جستجوی مقالات مرتبط با کلیدواژه « voltage stability » در نشریات گروه « برق »

This paper proposes a new fuzzy control for photovoltaic static compensator (PV-STATCOM) system in order to improve voltage stability. The task of proposed system is the dynamic voltage control of a solar PV system connected to load bus in different operating modes as STATCOM and/or PV active power generation. In this strategy, in case of perturbation, the proposed fuzzy controller by detecting it and considering the severity of disturbance, when there is no or insufficient remaining capacity of the inverter to compensate the reactive power, stops the active power production of the PV solar system, and then the entire capacity of the inverter is used as a STATCOM to regulate the voltage at the load bus. Then, after fixing the problem, the system returns to the active power generation mode as before. To evaluate the performance of the proposed fuzzy controller, different modes are simulated with EMTDC/PSCAD software to prove the ability of the controller to improve the stability of the power system. The results confirm that the PV-STATCOM with the proposed controller can improve the dynamic performance of the system.

Renewable energy sources can provide a suitable solution to meet the increasing load demand. Therefore, based on the objective functions and according to the structure of the distribution network, and the variety of solar radiation intensity, ambient temperature, and wind speed in different network nodes, the location, and capacity of renewable sources should be determined optimally. As in the distribution networks, the voltage stability of the lines and the voltage profile of the buses are usually not in the desired condition, so improving the voltage stability can be considered as one of the main goals in the allocation and capacity determination of renewable sources. For this purpose, in this paper, the optimal location and capacity of hybrid distributed generation sources including photovoltaic power plants, wind farms, diesel generators, and energy storage systems are done. The objective functions include reducing the probability of loss of power supply, minimizing the total net present costs, and improving the network voltage stability. For this purpose, based on annual information of radiation intensity, wind speed, temperature, and profile of residential, commercial, and industrial loads, optimal allocation and capacity determination of hybrid distributed generation are done in IEEE 33-bus radial distribution system using multi-objective genetic algorithm.

Today, power systems are operated close to their stability limits for economic reasons. On the other hand, with the occurrence of outage, the stability of the system has a problem that there are various solutions to compensate. The last and safest way to control and maintain system stability is load shedding. In this paper, under voltage load shedding is presented considering voltage dependent feeders load and also using the improved discrete particle swarm optimization algorithm (IDPSO). Since the load model is particular importance in the real load analysis, the decisions will be applied by considering voltage dependent load modeling. To ensure proper operation, the proposed method has been implemented using MATLAB software on the IEEE 30-bus test system by considering related constraints. For this purpose, two critical loads for the test system are considered and the results are examined. The results show that the proposed method provides the best location and amount of load shedding and indicates its effectiveness.

After reading the ATC concepts and static ATC procedures, In this paper, the methods for determining Dynamic ATC (DATC) are collected. In this paper, researchers, efforts to provide new methods for determining DATC power systems have been compiled and the merits and weaknesses of these methods are highlighted. Uncertainty in ATC calculations is discussed and important methods of transient stability and voltage stability have been investigated in DATC determination. At the end of the paper, the strengths and weaknesses of all methods for determining DATC are specified. In order to be able to provide faster and more precise methods in the future.

This paper proposes a new voltage stability assessment method based on vector analysis method. This index extraction process relies on measurements of active and reactive powers from connected buses to the generator buses. Therefore, a limit for beginning of voltage collapse is determined based on the maximum power transfer theory. On the other hand, when the system requires load shedding, a new voltage-frequency load shedding has been employed. This load shedding makes voltage and frequency stabilities be guaranteed via clustering of all loads as allowable and unallowable, and prioritizing allowable cases. Simulation results in DIGSILENT Power Factory software on IEEE-39 bus dynamic test system demonstrate the efficiency of proposed approach with respect to other methods.

Due to the development of electricity market in a sustainable and competitive way in most countries, investigating the ability to transfer power has increased dramatically. Also, the increasing consumption and the lacking expansion of the transmission network have left most components of the power system within their authorized limits, which reduces the efficiency. Therefore, determining the exact amount of available transfer capability (ATC) is crucial for planning, operating and controlling the power system. There are many ways to calculate the ATC. The algorithms are either fast but not precise or accurate but not fast enough. This paper provides a comprehensive review of the various methods for determining ATC in both static and dynamic methods. First, the concepts and definitions essential to a better understanding of ATC are presented then in two separate parts the, static methods and dynamic methods are examined. These studies show that simultaneously with the development of static methods, dynamic methods have been also developed. This paper is useful both for those who already work in this field and also those willing to enter the field.

Nowadays, distributed generation (DG) is widely used in power systems. However, the use of DGs has caused new challenges in different aspects of power system operation, one of which is the effect of DGs on the optimal load shedding. Load shedding is a remedial action triggered after disturbances such line tripping. In fact, due to the line outage, the power flowing through other lines will increase which may cause protection systems to operate to trip the overloaded lines and in severe cases result in the system collapse. In this paper, a general load shedding method is proposed to prohibit the system from moving toward collapsing and helping the system to restore in the presence of DGs. In the proposed method, firstly the most critical line whose outage leads to the minimum values of stability indices is determined. Then, after putting this line out of service, harmony search algorithm is used to find the minimum amount of load shedding as well as the optimal location of DGs so that the loadability of the system is maximized preventing the system to collapse. The efficacy of the proposed methodology is demonstrated through applying it on IEEE 14 and 30-bus systems using various scenarios.

This paper presents a modified method based on teaching learning based optimization algorithm to solve the problem of the single- and multi-objective optimal location of distributed generation units to cope up the load growth in the distribution network .Minimizing losses, voltage deviation, energy cost and improved voltage stability are the objective functions in this problem. Load growth in a system is a natural phenomenon. As the value of distribution system indices depend on load growth, any change in load causes changes in distribution system indices. Therefore, for assessing the current studies the level of validity and the adequacy of system in future, load growth in future are discussed. The proposed algorithm integrates an adaptive teaching factor, and a crossover and mutation strategy. In the proposed algorithm, an external repository is considered to save non-dominated (Pareto) solutions. Since the objective functions are not the same, a fuzzy clustering technique is used to select the best compromise solution from the repository. The proposed algorithm is tested on the 33-bus IEEE test system. To demonstrate the effectiveness of the proposed approach, simulation results are compared with the results obtained by other methods.

In recent years, methods for timely detection of areas close to voltage instability have been proposed, which, unlike conventional methods, have simpler and faster calculations based on the measurement of local voltage and current phases at bus or grid lines. But some of them do not work well in real networks, so in this article, we will compare the performance of two of these indices and finally show that the performance of the ZL / ZS index is better and more reliable than the Indicator index.

The distribution system establishes the relationship between the transmission system and the consumer and it is the closest part of the power system to the consumer. Due to increasing demand for electricity, environmental constraints and competition in the energy supply market, transmission and distribution systems often operate under heavy load conditions. Severe voltage drops, multiple blackouts and high losses are major problems in distribution networks. Reconfiguration is the simplest and least costly way to meet the above goals relatively. In this study, the Reconfiguration of distribution networks is presented as an optimization problem. An objective function including active power loss indices and voltage profiles is introduced. Various scenarios have been introduced to examine this approach. To solve this problem, the Imperialist Competition Optimization (ICA) algorithm is used in Matlab software environment. Simulation results on IEEE standard radial distribution systems 33, 69 and 118 show that optimizing the opening and closing position of the switches will greatly improve the performance of the distribution system.

Cascading failures and blackouts are the most significant threats for power system security. If the process of cascading failures proceeds by further line tripping, the system will face uncontrolled islanding. Establishing of uncontrolled islands with deficiency in active or reactive power balance is the main reasons for system blackouts.
Controlled islanding is an active and effective way of avoiding catastrophic wide area blackouts. It is usually considered as a constrained combinatorial optimization problem. However, the combinatorial explosion of the solution space that occurs for large power systems increases the complexity of this problem. This study proposes a controlled islanding algorithm using genetic algorithm to find a suitable islanding solution for preventing the initiation of wide area blackouts by un-damped electromechanical oscillations or voltage instability. The objective function used in this controlled islanding algorithm is the minimal power-flow disruption. In this study to improve voltage stability after separation, minimal active and reactive power disruption is considered.
The sole constraint applied to this solution is related to generator coherency. In the first step of the algorithm, the generator nodes are grouped using normalized spectral clustering, based on their dynamic models, to produce groups of coherent generators. In the second step of the algorithm, GA search for islanding solution that provides the minimum power-flow disruption while satisfying the constraint of coherent generator groups is determined by grouping all nodes. Simulation results, obtained using MATLAB and DigSilent software on the IEEE 39 bus test systems show that the proposed algorithm is efficient and have a well performance regarding voltage and transient stability when solving the controlled islanding problem. Also, results compared with spectral clustering algorithm that is newest and strongest research in this field.