Voltage Quality Improvement Research Articles

The Unified Power Quality Conditioner Control Method Based on the Equivalent Conductance Signals of the Compensated Load

This paper proposes a new control method for a Unified Power Quality Conditioner (UPQC). This method is based on the load equivalent conductance approach, originally proposed by Fryze. It can be useful not only for compensation for nonactive current and for improving voltage quality, but it also allows one to perform some unconventional functions. This control method can be performed by extending the orthodox notion of ‘static’ load equivalent conductance into a time-variable signal. It may be used to characterize energy changes in the whole UPQC-and-load circuitry. The UPQC can regulate energy flow between all sources and loads being under compensation. They may be located as well for UPQC’s AC-side as DC-side. System works properly even if they switch their activity to work either as loads or generators. The UPQC can operate also as a buffer, which can store/share the in-load generated energy amongst other loads, or it can transmit this energy to the source. Therefore, in addition to performing the UPQC’s conventional compensation tasks, it can also serve as a local energy distribution center.

Dynamic Performance of Fuel Cell DG System with Voltage Quality Improvement Capability (Dept.E)

Dynamic Performance of Fuel Cell DG System with Voltage Quality Improvement Capability (Dept.E)

Fuzzy-PI Controller based Modulated Multilevel UPQC under Faulty Conditions

Background: This paper presents voltage and current quality improvement in high/medium electrical distribution system using modulated multilevel unified power quality conditioner (MM-UPQC). Nowadays, power quality is one of the major issues due to the increase in usage of more non-linear loads in agricultural, commercial, industrial sectors. The industrial loads produce large amount of harmonics and power imbalances, which cause various power quality related issues like poor power factor, voltage sag, voltage swell, voltage interruption etc. Methods: The prime objective of this work is to design fuzzy-PI based controller based modulated multilevel UPQC for mitigation of issues related to power quality under unsymmetrical fault conditions such as LG fault and LLG fault. Results: This paper uses Instantaneous Reactive Power Theory (IRP) for phase angle adjustment with PI-fuzzy controller scheme to generate accurate reference signal for shunt and series controller of MM-UPQC. The detailed comparative analysis results of simultaneous voltage sag, swell, harmonics compensation and unsymmetrical faults mitigation are presented alongwith the MATLAB/SIMULINK software. Conclusion: Total harmonic distortion analysis is tabulated with PI and fuzzy-PI controller based MM-UPQC for different operating conditions in 4.16 KV distribution system.

Assessment method of comprehensive energy saving potential of distribution network considering source-load power uncertainty

Abstract The comprehensive energy-saving potential evaluation method of the energy-saving schemes of a distribution network considering the power uncertainty of source and load is studied in this paper. The K-means clustering method is firstly employed to extract typical scenarios of distribution network, and the forward-push back method is used to calculate the power flow in typical scenarios, then energy-saving reconstruction schemes are formulated according to the power flow calculation results. A comprehensive energy saving potential evaluation index system that consists the improvement rate of network loss, line loss rate, transformer loss rate, annual electricity saving cost, annual equipment investment cost, annual maintenance cost and voltage quality improvement rate is built, and the comprehensive evaluation method based on DEMATEL-ANP-TOPSIS mixed decision model is used to evaluate the comprehensive energy-saving potential of the energy-saving reconstruction schemes regarding the index system. Finally, the optimal reconstruction scheme is selected based on the evaluation results of energy saving potential in multiple scenarios. The effectiveness of the proposed method is verified by an example in IEEE-33 node distribution network.

Power Quality of Electrical Distribution Systems Considering PVs, EVs and DSM

This paper investigates the effect of photovoltaic panels (PVs) and electric vehicles (EVs) on power quality of electrical distribution systems, while proposing an approach of demand-side management (DSM). Electricity generation of PVs is estimated based on technical parameters and weather data, whereas electricity consumption of EVs is evaluated using travel data of conventional cars. Calculations of three-phase power flow are developed in this study to assess the impact of PVs and EVs on voltage magnitude and voltage unbalance of residential grids. Simulation results of different case studies show that additional power generation of PVs increases voltage magnitude. However, uncoordinated electricity consumption of charging EVs degrades voltage unbalance. Therefore, a strategy of DSM is proposed to coordinate EV charging using deterministic programming, while considering historical data of system components. The proposed scheme of DSM is able to improve voltage quality by re-scheduling EV consumption in line with PV generation, postponing upgrading requirements of power grids.

Deployment of a Resistive Superconducting Fault Current Limiter for Improvement of Voltage Quality and Transient Recovery Voltage

This article presents a theoretical investigation of a resistive superconducting fault current limiter (R-SFCL) operating in a medium-voltage network. The considered power system presents a high level of fault current as well as a high transient recovery voltage. The simulation result shows that the R-SFCL not only limits the fault current to a desirable value, but also improves transient recovery voltage of circuit breakers by eliminating high-order harmonics generated by the opening of the circuit breaker.

Comparative analysis of fuzzy-PI and hybrid fuzzy-multi-layer perceptron network-based UPQC for voltage and current quality improvement

Uninterrupted power supply delivered to the customers, maintaining power factor, frequency and voltage within permissible limits with good shape close to ideal format, is the highest priority for power engineers. Some power quality issues like sag/swell and harmonics depreciate the standard of the power distribution network and power quality enhancement in power distribution system increases the performance efficiency and life of the equipment. The little enhancement in voltage and current quality makes a significant increase in the performance and life of the equipment. One FACTS controllers like UPQC delivers a solution to nullify the power quality issues and this paper presents a multi-level UPQC for power quality augmentation. The proposed control scheme uses a multi-layer perceptron neural network and weights are updated by the fuzzy logic to generate a reference signal. Control of UPQC makes power quality issues to be resolved effectively under fault conditions and this paper presents the comparative analysis of PI, fuzzy-controlled UPQC with hybrid fuzzy-multi-layer perceptron network (MLPN)-based control scheme for power quality improvement using MATLAB/SIMULINK software. The obtained results proved that fuzzy-MLPN UPQC compensated voltage sag/swell, harmonics, unsymmetrical LG and LLG faults voltage and current imbalance in the power distribution system.

Model Predictive Control of Grid-Connected Wind Energy Conversion System

ABSTRACT Wind power technology can contribute to the distribution system by regulating its active power output to enhance the system reliability. Additionally, it could be economically beneficial to improve voltage quality as well as load sharing with generation at various times, avoiding load shedding and risk of potential blackouts. However, output power of the wind turbine system is variable in nature and it is difficult to export this power into the distribution system without having any appropriate control strategy. To address this issue, a model predictive control (MPC) strategy has been proposed to regulate the voltage of the feeder to balance sinusoid and for power flow control, a reference phase angle delta is generated which maintains power balance at grid terminal during wind and load variations. Effectiveness of the proposed control strategy is investigated using MATLAB/Simulink simulation studies and a hardware design of a single-phase distribution system using dSPACE platform.

Voltage quality improvement using statcom in grid connected wind turbines

Voltage Quality Improvement using Statcom in Grid Connected Wind Turbines - written by Le Viet Tien , Vu Anh Tuan , Pham Ngoc Hung published on 2020/05/30 download full article with reference data and citations

A multilevel UPQC for voltage and current quality improvement in distribution system

Unified Power Quality Conditioner (UPQC) is substantial power conditioner in power system to filter the power system parameters with an objective to improve the quality of power delivered to the customers/utility point. This paper presents a multi-level UPQC to enhance the quality in power distribution system. The series and shunt controllers of UPQC gives out five leveled output which is further filtered to feed compensating signals to improve voltage and current profiles in power distribution system. Series and shunt controllers of UPQC are structured with cascaded H-Bridge (CHB) topology to deliver compensating signals. Two separate control strategies are employed to regulate the power switches of 5-level CHB series and shunt controllers of UPQC. Sag and swell in source voltage and harmonics in source current are strained with UPQC. The proposed system is developed and results are obtained using MATLAB/SIMULINK software.

A review on voltage control for distribution systems with large-scale distributed photovoltaic power integration

In order to solve the problems of voltage wide-range fluctuations and over-limitation after large-scale distributed photovoltaic (DPV) integrated into distribution networks, this paper conducts a comprehensive and detailed analysis of voltage control strategy by summarizing existing voltage control technology and experience at home and abroad. The technical points and a comprehensive comparison from the perspectives of active power curtailment (APC), reactive power control (RPC) and active-reactive power coordination control (A/RC) are made. Through comparative analysis, it is found that adopting active-reactive power coordination control is a key measure to effectively improve voltage quality and increase the PV hosting capacity of distribution networks. The optimization of the control strategy can effectively improve the friendliness of large-scale PV system integration. The method and control strategy can provide a theoretical basis and practical reference for voltage management of distribution networks with high penetration PV integration.

Study on the Influence of Large-Scale Wind Power Connecting to Power Grid on Voltage Quality Control

As a kind of clean renewable energy, wind power has important application value in the power generation industry. Wind power grid-connected has become one of the important development trends of new energy power generation. Based on large-scale wind power projects, in-depth research on the control of voltage quality in the paper is conducted by large-scale wind power grids. The influence of wind power generation on power quality of power grid is analyzed, and the problems of voltage fluctuation, flicker and harmonics are taken as research objects. Voltage fluctuation and flicker suppression techniques, and power harmonic suppression techniques have been studied as control methods for improving voltage quality. The experimental results prove that the research content of the paper has a good application effect, and it guarantees the voltage quality control for large-scale wind power access to the power grid.

Voltage Quality Improvement using a Series Connected Photovoltaic Distributed Generator System

Voltage Quality Improvement using a Series Connected Photovoltaic Distributed Generator System

Voltage Quality and Power Factor Improvement in Smart Grids Using Controlled DG Units

The increased penetration of renewable energy sources in the electrical grid, due to the rapid increase of power demand and the need of diverse energy sources, has made distributed generation (DG) units an essential part of the modern electrical grid. The integration of many DG units in smart grids requires control and coordination between them, and the grid to maximize the benefits of the DG units. Smart grids and modern electronic devices require high standards of power quality, especially voltage quality. In this paper, a new methodology is presented to improve the voltage quality and power factor in smart grids. This method depends on using voltage variation and admittance values as inputs of a controller that controls the reactive power generation in all DG units. The results show that the controller is efficient in improving the voltage quality and power factor. Real data from an electrical network have been used in the simulation model in MATLAB Simulink to test the new approach.

Investigation of distributed generation units placement and sizing based on voltage stability condition indicator (VSCI)

Voltage instability in power distribution systems can result in voltage collapse throughout the grid. Today, with the advanced of power generation technology from renewable sources, concerns of utility companies are much being focused on the stability of the grid when there is an integration of distributed generation (DG) in the system. This paper presents a study on DG units placement and sizing in a radial distribution network by using a pre-developed index called Voltage Stability Condition Index (VSCI). In this paper, VSCI is used to determine DG placement candidates, while the value of power losses is used to identify the best DG placement. The proposed method is tested on a standard 33-bus radial distribution network and compared with existing Ettehadi and Aman methods. The effectiveness of the method is presented in terms of reduction in power system losses, maximization of system loadability and voltage quality improvement. Results show that VSCI can be utilized as the voltage stability indicator for DG placement in radial distribution power system. The integration of DG is found to improve voltage stability by increasing the system loadability and reducing the power losses of the network.

Power Quality Services Provided by Virtually Synchronous FACTS

The variable and unpredictable behavior of renewable energies impacts the performance of power systems negatively, threatening their stability and hindering their efficient operation. Flexible ac transmission systems (FACTS) devices are able to emulate the connection of parallel and series impedances in the transmission system, which improves the regulation of power systems with a high share of renewables, avoiding congestions, enhancing their response in front of contingencies and, in summary, increasing their utilization and reliability. Proper control of voltage and current under distorted and unbalanced transient grid conditions is one of the most critical issues in the control of FACTS devices to emulate such apparent impedances. This paper describes how the synchronous power controller (SPC) can be used to implement virtually synchronous FACTS. It presents the SPC functionalities, emphasizing in particular the importance of virtual admittance emulation by FACTS devices in order to control transient unbalanced currents during faults and attenuate harmonics. Finally, the results demonstrate the effectiveness of SPC-based FACTS devices in improving power quality of electrical networks. This is a result of their contribution to voltage balancing at point of connection during asymmetrical faults and the improvement of grid voltage quality by controlling harmonics flow.

Constrained Modulated Model-Predictive Control of an LC-Filtered Voltage-Source Converter

This paper proposes a constrained modulated model-predictive control (M $^{2}$ PC) scheme for an LC -filtered voltage-source converter (VSC). To tackle the coupling effects of the state variables in a second-order LC filter, a dual-objective cost function (CF) is used to explicitly track both capacitor voltage and inductor current references, which can achieve an improved voltage quality. To handle the state and control input constraints of VSCs, a constrained M $^{2}$ PC scheme is proposed with an “online post-correction” constraint-handling technique. First, the unconstrained optimal voltage vector (OVV) is derived. It is generated by seeking the minimum analytical solution of the CF offline, simplifying the online implementation. Then, an “online post-correction” strategy is employed by reconsidering the constraints to correct the precalculated OVV online, which guarantees the future states within the allowed range. Finally, the corrected OVV is synthesized by the space vector modulation, resulting in a fixed switching frequency and low harmonics. Compared with the typical constrained model-predictive control, the presented scheme has the advantages of improved steady-state performance, flexible constraint-handling ability, and lower computational cost. Additionally, design procedures for weighting factor selection in the CF are given. Comparative experiments are investigated to verify the presented control strategy.

Model Predictive Voltage and Power Control of Islanded PV-Battery Microgrids With Washout-Filter-Based Power Sharing Strategy

This paper proposes a new control strategy of microgrids for the improved voltage quality. In the existing control techniques, the droop control is commonly adopted as a decentralized power sharing method at the cost of voltage deviations. Besides, the conventional cascaded control featuring relatively slow dynamic response shows difficulties in handling the fluctuation of renewable energy outputs, leading to further voltage quality deterioration. In this paper, an advanced model predictive power control strategy by considering the battery constraints is proposed for the bidirectional dc–dc converters to smooth the solar photovoltaic (PV) outputs and stabilize the dc-bus voltages. A model predictive voltage control scheme taking into account the voltage changing trend is then developed to control the distributed inverters to improve the output ac voltages. Furthermore, a washout-filter-based power sharing approach with the plug-and-play capability is adopted to achieve a proper load sharing among parallel inverters and mitigate the voltage deviation. The proposed control strategy is numerically simulated in MATLAB/Simulink and experimentally verified by hardware-in-the-loop tests under the condition of fluctuating PV outputs and variable power demands. (This paper is accompanied by a video showing the hardware-in-the-loop test.)

An Optimal Compensation Method of Shunt Active Power Filters for System-Wide Voltage Quality Improvement

Conventional control strategy of a shunt active power filter (SAPF) for harmonic and unbalance mitigation is to locally compensate the harmonic and unbalance component of load current, which may not be economical enough for a multinode system with distributed nonlinear loads (NLLs) and unbalanced loads (UBLs). Actually the SAPF will influence voltage at neighboring nodes, therefore it is promising to optimize SAPF control method from a system perspective. For this purpose, first this paper analyzes the drawbacks of a local compensation method and proposes the optimization problem for the system-wide control of SAPF in a simple single-phase system. Next, the idea is extended to a complex multinode three-phase system, and a matrix model for harmonic and unbalance analysis is established. Finally, a matrix-based least square method is utilized to solve the optimization problem, thus a generalized SAPF optimal compensation method for system-wide voltage quality improvement is obtained. Based on the proposed method, a small amount of SAPFs can be scientifically utilized to improve the overall voltage quality of a multinode system with a large amount of distributed NLLs and UBLs, with fast response, good performance, and reduced cost. Simulations and experimental results are provided to verify the effectiveness of the proposed method.

Control strategy for improving voltage quality in residential power distribution network consisting of roof-top photovoltaic-wind hybrid systems, battery storage and electric vehicles

In this paper, a combined voltage control scheme is presented for improving the voltage profile, fluctuations, and imbalance of balanced and unbalanced residential distribution networks with a high penetration level (100% penetration level) of rooftop photovoltaic-wind turbine hybrid generation systems (PVWHSs) and electric vehicles (EVs). The combined control scheme includes both local and central control methods. Local controls in the inverter of EVs and PVWHSs of homes try to maintain their point of connection (POC) voltage within the acceptable range. Then the central controller does a complementary action for voltage improvement, by remotely controlling a battery energy storage (BES) and the network on-load tap changer (OLTC).The proposed control scheme is tested in DIgSILENT PowerFactory15.1.7 environment based on the weather and daily load data (wind speed, solar radiation, temperature, active and reactive power consumption of residential homes) during a year with a 1-min resolution in a three-phase four-wire network. The obtained results demonstrate the desired performance of the proposed scheme on voltage profile improvement, reducing voltage fluctuations, decreasing voltage imbalances of the phases and reduced number of tap operations, in the face of fast growth of distributed energy resources (DERs) penetration in the residential networks.