Three-phase Distribution System Research Articles

FLC-Based SOGI Controller for Photovoltaic-Operated STATCOM for Current Harmonic Elimination

Abstract In this paper, a photovoltaic (PV)-array-interfaced static synchronous compensator (STATCOM) with a fuzzy-logic-controller (FLC)-based second-order generalized integrator (SOGI) is presented to compensate for the current harmonics in the three-phase four-wire distribution system. The compensation ability and the effectiveness of the compensation depend on the capability of the dc link and the control techniques employed. The control techniques used in the system decides the required quantity of the measurement devices and the cost of the control unit. The proposed SOGI controller uses only the currents measured at the converter and load terminals. It does not require any voltage sensor. The proposed topology of STATCOM uses the energy generated in the PV array and FLC-based SOGI to offer the sufficient energy and provide the sustainable compensation against the current disturbances. The simulation results and experimental results of the prototype model are presented to validate the performance of the proposed STATCOM in compensating the current harmonics.

Generalised neural network‐based control algorithm for DSTATCOM in distribution systems

This study presents a new concept to control a distribution static compensator (DSTATCOM) based on generalised neural network in a three-phase power distribution system. Artificial neural network (ANN)-based controllers play the vital role in the performance improvement of DSTATCOM. However, their application is limited by the increase in complexity as well as the computational time. The proposed generalised neural network algorithm is a combination of Gaussian, sigmoidal and linear transfer functions within a layer to improve the DSTATCOM control strategy. This algorithm estimates the amplitude of the wattful and wattless current components of the load currents for harmonics elimination and reactive power compensation by the DSTATCOM. The algorithm is developed in MATLAB. The case studies validate its superiority over ANN-based control algorithms. The proposed method needs a less number of training patterns and unknown weights compared to other algorithms which reduces the complexity and the computational time. It also improves the performance of DSTATCOM estimating the weights and its learning online which is of the main merits of this algorithm. Its other inherent advantages are ease in design, robustness and its adaptivity with dynamics of load at utility end.

Comprehensive Modeling of Three-Phase Distribution Systems via the Bus Admittance Matrix

The theme of this paper is three-phase distribution system modeling suitable for the Z-Bus load-flow. Detailed models of wye and delta constant-power, constant-current, and constant-impedance loads are presented. Models of transmission lines, voltage regulators, and transformers that build the bus admittance matrix (Y-Bus) are laid out. The Z-Bus load-flow is then reviewed and the singularity of the Y-Bus in case of certain transformer connections is rigorously discussed. Based on realistic assumptions and conventional modifications, the invertibility of the Y-Bus is proved. Last but not least, the MATLAB scripts that construct the detailed component models for the IEEE 37-bus, IEEE 123-bus, and 8500-node feeders as well as the European 906-bus low-voltage feeder are provided.

Multiple gross errors detection, identification and correction in three-phase distribution systems WLS state estimation: A per-phase measurement error approach

This paper presents an analytical methodology for multiple measurement gross error detection, identification and correction for three-phase distribution systems weighted least square (WLS) state estimation. Initially, a three-phase WLS state estimator, considering the inherent distribution systems characteristics, as unbalance operation and different load types, is presented. Extended formulations for Jacobian matrix elements calculation, relating to different load models are proposed. Detection, identification and correction of gross errors are performed considering hypothesis testing in a per-phase component approach. Gross error detection is made through a Chi-square (χ2) Hypothesis Testing (HT) applied to the phase composed measurement error (CME). Composed errors are estimated with measurements’ phase innovation index (II). Gross error identification is made through the Largest Normalized Error Test property. Gross error correction is made considering the phase composed normalized error (CNE). A method to correct pseudo measurements identified as having gross errors is proposed. Validation is made with the IEEE 123 bus test system. Comparative tests with the state of art are presented. Test results are encouraging, indicating potential aspects for real-life applications.

An Adjustable DC Link Voltage-Based Control of Multifunctional Grid Interfaced Solar PV System

This paper presents a grid supported solar energy conversion system with an adjustable dc link voltage for common point of interconnection (CP) voltage variations. A two-stage circuit topology is proposed, wherein the first stage is a boost converter, which serves for maximum power point tracking, and the second stage is a grid tied voltage source converter (VSC), which not only feeds extracted solar photovoltaic (PV) energy into the three-phase distribution system but also serves for harmonics mitigation, reactive power compensation, and grid current balancing. An interweaved double-frequency second-order generalized integrator-based control algorithm is proposed for control of this multifunctional VSC, which possesses the feature of good steady-state performance along with fast dynamic response even under sudden load changes at CPI. Moreover, a feed-forward term for the solar PV contribution is used to enhance the dynamic response for climatic changes and CPI voltage variation. An adjustable dc link voltage structure is used to accommodate CPI voltage variation, which helps in reduction of losses in the power circuit. To implement adjustable dc link voltage structure, the reference dc link voltage is adjusted with variation in CPI voltage in real time. A proportional–integral controller is used to regulate dc link voltage to set reference value. A wide range of experimental results are shown to demonstrate the features of the proposed system. The total harmonic distortion of grid current has been found well under IEEE-519 standard even under nonlinear loads at CPI.

Bad area detection and whitening transformation‐based identification in three‐phase distribution state estimation

This study addresses state estimation in three-phase distribution systems, and proposes a new method for bad area detection (BAD) and identification of bad data. The proposed BAD utilises key features of the system such as strong correlation among measurements to identify both bad measurement areas and phases, via decoupled Chi-squares test with newly proposed metrics. The bad data identification detects multiple bad measurements using the whitening (sphering) transformation for re-parameterisation of the measurement residuals. The proposed methodology is verified on two characteristic test examples: (i) modified IEEE 13-bus benchmark test system, and (ii) 186-bus real-world distribution utility feeder.

Performance Analysis of Voltage-Stateless Controller for Renewable-Energy-Supported Shunt-Active Power Filter

Abstract The shunt-active power filter (APF) is one of the most efficient solutions to power-quality issues. The topology has a parallel, connected voltage-source inverter, which offers compensation for current-based disturbances. The effectiveness of compensation is influenced by the control technique employed. Moreover, the controller decides the required quantity of sensors and measurement practices; therefore, it decides related costs. This study uses a second-order generalized integrator (SOGI) to extract the reference current of shunt APF. The proposed strategy uses only measuring of the converter and load currents, thereby does not require voltage measurement and sensors. The proposed topology uses the photovoltaic (PV) energy with an energy-storage unit to generally meet the active power requirement of the utility grid and provides the sustainable compensation of current disturbances and voltage interruption of the three-phase distribution system. The PV-supported shunt APF, tested with different types of loads, can evaluate the performance of the system under steady-state and dynamic conditions. To confirm the efficiency of the proposed controller for PV-supported shunt APF, the simulation and experimental results are presented.

Distributed Computing Architecture for Optimal Control of Distribution Feeders With Smart Loads

This paper presents a distributed computing architecture for solving a distribution optimal power flow (DOPF) model based on a smart grid communication middleware (SGCM) system. The system is modeled as an unbalanced three-phase distribution system, which includes different kind of loads and various components of distribution systems. In this paper, fixed loads are modeled as constant impedance, current and power loads, and neural network models of controllable smart loads are integrated into the DOPF model. A genetic algorithm is used to determine the optimal solutions for controllable devices, in particular load tap changers, switched capacitors, and smart loads in the context of an energy management system for practical feeders, accounting for the fact that smart loads consumption should not be significantly affected by network constraints. Since the number of control variables in a realistic distribution power system is large, solving the DOPF for real-time applications is computationally expensive. Hence, to reduce computational times, a decentralized system with parallel computing nodes based on an SGCM system is proposed. Using a “MapReduce” model, the SGCM system runs the DOPF model, communicates between master and worker computing nodes, and sends/receives data among different parts of parallel computing system. Compared to a centralized approach, the proposed architecture is shown to yield better optimal solutions in terms of reducing energy losses and/or energy drawn from the substation within adequate practical run-times for a realistic test feeder.

Harmonic state estimation for distribution networks using phasor measurement units

This paper presents a novel approach for harmonic state estimation for unbalanced three-phase distribution systems using Phasor Measurement Units (PMUs), considering the presence of harmonic sources connected to the system. Harmonic branch currents in rectangular coordinates are the state variables to be estimated by the proposed methodology. Harmonic voltages and branch currents phasors are measured at monitored buses by PMUs. For the non-monitored buses, load pseudomeasurements are considered as inequality constraints in a proposed optimization problem solved via Safety Barrier Interior Point Method. The main contribution of the method is providing satisfactory estimation results considering non-fully observable power distribution networks with long feeders, requiring a small number of field measurements. Tests on the modified Baran and Wu's 33-bus test system are used to validate the methodology and demonstrate its effectiveness on evaluating power quality indexes, identifying harmonic sources and monitoring harmonic components and their propagation through the network.

3상 4선식 저압 배전선로에서 선형 및 비선형 부하의 사용시 전압 불평형률 비교 분석

In the three-phase four-wire low-voltage power distribution equipment, single-phase and three-phase load have been used mainly mixed. Also linear and nonlinear loads have been used together in the same conditions. In a three-phase four-wire distribution line, the current distribution of three-phase linear load is almost constant in each phase during driving or stopping, but the single-phase load is different from each other for each phase in accordance with the operation and stop. So that the voltage unbalance is caused by the current difference of each phase. In the three-phase four-wire distribution system, non-linear load is used with linear load. The presence of single-phase nonlinear loads can produce an increase in harmonic currents in three-phase and neutral line. It can also cause voltage unbalance. In the present study, we analyzed for the voltage unbalance fluctuations by the operation pattern of the single and three-phase linear and non-linear load in three-phase four-wire low voltage distribution system.

Power Quality Improvement Based on Five-Level Shunt APF Using Sliding Mode Control Scheme Connected to a Photovoltaic

This paper presents a compensating system for the harmonic currents, the reactive power in three-phase distribution system by using a five-level inverter based shunt active power filter (SAPF) connected by a photovoltaic system. A controller based on the p-q theory is introduced for the SAPF. The distribution network which supplies non-linear load and employing five-level inverter based SAPF connected by a photovoltaic system is simulated by MATLAB/SIMULINK software. The performance of SAPF is analyzed by using the proposed control technique on the total harmonic distortion of source current, power factor and reactive power. Besides, it is illustrated by extensive simulation results, the effectiveness of five-level SAPF connected by a photovoltaic system.

Power quality issues in small rating wind generation in weak distribution system

In this paper, a wind generator system (WG) comprising of squirrel cage induction generators (SCIGs) is described and its impact on three-phase four-wire weak distribution system is analysed with different short circuit ratio. This integrated system has various power quality issues such as voltage variation, harmonics, and unbalancing, etc. These issues are thoroughly examined and addressed in this paper with use of a distribution static compensator (DSTATCOM). The voltage source converter (VSC) of DSTATCOM is controlled to provide needed compensation to the foresaid system. DSTATCOM injects compensating current to the distribution system for reactive power and transient voltage support for zero voltage regulation (ZVR). A complete power balance analysis of the proposed system is also presented under different operating conditions of the distribution system through simulation in MATLAB 2011b.

Power Quality Improvement in Three-phase Four-wire Distribution System using STATCOM with Reduced Switches

Power Quality Improvement in Three-phase Four-wire Distribution System using STATCOM with Reduced Switches

A Sustainable Solar Photovoltaic Energy System Interfaced with Grid-Tied Voltage Source Converter for Power Quality Improvement

This paper deals with the design, modeling, and implementation of a photovoltaic (PV) array interfaced with a DC–DC boost converter feeding three-phase grid-tied voltage source converter. The system uses an Instantaneous Reactive Power Theory-based control algorithm and is operated in unity power factor mode. This three-phase shunt-connected solar PV energy conversion system is also used for load currents harmonics elimination, power factor correction, reactive power compensation, and grid currents balancing in a three-phase distribution system. A Perturb and Observe-based maximum power point tracking algorithm is used to generate maximum power from the PV array. This system is designed and modeled, and its performance is verified through simulation in MATLAB/Simulink. A prototype of the proposed renewable energy system is developed in the laboratory using a digital signal processor to validate its design and control.

Fast multilayer perceptron neural network‐based control algorithm for shunt compensator in distribution systems

In this study, a fast learning method of back-propagation (BP) multilayer perceptron neural network-based control algorithm for shunt compensator in three-phase distribution systems is presented. The proposed method comprises of quadratic linear and non-linear errors to determine optimisation criterion error function to train the BP algorithm while the existing methods have used only linear quadratic error term. The newly developed optimisation criterion error function accelerates the convergence efficiency of BP algorithm for performance improvement of shunt compensator at point of common coupling under non-linear loading conditions. With the help of the proposed algorithm, the weighted amplitude of fundamental active and reactive current components of the load current are extracted from which the reference source currents are estimated. The performance analysis of the proposed algorithm has been evaluated using two case studies for zero-voltage regulation and power factor correction. The total harmonic distortions are improved in comparison with standard BP algorithm which has been validated in above-mentioned two case studies. This is the quite important advantage of the proposed control algorithm to improve the power quality over existing control algorithms for shunt compensator.

Efficient signal processing technique for information extraction and its applications in power systems

This paper describes a novel mathematical method for decomposing power system signals obtained from measurements and monitoring of power systems. The technique is characterized as a self-based decomposition since the own system signals generate the basis used in the analysis. The resulting decomposition is sensitive to the system operation and is strongly related to the system operating parameters and power consumption, even when signals are non-purely sinusoidal. Mathematical theory is carefully exposed and three potential applications in power systems are presented to prove the efficiency of the signal processing method: high-impedance fault detection in three-phase distribution systems, single-phase VAR and harmonic compensator and three-phase voltage filtering. The investigation demonstrates that the technique is an effective signal-processing tool for power system applications, such as signal filtering and nonlinear process detection.

Second order sliding mode control of three-level four-leg DSTATCOM based on instantaneous symmetrical components theory

In this paper, a second order sliding mode controller (SOSMC) is proposed to control a three-level four-leg DSTATCOM connected to three-phase four-wire distribution system. The controller is designed in synchronous reference frame using super twisting algorithm based on symmetrical components theory. The proposed DSTATCOM control is aimed for the power factor correction in both capacitive and inductive operation modes. It has also purpose the regulation of excessive neutral current in the fourth wire of the distribution utility system under unbalanced loads or asymmetrical fault in the grid cases. This paper also presents a simplified three-level three-dimensional space vector modulation (3DSVM) with DC-bus capacitor voltages balancing strategy based on the effective use of the redundant switching states of the inverter voltage vectors. The effectiveness and validity of the proposed SOSMC system and 3DSVM are maintained by computer simulation. From simulation results, the comparison between the SOSMC, first order integral SMC, and conventional PI controller shows superiority of the SOSMC with high performance under both dynamic and steady state operations even in worst cases such as fault and unbalancing loads.

A Versatile Unified Power Quality Conditioner Applied to Three-Phase Four-Wire Distribution Systems Using a Dual Control Strategy

This paper presents the study, analysis, and practical implementation of a versatile unified power quality conditioner (UPQC), which can be connected in both three-phase three-wire (3P3W) or three-phase four-wire distribution systems for performing the series–parallel power-line conditioning. Thus, even when only a 3P3W power system is available at a plant site, the UPQC is able to carry out power-line compensation for installed loads that require a neutral conductor to operate. Different from the control strategies used in the most of UPQC applications in which the controlled quantities are nonsinusoidal, this UPQC employs a dual compensation strategy such that the controlled quantities are always sinusoidal. Thereby, the series converter is controlled to act as a sinusoidal current source, whereas the parallel converter operates as a sinusoidal voltage source. Thus, because the controlled quantities are sinusoidal, it is possible to reduce the complexity of the algorithms used to calculate the compensation references. Therefore, since the voltage and current controllers are implemented into the synchronous reference frame, their control references are continuous, decreasing the steady-state errors when traditional proportional–integral controllers are employed. Static and dynamic performances, as well as the effectiveness, of the dual UPQC are evaluated by means of experimental results.

Combined LMS–LMF-Based Control Algorithm of DSTATCOM for Power Quality Enhancement in Distribution System

This paper deals with the combined least mean square–least mean fourth (LMS–LMF)-based control algorithm for distribution static compensator (DSTATCOM) in three-phase distribution system to alleviate the power quality problems caused by solid-state equipments and devices. The combined LMS–LMF-based algorithm is simulated using Sim Power System (SPS) toolbox in MATLAB for obtaining the corresponding active and reactive weights and supply reference currents. The proposed control algorithm has advantages of both LMF- and LMS-based control algorithms, which helps in fast and accurate response with a robust design. Depending on the value of error signal obtained in any of the phases either of LMS- or LMF-based control is used to minimize the error. The developed combined LMS–LMF-based algorithm is implemented on the prototype of the proposed system and responses obtained are found satisfactory with harmonic spectra of the supply currents meeting the power quality standards.

Reduced-rating Hybrid Active Power Filter Comprising Zero-sequence Transformer and Three-phase Three-wire Active Power Filter for Three-phase Four-wire Distribution System

A three-phase four-wire active power filter is proposed in this article that consists of a three-phase three-wire active power filter, zero-sequence transformer, and single-phase active power filter. The reference current for tracking the desired source current is based on the neural network (constraint anti-Hebbian rule algorithm). The three-phase three-wire active power filter compensates current harmonics and reactive power requirement of the non-linear load. A zero-sequence transformer and single-phase active power filter are used to mitigate the neutral current. The proposed hybrid scheme (three-phase four-wire active power filter) significantly reduces the volt–ampere rating of the active power filter and improves the performance under different utility voltage conditions. The simulation of the proposed three-phase four-wire active active power filter is carried out for different voltage conditions. Further, the MATLAB-simulated (The MathWorks, Natick, Massachusetts, USA) response of the three-phase four-wire active active power filter has been validated on a prototype of the three-phase four-wire active-active power filter. The experimental result obtained from the prototype verifies the effectiveness and viability of the proposed scheme.