Flux Orientation Research Articles

SLIDING MODE CONTROL OF THE DFIG USED IN WIND ENERGY SYSTEM

This paper, presents the application of the direct vector control using the sliding mode control (SMC) on the doubly fed induction generators (DFIG). The synthesis of the control laws is based on the model obtained by the orientation of the stator flux. The active and reactive powers that are generated by the doubly fed induction generators will be decoupled by the orientation of the stator flux and controlled by sliding mode controllers that have been developed. In order to rule on the validity as well as the performance of this type of adjustment, we will check its robustness by varying some parameters of the machine doubly fed induction.

A Robust Control Scheme Based on ISMC for the Brushless Doubly Fed Induction Machine

The brushless doubly fed induction machine (BDFM) has great potential in the wind energy generation system because it offers the advantages of higher reliability and maintenance-free operation. In this paper, a mathematical model in the power windings stator flux orientation frame is discussed by taking the rotor flux as the disturbance. Consequently, the control of the BDFM system is implemented by generating suitable control winding currents. Moreover, in order to eliminate the speed error and compensate the system uncertainties caused by the rotor flux and parameter perturbations, an integral sliding mode variable structure controller for the rotor speed is developed, and the reactive power is adjusted by a proportional-integral (PI) controller in the outer-loop. Furthermore, the control winding currents are regulated by the PI control scheme in the inner-loop. The proposed control frame achieves a good static and satisfactory dynamic control performance. Finally, simulation and experimental results are used to verify the correctness and feasibility of the proposed method.

First quantification of relationship between dune orientation and sediment availability, Olympia Undae, Mars

Dunes provide unique information about wind regimes on planetary bodies where there is no direct meteorological data. At the eastern margin of Olympia Undae on Mars, dune orientation is measured from satellite imagery and sediment cover is estimated using the high contrast between the dune material and substrate. The analysis of these data provide the first quantification of relationship between sediment availability and dune orientation. Abrupt and smooth dune reorientations are associated with inward and outward dynamics of dunes approaching and ejecting from major sedimentary bodies, respectively. These reorientation patterns along sediment transport pathways are interpreted using a new generation dune model based on the coexistence of two dune growth mechanisms. This model also permits solving of the inverse problem of predicting the wind regime from dune orientation. For bidirectional wind regimes, solutions of this inverse problem show substantial differences in the distributions of sediment flux orientation, which can be attributed to atmospheric flow variations induced by changes in albedo at the boundaries of major dune fields. Then, we conclude that relationships between sediment cover and dune orientation can be used to constrain wind regime and dune field development on Mars and other planetary surfaces.

Modeling and comparison of IP and fuzzy-pi regulators of speed control of DFIM for supply of power to the electrical network

This paper deals with a comparison between a fuzzy logic controller and a conventional IP controller utilized for speed control with a direct stator flux orientation control of a doubly fed induction. The effectiveness of the proposed control strategy is measured under diverse operating conditions such as of reference speed and for load torque step changes at nominal parameters and in the presence of parameter variation. Results obtained from simulation indicte that the fuzzy logic controller is more robust than a conventional IP controller against parameter variation and uncertainty, and is less sensitive to external load torque disturbance with a fast dynamic response; the stator side power factor is controlled at unity level. Then, an intelligent artificial fuzzy control of a wind energy system based on DFAM for supply of power to the electrical network. Its simulated performances are then compared to those of a classical PI controller. Specifically fuzzy systems are created to overcome the disadvantages of fuzzy systems. Results obtained in Matlab/Simulink environment show that the fuzzy control is more robust, have superior dynamic performance and hence found to be a suitable replacement of the conventional PI controller for the high performance drive applications. Key words : Doubly fed asynchronous machine (DFAM); Field oriented control; Fuzzy control, Fuzzy PI controller, conventional IP controller.

Speed Sensorless Control of a Doubly Fed Induction Motor Drives using MRAS Estimator

In this paper, direct vector control by rotor flux orientation for doubly fed induction motor without mechanical sensor based on the MRAS estimator is discussed, this method consists in developing two models one of reference and the other adjustable for the estimation of the two components of the rotor flux from the measurement of currents, statoric and rotor voltages respectively, the speed estimated is obtained by canceling the difference between the rotor flux of the reference model and the adjustable one, while using the theory of hyperstability to obtain the adaptive mechanism the simulation results are presented to validate the proposed method.

Monte Carlo simulation of column growth in plasma spray physical vapor deposition process

Plasma spray-physical vapor deposition is used to produce columnar microstructure coatings under particular operating parameters. Simulations of the growth of columns were carried out through a two-dimensional Monte Carlo model. The modeling was performed using inclined vapor flux impinging onto a substrate due to shadowing effects. An incoming particle travels along a straight line and attaches itself to already deposited particles. Furthermore, the newly deposited particle will relax to a stable surrounding position along the incoming velocity direction. The modeling results predicted the linking of an oblique vapor flux and column orientation. The numerical simulations were validated in three ways. Firstly, the porosity of simulated columns was predicted and compared to that obtained in the experimental columnar microstructure of coatings. Secondly, the morphology of simulated structures is compared to that of experimental coatings produced by plasma spray physical vapor deposition. Finally, the simulated orientation of columns is compared to the experimental one.

Maximum power extraction under different vector-control schemes and grid-synchronization strategy of a wind-driven Brushless Doubly-Fed Reluctance Generator

This paper proposes an advanced strategy to synchronize the wind-driven Brushless Doubly-Fed Reluctance Generator (BDFRG) to the grid-side terminals. The proposed strategy depends mainly upon determining the electrical angle of the grid voltage, θv and using the same transformation matrix of both the power winding and grid sides to ensure that the generated power-winding voltage has the same phase-sequence of the grid-side voltage. On the other hand, the paper proposes a vector-control (power-winding flux orientation) technique for maximum wind-power extraction under two schemes summarized as; unity power-factor operation and minimum converter-current. Moreover, a soft-starting method is suggested to avoid the employed converter over-current. The first control scheme is achieved by adjusting the command power-winding reactive power at zero for a unity power-factor operation. However, the second scheme depends on setting the command d-axis control-winding current at zero to maximize the ratio of the generator electromagnetic-torque per the converter current. This enables the system to get a certain command torque under minimum converter current. A sample of the obtained simulation and experimental results is presented to check the effectiveness of the proposed control strategies.

Virtual-Torque-Based Control of Three-Phase Rectifier Under Grid Imbalance and Harmonics

The paper deals with a new control method of three-phase rectifier operating under simultaneous grid voltage imbalance and harmonics. The proposed method uses virtual electromagnetic torque, which is calculated on the basis of converter current and virtual flux of the power grid. Direct calculation of reference alpha/beta components of current vector does not require any synchronization procedure or grid voltage/virtual flux orientation of the reference frame. On the other hand, the proposed control is still as simple in implementation as other vector control methods such as voltage-oriented control or virtual-flux-oriented control. The introduced variable (virtual torque) allows us to calculate reference current vector components in alpha/beta frame without symmetrical components decomposition. The current vector obtained by using the proposed control method has the same asymmetry factor as unbalanced grid voltage. It means that the rectifier is seen by the grid as a resistive load with the same resistance in each phase. For the grid it is preferable target because the phase with the highest voltage is loaded most, while the other phases are less loaded. Converter power can be increased by progressive balancing of three-phase converter current keeping the phase current limit.

Direct Resonant Control Strategy for Torque Ripple Mitigation of DFIG Connected to DC Link through Diode Rectifier on Stator

This paper presents a torque ripple mitigation method for the doubly-fed Induction generator (DFIG) connected to the dc link through a diode rectifier on the stator winding. A resonant regulator based on torque compensator is directly added to the conventional rotor current control loop, and the sequential separations and calculations of rotor harmonic current references can be avoided. Then, a novel stator flux orientation method is achieved by indirectly controlling the q -axis stator flux linkage to be zero without calculating the stator flux linkage angle. The stator frequency is controlled by regulating the stator flux without calculating the stator frequency. Based on a mathematical model of the DFIG control system, the effects on system stability using the resonant controller, analysis of the steady-state error, and the dynamic performance are discussed. Finally, the proposed control method is validated by the experiment results.

Indirect field‐oriented torque control of induction motor considering magnetic saturation effect: error analysis

This study investigates the causes and calculation formulas of steady-state torque and rotor flux errors, when an induction motor considering magnetic saturation effect is controlled by standard indirect field-oriented control algorithm. First, two reasons that causing the errors are analysed. One is mutual inductance mismatch between controller and motor. Another is rotor flux orientation deviation, resulting in the failure of decoupling of the magnetising and torque-producing currents. Then, the equations for calculating steady-state errors (orientation error, rotor flux error and torque error) are derived. The errors are related to reference torque, reference rotor flux and mutual inductance deviation. In addition, the characteristic maps of errors with respect to reference values are drawn. The accuracy and correctness of derived equations are validated by simulation and experimental results.

Active Disturbance Rejection Control of Bearingless Induction Motor

To improve the dynamic control performance of bearingless induction motor (BLIM), the active disturbance rejection control strategy is presented. Based on the rotor flux orientation inverse decoupling strategy, an active disturbances rejection control (ADRC) system is designed to replace the PID control system. The cross coupling items, motor parameter change and load are all regarded as disturbance. The total disturbance is estimated by an extended state observer (ESO), and compensated by a nonlinear state error feedback (NLSEF) controller. Simulation results show that the system has better dynamic decoupling performance and strong robustness.

Vector Control of Induction Machine with Estimates and Adaptation of Rotor Time Constant

The variation of the rotor time constant exerts a dominant effect in the performance degradation of the orientation of the rotor flux method of induction machine and the online estimation of the time constant (Tr) is necessary in order to use it in the flux orientation and keeping the performance of the vector control. We presented our work vector control of induction machine by estimating and online adaptation of the rotor time constant of our machine only by measurement of voltage, current and speed, in line on the machine, to provide information to the orientation block on the variation of the parameter studied Tr.

Comparative study of integral and classical backstepping controllers in IFOC of induction motor fed by voltage source inverter

A comparative study between Integral and Classical Backstepping IFOC structures of induction motor is proposed in this work. The Integral one is based mainly on a suitable combination of a nonlinear integral backstepping approach and an indirect field orientation control (IFOC). The first part ensures a global system stability using recursive Lyapounov design and increases robustness despite disturbances and model uncertainties. The second part will guarantee flux orientation, decoupling, and current regulation.The effectiveness of the proposed control structure is validated by simulation as well as by experiment under critical disturbance conditions. Obtained results show a fast dynamic response, better load disturbance rejection capability, less parameters sensitivity and better tracking performance.

Direct power control in pulse-width modulation rectifier based on virtual flux estimation

Pulse-width modulation rectifier plays an important role in the field of electric energy conversion. It has many advantages such as the grid side current sinusoidal, bidirectional energy flow, and unit power factor. In order to improve the power factor, this article proposes a new control method for the three-phase pulse-width modulation rectifier, that is, direct power control strategy based on virtual flux orientation. The original concept of AC motor stator flux is introduced into the proposed scheme for the three-phase pulse-width modulation rectifier so as to remove the grid voltage sampling circuit. The instantaneous power is estimated by the virtual flux vector orientation to realize the pulse-width modulation rectifier control in unbalanced condition. The two-order filter replaces the pure integrator in this process of implementation to solve the initial value problem of this pure integrator and achieve the better filtering property. With the estimation of virtual flux, the control strategy with s...

Power Control of DFIG-generators for Wind Turbines Variable-speed

In this paper, we focus on the modeling and control of a wind power system based on a double-fed induction generator DFIG. We proposed a technique of active and reactive power control to improve the performance and dynamics of variable speed wind system. The objective of the modeling is to apply the direct and indirect vector control stator flux orientation to control independently, the active and reactive power generated doubly-fed induction generator (DFIG). The simulation results are tested and compared in order to evaluate the performance of the proposed system.

Inverse system modeling and decoupling control of bearingless induction motor based on air gap flux orientation

Inverse system modeling and decoupling control of bearingless induction motor based on air gap flux orientation

A smartphone-based introductory astronomy experiment: Seasons investigation

Light sensor probes are useful in experiments that investigate seasonal variations and the nature of light. However, having a dedicated light probe is not always possible or even convenient for many instructors. Modern smartphone technology gives instructors the ability to use built-in light sensors as an inexpensive alternative. This introductory experiment will have students use a smartphone loaded with a light detection app to quantitatively determine how changing latitude on Earth changes flux received. The purpose is to have students discover how the different seasons arise from the Earth-Sun system. While performing the experiment and analyzing the data, students will also discover the following important and relevant physical relationships: distance from light source and light brightness (flux), latitude and flux, and Earth’s orientation and location (latitude) of maximum flux. By piecing all of these relationships together, students are able to explain the origins of the different seasons based on the data they collected.

Indirect Field Oriented Control of Three-phase Induction Motor Based on Current-source Inverter

Medium-voltage drives are generally based on either voltage-source inverter(VSI) or current-source inverter (CSI). Three-phase CSI fed induction motor (IM) drives become a strong candidate in medium-voltage applications for the features of the simple topology, power reversal capability and a reliable short circuit protection. By decoupled control of the machine flux and torque, the conventional direct field oriented control(DFOC) CSI fed induction motor drives has gained the improved performance, however, this scheme faces practical challenges, like poor good dynamic response and machine parameter dependence. A high performance CSI fed indirect field oriented control (IFOC) method is described in this paper. A rotor flux observer and two proportional–integral controllers are used to get good dynamic response of the system. The rotor flux orientation is also obtained. The transient response analysis of the induction motor are also discussed in detail. The simulation results bases on MATLAB show that the control system has good dynamic performance and stability.

Transient and steady state performance analysis of power flow control in a DFIG variable speed wind turbine

Abstract This paper presents transient and steady state performance analysis of power flow control in a 5.0 kW Doubly-Fed Induction Generator (DFIG) Variable Speed Wind Turbine (VSWT) under sub synchronous speed, super synchronous speed and synchronous speed modes of operation. Stator flux orientation is used for the control of the rotor-side converter (RSC) and DFIG whereas the grid (or stator) voltage orientation is the preferred choice for the control of the grid-side converter (GSC). In each of the three speeds modes, power is always supplied to the grid through the stator of the DFIG. The magnitude of net power (stator power plus rotor power) is less than stator power during the sub synchronous speed mode; it is greater than stator power during the super synchronous speed mode while it is equal to the stator power during the synchronous speed mode. In synchronous speed mode, the rotor power is zero indicating that power is neither supplied to the grid from the rotor nor supplied to the rotor from the grid; here the magnitude of net power is equal to stator power. The simulation results thus obtained in a MATLAB/SIMULINK environment laid credence to the controllability of power flow reversal in a DFIG-VSWT through back-to-back power electronic converter.

Probing Statistical Isotropy of Cosmological Radio Sources using Square Kilometre Array

There currently exist many observations which are not consistent with the cosmological principle. We review these observations with a particular emphasis on those relevant for Square Kilometre Array (SKA). In particular, several different data sets indicate a preferred direction pointing approximately towards the Virgo cluster. We also observe a hemispherical anisotropy in the Cosmic Microwave Background Radiation (CMBR) temperature fluctuations. Although these inconsistencies may be attributed to systematic effects, there remains the possibility that they indicate new physics and various theories have been proposed to explain them. One possibility, which we discuss in this review, is the generation of perturbation modes during the early pre-inflationary epoch, when the Universe may not obey the cosmological principle. Better measurements will provide better constraints on these theories. In particular, we propose measurement of the dipole in number counts, sky brightness, polarized flux and polarization orientations of radio sources. We also suggest test of alignment of linear polarizations of sources as a function of their relative separation. Finally we propose measurement of hemispherical anisotropy or equivalently dipole modulation in radio sources.