Sequence Components Research Articles

Thalamic control of cortical dynamics in a model of flexible motor sequencing.

SUMMARYThe neural mechanisms that generate an extensible library of motor motifs and flexibly string them into arbitrary sequences are unclear. We developed a model in which inhibitory basal ganglia output neurons project to thalamic units that are themselves bidirectionally connected to a recurrent cortical network. We model the basal ganglia inhibitory patterns as silencing some thalamic neurons while leaving others disinhibited and free to interact with cortex during specific motifs. We show that a small number of disinhibited thalamic neurons can control cortical dynamics to generate specific motor output in a noise-robust way. Additionally, a single “preparatory” thalamocortical network can produce fast cortical dynamics that support rapid transitions between any pair of learned motifs. If the thalamic units associated with each sequence component are segregated, many motor outputs can be learned without interference and then combined in arbitrary orders for the flexible production of long and complex motor sequences.

Differential positive sequence power angle-based microgrid feeder protection

Abstract Integration of distribution generation (DG) makes the growth of the microgrid protection scheme very challenging issues. Researchers from all over the world continuously are doing hard work for developing the microgrid protection schemes. A differential positive sequence power angle (DPSPA) based microgrid protection scheme is proposed in this paper using positive sequence (PS) components of voltages and currents. The DPSPA for the feeder is calculated considering both ends of voltage and current signal information, when it is more than threshold, internal fault is reported otherwise, it is an external fault. Taking into consideration the varying operational modes of the microgrid, variations in DG penetration, and variations in fault variables namely fault types, and fault locations, the proposed protection scheme is verified on a modified IEEE-13 bus feeder. Moreover, to test the robustness and efficacy of the suggested scheme, various non-faulty events including induction motor starting, non-linear loading, load switching, capacitor switching, and section cutoff have been conducted. The proposed scheme is also verified for external faults and it is found that it continues to be stable for the external faults. The findings exhibit this proposed scheme, which is based on DPSPA, can successfully protect the microgrid under changing operating conditions.

Power Quality Improvement in Microgrids using STATCOM under Unbalanced Voltage Conditions

A large number of single-phase loads and sources create unbalanced voltage in microgrids. Voltage unbalance reduces the power quality, which results in misoperation or failure of customer equipment and microgrid. Also, voltage unbalance negatively impacts induction motors, power electronic converters, and adjustable speed drives. Static synchronous compensator (STATCOM), as an influential segment of the Flexible Alternative Current Transmission Systems (FACTS), has been extensively utilized as shunt compensators for controlling reactive power and regulation voltage in transmission and distribution networks. Under unbalanced conditions, an oscillating couple between the positive and negative sequence components of control loops emerge in the d-q frame. This paper suggests an innovative point of common coupling (PCC) voltage controller in Decoupled Double Synchronous Reference Frame (DDSRF) to compensate for an unbalanced PCC voltage and reduce the oscillating couple using STATCOM. Implementation of the proposed DDSRF involves several steps. Firstly, unbalance signals are rotated counterclockwise to split up the positive sequences. Secondly, those signals are rotated clockwise to separate negative sequences. Finally, by utilizing mathematical equations, the proposed DDSRF is introduced, which enables independent control of positive and negative sequence components. This study controls DC capacitor voltage for unbalanced conditions. Furthermore, the regulation voltage at PCC is performed. The control system scheme is also designed under unbalanced conditions, and simulation results guarantee the suggested control strategy.

An augmented state observer-based sensorless control of grid-connected inverters under grid faults

The increasing integration of grid-connected renewable energy systems impose major challenges of reliability and power quality within power grid system. Grid-connected systems must ensure grid stability, accommodate low voltage ride-through capability, and comply with grid codes under unbalanced voltage dips to avoid any grid-disconnection. In this context, this paper proposes a novel control strategy to improve grid-connected inverter control under unbalanced grid voltage conditions. Positive and negative sequence components of grid voltage are estimated using an augmented state and disturbance observer. The estimated values of grid voltage and phase-angle are used to protect the inverter from any over-current tripping even at unbalanced grid voltage dips. This can be achieved by reducing active power and suppressing its fluctuations with new current references, which are obtained in the synchronous reference frame according to grid codes. The effectiveness and flexibility of the proposed power control strategy have been demonstrated by numerical simulation and validated by experiments in both balanced and unbalanced grid fault conditions.

Распознавание короткого замыкания при каскадном отключении повреждённой цепи в двухцепной линии электропередачи

The article supplements the previously published analysis of the informational contribution of a cascade disconnection of a power line to the recognition of a short circuit (SC) that has occurred in it. The determination of the short circuit in one-way observation of the line increases due to the disconnection of the opposite side, but there is still a need to attract full information about the phase values, including, which is undesirable, their components of the zero sequence. The article shows that in the case of a double-circuit power transmission line, including bypass communication, cascade disconnection of the damaged circuit opens up a fundamentally new opportunity to evaluate the voltage and current on its unobservable side. The situation is very much, though not in all, reminiscent of two-way observation of a damaged circuit. The main thing is that quasi-two-sided observation, like ordinary two-way observation, can be carried out in two-wire channels of phase quantities that are freed from the components of the zero sequence. The efficiency of dividing zero - free phase currents into two components is shown: the normal one, determined in the model of an undamaged line, and the local one, operating in channels shunted on both sides. The measurement based on which the location of the fault is recognized is characterized by a priori dependence on the line coordinate. The theoretical provisions are illustrated by examples of two-chain lines, including real power transmission with branches.

Fault zone identification and phase selection for microgrids using decision trees ensemble

Microgrid protection is one of the main challenges that hinders the growth in the number and variety of microgrids being developed. Fault zone identification and phase selection are among protection challenges that existing protection schemes fail to address. This paper proposes a voltage-restrained classifier-based relaying scheme to address the two protection selectivity problems. While fault detection is achieved via an undervoltage function to ensure the sensitivity of the proposed method, Decision Trees (DTs) ensemble functions are used for fault zone identification and phase selection to guarantee the selectivity of the protection scheme. The proposed approach can identify three zones, forward internal, forward external, and reverse external, which (i) facilitates the operation of a relay in primary and remote backup modes, and (ii) avoids nuisance operation under reverse faults, i.e., works as a directional element. The proposed phase selection function can identify all ten types of faults, which enables the isolation of the faulted phase(s) only. The proposed relaying logic does not require any form of communication, instead it relies on readily available sequence component measurements. Transient studies in PSCAD/EMTDC verify the performance of the proposed scheme under various faults and different microgrid operation modes.

Dead-Time Compensation Based on a Modified Multiple Complex Coefficient Filter for Permanent Magnet Synchronous Machine Drives

In field-oriented vector control of permanent magnet synchronous machine (PMSM) drives, the dead time will cause the 5th and 7th current harmonics in the stationary reference frame. They are mapped to the negative and positive 6th harmonic current in the synchronous reference frame (SynRF), resulting in torque ripple and deterioration of control performance. To solve this problem, a new dead-time compensation method is proposed in this article. First, a multiple complex coefficient filter is modified with a low-pass filter being paralleled to extract positive and negative sequence components of 6th harmonic from <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> -axes currents. Then, based on the extracted harmonics, a voltage feedback path with variable gains is designed in SynRF to eliminate the dead-time effect. Finally, the proposed method is implemented in a prototyped PMSM drive to verify its effectiveness. Both the simulations and experiments indicate that the proposed method can significantly weaken the dead-time effect with no additional hardware. Besides, it is also proved robust to the variable machine parameters.

Stator Faults Detection on Induction Motors Using Harmonic Sequence Current Components Analysis

In this paper we propose a strategy for detecting interturn short circuits on stator windings of three-phase induction motors (IM). The strategy is based on an analytical model that includes a stator fault in any of the phase windings considering the h-th harmonic in the supply voltage. To find the adequate model, we propose an equivalent electrical circuit of the IM in steady state, considering each sequence component. The proposed strategy allows the detection of an interturn short-circuit fault by monitoring the fifth-order harmonic component. We present simulation and experimental results for the faulty IM and different operating conditions. In the laboratory tests, we use a programmable power supply in order to synthesize distorted and unbalance voltages. Also, the windings of a three-phase IM have been modified to generate stator faults and validate the proposed model. The results show that the sustained increase of the fifth-order harmonic of positive-sequence current is a good indicator of the fault severity.

The surface brightness–colour relations based on eclipsing binary stars and calibrated withGaiaEDR3

Aims.The surface brightness–colour relation (SBCR) is a basic tool for establishing precise and accurate distances within the Local Group. Detached eclipsing binary stars with accurately determined radii and trigonometric parallaxes allow calibration of the SBCRs with unprecedented accuracy.Methods.We analysed four nearby eclipsing binary stars containing late F-type main sequence components: AL Ari, AL Dor, FM Leo, and BN Scl. We determined very precise spectroscopic orbits and combined them with high-precision ground- and space-based photometry. We derived the astrophysical parameters of their components with mean errors of 0.1% for mass and 0.4% for radius. We combined those four systems with another 24 nearby eclipsing binaries with accurately known radii from the literature for whichGaiaEDR3 parallaxes are available in order to derive the SBCRs.Results.The resulting SBCRs cover stellar spectral types from B9 V to G7 V. For calibrations, we used Johnson opticalBandV,GaiaGBPandG, and 2MASSJHKbands. The most precise relations are calibrated using the infraredKband and allow angular diameters of A-, F-, and G-type dwarf and subgiant stars to be predicted with a precision of 1%.

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Improved observer-based quadrature signal generator

In this paper, an improved quadrature signal generator (QSG) parameter tuning procedure is proposed, based on a modification of an existing adaptive observer QSG algorithm. Namely, in the existing solution an observer-based QSG is proposed with a parameter tuning procedure that results in a bandwidth frequency equal to the QSG input signal frequency, while in this paper, a modification of this parameter tuning procedure is proposed that enables the QSG to operate with increased bandwidths. A comparative analysis is presented, which evaluates both the existing solution and the solution based on the novel observer parameter tuning algorithm. Also, it is shown that when existing and proposed observer-based QSG operates with bandwidths that surpass the input signal angular frequency, the high-pass resulting observer frequency characteristics are obtained. By using frequency responses, and simulation and experimental tests, which include basic QSG operation and the PLL based on the proposed QSG, the resulting improvements are presented and compared. Also, the adaptive observer-based QSG with improved parameter tuning procedure is employed in the positive sequence component separation algorithm for the nonsymmetrical three-phase system, which represents an original application this type of QSG structure.

Stockwell‐transform and random‐forest based double‐terminal fault diagnosis method for offshore wind farm transmission line

Due to the difficulty and time-consumption in locating short-distance transmission lines for deep-sea offshore wind farm (DOWF)，this paper proposes a novel double-terminal fault location method by using Stockwell-transform (ST) and random-forest (RF). After the fault type and branch are accurately determined, the accurate transmission line fault location is located. Firstly, Stockwell-transform is employed to extract fault eigenvalues from the collected wind turbine (WT) current signals, which will reduce the sensitivity of eigenvalues to noise. And the Pearson correlation coefficient (PCC) is introduced to remove duplicate eigenvalues. Secondly, the reserved fault eigenvalues are taken as inputs to the different random-forest to classify fault types and identify the fault branch, respectively. Finally, the double-terminal fault location principle is established in fault negative sequence network (only ABCG uses positive sequence components). Newton-Raphson method (NRM) is used to eliminate the influence of asynchrony data, which implies an accurate transmission line fault location for deep-sea offshore wind farm. More than 4000 fault cases data obtained by Simulink simulation verify the feasibility and performance of the proposed method. The results show that the proposed location method has a high fault recognition rate and is immune to fault inception angle, resistance, location and noise.

Classification of Voltage Sag Propagation under Double Line to Ground Fault on a Low Voltage Distribution Power Network

The key issue of the voltage-sag propagation on the different types of winding connections for the low voltage transformer in the distribution power network is considered in this study. The issues of voltage sag propagation depend upon the type of asymmetrical fault and the connection of the transformer windings. In this paper, the double line to ground fault is adopted for the voltage sag characterization. The depiction of the sage propagation is an outcome of the zero sequence components. Voltage sag propagation detection can be used to improve the power quality of the system. The obtained results reveal the characteristics of the voltage drop propagation from the primary to the secondary winding of the transformer throughout different connection. The implemented method will help analyze the Power Quality (PQ) problem in terms of voltage sag of the distributed transmission networks of the power system.

Development on Compensating Unbalanced Load of Energy Storage Converter in Distribution Network

By analyzing the current equivalent circuit of unbalanced load, the mathematical model of the three-phase four-wire energy storage converter in the dq0 coordinate system is established. Comparing the characteristics of the Decouple Double Synchronous Reference Frame (DDSRF)and the Delay Signal Cancellation (DSC) to decompose the positive and negative sequence line parameters, the DSC with faster dynamic response is selected for the practical application effect. Compensate the decomposed zero sequence component and negative sequence component. The DC component is adjusted by Proportional Integral (PI) controller, and the AC component is controlled by Proportional Resonance controller (PR) to achieve no static error. Finally, a split capacitive energy storage converter system is built in Matlab/Simulink for simulation verification, which proves that the control strategy can effectively compensate the current asymmetry caused by load unbalance.

A modified energy management scheme to support phase balancing in grid interfaced photovoltaic/fuel cell system

This paper presents improved energy management for grid-inverter of a hybrid photovoltaic (PV)/fuel cell (FC) energy system with unbalanced sensitive loads. In the system, unbalanced loads draw unbalanced currents at each phase and consume power from energy units at different levels. This condition makes the grid unbalanced, which cannot be compensated by a conventional energy management controller used in grid inverters. For this, a phase balancing control method is proposed in order to improve the grid quality under unbalanced loading conditions. The proposed method calculates power differentiation values based on multiple-frame αβ/dq transform instead of abc/dq transform in the conventional method. Thus, it eliminates negative & zero sequence components in addition to power flow control. Under unbalanced loading conditions, the proposed method removes the deficiency of the conventional energy management method which generates the symmetrical current references to trigger the switching elements of the inverter. In performance results, the system with unbalanced loads is tested for different case studies, which supply different power from energy units to grids. The results show that the proposed method provides power balancing at the grid-side and eliminates negative & zero sequence components at grid-side currents.

Direct-Quadrature Sequence Models for Energy-Function Based Transient Stability Analysis of Unbalanced Inverter-Based Microgrids

The reliability of supply in distribution networks can be improved by islanding (parts of) the network as autonomous microgrids in case of a contingency. Microgrids are commonly fed by inverter-based distributed energy resources, which causes transient stability challenges due to the lack of inertia and strongly coupled dynamics. The transient stability of inverter-based microgrids is conventionally analyzed by time-domain analysis. However, energy-function based transient stability analysis has advantages over time-domain analysis, as it provides a stability result for all initial conditions and allows uncertainty to be taken into account with the domain of attraction. Microgrids are generally unbalanced, however models for unbalanced energy-function based transient stability analysis are lacking in the literature. In this paper, coupled sequence components models of distributed energy resources and load devices in the dq reference frame are proposed, and experimentally validated with unbalanced voltage transients. The validated models are used for energy-function based transient stability analysis of an unbalanced inverter-based case study microgrid. Finally, the impact of unbalanced connection of devices on transient stability is analyzed. The results indicate that the proposed models accurately represent the behavior of physical devices and that the unbalanced connection of devices significantly impacts the transient stability of inverter-based microgrids.

Stator Winding Fault Diagnosis Method Based on Dc Side Current of Inverter

This paper analyzes the influence of the fundamental negative sequence component of the grid voltage on the output voltage of the variable frequency power supply, and points out that the fundamental negative sequence component of the grid voltage will not generate the fundamental negative sequence current component in the stator current of the induction motor, so when the stator winding fault is diagnosed, the influence of the negative sequence voltage of the grid does not need to be compensated. Based on the characteristic that the fundamental negative sequence current component in the stator current is converted into two times of the inverter output frequency component in the DC side current of the inverter, a stator fault diagnosis method based on the DC side current of the inverter is proposed. The method of connecting the short-circuit resistance between the two phases of the motor is used to simulate the nonmetallic short-circuit fault of the stator coil. The experimental results show that this method does not need to compensate the negative sequence voltage, and only needs to collect one current signal, and the algorithm is relatively simple, which is a simple and effective method.

Effective power transfer and reduced-order generalized integrator sequence based fault ride through strategy in grid connected DFIG based WECS

This paper deals with the control strategies of Doubly Fed Induction Generator (DFIG) based grid connected Wind Energy Conversion System (WECS) delivering power during normal and grid fault conditions. The system encompasses DFIG, Rotor Side Converter (RSC) and Grid Side Converter (GSC) connected back-to-back with a dc link, utility grid and local loads at point of common coupling. During normal system conditions, Tip Speed Ratio basedMaximum Power Point Tracking and Instantaneous Power Theory based reference current generation technique are employed for RSC, and GSC respectively to achieve maximum bidirectional power transfer and meeting the demand. Also, the power transfer operations during occasional conditions such as overloading and shorted stator winding are investigated. During grid fault conditions, a Reduced Order Generalized Integrator (ROGI) based Sequence Controller is employed to achieve stabilized real and reactive power injection to the grid by extracting the positive and negative sequence components of the grid voltages and currents. A supervisory control algorithm is developed for effecting a smooth transition of control schemes thereby avoiding system disturbances. The proposed control strategy is implemented in a simulation environment of a 10 MW grid connected DFIG based wind farm in MATLAB 2018b version. Various case studies are performed to validate the effectiveness of the proposed control strategies. The system is subjected to all possible grid faults including the most severe symmetrical fault and the controller is found to provide better grid support with appropriate real power transfer and reactive power injection. Also, the dynamic performance of the control strategy is experimentally investigated in the hardware setup of 1 kW grid connected DFIG based WECS. The system is operated under MPPT and FRT modes of operation under normal and grid fault conditions to prove the efficacious working of the proposed control strategies in DFIG based WECS.

A Method for the Approximate Location of High Impedance Faults using Neural Networks

This paper describes an algorithm for ground to earth high-impedance fault identification and location in medium-voltage of unbalanced distribution systems. The daily variation of the load is considered, the fault resistance variation, inaccuracy in feeders data, and errors from phasor measurement units. The method is based on artificial neural networks associated with phasor measurement units to detecting the faulty area of the distribution system. Three types of neural network structures are proposed, (i) using phasor inputs, (ii) using non-phasor inputs, and (iii) using inputs to sequence components. To test the proposed method, thousands conditions of normal operation and fault operation were simulated to assemble the database. The method uses the current data obtained from meters that can be allocated at different points of the distribution system. The IEEE 123 test system is used to validate the proposed algorithm.

Power Quality Improvement in PV System Tied to Weak Grid

An integrator-based positive sequence estimator control is presented in this article for the enhancement of power quality of a grid interfaced double stage solar PV system. This control extracts positive sequence components from the grid voltages (distorted and unbalanced) for the computation of unit templates and grid reference currents even during grid anomalous situation of distortion, unbalance, sag/swell, dc offset, etc. In order to achieve a rapid transient response of the system, a feedforward term for the photovoltaic array is also applied. The dc-link voltage is also adjusted adaptively for the reduction of the voltage source converter losses during the conditions of the weak grid. The system with an integrator-based positive sequence estimator control is simulated in the environment of MATLAB and experiments are performed on a prototype built in the laboratory. Simulation and experimental results validate the satisfactory system performance at different odd states such as intermittent solar irradiations, dc offset, voltage distortions, unbalance, voltage sag, and swell. During the grid disturbance and other intermittent conditions, grid currents total harmonics distortion is found as per the IEEE standard-519.