Positive Sequence Components Research Articles

A Simple Method for Detection of Voltage Sags and their Mitigation using a Dynamic Voltage Restorer

Power quality is the major focus of progressive nations.In the era of smart grid,power quality receives a lot of thrust at all voltage levels namely,medium ,high and low.The objective of this paper is to present a simple and cost effective method of sag detection and mitigation in three phase systems at the consumer's end. The use of the concept of space vector representation of three phase quantities, effectively in the detection ,quantification and mitigation of short duration voltage disturbances such as sags in three phase supply systems under both balanced and unbalanced conditions of operation is presented.Three phase balanced quantities can be represented by a synchronously rotating space vector of constant magnitude .The two phase equivalent of which on a stationary reference frame are orthogonal to each other.When balanced sags occur,the magnitude of the rotating space vector obtained as a resultant of its orthogonal components is sensed for magnitude deviations from its constant nominal value.A trigger signal of varying amplitude is generated in proportional response to the detection of the deviation in its magnitude . In case of sags occurring on one or two phases of the supply, (unblanced),the positive sequence components of the unbalanced three phase quanities are determined using mathematical transformations and the magnitude of the resultant is found out. This resultant is sensed and its deviations from nominal value are measured and used to generate the trigger after processing.The trigger thus generated, initiates the control system of a Dynamic Voltage Restorer(DVR).When a sag is detected,the trigger signal generated, switches on the control circuit of the inverter which uses the space vector pwm control using sampled phase amplitudes of the control signal to generate the modulating wave in proportion to the deviation of the sag voltage from the reference value.The fundamental component of the output voltage which in proportion to the deviation from the nominal value is injected in series with the three phase disturbed signal through a transformer of suitable gain .The results show the successful operation of the DVR in maintaining nominal value of the voltage across the load through out the duration of the disturbance for all cases of balanced and unbalanced operation. The paper presents the detection algorithm as well as the control algorithm for restoration of voltage which are simple and easy to implement .

A Novel Frequency and Positive Sequence Detector for Utility Applications and Power Quality Analysis.

Based on multi-dimensional representation and vector calculus definitions, this paper proposes two novel and quite simple algorithms for utility applications and power quality analysis. The first one is a synchronizing procedure, based on a digital PLL (Phase Locked Loop). Its design and dynamic behavior are analyzed for single and three-phase systems. The second one is a positive sequence detector, which uses the proposed PLL to ensure that the positive sequence components can be calculated even under distorted waveform conditions or frequency variations. Since it is not based on Fortescue’s classical decomposition and no special input filtering are needed, its dynamic response may be as fast as one fundamental cycle. In order to validate the proposed models, simulations are shown and experimental results were obtained by means of a DSP-based system and a prototype of Power Quality Monitor. Furthermore, the PLL algorithm was implemented in a selective active filter to confirm the expectations in a closed-loop application.

Local positive sequence component based protection of series compensated parallel lines connecting solar photovoltaic plants

Local positive sequence component based protection of series compensated parallel lines connecting solar photovoltaic plants

An Enhanced Filtering Generalized Integrator-Based Control for Improved Performance of a Grid-Tied PV System at Adverse Grid Voltages

This paper deals with a single stage photovoltaic (PV) system with improved resilience against adverse grid conditions. This is majorly achieved in two ways. First, it presents an enhanced filtering generalized integrator (EFGI) based filtering stage, to process the prevalent grid voltages and derive their positive sequence components free of harmonics components, unbalance, and DC offset. The presented EFGI delivers a considerable improvement over the conventional filters and helps to improve the power quality (PQ) in case of unequal or distorted voltage conditions. Second, to address large voltage dip or rise scenarios, a dual mode mechanism is applied for the selection of the DC link voltage ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V_dc</i> ) reference and the corresponding generated PV array power. At regular voltage scenario and at availability of PV power, the reference <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V_dc</i> is governed by the necessity to keep the PV array operating at its peak generation levels. However, at loss of PV power or divergent grid voltages, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V_dc</i> control is quickly transferred to an alternate approach, varying <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V_dc</i> as per the existing grid voltages. Using this, the injected currents are limited, and system de-synchronization is prevented at voltage dips. The increased <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V_dc</i> at grid voltage rise avoids deterioration in the grid PQ. The grid PQ is also assured despite the presence of local non-ideal loads. The EFGI benefits and the real time performance of the presented system, are assessed using test results.

Alleviation of Power Quality Issues in MVF-DEANF-PLL Based Solar PV Systems under Polluted Grid Conditions

Solar energy is a sustainable and environmentally safe power source due to its widespread availability and cleanliness. Nowadays, the grid-integrated solar photovoltaic system (SPVS) has to work with a polluted grid, an imbalanced load, and changing solar irradiation. When the grid is polluted, it is also crucial to enhance power quality (PQ) at a common coupling point (CCP) while supplying significantly distorted and unreliable loads. For effective synchronization and the production of unit templates, it is necessary to retrieve positive sequence components (PSCs) from distorted/imbalanced grid voltages. In this study, a control algorithm for a grid-integrated SPVS is developed using a multi-variable filter dual-enhanced adaptive notch filter phase-locked loop (MVF-DEANF-PLL) which offers seamless grid synchronization and PQ issue alleviation. In a polluted grid environment, the proposed control approach aids in the reduction in current/voltage harmonics, DC offset, unity power factor (UPF) operation, and rapid estimation of sequence components. Even in unbalanced grid conditions, the proposed control approach efficiently extracts PSCs of both unbalanced load current and polluted CCP grid voltages. These PSCs are utilized to generate unit templates and reference source currents. By using a flexible step-size incremental conductance (FSSINC) maximum power point tracking (MPPT) technique, the highest available power of SPVS is gathered. MATLAB/Simulink is utilized for modelling a 7.22 kW SPV system, and results from simulations which depict that the proposed algorithm efficiently resolves PQ concerns in distribution networks with a polluted grid. Test observations of a 1 kW laboratory-developed SPVS prototype were recorded in compliance with the IEEE-519 standard. The suggested control technique complies with the aforementioned standards by providing a sinusoidal balanced source current that has a THD of 2.5%. Comparisons between the proposed control’s performance and that of a conventional SRF-PLL-based control technique were also performed.

Analysis and modelling of a phase‐locked loop based on a novel cascade structure of SOGI

AbstractIn order to attenuate the oscillations on the estimated frequency of a phase‐locked loop (PLL), the effective suppression of low‐order harmonics in grid voltage is a crucial issue in three‐phase grid‐connected inverters, which use the standard PLL based on a double second‐order generalized integrator (DSOGI‐PLL). Analysis shows that the SOGI module exerts a stronger filtering effect in generating the quadrature signal than the in‐phase signal. In this context, two novel cascaded SOGI module filtering structures have been developed, based on which the PLLs are proposed. In comparison to the previously proposed method for addressing the problem of input voltage harmonics, the proposed method has stronger filtering ability and can flexibly select the levels of SOGI module cascading based on the degree of grid voltage distortion to achieve a balance between system dynamic performance and filtering performance. The proposed PLLs' approximation small signal model is established, and the method for designing the system control parameters is also provided. In the case of frequency steps, phase angle jumps, harmonic injection, and unbalanced voltage sag, Matlab modelling and experimental results demonstrate that the proposed PLLs can efficiently extract the frequency and phase of the fundamental positive sequence component and behave better in steady‐state and dynamic performance.

A Grid Connected PV Array and Battery Energy Storage Interfaced EV Charging Station

In this work, a charging station for EV (Electrical Vehicle) integrated with a BES (Battery Energy Storage) is presented with enhanced grid power quality. The positive sequence components of the three phase grid voltages are evaluated for the estimation of the unit templates and the reference grid currents. The EV and battery energy storage are connected at DC link using a bidirectional buck-boost converter. During the daytime, EV takes power from the solar array while in its absence it consumes the power from the grid. Additionally, when the system is connected to the grid, the point of common coupling voltages synchronizes with the voltages of the grid. Tests are conducted on a hardware prototype developed in the laboratory for the validation of the satisfactory response under different dynamics conditions.

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

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

Passive Island Detection Method Based on Positive Sequence Components for Grid-Connected Solar–Wind Hybrid Distributed Generation System

This paper presents the development and practical implementation of a new passive island detection method for grid-connected hybrid distributed generating systems. The method employs positive sequence voltage and current components at the point of common coupling. The product of the difference in positive sequence voltage and the difference in positive sequence current is used to produce the Islanding Detection Index (IDI). Islanding is identified when the IDI magnitude surpasses a predefined threshold over a predefined delay time. Even in the case of a zero power mismatch condition, the proposed method can identify the islanding condition in under 70 msec. Its effectiveness is validated under various operating circumstances. It provides excellent stability against various non-islanding situations, avoiding unwanted tripping. The suggested method also has the advantages of being simple and inexpensive to implement, having no adverse effects on output power quality, not requiring a classifier, not being system-dependent, and working regardless of the quantity and type of distributed generation connected to the utility grid. The obtained detection timings were compared to those previously reported in the literature, confirming the proposed approach’s superiority. The suggested work utilizes the OPAL-RT real-time hardware-in-loop environment and MATLAB/Simulink.

Disturbance-Suppression Method of Direct-Driven PMSG-Based Wind Power System in Microgrids

In order to solve the current fluctuation problem in microgrids, a suppression method called the Direct-driven Permanent Magnet Synchronous Generator (DPMSG)-based Wind Power System (WPS) based on an adaptive enhanced moving average filter algorithm is proposed. Firstly, the mathematical model of the WPS is established. On this basis, the suppression method under unbalanced conditions is derived by the instantaneous power equation to ensure the stable operation of the microgrid. In order to improve the dynamic compensation capability of the DPMSG-based WPS, an enhanced moving average filtering algorithm with frequency adaptability is proposed. The positive and negative sequence components are obtained in the dq frame by this filtering algorithm. Subsequently, the angular frequency of the microgrid is obtained according to the changing phase, which realizes the high-performance control of the WPS and avoids the complicated parameter adjustment of traditional methods. The correctness of this method is verified by the simulation results. The DPMSG-based WPS with the proposed method can improve the stability of the microgrid.

CNISOGI and VSSMCLMS Filters for Solving Grid and Load Abnormalities for a Microgrid With Seamless Mode Transfer Capability

A cascaded non-identical second-order generalized integrator (CNISOGI) and a variable step size modified clipped least mean square (VSSMCLMS) adaptive filter are proposed for a microgrid to solve the grid and load abnormalities. The CNISOGI filter estimates the positive sequence components (PSCs) from polluted (unbalanced/distorted) grid voltages. Hence improved quality grid currents are realized even though the grid voltages are polluted. Moreover, the CNISOGI filter estimates the accurate phase angle and frequency of voltages; thus, seamless transition of the microgrid is achieved between different modes. The comparative performance of the CNISOGI filter is studied over different control techniques and it demonstrates the better filtering capability of the proposed control. The microgrid is connected to the grid or a diesel generator (DG) set in subject to the availability of energy sources and the load demand to supply uninterrupted electricity to loads. Therefore, it provides an attractive solution for powering critical loads. The load compensation is achieved with the help of a VSSMCLMS filter. It estimates the active fundamental component of the load currents with faster response and lesser weight oscillations. The comparative performance of the VSSMCLMS filter is studied over conventional filters in MATLAB/Simulink and under laboratory conditions to ascertain its superiority in the filtering process.

Parallel filtering scheme for fast symmetrical component extraction based on asynchronous coordinate transformation

The common shortage of the existing methods for extracting symmetrical components from unbalanced and distorted three-phase voltages is that they introduce significant time delay before reaching an accurate result. Therefore, this paper presents a new filtering method to fast extract the positive sequence component based on asynchronous coordinate transformation. Unlike the conventional methods that filter out the harmonics in sequence, resulting in cascading delay, the proposed method has two signal streams operating in parallel, which in particular refer to the negative sequence component extraction and harmonic filtering, respectively, and then the positive sequence component can be easily derived by skillfully combining the results of two signal streams. In theory, the proposed method only suffers the largest delay introduced by these two streams. By carefully designing the asynchronous coordinate transformation, the delay can be restricted, thus improving the overall performance. Simulation and experimental results verified the performance of the proposed method.

Diagnosis of Interturn Short-Circuit of SRM Based on Ratio of Current Components

Inter-turn short-circuit is a common fault mode of switched reluctance motors (SRM) that causes changes in the parameters of the motor that can cause vibrations and noise. In this paper a diagnosis method is proposed to detect short circuit fault. Firstly, the model of a phase winding with inter-turn short-circuit is built and the fault characteristics are analyzed. Under normal condition, the sinusoidal components of phase currents are mostly a positive sequence with minimum distortion. The frequency signature of the motor is extracted by Fourier analysis when operating in normal conditions. When a fault condition occurs, symmetry of the phase currents is broken and both negative and zero sequence component of the phase currents appear. According to the asymmetry, an index, the ratio of negative to positive sequence component of the phase currents, is defined to identify whether the motor is working normally. The proposal is verified by simulations and experiments on a three-phase 12/8 structure SRM under different mechanical operating conditions. In normal condition, the fault index is about 0.02; in 12.5% fault condition, the fault index rises to about 0.07; in 25% fault condition, the fault index rises to about 0.08. According to the experimental results, fault index is robust because it is not influenced by the following parameters: turn on angle, turn off angle, rotor speed, load torque, etc.

An individual sequencing control strategy for three-phase four-leg inverter under unbalanced loads

Under the influence of the unbalanced load, the negative and zero sequence components in the output voltage of the three-phase four-leg voltage source inverter(TPFL-VSI) will cause asymmetry voltage. This paper designs an individual sequencing control for the three-phase four-leg inverter to address this problem. The second-order generalized integrator is adopted to extract the current’s positive and negative sequence components. The virtual oscillator control(VOC) controls the positive sequence component, and the negative sequence component is suppressed by designing the virtual impedance and the multiple proportional resonance controller. The proportional resonance control is used to control the zero-sequence voltage of the fourth bridge arm. Considering that voltage deviation is caused by the access of negative sequence virtual impedance and load step, the secondary voltage compensation strategy is further added in the individual sequencing control to improve the droop relationship in the VOC and effectively solve the problem of system voltage instability. Ultimately, a TPFL-VSI model is built in Matlab/Simulink, and simulation results verify the feasibility and effectiveness of the proposed control strategy under different conditions.

Fault Analysis of Inverter-Interfaced RESs Considering Decoupled Sequence Control

To adapt to the operation under asymmetric conditions, an increasing number of grid-following inverter-interfaced renewable energy sources (IIRESs) start to employ the decoupled sequence control (DSC). However, due to the variety and complexity of the positive and negative sequence components calculation (PNSCC) modes used for DSC, the fault response of IIRESs with DSC has rarely been studied using the analytical method. To this end, this paper proposes a Laplace domain fault modeling method to investigate fault characteristics of IIRESs with DSC. The high-order and coupling features of commonly used PNSCC modes are analyzed, and then they are taken into account to establish a detailed fault model of IIRESs with DSC. To further apply the fault model to the practical fault analysis, different PNSCC modes are generalized to obtain a unified form, and thus a reduced-order fault model of IIRESs with DSC covering the complete fault phases can be yielded. Based on this model, contributing factors of the IIRES&#x0027;s fault response within different fault phases can be explored. Simulation and hardware-in-loop experiments indicate that this model can be applied to various fault scenarios with an error less than 7&#x0025;, providing a theoretical foundation to support the protection scheme.

Current Differential Protection for Active Distribution Networks Based on Adaptive Phase Angle Compensation Coefficient

The high penetration rate of distributed generations (DGs) makes the distribution network’s fault characteristics complex and variable, which limits the application of traditional current differential protection (CDP) in active distribution networks. According to the amplitude and phase characteristics analysis of positive-sequence current fault components (PSCFCs) in the active distribution network, a novel CDP method based on the adaptive phase angle compensation coefficient is proposed. The method improves the traditional CDP by introducing an adaptive phase angle compensation coefficient, which adaptively compensates the phase of PSCFCs on the DG side according to the phase difference and amplitude ratio of PSCFCs on both sides of the protected feeder. To effectively cope with the negative impact of unmeasurable load branches on protection reliability, the polarity information of the action impedance is used to construct an auxiliary criterion. The effectiveness of the proposed protection scheme is verified in the PSCAD/EMTDC. Compared with the traditional CDP, this scheme can meet the protection needs of active distribution networks under various fault scenarios with high sensitivity and reliability. The proposed method can withstand high fault resistance and large time synchronization errors, and it can still trip correctly under 150 Ω fault resistance or 4.6 ms time synchronization errors.

A Novel Sequence-Based Unified Control Architecture for Multiple Inverter Modes of Operation in Unbalanced Distribution System

Control of multiple inverters in the distribution grid can be achieved by adopting appropriate droop laws. However, in an unbalanced power distribution system with single-phase and two-phase laterals, droop-based control methods fail thus requiring dedicated inverter control methods that can supply required positive and negative sequence (PNS) components. In this article, a unified control architecture is proposed for stable multiple inverter operation that can improve the accuracy of active and reactive power sharing alongside maintaining the voltage and frequency of the system close to the nominal values. The proposed control strategy further ensures the supply of required negative sequence components to maintain balanced steady-state system voltage and mitigate the active power ripples during unbalanced faults. The unified control architecture is devised through a systematic definition of steady-state operating modes and the interaction among hierarchical grid entities, facilitating the coexistence of PNS controllers to meet the defined objective. The results are verified using a real-time simulator-based multi-rate model-in-the-loop set-up. Furthermore, appropriate communication network latency is considered for the verification of the performance of the proposed PNS controller. The verification for various grid events confirms the capability and effectiveness of the proposed control architecture, and suitability for 100% inverter-based grid operation.

Performance analysis of a stand-alone synchronous reluctance generator under unbalanced conditions

&lt;span lang="EN-US"&gt;A stand-alone self-excited wind energy conversion system (WECS) is considered commonly used in remote areas due to its simple control and low cost. This paper introduces the performance analysis of a stand-alone self-excited reluctance generator (SERG) under balanced and unbalanced operations. An asymmetrical component is proposed to obtain the positive and negative sequence components of voltages and currents in addition to the unbalanced voltage factor of SERG. The obtained results have been validated and compared with experimental results obtained from a laboratory prototype of a 5.5 kW synchronous reluctance generator driven by a dc motor as a prime-mover under unbalanced excitation capacitors and unbalanced loads. The comparison verifies the applicability of the proposed model.&lt;/span&gt;

Power Decoupling Method for Voltage Source Inverters Using Grid Voltage Modulated Direct Power Control in Unbalanced System

The grid voltage modulated direct power control (GVM-DPC) is a novel power regulation method for grid-connected voltage source inverters (VSI). However, interactions between real and reactive powers still exist in GVM-DPC under unbalanced grid voltage condition, which may deteriorate its transient performance. This article proposes a power decoupling method for GVM-DPC-based VSI in unbalanced systems based on the dynamic feedforward power compensation strategy, which can reduce the coupling magnitudes of real and reactive powers in the transient stages. First, the power coupling mechanism of positive and negative sequence real and reactive powers of VSI under the unbalanced voltage condition is analyzed. Then, the power coupling magnitudes (PCM) are derived according to relationships among the positive sequence components of real power, reactive power and point of common coupling (PCC) voltages. Next, the PCM are compensated into the GVM-DPC for the better decoupling performance. Furthermore, a stability analysis of the proposed control system is studied based on the impedance model, and a comparison with the traditional power decoupling method based on virtual impedance is conducted to show the superiority of the proposed method. Finally, simulations, hardware-in-loop test and experiment are conducted to validate the effectiveness of the proposed method.

A Novel Control Scheme Using UAPF in an Integrated PV Grid-Tied System

This article investigates the photovoltaic fed universal active power filter (PV-UAPF) system for enhancing power quality indices. A novel comb filter together with second-order generalized integrator (CFSOGI) based instantaneous power balance theory with power angle (IPBTPA) control scheme is implemented. Under distorted or adverse grid conditions, the CFSOGI effectively extracts the phase angle, frequency, and fundamental positive and negative sequence components (FPNSC) to overcome the limitations of adaptive notch filters. Here, a comb filter constitutes a cluster/group of zeros at multiple harmonic frequencies to achieve notch peaks thereby providing superior harmonic rejection ability. Whereas, IPBTPA generates the reference signals to operate the system at dual compensation strategy with or without solar PV. The power angle is used to extract the desired load voltages under grid voltage fluctuations thereby reducing the burden on the shunt converter. Moreover, the hysteresis controller generates the switching pulses based on the calculation of reference and load powers which improves the dynamic performance by maintaining system power balance and effective DC voltage regulation. Besides, reactive power compensation, suppression of harmonic currents and mitigation of grid voltage fluctuations is also carried out to strengthen the system further. The system is also tested in grid voltage interruption for islanding mode to realize a microgrid system. The overall system performance is also validated using simulation and in a real-time experimental set-up, and results are demonstrated under various conditions.