Estimation Of Symmetrical Components Research Articles

ESTIMATION OF SYMMETRICAL COMPONENTS WITH FAST DYNAMICS FOR VSC-HVDC

This work presents an innovative symmetrical components estimation algorithm for three-phase ac systems by transforming the time-domain voltages into the complex variable domain. The symmetrical components estimation is attained without the need of a phase-locked loop (PLL). Moreover, as opposed to the standard PLL approach, the estimation of ac frequency and phase is decoupled in this work. The proposed method outperforms a standard PLL in terms of its open-loop phase step response. Furthermore, the estimated phase angle generated by the proposed method has been used to successfully control a VSC-HVDC scheme during steady-state and transient operating conditions in a computer simulation environment. In summary, the proposed method presents an efficient mechanism to generate a reliable ac phase estimation under fast dynamics of the ac system voltage, with minimal computational effort, for VSC-HVDC converters connected to weak ac grids.

Power System Analysis Using LabVIEW

The focus of this work is on investigation of LabVIEW electric power tool in particular and LabVIEW software in general for the analysis and design of electric power systems. Here we are targeting the solution of different electrical engineering problems which we very often face in teaching the course of power system analysis. At the time being, at Zarqa University, we are preparing a self study report for submission to ABET for accreditation of electrical engineering program. ABET considers that the application of different software tools during the learning process is essential and must be covered. Thus, power system analysis course has been selected as one of the courses that are decided to reach this outcome. As a result of that, a literature survey was conducted and several relevant topics were selected to be investigated. This included the following: simulation of on-line measurement of RMS and instantaneous values of electric power, calculation of symmetrical components using matrix analysis, on-line estimation of symmetrical components, use of phasor analysis to find phasor magnitude and phase angles, conversion of star to delta and delta to star configurations, and simulation of rotating phasors. All designed virtual instruments were analyzed, tested, and chosen solved examples gave very accurate results.

Gain normalized adaptive observer for three-phase system

This paper proposes the estimation of parameters and symmetrical components of unbalanced grid using adaptive observer framework. Recent adaptive observers proposed in the literature doesn’t employ any gain normalization in their frequency estimation loop. This can be problematic in the presence of large voltage dip. This paper proposes a solution to overcome this limitation using a novel gain normalized - frequency-locked loop (GN-FLL). Technical details of GN-FLL, stability analysis and tuning are provided in this paper. Comparative experimental results with adaptive Luenberger observer, second-order generalized integrator - phase-locked loop (SOGI-PLL) and enhanced PLL (EPLL) are provided to demonstrate the effectiveness the proposed technique in the single-phase case. Comparative experimental results with double SOGI-FLL (DSOGI-FLL) and adaptive notch filter (ANF) are provided to demonstrate the effectiveness the proposed technique in the three-phase case.

Recognition Algorithm of Transient Overvoltage Characteristic Based on Symmetrical Components Estimation

The recognition of transient overvoltage characteristics is the premise of disturbance compensation of the transient overvoltage. Based on that, the recognition algorithm of transient overvoltage characteristics based on symmetrical components estimation was proposed. The generation mechanism of the transient overvoltage in gas insulated switchgear (GIS) was analyzed. Then, the transient overvoltage was measured via the capacitive sensor method. The three-phase voltage of ultra-high voltage grid was asymmetrical when the transient overvoltage appeared. At present, the asymmetrical three-phase voltage was decomposed into the superposition of a symmetrical positive-sequence component, a negative-sequence component, and a zero-sequence component via the symmetrical components estimation to build the superposition model. The model was decomposed via the trigonometric identity and the modified neural network of the least mean square learning rule was used to estimate the parameter vector of the characteristic quantity of the transient overvoltage in real time. The feasibility of the proposed algorithm was verified via comparing the simulation of the proposed algorithm and the algorithm based on dp transformation. The experimental results show that the proposed algorithm has the advantages of a small operand, high detection precision, and fast action.

Adaptive Three-phase Estimation of Sequence Components and Frequency Using H∞ Filter Based on Sparse Model

The estimation of sequence or symmetrical components and frequency in three-phase unbalanced power system is of great importance for protection and relay. This paper proposes a new H ∞ filter based on sparse model to track the sequence components and the frequency of three-phase unbalanced power systems. The inclusion of sparsity improves the error convergence behavior of estimation model and hence short-duration non-stationary PQ events can easily be tracked in the time domain. The proposed model is developed using l 1 norm penalty in the cost function of H ∞ filter, which is quite suitable for estimation across all the three phases of an unbalanced system. This model uses real state space modeling across three phases to estimate amplitude and phase parameters of sequence components. However, frequency estimation uses complex state space modeling and Clarke transformation generates a complex measurement signal from the unbalanced three-phase voltages. The state vector used for frequency estimation consists of two state variables. The proposed sparse model is tested using distorted three-phase signals from IEEE-1159-PQE database and the data generated from experimental laboratory setup. The analysis of absolute and mean square error is presented to validate the performance of the proposed model.

Square‐root‐extended complex Kalman filter for estimation of symmetrical components in power system

The paper presents a square-root-extended complex Kalman filter (SRECKF) by decomposing covariance matrix with its square-root forms to improve stability of the filter for estimating complex number. αβ transformation is used to map three-phase instantaneous voltages in the abc phases into instantaneous voltages on the αβ axes, and a non-linear state equation and observation equation of the three-phase voltages are built by introducing a complex vector and defining state variables. Positive symmetrical component, negative symmetrical components, and frequency of the three-phase voltages are estimated using traditional extended complex Kalman filter (ECKF), the estimation results show that the method proposed here are superior to traditional extended complex Kalman filter on estimation accuracy and convergence rate.

Estimation of symmetrical components and their orthogonal components under unknown frequencies and unknown biases

An algorithm to estimate symmetrical components, orthogonal components and amplitudes of each sinusoidal component in three-phase power system signal under unknown frequencies and unknown biases is presented. The algorithm consists of a signal transformation, a biased adaptive orthogonal decomposition (BAOD) and a symmetrical component estimation. The BAOD can be regarded as a combination of a low pass filter and a number of three-phase frequency estimators in parallel. The symmetrical component estimation employs addition and multiplication rather than operations of trigonometry, division and phase shift. The decomposition property and the convergence property were investigated by Lyapunov theorem, integral manifold of slow adaptation and average method. Two design parameters, bandwidth parameter and frequency adaptive gains, give different effects on the convergence property of frequency adaptation and amplitude estimation independently. Simulation results demonstrate the performance of the method.

A new fast-converged estimation approach for Dynamic Voltage Restorer (DVR) to compensate voltage sags in waveform distortion conditions

The on-line estimation of symmetrical components from network voltages and currents is widely used in the field of power quality monitoring and improvement of relevant disturbances, especially by CUstom Power Systems (CUPS). This paper proposes a new fast-converged estimation approach, which directly extracts amplitudes and phase angles of symmetrical components of desired frequencies from harmonic-distorted network voltages. The adequate convergence time and accuracy of this approach make it applicable in Dynamic Voltage Restorer (DVR) as an application in which the quickness of response is of the most important requirements. According to this objective, sensitivity analyses are prepared to assess the impacts of sag depth variations, phase angle jumps and frequency variations on the performance of the proposed algorithm. Further, in these analyses complete comparisons are made between the proposed approach and well-known algorithms such as KF, ADALINE and FFT using MATLAB/SIMULINK. The application of the proposed estimation approach in the DVR is realized by introducing a new control scheme. The proposed control scheme provides the compensation of different voltage sags through both pre-sag and in-phase strategies. Finally, simulation results, carried out in PSCAD/EMTDC environment, confirm the effectiveness of the suggested control scheme.

A Flexible DG Interface Based on a New RLS Algorithm for Power Quality Improvement

Distributed generation (DG) exists in distribution systems and is installed by either the utility or the customers. This paper proposes a novel utilization of the existing DG interface to not only control the active power flow, but also to mitigate unbalance, harmonics and voltage flicker, and manage the reactive power of the system. The proposed flexible distributed generation (FDG) is similar in functionality to FACTS, but works at the distribution level. Moreover, a novel recursive least square (RLS) structure is presented. The new structure is applied to multi-output (MO) systems for parameter tracking/estimation, and is called MO-RLS. It is dedicated to symmetrical components estimation. An innovative processing unit-based RLS is investigated to deal with unbalance, harmonics, and reactive power compensation. In addition, this paper portrays a technique for flicker mitigation based on the RLS algorithm for instantaneous tracking of the measured voltage envelope. One advantage of the proposed control system is its insensitivity to parameter variation, a necessity for distribution system applications. Simulations of the suggested FDG based control algorithm are conducted to evaluate the performance of the proposed system.

Symmetrical Components Estimation Through Maximum Likelihood Algorithm and Adaptive Filtering

An algorithm that is suitable for the computation of symmetrical components is presented in this paper. The structure of the algorithm consists of four decoupled linear modules: the first for adaptive filtering of input signals, the second for frequency estimation, the third for symmetrical components estimation, and the fourth for the amplitudes of the component estimation. Filters are used to minimize the noise effect and to eliminate the presence of harmonics. A simple method for online designing of digital filters of sinusoidal signals is used in this paper. This method uses closed forms for calculation of filter coefficients and requires modest computations. The symmetrical components estimation through adaptive transformation matrix of phase shifters used in this paper makes it possible to get instantaneous symmetrical components independently on the frequency variation with modest-computation requirements. The technique used in this paper provides accurate frequency estimates with the maximum error of 0.002 Hz and symmetrical components estimation with the maximum error of 0.03% for in about 25 ms. The algorithm is not sensitive to power-system frequency changes and to the harmonic distortion of the input signals. To demonstrate the performance of the developed algorithm, computer-simulated data records have been processed. It has been found that the proposed algorithm is suitable for real-time applications.

Processing of Symmetrical Components in Time-Domain

A novel system for decomposing a set of three-phase signals into its constituting symmetrical components is proposed. The system also estimates the frequency, the magnitudes and phase-angles of the sequence components. The system is useful for online estimation of instantaneous symmetrical components and their attributes in the presence of frequency variations. The proposed system can be considered as a fundamentally improved version of the conventional three-phase Phase-Locked Loop (PLL) system which is widely used in power system applications. From this viewpoint, the proposed system obviates the inherent shortcoming of the conventional PLL system which is its erroneous response in the presence of negative-sequence component. Mathematical derivations and computer simulations are presented to describe the principles of operation and the performance of the proposed system. Examples of applications of the proposed system are in Flexible ac Transmission Systems (FACTS), HVDC systems, and Custom Power Controllers

Online condition monitoring of electrical power system imbalance

Symmetrical components are of great importance in many applications in electrical power systems, such as power protection and condition monitoring. This paper presents a computer-based algorithm for online symmetrical components estimation. The proposed algorithm uses the samples of the phase variables (currents or voltages) to estimate the magnitude and phase angle of each phase phasor at each sampling instant, and then these estimated phase phasors are used to formulate the symmetrical components as phasors and time-domain functions as well. Then the identified symmetrical components are used for condition monitoring of the electrical power system. Test examples of different power-system unbalanced conditions are computed to validate the developed algorithm.

An improved technique for the estimation of local frequency, fundamental component phasor and instantaneous symmetrical components

Fundamental component estimation, including its phase and amplitude information along with instantaneous fundamental symmetrical components, is of great importance for grid connected power electronics converters control, namely in power conditioning applications such as Dynamic Voltage Restorers (DVRs) and Unified Power Flow Controllers (UPFCs). Several methods have been proposed to estimate these parameters recently, particularly digital ones. The developments of new and more efficient microprocessor-based relays and supervising and monitoring systems have given support to those estimation methods. In this paper, an adaptive FIR filter based method for fundamental component estimation is used as support for a new proposed method. It enables fundamental component phasor, frequency and instantaneous fundamental symmetrical components estimation based on the grid voltage fundamental component. The method is tested under typical grid perturbations and is compared with two high performance alternative methods through objective and quantitative criteria.

Analysis and Implementation of Model-Based Linear Estimation of Dynamic Phasors

The paper presents analytical and experimental results on model-based linear estimation of dynamic phasors and dynamic symmetrical components in energy processing systems. The procedure is based on the Kalman filter, and shares its features regarding the simultaneous effective suppression of measurement noise and a very good tracking ability. The procedure is illustrated experimentally with examples involving single and three-phase inductors.

A Processing Unit for Symmetrical Components and Harmonics Estimation Based on a New Adaptive Linear Combiner Structure

Symmetrical components as well as harmonic tracking are of great importance in many applications in power systems such as power quality and protection. This paper introduces a novel Adaptive linear combiner (ADALINE) structure for symmetrical components estimation. This structure is capable of dealing with multi-output systems for parameter tracking/estimation rather than the existing ADALINE, which deals only with single output systems. As the new topology deals with Multi-Output systems, it is called MO-ADALINE. Moreover, the paper presents a new processing unit, which can estimate symmetrical and harmonic components from the measured current signals. The advantages of this proposed unit are its independence of the voltage waveform and its ability to give information about the reactive component of the resolved current. Simulation results are given to validate the proposed algorithms.

A Novel Control Algorithm for the DG Interface to Mitigate Power Quality Problems

Distributed Generation (DG) exists in distribution systems and is installed by either the utility or the customers. This paper proposes a novel utilization of the existing DG nonlinear interface not only to control the active power flow, but also to mitigate unbalance and harmonics, and to manage the reactive power of the system. The proposed Flexible Distributed Generation (FDG) is similar in functionality to FACTS, but works at the distribution level. Moreover, a novel ADAptive LINEar neuron (ADALINE) structure is presented. The new structure is applied to multi output (MO) systems for parameter tracking/estimation, and is called MO-ADALINE. It is dedicated to symmetrical components estimation. The control loop combines a Fuzzy Logic Controller (FLC) for voltage regulation, and a processing unit-based ADALINE to deal with unbalance, harmonics and reactive power compensation. One advantage of the proposed control system is its insensitivity to parameter variation, a necessity for distribution system applications. Simulations of the suggested FDG based control algorithm are conducted to evaluate the performance of the novel system.

Symmetrical components estimation through nonrecursive newton-type numerical algorithm

The paper reports new software developments for symmetrical components estimation. Nonrecursive Newton-type algorithm is extended with the second stage algorithm for symmetrical components calculation from the estimated fundamental phasors of three-phase signals (arbitrary voltages or currents). The algorithm is not sensitive to power system frequency changes and to the harmonic distortion of input signals. The algorithm is tested through computer simulations and by using laboratory obtained input signals and those recorded in the real distribution network.

Two digital filtering algorithms for fast estimation of symmetrical components in a power system: a static estimation approach

This paper presents the application of two digital filters working together for fast estimation of power systems symmetrical components. The three-phase unbalanced system is transformed to two phases using α–β-transformation. Using such a transformation, harmonics of order 3 and their multiples, in the input signal, are suppressed. Having identified the two-phase voltages, the positive and negative sequence phase voltage can be calculated using a constant transformation matrix. The zero sequence component is easily estimated by averaging the unbalanced three-phase voltage at every sample instant. Least error square algorithm is used to identify the magnitude and phase angle of sequence components from the available samples of the specified component.

Online estimation of steady state and instantaneous symmetrical components

An approach to the estimation of steady state and instantaneous symmetrical components is presented. The proposed method is based on an enhanced phase-locked loop mechanism which offers structural simplicity while maintaining performance robustness and controllable speed and accuracy. Computer simulations are presented to verify the performance of the proposed algorithm. It is demonstrated that the proposed method can provide an accurate estimation of the symmetrical components in the presence of frequency variations. The simplicity of the structure and ease of tuning render the proposed method suitable for both software and hardware implementations.

Symmetrical Components Estimation through Nonrecursive Newton Type Numerical Algorithm

This paper reports on new software developments for symmetrical components estimation. The nonrecursive Newton type algorithm is extended with the second stage algorithm for symmetrical components calculation from the estimated fundamental phasors of three-phase signals (arbitrary voltages or currents). The algorithm is not sensitive to power system frequency changes and to the harmonic distortion of input signals. The algorithm is tested through computer simulations and by using laboratory obtained input signals and those recorded in the real distribution network.