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.

A Novel Open-winding Permanent Magnetic Starter-generator

针对永磁电机应用于车载起动／发电系统时存在的电压调节困难、适用转速范围窄、功率因数较低等问题，提出一种新型永磁车载起动／发电系统。通过引入绕组开路型永磁电机，绕组一端接整流桥形成输出直流侧，另一端接逆变桥形成控制端，构成具有宽转速范围和高效率的永磁电机起动／发电系统。分析该系统的起动、发电一体化工作原理，给出了通过逆变侧变换器实现发电机电压、电流控制的方案。仿真和实验结果表明，该新型车载起动／发电系统具有优良的发电调压控制性能，并且适应较宽的转速范围。

Missing interpolation model for wind power data based on the improved CEEMDAN method and generative adversarial interpolation network

Randomness and fluctuations in wind power output may cause changes in important parameters(e.g.,grid frequency and voltage),which in turn affect the stable operation of a power system.However,owing to external factors(such as weather),there are often various anomalies in wind power data,such as missing numerical values and unreasonable data.This significantly affects the accuracy of wind power generation predictions and operational decisions.Therefore,developing and applying reliable wind power interpolation methods is important for promoting the sustainable development of the wind power industry.In this study,the causes of abnormal data in wind power generation were first analyzed from a practical perspective.Second,an improved complete ensemble empirical mode decomposition with adaptive noise(ICEEMDAN)method with a generative adversarial interpolation network(GAIN)network was proposed to preprocess wind power generation and interpolate missing wind power generation sub-components.Finally,a complete wind power generation time series was reconstructed.Compared to traditional methods,the proposed ICEEMDAN-GAIN combination interpolation model has a higher interpolation accuracy and can effectively reduce the error impact caused by wind power generation sequence fluctuations.

Maximum Power Point Tracking in Variable Speed Wind Turbine Based on Permanent Magnet Synchronous Generator Using Maximum Torque Sliding Mode Control Strategy

The present study was carried out in order to track the maximum power point in a variable speed turbine by minimizing electromechanical torque changes using a sliding mode control strategy. In this strategy, first, the rotor speed is set at an optimal point for different wind speeds. As a result of which, the tip speed ratio reaches an optimal point, mechanical power coefficient is maximized, and wind turbine produces its maximum power and mechanical torque. Then, the maximum mechanical torque is tracked using electromechanical torque. In this technique, tracking error integral of maximum mechanical torque, the error, and the derivative of error are used as state variables. During changes in wind speed, sliding mode control is designed to absorb the maximum energy from the wind and minimize the response time of maximum power point tracking(MPPT). In this method, the actual control input signal is formed from a second order integral operation of the original sliding mode control input signal. The result of the second order integral in this model includes control signal integrity, full chattering attenuation, and prevention from large fluctuations in the power generator output. The simulation results, calculated by using MATLAB/m-file software, have shown the effectiveness of the proposed control strategy for wind energy systems based on the permanent magnet synchronous generator(PMSG).

Performance analysis of 20 Pole 1.5 KW Three Phase Permanent Magnet Synchronous Generator for low Speed Vertical Axis Wind Turbine

This paper gives performance analysis of a three phase Permanent Magnet Synchronous Generator (PMSG) connected to a Vertical Axis Wind Turbine (VAWT). Low speed wind condition (less than 5 m/s) is taken in consideration and the entire simulation is carried in Matlab/Simulink environment. The rated power for the generator is fixed at 1.5 KW and number of pole at 20. It is observed under low wind speed of6 m/s, a turbine having approximately1 mof radius and2.6 mof height develops 150 Nm mechanical torque that can generate power up to 1.5 KW. The generator is designed using modeling tool and is fabricated. The fabricated generator is tested in the laboratory with the simulation result for the error analysis. The range of error is about 5%-27% for the same output power value. The limitations and possible causes for error are presented and discussed.

A fault warning for inter-turn short circuit of excitation winding of synchronous generator based on GRU-CNN

Synchronous generators are important components of power systems and are necessary to maintain its normal and stable operation.To perform the fault diagnosis of mild inter-turn short circuit in the excitation winding of a synchronous generator,a gate recurrent unit-convolutional neural network(GRU-CNN)model whose structural parameters were determined by improved particle swarm optimization(IPSO)is proposed.The outputs of the model are the excitation current and reactive power.The total offset distance,which is the fusion of the offset distance of the excitation current and offset distance of the reactive power,was selected as the fault judgment criterion.The fusion weights of the excitation current and reactive power were determined using the anti-entropy weighting method.The fault-warning threshold and fault-warning ratio were set according to the normal total offset distance,and the fault warning time was set according to the actual situation.The fault-warning time and fault-warning ratio were used to avoid misdiagnosis.The proposed method was verified experimentally.

An analytic electromagnetic calculation method for performance evolution of doubly fed induction generators for wind turbines

An analytic electromagnetic calculation method for doubly fed induction generator(DFIG) in wind turbine system was presented. Based on the operation principles, steady state equivalent circuit and basic equations of DFIG, the modeling for electromagnetic calculation of DFIG was proposed. The electromagnetic calculation of DFIG was divided into three steps: the magnetic flux calculation, parameters derivation and performance checks. For each step, the detailed numeric calculation formulas were all derived. Combining the calculation formulas, the whole electromagnetic calculation procedure was established, which consisted of three iterative calculation loops, including magnetic saturation coefficient, electromotive force and total output power. All of the electromagnetic and performance data of DIFG can be calculated conveniently by the established calculation procedure, which can be used to evaluate the new designed machine. A 1.5 MW DFIG designed by the proposed procedure was built, for which the whole type tests including no-load test, load test and temperature rising test were carried out. The test results have shown that the DFIG satisfies technical requirements and the test data fit well with the calculation results which prove the correctness of the presented calculation method.

Battery Energy Storage to Strengthen the Wind Generator in Integrated Power System

The wind energy generation,utilization and its grid penetration in electrical grid are increasing world-wide.The wind generated power is always fluctuating due to its time varying nature and causing stability problem.This weak interconnection of wind generating source in the electrical network affects the power quality and reliability.The localized energy storages shall compensate the fluctuating power and support to strengthen the wind generator in the power system.In this paper,it is proposed to control the voltage source inverter （VSI） in current control mode with energy storage,that is,batteries across the dc bus.The generated wind power can be extracted under varying wind speed and stored in the batteries.This energy storage maintains the stiff voltage across the dc bus of the voltage source inverter.The proposed scheme enhances the stability and reliability of the power system and maintains unity power factor.It can also be operated in stand-alone mode in the power system.The power exchange across the wind generation and the load under dynamic situation is feasible while maintaining the power quality norms at the common point of coupling.It strengthens the weak grid in the power system.This control strategy is evaluated on the test system under dynamic condition by using simulation.The results are verified by comparing the performance of controllers.

GENERATOR VIBRATION FAULT DIAGNOSIS METHOD BASED ON ROTOR VIBRATION AND STATOR WINDING PARALLEL BRANCHES CIRCULATING CURRENT CHARACTERISTICS

Rotor vibration characteristics are first analyzed, which are that the rotor vibration of fundamental frequency will increase due to rotor winding inter-turn short circuit fault, air-gap dynamic eccentricity fault, or imbalance fault, and the vibration of the second frequency will increase when the air-gap static eccentricity fault occurs. Next, the characteristics of the stator winding parallel branches circulating current are analyzed, which are that the second harmonics circulating current will increase when the rotor winding inter-turn short circuit fault occurs, and the fundamental circulating current will increase when the air-gap eccentricity fault occurs, neither being strongly affected by the imbalance fault. Considering the differences of the rotor vibration and circulating current characteristics caused by different rotor faults, a method of generator vibration fault diagnosis, based on rotor vibration and circulating current characteristics, is developed. Finally, the rotor vibration and circulating current of a type SDF-9 generator is measured in the laboratory to verify the theoretical analysis presented above.

Enhancement of Wind Energy Conversion Using Axial Flux Generator

This paper investigates the application of the axial flux machine (AFM) to the wind energy conversion systems (WECS) to obtain high power and torque at reduced cost. By developing mathematical equations using the phase and active transformations, the three-phase model is transformed to two-phase equations by making both the stator and rotor as reference frames, finally converting to arbitrary reference frame, which is useful for the modelling of the axial flux machine. The torque, current, and voltage equations are expressed to improve the simulation reliability. Based on the developed equations, the mathematical model for the axial flux machine is developed using the MATLAB/Simulink. Starting with the axial flux motor model, when the load on the motor increases, how the parameters like torque, current, and speed of the motor vary are explored in this paper. Then for the axial flux generator model, when the wind speed exceeds the rated speed how the torque, line voltages, currents, power and speed of the generator behave are investigated and presented in this paper. The developed model in this paper could be extended to a twin-rotor axial flux synchronous machine, which will lead to the development of more efficient WECS.

Performance Analysis of Composite Magnetic Circuit Permanent Magnet Wind Generator

In order to reduce the starting wind speed of the wind wheel and improve the efficiency of the wind wheel, this paper proposes a new type of composite magnetic circuit permanent magnet generator, which changes the relationship between the magnetic induction intensity and the air gap by changing the structure of the main magnetic circuit. The structure greatly improves the air gap sensitivity of the generator, which makes the structural design of the permanent magnet generator easier to implement. Finally, the effectiveness and feasibility of the method are verified by simulation.

Switched Reluctance Generator for Variable Speed Wind Energy Applications

The aim of this paper is to analyze the potential of switched reluctance generator (SRG) in wind energy application. The machine comprises of switched reluctance generator, power converter and controller. In this paper the main ele-ments that form the generator system is discussed. It also highlights the common type of converter and structure used for SRG in wind energy application and types of control strategy available. Using power converter for switching the generator can operate over a wide speed range. Its applications in high speed area such as starter/generator for air-craft and gas turbine has been established, however the low/medium speed operation is still at an early stage of re-search. In order to subject the machine to various parameters, offline modeling is being investigated to produce the best optimum design.

Isolated MicroGrid’s Voltage and Frequency Characteristic with Induction Generator Based Wind Turbine

To save on the island area's power supply cost and protect the clean environment, the Isolated MicroGrid is being duly considered. Consisting of the Wind Turbine Generator (WT), photovoltaic generator, battery system, back-up diesel generator, etc., Isolated MicroGrid, which usually uses the inverter to maintain voltage and frequency of the system, is very weak in terms of voltage and frequency stability compared to the large-scale electrical power system. If wind turbine generator is applied to this weak power system, it could experience many problems in terms of maintaining its voltage and frequency. In this paper, the measurement result of voltage and frequency is presented for MicroGrid, which consists of the Wind Turbine Generator adopting the induction generator and the battery system. MicroGrid’s voltage waveform distortion and Wind Turbine Generator’s output oscillation problems are analyzed using PSCAD/EMTDC. Based on the analyzed result, the importance of type and capacity choice has been suggested in case the Wind Turbine Generator is applied to the Isolated MicroGrid.

Ventilation Structure Optimization and Performance Analyses of Permanent Magnet Wind Generators

为了提高永磁风力发电机的通风冷却效果,以一台2.5 MW永磁风力发电机为例,基于计算流体力学（computational fluid dynamics,CFD）以及传热传质学基本理论,根据流–热协同机理,建立了包括外部通风系统的三维流体流动与传热的求解模型。应用有限体积元法,对电机通风冷却性能进行了数值研究,并与实验数据进行对比分析,实验结果验证了计算结果的准确性以及求解方法的合理性。通过改变电机内径向通风沟结构尺寸,提出4种优化方案,通过对不同结构方案条件下通风冷却性能进行对比研究,给出了发电机最佳的结构方案。所得结论可以为永磁风力发电机通风结构的设计提供参考。

Electromagnetic and Mechanical Stress Analysis of Wind-Driven Synchronous Reluctance Generator

The investigation explores the mechanical stress and electromagnetic performance for a wind-driven synchronous reluctance generator(SRG).The change in the mechanical stress due to the presence of centripetal force,wind speed,and rotor speed are evaluated for different thickness of tangential and radial ribs.Moreover,the variation in the electromagnetic feature such as the q−and d−axes flux,reactance ratio,inductance,torque and torque ripple are discussed for different thickness of tangential and radial ribs.Increasing both tangential and radial ribs thickness has an effect on the electromagnetic performance,but it is observed that effect is significantly more with the variation of tangential rib thickness.Similarly,the mechanical stress analysis for rotor design has been explored in this paper.It is observed that high concentration of peak stress on the rotor ribs,which limits the range of rotor speed.

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.

Effects of Wind Turbines Equipped with Doubly-fed Induction Generators on Distance Protection

Nowadays wind energy is the fastest growing renewable energy resource in the world.The problems of integrating wind farms are caused by changes of wind speed during a day.Moreover,the behaviors of wind turbines equipped with doubly-fed induction generators differ fundamentally from synchronous generators.Therefore,more considerations are needed to analyze the performances of the distance protection relays.The protection of a wind farm with distance relay is inspected.By changing the conditions of the wind farm,the characteristics of the distance relay are studied.

Research Status of Wind Energy Piezoelectric Generator

It is of great significance for developing self-powered micro-devices to explore the research of piezoelectric effect in conversion of wind energy into electricity. Based on the different excitation modes, the existing wind energy piezoelectric generators are firstly classified. The research status of wind piezoelectric generators is further analyzed, and characteristics of various types of wind energy piezoelectric generators are summarized. Finally, the future research direction and emphasis of wind energy piezoelectric generators is proposed to carry out its miniaturization, lightweight and integration.