A.H.M. Yatim

A study of maximum power point tracking algorithms for wind energy system

This paper reviews and studies the state-of the-art of available maximum power point tracking (MPPT) algorithms. Due to the nature of the wind that is instantaneously changing, hence, there is only one optimal generator speed is desirable at one time that ensures the maximum energy is harvested from the available wind. Therefore, it is essential to include a controller that is able to track the maximum peak regardless of any wind speed. The available maximum power point tracking (MPPT) algorithms can be classified according to the control variable, namely with and without sensor, and also the technique used to locate the maximum peak. A comparison has been made on the performance of the selected MPPT algorithms on the basis of various speed responses and the ability to achieve the maximum energy yield. The tracking performance is performed by simulating wind energy system using MATLAB/Simulink simulation package. Besides that, a brief and critical discussion is made on the differences of available MPPT algorithms for wind energy system. Finally, a conclusion is drawn.

Overcurrent Relays Coordination in Interconnected Networks Using Accurate Analytical Method and Based on Determination of Fault Critical Point

Overcurrent relays should be coordinated for different operation conditions in interconnected networks. In addition, the time interval should not reach under the predefined threshold for each pair of primary and backup relays for the faults occurring in the protection zone of the primary relay. An analytical approach is presented in this paper to calculate the impedance matrix of the network in fault condition in order to determine the critical fault point accurately. Overcurrent relays are coordinated by using the presented critical fault point instead of the close-in fault used in previous studies. Simulation results show the accuracy of the proposed method for overcurrent relays coordination in comparison with other methods.

Application of Hyper-Spherical Search algorithm for optimal energy resources dispatch in residential microgrids

Applying using Hyper-Spherical Search algorithm to the problem of optimal dispatching.Economic modeling of the residential energy system.Determining optimal dispatch strategy of different energy resources. This paper presents a residential hybrid thermal/electrical grid-connected home energy system (HES), including a fuel-cell with combined heat and power and a battery-based energy storage system. The minimum operation cost of this integrated energy system is achieved by proper scheduling of different energy resources, found by applying a new powerful optimization algorithm, the Hyper-Spherical Search (HSS) algorithm, to the systems scheduling problem. This is the first time that HSS is used to face the energy resource dispatch problem. The HSS has been only tested in mathematical problems in the previous study. The optimization procedure generates an efficient look-up table in which the powers generated by different energy resources are determined for all time intervals. The effect of different electricity tariffs for purchasing electricity from the main grid on the operation costs of the system is investigated. Moreover, a battery is properly dispatched in the energy system to decrease the operation costs. A real load demand is used in the simulation. The results of HSS are compared with the harmony search algorithm and the colonial competitive algorithm to show the power and effectiveness of HSS to find the optimal dispatch strategy of energy resources for the first time. This is the first time that HSS is compared with CCA. The results of this paper are expected to contribute to home energy systems and real projects.

Constant frequency torque and flux controllers for direct torque control of induction machines

This paper proposed a simple solution to the variable switching frequency and high torque ripple problems encountered in hysteresis-based DTC drives. The method replaces the hysteresis-based controllers with fixed switching controllers, which operate based on the comparison between the error signals and the triangular waveforms. Implementation of these controllers using digital circuits is highly suitable since they only require comparisons of waveforms rather than calculations of duty cycles or voltage vectors. Modeling and simulation of the DTC drives using these simple controllers are presented and the results show that they are capable of reducing the torque ripples significantly.

An online optimum-relation-based maximum power point tracking algorithm for wind energy conversion system

Due to the unpredictable nature of wind, determining the optimal generator speed necessary to extract the maximum available wind power at any wind speed is essential. Amongst the available MPPT algorithms, optimal-relation-based (ORB) method is considered the fastest in terms of tracking speed, however, this strategy requires knowledge of system parameters, which are difficult to be calculated and vary from one system to another. Another common and simple algorithm that does not need any prior knowledge of system parameters is the perturb and observe (P&O) method. However, this method has two drawbacks, which are slow response and incorrect directionality under rapid wind change. This paper proposes a new MPPT algorithm based on hybridization of the ORB and P&O methods. In the proposed algorithm, the P&O method is used as an initialization algorithm to search online for a maximum power point (MPP) of a local wind speed in order to extract the parameters needed to perform the ORB method. MATLAB/Simulink software is used to simulate the performance of the proposed MPPT algorithm.

Design of Power Stage and Controller for DC-DC Converter Systems Using PSPICE

A complete set of SPICE-compatible design equations for design buck converter system is developed in this paper. In this approach, the power stage and controller design equations are programmed in PSPICE. For this purpose, an option available in PSPICE called analog behavioral modeling (ABM) is used. In this manner, the parameter of power stage and the component values of the error amplifier can be easily obtained by means of PSPICE bias point analysis. The obtained parameters can be passed to other circuit models to perform frequency response and transient analysis. The methodology of development is presented in details. A design example is included to demonstrate the effectiveness of the proposed approach in designing DC-DC converter systems

Online dynamic security assessment of microgrids before intentional islanding occurrence

Abstract This paper presents a statistical learning-based method for security assessment of microgrids (MGs) in case of isolation from the main grid. Based on the stability criteria, the MG pre-islanding conditions are divided into secure and insecure regions. Critical system variables regarding the MG dynamic security are first selected via a feature selection procedure, known as minimum redundancy maximum relevance. An unsupervised learning method called pattern discovery method is then performed on the space of the critical features to extract the organization (patterns) among samples. Geometrically, the patterns are hyper-rectangles in the features space representing the system dynamic secure/insecure regions and can be effectively used for online MG security monitoring before islanding condition. Simulation results are carried out in the time domain, by using MATLAB, which demonstrate the effectiveness and accuracy of the proposed method in the MG security assessment.

Hybrid maximum power point tracking technique based on PSO and incremental conductance

This paper presents a control method proposed for power optimization in photovoltaic system. This is to ensure that power generated is maximized under different conditions. Due to partial shading conditions, the power-voltage characteristics exhibit multiple local maxima; one of such phenomena is the global maximum. Such conditions are very challenging for maximum power point tracking (MPPT) technique to locate the global maximum. Many tracking algorithms have been proposed for this purpose. One of the most commonly used techniques is the incremental conductance. In this paper, a hybrid MPPT technique combining particle swarm optimization and incremental conductance for photovoltaic system is proposed. Initially, the incremental conductance method is employed to locate the nearest local maximum; then, the PSO method is used to search for the global maximum point. The advantage of using the proposed hybrid method is that the searching area of the PSO is reduced, and hence, the time that is required for convergence greatly reduced. The excellent performance of the proposed method is verified by comparing it against the conventional PSO method using simulation model. The results show better response time of the proposed system.

Modeling and simulation of stand-alone fuel cell system for distributed generation application

Fuel cell (FC) is one of the most suitable candidates for distributed generation system either in standalone or grid connected mode. Due to the cleanness, modularity and higher potentiality, FC systems can be used in both single and hybrid systems for power generation. In this study a 26 kW standalone proton exchange membrane fuel cell (PEMFC) based energy system is developed using MATLAB/Simulink®. The PEMFC stack is modeled based on the mathematical equations and implemented using the Simulink blocks. Similarly the power converters are also modeled using the Simulink block sets. The PEMFC output DC voltage is stepped up using a boost DC-DC converter then fed to a PWM based inverter. The controller for DC-DC boost converter is a PI based single loop voltage controller. The inverter controller uses RMS feedback controller and LC filter. The AC output power is tested with resistive (R) and inductive (RL) loads. The dynamic performance of FC stack is also verified by applying step changes in both resistive and inductive loads. Simulation results shows that the PEMFC stack is capable of delivering the maximum output power with voltage and current ripple within tolerable range. Moreover, the AC output voltage, frequency are within the acceptable range.

A simulation study of hybrid wind-ultracapacitor energy conversion system

Wind energy conversion system (WECS) is controlled to capture the maximum available power upon the available wind speed to make the system economical and operates at optimized efficiency. The nature characteristic of wind generator is nonlinear which leads to variable power output generation. In addition, the demanded load power is subjected to a change due to any disturbances may happen in the load voltage or current. Therefore, it is essential to integrate the WECS with a suitable storage element to either, act as a source of compensating the inadequate in power, or act as a load to absorb the excess power generated by the wind generator. Although the AC rectified voltage of the wind generator is proportional to the wind speed which is variable, however, the DC-bus voltage is usually regulated by the bidirectional converter at a specified value. Hence, the output power of the system can be investigated by means of the output currents from the WECS and the ultracapacitor. This paper presents several different test scenarios of the proposed hybrid WECS-ultracapacitor simulated using MATLAB/Simulink software. It also highlights the important role of the ultracapacitor in ensuring a continuous power flow.