The conventional electrical generators, used in wind power systems, are generally coupled to a turbine shaft via a gearbox to get the required speed. These types of speed adaptation system have several disadvantages; for example, they are bulky, costly, and require regular maintenance. To overcome these problems, new structures of variable reluctance machines, operating at low speeds, called slow machines or direct attack machines are proposed [1–10]. One of these structures, named DoublySalientPermanentMagnet Machine (DSPM), a variable reluctance machine, with a large number of rotor and stator teeth excited by non-rotating permanent magnets housed in the stator yoke, attracts more and more attention [2, 9, 13]. This kind of machines is naturally well suited for low speed because its speed is directly related to the number of rotor teeth. It has no magnets or windings on the rotor, and its stator windings, which are easy to manufacture, do not require any particular technique or professional competence to use. The windings are supported with shorter coil heads which minimizes the quantity of the copper and reduces their resistance. Furthermore, this machine has a simple geometry which reduces its manufacturing cost.
At present, the study of torque ripple is mainly focus on DoublySalientPermanent-magnetGenerator, but rarely on WFDSG . The main study method on WFDSG is linear or approximate nonlinear. Because of the stator and rotor having the structure of salient pole, the obvious fringe effect and local saturation can be ob- served when motor works normally. So it is difficult for analytical algorithm since the electromagnetic torque (T em for simplification) is the nonlinear function of rotor position, exciting current and winding current. Paper 
Generation of electricity is challenged by the reduction in the availability of the natural resources around the globe. The generation of electrical power needs to be increased rapidly due to the various forms of energy requirement to support the global demand. Generally, electrical generator is a device that converts mechanical energy obtained from an external source into electrical energy. The source of the mechanical power could be of diesel engine, steam turbine, water turbine, or any similar device . Structural variations of the electromechanical devices through magnetic ﬂow control are proposed by several researchers through dual magnetic circuit inclusive double stators [2–7] and double rotors [8, 9]. In 2005, Feng et al. designed a double-stator starter generator for a hybrid vehicle to increase the performance per volume and performance cost ratio . In 2006, Chau et al. designed and analyzed a doubly-salientpermanentmagnet machine with a new outer-rotor with the capability of ﬂux control . In 2008, Liu et al. designed and fabricated a new outer-rotor permanentmagnet hybrid machine for wind generation, where the machine with a two-excitation permanentmagnet and a Direct Current (DC) ﬁeld winding in order to maintain constant output voltage at a wide range of speeds and currents . Norhisam et al.  developed a single-phase permanentmagnetgenerator to obtain high output power and high eﬃciency, and the slot pole combination and length of the outer stator yoke of the generator are varied to ﬁnd best possible conﬁgurations. Reference  presents comparative evaluations on the power density of several types of double-stator slot and slot-less topologies of PermanentMagnetGenerator (PMG) which are purposely designed for agriculture sectors. This double-stator topology maximizes the usage of ﬂux linkage that leads to high power density [10–12]. In , a new structure for a double- stator brushless DC motor with thick pole shoe with improved energy density compared to conventional
Moreover, double fed induction generators (DFIG) are also used for wind turbine. They are an induction machines with a wound rotor where the rotor and stator are both connected to electrical sources. They offer several advantages including; they operate at variable rotor speed while the amplitude and frequency of the generated voltages remain constant. Generation of electrical power at lower wind speed, virtual elimination of sudden variations in the rotor torque and control of the power factor in order to maintain the power factor at unity. However, DFIG requires complex power conversion circuitry, the slip rings on the wound router induction machine used to implement the doubly-fed induction generator requires periodic maintenance .
In this paper no-load and full-load performance of PermanentMagnet Vernier Generators (PMVGs) is investigated in fully-aligned con- dition and under different types of mechanical faults. The studied mechanical faults are Static Eccentricity (SE), Dynamic Eccentricity (DE), Inclined Rotor (IR), and Run-out (RO). Furthermore, an analytical model is developed to calculate the permeance of the air-gap and the induced voltages in the health machine and under studied mechanical faults. Then, 2-D and 3-D time stepping finite element method is utilized for performance evaluation of the generator. Some discussions are made on the quality of induced voltages, torque ripples, variations of axial and radial forces and the output power of the generator under the mechanical faults considering resistive, inductive and capacitive loads connected to the terminals of the generator. Finally, the performance of an outer rotor conventional permanentmagnetgenerator (CPMG), considering constant dimensions, constant PM, copper and iron usage is compared with the studied PMVG. The performance of two generators is studied in fully-aligned condition as well as under SE and DE.
In this work, the AFPM generator is assembled at the ventilator base. The system can be installed on the roof, bathroom intake, or at ventilated place to provide a spare source. When the ventilator rotates, the flux of the per- manent magnet rotor part moves across the air gap and induces the emf. AFPM machines with coreless stators are regarded as high efficiency and simplicity of con- struction and very low rotor losses for distributed power generation systems [6-9]. Because of the absence of core losses, a generator with this type of design can poten- tially be operated at a higher efficiency than conventional machines. Besides, the high compactness and disk- shaped profile make this type of machine particularly suitable for mechanical integration with ventilator.
Figure 6 shows the short circuit current change waveform. The short-circuit current is six times the load current. The short circuit current increases, causing the motor winding to heat up and the loss is too large. Figure 6 Torque fluctua- tion curve during short circuit, sudden increase in torque produces vibration and noise, increases mechanical losses, and reduces motor life. From the short circuit of Figure 7, the minimum magnetic density of each permanentmagnet is 0.4 T, which is larger than the permanentmagnet demagnetization inflection point, so there is no irreversible demagnetization problem.
emissions has been demonstrated by the introduction of more-electric drive concepts for road transportation. Although the application of electrical machines and drive systems in all- electric and hybrid-electric vehicles has been widely reported in recent years [7-9], there has been a relatively slow progress in these fields due to the cost of major vehicle technological changes. However, mild hybrid solutions have been recognized as the next solution, since they are viable within the existing automotive infrastructure. The Switched Reluctance Generator (SRG) is an attractive solution for worldwide increase in the demand for electrical energy. It is low cost, fault tolerant with a rugged structure and operates with high efficiency over a wide speed range. In , the principle operation of SRG has been presented and the necessity for closed loop control is proven. In , the excitation control of SRG for maximum efficiency at single pulse mode of operation has been presented. It is important to mention that, due to the obvious differences in the stator pole configurations and arcs, the newly designed motor is not a switched reluctance motor of any kind. Therefore, the primary design procedures for the switched reluctance motor are not applicable in this case.
The 2kW wind turbine is connected with the wind generator. The mechanical energy from the wind turbine is converted into electrical energy. Energy produce from the permanentmagnet synchronous generator is AC. Again the AC is converted in dc by using AC to Dc converter. Rectifier circuit is used to convert AC to DC. The dc output is given to the zeta converter which provides required dc voltage. The dc voltage is stored in the energy storage device through the single phase inverter to the load. The output voltage of our system should be stay constant for various speed and load condition. Wind speed will be at high and low speed. When the wind speed is too high at the condition means output power will be stored in battery.
The sample hydrofoil is connected to a PMLSG and a rectifier is used to transfer the resultant power to a battery to charge it. The battery is connected to a SPWM inverter to produce a sinusoidal voltage which is suitable for the sample load. In Fig. 7 the block diagram shows the whole system. As mentioned before, tidal currents (a horizontal motion) are a result of the rise and fall of the water level due to tides (a vertical motion). The effects of tidal currents on the movement of water in and out of bays and harbors can be substantial, in fact the tidal current profile forms a sinusoidal shape with a cycle time of 12 hours and 25 minutes . Because of this quite long time the simulation is done during a specified device cycle time for a 2m/s tidal current velocity. The translator of the PMLSG moves with the heave speed of the hydrofoil so the speed is used as the relevant input into the generator. The way that the battery is charged and discharged is of great significance and should be carefully noted. For instance in high velocities of tidal current the battery is charged and the load provided and in low velocities of tidal current which the device is not capable of providing the load energy, the battery does its role to support the load. A transformer has been inserted to regulate the voltage and eliminate the harmonics.
Arash Kiyoumarsi was born in Shahr- e-Kord, Iran, in the year 1972. He received his B.Sc. (with honors) from Petroleum University of Technology (PUT), Iran, in electronics engineering in 1995 and M.Sc. from Isfahan University of Technology (IUT), in electrical power engineering in 1998. He received Ph.D. degree from the same university in electrical power engineering in 2004. In March 2005, he joined the faculty of University of Isfahan, Faculty of Engineering, Department of Electrical Engineering as an assistant professor of electrical machines. He was a Post- Doc. research fellow of the Alexander-von-Humboldt foundation at the Institute of Electrical Machines, Technical University of Berlin from February to October 2006 and July to August 2007. In March, 5th, 2012, he became an associate professor of electrical machines at the Department of Electrical Engineering, Faculty of Engineering, University of Isfahan. He was also a visiting professor at IEM-RWTH- Aachen, Aachen University, in July 2014. His research interests have included application of time-stepping finite element analysis and design of electromagnetic and electrical machines; and interior permanent-magnet synchronous motor- drive.
and is the resistivity of copper at 20 C (1.78 10 m). The normalized self-inductance , corresponds to the effec- tive permeance associated with the coil flux, and can be deter- mined from finite-element analysis. It is a function of the rela- tive position of the armature and stator poles. However, finite-el- ement analysis shows that for the generator having the parame- ters given in Table I, the variation of over a complete stroke is less than 20%, having a maximum value of 0.954 H and a min- imum value of 0.847 H. This relative insensitivity to armature position is due to the fact that a permanentmagnet with a recoil permeability which is close to is situated in the main flux path of the coils, and that a significant proportion of the self-induc- tance is due to the “slot-leakage” flux component. Thus, can
The GreenSpur approach utilises an axial flux machine, which can offer comparable torque density to the radial flux counterpart . Axial flux machines show promise but to date there has been limited development of these machines [20–24]. The decision to use ferrite magnets is the second major difference. The deployment of wind turbine generators in recent years has employed the use of rare-earth permanent magnets which has increased significantly. The large price fluctuations encourage us to look at alternative magnet materials. Some sample comparative data are given in Table 1, showing that the remanent flux density of ferrite magnets is lower than that of rare earth magnets, as is well known, while the cost of ferrite magnets is much lower – about one fortieth (at the current pricing levels) by weight – and they are readily available.
In this paper, a novel structure of double-stator permanentmagnetgenerator integrated with a magnetic gear has been proposed, and its performance characteristics have been analyzed with 2-D FEM. The performance characteristics show that when the machine functions as a magnetic gear, the ratio of the transmission torque between the prime PMs and ﬁeld PMs is 1 : 3 . 25, and the gear can scale up the rotational speed of both outer and inner rotor ﬁeld PMs. It was found that for various load resistances at variable speeds, the calculated eﬃciency of the generator was 88%. Also the FEM analysis showed that the transmission torque of the magnetic gear was greater than the torque produced by the generator on load with generated power of 1 kW, therefore validating the proposed machine design. The proposed machine can be applied in wind power turbines to address ineﬃcient power generation in low wind speed conditions by directly coupling the prime rotor to the wind turbine blades. The proposed generator has a complex mechanical structure, but future research can lower manufacturing cost by better utilization of PMs and ferromagnetic materials using optimization. Future work related to this study will construct a prototype for experimental validation.
Winding of generator can be divided into overlapping and non-overlapping winding. Over lapping winding can be further divided into distributed and concentrated. Non over- lapping winding is solely in concentrated way. Distributed winding is very popular in Brushless Alternative current machines. One key advantage is that it can give high winding factor when full pole pitch is chosen. Distributed winding is capable of giving smooth sinusoidal MMF. One disadvantage is long-end winding which are only to carry current from one coil to other. So long end windings are associated with copper losses and it is desirable to keep end windings as short as possible. Distributed winding also tends to have high production cost. Distributed winding should not be used if the size of machine is important parameter of design. For this purpose concentrated winding is chosen for building prototype and it is better choice for the construction of cost-efficient generator . In concentrated winding coil is wound in concentrated manner around one tooth which has main advantage of having short end windings unlike distributed winding which has long end windings and cause copper-losses. Concentrated windings show a very high fault tolerance in surface- mounted permanent magnets  which are already shown to better option in designing. Furthermore, concentrated winding limits high currents in short circuit conditions (by increasing leaking inductance and higher leakage inductance may be an advantage in this aspect). Voltage induced in stator has trapezoidal profile unlike distributed winding. One key advantage of concentrated winding is that coils are physically separated in a better way as compared to distributed winding, which is also desirable for better cooling of generator coils. Also synchronous generators with surface mounted magnets have little fluctuation in torque during each revolution (torque ripple).
This paper studied the direct-drive permanentmagnet synchronous machine (permanentmagnet synchronous generator, PMSG) Chopper optimal topology and resistance value. Compared the dif- ferent Chopper circuit low voltage ride-through capability in the same grid fault conditions in si- mulation. This paper computes the dump resistance ceiling according to the power electronic de- vices and over-current capability. Obtaining the dump resistance low limit according to the tem- perature resistance allows, and calculating the optimal value by drop voltage in the DC-Bus during the fault. The feasibility of the proposed algorithm is verified by simulation results.
Wind power is an important renewable energy resource and the fastest growing technology amongst different renewable energy generation technologies .wind energy conversion system consist of wind turbine, pitch angle control, drive train , generator and power converter. There are various kinds of generators used in WECS such as induction generator (IG), double feed induction generator (DFIG) and permanentmagnet synchronous generator (PMSG). The PMSG based on WECS can connect to the turbine without using gearbox. The gearbox causes in the cost maintenance and then it will decrease the weight of nacelle.  many developed generation systems are used to extract maximum wind energy. Optimum wind energy extraction is achieved by running wind turbine generator in a variable speed mode because of the higher energy gain and reduced losses and stresses . Wind turbines are classified with a view to the rotational speed, the power regulation, and the generator system. When considering the construction of the direct drive system, the turbines are classified in to the geared and the direct- driven types [4, 5]. The direct-drive type is known with its advantages, as it has a lower cost, smaller size, and
The realization of a wind turbine as a source ofclean, non-polluting and renewable energy maydepend on the optimum design of the system andthe control strategies of the different possible parameters that can operate efficiently underextreme variations in wind conditions. Thegeneral goal of this paper is to optimize theelectromechanical energy conversion of the windturbines, developing suitable strategies of control.Both induction and synchronous generators can be used for wind turbine systems . Mainly, three types of induction generators are used in wind power conversion systems: cage rotor, wound rotor with slip control and doubly fed induction rotors. The last one is the most utilized in wind speed generation because it provides a wide range of speed variation.
Wind turbines capture the power from the wind by means of aerodynamically designed blades and convert it to rotating mechanical power. The generator converts the mechanical power into electrical energy, which is fed into a grid through power electronic converter. The connection of wind turbines to the grid is possible even at the extra high voltage system since the transmittable power of an electricity system usually increases with increasing the voltage level. It is desirable to operate wind energy system at its Maximum PowerPoint (MPP) in operating region for economic reasons. The amount of mechanical energy that can be extracted from wind is not only depending on wind speed, but also depending on the wind turbine rotational speed. The wind turbine rotational speed can be adjusted as the wind speed changes to tracking the maximum power point in the operating region. A unique limitation of energy conversion systems such as wind and solar is their inability to track peak power production efficiently at varying wind speeds and solar insulation respectively.