Direct-drive PM Research Articles

Analysis of MW-Level Offshore Wind Turbine Generators with Dual Star–Delta Fractional-Slot Windings

This paper investigates the use of fractional-slot concentrated windings (FSCWs) in large-scale (MW level) offshore wind generators. It focuses specifically on a power rating of 3 MW and uses an existing direct-drive synchronous PM machine (DD-SPM) with 480s/160p and dual three-phase integer-slot winding (ISW) as a baseline. A multiple of the common 12s/10p FSCW machine is used that matches the electrical frequency of the ISW machine, yielding a 192s/160p dual three-phase machine. The hybrid star–delta connection has grown increasingly popular owing to its unique harmonic cancellation properties, which can help reduce rotor and PM eddy current losses in FSCW machines. In this paper, two dual three-phase star–delta-wound machines are scaled to 3 MW and included in the investigation. Specifically, a 384s/160p dual three-phase and dual star–delta winding machine, which is a multiplication of the 24s/10p machine, and a 192s/176p dual three-phase and dual star–delta winding machine, which is a multiplication of the 24s/22p machine, are used. These machines are investigated using finite element analysis (FEA) and compared on the basis of their air-gap flux density harmonics, open-circuit electro-motive force (EMF), torque performance, and losses and power. It is found that the proposed 384s/160p dual star–delta winding machine has the best electromagnetic performance of all, with a stator power that is 1.2% greater than that of the baseline ISW machine. However, this machine has a coil pitch of 2 and so loses the manufacturing and fault-tolerant advantage of having concentrated windings. If concentrated windings are desired, then the proposed 192s/176p dual star–delta winding machine is the best choice, with the stator power only 2.6% less than that of the baseline ISW machine, but unfortunately still has significant rotor and PM eddy current losses.

Research on Slot-pole Combination in High-power Direct-drive PM Vernier Generator for Fractional Frequency Transmission System

Offshore wind energy is an important part of clean energy, and the adoption of wind energy to generate electricity will contribute to the implementation of the carbon peaking and carbon neutrality goals. The combination of the fractional frequency transmission system (FFTS) and the direct-drive wind turbine generator will be beneficial to the development of the offshore wind power industry. The use of fractional frequency in FFTS is beneficial to the transmission of electrical energy, but it will also lead to an increase in the volume and weight of the generator, which is unfavorable for wind power generation. Improving the torque density of the generator can effectively reduce the volume of the generators. The vernier permanent magnet machine (VPM) operates on the magnetic flux modulation principle and has the merits of high torque density. In the field of electric machines, the vernier machine based on the principle of magnetic flux modulation has been proved its feasibility to reduce the volume and weight. However, in the field of low-speed direct-drive machines for high-power fractional frequency power generation, there are still few related researches. Therefore, this paper studies the application of magnetic flux modulation in fractional frequency and high-power direct-drive wind turbine generators, mainly analyzes the influence of different pole ratios and different pole pairs on the generator, and draws some conclusions to provide reference for the design of wind turbine generators.

Permanent Magnet Vernier Machines for Direct-Drive Offshore Wind Power: Benefits and Challenges

Permanent magnet Vernier (PM-V) machines, at low power levels (few kWs), have shown a great potential to improve the torque density of existing direct-drive PM machines without much compromising on efficiency or making the machine structure more complicated. An improved torque density is very desirable for offshore wind power applications where the size of the direct-drive machine is an increasing concern. However, the relatively poor power factors of the PM-V machines will increase the power converter rating and hence cost. The objective of this paper is to review the benefits and challenges of PM-V machines for direct-drive offshore wind power applications. The review has been presented considering the system-level (direct-drive generator + converter) performance comparison between the surface-mounted permanent magnet Vernier (SPM-V) machines and the conventional SPM machines. It includes the indepth discussion on the challenges facing the PM-V machines when they are scaled up for multi-MW offshore wind power application. Other PM-V topologies discussed in literature have also been reviewed to asses their suitability for offshore wind power application.

연 풍력시스템의 회전속도 측정 및 발전기 시스템에 적용 가능한 영구자석 발전기 설계에 관한 연구

A direct PM generator has the effect of reducing the mechanical noise and ease of maintenance by eliminating a number of power transmission components. In addition, wind turbines operating at low speed with the advantages of high output, high efficiency, and small size. The generator was designed as a small direct-drive PM generator that can be applied to a kite even at low wind speeds. The RPM (Revolutions Per Minute) of the reel was measured in two ways using a cadence/speedometer sensor and a tachometer while the actual kite. The RPM derived from the experiment was applied to the simulation on the designed generator. The no-load characteristic analysis for the magnetic fields produced for the permanent magnet generator by a permanent magnet and stator winding currents is achieved using a 2D coordinate system. A commercial electromagnetic analysis program, ANSYS Maxwell, was used to model the electromagnetic dynamics.

The Effect of the Electrical Steel Properties on the Temperature Distribution in Direct-Drive PM Synchronous Generators for 5 MW Wind Turbines

The effect of the magnetic and thermal properties of four electrical steel grades were compared for a permanent magnet synchronous generator (PMSG). The low loss grades are expected to have less iron loss in the stator laminations, but their thermal conductivity may be lower. Therefore, the evacuation of the heat may be less effective. This has an influence on the temperature distribution, which is crucial in case of PMSG. The investigated generator is a 5 MW, radial flux machine designed for direct-drive wind turbines. A thermal finite-element model was used to simulate the temperature distribution in the generator. The influence of the steel grade on the thermal distribution was compared for four geometries of PMSG with varying air-gap diameter and pole-pair number. In conclusion, the number of pole pairs has a major influence on the importance of electrical and thermal properties of the steel grades applied.

Analysis on Effect of Parameters of Different Wind Generator on Power Grid Transient Stability

To analyze the factors which affecting transient stability of power system, the dynamic model of doubly-fed induction generator and direct-drive PM synchronous generator has been built using PSCAD. Impact of different wind farm integration on grid typically in China has been presented. The influence of the variations of transient reactance, negative sequence reactance and rotary inertia on critical clearing time of power system transient stability is analyzed by time-domain simulation. Mixture operation of DFIG and PMSG to optimize the stability of system has been analyzed firstly. The digital simulation results show that doubly-fed induction wind turbines is a better choice to meet the requirement of system instability due to large wind farm integration in comparison with direct-drive PM synchronous wind turbines. With a rather large rotary inertia, the proper ratio of direct-drive PM synchronous wind turbines used in wind farm could be comprehensive planning by optimized the stability of system. Analysis of this paper should be provided as academic reference for improving design of wind farm system. Keyw

Optimal design of direct-driven PM wind generator using adaptive univariate dynamic encoding algorithm for searches (uDEAS)

Optimal design of direct-driven PM wind generator using adaptive univariate dynamic encoding algorithm for searches (uDEAS)

Design of a unique direct driven PM generator adapted for a telecom tower wind turbine

A vertical axis wind turbine has been designed to electrify a novel kind of telecommunication tower. This paper presents the design of a generator for this purpose. The generator is a permanent magnet generator rated at 10 kW. It has an unusually large diameter to fit on the outside of the telecommunication tower. The generator has been designed by using a two-dimensional FEM model. Simulations show that the generator has high efficiency through the whole operational interval. Furthermore, the generator has a high overload capability enabling electric control of the turbine. The generator has been built and the design shown feasible. Preliminary experimental results show that the induced voltage is lower than expected from simulations indicating insufficient modelling of three-dimensional effects, which are particularly large in a generator with these unusual dimensions. ► A permanent magnet ring generator with unique design constraints has been designed. ► The generator has been built and the design shown feasible. ► Preliminary experimental results show a voltage lower than expected from simulations. ► Generator modelling of 3D effects is not sufficient for these extreme dimensions.

CHALLENGES AND OPPORTUNITIES OF ELECTRIC MACHINES FOR RENEWABLE ENERGY

This paper gives an overview of various electric machines for application to renewable energy harvesting, and reveals the corresponding challenges and research opportunities. After introducing various renewable energies and electric machines, the concept of renewable energy machines is coined. Then, the existing machines, including the DC, induction and synchronous types, for renewable energy harvesting are challenged. Consequently, research opportunities of advanced machines, including the stator-permanent magnet (PM), direct-drive PM and magnetless types, are elaborated. Finally, both near-term and long-term renewable energy machines are identifled especially the emerging stator-PM, vernier PM and stator doubly fed doubly salient types.

A 225 kW Direct Driven PM Generator Adapted to a Vertical Axis Wind Turbine

A unique direct driven permanent magnet synchronous generator has been designed and constructed. Results from simulations as well as from the first experimental tests are presented. The generator has been specifically designed to be directly driven by a vertical axis wind turbine and has an unusually low reactance. Generators for wind turbines with full variable speed should maintain a high efficiency for the whole operational regime. Furthermore, for this application, requirements are placed on high generator torque capability for the whole operational regime. These issues are elaborated in the paper and studied through simulations. It is shown that the generator fulfils the expectations. An electrical control can effectively substitute a mechanical pitch control. Furthermore, results from measurements of magnetic flux density in the airgap and no load voltage coincide with simulations. The electromagnetic simulations of the generator are performed by using an electromagnetic model solved in a finite element environment.

Robust design of a direct-drive PM hub motor by fuzzy-inference taguchi method

Robust design of a direct-drive PM hub motor by fuzzy-inference taguchi method

Design and Optimization of a Radial Flux Direct-drive PM Generator using Ant Colony Algorithm

Design and Optimization of a Radial Flux Direct-drive PM Generator using Ant Colony Algorithm

Novel Memetic Algorithm implemented With GA (Genetic Algorithm) and MADS (Mesh Adaptive Direct Search) for Optimal Design of Electromagnetic System

This paper presents the novel implementation of the memetic algorithm with GA(Genetic Algorithm) and MADS(Mesh Adaptive Direct Search), which is applied for the optimal design methodology of the electric machine. This hybrid algorithm has been developed for obtaining the global optimum rapidly, which is effective for the optimal design of a electric machine with many local optima and much longer computation time. As a meta-heuristic search algorithm, MADS combined with a GA is validated with the Rastrigin function and the Shubert function with distinguished multimodal characteristics by investigating the evaluation number for optima convergence. In particular, the proposed algorithm has been forwarded to the optimal design of a direct-driven PM wind generator for maximizing the Annual Energy Production(AEP), of which design objective should be obtained by FEA(Finite Element Analysis). Finally, it is shown that MADS combined with GA has contributed to reducing the computation time effectively for the optimal design of a PM wind generator when compared with the purposely developed GA implemented with the parallel computing method.

MADS를 이용한 직접구동형 풍력발전기 최적설계

본 논문에서는 FEM(Finite Element Method)을 이용한 직접구동형 영구자석 풍력발전기의 최적설계를 위해 최신의 최적화 기법인 MADS(Mesh Adaptive Direct Search)를 적용하였으며, 최적설계 목표는 연간 에너지 생산량(Annual Energy Production : AEP)을 최대화 하는 방향으로 선정하였다. 또한, 풍력발전기의 전 운전영역을 고려하기 위해 해당풍속에서의 통계적 확률밀도와 연간 운전시간을 적용하여 연간 최대에너지 생산량을 산정하였다. 아울러, MADS의 최적설계 결과와 병렬분산 컴퓨팅을 결합한 유전 알고리즘(Genetic Algorithm : GA)의 최적설계 결과를 비교하였으며, MADS는 병렬분산 유전알고리즘에 비해 상대적으로 빠른 수렴성을 나타내었다.

DEAS를 이용한 직접구동형 풍력발전기 최적설계

Optimal design of the direct-driven PM Wind Generator, combined with DEAS(Dynamic Encoding Algorithm for Searches) and FEM(Finite Element Method), has been proposed to maximize the Annual Energy Production(AEP) over the whole wind speed characterized by the statistical model of wind speed distribution. In particular, DEAS contributes to reducing the excessive computing time for the optimization process.

Optimal Design of Direct-Driven PM Wind Generator for Maximum Annual Energy Production

Optimal design of the direct-driven PM wind generator, coupled with finite element analysis and genetic algorithm, has been performed to maximize the annual energy production over the whole wind speed characterized by the statistical model of wind speed distribution. Particularly, the parallel computing via internet web service has been applied to loose excessive computing times for optimization.

FEM Simulations and Experiments of Different Loading Conditions for a 12 kW Direct Driven PM Synchronous Generator for Wind Power

Results from experiments on a direct driven permanent magnet synchronous generator are presented. Dynamic simulations have been performed using the finite element method in order to study the generator. The simulations are performed by using an electromagnetic model, which is described by a combined field and circuit equation model and is solved in a finite element environment. The stator winding of the generator consists of circular cables and the rotor has surface-mounted, arched, permanent magnets. A complete experimental setup has been used consisting of a motor, a frequency converter, a gearbox and electrical loads. The generator is connected to a purely resistive load. Measurements have been performed for different rotational speeds and different loads. Furthermore, the generator has been studied for the realistic wind turbine loading conditions for operation at the optimum tip speed ratio. The variable speed operation in a wind turbine is evaluated and discussed. The agreement between experimental results and simulations based on finite element calculations is high, indicating precise simulations. The measurement errors are calculated and discussed. Furthermore, other sources of error are suggested and discussed that could explain the differences between the simulations and the measured data.

Investigation on Multi-star Structures for Large Power Direct-drive Wind Generator

In order to increase the power capability of direct-drive PM wind generators with respect to established quality criteria like the electromagnetic torque and the power transferred to the grid, a polyphased multi-star system is studied. The influence of the number of stars, their phase shift and the waveform of the electromotive force are investigated. The possible configurations, i.e. the numbers of magnets and slots, are found and compared.

Power Electronic Converters Devoted to Stand-Alone Wind-Energy Generating Systems

Small to medium rating (up to 25 kW wind generators are usually used in stand-alone generation-battery systems in remote areas where the cost of transmitting energy is prohibitive. Wind-energy generating systems, operating at variable-speed. need power electronic converters in order to achieve best wind energy exploitation. Selection of the most suitable converter topology for wind energy generating systems depends-on the medium amount of wind available, the user devices voltage level, the sizing and the number of semiconductor and passive power components used in the electronic converter. This paper deals with prototypal generating systems composed of direct-drive PM synchronous generator, diode bridge rectifier, d.c.-d.c. converter and storage battery. Different d.c.-d.c. converter topologies are analyzed; first theoretical investigations highlight the clear superiority of step-up converter and step-down converter with respect to the other topologies. Computer simulations allowed an exhaustive investigation of both the step-up and the step-down converter configurations. Experimental comparison between different power electronic converter topologies for wind-energy generation was achieved during the carried our laboratory tests on a prototypal system.