Frequency Power Fluctuations Research Articles

Identification Method for Pulse Wave Resulted From Fault Transient of Overhead Transmission Line

This paper presents a simple and effective method to extract the identification quantity of transient pulse waveform produced by the overhead transmission line short-circuit fault. This method employs the second-order time harmonic equation of the power frequency component to convert the fault full-wave data. After the conversion, only the identification quantity remains. This method can amplify high-frequency spectral content by the times of the square of the angular frequency, and hence improve the sensitivity of identifying fault transient. Using the identification quantity, one can clearly observe the arrival time and relative intensity of fault transient. A three-phase half wavelength transmission line of 50Hz/3000km is simulated with PSCAD to illuminate the effectiveness of this method. The effects of fault type, soil resistivity, fault resistance, power frequency fluctuation, sampling rate, transposition length,fault inception angle and white noise are analyzed. Calculated results show that this method can distinguish different fault type and can work effectively at low sampling rate down to 10kHz. This method is helpful for improving the performance of the traveling-wave based fault location method.

Grid-connected power oscillation study of hybrid storage direct-drive wind farms based on SVG

This paper studies the control strategy of hybrid energy storage to suppress power fluctuation of direct-drive wind turbine based on static var generator, and proposes a grid-connected power oscillation suppression of hybrid energy storage direct-drive wind turbine based on static var generator (SVG). Method, the static var generator is mainly to solve the reactive current generated by the large and impact load and the resulting reactive power, and the SVG connected in parallel with the fan outlet busbar performs reactive power coordinated control to support the grid voltage. This control strategy control The lead-acid battery compensates for the intermediate frequency power fluctuation and the super capacitor (SC) quickly absorbs the high frequency power fluctuation, thereby smoothing the wind power and improving the power quality. sexual demands. Finally, a system simulation model is established in the Matlab/Simulink environment to verify the effectiveness of the proposed method.

Optimal Flow of MVDC Shipboard Microgrids With Hybrid Storage Enhanced With Capacitive and Resistive Droop Controllers

Hybrid storage system composed of battery energy storage systems (BESSs) and supercapacitors is a promising solution to mitigate the high frequency power fluctuations of pulsed power loads (PPLs) in medium voltage DC (MVDC) shipboard power systems. Due to the presence of multiple storage units, a power sharing algorithm needs to be considered within the energy management system (EMS) in the shipboard power system. In this paper, an optimal power flow problem is formulated for MVDC shipboard power systems with hybrid energy storage systems. Battery energy storage systems (BESSs) and conventional generation units are enhanced with virtual resistive droop controllers to share the steady-state power fluctuations. Supercapacitors are enhanced with virtual capacitive droop controllers to share the high frequency fluctuations in the load. The optimal flow accounts for minimizing the operational cost of the generation units in the shipboard power system considering the constraints of network, load balance, voltage profile, and power/energy limits. Second-order cone programming (SOCP) relaxation is used to approximate the nonconvexity of the optimal flow formulation and necessary conditions for global optimality of the solution are discussed. Results confirm the effectiveness of the proposed formulation in load support and managing the energy between storage units.

Cooperative control strategy for distributed wind-storage combined system based on consensus protocol

To realize real-time wind farm output power regulation with power-sharing among storage devices that have different state of charges (SoCs), this paper proposes the cooperative control of the distributed wind-storage combined systems (WSCSs). It firstly establishes the mathematical model of doubly-fed induction generator (DFIG) and hybrid energy storage system (HESS) and implements the controls for two devices, respectively. Secondly, based on the power consensus protocol, an active power cooperative control strategy of the distributed WSCSs is proposed. It ensures that the energy storage devices can cooperatively compensate for wind power according to their different capacities to regulate the output power of the wind farm (WF) in real-time. At the same time, the high- and low- frequency power fluctuations can be effectively shared by the supercapacitors (SCs) and batteries, overcoming the deficiencies of the conventional battery energy storage system (BESS). Then, considering that the SoCs of the batteries are not identical, this paper further proposes a DFIG grid-side reference power adjustment strategy based on consensus protocol. It guarantees that each HESS can effectively achieve power-sharing while regulating the output power according to the SoCs of batteries. Finally, simulations in PSCAD/EMTDC under various scenarios are conducted to demonstrate the effectiveness of the proposed control strategy.

Hybrid energy storage system control method based on model predictive control

The traditional PI controller for a hybrid energy storage system (HESS) has certain drawbacks, such as difficult tuning of the controller parameters and the additional filters to allocate high- and low- frequency power fluctuations. This paper proposes a model predictive control (MPC) method to control three-level bidirectional DC/DC converters for grid-connections to a HESS in a DC microgrid. First, the mathematical model of a HESS consisting of a battery and ultra capacitor (UC) is established and the neutral point voltage imbalance of a three-level converter is solved by analyzing the operating modes of the converter. Secondly, for the control of the grid-connected converters, an MPC method is proposed for calculating steady-state reference values in the outer layer and the dynamic rolling optimization in the inner layer. The outer layer ensures the voltage regulation and establishes the current predictive model, while the inner layer, using the model predictive current control, makes the current follow the predictive value, thus reducing the system current ripple. This cascaded topology has two independent controllers and is free of filters to realize the high-and low- frequency power allocation for a HESS. Therefore, it allows two types of energy storage devices to independently regulate the voltage and realizes the power allocation of the battery and UC. Finally, simulation studies are conducted in PSCAD/EMTDC, and the effectiveness of the proposed HESS control strategy is verified in a case, such as a controller comparison and fault scenario.

Multilayer MEG functional connectivity as a potential marker for suicidal thoughts in major depressive disorder

Major depressive disorder (MDD) is highly heterogeneous in its clinical presentation. The present exploratory study used magnetoencephalography (MEG) to investigate electrophysiological intrinsic connectivity differences between healthy volunteers and unmedicated participants with treatment-resistant MDD. The study examined canonical frequency bands from delta through gamma. In addition to group comparisons, correlational studies were conducted to determine whether connectivity was related to five symptom factors: depressed mood, tension, negative cognition, suicidal thoughts, and amotivation. The MDD and healthy volunteer groups did not differ significantly at baseline when corrected across all frequencies and clusters, although evidence of generalized slowing in MDD was observed. Notably, however, electrophysiological connectivity was strongly related to suicidal thoughts, particularly as coupling of low frequency power fluctuations (delta and theta) with alpha and beta power. This analysis revealed hub areas underlying this symptom cluster, including left hippocampus, left anterior insula, and bilateral dorsolateral prefrontal cortex. No other symptom cluster demonstrated a relationship with neurophysiological connectivity, suggesting a specificity to these results as markers of suicidal ideation.

Hierarchical control of DC micro-grid for photovoltaic EV charging station based on flywheel and battery energy storage system

For micro-grid systems dominated by new energy generation, DC micro-grid has become a micro-grid technology research with its advantages. In this paper, the DC micro-grid system of photovoltaic (PV) power generation electric vehicle (EV) charging station is taken as the research object, proposes the hybrid energy storage technology, which includes flywheel energy storage and battery energy storage. Flywheel energy storage is used to stabilize high frequency power fluctuations and some low frequency power. Lithium iron phosphate (LiFePO4) battery is used for balancing the reference power to maintain the DC bus voltage balance. Composition of the DC micro-grid and various operating modes are analyzed, a hierarchical coordinated control based on the power monitoring steps of the 5-layer DC bus voltage is proposed. Finally, simulation analysis is carried out on the MATLAB/Simulink software platform. Under different working states such as PV input power change, AC and DC loads change, EV charging condition change, and battery over-discharge, the proposed control strategy can make the DC bus voltage at different voltage layers effectively switch, and keep the DC bus voltage balance, thus to achieve flexible and reliable operation of the DC micro-grid system.

Online generalized droop-based demand response for frequency control in islanded microgrids

Frequency stability, as one of the most important issues in the modern power grids, requires more efficient control methods due to the increasing complexity of the power system, high penetration of distributed generation sources as well as high electrical energy consumption. The challenges become more critical in the case of islanded microgrids (MGs), due to existing no traditional ancillary services of the upstream electric power network. Thus, the modern power grids, such as MGs, need advanced regulation methods to keep the generation-consumption balancing. Demand response (DR) is the recently introduced control approach which guarantees continuous contribution of controllable loads in the system frequency control. In this paper, a new online droop-based DR, generalized droop control (GDC), is introduced to apply in islanded MGs frequency control. An artificial neural network is used for online tuning of droop coefficients in the presented GDC framework. The proposed control approach changes controllable active and reactive loads, using a set of equations based on satisfying dynamics. To evaluate the effectiveness of the proposed control method, several scenarios are simulated in which changes of the system frequency and voltage are studied. Results show significant damping of power–frequency fluctuation and a desirable performance of the closed-loop system.

Analysis of a new design of the hybrid energy storage system used in the residential m-CHP systems

The energy balancing problem is the main challenge for the effective application of micro combined heat and power (m-CHP) in a residential context. Due to its high energy density and relative robustness, the lead-acid battery is widely used for power demand management to compensate the mismatch between the m-CHP electrical output and domestic demand. However, batteries are not suited to respond effectively to high frequency power fluctuations, but when coupled to the m-CHP, they experience frequent short-term charge/discharge cycles and abrupt power changes, which significantly decreases their lifetime. This paper addresses this problem by hybridising the lead-acid battery storage with superconducting magnetic energy storage (SMES) to form a hybrid energy storage system (HESS) that is coordinated by a novel sizing based droop control method. The control method for the first time considers both the capacity sizing of the HESS technologies and the droop control method of the battery and the SMES. A hardware in the loop test circuit is developed coupling with the real time digital simulator (RTDS) to verify the performance of the HESS with the new control algorithm. The experimental results show that control method is able to exploit the different characteristics of the SMES and the battery to meet the mismatch of m-CHP power generation and domestic demand. In addition, the lifetime analysis is implemented in this paper to quantify the battery lifetime extension in the HESS, which further proves the validity of the proposed control strategy.

Energy management with dual droop plus frequency dividing coordinated control strategy for electric vehicle applications

In this paper, a dual droop-frequency diving coordinated control strategy is proposed for electric vehicle (EV) applications, where the hybrid energy storage system (HESS) with supercapacitors and batteries is integrated to prolong the life time of storage elements. The dynamic power allocation between the supercapacitor and batteries are obtained through the voltage cascaded control, upon which the high and low frequency power fluctuation are absorbed by the supercapacitors and batteries respectively to fully exploit the advantages of the supercapacitors and batteries. Moreover, the power capacity is scaled up by connecting storage blocks in parallel. A dual droop control scheme for parallel-connected energy storage system and its operation principle is introduced on the aspect of current sharing characteristic and state-of-charging (SOC) management. After detailed analysis and formula derivation, the corresponding loop parameters are designed. Through this control method, the current sharing performance is ensured and each block makes the self-adaptive adjustment according to their SOC. Consequently, the load power can be shared effectively, which helps to avoid the over-charge/over-discharge operation and contributes to the life cycle of the energy storage system. Each module is autonomous controlled without the necessity of communication, which is easy, economic and effective to realize. Finally, the simulation and experimental results are exhibited to verify the effectiveness of the proposed control scheme.

Research on a New Digital Algorithm to Improve the Monitoring Accuracy of the Dielectric Loss Factor

Based on Hilbert transform and complex trigonometric operation, this paper presents a new digital algorithm to improve the monitoring accuracy of the dielectric loss factor, and the theoretical basis of the algorithm is also deduced. Simulation results show that, the new algorithm renders good application performance when there exists power frequency fluctuation or the sampled data length is not exactly an integer fold of a power cycle, which demonstrates the algorithm can effectively solve the issues incurred from asynchronous sampling.

A novelty digital algorithm for online measurement of dielectric loss factor of electronic transformers

There are many inherent performance limitations using traditional algorithms for online measurement of dielectric loss factor including synchronous sampling, no interharmonics and power system frequency must be invariable. In a non-stationary signal environment where power frequency fluctuation and interharmonic components exist, there is no guarantee of measurement accuracy by using traditional methods. The paper proposed a high-accuracy digital algorithm for online measurement of dielectric loss factor of electronic transformers. Theoretical basis of the new algorithm is based on a new data processing procedure including data truncation and data addition which compensates phase distortion as a result of the spectrum of addition data contains offsets. The algorithm can accurately extract the fundamental signal and calculate dielectric loss factor. Measured results from simulations and practical engineering projects show that the new algorithm has good application feasibility without being affected by the limitations rendered above.

516 多層ニューラルネットによる味覚誘発脳波時系列パタン解析 : 塩味及び酸味味覚刺激反応度解析(OS5-(9)オーガナイズドセッション《ライフサポートにおける工学技術》)

This study aims at quantifying the objective individual gustatory reactive level. We extracted the individual reference EEG sequence pattern evoked by gustatory stimuli. Obvious differences were observed among individual gustatory reaction. We constructed the automatic H2(E) pattern matching discriminator and investigate the discrimination performance and used a neural network to improve this discrimination performance. We measured the EMG of the mouth to investigate its effect on the gustatory stimuli evoked EEG. We analyzed the time sequence frequency of the gustatory stimuli evoked EEG to confirm, could confirm the frequency power fluctuation in gustatory reactive part.

Wind model for low frequency power fluctuations in offshore wind farms

AbstractThis paper investigates the correlation between the frequency components of the wind speed Power Spectral Density. The results extend an already existing power fluctuation model that can simulate power fluctuations of wind power on areas up to several kilometers and for time scales up to a couple of hours, taking into account the spectral correlation between different wind turbines. The modelling is supported by measurements from two large wind farms, namely Nysted and Horns Rev. Measurements from individual wind turbines and meteorological masts are used. Finally, the models are integrated into an aggregated model which is used for estimating some electrical parameters as power ramps and reserves requirements, showing a quite good agreement between simulations and measurement. The comparison with measurements generally show that the inclusion of the correlation between low frequency components is an improvement, but the effect is relatively small. The effect of including the low frequency components in the model is much more significant. Therefore, that aggregated model is useful in the power system planning and operation, e.g. regarding load following and regulation. Copyright © 2009 John Wiley & Sons, Ltd.

バイオマスガスタービン発電機とフライホイール電力貯蔵装置を用いた風力発電の変動電力補償法

The power generation using natural energy contains electric power fluctuation. Therefore, in order to put such power generation system to practical use, compensation for system power fluctuation is needed. In this paper, we propose a power compensation method using biomass gas turbine generator and flywheel energy storage equipment. The gas turbine generator is used for compensation of low frequency power fluctuation in order to decrease capacity of flywheel. Usefulness of the proposed system is confirmed by experiment using a test plant.

Definition and digital algorithms of dielectric loss factor for condition monitoring of high-voltage power equipment with harmonics emphasis

Experience and applications of currently available methods for online monitoring and diagnostics of high-voltage power apparatus are briefly reviewed. Based on dielectric physics, a new definition of dielectric loss factor with harmonics emphasis is proposed to evaluate the operational conditions of power apparatus on a more reasonable basis, along with corresponding digitised algorithms. Two approaches, namely the decoupling algorithm and the approximating algorithm, are presented to implement the methodologies with the new definition of dielectric loss factor. The impact of background noise and power-frequency fluctuation on estimation accuracy are analysed by computer simulations, showing better application qualities of the approximating algorithm than the decoupling algorithm. A comprehensive strategy of simultaneous monitoring of sum current, dielectric loss factor, resistive current and capacitive current is recommended to give an effective assessment and diagnosis.

A microprocessor-controlled high-voltage current-comparator-based capacitance bridge

A microprocessor-controlled high-voltage current-comparator-based capacitance bridge is described. The bridge has a capacitance ratio and a dissipation factor (loss tangent) measurement range of 1/1 to 100/1 and 0 to 10%, respectively, with a resolution of 1 PPM (part per million). To accommodate capacitance ratios larger than 100/1 (up to 100000/1) and load currents of up to 1000 A, an additional range-extending two-stage current transformer is employed. The overall accuracy of the bridge including the ratio extender is better than 5 PPM in both magnitude and phase. The automatic balancing feature facilitates the use of the bridge for accurate load loss measurements of large high-voltage inductive loads, such as shunt reactors and power transformers. It allows tracking of the changes in the inductive and loss tangent balance due to power frequency fluctuations and heating effects, respectively.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Measurement of Power Frequency Fluctuations Using the FFT

A new method for detecting fluctuations in the fundamental frequency component of a power system, by relating it to a leakage coefficient in the FFT, is presented. The phenomenon of leakage in the FFT is used advantageously to increase spectral resolution. The leakage coefficient is a quantitative measure of the deviation from the fundamental frequency component with respect to the sampling frequency. Theoretical aspects are considered along with a method for on-line implementation.