Magnetic Barrier Rotor Research Articles

A Novel Thermal Network Model Used for Temperature Calculation and Analysis on Brushless Doubly-Fed Generator With Winding Encapsulating Structure

In recent years, magnetic-barrier rotor has been put forward for brushless doubly-fed generator (BDFG) application owing to its desirable performance, such as high power density and strong magnetic coupling ability. However, it also causes significant losses induced by harmonics and high temperature problem. Hence, it is a major challenge to evaluate Bref_DFG temperature rise fast and accurately. So far, aiming at magnetic-barrier rotor, there has been no accurate thermal network model established achieving this goal. In addition, wingding end encapsulating technology has been used for a few years and its heat dissipation potential is determined by the materials. Therefore, the application of novel material in winding encapsulating structure is desirable to improve the heat dissipation potential. In this paper, an equivalent thermal network model, thermal resistance models of magnetic-barrier rotor, and a winding encapsulating structure with novel materials are further established for thermal analysis. Subsequently, temperature distributions for BDFG components are also calculated by finite element method, while the results are compared with those by analytical method. The BDFG prototype is manufactured with experimental tests performed. The correctness of the equivalent thermal network models proposed in this paper is verified by the test results.

Improved E&S Model for Core Loss Calculation of Brushless Doubly Fed Machine With Hybrid Rotor

Brushless doubly fed machine (BDFM), is a new type of machine with special structure, shows promising features for the field of variable frequency speed regulation and wind power generation due to its inherent characteristics, which has the advantages of reliable operation, adjustable power factor, lower operation and maintenance costs as well as requiring a smaller capacity converter [1], [2]. Since core loss has an important effect on efficiency and temperature distribution, it is vital to accurately calculate such component in an optimal design procedure. Furthermore, rotor core loss is also a significant factor which can affect the performance characteristics of BDFM due to the complex magnetic field distribution and relatively high value of slip. Specifically, a novel hybrid rotor structure which is combined with magnetic barrier and assisted cage has better coupling ability than the commonly used rotor structures such as cage rotor and reluctance rotor is presented but it also increases the difficulty of core loss calculation. E&S model is a vector magnetic hysteresis property model [3], [4], in which H (magnetic field intensity) is dependent not only on B (magnetic flux density) but also on time derivative of B. Increase of core loss when the phase difference between B and H occurs, is well expressed in this method, while the conventional analysis was not able to consider the phase difference between B and H. Furthermore, the total core loss including both alternating and rotational losses can be directly calculated from the fundamental terms of obtained $B_{x}$, $B_{y}$, $H_{x}$ and $H_{y}$ without other fitting data, which can improve the core loss computation accuracy of BDFM with hybrid rotor in contrast with conventional core models. In this paper, an improved E&S model based on a 2-D rotational magnetic property analysis for core loss of BDFM with hybrid rotor is proposed by considering the high-order harmonic magnetic field. The finite element analysis model of BDFM with hybrid rotor is established. The core loss calculation results are compared with the simulation results to verify the correctness and feasibility of the proposed E&S model. Fig. 1 shows the finite element model, hybrid rotor of prototype and special points distribution diagram of BDFM with hybrid rotor. As shown in Fig. 1 (a)-(b), the cage bars are added on the non-magnetic layer of the radial magnetic barrier rotor, and the cage bars are respectively divided into concentric cage bar and common cage bar. There are two kinds of rotating magnetic fields with different poles and frequencies in the air-gap of BDFM, which renders that the air-gap magnetic density harmonic contents are rich and the magnetic properties of each part of core are different. According to the basic principle, structure characteristics and magnetic field distribution of BDFM with hybrid rotor, some special points of stator and rotor are analyzed and calculated. The relationship between B vector and H vector, and the relationship between the waveform of $B_{x}$, $B_{y}$ and the waveform of $H_{x}$, $H_{y}$, obtained by the combination of the improved E&S model and finite element analysis, is shown in Fig. 1 (c), which is seen that the phase between B and H is different. The improved E&S model can consider higher order harmonic magnetic field than the conventional E&S model. As shown in Fig. 2 (a), the stator and rotor core loss calculation process of BDFM with hybrid rotor is described by the flow diagram. The datum of $B_{x}$, $B_{y}$, $H_{x}$, $H_{y}$ are obtained by the combination of the improved E&S model and finite element method, and all order harmonic of $B_{x}$, $B_{y}$, $H_{x}$, $H_{y}$ are computed by fourier series expansion. Therefore, the total core loss of BDFM with hybrid rotor can be calculated by the formula in the flow diagram, where, $\rho$ is the magnetic material density, T is the period, $m$ is the amount of the special points, $n$ is the harmonic order, and $M_{i}$ is the mass. In addition, in order to verify the accuracy of the core loss calculation, the 2-D finite element model of BDFM with hybrid rotor is established, and the simulation results are shown in Fig. 2 (b). The validity and feasibility of the improved E&S model is verified by comparing with the simulation results. In addition, the full paper will present the detailed calculation procedure and analysis.

Design and Performance Comparisons of Brushless Doubly Fed Generators With Different Rotor Structures

The brushless doubly fed generator (BDFG) shows the great potential for use in large variable speed wind turbines due to its high reliability and cost benefits of a partially rated power electronics converter. However, it suffers from the compromised efficiency and power factor in comparison with conventional doubly fed induction or synchronous generators. Therefore, optimizing the BDFG, especially the rotor, is necessary for enhancing its torque density and market competitiveness. In this paper, a novel cage-assisted magnetic barrier rotor, called the hybrid rotor, is proposed and analyzed. The detailed analytical design approaches based on the magnetic field modulation theory are investigated. In addition, the machine losses and mutual inductance values using the proposed rotor designs are calculated and their performance implications evaluated. Finally, the comparative experimental results for two BDFG prototypes are presented to verify the accuracy and effectiveness of the theoretical studies.

Parameter Calculation and Analysis of a Novel Wind Power Generator

Compared with the commonly used generators, the brushless doubly fed generator (BDFG) has a commercial potential for wind power generation due to its inherent characteristics. In this paper, a novel BDFG with hybrid rotor is proposed and its structural features and operation principle are presented. Meanwhile, the performance of the proposed BDFG is analyzed in comparison with the BDFG using a radial laminated magnetic barrier rotor. Furthermore, due to the complexity of the magnetic field and the particularity of the structure, the calculation and analysis of the parameters, especially the inductance, are extremely important for the performance analysis of the proposed BDFG. Therefore, an inductance calculation method based on modified winding function is investigated. For accurate inductance calculation, the effects of magnetic layers and cage bars on the air-gap permeance of the proposed hybrid rotor are both considered. Tests are performed on a 25 kW prototype machine to verify the performance of the proposed BDFG. The experimental results show the correctness and feasibility of the proposed inductance calculation method.

Asynchronous Operation Analysis of Brushless Doubly-Fed Machine with Magnetic Barrier Rotor

To restrain the influence of armature reaction, flux barriers is added to rotor structure and enhance the output power ability of brushless doubly-fed machine. Design scheme of brushless doubly-fed machine with barrier rotor is provided. Based on field-circuit coupled finite element method, The asynchronous operation performance of brushless doubly-fed machine with barrier rotor is studied under the condition of no-load, including adjusting voltage adjusting speed and series resistance adjusting voltage. The prototype is carried out on the condition of no-load asynchronous operation; comparison analysis of simulation speed values and tested speed values is realized. The designed machine is reasonable and reliable.

Performance Analysis of Doubly Excited Brushless Generator with Outer Rotor for Wind Power Application

In this paper, a novel doubly excited brushless generator (DEBG) with outer radial laminated magnetic barrier rotor (RLMB-rotor) for wind power application was designed and analyzed. The DEBG has 10 rotor pole numbers with outer rotor. Its performance was investigated using the 2D transient finite element method. The magnetic fields, torque capability, end winding voltage characteristics, radial magnetic force and energy efficiency were analyzed. All studies in this paper show that the simplicity, reliability, high efficiency and low vibration and noise of the DEBG with outer rotor were attractive for variable speed constant frequency (VSCF) wind power generation system.

Performance Analysis of Doubly Excited Brushless Generator with Outer Rotor for Wind Power Application

In this paper, a novel doubly excited brushless generator (DEBG) with outer radial laminated magnetic barrier rotor (RLMB-rotor) for wind power application was designed and analyzed. The DEBG has 10 rotor pole numbers with outer rotor. Its performance is investigated using the 2D transient finite element method. The magnetic fields, torque capability, end winding voltage characteristics, radial magnetic force and energy efficiency were analyzed. All studies in this paper show that the simplicity, reliability, high efficiency and low vibration and noise of the DEBG with outer rotor are attractive for variable speed constant frequency (VSCF) wind power generation system. DOI: http://dx.doi.org/10.11591/telkomnika.v10i3.606

Performance Analysis of Doubly Excited Brushless Machine with Radially Laminated Magnetic Barrier Rotor

The performance of a doubly excited brushless machine (DEBM) with radially laminated magnetic barrier rotor (RLMB-rotor) is investigated by using the 2D transient finite element analysis model and the experimental method. The magnetic fields, the mutual coupling of the dual stator windings, the no-load characteristics and the electromagnetic torque characteristics of the sample machine are presented. The results of the experiment validate the theoretical analysis and simulation results.

Radial Laminated Magnetic-Barrier Rotor Optimization Design of Brushless Doubly-Fed Machine

This paper establishes four kinds of Brushless Doubly-Fed Machine (BDFM) models with radial laminated magnetic-barrier rotor using ANSOFT finite element software, calculates the electromagnetic field of these four kinds of models, comparatively analyzes the magnetic field distribution, the torque capability, the end winding characteristics ,the rotor’s radial magnetic forces, the core losses and the motor operating performance of motor with different rotor structures, and thus provides theoretical guidance for optimization design of radial laminated magnetic-barrier rotor structure.

Radial Force Analysis of Radial Laminated Magnetic-Barrier Rotor Brushless Doubly-Fed Machine

In this paper, the respective harmonic magnetic field generated by the two sets of stator windings of radial laminated magnetic-barrier rotor brushless doubly-fed machine has been analyzed with the winding function method, the calculations of the radial forces on stator’s inner edge which are resulted from the fundamental and harmonic magnetic field that generated by the two sets of stator windings have been made, and the radial forces of three kinds of such machines with different rotor pole numbers have been compared, all the above can provide theoretical guidance for optimized design of radial laminated magnetic-barrier rotor brushless doubly-fed machine.