Showing papers on "Rotor (electric) published in 2017"

Advanced Control Strategies of PMSG-Based Wind Turbines for System Inertia Support

Abstract: This paper investigates two novel control strategies that enable system inertia supports by permanent magnet synchronous generator (PMSG) wind turbines during transient events. The first strategy seeks to provide inertia support to the system through simultaneous utilization of dc-link capacitor energy, and wind turbine (WT) rotor kinetic energy (KE). The second strategy supports system inertia through orderly exerting dc-link capacitor energy of WT and then WT rotor KE via a cascading control scheme. Both strategies can effectively provide system inertia support by fully utilizing WT's own potentials, while the second strategy distinguishes itself by minimizing its impacts on wind energy harvesting. Case studies of one synchronous generator connected with a PMSG-based WT considering sudden load variations have been studied to validate and compare the two proposed strategies on providing rapid inertia response for the system.

Design and Initial Testing of a High-Speed 45-kW Switched Reluctance Drive for Aerospace Application

Abstract: This paper presents innovative research toward the development of a 45-kW high-speed switched reluctance drive as an alternative starter–generator for future aeroengines. To perform such a function, the machine had to be designed with a very wide constant power–speed range. During engine-start/motoring mode, a peak torque demand of 54 N · m at 8 kr/min was met, while in generating mode, 19.2–32 kr/min, the machine was designed to deliver a constant power of 45 kW. The key enabling feature of the design lies in the novel rotor structure developed so as to allow for such a wide speed range. The results presented are those measured during the initial testing phase and validate the system design and performance in the low-speed region with the machine operated in starting mode. The measured machine power density is at 9.8 kW/L, while the global system efficiency is at 82%.

Application of Split Ring Resonator (SRR) Loaded Transmission Lines to the Design of Angular Displacement and Velocity Sensors for Space Applications

Abstract: The accurate measurement of the angular displacement and velocity of reaction wheels is necessary for attitude (orientation) control in space vehicles (satellites). In this paper, microwave, contactless, and low-cost (as compared to optical encoders) sensors useful for that purpose are analyzed in detail. The sensor consists of a rotor and a stator. The rotor is a disk (or a circular crown) of dielectric material, where one or several arrays of equidistant single-loop split ring resonators (SRRs) are etched along its edge, forming circular chains of hundreds of SRRs. The stator is a coplanar waveguide (CPW) also loaded with pairs of single-loop SRRs (etched in the back substrate side), with the centers located in the slot region. The sensing principle is based on the amplitude modulation of a harmonic (single-tone continuous wave) feeding signal, achieved when the chains of the rotor are displaced over the SRR pairs of the stator. Both sensor elements (rotor and stator) must be parallel oriented, with the SRR pairs of the CPW in close proximity to the SRR chains of the rotor (and rotated 180°), in order to favor their coupling. By this means, the transmission coefficient of the CPW is varied by the circular motion of the rotor, and significant amplitude modulation of the feeding signal is achieved. From the envelope function, the angular velocity can be accurately determined. With the proposed sensors, instantaneous and practically unlimited rotation speeds can be measured.

Turbofan Broadband Noise Prediction Using the Lattice Boltzmann Method

Abstract: The present work describes a numerical reproduction of the 22-in source diagnostic test fan rig of the NASA Glenn Research Center. Numerical flow simulations are performed for three different rotor...

Inductance-Emulating Control for DFIG-Based Wind Turbine to Ride-Through Grid Faults

Abstract: For doubly fed induction generator (DFIG)-based wind turbines, the rotor side of DFIG is prone to suffering from overcurrent during grid faults, due to large electromotive force (EMF) induced in the rotor circuit. To solve this problem, this paper proposes an inductance-emulating control strategy for DFIG-based wind turbine to suppress the postfault rotor current, thereby enhancing its low-voltage ride through capability. Under the proposed control strategy, once the grid fault is detected, the rotor side converter (RSC) is controlled to emulate an inductance. Furthermore, with proper inductance value, both the required rotor voltage and postfault rotor current can be reduced within the permissible ranges of RSC, thus the controllability of control system can be maintained during transient process. Moreover, the oscillation of electromagnetic torque can be effectively suppressed during transient state of both grid fault and fault recovery. Finally, the simulation and experimental results are presented to demonstrate the effectiveness of the proposed method.

Small Signal Dynamics of DFIG-Based Wind Turbines During Riding Through Symmetrical Faults in Weak AC Grid

Abstract: Instability issues of the grid-connected doubly fed induction generator (DFIG) based wind turbines (WTs) during low-voltage ride-through (LVRT) have got little attention yet. In this paper, the small-signal behavior of DFIG WTs attached to weak ac grid with high impedances during the period of LVRT is investigated, with special attention paid to the rotor-side converter. First, based on the studied LVRT strategy, the influence of the high-impedance grid is summarized as the interaction between phase-looked loop (PLL) and rotor current controller (RCC). As modal analysis result indicates that the underdamped poles are dominated by PLL, complex torque coefficient method, which is conventionally applied in power system to study the interaction between mechanical and electrical subsystems of synchronous generator, is generalized to analyze how the PLL-RCC interaction influence the phase motion of PLL. Then, the concerned small-signal stability of the PLL-synchronized DFIG system can be discerned by the developed complex phase coefficients. Impacts of PLL's and RCC's parameters are highlighted, as well as the system's operating conditions during LVRT. Finally, the analytical result is validated by experiments.

A Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Opening

Abstract: Permanent-magnet vernier (PMV) machines are attracting more and more attention due to their high torque density and simple mechanical structure. In this paper, a novel PMV machine with an improved permanent-magnet circuit is proposed. Compared with the regular PMV machine, half of the permanent magnets (PMs) in the rotor are moved to the stator slot opening, and Halbach array PMs are employed in the stator while the consequent pole is employed in the rotor. The analysis of this machine indicates that the back electromotive-force amplitude of the proposed PMV machine could be two times that of the regular PMV machine with similar magnet usage, and for the same torque density, viz., 23.1 kNm/m 3 , the power factor of the proposed machine can reach 0.89, while this value is only 0.65 in the regular PMV machine.

Power Loss and Thermal Analysis of a MW High-Speed Permanent Magnet Synchronous Machine

Abstract: High-speed permanent magnet synchronous machines (PMSMs) have attracted much attention due to their high power density, high efficiency, and compact size for direct-drive applications However, the consequent power loss density is high, and hence heat dissipation is a major technical challenge This is particularly the case for high-speed operation In this paper, a MW level high-speed PMSM is designed and its electromagnetic and mechanical power losses comprehensively investigated using finite element analysis The transient machine demagnetization performance is studied, and a composite rotor structure is proposed to improve machine antidemagnetization capability The temperature distribution of the proposed high-speed PMSM is also analyzed using a fluid-thermal coupling method with calculated power loss Experiments conducted on a prototype of the high-speed PMSM demonstrate the effectiveness of the numerical models developed and validate the results obtained

Locked synchronous rotor motion in a molecular motor.

Abstract: Biological molecular motors translate their local directional motion into ordered movement of other parts of the system to empower controlled mechanical functions The design of analogous geared systems that couple motion in a directional manner, which is pivotal for molecular machinery operating at the nanoscale, remains highly challenging Here, we report a molecular rotary motor that translates light-driven unidirectional rotary motion to controlled movement of a connected biaryl rotor Achieving coupled motion of the distinct parts of this multicomponent mechanical system required precise control of multiple kinetic barriers for isomerization and synchronous motion, resulting in sliding and rotation during a full rotary cycle, with the motor always facing the same face of the rotor

PMSM Sensorless Control by Injecting HF Pulsating Carrier Signal Into ABC Frame

Abstract: Spatial-saliency-tracking-based high-frequency (HF) pulsating carrier injection method is widely employed in permanent-magnet synchronous machines sensorless control. In order to avoid the problems of long convergence time, potential start-up failure and limited system stability existing in tracking observers, a strategy to inject three HF pulsating voltages with different frequencies and amplitudes into ABC frame is proposed in this paper. With the proposed method, three frequency components in the response current signals are demodulated and then combined together to calculate the rotor position directly. Different from the conventional method, the proposed solution utilizes both d- and q-axis carrier current instead of only the q-axis carrier current to enhance the acquisition of the rotor position information. Meanwhile, a new signal processing strategy is developed to completely eliminate the effects of system delay. Furthermore, the compensation of cross-saturation effect is deduced in detail to improve the accuracy of rotor position estimation. In addition, magnetic polarity detection is implemented with the same proposed solution by demodulating the second harmonic components from the response current signals, which simplifies the magnetic polarity process. Finally, the experimental results demonstrate that the proposed strategy can obtain an accurate rotor position with good steady-state and dynamic performance.

Frequency Divider

Abstract: The paper proposes an approximated yet reliable formula to estimate the frequency at the buses of a transmission system. Such a formula is based on the solution of a steady-state boundary value problem where boundary conditions are given by synchronous machine rotor speeds and is intended for applications in transient stability analysis. The hypotheses and assumptions to define bus frequencies are duly discussed. The rationale behind the proposed frequency divider is first illustrated through a simple 3-bus system. Then the general formulation is duly presented and tested on two real-world networks, namely a 1,479-bus model of the all-island Irish system and a 21,177-bus model of the European transmission system.

Three-Phase 24/16 Switched Reluctance Machine for a Hybrid Electric Powertrain

Abstract: This paper presents the design process of a 60-kW switched reluctance motor for traction application in a hybrid electric vehicle. The motor has 24 stator poles and 16 rotor poles. A multiobjective optimization method has been employed in the optimization of conduction angles for priority operating points and over the entire operating range. Two objectives, maximizing output torque and minimizing torque ripple, are used in the optimization problem. A comprehensive comparative performance analysis with varying stator pole height, stator taper angle, rotor pole arc angle, and pole shoe shape is also presented. The performance of the proposed motor over the entire operating range has been characterized based on the optimized conduction angles. The finite element analysis results of the machine demonstrate the potential of the proposed motor in hybrid powertrains in terms of output torque, torque quality, and efficiency.

Rotor Design for High-Speed High-Power Permanent-Magnet Synchronous Machines

Abstract: Permanent-magnet synchronous machines (PMSMs) are considered a very promising machine type for high-speed (HS) applications. As permanent-magnet (PM) materials are generally fragile, a high-strength sleeve is required to protect the PMs from damage due to the extreme centrifugal forces. The rotor sleeve occupies space of the effective airgap of the PMSMs; therefore, it is difficult to perform the electromagnetic (EM) design without an accurate estimation of the sleeve thickness, which is determined by mechanical issues. In this paper, an integrated mechanical- EM design method is proposed for the rotor design of HS PMSMs. A 200-kW 40 000 r/min surface mounted PM machine is taken to illustrate the design procedure of the proposed method. Three commonly used sleeve materials are investigated and their mechanical performances are analyzed. The optimal dimensions for the rotors with different sleeves are obtained by considering the strength and EM limits. The EM, thermal, and rotor dynamic performances of the designed rotors are analyzed and compared. In the end, a new rotor sleeve topology is proposed to reduce the rotor eddy current losses.

Design Optimization and Comparative Study of Novel Dual-PM Excited Machines

Abstract: This paper systematically studies a new kind of PM machines with both stator and rotor PM excitations, namely, dual-PM excited machines. The key is to rely on the PM-iron structure in the machine to provide both PM excitation and flux modulation. Besides the fundamental field component in the air-gap, some other predominant harmonics introduced by the flux modulating effect can also contribute to the electromagnetic torque production. Therefore, this kind of machines can be designed with high torque density. Four dual-PM excited machine concepts with the same rotor configuration but different stator structures are comparatively studied, which include double-stator PM machine, stator multitooth-PM machine, stator slot-PM machine, and stator tooth-PM machine (STPM). Based on the flux modulating effect, the general design principle of the dual-PM machines is proposed in this paper. Through analytically investigating the air-gap field harmonics, the physical insight of the dual-PM machines is brought forward. All the four machines are optimized using an improved Tabu search coupled with finite element method, and their electromagnetic performances are comprehensively studied and compared. A prototype of STPM is manufactured. Experimental tests are conducted and the results well verify the electromagnetic design.

An Experimental Investigation on Rotor-to-Rotor Interactions of Small UAV Propellers

Abstract: In the present study, an experimental investigation was performed to study the effects of rotor-to-rotor interactions on the aerodynamic and aeroacoustic performances of small UAVs. It was found that, while the thrust coefficients of rotor were independent of the separation distance, the thrust fluctuations were found to increase dramatically as the separation distance decreased. An enhancement of ~ 250% was confirmed for the twin-rotor case (i.e., L= 0.05D) in comparison with that of the single rotor case, which is believed to be caused by the complex flow interactions within rotors as revealed by the detailed PIV and Stereoscopic PIV measurements. Reducing the separation distance not only intensified the force fluctuations, but also increased the aeroacoustic noise level of the baseline case. Comparing to the L = 1.0D case, a maximum enhancement of ~3 dB in aeroacoustic noise was recorded for the L = 0.05D case, which is caused by the severely thrust fluctuations and turbulent flow interactions within rotors.

Grid-Interfaced DFIG-Based Variable Speed Wind Energy Conversion System With Power Smoothening

Abstract: This paper deals with the analysis, design, and control of grid-interfaced doubly fed induction generator (DFIG) based variable speed wind energy conversion system (WECS) for power smoothening with maximum power point tracking (MPPT) capability. This DFIG uses rotor position computation algorithm for the sensorless control through rotor position estimation. Power fluctuations due to the unpredictable nature of the wind are eliminated by introducing battery energy storage system (BESS) in the dc link between two back-to-back connected voltage source converters. The design of BESS is presented for feeding regulated power to the grid irrespective of the wind speeds. The control algorithm of the grid-side converter is modified for feeding regulated power to the grid. Rotor-side converter is controlled for achieving MPPT and unity power factor operation at the stator terminals. A prototype of the proposed DFIG-based wind energy conversion system is developed using a digital signal processor (DSP-dSPACE DS1103). This developed DFIG is tested extensively at different wind speeds and also presented some of the steady-state test results. Dynamic performance of this DFIG is also demonstrated for the variable wind speed operation.

Design Aspects of High-Speed Electrical Machines With Active Magnetic Bearings for Compressor Applications

Abstract: Two-stage oil-free centrifugal air compressors can bring significant advantages and open new market opportunities for compressor manufacturers. One of the core technologies behind this compressor type is the high-speed electrical machine supported by active magnetic bearings. In this paper, the requirements set by the compressor on the electrical machine design are presented. The design solutions aimed to satisfy these requirements are discussed. Two case studies illustrate possible design approaches for the target application with examples of a 120-kW, 60 000-r/min induction machine with a solid rotor and a 225-kW, 50 000-r/min permanent-magnet synchronous machine (PMSM) with a full cylindrical magnet. The system design and simulation results are confirmed by measurements of a PMSM prototype.

An Outer-Rotor Flux-Switching Permanent-Magnet-Machine With Wedge-Shaped Magnets for In-Wheel Light Traction

Abstract: This paper proposes a novel outer-rotor flux-switching permanent-magnet (OR-FSPM) machine with specific wedge-shaped magnets for in-wheel light-weight traction applications. First, the geometric topology is introduced. Then, the combination principle of stator slots and rotor poles for OR-FSPM machines is investigated. Furthermore, to demonstrate the relationship between performance specifications (e.g., torque and speed) and key design parameters and dimensions (e.g., rotor outer diameter and stack length) of OR-FSPM machines at preliminary design stage, an analytical torque-sizing equation is proposed and verified by two-dimensional (2-D) finite-element analysis (FEA). Moreover, optimizations of key dimensions are conducted on an initially designed proof-of-principle three-phase 12-stator-slot/22-rotor-pole prototyped machine. Then, based on 2-D-FEA, a comprehensive comparison between a pair of OR-FSPM machines with rectangular- and wedge-shaped magnets and a surface-mounted permanent-magnet (SPM) machine is performed. The results indicate that the proposed OR-FSPM machine with wedge-shaped magnets exhibits better flux-weakening capability, higher efficiency, and wider speed range than the counterparts, especially for torque capability, where the proposed wedge-shaped magnets-based one could produce 40% and 61.5% more torque than the rectangular-shaped magnets-based machine and SPM machine, respectively, with the same rated current density (5 A/mm2). Finally, the predicted performance of the proposed OR-FSPM machine is verified by experiments on a prototyped machine.

Comparative Study of Small Electrical Machines With Soft Magnetic Composite Cores

Abstract: In this paper, various kinds of electrical machines with soft magnetic composite (SMC) cores are compared, based on the qualitative and quantitative comparison methods. In the first part, the performances of five typical electrical machines with SMC cores are qualitatively compared. Simplified power equations for transverse flux, axial flux, and radial flux electrical machines are deduced to show the main difference among them and key design points of each machine. In the second part, the outer rotor claw pole machine (CPM) and outer rotor transverse flux machine (TFM) are comprehensively compared in a quantitative way, based on the three-dimensional finite-element method. It shows that the power capability of the outer rotor CPM is much higher than that of the TFM. On the other hand, the outer rotor CPM has higher cogging torque and no-load losses than the TFM. Furthermore, the four outer rotor radial flux machines are optimized and compared with the outer rotor CPM. The calculated results of the outer rotor TFM are compared with the experiment results, showing that the analysis results match well with the experiment ones. Several useful and interesting conclusions have been obtained for the electrical machines with SMC cores.

Geometry Analysis and Optimization of PM-Assisted Reluctance Motors

Abstract: This paper deals with a detailed geometry analysis of the rotor structure for both synchronous reluctance and permanent magnet (PM)-assisted reluctance motor in order to suggest an automatic procedure to design the rotor structure. The shape of flux barriers is selected to achieve both high d-axis inductance and low q-axis inductance to obtain high output torque and high power factor. Methods to properly design the geometry of the ends of each barrier and PMs are adopted. In order to draw a rotor with proper shape, different modifications are discussed. All details are described to allow any reader to adopt the same procedures. After that, such a procedure is used to rapidly analyze the impact of some geometry changes on the machine performance to give a design guideline. The analyzing process starts from a reluctance motor considering the number of barriers, insulation ratio, split ratio, and slots per pole per phase. Then, the PMs are inset into flux barriers and the effect of PM width on torque, power factor, and flux weakening capability is investigated. At last, the demagnetization limit under overload operations is analyzed.

Integration of Six-Phase EV Drivetrains Into Battery Charging Process With Direct Grid Connection

Abstract: The paper proposes two novel topologies for integrated battery charging of electric vehicles. The integration is functional and manifests through re-utilization of existing propulsion drivetrain components, primarily a six-phase inverter and a six-phase machine, to serve as components of a fast (three-phase) charging system. An important feature of the proposed charging systems is that they are with direct grid connection, thus nonisolated from the mains. Torque is not produced in machines during the charging process. The paper provides a comprehensive evaluation of the novel systems, together with an existing topology. Various aspects of the considered chargers are detailed and elaborated, including current balancing, interleaving modulation strategy, and influence of rotor field pulsation on control and overall performance. A control strategy is proposed and the theory and control scheme are verified by experiments.

Rotor Configurations for Improved Starting and Synchronous Performance of Line Start Permanent-Magnet Synchronous Motor

Abstract: This paper presents two new rotor configurations for the line start permanent-magnet synchronous motors (PMSMs). The first configuration proposed here uses inset consequent magnet pole arrangement with double cage, and results into improved starting performance when compared to the other rotor configurations previously used. The second configuration proposed uses a combination of circumferentially and radially magnetized magnets (hybrid rotor), with induced magnet poles, which results into improved synchronous performance. Two-dimensional finite-element analysis has been employed in the analysis of transient and steady-state performances. The experimental prototypes for the second configuration are built and tested extensively. To demonstrate the effectiveness of the hybrid rotor configuration, an additional prototype is made that employs the circumferentially magnetized magnets (spoke magnet type rotor), and performance of the proposed rotor is benchmarked with this. Analysis, simulation, and experimental results indicate that the proposed rotor configuration leads to improved steady-state performance, by utilizing 10% less magnet volume than the benchmarked spoke rotor. The proposed configurations are also suitable for inverter-fed brushless dc, and PMSMs.

Structural Reliability Analysis of Wind Turbines: A Review

Abstract: The paper presents a detailed review of the state-of-the-art research activities on structural reliability analysis of wind turbines between the 1990s and 2017. We describe the reliability methods including the first- and second-order reliability methods and the simulation reliability methods and show the procedure for and application areas of structural reliability analysis of wind turbines. Further, we critically review the various structural reliability studies on rotor blades, bottom-fixed support structures, floating systems and mechanical and electrical components. Finally, future applications of structural reliability methods to wind turbine designs are discussed.