Steady-state Power Research Articles

Voltage sag sensitive load type identification based on power quality monitoring data

This paper focuses on identifying voltage sag-sensitive loads within unknown load type or when the load is already in operation. To achieve this, a new method of sensitive load identification based on power quality monitoring data is proposed. Firstly, the active power RMS monitoring data is used as the base data. The Hodrick-Prescott filtering and sliding mean segmentation are used to divide the period of the voltage sag event. Next, based on the division result, the differences of steady-state power quality monitoring data before and after each event are calculated as the dataset. The dynamic K-means is used to divide various load action areas. Finally, the voltage tolerance curves of each action area are fitted and compared with the preset curves, then according to the constituted rules in this paper, the type of sensitive load contained by user is recognized. The feasibility and accuracy of the proposed method are verified by analyzing the simulation examples and actual power quality monitoring data.© 2017 Elsevier Inc. All rights reserved.

Experimental measurement of a multi-pole magnetorheological fluid clutch under air cooling.

Thermal characteristics have a profound effect on the allowable slip power and torque transmission stability of magnetorheological (MR) fluid devices. This paper investigates the thermal properties of a multi-pole MR clutch under different heat dissipation methods. First, the structure of the clutch is described, and heat generation and heat dissipation of the designed clutch are studied theoretically. Then, a numerical model is established, and several simulations are conducted on steady-state and transient temperatures under various operation conditions. After that, a temperature testing platform for the MR clutch is built, and several temperature experiments are carried out. The results show that the allowable steady-state slip power of the clutch under natural air cooling is about 147W. Under forced air cooling, the allowable steady-state slip powers are 1.295, 1.555, and 1.790 kW, respectively, when the wind speeds are 3.5, 7.0, and 10.5m/s. Furthermore, it turned out that the transmission torque of the MR clutch decreases with the increase in temperature. The experimental and simulated values of temperature are in good agreement in terms of numerical values and trends, indicating that the established temperature field simulation model can better reflect the temperature characteristics of the actual operation of the proposed multi-pole MR clutch. This research achievement can provide support for research on heat dissipation technology for MR devices with multiple excitation sources.

Исследование точности определения места повреждения воздушных линий по данным от устройств синхронизированных векторных измерений различных классов и производителей

The technology of synchronized phasor measurements has been widely used in the Russian power system to analyze the parameters of steady-state electrical power modes and to record electro-mechanical transient processes. Issues on fault location based on synchronized phasor measurements have mainly been discussed in foreign publications. A significant drawback of most research papers on this issue is simplified modeling of both overhead lines and current and voltage measurement channel as well as digital filters of phasor measurement units (PMUs). The goal of this research is to develop a fault location algorithm based on synchrophasor measurements and to study its accuracy by using specialized equipment including a real-time digital simulator (RTDS), PONOVO current and voltage amplifiers and production-grade PMUs. A PMU-based double-ended fault location algorithm is developed using long-line equations and well-known electromagnetic transient theory concepts. Currents and voltage oscillograms of both overhead transmission line ends are modelled in the MATLAB/Simulink software package. These oscillograms are saved as COMTRADE files and played back using the RTDS hardware and all-in-one software package RSCAD. In addition, the study uses two production-grade PMUs, the first one is TPA-02, and the second one is a merging unit ENMU acting as a PMU, thus imitating PMUs at the line terminals. To time-align all the measurements and to aggregate PMU data frames, various auxiliary software such as PMU Connection Tester, and hardware is used. A double-ended fault location (FL) method utilizing synchrophasors under a fault has been developed. The method is based on an overdetermined system of nonlinear equations that describes physical processes in an overhead power line and can be applied under various fault types. An integrated study of the efficiency of the developed FL method has been conducted. FL errors have been computed using production-grade PMUs ENMU and TPA-02, along with the RTDS and other equipment. The authors have considered the case of configuring PMUs of different classes at the overhead line terminals, and different phasor reporting rates as well. The conducted experiments make it possible to reveal that the fault location errors do not exceed the thresholds imposed by the standard STO 56947007-29.120.70.241-2017 in 88 % of all the analyzed fault scenarios. The developed FL method makes it possible to achieve the accuracy required by regulatory guide in calculating the distance to the short circuit point in most of the cases examined. Based on the results of numerical experiments for various types of fault cases, it can be concluded that the PMU class and phasor reporting rate do not have a significant impact on the FL accuracy, provided that the fault duration is enough for the PMU filter to approach a steady output.

Decentralized Control for Multi-Terminal Cascaded Medium-Voltage Converters Considering Multiple Crossovers

Decentralized control with multiple droop characteristics can significantly improve the accuracy of power flow in medium-voltage direct-current (MVdc) networks. However, multiple crossovers caused by different control characteristics can lead to the drifts of power and voltage and instability issues. When this type of control is implemented in the cascaded three-level neutral-point-clamped (C3L-NPC) converters, on one hand, the mechanism of such the power and voltage drifts was not investigated. On the other hand, power control accuracy, dc voltage balancing across submodules (SMs) and multiple crossovers should all be considered, which requires suitable control methods. To address the challenges, firstly, the mechanism behind the power and dc voltage drifts is analyzed. Secondly, a control scheme is presented to improve the power control accuracy and dc voltage balancing and concurrently, to avoid the multiple crossovers. This is achieved by suitable droop gain design and adding a secondary power compensator. The presented control scheme is verified in MATLAB/Simulink simulation and experimentally validated in a three-terminal MVdc testbed. Results show that the accuracy of steady-state power flow is improved by 15% due to the elimination of multiple crossovers, while the power accuracy at dynamics improved by 13% with the secondary power compensator.

Sequential power flow algorithm and post-event steady-state power distribution analysis in hybrid AC/MT-MVDC systems

In hybrid ac/multi-terminal medium-voltage dc (AC/MT-MVDC) systems with multiple voltage source converters (VSCs) and dc/dc converters, it is essential to attain accurate initial power flow (PF) and post-event power distribution solutions efficiently. This paper proposes: (i) a novel sequential PF algorithm for hybrid AC/MT-MVDC systems by a Fibonacci search-based Newton–Raphson (FSNR) approach with uniform MVDC bus type definition, while considering power losses and varied control schemes of different converters; (ii) a zero error steady-state post-event power distribution calculation method under droop control by the introduction of dynamic I/V droop coefficients based on the FS algorithm. The FSNR approach simplifies the MVDC PF derivation by only requiring the definition of the dc current bus type, effectively eliminating the need to solve multiple sub-Jacobian matrices. Furthermore, the post-event power distribution analysis offers precise power redistribution calculation approach following disturbances by considering both open- and closed-loop operation in an MT-MVDC distribution system. The computational efficiency and validity of the proposed PF algorithm, along with the accuracy of presented post-event power distribution calculation method are verified through Python and RTDS real-time simulators in an extended MT-MVDC distribution network incorporated with the IEEE 14/33/69 bus transmission/distribution systems.

Wind generation and power system interaction analysis using probabilistic techniques

. Energy power from renewable sources, especially wind turbine generators, are being considered as an important generation alternative in the electrical power systems around the world due to their non contaminant nature and low environmental effects. In particular, the power supplied by wind generators is widely random following the random nature of weather conditions; therefore a probabilistic approach during planning seems much more appropriate than the deterministic approach actually used in the electrical utilities. This paper presents a methodology that allows the application of probabilistic analysis, thru the use of programming tools, in the load flow planning studies. The methodology described provides the opportunity to obtain the steady state response in systems where wind power exists using a wind power generation model (WPGM) and an iterative routine to the load flow analysis considering each value of generation of the wind sources. A wind power generation model (WPGM) was developed using a random wind speed generator. The random wind speed generator describes the Weibull distribution of wind measurements, and then using Montecarlo simulation techniques, a program in Visual Basic executes the automatic evaluation of random samples of speed of wind considering the characteristic power curve of a wind turbine, obtaining a widely database of wind generation conditions. As a result of the investigation, a computational tool was developed in order to use it, in combination with the PSS/E load flow analysis software, for steady state power system analysis. The methodology was used as an assessment tool to identify the effects of wind turbines generation into the substation voltages and power flow profiles in the power network, for a wind farm project intended to be installed in Margarita Island. The analysis aimed to identify the transmission adjustments, reinforcements and expansions needed to guarantee the wind farm project integration successful into the power system.

Magnitude-phase equivalent circuit and steady-state power-angle characteristic analysis of DFIG

Circuit model representing generator characteristics is essential in stability analysis and control system design of doubly-fed induction generator (DFIG). This paper develops the relationship between generated voltage and magnetic field in DFIG, and establishes an equivalent circuit model considering rotor motion. The novel magnitude-phase equivalent circuit (MPEC) model is established based on vector magnitude and angle. Furthermore, the paper analyzes phasor diagrams, calculates the power expression under the MPEC, and obtains steady-state power-angle characteristic of the DFIG. In the proposed power-angle characteristic, the DFIG's output incorporates variations in slip ratio and power-angle, which combines the characteristics of asynchronous and synchronous machines. Based on the proposed MPEC and power-angle characteristic, the steady-state maximum power of the DFIG is determined at the critical stable power-angle of π/2. Finally, simulation and experimental results are given to validate the effectiveness of the proposed equivalent circuit model and power-angle characteristic of DFIG. The results show that the MPEC model is capable of analyzing the DFIG stability from the power-angle motion perspective, and the system exhibits a potential for instability when the power-angle exceeds 1.5.

Voltage Drop Compensation Technology for High-Voltage and High-Power DC Energy Storage Power Supply System

This paper presents an output voltage drop compensation technology for high-voltage and high-power DC energy storage system (DC-ESS). This technology is used to improve the output voltage stability of high-voltage high-power DC-ESS in high rate discharge. The proposed output voltage drop compensation technology includes an ESS architecture and a corresponding control method. The proposed ESS architecture adopts DC dynamic voltage regulator (DC-DVR) to compensate for output voltage drop. DC-DVR adopts 6-phase interleaved parallel buck converter. This architecture not only maintains the system output voltage stability, but also reduces the system cost. Moreover, the proposed ESS architecture does not change the original energy storage capacity. The dynamic power flow of the proposed ESS architecture is analyzed and a direct power control method based on full response power compensation is proposed. The steady-state power and dynamic power of the proposed ESS architecture are compensated respectively, so that the input power can quickly track the change of the output power. The proposed control method improves the stability and dynamic response speed in the system dynamic process. Simulation and experiment verify the effectiveness of the proposed ESS architecture and control method.

Comparison of NIRS exercise intensity thresholds with maximal lactate steady state, critical power and rowing performance.

This study aimed to compare the intensity of deoxygenated haemoglobin concentration ([HHb]) and tissue saturation index (TSI) breakpoints ([HHb]-BP and TSI-BP) with maximal lactate steady state (MLSS) and critical power (CP), and to describe their association with 2000-m rowing ergometer performance. Fourteen male rowers performed on a rowing ergometer: I) a discontinuous incremental test with 3-min stages (INC3); II) a continuous incremental test with 1-min stages (INC1); III) constant workload tests to determine MLSS; and IV) performance tests of 500 m, 1000 m, 2000 m and 6000 m to determine CP.CP (257 ± 39 W; 3.79 ± 4.1 L · min-1) was higher than [HHb]-BP3 (205 ± 26 W; 3.48 ± 2.9 L · min-1), [HHb]-BP1 (207 ± 27 W; 3.27 ± 3.2 L · min-1), and TSI-BP3 (218 ± 31 W; 3.51 ± 3.0 L · min-1), but not higher than TSI-BP1 (222 ± 34 W; 3.43 ± 3.2 L · min-1). MLSS (187 ± 26 W; 3.33 ± 3.2 L · min-1) was lower than TSI-BP3 and TSI-BP1 for power output, but not different in any comparison for ⩒O2. The limits of agreement for power output and ⩒O2 suggest poor agreement among these thresholds. The low level of agreement compromises the use of [HHb]-BP and TSI-BP for estimating MLSS and CP; therefore, these thresholds should not be considered interchangeable.

Alleviating nanostructural phase impurities enhances the optoelectronic properties, device performance and stability of cesium-formamidinium metal-halide perovskites.

The technique of alloying FA+ with Cs+ is often used to promote structural stabilization of the desirable α-FAPbI3 phase in halide perovskite devices. However, the precise mechanisms by which these alloying approaches improve the optoelectronic quality and enhance the stability have remained elusive. In this study, we advance that understanding by investigating the effect of cationic alloying in CsxFA1-xPbI3 perovskite thin-films and solar-cell devices. Selected-area electron diffraction patterns combined with microwave conductivity measurements reveal that fine Cs+ tuning (Cs0.15FA0.85PbI3) leads to a minimization of stacking faults and an increase in the photoconductivity of the perovskite films. Ultra-sensitive external quantum efficiency, kelvin-probe force microscopy and photoluminescence quantum yield measurements demonstrate similar Urbach energy values, comparable surface potential fluctuations and marginal impact on radiative emission yields, respectively, irrespective of Cs content. Despite this, these nanoscopic defects appear to have a detrimental impact on inter-grains'/domains' carrier transport, as evidenced by conductive-atomic force microscopy and corroborated by drastically reduced solar cell performance. Importantly, encapsulated Cs0.15FA0.85PbI3 devices show robust operational stability retaining 85% of the initial steady-state power conversion efficiency for 1400 hours under continuous 1 sun illumination at 35 °C, in open-circuit conditions. Our findings provide nuance to the famous defect tolerance of halide perovskites while providing solid evidence about the detrimental impact of these subtle structural imperfections on the long-term operational stability.

Reliability Assessment of Power System based on Load Flow Analysis of the IEEE 57 Bus used in Micro Grid Applications

The complex power system consists of more interconnections; therefore, modelling such a type of network is a very difficult task in the commercialization area cycle. MATPOWER has all steady-state power system models, which are extensively used in academic research for power flow (PF) modeling. The PF architecture designed in this is extensible; it is easy to add or modify variables and constraints in the standard case structure. This paper presents the details of the mathematically scaled loads in IEEE 57 bus power system network modelling by using the standard test case data. Internally, all the bus voltages are expressed in p.u., and phase angles are expressed in radians, but the generators and loads are expressed in terms of power ratings. The scaling of these is defined based on the scaled voltage of the corresponding bus voltage. The scaling load procedure used in this paper is very useful for designing a low-voltage power system network for practical analysis purposes. Two simulations are performed in this paper for the analysis of the actual load flow (ALF) and scaled load flow (SLF) power system models. The voltage, phase angle, and power flow through the lines are compared to analyze the accuracy of both simulations. When compared with ALF, it has shown good accuracy, computational efficiency, and convergence properties.

A Comparative Analysis of VS-CNTFET and CMOS Based Inverter Circuit

This abstract delves into the comparative exploration between Carbon Nanotube Field Effect Transistors (CNTFETs) and traditional CMOS (Complementary Metal-Oxide-Semiconductor) transistors, with a specific emphasis on digital inverter circuits. Utilizing carbon nanotubes derived from the graphene allotrope, CNTFETs are introduced as a technological advancement, providing advantages such as reduced size and lower power consumption. The investigation centres on the evaluation of the Stanford model, particularly focusing on the Virtual Source Carbon Nanotube Field Effect Transistor. This specific model showcases superior performance, compact dimensions, and decreased power requirements when contrasted with silicon-based MOSFETs. The analytical process involves subjecting virtual source CNTFET inverter circuits and MOSFET-based circuits to testing via the Symica software tool, encompassing the examination of transient response, voltage transfer characteristics, and steady-state power consumption. The outcomes underscore the potential of CNTFETs as promising alternatives in the progression of digital design, offering heightened efficiency and diminished power consumption.

Limitations of Bulk Diamond Sensors for Single-Cell Thermometry.

The present paper reports on a Finite Element Method (FEM) analysis of the experimental situation corresponding to the measurement of the temperature variation in a single cell plated on bulk diamond by means of optical techniques. Starting from previous experimental results, we have determined-in a uniform power density approximation and under steady-state conditions-the total heat power that has to be dissipated by a single cell plated on a glassy substrate in order to induce the typical maximum temperature increase ΔTglass=1 K. While keeping all of the other parameters constant, the glassy substrate has been replaced by a diamond plate. The FEM analysis shows that, in this case, the maximum temperature increase is expected at the diamond/cell interface and is as small as ΔTdiam=4.6×10-4 K. We have also calculated the typical decay time in the transient scenario, which resulted in τ≈ 250 μs. By comparing these results with the state-of-the-art sensitivity values, we prove that the potential advantages of a longer coherence time, better spectral properties, and the use of special field alignments do not justify the use of diamond substrates in their bulk form.

Cross gain modulation in quantum dot semiconductor optical amplifiers under the influence of the Probe

The Pulse effect on the cross-gain modulation (XGM) in the quantum dot (QD) semiconductor optical amplifiers (SOAs) is investigated using the combining of the SOA power with the QD rate equations system. The QDs structure includes three regions: ground state (GS), excited state (ES) and wetting layer (WL). Thus, a set of rate equations for pump and probe signals is introduced for both steady-state and small-signal power values, which are solved numerically. The pulse shape was included in the analysis, for pump and probe signals. The theoretical results showed a good agreement with the experimental results. It was found that decreasing pulse width of pump/probe ratio is efficient to increase XGM efficiency and bandwidth.

Mitigation of transient effects due to partial shading in a grid-connected photovoltaic farm through controlled vehicle to grid operation

Environmental issues and air pollution in urban areas are driving forces behind the shift to electric vehicles (EVs). The energy storage element of the EVs can be used in many effective ways, such as increasing spinning reserve, shaving peak load, load levelling, voltage regulation etc. So, establishing a smart grid with several renewable energy sources along with the grid integration of EVs is the recent trend in power systems. One of the commonly observed essential phenomena in the smart grid including a PV system is partial shading (PS), which implicates the reduction of solar irradiation over the PV module, mainly due to leaves or branches of trees, clouds, and dust. Though most previous researchers were concerned about the steady state power reduction during PS, in this research, we focused on the reduction of transient impact on a grid-connected PV system using the controlled Vehicle to Grid (V2G) operation of the EVs. A small-scale microgrid consisting of a PV farm and a diesel generator is considered, where the PV farm experiences different degrees of shading varying from 30 to 70%. The simulation results show that due to the increase of the PS, the percentage overshoot (% OS) and settling time of rotor speed, active power and load current are increased. To mitigate this issue, we proposed the integration of plugged-in electric vehicles (PEVs), through the controlled V2G operation, which is done here by a PI controller. The proposed system improves the transient effects at both the load and generator sides. It has been found that the PS creates an oscillation in rotor speed, which is settled down by the governor system of the generator at the 20s, while the controlled V2G operation reduced this settling time to 10s. On the load side, the % OS of active power has been reduced from 4.24% to 0.44% and the settling time has been decreased from 28s to 18s by the controlled integration of the PEVs.

Effect of Phase Shift Definition on Power Characterization of Isolated DC–DC Converter Under PWM Plus Phase Shift Modulation

PWM plus phase shift (PPS) modulation is a popular modulation technique for the current fed dual active bridge (CFDAB) converter. Power transfer characteristics for any modulation technique are important for converters. However, in the literature, different power characteristics of CFDAB are presented for PPS modulation. This disparity in power transfer behavior creates confusion and ambiguity to the readers. This brief reveals the reason for such disparity. This is primarily due to the definition of the phase shift considered. When the phase shift is considered between the rising edges of high frequency voltages, asymmetric power transfer characteristics are obtained. On the contrary, symmetric power transfer characteristics are obtained if phase shift is considered between the mid point of high level of high frequency voltage signals. Thus the latter provides useful features and universal conditions for power reversal and peak power transmission individually. Steady state power under different modulation is obtained from unified model of CFDAB. The analytical results and experimental investigations are in agreement with each other.

Steady-State Security and Power System Contingency Analysis: A Review

Steady-State Security and Power System Contingency Analysis: A Review

An intelligent momentum perturbed variable step-size adaptive algorithm for fast converging HNANC systems

The existing methodologies for hybrid narrow-band active noise control (HNANC) systems utilises variants of the FXLMS algorithm, which typically resulted in degraded convergence and steady-state performance. In this paper, a class of variable step size (VSS) adaptive algorithms are explicitly developed for a HNANC system analyses and the convergence as well as the steady-state performance of the proposed framework are evaluated in comparison to the existing state-of-the-art. For an HNANC system designed to operate in a multiple noise environment, the VSS filtered-x LMS (VSSFXLMS) and momentum VSS filtered- x weight accumulated least mean square (MVSS-FXWALMS) algorithms are proposed. The proposed algorithm employs a variable step size that is inspired by the variable momentum factor, and combines these two parameters to drive the FXWALMS algorithm for an HNANC system in order to accomplish maximum noise reduction. In a multiple noise environment setup for an HNANC system, the proposed algorithm surpasses the state-of-the-art in nearly all conventional operating conditions. A detailed performance analysis of the proposed algorithm has been carried out using mean noise reduction ratio, steady-state power spectra at different conditions. The results demonstrate a significant improvement in noise reduction performance compared to the counterparts.

Estimation of the power of a geothermal energy recovery system that uses a heat exchanger

Access to new sources of renewable energy free of CO2 emissions is one of the priority needs of the global economy. At great depths underground there are geothermal sources with temperatures of up to several hundred degrees. Recovery of energy from such sources may take place using a heat exchanger placed in rocks at great depths. Before starting the exploitation of such resources, it is necessary to estimate the performance and power of the source with the assumed system parameters. In the conducted research, simulations of the energy acquisition system in the Matlab-simulink environment were carried out. The model of heat flows with distributed variables was used for the simulation, describing changes in the temperature distribution in time and space. The steady-state power of the system, which is possible to download over a long period of time, was also estimated. The most important conclusion from the conducted is that after some time, depending on the power consumed, the system may experience a significant decrease in power. The decrease in power is caused by the cooling of the rocks around the heat exchanger and the thermal resistivity of the medium, which are the rocks.

Three-Stage CMOS LDO with Optimized Power and Dynamic Performance for Portable Devices

Low dropout (LDO) regulators are crucial components in power management systems for portable, i.e., battery-powered, devices. However, the design of LDO regulators presents a challenging trade-off between dynamic performance, power consumption, and area efficiency. This paper proposes a novel LDO regulator design that addresses these challenges by employing the reverse nested Miller compensation (RNMC) with current buffers embedded within the own class AB high gain error amplifier (EA) topology, and a time response enhancement circuit (TREC). High-gain (>120 dB) class AB EA renders good regulation performance with enhanced dynamic performance. The proposed compensation scheme improves the gain bandwidth product (GBW) and stability of the regulator, while the TREC reduces overshoot and undershoot during load transients without additional steady-state power consumption. Post-layout simulations confirm the robustness of the proposed 180 nm CMOS design across a wide range of operating conditions, achieving a regulated output voltage of 1.8 V with 100 mV dropout, good load and line regulating performance, and excellent load transient response with reduced undershoot and overshoot at minimum power (Iq = 13.8 μA) and area (314 μm × 150 μm) consumption. The proposed LDO regulator thus offers a compelling compromise between power consumption, area efficiency, and dynamic performance, making it highly suitable for portable applications.