Showing papers on "Rotor (electric) published in 2011"

Direct Current Motor with Independently Driven and Switchable Stators

Abstract: An apparatus and method are provided for adjusting torque and speed of a motor, while remaining within the voltage limit of a power supply. The invention provides a brushless direct current motor with independently driven and switchable stators. In an aspect, each stator and the rotor is structured to function as an independent motor separate from another stator and the rotor. A first power electronics directs energy to a first stator, and a second power electronics directs energy to a second stator. A rotor rotates relative to the stators. In an aspect, a commutation electronics determines electrical position of the rotor relative to the stators, and synchronizes current pulses directed to a sequentially selected phase of the stators, to generate a rotating magnetic field that communicates with the rotor. A controller sets the connection of the first power electronics in series or in parallel with the second power electronics.

Stabilization of a power system with a distributed generator by a Virtual Synchronous Generator function

Abstract: The power capacity of distributed generators such as photovoltaic and wind turbine is growing, many of distributed generators are connected to a grid by inverters. The inverters are controlled by a PLL (Phase Locked Loop) in order to be synchronized with power system frequency. Power system will become unstable, if the capacity of inverter-connected-type distributed generators becomes larger and larger, because inverter frequency is controlled to follow the grid frequency. The concept of “Virtual Synchronous Generator” (VSG), which is to control inverters to behave like a synchronous generator, has been proposed. VSG has virtual inertia which is realized by an energy storage device to pretend rotor's inertia. In this paper, the control scheme of VSG is investigated which is based on the swing equation of a synchronous generator. Numerical simulation results show both ride-through capability of voltage dip and enhancement ability of grid stability.

Torque Density and Efficiency Improvements of a Switched Reluctance Motor Without Rare-Earth Material for Hybrid Vehicles

Abstract: A machine design of a switched reluctance motor having competitive torque and efficiency as well as compactness with respect to an interior permanent-magnet (IPM) synchronous motor (IPMSM) in a hybrid electric vehicle (Toyota Prius 2003) has been investigated. A torque of 400 N·m is set as a target with an outer diameter of 269 mm with an axial length of 156 mm, including coil end lengths. In addition, a 50-kW field weakening capability must be competitive to the IPMSM. The highest efficiency of 95% is also aimed. Stator and rotor structures and iron material are investigated. Test machines are built. Static and light load tests are carried out.

An Improved Low-Voltage Ride-Through Control Strategy of Doubly Fed Induction Generator During Grid Faults

Abstract: This paper presents a control strategy to improve the low-voltage ride-through capability of a doubly fed induction generator (DFIG); since the stator of a DFIG is directly connected to a grid, this sort of machine is very sensitive to grid disturbance. Grid voltage sag causes overcurrents and overvoltages in rotor windings, which can damage the rotor-side converter (RSC). In order to protect the RSC, a classical solution based on installation of the so-called crowbar is adopted; however, as the DFIG absorbs reactive power from the grid, this type of solution deteriorates grid voltage sags and cannot meet the requirements of a new grid code. An improved control strategy which uses virtual resistance to limit rotor side overcurrents is proposed in this paper, which can make a crowbar inactive and supply reactive power to fulfill the latest grid code requirement during voltage sags. In order to validate the proposed strategy, simulations and experiments have been carried out, and the results demonstrate the effectiveness of the proposed strategy.

Wind Turbines Theory - The Betz Equation and Optimal Rotor Tip Speed Ratio

Abstract: The fundamental theory of design and operation of wind turbines is derived based on a first principles approach using conservation of mass and conservation of energy in a wind stream. A detailed derivation of the “Betz Equation” and the “Betz Criterion” or “Betz Limit” is presented, and its subtleties, insights as well as the pitfalls in its derivation and application are discussed. This fundamental equation was first introduced by the German engineer Albert Betz in 1919 and published in his book “Wind Energie und ihre Ausnutzung durch Windmuhlen,” or “Wind Energy and its Extraction through Wind Mills” in 1926. The theory that is developed applies to both horizontal and vertical axis wind turbines. The power coefficient of a wind turbine is defined and is related to the Betz Limit. A description of the optimal rotor tip speed ratio of a wind turbine is also presented. This is compared with a description based on Schmitz whirlpool ratios accounting for the different losses and efficiencies encountered in the operation of wind energy conversion systems. The theoretical and a corrected graph of the different wind turbine operational regimes and configurations, relating the power coefficient to the rotor tip speed ratio are shown. The general common principles underlying wind, hydroelectric and thermal energy conversion are discussed.

Modeling of Surface-Mounted Permanent Magnet Synchronous Motors With Stator Winding Interturn Faults

Abstract: This paper develops and analyzes a parametric model for simulating healthy and faulty surface-mounted permanent magnet synchronous motors. It allows studying the effects of stator winding interturn short-circuit faults. A relevant feature of the developed model is that it deals with spatial harmonics due to a nonsinusoidal rotor permanent magnet configuration. Additionally, the proposed model is valid for studying the behavior of these machines running under nonstationary conditions, including load or speed variations. Stator current spectra obtained from simulations performed by applying the proposed model show a close similitude with experimental results, highlighting the potential of such a model to understand the effects of stator winding failures on the current spectrum and allowing it to carry out an automatic diagnosis of such faults.

Dynamic Modeling and Improved Control of DFIG Under Distorted Grid Voltage Conditions

Abstract: This paper presents a mathematical model of a doubly fed induction generator (DFIG) in the positive synchronous reference frame under distorted grid voltage conditions. The oscillations of the DFIG's electromagnetic torque and the instantaneous stator active and reactive powers are fully described when the grid voltage is harmonically distorted. Four alternative control targets are proposed to improve the system responses during grid harmonic distortions. A new rotor current control scheme implemented in the positive synchronous reference frame is developed. The control scheme consists of a proportional-integral (PI) regulator and a harmonic resonant (R) compensator tuned at six times the grid frequency. Consequently, the fundamental and the fifth- and seventh-order components of rotor currents are directly regulated by the PI-R controller without sequential-component decompositions. The feasibility of the proposed control strategy is validated by simulation studies on a 2.0-MW wind-turbine-driven DFIG system. Compared with the conventional vector control scheme based on standard PI current controllers, the proposed control scheme leads to significant elimination of either DFIG power or torque oscillations under distorted grid voltage conditions.

High Power Density Design of 6-Slot–8-Pole Hybrid Excitation Flux Switching Machine for Hybrid Electric Vehicles

Abstract: Over the last decade, many automotive companies have been commercializing hybrid electric vehicles (HEVs) as one of candidates for sustainable human life. Some of the recent HEVs employ electric propulsion systems using a combination of reduction gear and interior permanent magnet synchronous motors (IPMSM) operated by relatively high-speed more than 12 000 r/min, resulting in achieving high torque and power densities simultaneously. In the combination, since all rare-earth permanent magnets are embedded in its rotor core, a machine design of high-speed IPMSM tends to be difficult. This is due to a design confliction between keeping enough mechanical strength of the rotor core and bringing out better electromagnetic performances. To cope with this problem, this paper deals with a 6-slot-8-pole hybrid excitation flux switching machine, in which both permanent magnets and wound field excitation are employed as magnetomotive force sources. This machine has all active parts on the stator body and a rugged rotor structure similar to that of switched reluctance motor suitable for high-speed operation. Some design parameter refinements are conducted to the machine in order to elevate maximum torque capability and maximum power density as much as possible under given design requirements and constraints. As a result, it is demonstrated that the machine designed becomes a good candidate for the target HEV drive application.

Application of Adaptive Network-Based Fuzzy Inference System for Sensorless Control of PMSG-Based Wind Turbine With Nonlinear-Load-Compensation Capabilities

Abstract: The precise information of permanent-magnet synchronous generator (PMSG) rotor position and speed is essentially required to operate it on maximum power points. This paper presents an adaptive network-based fuzzy inference system (ANFIS) for speed and position estimation of PMSG, where an ANFIS-based model reference adaptive system is continuously tuned with actual PMSG to neutralize the effect of parameter variations such as stator resistance, inductance, and torque constant. This ANFIS-tuned estimator is able to estimate the rotor position and speed accurately over a wide speed range with a great immunity against parameter variation. The proposed system consists of two back-to-back connected inverters, where one controls the PMSG, while another is used for grid synchronization. Moreover, in the proposed study, the grid-side inverter is also utilized as harmonic, reactive power, and unbalanced load compensator for a three-phase, four-wire (3P4W) nonlinear load, if any, at point of common coupling (PCC). This enables the grid to always supply/absorb a balanced set of fundamental currents at unity power factor. The proposed system is developed and simulated using MATLAB/SimPowerSystem (SPS) toolbox. Besides this, a scaled laboratory hardware prototype is developed and extensive experimental study is carried out to validate the proposed control approach.

Optical unit with shake correcting function

Abstract: An optical unit with a shake correction function may include an optical module having a movable body holding an optical element, a support body swingably supporting the movable body around two axial lines perpendicular to an optical axis of the optical element, and a swing drive mechanism structured to be capable of reciprocatedly swinging the movable body with respect to the support body around the two axial lines, and a rolling correction drive mechanism structured to be capable of reciprocatedly turning the optical module around the optical axis. The rolling correction drive mechanism includes a single phase motor in which the number of salient poles of a stator core around which a stator coil is wound is two times of the number of magnetic poles of a rotor magnet.

Direct Torque and Indirect Flux Control of Brushless DC Motor

Abstract: In this paper, the position-sensorless direct torque and indirect flux control of brushless dc (BLDC) motor with nonsinusoidal back electromotive force (EMF) has been extensively investigated. In the literature, several methods have been proposed for BLDC motor drives to obtain optimum current and torque control with minimum torque pulsations. Most methods are complicated and do not consider the stator flux linkage control, therefore, possible high-speed operations are not feasible. In this study, a novel and simple approach to achieve a low-frequency torque ripple-free direct torque control (DTC) with maximum efficiency based on dq reference frame is presented. The proposed sensorless method closely resembles the conventional DTC scheme used for sinusoidal ac motors such that it controls the torque directly and stator flux amplitude indirectly using d-axis current. This method does not require pulsewidth modulation and proportional plus integral regulators and also permits the regulation of varying signals. Furthermore, to eliminate the low-frequency torque oscillations, two actual and easily available line-to-line back EMF constants ( kba and kca) according to electrical rotor position are obtained offline and converted to the dq frame equivalents using the new line-to-line park transformation. Then, they are set up in the look-up table for torque estimation. The validity and practical applications of the proposed sensorless three-phase conduction DTC of BLDC motor drive scheme are verified through simulations and experimental results.

Estimation of Rotor Position and Speed of Permanent Magnet Synchronous Motors With Guaranteed Stability

Abstract: The control algorithms used in high performance ac drives require the knowledge of rotor position and, in the case of speed regulation, also of speed. Since in many applications rotational transducers cannot be installed, their reconstruction is needed. The use of observers is stymied by the fact that the dynamics of electrical machines are highly nonlinear and does not belong to the class studied by the nonlinear control community. In this paper solutions to both problems, which are particularly tailored for the widely popular permanent magnet synchronous motors, are provided. A key step for the design of both observers is the choice of a suitable set of coordinates. The position observer is a standard gradient search whose detailed analysis reveals outstanding (global asymptotic) stability properties. Furthermore, the analysis clearly exhibits the interplay between rotor speed and the gain of the gradient search-that (essentially) determines its convergence rate. The position observer is a simple two-dimensional nonlinear system, hence is easily implementable. The speed observer is designed following the immersion and invariance technique and is also shown to be globally convergent. Simulation and experimental results of the position observer, used together with a classical field-oriented control algorithm, are presented.

A Novel Axial Flux Permanent-Magnet Machine for Flywheel Energy Storage System: Design and Analysis

Abstract: This paper presents the design and analysis of a novel axial flux permanent-magnet (AFPM) machine for a flywheel energy storage system (FESS). Its design and control facilitate significant reduction in axial bearing stress and losses. Due to the unconventional flux distribution in this machine, a 3-D finite element method was employed for its design and analysis, including its electromagnetic torque and axial force performances. The effects of the rotor PM skew angle on the cogging torque and the axial force have been studied. It is found that an optimum skew angle is effective in reducing the overall cogging torque with negligible effect on the static axial force. The latter is crucial as it can be utilized to minimize the axial bearing stress in FESS application. The concept, design, and analysis methodology have been validated by experimental results from an experimental AFPM machine prototype.

Modular and morphable air vehicle

Abstract: An unmanned air module includes one or more rotors, engines, a transmission and avionics. Any of several different ground modules may be attached to the air module. The air module may fly with and without the ground module attached. The ground module may be a vehicle ground module and may be manned. The vehicle ground module may transport the attached air module across the ground. The air module may have two rotors, which may be ducted fans, and three different configurations: a tandem rotor configuration, a side-by-side configuration, and a tilted-rotor configuration.

Comparison of Five Topologies for an Interior Permanent-Magnet Machine for a Hybrid Electric Vehicle

Abstract: This paper presents a detailed comparison of the characteristics of five different rotor topologies for a distributed winding permanent-magnet (PM) machine for high-performance traction applications, including hybrid electric vehicles. These rotor topologies include one surface PM topology and four single-layer interior PM topologies (conventional, segmented, V shape, and W shape). The performance characteristics, which include the back-electromotive force and its harmonics, magnet mass, iron loss, and ripple torque are compared and analyzed. A 7.5-kW interior permanent-magnetic (IPM) prototype using the conventional rotor topology was tested and the finite-element analysis results were compared. The aim of the paper is to give some guidance and reference for machine designers who are interested in IPM machine selection for high-performance traction applications.

A Novel Hybrid-Excited Switched-Flux Brushless AC Machine for EV/HEV Applications

Abstract: A novel E-core hybrid-excited switched-flux permanent-magnet (SFPM) brushless machine is proposed based on an E-core SFPM machine, which has significantly less magnet and higher torque density than those of a conventional SFPM machine. The proposed machine has a simple structure. The main flux path of dc excitation does not affect the magnet excitation because it is not through magnets. The combination of stator and rotor pole numbers of the proposed machine is optimized, and the flux-enhancing and flux-weakening capabilities are investigated by 2-D finite-element analyses and experimentally validated.

Design Considerations for a Fault-Tolerant Flux-Switching Permanent-Magnet Machine

Abstract: In safety critical aerospace applications, fault-tolerant drives can help reach the necessary system reliability levels without replicating the entire drive system and thus minimizing the overall system weight. Machine selection and design for fault tolerance has to be considered at an early stage to ensure optimal performance at a system level. This paper looks at the fault-tolerant properties of permanent-magnet flux-switching machines (PMFSMs) and proposes a new configuration able to fulfill the fault-tolerant requirements. PMFSMs have the distinct property of having a robust rotor construction with the permanent magnets embedded in the stator while having their operational characteristics similar to those of synchronous permanent-magnet machines. While these machines have numerous inherent advantages for achieving a high power density, in their basic form, they are not tolerant to short-circuit winding failures. This paper will look at a novel stator structure able to achieve a 1-p.u. winding inductance and will subsequently look at design iterations to maximize the torque density.

Metal matrix composite brake rotor: Historical development and product life cycle analysis

Abstract: Metal matrix composites (MMCs) have become attractive for engineering structural applications due to their excellent specific strength property and are increasingly seen as alternative to the conventional materials particularly in the automotive industry. In this study, a historical background on the development and application of metal matrix composite for automotive brake rotor is presented. The discussion also includes analysis of the product life cycle with stir casting as a case study. The historical review analysis revealed that gradual development of material and processing technique have lead to a lighter weight, lower cost, and higher performance brake rotor as a result of the better understanding of the mechanics of metal matrix composite. It emerged from the study that stir casting technique provides ease of operation, sustainability and most significantly very competitive without sacrificing quality relative to other techniques; and as such is the most attractive manufacturing process in the industry. These findings can be used for future design and manufacture of an efficient and effective aluminium matrix composite brake rotor for automotive and other applications.

Control method for a wind turbine

Abstract: The invention relates to a method of controlling a wind turbine having a rotor with pitchable wind turbine blades and a generator for producing power, where a pitch reference value for the wind turbine blades is determined, and an operational parameter representing a loading on the wind turbine rotor exerted by the wind is measured at time intervals. A variation parameter reflecting a variation of the operational parameter over time is determined and used in the determination of a minimum pitch limit value of the pitch reference value. The wind turbine is then controlled according to the pitch reference value only if the pitch reference value is above or equal to the minimum pitch limit value, and otherwise according to the minimum pitch limit value. The invention further relates to a method of controlling the change in the operational parameter as measured in two successive time steps is determined and the turbine then being controlled according to a safety control strategy if the difference between the operational parameter change and the variation parameter is above a certain alert threshold. The invention further relates to a control system configured to perform the above control method, and a wind turbine comprising such system.

Stabilized space---time computation of wind-turbine rotor aerodynamics

Abstract: We show how we use the Deforming-Spatial-Domain/Stabilized Space---Time (DSD/SST) formulation for accurate 3D computation of the aerodynamics of a wind-turbine rotor. As the test case, we use the NREL 5MW offshore baseline wind-turbine rotor. This class of computational problems are rather challenging, because they involve large Reynolds numbers and rotating turbulent flows, and computing the correct torque requires an accurate and meticulous numerical approach. We compute the problem with both the original version of the DSD/SST formulation and a recently introduced version with an advanced turbulence model. The DSD/SST formulation with the advanced turbulence model is a space---time version of the residual-based variational multiscale method. We compare our results to those reported recently, which were obtained with the residual-based variational multiscale Arbitrary Lagrangian---Eulerian method using NURBS for spatial discretization and which we take as the reference solution. While the original DSD/SST formulation yields torque values not far from the reference solution, the DSD/SST formulation with the variational multiscale turbulence model yields torque values very close to the reference solution.

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

Abstract: 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.

Numerical-performance studies for the stabilized space–time computation of wind-turbine rotor aerodynamics

Abstract: We present our numerical-performance studies for 3D wind-turbine rotor aerodynamics computation with the deforming-spatial-domain/stabilized space–time (DSD/SST) formulation. The computation is challenging because of the large Reynolds numbers and rotating turbulent flows, and computing the correct torque requires an accurate and meticulous numerical approach. As the test case, we use the NREL 5MW offshore baseline wind-turbine rotor. We compute the problem with both the original version of the DSD/SST formulation and the version with an advanced turbulence model. The DSD/SST formulation with the turbulence model is a recently-introduced space–time version of the residual-based variational multiscale method. We include in our comparison as reference solution the results obtained with the residual-based variational multiscale Arbitrary Lagrangian–Eulerian method using NURBS for spatial discretization. We test different levels of mesh refinement and different definitions for the stabilization parameter embedded in the “least squares on incompressibility constraint” stabilization. We compare the torque values obtained.

Control Strategy for Harmonic Elimination in Stand-Alone DFIG Applications With Nonlinear Loads

Abstract: This paper proposes a new control strategy of effective fifth and seventh harmonic elimination in the stator output voltage at the point of common coupling for a stand-alone doubly fed induction generator (DFIG) feeding a three-phase diode rectifier. This load regularly causes such harmonic distortions, which harmfully affect the performance of other loads connected to the DFIG. In order to allow the DFIG to deliver a pure sinusoidal stator output voltage, these harmonics must be rejected. The proposed elimination method is investigated based on the rotor current controller employing a proportional integral and a resonant controller, which is implemented in the fundamental reference frame. In this frame, both positive seventh and negative fifth voltage harmonic can be eliminated by using only single resonant compensator tuned at six multiples of synchronous frequency in the rotor current controller. The control scheme is developed in the rotor-side converter for the control and operation of the DFIG. Simulations and experimental results with 2.2-kW DFIG feeding a nonlinear load are shown to verify prominent features of the proposed control method.

Rotor Position Estimation

Abstract: High-frequency excitation sensorless control methods measure the response of the machine to some form of high-frequency excitation from which the rotor position is estimated. The utilization of these meth ods is feasible in both induction and PMSMs. The design of the machine strongly influences its salient behavior, meaning that not all designs are adequate for their use in sensorless applications. All the methods respond to the same physical principles, with the main differences among them being the type of high frequency signal excitation and the type and number of signals that are measured. Stable operation, with similar values of accuracy, has been reported for PWM-based methods and for carrier-signal injection-based methods.