Influence of pole-pair combinations on the characteristics of the brushless doubly fed induction generator

The brushless doubly fed induction generator (BDFIG) is an alternative to the doubly fed induction generator (DFIG), widely used in wind turbines which avoids the need for brush gear and slip rings. The choice of pole numbers for the two stator windings present in the BDFIG sets the operating speed, typically in the medium speed range to eliminate a gearbox stage. This paper focuses on how both the total number of poles and the assignment of poles between the windings affect machine performance. Analytical expressions have been developed for parameters including pull-out torque, magnetizing current and back-iron depth. The results show that the pole count can be increased without unduly compromising pull-out torque and that in cases where more than one combination of pole number is acceptable only the back iron depth is significantly affected. In addition an output factor has been introduced to enable a direct comparison to be made with conventional DFIGs. The torque density of a brushless DFIG is compromised to a degree relative to a comparable DFIG as a consequence of the presence of two magnetic fields and finite element analysis is needed to achieve an optimized design. Finally, predictions of the performance of multi-MW machines are made based on data from an existing 250 kW machine which show that suitable efficiencies can be obtained and excessive control winding excitation can be avoided

A Light-Weight Rotor Design for Brushless Doubly Fed Machines

In this paper, a new optimized rotor design for Brushless Doubly Fed Machines (BDFMs) is proposed. The BDFM is considered as an attractive generator particularly for offshore wind power generation and also as a replacement for doubly fed slip ring induction generators. This is due to its higher reliability and lower maintenance reported in the literature. It is shown in this paper from the study of the magnetic field distribution in the rotor core that the conventional design of the BDFM rotor iron core can be modified, leading to a lighter machine. The proposed design method is supported by an analytical study and its practicality is validated using 2-D Finite Element (FE) analysis. A 250 kW experimental BDFM with frame size D400 is considered as the prototype machine

A study of rotor eccentricities effects on brushless doubly fed machines performance

This paper studies the unbalanced magnetic pull (UMP) in the Brushless Doubly-Fed Machine (BDFM). Analytical study is performed to derive the UMP, then, Finite element (FE) analysis, which has been verified experimentally, is used to verify the analytical method. The BDFM with different types of rotor eccentricities including static and dynamic eccentricities, are also modeled in FE method and their resultant UMPs are obtained. The results are compared with the case at which a perfectly constructed rotor is considered. The study has been carried out on a prototype D400 250 kW BDFM

Numerical Analysis of Stator Magnetic Wedge Effects on Equivalent Circuit Parameters of Brushless Doubly Fed Machines

This paper studies the effects of magnetic wedges used for closing stator open slots on the Brushless Doubly Fed Machines' (BDFM) equivalent circuit parameters. The BDFM is an attractive generator solution for offshore wind power and can replace doubly-fed slip-ring induction generators. It is shown in this paper that the use of magnetic wedges, commonly used in large induction machines, reduces the stator windings magnetising currents, reflected in the values of magnetising inductances. But they also increase the leakage flux of the stator windings and hence change the series inductance in the equivalent circuit. The series inductance significantly affects the machine performance as well as the rating of its converter. 2-D Finite element analysis of a 250 kW experimental BDFM is used to investigate the effects of magnetic wedges on the machine's magnetic field distribution and how these can alter the machine's parameters values. Experimental tests have also been carried out to validate the analysis

A new optimized rotor design for brushless doubly fed machines

The brushless doubly fed machine (BDFM) is an alternative to the doubly fed induction generator, widely used in wind turbines, without use of brush gears and slip rings. Rotor design is important for designing an optimal multi-MW BDFM. To date, nested-loop rotors have been extensively used in various BDFMs but they may not be suitable for larger machines. In this paper, different methods of BDFM rotor equivalent circuit parameters determination are presented and validated by experimental tests. Then, a design optimization of BDFM rotors is proposed based on equivalent circuit analysis with the aim of minimizing the rotor parameters. Two optimized rotors, one bar cage rotor and one nested-loop rotor were designed and built from the outcomes of the optimization method for a BDFM with frame size D180. The characteristics of the conventional and optimized rotors in terms of the rotor equivalent circuit parameters and iron saturation at rated operating conditions are compared using analytical and Finite Element Analysis (FEA) methods

Simplified Experimental Estimation of Equivalent Circuit Parameters for Brushless Doubly Fed Machines

This paper presents a new and simplified method for estimating the equivalent circuit parameters of the Brushless Doubly Fed Machine (BDFM) using only stator terminal measurements. The proposed method utilises voltage, current, and power factor measurements to estimate the stator and rotor parameters of the BDFM. The stator winding resistances are determined through DC measurements and treated as fixed parameters during the estimation process. The accuracy of the estimated parameters is compared with those obtained from alternative parameter estimation methods for an experimental D180 BDFM to evaluate its accuracy

Root Tensile Force and Resistance of Several Tree and Shrub Species of Hyrcanian Forest, Iran

Shallow landslides are a frequently recurring problem in some parts of Iran, including the Hyrcanian forest. In addition to traditional civil engineering measures, a potential solution for this problem is the application of soil bioengineering techniques. The mechanical reinforcement effect of plant roots is one of the major contributions of vegetation to the mitigation of shallow landslides. Given the lack of information on the mechanical properties of common Hyrcanian forest species, the present study assessed the root strength of 10 common species of this forest. Eight tree species occurring in natural regeneration sites (Carpinus betulus, Fagus orientalis, Parrotia persica and Quercus castaneifolia) and plantations (Acer velutinum, Alnus glutinosa, Fraxinus excelsior and Picea abies) and two shrub species (Crataegus microphylla and Mespilus germanica) were selected. Fresh roots were collected and mechanical tests were carried out on 487 root samples. The ranges of root diameter, tensile force, and root resistance were 0.29–5.90 mm, 3.80–487.20 N, and 2.41–224.35 MPa, respectively. Two different algorithms, including the nonlinear least square method and logtransformation, were used to obtain power regressions for diameter-force and diameter-resistance relationships. The results of the two algorithms were compared statistically to choose the optimal approach for soil bioengineering applications. The nonlinear least square method resulted in lower Akaike information criteria and higher adjusted R2 values for all species, which means that this model can more efficiently predict tensile force and resistance based on root diameter. Log-transformation regressions generally underestimate tensile force and resistance. Significant differences were found among mean root tensile force (ANCOVA; F=37.36, p<0.001) and resistance (ANCOVA; F=34.87, p<0.001) of different species. Also, root diameter was significant as a covariate factor in tensile force (F=1453.77, p<0. 001) and resistance (F=274.26, p<0.001). Shrub species and trees in natural regeneration sites had higher tensile force and resistance values, while trees from plantation stands had lower values. The results of this study contribute to the knowledge on the root force and resistance characteristics of several shrub and tree species of the Hyrcanian forest and can be used in evaluating the efficiency of different species for bioengineering purposes

Experimental Analysis of Noise and Vibration for Large Brushless Doubly Fed Machines

In this work, a large-scale Brushless Doubly Fed Machine (BDFM) built in frame size D400 is tested at different operating conditions in order to examine its noise and vibration levels. A series of measurements were conducted on the machine to establish the main modes of excitation of vibration and noise developed by the machine. The harmonic spectrums of the vibration amplitudes are presented at two different rotor speeds at which the vibration level is highest, in order to determine the vibration components frequencies existed in the vibration spectrum. A harmonic analysis of the BDFM is then proposed in order to assess the sources of vibration in the machine

Nanotechnology markets in global competition: a review

Nowadays, nanotechnology is as a main way of in international competitiveness that is due to science and technology. Hence, nanotechnology is known as a new industry or science in the global market competition topics. Also, developed or developing countries would trend to acquire portions for future markets through the investment in nanotechnology (R&D) because of profitable products and services in the future which are consistency environmentally and green. The products or services of nanocan be supplied in different markets e.g. energy, industry, medicine, and so on. Moreover, each of them depends upon innovation in producing new features or materials for the future that can be considered as important factors for different solutions for problems of life and humanity. Most of big companies pursue nanotechnology business in the global market from different products and services through the intensive competitions especially energy sector in the future. Although it can be accounted as new business in the future, there are some weakness of the firms in competitiveness i.e. weakness in strategies, capabilities, assets and knowledge. Hence, the aim of this study is to understand variety of issues in the literature of nanotechnology and strategies from managerial views