In this paper, a simple and novel control strategy for a stand-alone doubly fed induction generator (DFIG)-based wind turbine under combined unbalanced and non-linear loads is presented. These types of loads cause negative sequence and harmonics in the stator voltage and current, which leads to power and torque oscillation. As a solution, a new control strategy is presented in the load side converter (LSC) which compensates for the stator current and voltage, simultaneously. The instantaneous active and reactive power theory is used to extract all of the harmonic components of the stator current and voltage. Based on the presented papers, the main task of LSC is to compensate for the stator current. In our proposed method, the per-unit values of stator voltage harmonics are added to the LSC's reference signals. Because the resulted reference signals are sinusoidal, the proportional-resonant (PR) controller is used to track the sinusoidal references. Therefore, the stator voltage is compensated in addition to the stator current for all types of loads, and the rotor side converter is only required to control the voltage amplitude and frequency. The harmonic components are extracted by algebraic equations. So, the system has a fast dynamic response, which is suitable for practical implementation. To validate the presented control strategy, simulation and experimental implementation for a 5.5 kW DFIG are done in the paper.

Stand-alone operation of electrical power generators is of increasing interest, because of geographical or financial limitations and reliability issues. This paper presents a simple and innovative approach for sensor-less vector control of stand-alone Doubly Fed Induction generators (DFIG). Unlike grid-connected DFIG, accurate estimation of speed/position of the rotor is crucial for frequency control of stand-alone DFIG. As a new work, an open-loop flux and speed estimator have been developed for the DFIG application. The advantage of a developed speed/angle estimator is its independency of rotor current sensors, the feature that enhances system robustness. Such as other off-line observers, developed estimators are sensitive to machine parameters. To overcome this problem, particle-swarm-optimization has been practically implemented in a digital-signal-processor for parameter identification. Both simulation and experimental results prove the acceptable performance of the proposed approach, especially in preserving the amplitude and frequency of sinusoidal load voltage.

There are some special phenomena like longitudinal end effect, saturation effect, skin effect, edge effect, and half-filled slots which make the single-sided linear induction motor (SSLIM) analysis more complicated compared to its rotary counterparts. Finite element method (FEM) can be the best choice for complete modeling of SSLIM considering all phenomena. But it is not possible to include the non-linear magnetization curve of iron into the time-harmonic FEM analysis. Thus, this article proposes a 2-D time-harmonic FEM considering all phenomena as well as the non-linear magnetization characteristics of iron using appropriate approximation. In order to overcome the Lorentz method calculation error of vertical force caused by inherent discontinuity of magnetic field intensity at the boundaries of elements, a combined Lorentz-Maxwell method is presented. Validity of the methods and final results is proved by comparing the results with analytical results and experimental measurements.

Finite element method (FEM) is widely used in the modeling of electromagnetic systems and as a reliable method to verify analytical modeling of electromagnetic devices in design step. As the method is based on discretization of domains, the electromagnetic continuity conditions at the boundaries of elements should be confirmed. Electromagnetic continuity conditions in FEM modeling were investigated in this article. It was shown that the continuity of tangential component of magnetic field intensity is not guaranteed at the boundaries of elements. The inability of FEM to establish the continuity condition leads to some virtual surface current densities at the boundaries of adjacent elements which does not exist in reality. The existence of virtual surface currents is proved in an example. Then, with the help of a complicated example, it is shown that large number of elements and, consequently, the large number of boundaries between elements may cause great errors in FEM postprocess results, especially in calculating magnetic stored energy and electromagnetic forces acting on moving parts. It has been shown that it is very important to take into account the impact of these virtual current densities in energy conversion analysis by FEM.

In this paper, the speed tracking for permanent magnet synchronous motor (PMSM) in field oriented control (FOC) method is investigated using linear proportional-integral (PI) controller, sliding mode controller (SMC) and its advanced counterparts. The advanced SMCs considered in this paper are fuzzy SMC (FSMC) and sliding mode controller with time-varying switching gain (SMC+TG) which can effectively cope with chattering, an inherent harmful phenomenon in SMC. Regardless of all the works done to replace PI controller with SMC and its advanced counterparts, a thorough comparison of the PMSM drive behavior under mentioned controllers is still missing. This paper attempts to fill in this gap, by providing a fair and in-depth comparison of the PMSM drive operation by using PI and sliding mode speed controllers. In this paper, in order to design and provide a fair framework for comparison the performance and robustness of these four controllers a suitable cost function is defined to manage the performance effectively. Thus, based on this cost function a nonlinear optimization problem is defined. To solve the optimization problem and consequently derive the optimal values for the parameters of the controllers, particle swarm optimization (PSO) and grey wolf optimization (GWO) algorithms are employed. The performance and robustness of the PMSM drive using four optimal controllers are studied in the presence of different conditions and uncertainties. Numerical results demonstrate that SMC and its advanced counterparts cannot offer the superior behavior for all conditions and their superiority is less than it is often stated in the literature.

In recent years, Synchronous generator parameters identification has been taken into consideration in many studies. This article presents an approach for parameters identification of the nonlinear fourth-order dynamic model of a synchronous generator. Past researches have shown that some perturbations can easily be applied to a working generator. This leads us to a proper choice of input and outputs needed for identification. By applying step perturbation to the field voltage, as input, generator outputs including electrical power, rotor speed and stator current are measured and parameter of the generator has been estimated by making comparison between the estimated model outputs and the measured ones, using Particle Swarm Optimization (PSO). The result of the simulation shows how efficient this method is.

Eddy current is the origin of resistive loss in magnetic cores. In conventional method of eddy loss calculation, flux density is assumed to be distributed uniformly. However, the eddy-current forces the magnetic flux to flow through the skin of magnetic core, the effect that is called flux skin effect. For wave forms other than the sinusoidal form or for non-linear relationship between H and B, there is not analytical solution for the field equations. In such cases, magnetic field and the eddy-current equations must be solved by numerical methods such as finite-element method. Moreover, numerical modeling is helpful in estimating the eddy-current patterns that are used in non-destructive tests to detect the presence of any possible cracks. In order to achieve the flux distribution in the presence of the eddy current, the diffusion equation should be solved. This paper presents a new approach for finite-element analysis of 2-D diffusion equation. The solution is in time-domain, and the hysteresis behavior of ferromagnetic material is included in it. Analysis results show that skin effect has considerable influence on the eddy and hysteresis losses. Presented method has the capability of eddy-current analysis for any shape of cores, including hysteresis behavior.

Self-Excited Induction Generators (SEIG) are widely used in industries such as wind-turbines and mini hydro power plants. The stator side voltage of the SEIG can be controlled by adding an adjustable resistance connected to the rotor winding in series. The combination of a three-phase diode rectifier with a boost converter can provide a symmetric three-phase controlled resistance. So, the controlled resistance is connected to the rotor windings, and the stator voltage is maintained at the reference value by adjusting the rotor resistance. However, the parameters of system vary due to aging and the operation temperature of the system in different seasons. Besides, the SEIG is usually designed to work at stand-alone mode. Therefore, an adaptive loop is designed in the control planned to select the parameters of the PI-controller based on the operation point and system parameters.

A new topology of multi-string single-stage unidirectional Inverter with high frequency AC-Link and soft switching ability has been introduced in this paper. This inverter has the ability of connecting several PV strings with different levels of voltage and currents to the AC grid. Moreover it has the ability of individual Maximum-Power-Point-Tracking (MPPT) for different PV strings that works in different situation of temperature and light radiation. High frequency AC-Link eliminates the need for large DC-Link Capacitor. It consists of a self-inductor which resonates with a small value capacitor in high frequency. This new topology of unidirectional single-stage multi-string PV inverter uses reverse blocking switches so it enhances the inverter reliability and makes it suitable for medium and low power levels. Presented simulations verify good performance of the introduced inverter.

Power system is a nonlinear time-variant system with a large variety of disturbances among them is the Low Frequency Oscillations (LFO). It is necessary to have an appropriate Power System Stabilizer (PSS) which can stabilize the power system in different operating points. In this paper fuzzy logic has been used to design the stabilizer for a multi-machine power system. The main advantage of fuzzy logic is that a person can involve the experiences he has about the system’s behavior, in the design process. These experiences are implemented as fuzzy rules. In this paper a fuzzy PSS is designed to stabilize a typical two-area four-machine power system under a short-term 3 phase short circuit fault. Results show the advantages of the proposed stabilizer over the classic one in damping the local and inter-area oscillations.

In this paper, complex Poynting theorem is used to calculate the power transmitted from primary to other areas of single-sided linear induction motor. By the help of Poynting theorem and boundary conditions, the longitudinal end effect is completely included into the analysis. Having comprehensive information about power flow and using the coenergy method, it is possible to calculate traction and normal forces due to each existing wave. So, it is shown that each of the traction and normal forces consists of five components. Then, the effect of some important design parameters on the calculated components of forces is analyzed. Results by the proposed model have been compared with those evaluated by finite-element method and with experimental measurements.

In this paper, a new approach is proposed for the optimum design of single-phase induction motor. By using the classical design equations and the evolutionary algorithms such as Genetic Algorithms (GA), Particle Swarm Optimization (PSO) and Modified Particle Swarm Optimization (MPSO), a Single Phase Induction Motor (SPIM) was designed with the maximum efficiency. The Finite Element Method (FEM) was used to achieve an accurate model of the motor. This model was used to validate the optimum design instead of implementing it practically that would be expensive. Results show that the efficiency of the motor designed by MPSO is higher compared to the ones designed by other methods. So this algorithm can be proposed as an appropriate tool in design of single-phase induction motors.

The efficiency in single-phase induction motors (SPIMs) are rather low due to the series capacitor also called run-capacitor which is connected to the auxiliary winding to provide 90 degree phase shift of the voltage source. This paper investigates this problem and tries to propose an appropriate procedure to solve. After carrying out a detailed motor analysis and investigating maximum efficiency condition, a new modified inverter-based method for eliminating the series capacitor and therefore optimizing the efficiency is proposed. Both conventional and proposed method was applied to a sample system and results of simulated system validates the proposed method.

Despite many advantages of BrushLess DC motor, torque pulsation is one of the most important disadvantages of it. At first, an optimum primary design of BLDC motor is done using PSO algorithm. Then, other parameters for reducing the torque pulsation are considered by finite element method. It is shown that fractional slot structure has many advantages than conventional one. Both cogging and ripple torque have been reduced for fractional structure. In the next steps, other important torque pulsation parameters, such as magnet embrace, offset and skew are considered. Proper embrace, skew and offset are achieved for reducing torque pulsation by nonlinear finite-element analysis.

This paper discusses a new vector control strategy for single-phase induction motor operating with two windings. The vector control is based on the Rotor Field Oriented (R.F.O) method that was adapted for this type of machine. This new vector control is suitable for all of the unbalanced induction motors. Moreover the rotor speed of the unbalanced motor is estimated by using Extended Kalman Filter (EKF). Results show the good performance of the proposed method.

All types of electrical machines can be modeled by an equivalent two phase machine. For example a balanced three phase induction motor can be modeled as an equivalent two phase induction motor (The dq Model). In the same way an unbalanced induction motor can be modeled as an unbalanced two phase induction motor. This paper shows this concept by modeling a faulty induction motor with one of its three feeding phases, open. Moreover the paper shows that the speed control of this faulty motor can be performed by a few modifications in the conventional vector control. This new vector control is suitable for unbalanced induction motors such as the single phase induction motor with unequal main and auxiliary windings. Computer simulation shows the good performance of the proposed method.

A factorable Preisach distribution function is a reasonable assumption in modeling soft magnetic materials. With this assumption it is possible to define and employ a single-input Preisach function for easier implementation and identification of a scalar Preisach model. On the basis of this simplification, we developed a new method for identification and implementation of the isotropic vector Preisach model. With the aid of a newly derived equation, the Preisach function of the vector Preisach model can be identified from the corresponding scalar one. We verified the correctness of the proposed method by comparing the results of scalar and vector models in a scalar condition of input variation.

Although complete compensation is only possible using true active filters, inductive shunt harmonic impedances (ISHI) have been shown to provide a considerable reduction of the harmonic propagation. In previous works, the resistive shunt harmonic impedances (RSHI) is presented that it is very effective, but RSHI have high loss power. In this paper we present a new inductive shunt harmonic impedances that reactor inductance decrease with frequency increment because flux skin effect. Modeling results show that the inductor reactance constructed with laminated iron core as functions of frequency, laminated thickness, core conductivity and permeability.

In this paper, we propose a model with flux skin effect to represent the behavior of laminated iron core inductors that are used in switching converters, i.e., for excitation frequencies above several kilohertz. Modeling results show that, the inductor reactance calculated as functions of frequency, laminated thickness, core conductivity and permeability and flux skin effect in the laminated core, causes decreasing in the reactor inductance at high frequencies.

Macroscopic behavior of ferromagnetic materials can be considered as the resultant of three phenomena: hysteresis, eddy current, and excess loss. Hysteresis is the behavior of the material under quasi-static variation of magnetic field. Eddy-current and excess losses are dependent on the rate of field variation and are evident in the fast variation of the magnetic field, so they are called dynamic effects. This paper presents a simple and practical technique in field analysis of electromagnetic systems having hysteresis and dynamic effects. Based on the Preisach model for hysteresis and existing formulations for eddy currents and excess loss, an equivalent expression for field intensity has been introduced. A new technique has been presented in order to include this expression in the finite-element code. A typical system has been modeled by this code. Effects of relaxation and time step were examined on the stability and the convergence rate of the method. The validity of the proposed model has been checked by comparing its results with experimental measurements