Sequence Components Of Currents Research Articles

Sequence component direction element based on power frequency variation

Unlike the relatively stable network structure of the transmission and distribution network, under the new distribution network, resulting in errors in the impedance tuning of the fault directional element, misjudgment of the fault directional element, and a decrease in sensitivity. For this reason, this paper proposes a sequence component adaptive fault directional element based on power frequency variation. The sequence impedance amplitude is calculated through the measured values of the voltage sequence component and the current sequence component of the relay location. Then the phase angle of the setting impedance is determined according to various sequence components in the system. It improves the problem that the setting impedance of power frequency distance directional element is greatly affected by the amplitude and phase angle fluctuation of distribution system impedance and line impedance. The reliability and stability of the sequence component adaptive fault directional element based on the power fresquency variation are verified by Matlab simulation.

Frequency‐adaptive complex‐coefficient filter‐based control for grid‐integrated PV system

This work deals with a frequency-adaptive complex-coefficient filter-based control for three-phase grid supportive double-stage photovoltaic (PV) system. This control eliminates harmonic components, DC offset at unbalanced loads and robust against phase frequency shift and on utility grid voltage disturbances. It uses harmonic-free positive sequence current components to generate sinusoidal reference currents without amplitude scaling. Moreover, tuning of parameters is not required due to the absence of gain parameters. This system responds quickly to balance the grid currents under unbalanced load currents, mitigates load current harmonics while feeding active power to the distribution network. The presented topology has enhanced the voltage source converter (VSC) utility, particularly in the absence of PV array generation, thus, VSC payback period is reduced. The PV dynamic term is utilized to enhance VSC input voltage profile, to avoid overshoots and undershoots in grid currents, and to mitigate transients in PV array current under varying irradiance. The behaviors under dynamic state and steady state of the presented system are validated under varying irradiance, load currents unbalance and grid voltage disturbances through simulated and test results. The power quality concerns are addressed, by achieving harmonic contents in grid currents below to 5% in accordance to the IEEE-519 standard.

Protection of transformer due to external fault between two voltage levels using overvoltage protection and sequence component of currents

The main role of the transformer protection is based on satisfying fast and reliable relay to isolate the power transformer from the grid with minimum damage. Also, to avoid the mal-operation of the protection system during different operating conditions. This paper presents a simple method to protect the power transformer due to the short circuit between two different voltage levels that may be produced when two overhead transmission circuits with different voltages intersect with each other. This leads to the failure of all equipment on the lower voltage especially the power transformer due to the resulting overvoltage. The proposed methodology depends on the combination between the sequence components of the currents from both sides of the transformer. Moreover, it uses the voltage measurements of the lower voltage side to detect the resulting overvoltage. The magnitude and phase angle of current measurements are computed using Fast Fourier Transform (FFT). The modelling and simulation of the fault between high-and medium-voltage are carried out using PSCAD/EMTDC program. The results reveal the accuracy, security and the applicability of the proposed methodology.

Deadbeat Predictive Current Control for Circulating Currents Reduction in a Modular Multilevel Converter Based Rail Power Conditioner

This paper presents a deadbeat predictive current control methodology to reduce the circulating currents in a modular multilevel converter (MMC) when it operates as a rail power conditioner (RPC) in a conventional railway system-based V/V connection. For this purpose, a half-bridge MMC based on half-bridge submodules, operating as an RPC is explained, and the total system is denominated as a simplified rail power conditioner (SRPC). The SRPC in this study is used to compensate harmonics, reactive power, and the negative sequence component of currents. This paper explains the SRPC system architecture, the key control algorithms, and the deadbeat predictive current control methodology. Mathematical analysis, based on the MMC equivalent circuit, is described and the reference equations are presented. Moreover, simulation results of the deadbeat predictive current control methodology are compared with the results of the conventional proportional-integral (PI) controller. This comparison is to verify the effectiveness of the proposed control strategy. Simulation results of the SRPC show reduced circulating currents in the MMC phases when using the predictive control approach, besides accomplishing power quality improvement at the three-phase power grid side.

Hybrid Power Quality Conditioner for Three-Phase Four-Wire Power Systems

In this paper hybrid power quality conditioner for three-phase four wire power systems is considered. The conditioner is composed of single modules installed at various locations of distribution power system. Individual modules ensure compensation of zero-sequence and negative- sequence voltage and current components. This open configuration of power quality conditioner composed of independent modules allows compensation voltage and current distortion caused by nonlinear and unbalanced single-phase loads. The performance of the proposed conditioner is validated through computer simulation using MatLab software. Simulation results show that the proposed conditioner achieves PQ normalization

Active Control Method for Torsional Vibration of DFIG Drive Chain Under Asymmetric Power Grid Fault

When the asymmetric fault occurs in power grid, it will cause the oscillation of the electromagnetic torque of the doubly-fed induction generator(DFIG). The oscillation of the electromagnetic torque will cause the torsional vibration of the drive chain, and the long-term torsional vibration will shorten the service life of DFIG. The analysis shows that the positive and negative sequence current components generated by DFIG terminals are the main factors that cause electromagnetic torque oscillation when the asymmetric faults occur. Therefore, the suppression of positive and negative sequence current components is the key to achieve active control of torsional vibration of drive chain, the traditional PID control can only adjust the direct-current(DC) component without static error, and cannot suppress the negative sequence alternating-current(AC) component. In this paper, based on the traditional PID regulator, the resonance(R) current regulator with the specific frequency is incorporated into the grid-side converter(GSC) to form the PID-R current controller. The PID-R current controller can realize accurate and effective control of the positive and negative sequence components in the forward rotation synchronous speed rotating coordinate system without decomposing the positive and negative sequence components, and can actively suppress the electromagnetic torque oscillation, thereby realize the active control of the drive chain torsional vibration. MATLAB/Simulink verifies the effectiveness of PID-R current controller.

Single-Phase Consensus-Based Control for Regulating Voltage and Sharing Unbalanced Currents in 3-Wire Isolated AC Microgrids

Chilean National Commission for Scientific and Technological Research/Formation of Advanced Human Capital Programme (CONICYT/PFCHA)/Doctorado Nacional/2017-21171858 Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT) CONICYT FONDECYT 1170883 National Agency of Research and Development/Associative Research Program (ANID PIA)/Basal AFB180003 Solar Energy Research Center (SERC), Chile ANID/FONDAP/15110019 National Agency of Research and Development (ANID)/Basal FB0008 National Fund for Scientific and Technological Development (FONDEQUIP) EQM160122

Virtual Frequency Construction-Based Vector Current Control for Grid-Tied Inverter Under Imbalanced Voltage

This paper proposes a fast phase capture (FPC) scheme and applies it to the control strategy of grid-tied inverters under imbalanced voltage. Firstly, a method for quickly extracting sequence components of power signals is derived through the symmetrical component method, and a real-time phase calculation method is proposed based on the rotating reference frame, thus avoiding the phase-locked loop (PLL) closed-loop adjustment process. Secondly, the grid-tied inverter suppresses the negative sequence current or power fluctuations through the direct resonance controller, so there is no need to separate the dynamically changing sequence current components. Finally, the experimental comparison with the PLL control strategy is carried out based on the RT-LAB platform. Compared with the previous phase-locking scheme, the FPC scheme has a faster phase-locking speed. Therefore, the fault ride-through capability of the grid-tied inverter is improved.

Sequence component based approach for fault discrimination and fault location estimation in UPFC compensated transmission line

This study presents an integrated approach for discrimination of internal and external fault, and to obtain pin-point location of the fault in a transmission line connected to unified power flow controller (UPFC). To detect internal fault, this method uses positive sequence component of voltage and current at the local and remote end bus. Fault location estimation technique requires both positive and negative sequence voltage and current components measured from both ends of the line. The performance of the proposed technique has been evaluated by simulating a 400 kV double circuit UPFC compensated transmission line. This technique can detect internal fault under stressed conditions, viz. high impedance fault (HIF), change in source strength, change in load angle, and power swing. Precise fault location has been achieved under wide variation of system and fault parameters. The comparative assessment has been provided to prove the efficacy of the proposed approach.

Induction Motor Stator Interturn Short Circuit Fault Detection in Accordance with Line Current Sequence Components Using Artificial Neural Network

The intention of fault detection is to detect the fault at the beginning stage and shut off the machine immediately to avoid motor failure due to the large fault current. In this work, an online fault diagnosis of stator interturn fault of a three-phase induction motor based on the concept of symmetrical components is presented. A mathematical model of an induction motor with turn fault is developed to interpret machine performance under fault. A Simulink model of a three-phase induction motor with stator interturn fault is created for extraction of sequence components of current and voltage. The negative sequence current can provide a decisive and rapid monitoring technique to detect stator interturn short circuit fault of the induction motor. The per unit change in negative sequence current with positive sequence current is the main fault indicator which is imported to neural network architecture. The output of the feedforward backpropagation neural network classifies the short circuit fault level of stator winding.

The fault detection method of islanded microgrid with the V/f controlled distributed generation

The fault characteristic of islanded microgrid is closely related to the control strategy of distributed generation (DG) and it is different from that of grid-connected microgrid. Also, the analysis of fault control strategy is an essential foundation of the fault location. This paper discussed the control strategy and output fault characteristic of V/f and PQ controlled DG. To establish the fault detection criterion of islanded microgrid, the coordinating control strategy between V/f and PQ controlled DG is presented. Based on the above fault analysis, the fault point is located by using a new fault detection method, which is based on the phase differences between the pre-fault bus voltage and the positive- sequence current fault component of the feeders. Finally, examples are simulated in PSCAD/EMTDC and the results verify the accuracy and effectiveness of the proposed fault detection method.

LS-Solar-PV System Impact on Line Protection

Large-scale photovoltaic power station access to the grid will profoundly change the fault current characteristics of the power station’s outgoing lines. This change results in adaptive problems in traditional protection phase selection components, which may cause incorrect actions in reclosing, protection ranging, and distance protection. Based on the fault current characteristics of the large-scale photovoltaic power station transmission line, this paper analyzes the adaptability of the phase current difference mutation and the sequence component phase selection component in protecting the Photovoltaic (PV) power plant side of the transmission line. Based on the fault current analytical formula, the phase relationship between the phase current difference and the current sequence component under different control targets, such as suppressing negative sequence current, suppressing the active power fluctuation, and suppressing the reactive power fluctuation, is derived. The operational performances of the phase–phase current difference of the abrupt phase selection component and the sequence component phase selection component of the power station side are degraded, which may cause incorrect operation of the phase selection component. Based on the actual engineering parameters of a PV power plant, a simulation model was built in Power System Computer Aided Design (PSCAD) to verify the correctness of the theoretical analysis.

Method of adaptive current protection against earth faults in 6–10 kV cable networks with an insulated neutral

Simple and reliable zero sequence overcurrent protection in distribution 6–10 kV cable networks with an insulated neutral is most widely used for protection against single phase earth faults. However, protection of this type in many cases does not provide the required sensitivity to internal (inside the protected zone) faults as it must be tuned to the response current from surge transients during external faults through an intermittent arc. It is possible to increase the sensitivity if adaptive current protection is applied. However, the known methods for its implementation are only effective for stable faults through transient resistance but do not provide high dynamic stability of operation in transient conditions in case of arc intermittent earth faults that are the most dangerous for the network. Therefore, an urgent problem to be solved now is improving the principles of adaptive current protection against earth faults. To compare the efficiency of the known and proposed principles of adaptive current protection implementation taking into account the complexity of transients during earth faults through an intermittent arc in 6–10 kV cable networks, we used Matlab simulation with the SimPowerSystem and Simulink extension packages. The research into the operation algorithms of adaptive current protection against earth faults was carried out on simulation models of 6–10 kV cable networks with an insulated neutral and with neutral grounding through a high-value resistor. The studies on the simulation models have shown that the known methods of implementation of adaptive current protection against earth faults based on the use of full zero sequence currents and voltage are ineffective during intermittent arc earth faults. The authors propose a method of adaptive current protection against earth faults in 6–10 kV cable networks with an insulated neutral and with neutral grounding through a high-value resistor that provides a significant increase in dynamic stability of transient operation with arc ground faults and allows using only zero sequence current and voltage components of the operating frequency of 50 Hz as the actuating quantities. The proposed method of implementing adaptive current protection against earth faults in 6–10 kV cable networks with an insulated neutral and with neutral grounding through a high-value resistor does not only increase the sensitivity of this protection type to earth faults through transient resistence and dynamic stability of operation in transient condiitons in case of arc intermittent earth faults but also broadens the range of its possible applications

Improved schemes for traditional current‐based phase selectors in wind power systems

This study shows that traditional current-based phase-selection (TCPS) schemes are not applicable to wind power systems, and subsequently proposes two improved phase-selection schemes. On the basis of the practical TCPS criteria, derivations of the essential conditions for correct phase selection, which show that the positive-to-negative sequence current branch coefficient (PNSCBC) ratio at the relay location should be within a certain range, are presented. Wind power generation systems are weak-infeed systems; consequently, the PNSCBC ratio on the wind power side is approximately equal to the negative-to-positive sequence impedance (NPSI) ratio of the wind power system. However, the authors’ theoretical and simulation analysis results show that the NPSI ratio of a wind power system may exceed the range required for reliable phase selection; therefore, TCPS schemes are not applicable to wind power systems. Thus, they propose improved phase-selection schemes based on sequence current fault components and phase current difference fault components. In the proposed schemes, the PNSCBC ratio is obtained using the backside system impedance measured by the relay, and it is then used for compensating the TCPS criteria. Simulation results and field fault test data verify the efficacy of the proposed schemes.

Current control based power management strategy for distributed power generation system

The integration of renewable energy sources (RES) based distributed generation (DG) systems into electric grid has many challenges such as synchronization, control, power management (PM) and power quality problems. This paper proposes a references current generator (RCG) based PM strategy to control three phase inverter and manage power flow among the DG energy sources, electric grid and load demand under balanced and unbalanced grid conditions. The amplitudes of active and reactive power oscillations are also eliminated and controlled through only one flexible control parameter (FCP) under grid faults and harmonic distortions. Compared with previous similar studies, one of the important contributions is capable to inject maximum active power and minimum reactive power into electric grid and load at inverter power capacity under grid faults Another contribution is to extract the positive and negative sequence (PNS) voltage and current components with the improved fast and robust dual adaptive filters based phase locked loop (DAF-PLL). Fractional order proportional integral (FOPI) is selected as an attractive solution for AC current regulation to exhibit fast transient response and to achieve zero steady-state errors as compared with conventional current regulation controllers in synchronous or stationary frames.

Open-Phase Fault Detection in Delta-Connected PMSM Drive Systems

This letter presents an open-phase fault detection method for delta-connected permanent magnet synchronous machine (PMSM) drive systems. This method is based on zero sequence current component (ZSCC) and stator currents. First, the model of the delta-connected PMSM is established under healthy and fault conditions. Then, the expression of the ZSCC is presented, and fault indicators are defined based on the ZSCC and stator currents, which are used for the open-phase fault detection and location. Finally, both the simulation and experimental results validate the effectiveness of the proposed method.

PQ improvement of Micro-Grid by Using DG and Power Quality Conditioner with BESS

DG Grid interfaced system has been focused through this paper. The objective is to improve power quality of the grid, which was polluted by various means. The improvement of power quality of the micro grid includes uses of a specially designed DG, BESS and Power Quality conditioner. The system consists of a two-stage power conversion. Solar PV supplies power for both DC and AC loads. Manufacturer datasheet is used for modeling the PV panel. In order to keep the BUS voltage stable a BESS is joined to DC BUS through power electronic converter, which is used to absorb the excess power whenever production is high and deliver power to the load on low production. The system continues to supply the local loads, incase of grid discontinuity. Thus it eliminates threats of islanding. This paper also focuses on control and stability of DC bus voltage and energy management scheme. The project uses Matlab/Simulink platform for efficient verification. For power quality improvement of Micro Grid it uses 3leg inverter, which is coupled with SPV and MPPT with Battery storage, which is used as compensator for the whole system. For prevention to reduce voltage current and power flow between DG and Grid, it is necessary to have an optimum control. Through the adjustment of power circulation between shunt paired DG ensures current voltage and power on micro grid. +ve, -ve and Zero sequence components of currents and voltage can be adjusted by the suggested methodology in Grid tied DG system. The said PQC have multiple uses. Firstly as a power converter and secondly as a shunt APF for harmonic compensation on voltage, current and power (both active and reactive) for both balanced and unbalanced loads in the Grid tied DG system. It also cares for the neutral conductor. Either individually or in grid connected mode all the above objectives can be achieved. For the entire Grid, it is realized that after compensation three phase four wired un-balance loads looks as balanced linear resistive load for the Grid. All these task significantly replicated on MATLAB/Simulink. After compensation the total harmonic distortion on input voltage and current reduced drastically. IEEE519 in the range of 5% suitably accepts it.

Effective design and implementation of GSS‐PLL under voltage dip and phase interruption

The robust operation of grid-connected converters under non-ideal grids is a challenging topic. Synchronising of converters requires accurate estimation of the grid vector angle which is traditionally performed by phase locked loops (PLLs). Separating the grid voltage and current sequence components is essential for controlling converters under non-ideal grids. In this study, an efficient method to separate the grid sequence components using cascaded delayed signal cancellation (CDSC) is developed. The proposed method is a reduced version of the conventional delayed signal cancellation separation technique. Implementing CDSC in the stationary frame enables for using a higher bandwidth without degrading its filtering capability which enables for using the GSS as a pre-filter stage for the traditional synchronous reference frame PLL. Therefore, the obtained grid sequence separator PLL (GSS-PLL) accurately estimates the grid vector angle under severe conditions. The performance of GSS method as well as GSS-PLL is compared to the conventional multiple second-order generalised integrator (MSOGI) method under unbalance, phase interruption and harmonically distorted grids. The accuracy of the proposed method is verified through simulation and experimental tests. The low computational effort of GSS scheme compared to the MSOGI is a significant advantage which encourages its implantation for most of the grid-connected converters.

A novel controller for harmonics reduction of grid-tied converters in unbalanced networks

This paper proposes a novel controller for a grid-tied converter interfaced to a network with unbalanced voltage conditions. Due to the influence of negative sequence voltage and current components created by unbalanced voltages, conventional PI controller alone cannot adequately deal with the fluctuations in active and reactive powers generated from converters. In order to overcome this inadequacy, a systematic and comprehensive controller, namely Linear Parameter Varying (LPV) controller is designed and presented in this work. The proposed LPV controller is implemented using the well-known voltage oriented control (VOC) approach. The unbalanced network voltages are first decomposed using a signal delay technique with the support of Clarke’s transformation in order to filter out the negative sequence components. An enhanced phase-locked loop (ePLL) is then developed to reduce the higher-order harmonics. The feasibility of the proposed controller and the effectiveness of ePLL are verified by experimental studies.

Control Strategy for a Grid-Connected Inverter under Unbalanced Network Conditions—A Disturbance Observer-Based Decoupled Current Approach

This paper proposes a new approach on the novel current control strategy for grid-tied voltage-source inverters (VSIs) with circumstances of asymmetrical voltage conditions. A standard grid-connected inverter (GCI) allows the degree of freedom to integrate the renewable energy system to enhance the penetration of total utility power. However, restrictive grid codes require that renewable sources connected to the grid must support stability of the grid under grid faults. Conventional synchronously rotating frame dq current controllers are insufficient under grid faults due to the low bandwidth of proportional-integral (PI) controllers. Hence, this work proposes a proportional current controller with a first-order low-pass filter disturbance observer (DOb). The proposed controller establishes independent control on positive, as well as negative, sequence current components under asymmetrical grid voltage conditions. The approach is independent of parametric component values, as it estimates nonlinear feed-forward terms with the low-pass filter DOb. A numerical simulation model of the overall power system was implemented in a MATLAB/Simulink (2014B, MathWorks, Natick, MA, USA). Further, particular results show that double-frequency active power oscillations are suppressed by injecting appropriate negative-sequence currents. Moreover, a set of simulation results provided in the article matches the developed theoretical background for its feasibility.