Power Quality Consideration for Off-Grid Renewable Energy Systems

Necessity of electricity access in remote area is the main reason for expanding decentralized energy system such as stand-alone power systems. The best electrical power supply must provide a constant magnitude and frequency voltage. Therefore, good power quality is an important factor for the reliable operation of electrical loads in a power system. However, the current drawn by most of electronic devices and non-linear loads are non-sinusoidal, which can result in a poor power quality, especially in off-grid power systems. Poor power quality is characterized by electrical disturbances such as transients, sags, swells, harmonics and even interruptions in the power supply. Off-grid power systems world- wide often struggle with system failures and equipment damage due to poor power quality. In this paper, MAT- LAB/Simulink is used to model and analyses power quality in an off-grid renewable energy system. The results show high voltage transient when the inductive loads were switched OFF. The voltage and current harmonics are also deter- mined and compared for various types of loads

Available transfer capability (ATC): a review

With the advanced development of electrical power markets, large amount of electric power is consumed and transacted which require, accurate determination of Available Transfer Capability (ATC) and broadcasting the ATC information to prevent and relieve transmission congestion effectively. In this paper existing deterministic and probabilistic methods for calculating ATC, are reviewed. Some suggestions for dealing with the technique challenges are given for the future research

Critical lines identification for ATC assessment in power system planning

Ability to evaluate the accurate available transfer capability (ATC) has important impact on the trade of energy in power marketing. The impact of the transmission element status of transmission path has a possibility to severely change the statistics of the ATC. The impact of the line outage is more significant among the other component outages. The ATC assessment requires N-1 security assessment under line outages scenarios. Moreover, an efficient contingency ranking method to determine critical lines has significant impact on the ATC computational time. In this paper, MW loss, MVAR loss and Load Margin Index are described to find the critical lines for computing the ATC under contingencies. These methods are tested on IEEE 118 bus system and the ATC based on Krylov algebraic method are calculated for each critical line. Based on ATC results calculated from these contingency ranking methods, the efficiency of these methods compare together

PID controller adjustment for MA-LFC by using imperialist competitive algorithm

In this paper a new evolutionary computing method based on Imperialist Competitive Algorithm (ICA) is used for tuning the elements of a PID controller which is applied in a Multi Area Load Frequency Control System (MA-LFC). If a large power imbalance is suddenly happened in a multi area power electric system, generation units and also consumer sides will be affected by the distortion in the energy balance between both two sides. This inequality is firstly handled by the kinetic energy of the system turning components, but, eventually, the frequency will change. Therefore, LFC is considered as one of the most challenging issues in power system control and operation. PID type controllers are conventional solutions for MA-LFC. The three parameters of the PID controllers have been adjusted traditionally. In this paper, a PID controller is applied for the MA-LFC problem and then its parts are modified by using ICA method. To validate the application of the technique, a multi area network with some uncertainties is provided. Finally the results of the ICAPID controller are compared with the ones of GA optimized controllers. The simulation results show the success and the validity of the ICA-PID controller in compare with the GA - PID controller

Wind farm reactive power optimization by using imperialist competitive algorithm

In this paper a new evolutionary computing method based on imperialist competitive algorithm (ICA) is used for optimization of the reactive power in a wind farm. The output power and also the reactive power of wind farms are not constant due to the oscillation in wind speed. Reactive power optimization is known as an efficient way to have an improvement in power quality and also to reduce power loss. The conventional optimization algorithms have some drawbacks, such as slow convergence and premature. ICA as one of the newest optimization algorithm could be applied in order to optimization of the reactive power and overcomes the difficulties which are coming from the traditional methods. In this paper, the reactive power consumption of a wind turbine is optimized by using (ICA) method. To illustrate the application of the method, a wind farm with some uncertainties is provided. Finally the results of the ICA method are compared with the one of conventional method. Results show that the proposed reactive power optimization method is simple and effective

Load Frequency Control for Hydropower Plants using PID Controller

Many development republics began to get rid of conventional energy and towards to use renewable energy like hydropower system, solar cells and wind turbines as soon as possible. Load Frequency Control (LFC) problem is coming to be the main topics for mentioning schemes due to not corresponding between main power system inputs such as change load demand and change in speed turbine settings. This paper illustrates a selftuning control of hydropower system that suggested and confirmed under Automatic Generation Control (AGC) in power scheme. The suggested power system involves one single area. The suggested self-tuning control system is employed in performing the automatic generation control for load frequency control request and compared it with conventional control structure. The power system dynamic modeling has regularly built in several essential parameters which have a significant influence According to frequency limitation. The main problem with all controllers is an exaggerated reaction to minor errors, producing the system to oscillate. The output response results for hydropower system obviously proved the benefit of using maximum load demand by tuning PID controller. Whereas, tuning PID controller has got properly more rapid output response and minimal overshoot

Linear optimization method by using a new iterative algorithm for available transfer capability (ATC)

Fast and accurate algorithms to compute Available Transfer Capabilities (ATC) are important for electricity markets. Most studies involved load flow based and contingencies that often can be performed in reasonable time with the use of linear methods. This paper presents a simple and accurate method for calculating ATC with a linear optimization method. Since the limitations of linear ATC calculations is the error produced by neglecting the nonlinear nature of real power flows. This paper presents Krylov Subspace methods that can reduce this error. By applying these methods for calculating ATC, the speed and the accuracy of them are calculated and compared to find the best one. All computations are tested on IEEE-30 bus system in MATLAB 7.1

Comparative analysis of ATC probabilistic methods

The price of power transfer between two areas is a key issue between buyers and sellers in the power market which is directly related to the ATC deal and security. ATC deal is computed by Deterministic methods and ATC security presented by probabilistic methods. Since the ATC is used for operation or planning of power system, ATC can be determined by Deterministic or Probabilistic methods. In this paper, existing probabilistic methods which could predict ATC for power system planning are reviewed and compared

Krylov subspace methods for available transfer capability margins calculations

Nowadays considering more accuracy and speed to compute Available Transfer Capabilities (ATC) are important for electricity markets. Most studies involved load flow based and contingencies that often can be performed in reasonable time with the use of linear methods. Since the limitations of linear ATC calculations is the error produced by neglecting the nonlinear nature of real power flows. This paper presents Krylov Subspace methods that can reduce this error. By applying these methods for calculating ATC, the speed and the accuracy of them are calculated and compared to find the best one. All computations are tested on IEEE-30 bus system in MATLAB 7.1