Distributed Parameter Line Research Articles

A Novel Model Predictive Controller for Distributed Generation in Isolated Microgrids—Part I: Development and Parameterization of the Data-Driven Predictive Model

In a low-voltage islanded microgrid, the distribution line impedance and relatively large power angle may lead to active and reactive power coupling during voltage and frequency control actions, which cause errors for conventional droop control at interfacing inverters of distributed generation (DG) units. To overcome this issue, in this two-part article, a novel model predictive controller for DGs is proposed to regulate voltage and frequency at the point of common coupling in isolated microgrids. In Part 1 of the article, a data-driven predictive model is developed and parameterized by system identification approach using nonlinear least square (NLS) method. Four NLS optimization algorithms (Gauss–Newton (GN), adaptive GN, Levenberg–Marquardt, and trust region reflective)] are evaluated and GN is chosen as the best performing algorithm. To initialize the iteration for NLS, the Backcast technique is chosen after comparing with Zero and Estimate techniques. Two optimization methods, “simulation” and “prediction” focus, are considered; and the prediction focus shows higher prediction accuracy and faster convergence, and the ability to avoid the necessity of data prefiltering by introducing a built-in weighted filter in the objective function. The polynomial input–output Box–Jenkins model is chosen as the model structure. The model incorporates distribution line parameters into the control algorithm and allows a wider variation of power angle without initiating nonlinearity. Therefore, it can substantially reduce the controller size and complexity, and widen the controller's operational range. The model is further implemented in the proposed model predictive controller in Part 2 of the article.

A Closed Form Solution for Line Parameter-Less Fault Location With Unsynchronized Measurements

This paper presents a novel two-terminal fault location algorithm without using line parameters. The algorithm is formulated using unsynchronized voltage and current phasors of the fundamental frequency at both ends. The novelty of the proposed method lies in the fact that it takes into account different angles of synchronism mismatch in pre-fault and fault conditions while considering distributed parameter line model and its solution is in closed form. Simulation results and performance comparison with existing methodology are presented under different fault conditions. The simulations were performed on EMTP-RV platform. The algorithm has also been tested with practical data of Power Grid Corporation of India Limited (PGCIL). The test result shows the validity and accuracy of the developed fault location algorithm.

Model parameter identification for scaled-down analogous HVDC transmission lines using broad spectral response analysis

Traditional analogous π-shape transmission line models are mainly designed based on the amplitude and phase response characteristics of the distributed-parameter transmission lines at the power frequency. It cannot be directly used to build analogous high-voltage direct current (HVDC) transmission line models because the signals in a wide frequency band from 0 Hz to 10 kHz are used to protect HVDC transmission lines instead of power frequency components. In this paper, a novel model parameter identification method for scaled-down analogous HVDC transmission lines is proposed based on broad spectral response analysis. The broad spectral responses of distributed parameter-based and π-shape lumped parameter-based models are analyzed and compared with each other first. And then frequency-dependent per-unit parameters of HVDC transmission lines are obtained and used to form a modified π-shape HVDC transmission line model with the same zero- and positive-sequence​ impedance as those of distributed parameter lines. The element parameters of the π-shape circuit model are identified optimally based on the weighted sum of the results at selected several frequencies in the broadband from 0 hertz to thousands of hertz. The simulation results show that the amplitude and polarity of the dc voltage and current in our scaled-down analogous lines are close to distributed parameter-based HVDC transmission lines once a fault occurred on the lines.

Topology and Parameter Identification of Distribution Network Using Smart Meter and µPMU Measurements

Incomplete and inaccurate information of network topology and line parameters affects state monitoring, analysis, and control of active distribution networks. To solve this issue, this article proposes a method for identifying distribution network topology and line parameters using the measurements obtained from smart meters (SMs) and microphasor measurement units (<inline-formula> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>PMUs) installed at various locations in a distribution network. A data-driven approach was developed, which uses a probabilistic method (unscented Kalman filter (UKF) based) and a deterministic method (Newton Raphson (NR) based) iteratively for accurate identification of network topology and parameters. The impact of the measurement noise with SMs and <inline-formula> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>PMUs is analyzed, and the acceptable noise levels are quantified. The impact of the identification algorithm on the network state estimation is examined. Moreover, optimal installation locations of the <inline-formula> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>PMU equipment are identified based on the estimation accuracy of the algorithm. The method is validated on benchmarked IEEE 33-bus and IEEE 123-bus test systems, while the impact of the renewable power injections at the different network nodes is studied as well. The qualitative and quantitative analysis is performed over the state-of-the-art methods, to highlight the effectiveness of the proposed methodology.

Fast and reliable differential protection based on traveling waves for HVDC transmission line

High voltage direct current (HVDC) technology is the ideal solution for long distance bulk power transmission. However, different from AC systems, differential protection of HVDC lines still faces a lot of challenges. We claim that from the perspective of state estimation, the essence of differential protection is to estimate state variables using measured data, of which the validity indicates whether there is a fault. Therefore, the performance of the differential protection is highly related to the model accuracy. Using a detailed distributed parameter line model, this paper developed a novel differential protection method for HVDC lines based on traveling waves with high reliability. The optimal differential point is also discussed to enhance protection rapidity. Experiments demonstrate that the proposed protection could soon detect internal faults with high fault resistance while maintaining reliability when external faults occur.

A fault‐location algorithm for parallel line based on the long short‐term memory model using the distributed parameter line model

A fault‐location algorithm for parallel line based on the long short‐term memory model using the distributed parameter line model

Efficient control techniques to enhance STATCOM performance with DE algorithm

This paper describes the performances of STATCOM by adopting various control techniques. In recent time, variety of control techniques are adopted in Power transmission systems. In this paper focused with reactive power control in STATCOM. In this paper both fundamental concepts associated with the reactive power control & its various techniques are studied. Normally harmonics are higher in normal Pulse Width Modulation (PWM) methods; So Space Vector Pulse Width Modulation (SVPWM) is adopted to reduce harmonics. The proposed system enhance the STATCOM performances in reduced harmonics, avoid voltage sag and swell, regulate the linear power flow and maintains healthy transmission and distribution line parameters. Apart from SPWM and SVPWM, Differently Evolution (DE) is used here to reduce harmonics and other parameters in order to enhance the performance and operation of STATCOM.

Transmission line fault location by solving line differential equations

The present paper describes a new algorithm for reliably locating the faults that frequently take place on electrical transmission lines. The proposed fault location technique considers a distributed-parameter line model that is given in the form of Partial Differential Equations (PDEs) whose boundary conditions are taken as synchronized time-domain data recorded from both sending and receiving terminals. The Adomian Decomposition Method is employed to spatially solve the sampled-time line model. The obtained solution provides phase voltages and currents profiles at each sample time as a function of line length. This function is expressed as a polynomial whose coefficients are simply determined by an easily-applied recursive procedure. One of the main interesting features of the developed scheme is that it can handle the case of unsymmetrical transmission lines without the need of modal decomposition that decouples the original three-phase system to an equivalent three independent single-phase systems. Simulations and calculations are all proceeded with MATLAB. The obtained results through different simulations show that the new methodology is operational, applicable, and accurate.

A Compensated Distributed-Parameter Line Decoupling Approach for Real Time Applications

This article proposes a new method called the Compensated Distributed-Parameter Line Decoupling (CDLD) method, and used for decoupling distribution networks among parallel processing cores in a real-time multi-core environment. Due to the short length of distribution grid lines, decoupling the distribution network for real-time processing is challenging and approaches such as Stublines and State Space Nodal (SSN) solvers have been proposed. Both approaches have limitations and the method proposed in this work addresses these limitations to implement improvements. Specifically, the CDLD method can be used as an enhanced Stubline decoupling, improving on its accuracy and transient response, or it can be combined with an SSN solver to improve its computational performance and remove bottleneck issues. The CDLD method was tested on three IEEE benchmark systems in a real-time environment, and significant improvement was realized in network response and computational performance compared to the prevailing methods. The combined SSN-CDLD method proved to be the most promising approach for network decoupling.

A Novel Fault Location Methodology for Smart Distribution Networks

Power distribution networks (PDNs) has played a crucial role in expediting transition towards cleaner and better distributed energy sources. Nowadays, more and more distributed generations (DGs) are used in PDNs which complicates the automatic fault location. This article presents an accurate impedance-based method to determine the fault location for smart PDN in the presence of DGs. In addition, phase domain equations of distributed line parameters are used to enhance the accuracy of fault location. Two types of networks are considered. The first type of network is assumed to be fully observable with μPMU and in the second type there are only a few μPMUs with data loggers on the rest nodes. Load impedances of all nodes are estimated using pre-fault recorded information by present μPMUs and data loggers. The proposed algorithm might suggest several points as possible fault locations for a PDN. To find out the actual location of fault same fault type is simulated for all suggested points. A matching value which is mathematically defined in the article, is calculated using recorded and simulated voltage to determine the actual fault point among all the suggested candidates. The accuracy of suggested method is analyzed against various conditions.

Circuit Model of Vertical Double-Circuit Transmission Tower and Line for Lightning Surge Analysis Considering TEM-mode Formation

The electromagnetic fields, which are produced by lightning currents flowing into a transmission tower and into overhead ground wires, spherically expand with time, and propagate as non-transverse electromagnetic (TEM) waves at least within the round trip time of the traveling wave along the tower. In this paper, a distributed-parameter line model of a vertical double-circuit transmission tower with an overhead line struck by lightning is composed considering the non-TEM characteristics. The surge impedances of the tower, ground wires, and phase conductors increase with time and reach their TEM-mode or steady state values with time constants determined from the configuration. In addition, the significant wave attenuation along the tower is included in the circuit model according to the propagation characteristic determined by the tower configuration. The virtual inductive grounding impedance or damping circuits for approximately representing the wave attenuation is no longer needed. The proposed model is applied to four types of transmission towers. Waveforms of voltages across insulator strings computed by the finite-difference time-domain method, which are regarded as the reference, are well reproduced by the proposed model. Computation efficiency is drastically improved by the proposed model comparing to the numerical electromagnetic field analysis.

PMU-based Fault Location Technique for Three-terminal Parallel Transmission Lines with Series Compensation

This study introduces a fault location technique for three-terminal series-compensated untransposed parallel transmission lines utilizing the three terminals’ synchronized data. The proposed technique is applicable for short or long lines as distributed parameter line model is employed and the potential couplings are considered. The fault location for both uncompensated line sections is obtained adopting previously introduced fault location technique. The faulty phases are required initially to be recognized for series-compensated transmission line. The adopted fault location technique for series-compensated line section is derived based on the resistive nature of the fault impedance. The obtained fault locations for each line section are compared with each other to distinguish the faulty branch and obtain the fault location. DIgSILENT Power Factory and MATLAB programs are utilized for simulation studies and required calculations. The obtained results prove the efficacy of the introduced technique.

Distribution line parameter estimation considering dynamic operating states with a probabilistic graphical model

Accurate distribution line parameters are critical for power system control, operation and management. Adjustment of the operating modes makes the estimation of real-time distribution line parameters dynamic and difficult. To calibrate the distribution line parameters from collected operating data, this paper proposes a Discrete Dynamic Bayesian Network (DDBN)-based distribution line parameter estimation model. The maximum likelihood estimation algorithm is utilized to train the DDBN model. The belief propagation (BP) algorithm is used to infer distribution line parameters with the DDBN model. The accuracy of the proposed model and the inference algorithm is investigated by carrying out experiments in a real-world medium voltage distribution network state estimation environment. The experimental results demonstrate that the proposed DDBN model performs better than existing approaches in providing accurate real-time line parameters.

Enhancements in vector fitting implementation by using stopping criterion, frequency partitioning and model order reduction

The Vector Fitting (VF) technique has become a mature rational approximation tool. This paper proposes two enhancements that increase the VF computational efficiency, resulting in reduced CPU time while maintaining a desired precision of the approximation. The first enhancement consists of a stopping criterion to automatically interrupt the VF iterative process when the fitting error does not vary significantly. The second one is based on frequency partition and order reduction of the rational model. The computational gain by the proposed enhancements is verified via fitting of a multi-input multi-output test system of considerable complexity that includes transmission lines modelled as distributed-parameter lines.

Sensitivity analysis of volt-VAR optimization to data changes in distribution networks with distributed energy resources

The Volt-VAR optimization (VVO) model is combined with distributed energy resources (e.g., solar photovoltaic (PV) systems and energy storage systems (ESSs)), advanced sensors and communication networks, as well as demand response programs for reliable and economical distribution grid operations. Unexpected changes in the data used for VVO can degrade the VVO performance. This study examines the impact of changes in VVO data on the optimal solutions of VVO (e.g., nodal voltage, real/reactive power flow at the substation, and total deviation of voltages from the nominal voltage). Using the perturbed Karush-Kuhn-Tucker conditions of the VVO formulation, we develop a linear matrix that evaluates the sensitivity of VVO with respect to change in various types of data—distribution line parameters, the predicted PV generation outputs, demand reduction, and load exponents in exponential load models. The proposed sensitivity matrix can be used by system operators as an analysis tool to quickly identify the data that influences the optimal VVO solution the most by accurately measuring and prioritizing sensitivities. The results of a simulation study using the developed sensitivity matrix are illustrated and verified in two distribution test systems (IEEE 33-node and 123-node systems) with an on-load tap changer (OLTC), capacitor banks (CBs), PV systems, and ESSs.

Impedance-based stability criterion for the stability evaluation of grid-connected inverter systems with distributed parameter lines

Impedance-based stability criterion for the stability evaluation of grid-connected inverter systems with distributed parameter lines

Time-domain based fault location for series compensated transmission lines without requiring fault type

Accurate fault location algorithms enable a quicker return to operation of faulted lines. The previously published fault location algorithms for series compensated transmission lines need the fault type and/or the compensator model to be known before fault location estimation. Thus, the accuracy of them is highly related to the fault type classification method and/or modelling of the compensator. This article suggests a fault location scheme for transmission lines compensated by series devices without requiring fault type based on synchronized instantaneous values collected from both ends of the line along with taking advantage of the distributed parameter line model in the time domain. The main advantages of this method are: (1) It not only determines faulty phases, but also estimates the fault location, simultaneously; (2) It is also independent on models of the series devices, so that the scheme is valid for transmission lines compensated by any series compensator. This paper examines the accuracy of the new algorithm for different fault situations with wide variations in system operating conditions in the presence of a Thyristor-Controlled Switched Capacitor (TCSC) and a Static Synchronous Series Compensator (SSSC). The results show that the fault type-classification and location accuracy of the method is high.

A Wideband Single End Fault Location Scheme for Active Untransposed Distribution Systems

This paper presents a single end fault location scheme for distribution networks with distributed generation (DG). The high frequency transients generated when a fault occurs are used to locate the fault point. An equivalent circuit at high frequencies is derived for both inverter based and synchronous DGs. The voltages and currents measured only at the main substation are used in conjunction with the proposed DG model to create the fault location scheme. The distributed parameter line model is employed in the derivation to account for the line characteristics, e.g., inductive and capacitive mutual coupling and untransposed lines. The inverter based DG model is validated experimentally on a 400 V, three-phase system. The IEEE 34-bus feeder is simulated and used to evaluate the proposed scheme for different operating conditions, e.g., fault resistance and DG conditions. The extensive simulation studies show the accuracy of the proposed scheme with 95.3% of the test cases having an absolute error in estimation of less than 200 m.

Energy storage system control algorithm for voltage regulation with active and reactive power injection in low-voltage distribution network

The voltage drop affecting consumers at the end of distribution lines is one of the problems regarding power quality. The solutions applied to transmission lines are not fully effective in distribution lines, where line parameters are significantly high. In low-voltage distribution network, the reactive power compensation method is not as effective as active and reactive power compensation. This effect occurs on lines where the significant series resistance becomes remarkable in relation to the total line impedance. This paper presents the design and implementation of a four-wire, three-phase voltage source converter (VSC) with output current control for voltage regulation at the point of common coupling (PCC), using active and reactive power injection. A reactive power prioritization and minimization of active power strategy is proposed to overcome the problem of distribution line parameters. Digital design methodology is used to design the management controllers and loops, and a digital signal controller (DSC) is used for the entire implementation. The mathematical analysis results are validated using numerical simulation and proven with the construction of a 3.8kVA prototype. The results showed that the converter accomplished an effective voltage regulation at the PCC with reduced active power.

A new single end wideband impedance based fault location scheme for distribution systems

This paper proposes an improved impedance based fault location scheme based on system analysis at non-fundamental frequencies. The fault is treated as a voltage source that injects high frequency components into the system and the analysis is carried out using these injected components. The proposed method only requires local measurements at the substation and therefore is classified as a single end method. The new contribution is that the proposed method uses the distributed parameter line model to account for inductive and capacitive effects of the line. It has been evaluated on the IEEE 34-bus feeder which is based on an actual distribution system which has the typical features such as non-homogeneous feeder sections, asymmetrical line configurations, unbalanced loads and single and three-phase laterals. The fault point, fault resistance and fault inception angle have been varied to check their influence on the accuracy of the method. The simulation results demonstrate the accuracy of the proposed method where for most cases, the error in fault location is less than 50m.