Hybrid Rotor Research Articles

Comparative investigations for performance and self-starting characteristics of hybrid and single Darrieus hydrokinetic turbine

Hydrokinetic turbine technology is an emerging field to produce clean energy from the riverine systems. Lot of hydrokinetic potential sites are available to provide the energy to the people living in those areas. Under the present work, two different hydrokinetic turbine rotors (hybrid and single Darrieus) are evaluated in term of performance and flow across the rotor. The flow velocity of water is considered as 1.0m/s and the model for both type of rotors are designed and modeled along with an open channel. Based on the investigations, it has been found that hybrid rotor is more efficient for hydrokinetic turbine and yields about 9.9% higher power coefficient (CP) than single Darrieus rotor. The average torque coefficient (CT) for hybrid rotor has also been found 15.9% higher than single Darrieus rotor with less fluctuations in torque. The results obtained from the numerical investigations are validated with experimentation results. Flow contours across the turbine rotor were plotted and smooth flow was observed with low-pressure range for hybrid rotor while the single Darrieus rotor experience a flow re-circulation zone with high-pressure range.

Loss Estimation of Brushless Doubly-Fed Generator With Hybrid Rotor Considering Multiple Influence Factors

The brushless doubly fed generator (BDFG) has been a research focus of wind power generation due to its inherent promising features. Although it is important to consider the effect of losses on the design and analysis of the BDFG, there are a few related comprehensive studies. Moreover, a hybrid rotor is studied to improve the performance of BDFG, which brings greater challenges to the loss calculation. The aim of this paper is to propose the accuracy calculation methods of core loss and copper loss for the studied BDFG with hybrid rotor. The core loss calculation model which taken the influence of harmonics, alternating magnetization, rotating magnetization and two-dimensional magnetic property of material into account is proposed based on the analysis of the magnetic field characteristics. In order to calculate the copper loss considering the skin effect, the inductive current of the assisted cage bars which is difficult to obtain directly is calculated. The accuracy and correctness of the proposed approaches and models are validated by experimental results from a 25kW prototype BDFG with hybrid rotor. In addition, the proposed loss calculation method, especially the core loss calculation model, is also applicable to BDFG with other rotor structure which is operated by the magnetic field modulation mechanism.

Разработка и исследование новых лабиринтных насосов с гибридным ротором

Разработка и исследование новых лабиринтных насосов с гибридным ротором

Electromagnetic Performance of the Novel Hybrid-Pole Permanent Magnet Machines for High Peak Torque Density

This paper proposes two novel hybrid rotors permanent magnet (PM) machines for the high torque density in short duration condition operation. In order to enhance the torque performance, the flux concentrated structure of spoke-type PM is employed to increase the air-gap flux density. Meanwhile, the non-magnetic connector of the rotor is employed to eliminate the magnetic flux leakage. The rotors of the conventional machines and the proposed machines are optimized by the finite element analysis (FEA). Furthermore, based on the comparisons of electromagnetic performances for the optimized machines, including the open-circuit flux density, torque, PM eddy current loss, overload capability, the characteristics of the proposed machines are analyzed. The results indicate that the proposed machine can improve the torque at rated and overload operation with growth rate 14.3% and 13.1%, respectively. Finally, a 12-slots/10-pole PM machine is prototyped and FEA is to be validated.

Influence of Slot Combination on Performance of Brushless Doubly Fed Generator With Hybrid Rotor

Brushless doubly fed generator (BDFG), a class of adjustable-speed machine with a special structure, shows great prospect in wind power generation. Since different rotor structures lead to great differences in the BDFG performance, the research of BDFG rotor structure has been a hotspot. However, only a few of the research studies have paid attention to the rotor and stator slot combination of the BDFG, especially for the BDFG with a novel hybrid rotor. Improper slot combination will lead to efficiency decrease, additional loss increase, and undesirable torque in an electrical machine. In order to study the principle of slot combination of the BDFG with the hybrid rotor, the combination approach of theoretical analysis and experiments is presented in this paper. Furthermore, a coupling factor which reflects the coupling ability of the BDFG with different slot combinations is proposed. Moreover, the best slot combination of the proposed BDFG is determined, and several parameters such as useful harmonic contents, total harmonic voltage distortion (THDu), core loss, and copper loss are considered as major criteria for judgment.

A Novel Mesh-Based Equivalent Magnetic Network for Performance Analysis and Optimal Design of Permanent Magnet Machines

This paper proposes a novel mesh-based equivalent magnetic network (EMN) model for performance analysis and optimal design of permanent magnet (PM) machines. The key contribution of the EMN model is that a generalized air-gap model solution is proposed by considering the machine motion of PM machines. Meanwhile, a modular modeling method is presented, and then the optimal design of PM machines can be investigated without repetitive programming and modeling. Two kinds of mesh elements are comprehensively utilized in the EMN model, and a hybrid rotor PM (HRPM) machine with interior PM and surface PM configuration is selected as an example to illustrate the development processes of EMN model. Meanwhile, the electromagnetic characteristics of HRPM machine are calculated by the proposed EMN model, such as back electromotive force, air-gap flux density distribution, and average torque. Finally, the accuracy and effectiveness of the proposed EMN model are verified through comparisons with finite element analysis and experimental tests.

Design and Implementation of a Low Power Outer-Rotor Line-Start Permanent-Magnet Synchronous Motor for Ultra-Light Electric Vehicles

Recently, while electric vehicles (EV) have substituted the fossil fuel vehicles, the design of the electrical motors with more efficient and less mechanical converters has become mandatory due to the weighting gears, mechanical differentials, and other cost-increasing parts. To overcome these problems, double electrical motors with low speed and high torque have been designed and used in the rear wheels of the EVs without any gearbox and mechanical differential. In this study, a novel outer rotor line-start hybrid synchronous motor is proposed as another solution. For this aim, four different hybrid rotor types, including magnets and rotor bars, have been designed and analyzed. Calculation and estimation of all parameters to design a motor are introduced. All of the analyses were carried out by Finite Elements Method (FEM). One of the analyzed motors, which is called Type-D was selected and implemented because of the best startup performance and better steady-state behavior under the rated load and overload. While holding this motor at synchronous speed under nominal load, in case of overloading, it remained in asynchronous mode, thus maintaining the sustainability of the system. Obtained results prove that the newly proposed outer rotor LSSM has the advantages of both synchronous motor and asynchronous motor. All of the experimental results validate the simulations well. The effects of the magnet alignments and dimensions on the performance of the motors are presented.

Principle of Torque-Angle Approaching in a Hybrid Rotor Permanent-Magnet Motor

This paper reveals a torque-angle approaching principle in a hybrid rotor permanent-magnet (HRPM) motor. The key is to obtain the relationship between angles of shifted surface-inserted PMs (SPMs) as well as assisted airspace barriers and the current angles of maximum PM torque as well as maximum reluctance torque. In order to find out this relationship, the PM torque and reluctance torque are separated accurately and effectively by the proposed torque separation method. In this method, the parameters in an abc reference frame are transformed to a d- - q reference frame via Park transformation, and then the model considering cross-coupling and magnetic saturation effect is used to calculate four torque components. Moreover, the shifting of SPMs has been confirmed to have both influence on the current angles of maximum PM torque and maximum reluctance torque, while the assisted airspace barriers only affect the current angle of maximum reluctance torque. Thus, the total torque can be enhanced by optimal angles of shifted SPMs and assisted airspace barriers because of higher utilization of both PM torque and reluctance torque. In order to evaluate the presented principle in the HRPM motor, a prototype is manufactured for experiments. Through theoretical analysis and experimental testing, it is verified that the proposed principle is feasible and effective.

Study on high pressure design of contra-rotating small hydroturbine

It is requested that the hydroturbine is small size and high performance. Therefore, we adopted contra-rotating rotors, which can be expected to achieve small size and high performance. However, when the rotors become smaller, the output power of conventional contra-rotating rotors, which is composed of axial flow rotors, is very low. In order to achieve small size and high output power, we propose new type contra-rotating rotors, which is composed of a hybrid rotor and a centrifugal rotor. In this research, we investigate performance of the new type contra-rotating small hydroturbine model by the numerical analysis. We report on the influence of deflection angle on the performance and internal flow condition.

Improvement torque performances of interior permanent-magnet machines

Due to their excellent efficiency, power density and constant power speed region, interior permanent-magnet (IPM) machines are very suitable for electric vehicles (EVs). This paper proposed a new IPM rotor topology, which can offer high reluctance torque, wide constant power speed range and excellent overload capability. Besides, five rotor topologies with integral-slot distributed-windings IPM machines, including four existing IPM topologies and the proposed IPM topology, are designed optimally. Their characteristics, which include d-q axis inductances, saliency ratios, electromagnetic torques, corresponding torque ripples, back-electromotive forces (EMFs), overload capabilities and flux weakening performances are evaluated quantitatively. Finally, a three phase 48s8p hybrid rotor PM machine is built to verify the performances of the proposed IPM machine. This work provides some general concepts for machine developers who are willing to build IPM machines for high-performance EV applications.

Rotor optimisation design and performance comparison of BDFG for wind power generation

Doubly fed induction generators and permanent magnet synchronous generators are widely used in wind power generation system in recent years. However, they still have technological and economic penalties, which limit their applications in wind power generation. This study presents a novel brushless doubly fed generator (BDFG) with the hybrid rotor, which has several outstanding advantages, so as to penetrate into large-scale offshore wind power generation. In this study, the magnetic field modulation of the hybrid rotor is studied in detail. Owing to the decisive role of ‘special rotor’ on the performance of BDFG, the effect of main rotor structure parameters on coupling capacity is analysed based on Taguchi method, and the effect of assisted cage bars on the coupling capacity is also researched. The simulation models are simulated and analysed to compare the different exciting winding conditions. A 25.8 kW, 8/4 pole prototype BDFG with the hybrid rotor is manufactured to examine the performance of the proposed BDFG. Finally, the simulation and experiment results verify that the optimised rotor has stronger coupling capacity and the few-pole (i.e. 4-pole) winding should be used as control winding.

The synchronous generator based on a hybrid excitation with the extended range of voltage adjustment

In the paper a synchronous generator based on a hybrid excitation, including permanent magnets and field coil, is studied. The structures of rotor magnetic circuit allowing one to expand the range of generator voltage adjustment are explained and compared with the standard hybrid rotor. The structures are described mathematically and their equivalent circuits are given. The results of theoretical analysis and experimental test are presented.

Analytical Model of Torque-Prediction for a Novel Hybrid Rotor Permanent Magnet Machines

This paper presents an analytical method for predicting the electromagnetic performance in permanent magnet (PM) machine with the spoke-type rotor (STR) and a proposed hybrid rotor structure (HRS), respectively. The key of this method is to combine magnetic field analysis model (MFAM) with the magnetic equivalent circuit model. The influence of the irregular PM shape is considered by the segmentation calculation. To obtain the boundary condition in the MFAM, respectively, two equivalent methods on the rotor side are proposed. In the STR, the average flux density of the rotor core outer-surface is calculated to solve the Laplace's equation with considering for the rotor core outer-surface eccentric. In the HRS, based on the Thevenin's theorem, the equivalent parameters of PM remanence BreB and thickness hpme are obtained as a given condition, which can be utilized to compute the air-gap flux density by conventional classic magnetic field analysis model of surface-mounted PMs with air-gap region. Finally, the proposed analytical models are verified by the finite element analysis (FEA) with comparisons of the air-gap flux density, flux linkage, back-EMF and electromagnetic torque, respectively. Furthermore, the performance that the machine with the proposed hybrid structure rotor can improve the torque density as explained.

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.

A comparative study between optimal metal and composite rotors for flywheel energy storage systems

Most recent research on flywheel rotors has focused on high-speed composite rotors as the storage element of the flywheel energy storage system (FESS). Literature research indicates that this is primarily due to the high specific energy of composites compared to metals. However, a quantitative comparison of the performance of flywheels made from these materials has not been conducted. This paper aims to answer the question - ‘Are composite flywheels better suited for energy storage than metal flywheels?’. This study uses three different performance indices: kinetic energy; specific energy; and, energy per cost, to compare the corresponding rotor designs. A plain-stress, linear elastic mathematical model of the flywheel rotor described by Krack et al. (2010) is used for analysis. Different optimization formulations corresponding to performance indices chosen based on the FESS application are then solved to study optimal FESS designs. The study indicates that for applications where the energy-per-cost is to be maximized, metals are superior to composite rotor materials. On a total energy basis, metals and composites are on par with each other. Composite rotors are however, superior for applications requiring high specific energy. A hybrid rotor, with a metallic energy storage element and a thin composite burst-rim, is also optimally designed and found to be a viable solution, because it offers the cost benefit of metal rotors, as well as the burst-safety provided by composites.

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.

Analysis of a Hybrid Rotor Permanent Magnet Motor Based on Equivalent Magnetic Network

An equivalent magnetic circuit (EMC) model is built for a hybrid rotor permanent magnet (HRPM) motor. The key of the EMC model is that a novel section modeling method for permanent magnet (PM) is proposed to take PM end-leakage and local saturation of magnetic bridge into consideration, and it is used to separate the main magnetic circuit and leakage magnetic circuit of PM. Besides, a generalized equivalent method of winding magnetomotive force is adopted for the modeling of distributed winding. Meanwhile, an improved iterative algorithm is presented to solve the problem that the iteration does not converge when iron core is severely saturated. Then, the accuracy of the proposed EMC model is evaluated by experimental test and finite-element analysis. Finally, frozen permeability method based on the proposed EMC model is utilized to separate the PM torque component and the reluctance torque, which is time saving, and can be used to investigate and optimize the torque-angle characteristic clearly.

Wide regulated series hybrid excitation alternator

Parallel hybrid excitation alternators (PHEAs) are large in size but offers wide flux regulation capability. Series hybrid excitation alternator has limited flux regulation capability but compact compared to PHEAs. A new rotor excitation topology has been proposed for a series hybrid rotor excitation alternator (SHREA). The proposed machine is not only small in size but also have wide flux regulation capability. The proposed machine can be classified as a series hybrid machine as permanent magnets and field windings are arranged in a single rotor ensuring series addition of permanent magnet flux and field winding flux. In this study, one more rotor configuration for quick maintenance SHREA is also proposed. As the name suggests, for any fault in excitation winding, they can be easily replaced. Two 1.3 kW prototypes with such designs have been validated with finite-element method simulation and hardware testing.

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.

Improvement of Torque Capability of Permanent-Magnet Motor by Using Hybrid Rotor Configuration

This paper proposes a novel hybrid rotor permanent-magnet (HRPM) motor to improve torque capability, including average torque and torque ripple. The key of the proposed motor is that it can utilize high PM torque of surface-inserted PM (SPM) rotor module and high reluctance torque of interior PM (IPM) rotor module at the same time. Meanwhile, the shifting angle of SPMs and open angle of air barriers are introduced to improve the average torque and reduce the torque ripple, respectively. The two variables are employed to create circumferential asymmetry of the rotor for generating an angular difference of the electromagnetic torque between adjacent N-pole and S-pole, thus minimizing torque ripple. In order to evaluate the proposed motor, an IPM motor and a SPM motor with the same dimension and volume of PM are used as benchmarks. Through theoretical analysis and experimental test, it is verified that the proposed HRPM motor can offer higher torque density and lower torque ripple simultaneously.