very detailed model of an overhead power line in MATLAB Simulink environment and conducted experimental measurement, this article specifically covers the exact evaluation of the impedance of the investigated overhead power line. Differences between calculation and experimental measurement are shown and discussed accordingly, where, surprisingly, the biggest deviation was observed in the positive resistance parameter. The connection between different measurement techniques (multiple single-phase and three-phase methods), as well as the power line asymmetry reflection in the impedance matrix is explained as well as compared to expected values from the computations. The complete mathematical approach for electrical parameters evaluation from different measurement methods is explained step-by-step, and the final equations are introduced for each method. Proposed methods of obtaining the electrical parameters of the power line are then concluded as the ones with great accuracy and wide usage in practical applications. It shows the great importance of correct input data for the electrical parameters’ theoretical computations and the need to know the measurement methodology and apparatus perfectly to process the measured data and interpret them correctly.

X-Type Current Source Converters

In this article, a novel topology generalization of a current source converter (CSC) that allows controlling of multiple single-phase ac converters independently sharing the same dc-bus, with the advantage of having a reduced number of conducting switches and a lower dc-bus current, is presented. A conventional n-output/port single-phase CSC that uses the same dc-bus needs to have n H-bridge converters connected in series, which means that it always has 2 n conducting switches. The new topology allows generating any n ac output currents always having only (n+1) conducting switches in a switching period. This represents (1-1/n)·50% less conduction losses when compared with the equivalent conventional multiport single-phase CSC. A scalar pulsewidth modulation to control the converters with switching optimization and its generalization is also presented. Details of topology, control strategy, and modulation are presented. Simulation and experimental results are provided to validate the theoretical approach.

Analysis and Comparative Evaluation of Multi Stack and Novel Single Stack Polyphase Transverse Flux Machines

Transverse flux machines (TFMs) originally have heteropolar arrangement of permanent magnets (PMs) on the rotor and a ring winding on the stator. These conventional TFMs are single stack single phase machines. To realize a multi stack polyphase machine, multiple single phase TFMs have to be stacked together. As an alternative to conventional multi stack polyphase TFM (T 0), a single stack polyphase TFM (T 1) is proposed in this paper. The proposed single stack polyphase TFM has homopolar arrangement of PMs on the rotor and a polyphase winding on the stator. Both the machines (T 0 and T 1) are analyzed using magnetic equivalent circuit (MEC) and finite element analysis (FEA). The machines are compared on the basis of their structure, material requirement, parameters and performance. The outcome of the comparative study of the TFM topologies under consideration, leads to correlation between structure of the TFMs and their performance. In this work benefits and limiting factors of the proposed topology over the conventional topology are discussed. Prototype of the proposed machine is developed and experimental validation of the proposal is presented.

A Benchmark Distribution System for Investigation of Residential Microgrids With Multiple Local Generation and Storage Devices

A benchmark distribution system is developed for investigating control and energy management of distributed generation (DG) at a residential level in the form of three single-phase microgrids. The benchmark is derived from a typical distribution network architecture with common parameters found in North-America systems including wiring specifications, line impedances and connection details for rooftop PV systems. This benchmark system can accommodate microgrids operating in both grid-connected and islanded modes. Within this benchmark, multiple single-phase DG sources located in different phases can be coordinated to form a dynamically balanced three phase system under different load and generation profiles in different phases. The coordination of DG sources in a particular phase is achieved through an intra-phase power management device, while mitigating loads and generation imbalance among all phases are done by an inter-phase power management scheme. It is expected that this benchmark system will facilitate investigation of impacts posed by proliferation of single-phase distributed generation devices and local storage systems in private residences. Three case studies have been carried out to demonstrate the versatility and effectiveness of this benchmark system.

Hierarchical Control with Fast Primary Control for Multiple Single-Phase Electric Springs

An electric spring (ES) is a new power compensation device which becomes useful for the large-scale integration of renewable energy sources into the grid. However, when the grid contains two or more ESs connected at different nodes, a voltage drop occurs between the nodes due to the line impedance. Therefore, the voltage of the ES-stabilized nodes cannot be set at the same reference (e.g., 220 V), otherwise one or more ESs break away because of the voltage windup. In this paper, a hierarchical control of multiple ESs tied to a microgrid is proposed to account for the line voltage drop. The primary control relies on the power decoupling control; it is designed for islanded operation of the microgrid, which improves the dynamics of both the voltage and frequency regulation. The secondary control relies on the droop control; it is introduced to coordinate the operation of the ESs by modifying the reference voltage of each ES dynamically. Advantages and disadvantages of the proposed hierarchical control are analyzed together with the explanations of the algorithms developed for its realization. At last, effectiveness of the arranged control system is validated by simulations on the MATLAB/Simulink platform.

Performance of UK Distribution Networks with single-phase PV systems under fault

Faults are a major concern to the dynamic performance of distribution networks. With the predicted increase in PV contribution, it is vital to understand the impact of PV on the distribution network. However, there is very little work published that address the impact of PV systems on the dynamic performance of distribution networks. Most PV systems connected at the distribution level are single-phase in nature. A generic single-phase dynamic PV model, including the protection mechanism, is presented in this paper. This enables the evaluation of the dynamic performance of distribution networks with multiple single-phase PV systems. The paper analyses the impact of faults on the PV inverter output using the models developed. The impact of PV on the network performance during fault is then analysed. The implications of the adoption of different regulations, viz. G-83, IEEE 1547:2018, IEC 61727 and VDE 0126-1-1, are also discussed. The results show that the presence of PV systems does not significantly affect the performance of the distribution network during faults. Also, the usual concern of loss of protection co-ordination does not occur at this voltage level. Faults that are far from the PV terminals would be cleared within 0.2 s. This indicates that the disconnection delay of 0.5 s as stipulated by G-83 is appropriate. However, a lower cut-off voltage for under-voltage disconnection than the current value stipulated in G-83 would enable more PV systems to stay connected during fault and avoid unnecessary loss of generation. The network used in this work is a representative of distribution networks and protection schemes in the UK. The results of this analysis are therefore extendable to any radial distribution network that uses standard protection, e.g. fuses and relays in low voltage distribution networks.

Coordinated single-phase control scheme for voltage unbalance reduction in low voltage network.

Low voltage (LV) distribution systems are typically unbalanced in nature due to unbalanced loading and unsymmetrical line configuration. This situation is further aggravated by single-phase power injections. A coordinated control scheme is proposed for single-phase sources, to reduce voltage unbalance. A consensus-based coordination is achieved using a multi-agent system, where each agent estimates the averaged global voltage and current magnitudes of individual phases in the LV network. These estimated values are used to modify the reference power of individual single-phase sources, to ensure system-wide balanced voltages and proper power sharing among sources connected to the same phase. Further, the high X/R ratio of the filter, used in the inverter of the single-phase source, enables control of reactive power, to minimize voltage unbalance locally. The proposed scheme is validated by simulating a LV distribution network with multiple single-phase sources subjected to various perturbations.This article is part of the themed issue 'Energy management: flexibility, risk and optimization'.

Permanent-Magnet Coupled Power Inductor for Multiphase DC–DC Power Converters

Using a coupled power inductor (CPI) in a multiphase dc–dc power converter instead of using multiple single-phase power inductors (PIs) reduces the inductor size and achieves better steady state and transient performances. To further reduce the inductor size and weight used in multiphase power converters, this paper presents a two-phase CPI that utilizes a permanent magnet (PM) to achieve almost doubled saturation current with the same size or equivalently achieve significant size and weight reduction. Operation principle of the presented permanent magnet coupled power inductor (PMCI) and required PM dimensions are derived and used as a design guide. The three-dimensional physical model of the PMCI is developed by using ANSYS/Maxwell software package to “visualize” the saturation current doubling. The fabricated PMCI design, with specifications of 24 A/phase, ∼4.25 μH/phase equivalent steady-state inductance, and ∼2.3 μH equivalent transient inductance, is tested in a 4–8 V two-phase dc–dc boost power converter with up to 50 A input current. Results show that compared to a conventional CPI design with the same size, weight, and inductance, the fabricated PMCI almost doubles the saturation current (from 13 to 24 A/phase). Compared to another CPI with a larger size but with even a smaller saturation current (18 A/phase), the core volume of the PMCI is reduced to 51.9% and the core weight is reduced to 51.2%. In addition, the PMCI achieves ∼76.3% core size and ∼73.4% core weight reductions compared to two separate single-phase PIs with the same steady-state inductance and similar saturation current (∼22 A) due to the dual flux cancelation effect from the coupling and PM realized by the presented PMCI structure.

Impact of Distributed Power Flow Controller to Improve Line Flow Based on PWM Control with PI Technique

<p>In this paper we presents a new component within the flexible ac-transmission system (FACTS) family, called Distributed Power-Flow Controller (DPFC). The DPFC is derived from the unified power-flow controller (UPFC). The DPFC can be considered as a UPFC with an eliminated common dc link. The active power exchange between the shunt and series converters, which is through the common dc link in the UPFC, is now through the transmission lines at the third-harmonic frequency. The DPFC employs the distributed FACTS (DFACTS) concept, which is to use multiple small-size single-phase converters instead of the one large-size three-phase series converter in the UPFC. The large number of series converters provides redundancy, thereby increasing the system reliability. As the D-FACTS converters are single-phase and floating with respect to the ground, there is no high-voltage isolation required between the phases. Accordingly, the cost of the DPFC system is lower than the UPFC. The DPFC has the same control capability as the UPFC, which comprises the adjustment of the line impedance, the transmission angle, and the bus voltage. The controller is designed to achieve the most appropriate operating point based on the real power priority.</p>

Analysis of Distributed Power Flow Controller in Power System Network for Improving Power Flow Control

<p>In this paper, a new power flow controlling device called Distributed Power Flow Controller (DPFC) is presented that offers the same control capability as the unified power-flow controller (UPFC) but with much lower cost and high reliability. The DPFC eliminates the common DC link within the UPFC, to enable the independent operation of the shunt and the series converter. The D-FACTS concept is employed to the series converter to increase the reliability. Multiple low-rating single-phase converters replace the high-rating three-phase series converter, which significantly reduces the cost and increases the reliability. The active power that is exchanged through the common DC link in the UPFC is now transferred through the transmission line at the 3rd harmonic frequency. The DPFC is modeled in a rotating dq-frame. The modeling and analysis of DPFC in a two area two bus interconnected system is done in MATLAB/Simulink environment and comparison between the DPFC and UPFC considering the power flow and cost are also shown.</p><p> </p>

Collaborative Dynamic Optimization on Post-earthquake Emergency Supply and Road Rehabilitation Based on Road Network Connectivity

Earthquakes often cause road damage, so the earthquake relief needs cooperative road rehabilitation and post- earthquake emergency supply. In the thesis, the definition of connectivity degree on post-earthquake road network is pro- posed, and the rehabilitation order for road network is resolved according to its extended meaning. Then, the multistage dynamic problem is decomposed to multiple single phase problems. For each single one, the mathematical model, which balances between efficiency and fairness, is established, and a simulated annealing algorithm is adopted for solving the model, at last its feasibility is verified by a numerical example.

A Unifying Approach to Single-Phase Synchronous Reference Frame PLLs

The three-phase synchronous reference frame phase-locked loop (3-SRF-PLL) is widely used in three-phase power electronics and power system applications thanks to its desirable performance and its simple yet robust structure. Inspired from the 3-SRF-PLL and due to the increasing interest in single-phase applications, multiple single-phase SRF-PLL (1-SRF-PLL) versions have also been proposed in the recent years. This paper presents a unifying approach to the understanding and analysis of the 1 -SRF-PLLs. This paper integrates several 1 -SRF-PLLs having apparently different structures into a single structure. The approach is much useful in understanding various PLLs and also in facilitating further developments in this field.

Reservoir Testing System Evolves to Meet New Frontier Challenges

Technology Update As today’s deep wells challenge the bounds of pressure and temperature, accurate reservoir testing has become essential to mitigate production risk. The information contained in a series of downhole pressure transient measurements and representative reservoir fluid samples can make or break a prospect’s potential. The consistent and accurate acquisition of this information requires the precision instrumentation and functionality of a drillstem testing system. Whereas excellent downhole logging instruments can describe the near-borehole regions, only a drillstem test can reach deeply into the reservoir to discover boundaries, faults, and fractures; confirm volumetric reserves estimations; and acquire the cleanest, most representative fluid samples to provide accurate fluid phase behavior, physical properties, and com-positional analyses. Safety, Reliability, and Efficiency The Schlumberger Quartet high-performance downhole reservoir testing system combines four proven downhole technologies into a package that can isolate the zone, control flow, measure pressure and temperature, and acquire multiple single-phase reservoir fluid samples on a single trip into the well. The system provides enhanced safety, increased efficiency, and improved reliability to testing operations. Compared with conventional downhole test strings, the system functions with a 35% lower tool operating pressure, 50% fewer seals, and 60% fewer connections, while requiring 90% less nitrogen. The system is four times shorter than a conventional tool string because it eliminates the requirement for a safety joint, jar, slip joints, and drill collars. Despite its smaller size, the system is sufficiently durable to permit perforating guns to be run below the packer and fired without incurring damage to the tools or impairing their accuracy or integrity. The system also includes a below-packer circulating valve to allow a more efficient well kill following the test, which is especially important when testing gas wells. Each of the four tools that make up the downhole reservoir testing system operates individually and collectively to perform the test. The CERTIS high-integrity reservoir test isolation system delivers production-quality well isolation. The isolation system combines the features of a retrievable drillstem test packer with a hydraulically set permanent packer, making the safety joint, jar, slip joints, and drill collars unnecessary. Because the system is actuated by annulus pressure, no rotational or set down forces are required.

Application of Cascade H-Bridge Inverter in Super-Capacitor Energy Storage System

This paper presents application of a CHB inverter based SESS. CHB inverter is characterized by cascade connection of multiple single-phase H-bridge (or full bridge) inverter cells. CHB inverter can make SESS flexible in circuit design, reduced voltage steps, and lower EMI. This paper presents circuit architecture design, modeling of CHB inverter based SESS, and control strategy focusing on power and energy balance control among Sub modules (SMs). The simulation results verify that the CHB inverter based SESS have a good performance in both fast power exchange and SM energy balance.

Overview of Electric Motor Technologies Used for More Electric Aircraft (MEA)

This paper presents an overview of motor drive technologies used for safety-critical aerospace applications, with a particular focus placed on the choice of candidate machines and their drive topologies. Aircraft applications demand high reliability, high availability, and high power density while aiming to reduce weight, complexity, fuel consumption, operational costs, and environmental impact. New electric driven systems can meet these requirements and also provide significant technical and economic improvements over conventional mechanical, hydraulic, or pneumatic systems. Fault-tolerant motor drives can be achieved by partitioning and redundancy through the use of multichannel three-phase systems or multiple single-phase modules. Analytical methods are adopted to compare caged induction, reluctance, and PM motor technologies and their relative merits. The analysis suggests that the dual (or triple) three-phase PMAC motor drive may be a favored choice for general aerospace applications, striking a balance between necessary redundancy and undue complexity, while maintaining a balanced operation following a failure. The modular single-phase approach offers a good compromise between size and complexity but suffers from high total harmonic distortion of the supply and high torque ripple when faulted. For each specific aircraft application, a parametrical optimization of the suitable motor configuration is needed through a coupled electromagnetic and thermal analysis, and should be verified by finite-element analysis.

Control of paralleled single-phase motors for a crop chopping machine

This article proposes a fuzzy control system for driving multiple single-phase induction motors in parallel connection. The drive system employs only a single PWM inverter controlled by a self-organizing fuzzy controller. This drive and control system has been utilized in an invented crop chopping machine. The article presents the control system concept, modeling of multiple motors in parallel connection, controller design, simulation of the closed-loop system and practical results. The control system stability is also analyzed on the basis of passivity theorem.