Three-phase Distribution System Research Articles

An adaptive method for tuning process noise covariance matrix in EKF-based three-phase distribution system state estimation

This paper proposes a new adaptive method for online tuning of process noise covariance matrix in the Extended Kalman Filter based three-phase distribution system state estimator. Specifically, a new form of exponential function is proposed for tuning the process noise covariance matrix, adapting it to the level of state changes. A new indicator derived from normalized innovations of the available real-time and virtual measurements is developed for tracking the level of state changes. The proposed method relies on measurements of the existing distribution networks, and therefore can be easily implemented in the advanced distribution management system. The method efficiently adapts process noise to system state variations and can deal with both quasi steady-state and unexpected sudden state changes caused by changes in the system topology, generation or demand. Comparison results with other state-of-the-art adaptive methods on the modified IEEE 37-bus and IEEE 123-bus distribution systems show that the proposed method achieves better accuracy under quasi steady-state condition while being more robust to unexpected sudden state changes.

Multi-Area Distribution System State Estimation Using Decentralized Physics-Aware Neural Networks

The development of active distribution grids requires more accurate and lower computational cost state estimation. In this paper, the authors investigate a decentralized learning-based distribution system state estimation (DSSE) approach for large distribution grids. The proposed approach decomposes the feeder-level DSSE into subarea-level estimation problems that can be solved independently. The proposed method is decentralized pruned physics-aware neural network (D-P2N2). The physical grid topology is used to parsimoniously design the connections between different hidden layers of the D-P2N2. Monte Carlo simulations based on one-year of load consumption data collected from smart meters for a three-phase distribution system power flow are developed to generate the measurement and voltage state data. The IEEE 123-node system is selected as the test network to benchmark the proposed algorithm against the classic weighted least squares and state-of-the-art learning-based DSSE approaches. Numerical results show that the D-P2N2 outperforms the state-of-the-art methods in terms of estimation accuracy and computational efficiency.

Robust three-Phase distribution system frequency measurement using a variable step-size LMS

Frequency estimation is an important power quality parameter that is also useful for the protection and control of distributed generators. This paper proposes a robust three-phase distribution system frequency estimation algorithm based on the widely linear complex least mean square using a variable step-size to provide accurate frequency estimation and fast convergence during islanding of distributed generation (DG) and faults. The performance of the proposed method was evaluated in islanding events of DG. Besides, unbalanced analytical signals in amplitude and phase were evaluated as well as the impacts of the sampling rate and noise. The proposed algorithm was compared to other least mean square-based methods and good results were achieved.

Experimental Validation of Photovoltaic System with Isolated Dual Inductor dc-dc Converter for Grid-Connected Application

Abstract This article presents a double inductor–based converter for a grid-connected photovoltaic (PV) system with the utilization of the battery bank. This converter used to give continuous power to the three-phase four-wire power distribution system from the PV array. In order to increase the low magnitude of the PV array output voltage into a high dc voltage required for the three-phase dc link, the proposed system offers two boost stages. The double inductor–based converter gives power to the load in both the switched ON and OFF conditions of the chopping switch over buck, boost, and Cuk converters utilized in the PV-coordinated grid-connected applications. The operations of the proposed double inductor–based converter sustained three-phase four-wire power distribution system are analyzed and presented. The digital simulation and hardware experimental prototype results are presented to examine the performance of the presented double boost converter fed to the three-phase four-wire power distribution system.

A Data-Driven Global Sensitivity Analysis Framework for Three-Phase Distribution System With PVs

Global sensitivity analysis (GSA) of distribution system with respect to stochastic PV and load variations plays an important role in designing optimal voltage control schemes. This paper proposes a data-driven framework for GSA of distribution system. In particular, two representative surrogate modeling-based approaches are developed, including the traditional Gaussian process-based and the analysis of variance (ANOVA) kernel ones. The key idea is to develop a surrogate model that captures the hidden global relationship between voltage and real and reactive power injections from the historical data. With the surrogate model, the Sobol indices can be conveniently calculated through either the sampling-based method or the analytical method to assess the global sensitivity of voltage to variations of load and PV power injections. The sampling-based method estimates the Sobol indices using Monte Carlo simulations while the analytical method calculates them by resorting to the ANOVA expansion framework. Comparison results with other model-based GSA methods on the unbalanced three-phase IEEE 37-bus and 123-bus distribution systems show that the proposed framework can achieve much higher computational efficiency with negligible loss of accuracy. The results on a real 240-bus distribution system using actual smart meter data further validate the feasibility and scalability of the proposed framework.

Dynamic Voltage Restorer Integrated with Photovoltaic-Thermoelectric Generator for Voltage Disturbances Compensation and Energy Saving in Three-Phase System

The dynamic voltage restorer (DVR) combined with a photovoltaic–thermoelectric generator (PV-TEG) system is proposed for voltage disturbance compensation in the three-phase four-wire distribution system. The PV-TEG hybrid energy source is used in the DVR system to improve the system ability for deep and long-period power quality disturbance compensation. In addition, the DVR will save grid energy consumption when the hybrid PV-TEG module generates sufficient power to meet the load demand. An enhanced variable factor adaptive fuzzy logic controller (VFAFLC)-based maximum power point tracking (MPPT) control scheme is proposed to extract the maximum possible power from the PV module. Since the PV and TEG combine a hybrid energy source for generating power, the DVR can work efficiently for the voltage sag/swell, outage compensation, and energy conservation mode with minimum energy storage facilities. The in-phase compensation method and the three-leg voltage source inverter (VSI) circuit are chosen in the present system for better voltage and/or power compensation. To confirm the effectiveness of the proposed hybrid PV-TEG integrated DVR system, a simulation-based investigation is carried out with four different operational modes with MATLAB software. The study results confirm that the proposed DVR system can compensate power quality disturbances of the three-phase load with less total harmonics distortion (THD) and will also work efficiently under energy conservation mode to save grid energy consumption. Moreover, the proposed VFAFLC-based control technique performs better to achieve the maximum power point (MPP) quickly and accurately, thereby improving the efficiency of the hybrid energy module.

Model Rangkaian-T Pembangkit Listrik Tenaga Bayu untuk Analisis Aliran Daya Tiga-Fase

Akhir-akhir ini, penetrasi Pembangkit Listrik Tenaga Bayu (PLTB) pada sistem distribusi tenaga listrik mengalami peningkatan yang cukup signifikan. Penetrasi PLTB ini dapat memengaruhi kondisi keadaan mantap dan dinamik sistem tersebut. Lebih lanjut, sistem distribusi tenaga listrik biasanya tidak seimbang, sehingga harus dianalisis secara tiga-fase. Oleh karena itu, agar kondisi-kondisi sistem dapat dievaluasi dengan baik, pembentukan model tiga-fase dari komponen-komponen sistem (termasuk PLTB) merupakan hal yang sangat penting. Makalah ini mengusulkan metode sederhana dalam memodelkan dan mengintegrasikan PLTB kecepatan tetap untuk analisis keadaan mantap (atau analisis aliran daya) sistem distribusi tiga-fase. Metode yang diusulkan tersebut didasarkan pada model rangkaian-T yang sebelumnya telah berhasil diaplikasikan pada sistem fase-tunggal. Pada makalah ini, model rangkaian-T fase-tunggal tersebut dimodifikasi dan diperluas sehingga dapat memfasilitasi analisis aliran daya tiga-fase pada kondisi sistem tak-seimbang. Aplikasi usulan model pada dua sistem distribusi tiga-fase, yaitu sistem 33-simpul dan 25 simpul, juga diselidiki dan disajikan pada makalah ini. Hasil-hasil penyelidikan yang dilakukan pada sistem tersebut memperlihatkan bahwa metode yang diusulkan valid dan akurat.

Voltage Source Inverter Filter with Improved Proportional Gain for Dynamic Power and Melodies Mitigation in Three-Phase Three-Wire Distribution Systems

Voltage Source Inverter Filter with Improved Proportional Gain for Dynamic Power and Melodies Mitigation in Three-Phase Three-Wire Distribution Systems

Power Quality Improvement for Grid-connected PV System Based on Distribution Static Compensator with Fuzzy Logic Controller and UVT/ADALINE-based Least Mean Square Controller

This paper presents a novel method of power quality enrichment in a grid-connected photovoltaic (PV) system using a distribution static compensator (DSTATCOM). The paper consists of two-step control processes. In the primary step, a fuzzy logic controller (FLC) is employed in the DC-DC converter to extract the peak power point from the PV panel, where the FLC produces a switching signal for the DC-DC converter. In the secondary step, a unit vector template (UVT)/adaptive linear neuron (ADALINE)-based least mean square (LMS) controller is adopted in the DC-AC converter, i.e., voltage source converter (VSC). The input to this VSC is the boosted DC voltage, which originates from the PV panel as a result of DC-DC conversion. The VSC shunted with the power grid is known as a DSTATCOM, which can maintain the power quality in the distribution system. The UVT controller generates reference source currents from the grid voltages and DC-link voltages. The ADALINE-based LMS controller calculates the online weight according to the previous weights by the sensed load current. The UVT/ADALINE-based LMS controller of a DSTAT-COM performs several tasks such as maintaining the sinusoidal source current, achieving a unity power factor, and performing reactive power compensation. The reference current extracted from the UVT/ADALINE-based LMS controller is fed to the hysteresis current controller to obtain the desired switching signal for the VSC. A 100 kW solar PV system integrated into a three-phase four-wire distribution system through a four-leg VSC is designed in MATLAB/Simulink. The performances of the FLC and UVT/ADALINE-based LMS controllers are demonstrated under various irradiances as well as constant temperature and nonlinear loading conditions.

Integrated Battery Energy Storage into an Optimal Low Voltage Distribution System with PV Production for an Urban Village

The feed-in tariff for rooftop photovoltaic (PV) systems has not yet been adopted in Cambodia, the utility thus does not purchase excess power by reverse power flows from PV production, and only unidirectional energy meters are used even in the capital. The power distribution systems are expanded in recent years due to load demand increase, and this issue makes the distribution system designers perform the planning. The design of a low voltage distribution system and suitable solutions are proposed to handle these issues. This paper purposes of designing an optimal low voltage distribution topology with the integration of PV and three different proposed solutions of reverse power relay (RPR), solar hybrid inverter (SHI) and battery energy storage (BES) in an urban village, which consists of improving a balanced load and existing PV production usage. Firstly, the repeated phase ABC is applied to minimize the power loss and unbalanced load in the three-phase distribution system. Next, the integration of RPR, SHI, and BES into household grid-connected PV production systems have been proposed as solutions. To confirm a proposed method, the urban village in Phnom Penh, Borey Mungkul Phnom Penh, Sangkat Veal Spov, is chosen and modelled for a case study. Simulation results allow concluding that the integrated battery energy storage into the optimal low voltage distribution topology provides the best solution to design the grid connection PV system.

A New Optimal Distributed Strategy to Mitigate the Phase Imbalance in Smart Grids

In a three-phase distribution system, due to unequal distribution of single-phase loads, load diversities, the different consumption patterns, and growing penetration of renewable energy resources in smart grids, the problem of unbalanced power flow becomes more challenging. In this paper, we propose a new innovative phase imbalance mitigation (PIM) scheme performed by smart meters. With aid of the proposed optimal phase assignment for 3-phase power distribution input feeders known as phase rearrangement (PR), Electrical storages (ES), and the Renewable energy sources (RES), smart meter owners are inspired to assist the distribution system operator (DSO) in diminishing the phase imbalance. This is achieved by employing a proposed connection point assignment system which has the flexibility of selecting the power input among the three phases and management of ESs and RESs. We model this problem into a mixed integer linear program, where smart meter owners minimize their electricity bill. Simulation results confirm the proposed approach and show smart meter owners will save on their electricity bill and the DSO will get benefit by improving the power quality of the grid and significant decrements of the power flow imbalance.

Design and analysis of Levenberg–Marquardt‐based adaptive SOGI

This study presents the design and analysis of an adaptive second-order generalised integrator (SOGI) technique for controlling voltage source inverter in a three-phase three-wire distribution system. The function of the proposed shunt active power filter involves compensation of reactive power for power factor correction, harmonic elimination, load balancing, voltage regulation under non-linear load condition. In this study, an effective approach for load compensation is proposed by designing an adaptive SOGI trained using Levenberg–Marquardt technique and compared with conventional techniques which ensure smooth operation under normal and distorted grid condition. An experimental setup is developed and its performance is analysed during different loading conditions. The experimental results are in line with the expected simulation results. Experimental and simulation results are verified and analysed using Bode plot.

Modeling of Grid-Forming and Grid-Following Inverters for Dynamic Simulation of Large-Scale Distribution Systems

Historically, distribution system planning studies mainly focused on steady state and quasi-steady state analysis, with limited attention paid to dynamic analysis. This paper develops three-phase, electromechanical models for both grid-forming and grid-following inverters, and integrates them into an open source, three-phase distribution network solver, thereby enabling dynamic simulation of large-scale, three-phase unbalanced distribution systems with high penetration of inverter-based DERs. The proposed inverter models are validated against electromagnetic simulation and field test data from the CERTS/AEP microgrid testbed, and simulated in an islanded 5252 node distribution system in the GridLAB-D simulation environment. Simulation verifies the effectiveness of the proposed inverter models for large-scale distribution system analysis. Study results show that compared to traditional grid-following inverters, the high penetration of grid-forming inverters can improve the voltage and frequency stability of islanded distribution systems.

A complete state estimation algorithm for a three-phase four-wire low voltage distribution system with high penetration of solar PV

Low Voltage Distribution Grids (LVDGs) become highly unbalanced due to the advent of single-phase solar PV plants. As a result, the voltage and current levels of the neutral conductor show a significant increase. Therefore, monitoring of the entire state of the network is essential. However, the existing state estimation algorithms estimate voltage states of the phase conductors while ignoring the state of the neutral conductor. This paper presents a novel approach to estimate the complete state of the LVDGs. A novel state reduction method was introduced to model the three-phase four-wire feeder line using a 3×3 admittance matrix, which incorporates the neutral coupling effect on phase conductors. Next, the reduced admittance matrix together with the linear approximations of active and reactive power functions were combined to formulate the Low Voltage-Linear State Estimation (LV-LSE) algorithm. Finally, the performance of LV-LSE algorithm was analyzed for different measurement uncertainties, scales of line lengths of the network, and data-loss conditions. Results show that, for all the cases, LV-LSE algorithm together with the proposed reduction method can estimate voltage states with an average maximum voltage magnitude error of less than 4.32×10-3 pu and current states with an average maximum current magnitude error of less than 1.81×10-3 pu.

Three-Phase Distribution System Load Flow Analysis Using Sequence Components

Electric power distribution system are usually unbalance. Therefore, a power flow method that can handle the three-phase configuration of the power system is needed so that the system planning and operation can properly be carried out. In the case of three-phase distribution system power flow analysis, for each system bus (except for substation bus), the voltage magnitude and angle of the three phases must be calculated. These calculations are carried out under certain loading conditions. After these voltages have been calculated, the electric power flows and losses in the distribution lines, and the substation power can also be determined. This paper proposes a new technique for three-phase distribution system power flow analysis using sequence components. The new formulation for the power flow problem in terms of sequence components is also proposed and developed in this paper. The application of sequence components has the advantage that the size of the problem can effectively be reduced, and solution to the power flow problem will be easier to find. Case study using a representative distribution test system confirms the validity of the proposed method where comparative studies between the proposed (i.e. sequence components based) method and the phase components based method are carried out.

Deep Reinforcement Learning Based Volt-VAR Optimization in Smart Distribution Systems

This paper develops a model-free volt-VAR optimization (VVO) algorithm via multi-agent deep reinforcement learning (DRL) in unbalanced distribution systems. This method is novel since we cast the VVO problem in distribution networks to an intelligent deep Q-network (DQN) framework, which avoids solving a specific optimization model directly when facing time-varying operating conditions in the systems. We consider statuses/ratios of switchable capacitors, voltage regulators, and smart inverters installed at distributed generators as the action variables of the agents. A delicately designed reward function guides these agents to interact with the distribution system, in the direction of reinforcing voltage regulation and power loss reduction simultaneously. The forward-backward sweep method for radial three-phase distribution systems provides accurate power flow results within a few iterations to the DRL environment. The proposed method realizes the dual goals for VVO. We test this algorithm on the unbalanced IEEE 13-bus and 123-bus systems. Numerical simulations validate the excellent performance of this method in voltage regulation and power loss reduction.

Laboratory Simulation of Numerical Over-Current Protection

The development of a hardware simulation of the power system faults and protection by a numerical over-current and earth fault relay in a laboratory environment is depicted in this paper. The development is aimed at providing motivation and creating interest in the students for the complex design of relay setting coordination, fault analysis, control circuit design, communication and configuration of the latest numerical relays. The hardware simulation panel setup comprises of a three-phase two-section radial distribution system. Flexible connections are provided to changeover the numerical relay current input source from the current transformer secondary to the relay test set output. It helps in the multiple uses of the panel for testing, configuring and application of the numerical relay. Two different models of numerical relays, namely SPAJ-140C and REF615 of ABB make are mounted on the panel. The installation, commissioning, testing and configuration for various IEC and IEEE characteristics are accomplished. The work progress is achieved through the final year student projects, thus providing technical and hands-on skills to the students. The laboratory manual has been developed for conducting experiments as a part of the laboratory curriculum for the power system protection course at UG and PG level. The manual and the panel developed are also useful in conducting the training programs for the state power utility company’s engineers as a part of industry–institute interaction.

A New Linear State Estimator for Fault Location in Distribution Systems Based on Backward-Forward Currents Sweep

This paper presents a new linear state estimation model based on a current summation load flow method for three-phase distribution systems. The developed estimator may be applied to both the supervision of distribution systems under normal operating conditions and the fault location in cases of low and high impedance faults. Our studies were conducted using a real distribution feeder. For fault location analysis, the system was modeled using the ATP (alternative transient program) in order to emulate measurements of voltages and currents at the substation, and voltage magnitudes registered by other meters during the fault. We used the MATLAB™ software to process the algorithms. The main contributions that arose after integrating the current method into system supervision in case of network failures under normal operating conditions and the fault location are as follows: (i) estimation of system losses; (ii) modeling of loads in real time to consider their contributions in the fault location process; and (iii) low influence of fault resistance in the location algorithm. The results show that the proposed method has good precision, low computational processing time, and is promising for distribution system supervision with a reduced number of meters.

Distribution System Operation and Expansion Planning using Network Reconfiguration

This paper presents an algorithm for network reconfiguration which could help in the operation and expansion planning of three-phase distribution systems. Considering the fact that power losses lead to decrease utility benefits, and the three-phase unbalanced voltage can damage electrical machines, the proposed algorithm is presented as a multi-objective optimization problem based on Evolutionary Algorithms where the power losses and three-phase unbalanced voltage are simultaneously minimized. In order to validate the efficiency of the proposed reconfiguration algorithm, a large-scale radial electric distribution system, under maximum load conditions, is considered for operation planning. In addition, different scenarios are compared to test the algorithm as an expansion planning tool. The proposed algorithm maximizes the utility profits and improves system performance reducing power loss and unbalanced voltage.

COMPARATIVE ANALYSIS OF UPQC WITH VARIOUS HYSTERESIS CURRENT CONTROLLERS

This paper deals the comparative analysis of a three-phase three wire Unified Power Quality Conditioner (UPQC) with various hysteresis current controllers. The UPQC is one among the custom power devices which is a integration of series and shunt active power filters (APF) connected by a common link capacitor. The construction of shunt and series APF is by using a three phase three wire Voltage source Inverter (VSI). In series active filter, synchronous reference frame technique is used to extract fundamental voltage; whereas in shunt active filters, instantaneous reactive power theory (IRPT) is used to extract fundamental current. Switching pulses for both filters generated by hysteresis current controller (HCC), multilevel vector based hysteresis current controller (MVHCC) and adaptive hysteresis current controller (AHCC).The performance of the various HCC based control algorithm of shunt active filter with series active filter is evaluated in a three-phase distribution system connected with non-linear and unbalanced load conditions. Fuzzy logic control is used for dc capacitance balancing. The control technique is executed by the use of MATLAB/Simulink-based simulations environment.