Power System’s Voltage Stability Improvement Using Static Var Compensator

In alternating current systems, voltage fluctuation is a common phenomenon. Most of the voltage fluctuation problems result from the changes in the system’s reactive power resulting from excessive supply or consumption of reactive power by the elements of the system and the variation in the consumers’ loads. In this paper, the effect of Static Var Compensator (SVC) in stabilizing power system’s voltage through effective reactive power compensation was investigated. Power flow equations involving voltage drop with/without SVC were developed. SVC modeling equations were also developed and used to determine its parameters. Based on the SVC parameters, SIMULINK blocks were used to implement the phase controlled Thyristor–Controlled-Reactor Fixed-Capacitor (TCR-FC) SVC. The Nigerian 28-bus power system used for the study was also modeled using SIMULINK/MATLAB. The 28-bus system was first simulated without SVC and then with two SVCs located at different buses to obtain the bus voltages in both cases. From the bus voltages the total voltage drops for the system with and without SVC were estimated and compared. The compared results clearly showed that, the system’s voltage drop was reduced by 33.78% indicating a significant improvement in the system’s voltage stability when SVCs were applied

Harmonic Impact in Induction Generator Voltage Using Thyristor Control Reactor

As commonly known that theload fluctuations that have been performed on an induction motor operated as an induction generator (IG) triggers unstable induced voltage and frequency. Asthe result, the load that receiving the power quality is not running properly and the efficiency is low. The problems that have beenmitigated in this research in such way is the stability of the voltage that generated by IG due to fluctuating loading, and the harmonics can be damped by single tuned due to the work of thyristors and non-linear loads. The used method is the Ziegler-Nichols method by measuring and testing the design of prototype to get the best performance in stabilizing the voltage by using thyristor control reactor (TCR). The results showed that the induced generator with single tuned filter and TCR to nonlinear load variation at 1618 RPM is maintained stably for the voltage and frequency. Although, 3rd order harmonics of voltage and current that has been tuned can be dampedby using THDI 8.36%. Furthermore, it can be said that the response that generated by voltage control system using proportionalintegral (PI) control in 1kW-4 poles three-phase IG with additional and reductionalload generated a stable response

Online Control of Modular Active Power Line Conditioner to Improve Performance of Smart Grid

This thesis is explored the detrimental effects of nonlinear loads in distribution systems and investigated the performances of shunt FACTS devices to overcome these problems with the following main contribution: APLC is an advanced shunt active filter which can mitigate the fundamental voltage harmonic of entire network and limit the THDv and individual harmonic distortion of the entire network below 5% and 3%, respectively, as recommended by most standards such as the IEEE-519

IMPROVING PERFORMANCE OF TRANSMISSION NETWORKS USING FACTS THROUGH CONTINUATION POWER FLOW METHOD

Over the past 50 years, modern electrical systems have become more complex, as they overrun the geographical boundaries of neighboring countries. The problem is that the power system faces many challenges, because it is exposed to difficult operating conditions. The phenomenon of voltage instability is the most frequent phenomenon, and this can lead to the collapse of the power system. To avoid power outages in the system (especially in blackout situations), the power system must be analyzed in order to maintain voltage stability in the expected difficult operating conditions. The main objective is to determine the maximum load capacity of the system and the causes of voltage instability. The voltage instability problem is related to the nature of nonlinear loads, so different load characteristics must be taken into consideration when analyzing voltage stability. This study aims to discover the maximum load capacity required by using the continuous power flow method (CPF) in the studied network. Then, the performance of this network using a Flexible Alternating Current Transmission System (FACTS) will be utilized. FACTS systems present a promising solution in improving the voltage stability by improving the power transmission capacity and controllability of the parameters of the existing power networks. This study will be conducted on a reference network platform under normal working conditions, then installation of one of the FACTS systems will show its effect on improving voltage stability. The continuous power flow method will be used to find PV curves, which in turn will help to determine the conditions of maximum loading while maintaining stability, and identify the bus bar with the smallest voltage, on which the flexible AC systems will be installed. The software environment MATLAB/PSAT will be used for modeling and simulation

Impact of intergrating teebus hydro power on the unbalanced distribution MV network

Small hydro power sources have been identified as one of the renewable energy technologies that the South African government is focusing on in order to generate more electricity from renewable/independent resources. Due to the low carbon output of most renewable energy technologies and the carbon intensive power generation technologies that are currently being used in South Africa e.g. Hydro, coal, gas, and etc. further pressure is increasing to incorporate cleaner forms of generation. In 2002 a study focusing on the hydropower potential was compiled providing an assessment according to conventional and unconventional possibilities for all the provinces. Nowadays, the power electricity demand is growing fast and one of the main tasks for power engineers is to generate electricity from renewable energy sources to overcome this increase in the energy consumption and at the same time reduce environmental impact of power generation. Eskom Distribution Eastern Cape Operating Unit (ECOU) was requested to investigate the feasibility of connecting a small hydro power scheme located in the Teebus area in the Eastern Cape. The Eastern Cape in particular, was identified as potentially the most productive area for small hydroelectric development in South Africa for both the grid connected and off grid applications. These network conditions are in contrast to the South African electricity network where long radial feeders with low X/R ratios and high resistance, spanning large geographic areas, give rise to low voltages on the network. Practical simulation networks have been used to test the conditions set out in the South African Grid Code/NERSA standard and to test the impact of connecting small hydro generation onto the unbalanced distribution network. These networks are representative of various real case scenarios of the South African distribution network. Most of the findings from the simulations were consistent with what was expected when comparing with other literatures. From the simulation results it was seen that the performance of the variable speed generators were superior to that of the fixed speed generators during transient conditions. It was also seen that the weakness of the network had a negative effect on the stability of the system. It is also noted that the stability studies are a necessity when connecting the generators to a network and that each case should be reviewed individually. The fundamental cause of voltage instability is identified as incapability of combined distribution and generation system to meet excessive load demand in either real power or reactive power form

Using sigmoid functions for representing limits of generators and static Var compensators and their impact on the voltage stability study

This work presents new equipment’s representation methodologies in the steadystate power flow analysis and their impacts on the voltage stability of electrical power systems. With special focus on system’s voltage collapse scenario, characterized by a stability to instability transition, the traditional power flow method is reformulated with the introduction of smooth functions. As an option to introduce the desired smoothness, it is opted to incorporate the sigmoid function into the power flow formulation. The sigmoid function can be implemented within the traditional Newton-Raphson power flow formulation in the modeling of various control equipments. For the purpose of this work, it will be proposed new modelings for generators and Static VAr Compensators (SVCs). On account of being able to actively participate in voltage regulation, by means of controling reactive power injection, absorption and flow, these equipments received an exceptional attention. In order to analyze the condition of voltage collapse, power systems are stressed with gradual increases in generation and load. The continuous power flow tool is, therefore, applied, considering equipment’s limits and saturation characteristics under study. On a general point of view, the voltage collapse is considered as a power system’s point of maximum loadability, on the threshold of voltage stability. In a mathematical point of view, however, the voltage collapse is characterized as a point where a bifurcation occurs. Since power flow solves a system of nonlinear equations, and the continuous power flow determines a sequence of nonlinear equations solutions, bifurcations can be present throughout power flow analysis and simulations. Hence, several types of bifurcations can be observed, being characterized by dierent mathematical conditions. The use of sigmoid function in the modeling of control equipment proposes a new condition of voltage stability for electrical systems. The bifurcations found within the system, that once may have had dierent characteristics, now have the same common characteristic. This condition is translated as an advantage for voltage stability of electrical power systems in terms of easily identification of critical scenarios, which are responsible for admitting collapse. All propositions were tested by means of several simulations on dierent test-systems. A Python-based program was developed and the result simulations were validated by CEPEL’s (Electric Energy Research Center) production-grade academic version software.Este trabalho apresenta novas metodologias de representação de equipamentos na análise de fluxo de potência em regime permanente e seus impactos na estabilidade de tensão de sistemas elétricos de potência. Com foco especial no cenário de colapso de tensão do sistema, caracterizado por uma transição de estabilidade para instabilidade, o método tradicional de fluxo de potência é reformulado com a introdução de funções suaves. Como opção para introduzir a desejada suavidade, optou-se por incorporar a função sigmoide na formulação do fluxo de potência. A função sigmoide pode ser implementada dentro da formulação tradicional de fluxo de potência de Newton-Raphson na modelagem de vários equipamentos de controle. Para o propósito deste trabalho, serão propostas novas modelagens para geradores e Compensadores Estáticos de Potência Reativa (CERs). Por poderem participar ativamente da regulação de tensão, por meio do controle de injeção, absorção e fluxo de potência reativa, esses equipamentos receberam uma atenção excepcional. Para analisar a condição de colapso de tensão, os sistemas de potência são estressados com aumentos graduais em geração e demanda. A ferramenta de fluxo de potência continuado é, portanto, aplicada, considerando as características de limite e saturação dos equipamentos em estudo. De um ponto de vista geral, o colapso de tensão é considerado como um ponto de carga máxima do sistema de potência, no limiar da estabilidade de tensão. Do ponto de vista matemático, porém, o colapso de tensão é caracterizado como um ponto onde ocorre uma bifurcação. Como o fluxo de potência resolve um sistema de equações não lineares, e o fluxo de potência contínuo determina uma sequência de soluções de equações não lineares, as bifurcações podem estar presentes em análises e simulações de fluxo de potência. Assim, vários tipos de bifurcações podem ser observados, sendo caracterizadas por diferentes condições matemáticas. A utilização da função sigmoide na modelagem de equipamentos de controle propõe uma nova condição de estabilidade de tensão para sistemas elétricos. As bifurcações encontradas dentro do sistema, que antes poderiam ter características diferentes, agora têm uma mesma característica comum. Esta condição se traduz como uma vantagem para a estabilidade de tensão dos sistemas elétricos de potência em termos de facilidade na identificação de cenários críticos, responsáveis por admitir o colapso. Todas as proposições foram testadas por meio de várias simulações em diferentes sistemas-teste. Um programa em Python foi desenvolvido e as simulações dos resultados foram validadas pela versão acadêmica do software do CEPEL (Centro de Pesquisas em Energia Elétrica)

Modular Multilevel Cascaded Flying Capacitor STATCOM for Balanced and Unbalanced Load Compensation

Voltage and current unbalance are major problems in distribution networks, particularly with the integration of distributed generation systems. One way of mitigating these issues is by injecting negative sequence current into the distribution network using a Static Synchronous Compensator (STATCOM) which normally also regulates the voltage and power factor. The benefits of modularity and scalability offered by Modular Multilevel Cascaded Converters (MMCC) make them suitable for STATCOM application. A number of different types of MMCC may be used, classified according to the sub-module circuit topology used. Their performance features and operational ranges for unbalanced load compensation are evaluated and quantified in this research. This thesis investigates the use of both single star and single delta configured five-level Flying Capacitor (FC) converter MMCC based STATCOMs for unbalanced load compensation. A detailed study is carried out to compare this type of sub-module with several other types namely: half bridge, 3-L H-bridge and 3-L FC half bridge, and reveals the one best suited to STATCOM operation. With the choice of 5-L FC H-bridge as the sub-module for STATCOM operation, a detailed investigation is also performed to decide which pulse width modulation technique is the best. This was based on the assessment of total harmonic distortion, power loss, sub-module switch utilization and natural balancing of inner flying capacitors. Two new modulation techniques of swapped-carrier PWM (SC-PWM) along with phase disposed and phase shifted PWM (PS-PWM) are analyzed under these four performance metrics. A novel contribution of this research is the development of a new space vector modulation technique using an overlapping hexagon technique. This space vector strategy offers benefits of eliminating control complexity and improving waveform quality, unlike the case of multilevel space vector technique. The simulation and experimental results show that this method provides superior performance and is applicable for other MMCC sub-modules. Another contribution is the analysis and quantification of operating ranges of both single star and delta MMCCs in rating the cluster dc-link voltage (star) and current (delta) for unbalanced load compensation. A novel method of extending the operating capabilities of both configurations uses a third harmonic injection method. An experimental investigation validates the operating range extension compared to the pure sinusoidal zero sequence voltage and current injection. Also, the superiority of the single delta configured MMCC for unbalanced loading compensation is validated