The state of the art of wind energy conversion systems and technologies: A review

This paper provides a technical review of position and speed sensorless methods for controlling Brushless Direct Current (BLDC) motor drives, including the background analysis using sensors, limitations and advances. The performance and reliability of BLDC motor drivers have been improved because the conventional control and sensing techniques have been improved through sensorless technology. Then, in this paper sensorless advances are reviewed and recent developments in this area are introduced with their inherent advantages and drawbacks, including the analysis of practical implementation issues and applications. The study includes a deep overview of state-of-the-art back-EMF sensing methods, which includes Terminal Voltage Sensing, Third Harmonic Voltage Integration, Terminal Current Sensing, Back-EMF Integration and PWM strategies. Also, the most relevant techniques based on estimation and models are briefly analysed, such as Sliding-mode Observer, Extended Kalman Filter, Model Reference Adaptive System, Adaptive observers (Full-order and Pseudoreduced-order) and Artificial Neural Networks.

https://www.mdpi.com/1424-8220/10/7/6901/pdf

Position and speed control of brushless DC motors using sensorless techniques and application trends.

The development of microgrids is an advantageous option for integrating rapidly growing renewable energies. However, the stochastic nature of renewable energies and variable power demand have created many challenges like unstable voltage/frequency and complicated power management and interaction with the utility grid. Recently, predictive control with its fast transient response and flexibility to accommodate different constraints has presented huge potentials in microgrid applications. This paper provides a comprehensive review of model predictive control (MPC) in individual and interconnected microgrids, including both converter-level and grid-level control strategies applied to three layers of the hierarchical control architecture. This survey shows that MPC is at the beginning of the application in microgrids and that it emerges as a competitive alternative to conventional methods in voltage regulation, frequency control, power flow management and economic operation optimization. Also, some of the most important trends in MPC development have been highlighted and discussed as future perspectives.

Model predictive control of microgrids – An overview

Undoubtedly, energy has a significant role in economic growth and technical developments. Renewable energy resources are becoming more important in recent years due to their tremendous contributions to the independence of power generation industry from traditional fossil energy resources. Wind energy has been outstanding among renewable energy resources since continuous harvestable potential on the earth is approximately around 10 6  MW. Concerning the variable nature of wind energy, the variable speed machines, especially doubly fed induction generators (DFIG) are one of the considerations for wind energy conversion systems (WECS). Their implementation in renewable energy conversion systems is dramatically increasing due to their numerous advantages such as low cost and small size, the elimination of external DC source, the ability to produce maximum power under various wind and rotational speeds, the capability of controlling active and reactive power, and the opportunity to employ cheaper and smaller convertors and controllers. This paper is an extensive review of researches in the past 30 years on DFIG. The study starts with describing general perspective on wind energy and commonly used generators in wind conversion. Then it presents more details on DFIGs operational modes, utilizations, their modeling and simulation. It is followed by DFIG control methods and overviews of different employed electrical and mechanical controlling methods. Finally the review on the mutual impact of DFIG on power networks and vice versa, including wind uncertainty, power and frequency stability, power and voltage quality, operation under steady state, dynamic and fault conditions, and protections is given. Based on the review DFIG has advantages in terms of electrical, mechanical, and economic perspectives. It can be concluded that the DFIG has the most promising future for WECSs in power generation to complement the conventional systems.

An overview on doubly fed induction generators′ controls and contributions to wind based electricity generation

This paper proposes a novel double-stator axial-flux spoke-type permanent magnet vernier machine, which has a high torque density feature as well as a high-power factor at low speed for direct-drive systems. The operation principle and basic design procedure of the proposed machine are presented and discussed. The 3-D finite element method (3-D-FEM) is utilized to analyze its magnetic field and transient output performance. Furthermore, the analytical method and a simplified 2-D-FEM are also developed for the machine basic design and performance evaluation, which can effectively reduce the modeling and simulation time of the 3-D-FEM and achieve an adequate accuracy.

A Novel Dual-Stator Axial-Flux Spoke-Type Permanent Magnet Vernier Machine for Direct-Drive Applications

A novel axial field flux-switching permanent magnet (AFFSPM) machine with a doubly-salient structure is presented as a wind power generator. One rotor is sandwiched between two stators in which both windings and permanent magnets are placed. This novel generator is suitable for the wind power generation system because of its shorter axial length and higher power density. A three-phase 12/10-pole 0.6 kW AFFSPM generator is designed. The power-size equation of the machine is deduced, and the size of generator is determined. Based on the 3-D finite element method, the electromagnetic performances of the generator are investigated. According to the theoretical calculation, a prototype is manufactured and the experiments are done. The analysis results are consistent with the experimental ones well.

A Novel Axial Field Flux-Switching Permanent Magnet Wind Power Generator

Axial field flux-switching permanent magnet machine (AFFSPMM) is a novel permanent magnet (PM) machine which incorporates the merits of flux-switching PM (FSPM) machine and axial field PM machine. AFFSPMM exhibits many advantages, such as sinusoidal back-EMF waveform, good flux weakening capability, favorable for cooling, high torque/power density and high efficiency [1]. However, compared to the traditional PM machines, the cogging torque of AFFSPMM is high due to the doubly salient structure and the extremely high flux density caused by the flux focusing effects. The cogging torque reduction of AFFSPMM by rotor tooth notching is investigated in this paper. Three different rotor tooth notching schemes are presented and the influence of the dummy slot parameters on the cogging torque for different rotor tooth notching is investigated based on 3-D finite element method (FEM). The dummy slot width, slot depth, and slot shape are optimized by response surface method (RSM), the cogging torque and output torque under different optimal combinations are calculated and compared.

Cogging Torque Reduction of Axial-Field Flux-Switching Permanent Magnet Machine by Rotor Tooth Notching

In this article, a novel high step-up interleaved dc–dc converter is presented, which is composed of an interleaved structure, an asymmetric voltage multiplier cell (AVMC), and a passive lossless clamped circuit. Compared to the classical interleaved boost converter, the proposed converter has a higher voltage gain owing to the employment of the AVMC and the coupled inductor. In addition, the input current ripple is limited to low values with the help of the interleaved structure, which gives more lifetime to the input power source. The voltage stresses of main switches are substantially low so that the MOSFETs with low voltage rate and ON-resistance ( $R_{\textrm {DS}(\mathrm{ON})} $ ) can be used. In addition, the voltage stresses and the reverse recovery problems of diodes are improved dramatically. Moreover, the zero current switching (ZCS) turn-on of switches and the ZCS turn-off of the clamp diodes are realized to reduce the switching losses. The leakage inductor energy is recycled and the voltage spikes are improved greatly by the passive lossless clamped circuit so that the efficiency can be upgraded further. Finally, a 400-W, 40-V-input, 400-V-output prototype is established to demonstrate the performance of this converter. The highest efficiency is about 97.3% and the full-load efficiency is approximately 97%.

High Step-Up Interleaved dc–dc Converter With Asymmetric Voltage Multiplier Cell and Coupled Inductor

A dual-rotor axial field flux-switching permanent magnet (DRAFFSPM) machine is proposed. A 3-phase 12/10-pole DRAFFSPM machine is designed. The topology and operation principle of the machine are described in detail. The power equation is deduced and the dimensions of the DRAFFSPM machine are determined. The electromagnetic characteristics including the air-gap field distribution, the PM flux-linkage, the back-EMF, and the cogging torque, are investigated based on the 3-D finite element (FE) analysis. The influences of the rotor pole width and the stator slot chamfer on the back-EMF and cogging torque are investigated. It shows that the sinusoidal back-EMF can be gained and the cogging torque can be greatly reduced.

Novel Dual-Rotor Axial Field Flux-Switching Permanent Magnet Machine

Axial field flux-switching permanent magnet machine (AFFSPMM) is a novel stator PM machine with high torque density and efficiency. The cogging torque in AFFSPMM is larger than that in the traditional PM machine because of the double salient structure. In order to decrease the cogging torque, the analytical expression of the cogging torque is deduced and a cogging torque reduction method by adding magnetic bridge in adjacent stator tooth is proposed. Based on the 3-D finite-element (FE) method, the influence of the magnetic bridge thickness on the cogging torque and the output torque is analyzed and compared with the rotor skewing and notching methods. The influence of the stator tooth and rotor pole width on the output torque is studied. The 3-D FE analysis is compared with the experimental results. The research results show that the proposed method is effective in the reduction of cogging torque for all kinds of stator structures. Moreover, the cogging torque can decrease greatly and the average output torque decreases slightly when combined with the optimization of the stator tooth width and rotor pole width.

Mingyao Lin

Papers

A Novel Axial Field Flux-Switching Permanent Magnet Wind Power Generator

Cogging Torque Reduction of Axial-Field Flux-Switching Permanent Magnet Machine by Rotor Tooth Notching

High Step-Up Interleaved dc–dc Converter With Asymmetric Voltage Multiplier Cell and Coupled Inductor

Novel Dual-Rotor Axial Field Flux-Switching Permanent Magnet Machine

Cogging Torque Reduction of Axial Field Flux-Switching Permanent Magnet Machine by Adding Magnetic Bridge in Stator Tooth