Voltage Phase Research Articles

Review on single‐phase high‐frequency resonant inverters for current sharing in multiple inverter system

SummarySingle‐phase high‐frequency resonant inverters (SPHFRIs) with high power density, fast dynamic response, and high energy conversion efficiency have been widely studied and used in academia and industry. With the development of the modularization concept, the operation of multiple inverter modules is desirable because it can remove the limitations of cost, heat dissipation, and component volume in single inverter operation. However, a critical challenge in multiple inverter systems is that the both the phase and magnitude of the output voltage of each inverter module must be controllable to eliminate circulating currents between inverter modules. Great efforts have been made to solve this problem from three aspects: topology, modulation, and control strategy. In this paper, modulation strategies and topologies of different inverters are presented and reviewed to provide guidance to researchers working in this field. Firstly, multiple inverter system based on the SPHFRI is described and its advantages and disadvantages are analyzed. An important issue in the study of multiple inverter systems is presented, that is, the suppression of circulating current. Secondly, the circulating currents in a multiple inverter system are analyzed and derived from two aspects: (1) magnitude and phase angle and (2) active and reactive currents. Thirdly, the inverters used in the multiple inverter system are introduced, and their operating principles, advantages, and disadvantages are reviewed. A key comparison of several inverters is presented for the benefit of the readers. Fourth, through PI closed‐loop simulation, the performance of different multiple inverter systems for suppressing the circulating current is compared in two situations: (1) with magnitude discrepancy only and (2) with both magnitude and phase discrepancy. Finally, the advantages and disadvantages of each inverter are summarized, and the state of the art and future trends are presented.

Introducing a New Method for DPMU in Detecting the Type and Location of the Fault

Introduction: Nowadays, due to the increasing development of distribution networks, their safety and high-reliability performance are of particular importance. One of the most important problems that endanger the security and reliability of these networks is the creation of some faults in them. In case of a fault in the network, identifying its location and type can be of great help in repairing faulty equipment. Also, by detecting the disconnection of one of the equipment or lines, it is possible to prevent accidents in the network. Methods: Phasor Measurement Unit (PMU) has been widely and successfully used as Transmission- Phasor Measurement Unit (T-PMU). The reporting time of PMUs is much shorter than the old Supervisory Control and Data Acquisition (SCADA) systems. They can provide synchronized phasor measurements that can generate voltage phasors of different network nodes. This study aimed to investigate the various applications of phasor measurement units in distribution networks and present a new method for detecting and analyzing the location and type of fault and topology fault of the distribution network using the Internet of Things (IOT) analysis method. Results: To implement this method, it is necessary to measure different parameters of the distribution network before and after the occurrence of a fault, which is used by the DPMU for measurement. The simulation results indicate that for both single-topology and multi-topology faults, the proposed method has higher accuracy and better detection than the remaining common methods and effectively detects single-topology and multi-topology faults in the distribution network. Conclusion: This method can provide a more accurate network topology to estimate the state of the distribution network, which improves the accuracy of the state estimation and is suitable for implementing various advanced functions of the distribution management system.

Fractional delay Newton structure for Lagrangian interpolation in PV integrated grid connected system

SummaryThis paper proposes a fractional delay (FD) Newton structure for Lagrangian interpolation in single phase grid integrated photovoltaic (PV) system. The structure has been designed for achieving shunt compensation and as a phase locked loop circuit for synchronization. The designed controller performs multiple tasks of feeding the active power to meet the load demand and simultaneously providing reactive power compensation, power factor improvement, and compensating other power quality voltage and load current harmonics. Further, synchronization poses a severe challenge in integrating the PV power electronic converters to the grid. The FD filter is used to discretize the continuous time signal at any time instant using interpolation algorithm employing the non‐integral value of the sampling rate delays. The FD delay filter is made adaptive and self‐learning by using least mean square algorithm. The designed synchronization technique meets the objective of faithfully tracking the phase of the grid voltage under all grid disturbances such as under voltage, overvoltage, frequency variations, and phase angle disturbances in a precise manner.

A robust crow search algorithm based power system state estimation

The State Estimation (SE) computational procedure plays a crucial role in modern electric power system security control by monitoring and analyzing operational conditions and predicting any emergency. In order to estimate state variables, Power System State Estimation (PSSE) takes into account the magnitudes and phases of voltage on each bus. To address the state estimation challenges in power systems, in this paper, we propose a novel application of the Crow Search Algorithm (CSA) specifically tailored for the state estimation problem. We have assessed the introduced algorithm using the frameworks of both the IEEE 14-bus and IEEE 30-bus test systems. The first formulation is the Weighted Least Square (WLS) method, and the second is the Weighted Least Absolute Value (WLAV) method, both of which are objective function formulations. By comparing the results, it is clear that CSA-based SE is superior to the other metaheuristic algorithms considered, namely Genetic Algorithm (GA), Particle Swarm Optimization (PSO), and Artificial Bee Swarm Optimization (ABSO). As a point of comparison, we use the Newton–Raphson method for calculating load flow. It has been shown that the proposed CSA-based SE technique has better accuracy than the other two algorithms in all different test systems. With this study, the power system is operated more accurately and reliably by the operators operating the system.

Robust dynamic and algebraic state estimation for microgrids: A generalized approach

AbstractNetwork control, optimization, and security analysis are facilitated by accurate microgrid state estimation. By utilizing phasor measurement units (PMUs), a combined robust centralized dynamic algebraic approach is proposed in this paper for estimating algebraic states (voltage phasors) as well as dynamic states (associated with synchronous generators and wind turbines). Assuming that a load is placed on each bus, an innovative PMU placement method is also presented to provide measurements for all dynamic and algebraic state variables. As a robust link between algebraic state estimation and dynamic state estimation, the output results of the least absolute value (LAV) estimator, which is robust against bad data, are fed to dynamic state estimators as pseudo measurements. Next, to address the nonlinearity of synchronous generator and wind turbine models, an unscented Kalman filter (UKF) is applied to estimate dynamic states precisely. The numerical tests on a microgrid test system show that the suggested approach is suitable for both algebraic and dynamic state estimation. Synchronous generators and wind turbines are modeled using nonlinear models of the 9th and third orders, respectively, and static loads are modeled as voltage‐frequency dependent ones.

Comparative Study of IGBT and SiC MOSFET Three-Phase Inverter: Impact of Parasitic Capacitance on the Output Voltage Distortion

This study investigates the nonlinearities in three-phase inverters for SiC-based systems and compares their performance to IGBT-based systems. An analytical model of inverter voltage distortion is developed, which accounts not only for dead time (td), switching delay time, switching frequency (fs), and voltage drops of power devices, but also for output parasitic capacitance (Cout). Experimental tests validate the model, which provides a more accurate estimate of the inverter’s output phase voltage distortion. The power device characteristics are obtained from datasheets, while Cout is determined through experimentation. Three-phase inverters with varying switching frequencies, fundamental frequencies, and dead-time values are used in simulations and experiments to determine the influence of nonlinearity on phase voltage deviation and current distortion. The results show that, due to SiC devices’ faster switching time, the phase voltage deviation and phase current distortion are lower in SiC-based inverters than in IGBT-based ones for high-frequency applications, as the dead time can be reduced.

The Efficacy of Multi-Period Long-Term Power Transmission Network Expansion Model with Penetration of Renewable Sources

The electrical energy demand increase does evolve rapidly due to several socioeconomic factors such as industrialisation, population growth, urbanisation and, of course, the evolution of modern technologies in this 4th industrial revolution era. Such a rapid increase in energy demand introduces a huge challenge into the power system, which has paved way for network operators to seek alternative energy resources other than the conventional fossil fuel system. Hence, the penetration of renewable energy into the electricity supply mix has evolved rapidly in the past three decades. However, the grid system has to be well planned ahead to accommodate such an increase in energy demand in the long run. Transmission Network Expansion Planning (TNEP) is a well ordered and profitable expansion of power facilities that meets the expected electric energy demand with an allowable degree of reliability. This paper proposes a DC TNEP model that minimises the capital costs of additional transmission lines, network reinforcements, generator operation costs and the costs of renewable energy penetration, while satisfying the increase in demand. The problem is formulated as a mixed integer linear programming (MILP) problem. The developed model was tested in several IEEE test systems in multi-period scenarios. We also carried out a detailed derivation of the new non-negative variables in terms of the power flow magnitudes, the bus voltage phase angles and the lines’ phase angles for proper mixed integer variable decomposition techniques. Moreover, we intend to provide additional recommendations in terms of in which particular year (within a 20 year planning period) can the network operators install new line(s), new corridor(s) and/or additional generation capacity to the respective existing power networks. This is achieved by running incremental period simulations from the base year through the planning horizon. The results show the efficacy of the developed model in solving the TNEP problem with a reduced and acceptable computation time, even for large power grid system.

Contingency-resilient PMU placement using Fuzzy Logic and Discrete Artificial Bee Colony algorithm for comprehensive network observability

In transforming traditional grid systems into intelligent and microgrid-based systems, the Phasor Measurement Units (PMUs) play a prominent role in enhancing monitoring, assessment, control, and protection by estimating voltage and current phasors correctly and quickly. However, since PMUs are not cost-effective, the decision to take the requisite number and their placement is a significant issue and needs to focus on a better approach. This study addresses the solution methodology to compute the optimal locations of a reduced PMU number to have complete network observability. A new hybrid optimization strategy based on the Fuzzy Logic (FL) and Discrete Artificial Bee Colony (DABC) algorithm has been suggested. The suggested method is titled FL-DABC algorithm, which has been applied to determining the optimal placement of PMUs in microgrid-based systems. The suggested approach tackles the problem of fully network-observable cost-effective PMU deployment. The effectiveness of the Algorithm is evaluated through simulations under various operating limitations, such as zero injection buses, a single PMU, and line outage scenarios. A topological observability analysis validates full network observability with the computed PMU placement. The study also includes branch PMU placement set computation and a comparative analysis with other techniques using standard IEEE test networks for simulations.

Discharge Characteristics of Needle Plate Electrode in Transformer Oil Under Low-frequency AC Voltage

Low-frequency transformer is the key equipment of flexible low-frequency AC transmission systems for offshore wind power. As the low-frequency voltage is applied, the transformer has significantly different insulation characteristics from those of the conventional transformer, it is necessary to study the typical characteristics of partial discharge of oil-paper insulation under such voltage. In this dissertation, the characteristics of discharge of needle plate electrodes in transformer oil under power frequency to low-frequency voltage are experimentally researched by adopting the pulse current method, and the discharge statistics, discharge atlas as well as feature parameters are analysed. With the decreasing of voltage frequency, the inception voltage (IV) value of partial discharge slightly increases, the extinction voltage (EV) phases of positive half-cycle (PHC) voltage waveform, as well as negative half-cycle (NHC) voltage waveform appear earlier, and the maximum discharge (MD), average discharge (AD), and pulse repetition rate (PRR) all show a downward trend.

On the Impact of the Grid on the Synchronization Stability of Grid-Following Converters

The research on the synchronization stability of Grid-Following Converter (GFL) is of great significance for the stable operation of inverter-based resources. Existing literature mainly focuses the stability factors from the point of view of the converter and assumes the grid to be an infinite-bus with constant frequency. However, faults cause the grid to experience interdependent variations of grid voltage amplitudes and phases, as well as of its frequency. The impact of these variations on the synchronization stability has not been systematically and comprehensively studied yet. Here we study the combined effect on GFL synchronization stability of all these quantities following a large disturbance. The theoretical appraisal shows that phase-angle jump affects the initial perturbance of the GFL while the grid frequency affects the following transient responses and the stability boundary. Simulation results also show that the variation of the frequency with higher RoCoF may be beneficial for the stability of the GFL, and that the effects of the various of the voltage and frequency can be studied separately.

Frequency-Locked Loop Based New Automatic Phase-Shift Method for Active Islanding Detection of Three-Phase MicroGrid

This paper proposes an active Islanding Detection Method (IDM) integrating Frequency Locked-Loop (FLL) for the detection of voltage phase and frequency at the point of common coupling (PCC) and a modified Auto Phase Shift (APS) method for three-phase Distributed Energy Resource (DER) serving a local RLC load. The FLL is composed of a double second-order generalized integrator (DSOGI) to attenuate the harmonics and pass the fundamental positive sequence components in a frequency adaptive manner. Different from traditional APS methods, a new variable frequency term with an exponential factor is injected into the phase shift algorithm to reduce the region of Non-Detection Zone (NDZ). This modified approach enables the decentralized power generation system to detect the islanding phenomenon more quickly. Simulations and experimental tests conducted on a DG system on OPALRT (OP5600) and hardware test-bed demonstrate the behaviour of the proposed model within IEEE Standards. Additionally, a comparative evaluation was performed on the seamless transition of a microgrid (MG) from Grid-connected mode to Islanded mode and vice versa, using two different MGs, each having a single voltage source converter (VSC) and a local load but with control circuits incorporating DSOGI-FLL and ROGI-FLL respectively. Hardware testing results indicated that the control circuit based on ROGI-FLL demonstrated superior performance.

Research on improved Harmonic current detection method based on SOGI-PLL instantaneous reactive Power

In view of the traditional instantaneous reactive power detection has low anti-harmonic interference ability, poor real-time performance, and insufficient accuracy when the power grid frequency fluctuates, this paper improved the detection link. The working principle of single-phase harmonic detection is analyzed, and the improved second-order generalized integrator is added to make the phase-locked loop detect the voltage phase accurately and efficiently. Based on the comparison and compensation simulation results of the active compensation device, the quality of grid-connected current of the inverter is improved effectively, and the precision of phase locking is increased.

Cryo-ET study from in vitro to in vivo revealed a general folding mode of chromatin with two-start helical architecture

The organization and dynamics of chromatin fiber play crucial roles in regulating DNA accessibility for gene expression. Here we combine cryoelectron tomography (cryo-ET), sub-volume averaging, and 3D segmentation to visualize the invitro and invivo chromatin fibers folding by linker histone. We discover that an increased nucleosome repeat length and prolonged fiber length do not change the two-start helical architecture in reconstituted chromatin of homogeneous composition. Additionally, an isolated chromatin fiber with heterogeneous composition was observed, which includes short-range regions compatible with two-start helix. Invivo, sub-volume averaging reveals similar subunits of two-start helical architecture in transcriptionally inactive chromatin in frog erythrocyte nuclei. Strikingly, unambiguous DNA trajectories that displayed a zigzag pattern universally between alternate N/N+2 nucleosomes were further determined by cryo-ET with voltage phase plate. Therefore, these structural similarities suggest a general folding mode of chromatin induced by linker histone, and heterogeneous compositions mainly affect local conformation rather than changing the overall architecture.

Experimental investigation of vibration amplitude control in additive manufactured PLA and PLA composite structures with MFC actuator

In this study, Macro Fiber Composite (MFC) as actuator has been used for open-loop active vibration control (AVC) in additive manufactured structures made of polylactic acid (PLA) and PLA composites, such as PLA with short carbon fibers (PLA-SCF composite) and PLA with continuous carbon fibers (PLA-CCF composite), when subjected to forced vibrations. The laser vibrometer has been used to find the natural frequencies and bending mode shapes of each beam structure. The MFC patch (M8507-P2), used here as an actuator, is very sensitive to supplied voltages. Thus, it is very crucial to find out the optimum phase and amplitude of the input voltage. The optimal phase angle and voltage for each structure (PLA, PLA-SCF, PLA-CCF) are estimated by a domain search in an incremental manner. Once tuned with the optimal input voltage values, the proposed technique shows exceptional performance in vibration suppression. The results confirmed that this technique can be used in a wide range of composite materials.

A single‐stage bridgeless isolated positive output Cuk configuration‐based unidirectional onboard battery charger

SummaryAs power factor correction rectifiers play a key component of electric vehicle (EV) battery charger, the advancements in designing of improved power quality‐based EV charger become more significant in modern era. This article exposes a single‐stage bridgeless isolated positive output (BIPO) Cuk PFC converter with a noninverted output signal. The input diode rectifier present at the input is redeemed by the bridgeless topology that eliminates the serious power quality (PQ) issues and proffers the eminent charging solution for the light electric vehicles (LEV). Unlike the conventional Cuk converter, the noninverted outcome of the BIPO converter does not require a separate amplifier for converting negative to positive output voltage. The preferred charger utilizes a single voltage and current sensor to synchronize the battery charging control in the constant current (CC) and constant voltage (CV) phases of charging. Therefore, the converter encompasses intrinsic zero current switching (ZCS) and offers low‐cost solution to the charger with reduced control complexities. The extensive state space approach is executed to analyze the marginal stability of the presented system. Moreover, the detailed loss modeling is addressed to show the charger's efficacy curve at the standard conditions. A hardware prototype of 350 W, 60 V/4 A charger is implemented to validate its steady‐state and dynamic performance.

O Splines-Based Fixed-Frequency Integral Sliding-Mode Controller for PFC Rectifier

This paper proposes a fast-response sliding mode controller (SMC) for a semi-bridgeless boost converter under large and quick load fluctuations to ensure tight output voltage regulation and unity power factor correction (PFC) at the line side. In this sense, a novel approach for estimating the reference current profile is presented focusing on the real-time phasor estimation via the O-splines of the discrete-time Taylor-Fourier transform (DTTFT). This method allows for improving the computational efficiency and dynamic performance of the estimations of amplitude, frequency and phase of the network voltage used for the generation of the reference current profile. Several aspects of the controller design are discussed, including the choice of the sliding surface, the existence and stability conditions, and the implementation of an adaptive hysteresis band to fix the switching frequency and reduce zero-crossing distortion. Experimental results of a GaN-based prototype validate the theoretical predictions, exhibiting a PF close to 1 and a total harmonic distortion lower than 3.2% in presence of load changes of up to 50% and changes in the output voltage set point. Several comprehensive experimental comparisons between the proposed framework and the most widely used methods recently reported in the literature are accomplished in terms of transitory and steady-state responses. The robustness of the proposed control approach is experimentally demonstrated under sag conditions and a wide operating range of the input voltage.

A Derivative-Feedback Based Compensation Control to Enhance the Small-Signal Stability for LCC-HVDC System

The small-signal stability of the LCC-HVDC system connected to the weak AC grid is of great concern. This paper derives the SISO model of the LCC inverter station. On this basis, the influence mechanism of AC system strength on system stability is studied via the Bode stability criterion, and the coupling interaction between different control loops is quantitatively evaluated. Results reveal that, as the AC grid becomes weaker, the system stability margin is diminished characterized by the larger phase lag in the phase-frequency response. Also, the interaction between DC voltage controller (DVC) and phase locked loop (PLL) control loops is intensified. Then, a derivative-feedback based compensation (DFC) control is presented to improve the LCC system stability under the weak AC grid condition. Theoretical analysis and simulation results indicate that the presented DFC control can effectively improve the stability and dynamic performances of the LCC system, which allows the system to operate stably even connected to the extremely weak AC grid.

A co-optimized approach for state estimation based micro phasor measurement unit allocation in power distribution infrastructure

Due to the highly complex and dynamic electrical characteristics of the 3-phase unbalanced power delivery networks (PDNs), it is challenging for utilities to observe the network entirely. This impediment necessitates the PDNs to become intelligent nowadays in the presence of various smart devices. Micro-phasor measurement units (µPMUs) are expected to play a crucial role in observing the smart power distribution system due to their micro-seconds resolution and millidegree precision accuracy. The placement of µPMUs in PDNs is also very challenging due to their associated costs. So, allocating a minimal number of µPMUs in PDN with fulfilling the topological observability can elucidate the issue of real-time visibility of the entire system. This paper presents a novel co-optimized placement strategy of µPMUs (CPMP) in PDNs that minimizes the µPMU numbers and the estimation error in the buses other than the µPMU assigned nodes. This work also displays a novel dynamic heuristic distribution system state estimation (DDSSE) to estimate the system's unknown states by using only the information of bus voltage phasors at the µPMU specified buses. The DDSSE is used to estimate the root mean square error (RMSE) in estimated voltage magnitudes and angles. Besides this, the efficacy of the grey-wolf optimizer (GWO) is presented in this work to solve the newly formulated placement problem. The results are validated on an Indian 19-bus and 34-bus unbalanced radial distribution system (URDS), and a detailed comparative study of different heuristic algorithms is also analyzed in this work.

Application of a Phase Resolved Partial Discharge Pattern Analysis for Acoustic Emission Method in High Voltage Insulation Systems Diagnostics

An alternative method for analysis of acoustic emission (AE) signals generated by partial discharges (PD), based on a correlation between voltage phase run and AE pulses, so called phase resolved PD pattern (PRPD), is presented in the paper. PRPD pattern is a well-known analysis tool commonly used in such PD diagnostic methods as conventional electrical and UHF ones. Moreover, it yields various signal analysis abilities and allows a direct correlation indication between measurement results achieved using different methods. An original PRPD measurement methodology applied for AE method as well as some exemplary measurement results and further data analysis capabilities are presented in the paper. Also a comparative analysis of PRPD patterns achieved using various measurement methods and different PD source configurations have been investigated. All presented experiments were done under laboratory conditions using PD model sources immersed in the insulation oil. The main purpose of the presented research is to indicate an all-embracing analytical tool that yields an ability to direct comparison (qualitative as well as quantitative) of the AE measurement results with other commonly applied PD measurement methods. The presented results give a solid fundamental for further research work concerning a direct correlation method for AE and other described in the paper diagnostic techniques, mainly in order to continue PD phenomena analysis and assessment in real life high voltage apparatus insulation systems under normal onsite operation conditions.

A modified mutual impedance based backup protection for series-compensated transmission lines

This paper proposes a modified mutual impedance based backup protection for series-compensated transmission line. In case of failure of current-differential scheme, distance relaying scheme provides protection by calculating and comparing positive-sequence impedance up to fault point. However, non-linear operation of metal-oxide varistor (MOV) result in continuously varying equivalent impedance across series-capacitor during fault which affects the reach and directional discrimination feature. Inter-phase mutual impedance of line up to fault point is proportional to the distance of fault from relaying point and therefore can be exploited as a reliable relaying parameter for backup protection purpose. The reason is that the equivalent impedance across MOV protected series-capacitor does not alter inter-phase mutual impedance up to fault point. This mutual impedance can be computed utilizing sequence components of voltage and current phasors measured by phasor measurement unit (PMU) at line ends. Existing mutual impedance based scheme is highly influenced by fault resistance and synchronization error. The proposed modified algorithm is developed to overcome the effects of fault resistance and synchronization error as compared to previously developed scheme. The performance is assessed for different single line-to-ground (SLG) and double line-to-ground (LLG) fault cases with variations in fault resistance, fault distance (FD) and compensation level. Simulation results affirm the advantages of proposed scheme as an extra layer of protection over conventional schemes and prove superiority in performance over existing mutual impedance based scheme. Experimental results also demonstrate the feasibility of deployment for practical applications.