Haiyang Fang

Rotor design for a high-speed high-power permanent-magnet synchronous machine

Permanent-magnet synchronous machines (PMSMs) are considered a very promising machine type for high-speed applications nowadays. As permanent-magnet (PM) materials are generally fragile, a high strength sleeve is required to protect the PMs from damage due to extreme centrifugal forces. The rotor sleeve occupies space of the effective air gap of the PMSMs, so 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-electromagnetic design method is presented for the rotor of a high-speed PMSM designed for 200 kW at 40,000 rpm. Three commonly used sleeve materials are investigated and their mechanical performances are analyzed. The mechanical strength limits for the proposed machine are calculated, as well as the EM design limits. The optimal dimensions for the rotors with different sleeves are then obtained by combining their strength and EM limits. The EM, thermal and rotor dynamic performances of the designed rotors are analyzed in order to select the best rotor type. In the end, a new rotor topology is proposed to reduce the rotor eddy current losses. The new rotor topology is characterized by a multi-layer sleeve which is thinner than a single-layer sleeve. The rotor losses are significantly lower in the new rotor and easier to be cooled.

Hybrid excited vernier PM machines with novel DC-biased sinusoidal armature current

In this paper, a novel class of hybrid excitation, stator vernier permanent magnet (VPM) machines (HE-VPM) are proposed. The proposed machines are with salient rotor structure, stator located PMs, and concentrated armature windings. Therefore, the superiority of the proposed machine is robust rotor structure, short and non-overlapping end-winding, and easy heat dissipation. Besides, a novel DC-biased sinusoidal current, which contains an alternating current (AC) component and a direct current (DC) component, is applied, with this novel current, a novel hybrid excited VPM machines without additional field windings are obtained. The simulation results shows that the proposed machines exhibit higher torque density, power factor, and efficiency, Also, the constant power operation range is broadened, as the injected DC biased current can weaken or enhance the exciting fields at high/low speed. Finally, a prototype has been designed and under built, and the corresponding experiments will be added later.

A Novel Vernier Reluctance Fully Superconducting Direct Drive Synchronous Generator With Concentrated Windings for Wind Power Application

In this paper, a novel vernier reluctance fully superconducting (FSC) low-speed direct-drive synchronous generator for a wind power application is proposed. The proposed superconducting (SC) generator is with an external rotor, and both the SC armature and SC dc field windings are in the inner stationary stator. Thus, compared with the existing FSC synchronous generators (FSCSGs), the slip ring is removed, and the cryostat and related refrigerate systems are stationary and greatly simplified. In addition, both the field and armature windings are single tooth-wound concentrated windings with very short end-windings. Compared with the regular FSCSGs, the usage of the SC material is greatly reduced in this proposed topology, as with the total cost. Furthermore, the torque ripple is much lower than that in a regular FSCSG. All these features are evaluated by the finite-element simulations.

Magnetization and performance analysis of a variable-flux flux-intensifying interior permanent magnet machine

This paper mainly investigates the magnetization process and the performances of a variable-flux flux-intensifying interior permanent magnet machine (VFI-IPM). In conventional permanent magnet synchronous machine (PMSM), large flux-weakening current is needed to achieve a wide speed range, resulting in extra copper loss and limited power capacity. Recently, the VFI-IPM has been studied due to its feature of variable flux controllability in order to extend the speed range and obtain high efficiency at the entire torque-speed rang. Although design methodology of the VFI-IPM has been reported in literatures, investigation of the magnetization process in VFI-IPM has not been published, however, proper magnetization ratio should be recommended as the criteria to give the pulse current and design VA capability of the inverter. In this paper, principle and finite-element (FE) method of the magnetization process are discussed based on a tangentially magnetized VFI-IPM using Alnico magnet. Moreover, the performances of the machine after the PMs magnetized to different magnetization states are investigated. By comparing the efficiency maps, an optimal efficiency map and the corresponding magnetization ratio map are obtained, based on which the highest efficiency can be achieved at the entire torque-speed region.

Structure optimization of rotor supporting of permanent magnet direct drive synchronous generators for large wind turbine based on genetic algorithm and finite element method

As wind turbines increase their power rating, the size and mass grows as well. The higher reliability is demanded in order to minimize the maintenance. Permanent magnet direct drive (PMDD) synchronous generators are a good solution since they omit the gearbox. While the large generator mass has been also a key difficult problem limiting the practical use of PMDD generator, which makes them difficult to build, transport and install. In this paper, the rotor supporting structure of a 7MW PMDD generator is optimized by combining finite element method with genetic algorithm (GA) in order to improve the optimization efficiency. In this optimization function, it takes the minimum weight as the objective, the structure parameters of rotor supporting as the key design variables, and the deflection as the constraint condition. Comprehensive simulations and comparisons demonstrate that the method is very feasible and efficient, which could give good reference to the structural optimization in practice.

A Novel Dual-Stator Vernier Permanent Magnet Machine

In many direct-drive applications such as servo system, wind power generation, etc., it is desirable to use motors having a high torque density at a low rotation speed without reduction gears for the improvement of noises, reliability and maintenance.

Comparison of two rotor topologies for high-speed permanent magnet synchronous machines

This paper aims to compare ring permanent magnet rotor and solid cylinder permanent magnet rotor for high-speed permanent magnet synchronous machine. Due to the difference between structures, sleeves of two kinds of rotors are made of different materials. Thus, assembling methods of sleeves and their thicknesses vary. Moreover, electromagnetic properties are also influenced. Then measures are taken to suppress rotor eddy current loss according to rotor mechanical structure. And thermal analysis is performed on different motors with cooling condition kept the same. Finally, demagnetization phenomenon is studied. In this paper, all comparisons are based on design procedure of a two-pole 40,000 rpm prototype machine. All these issues are discussed from economical, mechanical, electromagnetic, and thermal perspective in order to find an optimal solution. It is suggested that ring PM rotor is a better choice in this work under design.

Rotor eddy-current loss minimization in high-speed PMSMs

In high-speed permanent-magnet synchronous machines (PMSMs), the permanent magnets (PMs) are usually retained by high strength sleeves. Metallic sleeves are preferred in some cases where a high rotor stiffness is required. However, high frequency time and spatial harmonics of the air-gap field would induce considerable eddy-current losses in the conductive sleeve, and thus exposing the PMs to risk of overheating and demagnetization. In this paper an 80 kW, 80,000 rpm PMSM is designed for air blowers. The initial design and analysis show that the rotor is overheated due to the high rotor losses when a titanium sleeve is used. Some existing methods for rotor loss reduction, namely copper shield and grooving the sleeve, are investigated for the design. Furthermore, a hybrid sleeve, which contains an inner titanium cylinder and an outer cylinder made of carbon fiber composite (CFC), is also proposed for this machine. The performances of various sleeves are studied in detail, considering the rotor eddy-current losses, the mechanical stress, and the temperature rise. The conclusions may provide some references for the design of high-speed PMSMs.

Reduction of sub-harmonic effect on the fractional slot concentrated winding interior PM machines by using spoke-type magnets

In this paper, a spoke-type IPM motor (buried with circumferentially magnetized magnets) with fractional-slot concentrated windings is designed to block the two-pole sub-harmonic and, thus, reduce the iron core losses and torque ripple. This is demonstrated by the comparison of a conventional V-type IPM configuration and a designed spoke-type machine. Both of them have 12-slot/10-pole configurations with the same stator structure. The simulation results indicate that under the same design specifications, the spoke-type motor has less magnet consumption and exhibits much smaller iron core losses and torque ripple than that of its V-type counterpart, especially when operated at high speed. Finally, the mechanical stress of the designed spoke-type machine rotor is analyzed by finite element analysis.

Cogging torque minimization of SMC motor with axially tapered stator tooth tip

In this paper, a novel stator structure with axially tapered stator tooth tip is proposed to mitigate cogging torque and reduce the machine back EMF harmonics. Furthermore, the stator tooth tips are specifically designed to provide balanced axial electromagnetic force. In order to realize continuous variation of stator tooth tip widths, the soft magnetic composite (SMC) material is used for the stator core. It is theoretically demonstrated that the cogging torque of the new structure can be reduced greatly compared with the conventional stator structure. Finally, the theoretical analysis results are confirmed by the finite-element analysis (FEA) results. A prototype has been designed and under manufactured.