Voltage Stability Analysis of Grid-Connected Wind Farms with FACTS: Static and Dynamic Analysis

Recently, analysis of some major blackouts and failures of power system shows that voltage instability problem has been one of the main reasons of these disturbances and networks collapse. In this paper, a systematic approach to voltage stability analysis using various techniques for the IEEE 14-bus case study, is presented. Static analysis is used to analyze the voltage stability of the system under study, whilst the dynamic analysis is used to evaluate the performance of compensators. The static techniques used are Power Flow, V–P curve analysis, and Q–V modal analysis. In this study, Flexible Alternating Current Transmission system (FACTS) devices- namely, Static Synchronous Compensators (STATCOMs) and Static Var Compensators (SVCs) - are used as reactive power compensators, taking into account maintaining the violated voltage magnitudes of the weak buses within the acceptable limits defined in ANSI C84.1. Simulation results validate that both the STATCOMs and the SVCs can be effectively used to enhance the static voltage stability and increasing network loadability margin. Additionally, based on the dynamic analysis results, it has been shown that STATCOMs have superior performance, in dynamic voltage stability enhancement, compared to SVCs

A new method for power quality improvement

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.A new control method for active power filters in conjunction with a passive filter circuit are presented and analysed in this thesis. A new technique for load modelling is introduced in order to enable the design of compensators to improve the power factor and to reduce harmonic levels in electrical power systems. The principles of analysis, design, operation and control of the new circuit equipped with IGBTs are presented. This enables the compensation of rapidly changing loads and reactive power. A special circuit equipped with IGBTs is able to compensate for the reactive power and harmonic currents of different orders. The important aspect of the present work is based on the compensator control circuit for power factor correction and harmonic elimination, and its application. This new configuration improves the rating of the active power filter, reducing power losses in the switches compared to existing and newly developed active filters. Furthermore, it is very stable in operation and much faster by a factor of 20. The thesis also presents a detailed mathematical modelling of the proposed system with frequency and time domain equations. The frequency response of the proposed system is also discussed. This new proposal has been checked using a dedicated software simulation program, which was specifically developed for this purpose. An experimental set-up has been designed and implemented in order to apply the new method using IGBTs as well as some other devices. This thesis also presents a critical literature survey, which provides a critical overview of previous work relevant to the power quality improvement reactive power compensation and active filtering

Power quality improvement using passive shunt filter, TCR and TSC combination

Power system harmonics are a menace to electric power systems with disastrous consequences. The line current harmonics cause increase in losses, instability, and also voltage distortion. With the proliferation of the power electronics converters and increased use of magnetic, power lines have become highly polluted. Both passive and active filters have been used near harmonic producing loads or at the point of common coupling to block current harmonics. Shunt filters still dominate the harmonic compensation at medium/high voltage level, whereas active filters have been proclaimed for low/medium voltage ratings. With diverse applications involving reactive power together with harmonic compensation, passive filters are found suitable [41]. Passive filtering has been preferred for harmonic compensation in distribution systems due to low cost, simplicity, reliability, and control less operation [42]. The uncontrolled ac-dc converter suffers from operating problems of poor power factor, injection of harmonics into the ac mains, variations in dc link voltage of input ac supply, equipment overheating due to harmonic current absorption, voltage distortion due to the voltage drop caused by harmonic currents flowing through system impedances, interference on telephone and communication line etc. The circuit topologies such as passive filters, ac-dc converter, based improved power quality ac-dc converters are designed, modeled and implemented. The main emphasis of this investigation has been on a compactness of configurations, simplicity in control, reduction in rating of components, thus finally leading to saving in overall cost. Based on thesis considerations, a wide range of configurations of power quality mitigators are developed, which is expected to provide detailed exposure to design engineers to choose a particular configuration for a specific application under the given constraints of economy and desired performance. For bidirectional power flow applications, the current source converter is designed and simulated with R-L load. The necessary modeling and simulations are carried out in MATLAB environment using SIMULINK and power system block set toolboxes. The behavior of different configurations of passive tuned filters on power quality is studied. One of the way out to resolve the issue of reactive power would be using filters and TCR, TSC with combination in the power system. Installing a filter for nonlinear loads connected in power system would help in reducing the harmonic effect. The filters are widely used for reduction of harmonics. With the increase of nonlinear loads in the power system, more and more filters are required. The combinations of passive filters with TCR and TSC are also designed and analyzed to improve the power quality at ac mains. This scheme has resulted in improved power quality with overall reduced rating of passive components used in front end ac-dc converters with R-L load

An Evaluation of Quality Improvement Methods Regarding Output Power of Wind Plants` Inverters

Today, with respect to the problems derived from non-renewable energy such as environment pollution, increasingly growth of fossil fuels` costs and the process of running out of sources; using renewable energies has been highly considered. Meanwhile, wind energy has widely been utilized. Integrating wind energy within power systems minimizes their effects on environment while connecting wind generation systems within power systems causes technical challenges such as the problems related to power quality, voltage regulation and sustainability where power quality is of highest importance. The present study attempts to evaluate the methods of improving inventers` quality in wind plants. To this purpose, “Space vector pulse width modulation”, “using STATCOM” and “using UPQS” to improve power quality are discussed

A Practical Fast Acting Control Scheme For Fuzzy Logic-Based Voltage Stabilization Control

This paper presents a simplified control model for stabilizing a load voltage using a switched reactor in parallel with a fixed capacitor of static VAR compensator. Two IGBT’s are used to control the reactance of the switched reactor. A uniform pulse width modulation is used for controlling the two switches. The compensator has a simple control circuit and structure. A complete modeling and numerical simulation for the proposed systems is presented. A high speed Digital Signal Processor is used for implementing proportional-integral (PI) and fuzzy load voltage controllers. Experimental results indicate the superiority of fuzzy logic control over the conventional proportional-integral control method. Simulation results are reported and proved to be in good agreement with the relevant experimental results

STATCOM Controller (Design and Assessment) for Transmission and Distribution System Problems

Due to immense increase in needs of human being, the power generation system encounters a deficiency of key energy sources as a result the demand is increasing day by day without an increase in alternative generation resources and transmission line capability. The constantly increase of electrical power        demands and loads, especially non-linear loads making the power system network become more        complicate to operate and the system becomes unstable with large power flows without proper control and operation. The advancement in power system with time have brings new challenges and sometimes it is difficult to operate system in stable condition due to complex    system network. One of the invention of power electronics is FACTS technology. FACTS (Flexible Alternating Current Transmission Systems) devices are based on power electronics and other dynamic controllers that provide control of one or more AC transmission system parameters to upgrade the controllability and to increase power transfer capability. One way to improve the power system control is by applying FACTS controllers such as D-STATCOM (Distribution Static Synchronous Compensator) which can be introduced to the power    system to regulate terminal voltage and to improve power factor of system.A comprehensive D-STATCOM controller is to be established which when will be introduced in the    power system will eliminate the voltage fluctuations and improve power stability. A test power system is    being designed in MATLAB Sim Power System with non-linear load and wind energy source as          renewable source and then the systems is analyzed with and without the D-STATCOM controller and both the result are being compared to check the performance of the designed D-STATCOM Controller. Keywords: Unified Power Flow Controller (UPFC), Distribution Static Compensator (D-STATCOM), Static Synchronous Series Compensator (SSSC

Application of Static Synchronous Compensator (STATCOM) in Improving Power System Performance: A Case Study of The Nigeria 330 KV Electricity Grid

Slow response of the conventional traditional methods for improving power system performance creates the need for adoption of advanced control technologies such as Flexible Alternating Current Transmission System (FACTS) with fast response and low cost for  stabilizing electricity grid power and voltage. In this work, we examined the effect of application of Static Synchronous Compensator (STATCOM), a FACTS controller on the performance of the Nigeria 330 kV, 28-bus power system. The conventional and modified Newton-Raphson-based power flow equations describing the steady state conditions before and after compensation was made to the system were presented. Solutions to the developed equations were obtained using Matlab software (Version 7.9.0.529 ‘R2009b’). The results from the analysis showed that before the application of  STATCOM, five (5) of the twenty eight ( 28) buses of the sample system have their voltage magnitudes fell outside the statutory limit of 0.95 Vi 1.05 p.u, which were improved to 1.0 p.u. each at inclusion of STATCOM. Similarly, the total system active power loss was reduced by 5.88% from 98.21 to 92.44MW.  Evidence from this finding is that STATCOM application on the Nigeria electricity grid will stabilise the system’s voltage and reduce the overall transmission active power loss thereby releasing spare capacities for more consumers.http://dx.doi.org/10.4314/njt.v34i3.2

Analysis of Power Quality Problems on Nigerian 330 kV Power System Using Statcom with Voltage Sensitivity Index

Transmission system is the transportation of electrical energy from generating stations to load centers. However, increase usage of non-linear loads from the consumers has led to electrical Power Quality (PQ) problems which have negative impacts on the operation of the power system especially Nigerian power system. This research analyzed the PQ problem on Nigerian 330 kV power system. Newton-Raphson (NR) iterative method was used to performed load flow analysis on Nigerian 28-bus transmission systems. Then power injection model of the Static Synchronous Compensator (STATCOM) was incorporated to modify the NR mathematical model. The suitable placement for the STATCOM in the system was determined using Voltage Sensitivity Index (VSI) and simulation was done in MATLAB/SIMULINK. The results showed that, the suitable placements of STATCOM controller in the power system were buses 5, 8, 12 and 16. The corresponding STATCOM reactive power, sag voltage and sag duration for buses 5, 8, 12 and 16 were 72.56 MVar, 0.77454 p.u, 0.7336s; 65.35 Mvar, 0.7464 p.u,  0.7419 s; 50.86 Mvar, 0.7615 p.u, 0.6512 s and  53.75 MVar, 0.7442 p.u. 0.5972 s, respectively. Therefore, the results have established the importance of STATCOM with VSI in obtaining suitable solution for PQ problems on electrical power system. Keywords: Transmission System, Electrical Energy, Non-linear Load, Power Quality, Newton-Raphson, STATCOM, Voltage Stability Index. DOI: 10.7176/ISDE/12-6-03 Publication date:October 31st 2022