Permanent Magnet Wind Generator Research Articles

Permanent magnet wind generators: control strategies to manage voltage unbalances

The paper presents four different control strategies for grid connected voltage source inverters, devoted to the interface of permanent magnet synchronous wind generators with the distribution network. A common dq-axes control is compared with two modified controls in the dq frame which take into account also negative sequence components of voltages, and currents and a control approach in the stationary αβ frame which reduces the computational complexity of the control itself. An ATPDraw model of a 2 MW wind generator has been developed and employed for simulating the responses of the four control schemes to voltage unbalances and voltage dips. The improved control strategies have shown better performances in terms of reduction of 100 Hz oscillating power components during network voltage unbalances

Torque Ripple and Mass Comparison between 20 MW Rare-Earth and Ferrite Permanent Magnet Wind Generators

This article investigates the comparison between two configurations of 20 MW offshore synchronous wind generators using ferrite and rare-earth permanent magnets. The optimization-based comparison concerns the torque ripple and active mass, which are two crucial criteria for offshore wind generators. Both generators adopt surface-mounted permanent magnet type with direct-drive technology to avoid problems associated with the gearboxes. The result shows that at the full-load condition, the ferrite permanent magnet generator can reduce the torque ripple to as much as 0.12%, while the rare-earth counterpart can be about 2.5 times lighter than the former one.

Design and Analysis of a Variable-Speed Constant-Amplitude Wind Generator for Stand-Alone DC Power Applications

This paper presents the design and analysis of a permanent magnet (PM) wind generator which consists of two sets of windings, and two rotors. The proposed PM wind generator is designed for variable-speed constant-amplitude voltage operation in DC power applications, in order to maximize the utilization of wind energy and make the electricity more accessible to stand-alone situations, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e.g.</i> , remote areas and offshore islands. The operating principle of the variable-speed constant-amplitude voltage operation of the proposed PM wind generator is demonstrated in detail. A comparative study is carried out among the proposed generator, a conventional surface-mounted PM synchronous generator, and an existing counterpart generator used for the same application. The results show that compared to the conventional PM synchronous generator and the existing counterpart, the proposed PM wind generator exhibits the advantages of high induced voltage, high torque/power density, high efficiency, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">etc.</i> Finally, the proposed PM wind generator is prototyped and manufactured. The validity of the variable-speed constant-amplitude operation of the proposed generator under both steady-state and dynamic conditions, is verified by experimental results.

Modelling and Analysis of Inter-Turn Short-Circuit Faults for Large-Power SPM Wind Generators

This paper proposes a general analytical model for large-power surface-mounted permanent magnet (SPM) wind generators under inter-turn short-circuit (ITSC) faults. In the model, branch currents rather than phase currents are used as state variables to describe the electromagnetic behavior of the faulty machine. In addition, it is found that the multiphase Clarke transformation can be used to simplify the proposed fault model with the inductances calculated analytically or numerically using finite element analysis. With the latter, both linear and nonlinear inductances can be obtained, and the non-linear inductances are used for the fault modelling of large power rating machines due to larger electrical loading and heavier magnetic saturation. With the developed fault model, studies of scaling effects (different power ratings such as 3 kW, 500 kW and 3 MW) and the influence of fault location on the electromagnetic performance of SPM generators with series-parallel coil connections have been carried out. The simulation results show that large-power SPM wind generators are vulnerable to ITSC faults when a relatively small number of turns are short-circuited and a single-turn short-circuit fault at the top of the slot is found to be the worst case.

Analytical modeling for rotor eccentricity solution in wind power generator with bread loaf PMs

This paper presents a novel analytical solution for the magnetic fields of large permanent magnet (PM) wind generator with bread loaf PMs under normal and eccentricity conditions. To simplify the calculation, the generator is first approximately modeled in the Cartesian coordinate, and then the bread loaf PMs are equivalently considered by pairs of coils so that their effects can be expressed by mathematic equations. By applying the Fourier separation method, with the boundary and interface conditions, the magnetic fields in the calculation regions can be obtained by solving system equations. Afterward, the rotor eccentricity is investigated by transforming the corresponding model to a new orthogonal coordinate system by using a conformal mapping technique. Numerical examples validate the proposed method and the calculated results have a satisfactory agreement with the finite element analysis. The established model in this paper has a significant value for modeling large PM wind power generators, and the calculation time is deduced remarkably.

Environmental Condition Boundary Design for Direct-Drive Permanent Magnet (DDPM) Wind Generators by Using Extreme Joint Probability Distribution

In future engineering applications, it is important for a direct-drive permanent magnet (DDPM) wind generator to be designed with optimized environmental condition boundary. This paper presents a novel extreme joint probability distribution method of boundary design to formulate the evaluation model and correlation between component design and environmental conditions. With this method, the joint probability distributions of multidimensional parameters for typical wind resource areas in China are studied. A 3.3-MW DDPM wind generator is involved in the case study to validate the superiority of the method. Furthermore, to improve the generalizability of the method, some typical wind resource data platforms are calibrated regarding the measured data. It is shown that the ERA5 dataset can be used as a supplement to enhance the representativeness of the measured data for the joint probability distributions. Therefore, the proposed method can be potentially used to optimize the system design of future DDPM wind generators.

Analytical Performance Estimation of a Fall-Back Inner-Rotor Transverse-Flux Permanent Magnet Generator using Magnetic Equivalent Reluctance Circuit

The potential of wind energy resources is propelled fast and power extraction is increasing considerably due to the development of reliable and cost-effective wind turbine generators. Various permanent magnet (PM) wind generators have been implemented for wind power generation, among which, the conventional transverse-flux permanent magnet generator (TFPMG) is popular due to their higher torque density and simple coil design, but it has some disadvantages in comparison with radial flux PM generator, i.e., higher flux leakages and complex 3D flux pattern. In this article, a fall-back inner rotor transverse-flux PM wind generator FB-TFPMG has been investigated to override the disadvantages of conventional TFPMG. It employs half of the total PMs on the rotor and U-shaped stator cores. An analytical model of the proposed FB-TFPMG has derived using magnetic equivalent reluctance circuit (MERC) to predict the performance of the generator, i.e., flux densities in the air-gap, under aligned and unaligned conditions of rotor PMs with U-shaped stator cores. The results of the MERC model is verified with the results obtained through 3D finite element analysis.

Analysis of electromagnetic characteristics of typical faults in permanent magnet wind generators

Due to the harsh actual operating environment of the permanent magnet wind turbine, it is easy to break down and difficult to monitor. Therefore, the electromagnetic characteristics identification of major fault types of large-scale permanent magnet wind turbines is studied in this paper. The typical faults of rotor eccentricity, stator winding short circuit and permanent magnet demagnetization of permanent magnet wind turbines are analyzed theoretically. The wavelet analysis algorithm is used to decompose and reconstruct the abnormal electromagnetic signal waveform band, and the characteristic frequency of the electromagnetic signal is obtained when the fault occurs. In order to verify the effectiveness of the proposed method, a 3.680MW permanent magnet wind turbine was taken as the research object. Its physical simulation model was established, and an external circuit was built to carry out field co-simulation. The results show that the motor fault type can be determined by detecting the change rule of fault characteristic frequency in the spectrum diagram, and the electromagnetic characteristic analysis can be applied to the early monitoring of the permanent magnet wind turbine fault.

Study on Calculating Method of the Super-transient Reactance of Permanent Magnet Motor and Analysis of Influencing Factors

This paper takes a salient pole permanent magnet wind generator as the research object and summarizes the calculation method of its super-transient reactance parameters. The analytical method and parameter identification method are selected to analyze the influencing factors of the direct axis super-transient reactance parameters. Finally, the variation law of direct axis super-transient reactance parameters with the number of parallel branches, short pitch ratio, and diameter of damping windings is obtained, which provides a certain reference for the dynamic performance evaluation of permanent magnet motors.

A Novel Six-Phase V-Shaped Flux-Switching Permanent Magnet Generator for Wind Power Generation

Flux-switching permanent magnet (FSPM) machines have attracted wide attention in many rotating applications that require high-power density. In this research, we propose for the first time a novel six-phase FSPM generator with a stator featuring a V-shaped flux-focusing magnet arrangement. The design is targeted for low-speed wind power generation. To achieve the design objectives as a wind generator, the highly comprehensive structural parameters, including the number of rotor poles, split ratio, and rotor pole width, are designed and optimized using 2D finite-element analysis. From findings, the optimal stator/rotor pole combination is discovered to be 12/19 for the considered power and speed requirements. When compared to the initial structure, the optimized structure of the V-shaped FSPM generator is found to produce a significant improvement in EMF, cogging torque, electromagnetic torque, power, and efficiency. The power-generating performance of the proposed FSPM generator is found to be outstanding when compared to the radial-flux PM generators described in the literature. Therefore, the proposed V-shaped FSPM generator is capable of being used for low-speed wind power generation. The machine configuration adjustment approach presented in this work can also be utilized for the design of permanent magnet wind generators.

Interturn Short Fault Detection and Location of Permanent Magnet Wind Generator Based on Negative Sequence Current Residuals

This article proposes a model-based method for the detection and phase location of interturn short fault (ISF) in the permanent magnet synchronous generator (PMSG). The simplified mathematical model of PMSG with ISF on dq-axis is established to analyze the fault signature. The current residuals are accurately estimated through Luenberger observer based on the expanded mathematical model of PMSG. In current residuals, the second harmonics are extracted using negative sequence park transform and angular integral filtering to construct the fault detection index. In addition, the unbalance characteristics of three-phase current after ISF can reflect the location of the fault phase, based on which the location indexes are defined. Simulation results for various operating and fault severity conditions primarily validate the effectiveness and robustness of diagnosis method in this paper.

Fault tolerance analysis of double winding permanent magnet wind generator based on field circuit combination method

Aiming at the problem that the reliability of traditional double winding permanent magnet wind generator is low when it runs on the sea, and it cannot run normally when the fault occurs, the fault tolerance characteristics of the generator are studied. Taking a 60 kW double winding permanent magnet synchronous wind generator as an example, the finite element method is used to calculate the electromagnetic parameters of the generator under rated load, single winding fault condition and fault-tolerant condition, and the variation characteristics of magnetic density, electromagnetic torque and other electromagnetic parameters under various working conditions including fault-tolerant conditions are determined. At the same time, the thermal circuit method is used to check the hot spot temperature of the generator under various working conditions to explore the fault tolerance necessity and operation reliability of the dual winding permanent magnet wind turbine. Finally, by building a prototype platform, the rationality of the solution model and the accuracy of the calculation results are verified.

Non-Conventional, Non-Permanent Magnet Wind Generator Candidates

Global industrialization, population explosion and the advent of a technology-enabled society have placed dire constraints on energy resources. Furthermore, evident climatic concerns have placed boundaries on deployable energy options, compounding an already regrettable situation. It becomes apparent for modern renewable energy technologies, including wind generators, to possess qualities of robustness, high efficiency, and cost effectiveness. To this end, direct-drive permanent magnet (PM) wind generators, which eliminate the need for gearboxes and improve wind turbine drivetrain reliability, are trending. Though rare-earth PM-based wind generators possess the highly sought qualities of high-power density and high efficiency for direct-drive wind systems, the limited supply chain and expensive pricing of the vital raw materials, as well as existent demagnetization risks, make them unsustainable. This paper is used to provide an overview on alternative and viable non-conventional wind generators based on the so-called non-PM (wound-field) stator-mounted flux modulation machines, with prospects for competing with PM machine variants currently being used in the niche direct-drive wind power generation industry.

An Integrated Elitist Approach to the Design of Axial Flux Permanent Magnet Synchronous Wind Generators (AFPMWG)

This paper addresses an integrated and developed approach to the design of an Axial Flux Permanent Magnet Wind Generator (AFPMWG). The proposed analytical method of design employs the size equations and precise inductance calculations simultaneously, as well as considering the mechanical constraints of the back-iron disc of the rotor. An Elitist Genetic Algorithm (EGA), such as a high capability optimization method, has been used to solve the equations and design of a wind generator with predefined rating power. The objectives of the coreless AFPMWG design process are minimizing the magnet consumption, maximizing machine efficiency, and achieving maximum sinusoidal induction voltage, considering the wind properties of the geographical area of utilization. The optimal calculation of the permanent magnet thickness is also taken into consideration in this work. The flux density distribution in all parts of the machine has been investigated for the magnetic saturation phenomenon. In this regard, special attention is paid to rotor back discs, which are made from nonlinear material with an optimum thickness. The inductance of the leakage flux of the coreless machine has been considered by parallel computation via the Finite Element Method (FEM) and analytical equations. Finally, three-dimensional and two-dimensional finite element analyses are used to validate the performance of the machine design according to the characteristics of Iran wind resources. The results show the high ability of the proposed approach in AFPMWG design and in considering the objectives and constraints carefully.

Design Optimization of a HTS-Modulated PM Wind Generator

The flux-modulated machine based on air-gap magnetic flux modulation theory has become a focus in low speed and high torque density applications. In this paper, the optimal design of a large scale flux modulation (FM) permanent magnet (PM) generator with high temperature superconducting (HTS) bucks for wind energy conversion systems is presented. Firstly, the working performances of the generator with and without HTS bucks sandwiched between iron segments are analyzed and compared through finite element analyses (FEA). The FM effect enhancement by employing the HTS bucks is proved through the comparisons. Secondly, the sensitivities of the generator structural parameters on the back electromotive force (EMF) and the cogging torque amplitude are analyzed by Taguchi method to decide the optimization variables and their variation ranges. Thirdly, the structural parameters determined by the sensitivity analyses are optimized through the coupling of genetic algorithm (GA) and FEA to maximum the generator output power capacity. The calculation burden during optimization is reduced with a reduction on the optimization variable number through the Taguchi method based sensitivity analyses. Finally, the electromagnetic characteristics of the FMPM generator with optimized structural sizes are numerically investigated.

MADE3D: Enabling the next generation of high-torque density wind generators by additive design and 3D printing

Direct-drive wind turbine generators are increasing in popularity, thanks to recent project developments—especially offshore, where reliability and efficiency are major cost drivers. Yet, high capital costs are forcing many original equipment manufacturers to consider lightweight, high-torque density generators for next-generation multi-megawatt turbines that may be difficult to realize by traditional design or manufacturing methods. In this study, we present a new design framework enabled by advanced machine learning and multimaterial additive manufacturing to perform a magnetic topology optimization that maximizes the torque per rotor active mass for a 15-megawatt direct-drive permanent magnet wind generator. A comparison of the proposed approach against conventional topology optimization demonstrated a significant increase in computational efficiency and accuracy in performance predictions. Results using single and multimaterial compositions for rotor core and magnets identify a wider choice of 3D printable designs for a given specification. A hybrid combination of sintered and dysprosium-free polymer-bonded magnets shows good potential for torque performance by saving material costs up to 8.75%. More than 30% improvement in rotor torque densities is identified which can marginally improve the overall generator torque density. With the rapid evolution of multipowder deposition technolgies, this study can greatly inspire a new paradigm for design-driven manufacturing with novel material compositions and lightweight, low-cost, high-strength multimaterial geometries that were previously unexplored for direct-drive generators.

Design of small scale, axial flux, permanent magnet wind generator in Vietnam

This paper presents the design of light weight, small scale, disk type, axial flux, permanent magnet (AFPM) generator for wind applications. This article also shows the partial works done under state projects in renewable energy in Vietnam to find out the most suitable, reliable, self - made wind generator types for rural and remote areas. The collaboration project of Hochiminh City University (HCMUT) - Hanoi University of Science and Technology (HUST) - Berlin University of Technology (TU Berlin) resulted in some small scale, axial flux, slow speed, permanent magnet (PM) generators which best suited for Vietnam countryside areas. The researches in rare earth PM from HUST, the electrical machine design knowhow of TU Berlin and the renewable energy research experiences of HCMUT, especially in slow speed wind turbines have shown many promising applications. The small scale, permanent magnet wind generator for remote and rural areas as a cheap source of power supply is necessary in Vietnam. Though there are many large wind farms built in many provinces recently but the needs for telecommunication, family lighting in the heights, mountain, unreachable electric grid communes are still necessary. Further research should be done to match the generator for hydro power stations, diesel coupled internal combustion engine. These prospects are very promising.

Guest Editorial: Medpower 2018 Selected Papers

Guest Editorial: Medpower 2018 Selected Papers

Optimization of Ventilation Spacer for Direct-Drive Permanent Magnet Wind Generator

As the rated capacity of the Direct-Drive Permanent Magnet Wind Generator (DDPMWG) increases, the heat produced from the generator’s inner components also increases and it becomes difficult to transfer the inner heat to the ambient. The ventilation spacer has a significant influence on the heat transfer process of DDPMWG. Thus, this paper focuses on the optimization of the ventilation spacer on the thermal field of DDPMWG. Firstly, the fluid flow and heat transfer coupled numerical calculation model is established. The physical model, composed of two half-slots and one tooth of DDPMWG, is established due to the structural symmetries to save the calculations. The sources and boundary conditions for the thermal calculations are also given. Five new ventilation spacers, compared with the original one, are proposed to investigate the thermal fields. The pressure drop and temperature field are compared to find the optimized ventilation spacer for the DDPMWG. The criteria are also presented for judging the heat transfer capacity. To validate the optimized ventilation spacer, the temperature rises of the armature winding with original and optimized ventilation spacers are measured. It proves that the armature winding’s temperature rise of the optimized ventilation spacer is about 4.7 K lower than that with the original ventilation spacer.

Health condition assessment of wind turbine generators based on supervisory control and data acquisition data

As the running time of a wind turbine generator unit (WTGU) increases, the ageing and wear of its components will be aggravated gradually, which leads to deterioration of its operation condition. In order to ensure the safe and stable operation of WTGU and prolong its service life, it is of great significance to know the health condition of the WTGU and reasonably arrange maintenance. Based on the structure of the WTGU and the operation principle of the wind turbine generator (WTG), the condition assessment indexes of WTG were built, and the factors influencing the assessment index were determined. The relationship function between the assessment indexes and their influencing factors was established by using the least square support vector machine, which was used to determine the dynamic limitation of condition assessment index of WTG. The dynamic weight of each assessment index was used to characterise the influence of deterioration degree of different components on WTG conditions. Then the health conditions of WTG were evaluated using a similar cloud and fuzzy comprehensive assessment method separately. Finally, the proposed methods were verified by two examples including a direct-drive permanent magnet wind generator and a doubly-fed wind generator.