Improved vector control methods for brushless double fed induction generator during inductive load and fault conditions

A Brushless Double-Fed Induction Generator (BDFIG) has shown tremendous success in wind turbines due to its robust brushless design, less maintenance, smooth operation, and variable speed characteristics. These generators are composed of two back-to-back voltage source converters, a Grid Side Converter (GSC) and a Rotor Side Converter (RSC). Existing control techniques use a “trial and error” method that results in a poor dynamic response in machine parameters during the absence of load. The RSC control is used for reactive current control during the inductive load insertion. However, it is more suitable for stabilizing steady-state behaviour, but it suffers from slow response and introduces a double fundamental frequency component to the Point of Common Coupling (PCC) voltage. In addition, generally, a Low Voltage Ride Through (LVRT) fault is detected using a hysteresis comparison of the power winding voltage. The LVRT capability is provided by using fixed reference values to control the winding current. This approach results in an erroneous response, sub-optimal control of voltage drops at PCC, and false alarms during transient conditions. This thesis aims to solve the mentioned issues by using an improved vector control method. Internal Model Control (IMC) based Proportional-Integral (PI) gains calculation is used for GSC and RSC. These are controlled to enhance the transient response and power quality during no-load, inductive load, and fault conditions. Firstly, a GSC-based vector control method is proposed to suppress the PCC voltage fluctuations when a large inductive load is suddenly connected. The proposed technique is based on an analytical model of the transient behaviour of the voltage drop at the PCC. To block a double fundamental frequency component as a result of reactive current compensation, a notch filter is designed. Secondly, an RSC-based vector control method is proposed using an analytical model of the voltage drop caused by a short circuit. Moreover, using a fuzzy logic controller, the proposed technique employs the voltage frequency in addition to the power winding voltage magnitude to detect LVRT conditions. The analytical model helps in reducing the power winding voltage drop while the fuzzy logic controller leads to better response and faster detection of faults. However, the reference value for reactive current compensation is analysed using an analytical model of the voltage drop at the PCC in the event of a short-circuit fault. The results obtained from MATLAB/Simulink show that the GSC-based vector control method technique can effectively reduce about 10% voltage drop at PCCs. Total Harmonics Distortion (THD) is improved to 22.3% by notch filter in comparison with an existing technique such as instantaneous reactive power theory. The RSC-based vector control method can achieve up to 11% voltage drop reduction and improve the THD by 12% compared to recent synchronous control and flux tracking methods

Internal Model Control (IMC)-Based Active and Reactive Power Control of Brushless Double-Fed Induction Generator with Notch Filter

The increase in demand for electricity and, in particular, green energy has put renewable energy systems at the focal point of energy policy worldwide. The higher reliability of brushless doubly fed induction generators (BDFIGs) makes them suitable for offshore and remote wind energy generation (WEG) applications. Besides, controlling the active and reactive powers in an electrical power system is critical for optimal voltage regulation, reduced power losses, and enhanced utilization of installed equipment. However, the existing literature on BDFIG’s active and reactive power control highlights the poor dynamic response and high transients with harmonic generation during inductive load insertion. It is because the Ziegler technique was employed to select PI gains, and the instantaneous reactive power theory was used to mitigate harmonics. Considering that, this paper proposes a vector control (VC) method for BDFIGs in wind turbines, in which the proportional-integral (PI) gains for internal model control (IMC) are optimized to improve the dynamic response of the active and reactive power during inductive load insertion. The proposed method reduces the complexity, time consumption, and uncertainty in making the optimal choice. In addition, to reduce a double fundamental frequency component to the point-of-common-coupling (PCC) voltage, the excellent characteristics of the notch filter are utilized in the grid-side converter (GSC)-based vector control scheme. The simulation results in MATLAB/ Simulink show that the proposed IMC-based vector control scheme with a notch filter provides satisfactory results with a minimum peak value compared to existing techniques

Prediction of Pressure Difference and Velocity Profile in Steady Flow through Axi-Symmetric Plaque Deposited Arteries

Numerical simulations of blood flow through plaque deposited arteries at different Reynolds numbers have been performed to investigate the impact of atherosclerosis on pressure drop and velocity profile at down stream. The predicated results are presented in terms of non-dimensional pressure isobars and velocity profiles at distinct Reynolds numbers and various levels of deposition at downstream of the artery segment. The scaled non-dimensional graph of pressure drop is also illustrated. The incompressible Navier-Stokes equation in the axi-symmetric frame of reference is solved numerically by employing FEM (Finite Element Method). Semi-implicit Taylor-Galerkin/pressure-correction scheme has been utilised to obtain steady state solutions. The effects of atherosclerosis on hemodynamic factors have been investigated. The results show that blockage disturbs the flow field in the wake of plaque deposited arteries and the trend of pressure and velocity is increasing as level of deposition or Reynolds number increases. The application of this research work can be utilised in the field of cardio vascular disease, design of device and further planning towards treatment

Modelling and Predictions of Isothermal Flow Inside the Closed Rotor-Stator System

This paper describes the numerical predictions of isothermal closed rotor-stator flows. Steady-state finite-difference solutions are sought for two gap ratios and two rotational Reynolds number in the axisymmetric cylindrical polar coordinate frame of reference. Low Reynolds number models, low Reynolds number k-? and second moment closure models have been used to compute the necessary description of the flow inside the rotor-stator system without superpose flow. The most important dissimilarities among the computational calculations of both the turbulence models obtain at the lower radial locations, where k-? model predicted the premature transitional predictions from laminar to turbulent flow. The major feature of this computational work is the emergence of four regions of the flow i.e. source, sink and two boundary layers. Computed velocity components of both models are compared against the experimental measurements. Low Reynolds number second moment closure shows the improved level of matching with data, particularly on apex of the boundary layers and recirculating core in the middle of the rotor-stator cavity

Analytical Solutions of Viscoelastic Flow through Porous Channels

Viscoelastic flow in channel having transient hydrodynamic behavior, filled with and without porous medium is addressed. The boundary value problem is investigated through analytical and numerical solutions, for the governing system of partial differential equations, arising in the study for flow of viscoelastic fluids. Analytical solutions in terms of velocity, normal stress and shear stress at different values of time, viscosity and Darcy\'s number are obtained for constant viscosity Oldroyd-B constitutive model. Lie group technique is adopted to find solutions through symmetry of differential equations, whilst numerical solutions are realized by employing ND Solve, Mathematica Solver. Lie group technique is compared against numerical solutions by employing ND Solve, Mathematica Solver. The analytical solutions are observed in good agreement with the numerical solutions

Pilomatrixoma of the arm: A rare case with imaging features

Pilomatrixoma, a benign skin appendageal tumor, is seen commonly in head and neck. Occurrence of pilomatrixoma in the upper extremities is not common and has been reported infrequently in the available literature.We present the case of a 13-year girl with a pilomatrixoma of the arm, its radiological evaluation and the relevant review of literature

Stress Analysis of Mixing of Non-Newtonian Flows in Cylindrical Vessel Induced by Co-Rotating Stirrers

The impacts of rotational velocity and inertia on velocity gradients and stresses are addressed under present study. The non-Newtonian behaviour of inelastic rotating flows is predicted by employing Power law model. A numerical model has been developed for mixing flow within a cylindrical vessel along a couple of stirrers. A time marching FEM (Finite Element Method) is employed to predict the required solution. Predicted solutions are presented for minimum to maximum values in terms of contour plots of velocity gradients and shear stresses, over the range. The long term application of this research will be used to improve the design of mixers and processing products. The predicted results are used to generate the capability and are in good agreement with numerical results to the mixer design that will ultimately effect the processing of dough product

Influence of Blood Inertia on Vortex Enhancement in the Wake of Plaque Deposited Arteries

Flow of blood structure is presented in terms of stream line projections at different percentages of deposition against various Reynolds numbers. The impact of atherosclerosis is investigated on the vortex enhancement and intensity. The predicted results are computed in terms of stream function for quantifying the reattachment length and re-circulating flow rate of blood at various Reynolds numbers and different percentages of blockage. The results show that flow of blood is disturbs at the vicinity of blockage, especially in the down stream area that leads to the formation of vortexes. It is observed that the length of vortex increases along with the deposition levels as well as with increasing inertia .To solve the Navier-Stokes equations, together with the incompressibility constraints a semi-implicit time stepping procedure, namely Taylor- Galerkin/Pressure-correction finite element scheme has been employed

Reliable Requirements Engineering Practices for COVID-19 Using Blockchain

Improvement in the requirements for engineering practices is needed in areas such as requirement elicitation, validation, prioritization, and negotiations between stakeholders to create successful projects for COVID-19 (coronavirus disease 2019) software. Many algorithms and techniques are used to create quality software projects, but they still need more improvement to work effectively for global pandemic COVID-19 software. By improving the reliability of requirement engineering practices using blockchain-based technology, the software will be reliable and will make it easier for the users working in a lockdown situation because of COVID-19. Therefore, our purpose is to identify the factors for reliable software engineering practices using blockchain-oriented technology for COVID-19 software. A systematic literature review is conducted to identify challenges and offer solutions. Through using blockchain-based technology for requirement engineering practices, the requirements will be gathered accurately and validated, and the conflicts between stakeholders will also be solved. It will improve the quality and reliability of COVID-19 software projects, which will help society work effectively from home. Improvement in the quality and reliability of COVID-19 software will improve users’ interest, and their working capacity will be increased