High-Strength Undiffused Brushless (HSUB) Machine

Consequent pole (CP) permanent magnet (PM) machines offer scope for reducing the quantity of PM material and hence cost compared to more conventional PM machine topologies of the same rating. In this type of machine, the rotor pole arc is usually optimized to realize the largest output torque with pole shaping methods used to reduce torque ripple. However, such approaches tend to be limited by constraints imposed on the pole shapes. It is a common practice to adopt similar PM and iron pole shapes, an approach that does not fully account for the different characteristics of PM and iron poles in CPPM machines, often leading to large even order harmonics in the airgap flux density. This article proposes a shaping method with a variable rotor profile and pole arc span being established by means of optimization by Genetic Algorithm. It is demonstrated that for a fixed quantity of PM material, different PM and iron pole shapes in combination with optimal PM and iron pole arc spans are essential for ensuring both maximum output torque and lower torque ripple when the due account is taken of flux leakage. It also demonstrates that since the flux density in the region under a PM pole is governed by the magnetic potential produced by magnets while it is governed by magnetic reluctance under iron pole, different PM pole and iron pole shapes are necessary to reduce the even-order harmonics in a CPPM machine and consequently to reduce torque ripple. The performances of optimized and more conventional CP machines are compared by finite-element method on 12-slot/8-pole prototype motors.

I. IntroductionThere are many studies on axial flux permanent magnet machines (AFPMMs) due to their compactness [1]. The conventional AFPMMs comprise a stator and two rotors. In general, the stator with toroidal windings or overlapping windings is sandwiched between two rotors [2][3]. Toroidal windings have shorter ends than overlapping windings, which can reduce copper loss and ending effect. However, this structure also wastes the ends of windings, which means that the windings are not utilized sufficiently. To some extent, it reduces the torque density of the machine.This paper proposes a novel axial-radial flux permanent magnet machine (ARFPMM) to solve the problem. In the ARFPMM, the endings of windings are also used to produce torque with little increase of volume, which results in the improvement of torque density.II. Structure of ARFPMMThe proposed ARFPMM integrates both axial-flux and radial-flux machines in a compact space, which improves the torque density. As shown in Fig. 1(a), the ARFPMM is composed of one stator, two axial rotors and one radial rotor. Because the end of overlapping windings is useless, the machine adopts toroidal windings. Thus, the stator is equipped with opening slots on three faces. Permanent magnets are mounted on the surface of rotors. The radial rotor is fixed and aligned with two axial rotors, which can avoid the tilt of axial rotors and generation of harmonics in flux density per phase. The inner and outer diameters of permanent magnets on axial rotors are the same as those of stator. Similarly, the height of permanent magnets on radial rotor is equal to that of stator.In order to suppress air-gap flux density harmonics and get more sinusoidal waveform of air-gap flux [4], the permanent magnets are arranged as Halbach-array. It can also increase the flux density in the air gap. The magnetization direction of PMs is related to the number of segments per pole pair. As shown in Fig. 1(b), each pole pair is divided into six segments, so the magnetization direction of each segment varies 60° in turn.III. Design and AnalysisCompared with integer-slot concentrated windings, fractional-slot concentrated windings can enhance flux-weakening capability and reduce cogging torque [5]. Therefore, a 20 pole 24 slot fractional-slot concentrated-winding machine is chosen. In the case, the winding factor is 0.966. It is related to the no load back electromotive force (EMF) which can be calculated as equation (1). E0=4.44fkwNΦ10 (1)Where f is the electric frequency of the machine, kw is the winding factor, N is the number of coils per phase in series, Φ10 is the magnetic flux. In the ARFPMM, three rotors are used to increase the magnetic flux in air gap. The result of 3D FEA for back EMF is shown in Fig. 2(a). Fig. 2(b) is the fast Fourier transform of back EMF. It shows that the maximum harmonic is the third order harmonic, which can be neglected due to the star-connection of three phase windings.Because the magnetic flux in air gap is increased under the same operating state, the torque of ARFPMM is also increased. Fig. 2(c) shows the torque of the machine at rated conditions when the current is 7 A and rotor speed is 600 rpm. In the condition, the average torque is 41.63 Nm and the torque density is 28.58 Nm/L. The torque ripple is 3.4 Nm, 8.1% of the rated torque. As shown in Fig. 2(c), the peak-peak value of cogging torque is 3.26 Nm.IV. ConclusionThis paper proposes a novel ARFPMM with a unique structure of two axial rotors and one radial rotor, and implements its design and FEA. Due to the Halbach-array PMs, the main harmonics of back EMF is the third order harmonic, which is negligible when the windings are connected in star-connection. Compared with conventional AFPMM, the structure increases the torque through increasing the magnetic flux through windings per phase. Thus, the ARFPMM reaches an extremely high torque density of 28.58 Nm/L. On the other hand, fractional-slot concentrated winding configuration reduces the cogging torque, of which the peak-peak value is only 3.26 Nm.AcknowledgeThis work is supported in part by NSFC (52077186&51677159), in part by STIC of Shenzhen Municipality (JCYJ20180307123918658), and in part by ITF (ITP/027/19AP), HK. **

Design of a New Consequent-Pole Segmented Dual-Stator Permanent Magnet Machine

The increase of pole numbers of the interior permanent magnet (IPM) synchronous machine can boost its air gap flux density, raise its efficiency and torque, and reduce its volume and weight. With the help of geometry module, this paper analyzes the relation between "flux concentration function" and the pole pair numbers of IPM synchronous machine, discusses connections between pole numbers and air gap flux density, per pole flux, non-load electric potential, flux density of rotor lead magnet material, flux density of stator tooth, flux density of stator yoke, and power which permanent magnet of unit volume produce respectively. Finally, authors point out: (1) when the saturation of lead magnet material was considered, the air gap flux density and the sums of the per pole flux will produce a the maximum with the increase of pole pairs, that is, IPM machine has a suitable pole pairs; (2) IPM machine bears "flux concentration function", when its pole pairs is more than or equal to 3, B/sub /spl delta///B/sub M/>1 or 4, B/sub /spl delta///B/sub r/>1; (3) the pole pairs of the IPM machine, which be from 3 to 6, is suitable. (4) the inner flux density of permanent magnet and power produced by the permanent magnet of unit volume will drop with the increase of pole pairs of the IPM machine.

Permanent magnet brushless motor used for deep-sea human occupied vehicle's (HUV's) propeller was studied in this paper. Based on analyzing the influences of waveform of phase current on flux density in air gap, rotor eddy-current losses were determined in BLAC and BLDC modes. This paper proposed that rotor loss is the minimum in BLAC mode. In BLDC mode, with optimal commutation advance angle (20°), rotor loss is the lowest. Finally the temperature distribution of the motor was gained considering the rotor eddy-current loss.

The shape of permanent magnet (PM) in surface-mounted permanent magnet (SPM) machine plays an important role in the electromagnetic performance of PM machine. This paper, taking multi-phases permanent magnet synchronous machine as an example, deduced the permanent magnet thickness formula by sine + 3rd harmonics shaping pole. Air gap flux density, back electromotive force (EMF) and output torque are simulated respectively by eccentric shaping pole and sine + 3rd harmonic shaping pole, which shows the latter could enhance the output torque of permanent magnet machine, providing reference for engineering design.

This paper investigates the influence of different magnetization patterns on the performances of the surface-mounted permanent magnet synchronous machines (SMPMSMs). Three magnetization patterns are employed, which are radial, parallel, and ideal Halbach magnetizations. These magnetization patterns are applied to 9-slot/10-pole and 15-slot/4-pole permanent magnet (PM) machines. The PM machines are designed and simulated by using Opera 2D finite element. The performances of three PM motors, such as airgap flux density, phase back-EMF, and cogging torque, are evaluated under the influence of different magnetization patterns. The total harmonic distortion of phase back-EMF (THDv) for the motors are investigated. The PM motors with ideal Halbach magnetization provide the lowest cogging torque and the lowest total harmonic distortion of phase back-EMF. Besides that, the optimum setting of the magnet pole-arc can reduce the total harmonic distortion of phase back-EMF and achieve lower cogging torque. The optimum magnet pole-arc produced by radial magnetization in 9-slot/10-pole motor is 24.8° mech., with cogging torque of 0.45 Nm, and THDv of 2.69 %. Meanwhile, the optimum magnet pole-arc produced by parallel magnetization in 9-slot/10-pole motor is 26.0° mech., with cogging torque of 0.41 Nm, and THDv of 2.00 %.

This paper presents an analytical method to design the high-efficiency surface permanent magnet synchronous motor (SPMSM) or generator (SPMSG). The air-gap and permanent magnet size can be approximately determined based on our mathematics model, which is the most important part of SPMSM design. From our method, we can know that motor's power out torque is related to the torque angle that we selected in our design and it affects the air-gap and permanent magnet size. If we choose a low torque angle, the motor or generator's overload power handing capability will increase. The embrace value has a vital place in designing a motor or generator due to its effects on air gap flux density, cogging torque, efficiency and so on. In order to avoid the knee effect, the working point of the permanent magnet we selected in the design should be bigger than 0.5. The developed 36 slots, 4 poles, surface mound permanent generator is proposed. The corresponding finite element analysis (FEA) model is built based on our design method. Structure optimization includes stator and rotor structure size, permanent magnet size, magnetic bridge and air gap length which are analyzed and simulated by ANSYS Maxwell 2D FEA. Thermal analysis is conducted, and the housing of the alternator is designed. The alternator prototype is fabricated and tested based on our design.

The increase of pole pairs numbers of the interior permanent magnet (IPM) synchronous machine with concentration structures can boost its air gap flux density, raise its efficiency and torque, and reduce its volume and weight. But there exists a suitable value. With the help of geometry module, this paper analyzes the relation between concentration function and the pole pair numbers of IPM synchronous machine, and, by the use of finite element analyze (FEA) software, discusses connections between pole pair numbers and air gap flux density, per pole flux, non-load electric potential, flux density of rotor lead magnet material, flux density of stator tooth, flux density of stator yoke, and power which permanent magnet of unit volume produce respectively. Furthermore a suitable pole pair numbers value for IPM synchronous machine with concentration function is presented

Permanent magnet (PM) machines generally employ rare-earth PMs. The rare-earth PMs increase the manufacturing cost of PM machines due to their high material cost. To reduce the manufacturing cost of PM machines, this paper studies a consequent-pole configuration. Consequent-pole PM machines have poles with magnets and poles composed of iron-cores. The rotor design can adjust the air-gap flux density distribution. This improves the average torque and reduces the volume of PMs simultaneously. In this paper, the rotor of a consequent-pole surface-mounted PM machine is designed to reduce the volume of PMs. The characteristics are investigated for the rotor structure through a theoretical calculation and a finite-element method analysis. These results show that the consequent-pole configuration can reduce the volume of PMs in comparison with a conventional one.

Permanent magnet (PM) machines have been widely applied in industrial applications due to the advantages of high torque density, high reliability, and high efficiency. In this paper, the magnetic gear effect (MGE) in PM machines is investigated in depth. A comprehensive derivation of the torque-generating process is carried out and a quantitative analysis of the air-gap harmonics contributing to average torque under different configurational freedoms is studied. The improvement of torque capability for the PM machines with MGE is discussed. The electromagnetic properties of typical PM machines with MGE are analyzed based on the magnetic circuit analytical model, and the effectiveness of theoretical analysis is verified by finite element analysis and experimental prototype. It is shown that the PM machines with an independent modulation unit possess the characteristics of high torque density and large PM utilization rate. And the PM machines with tooth-pole modulation unit have strong overload capability.

There is increasing popularity of using permanent magnet (PM) machines in vehicle propulsion systems. Due to the pre-excitation of PM, the machines could offer higher efficiency and torque density. However, their inherent torque ripple could be problematic for electric vehicles (EVs) due to low damping of torsional vibration which may affect passenger comfort. This can prohibit the use of PM machines to improve vehicle energy efficiency. This paper presents the application of resonant control (RC) to suppress the impact of the PM torque ripple, which aims to reduce the vibration of a vehicle. A prototype PM machine and driveline have been fitted to a light-duty off-road vehicle. Firstly, the drivetrain frequency response was analyzed. The main source of the vibration is identified as the 24 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> harmonic torque ripple of the 12-slot/8-pole PM machine, which originates from the cogging torque and air-gap flux harmonics. The vibration becomes more severe when the torque ripple frequency is close to the natural frequency of the drivetrain. Then, the RC in conjunction with PI controller (PIR) was introduced to be used at the outer speed loop, so that an accurate current reference signal can be generated for the inverter to mitigate the speed ripple. When compared to the conventional Proportional-Integral (PI) controller, PIR controller has demonstrated over 80% reduction in speed ripple, even when the torque ripple frequency is close to the natural frequency of the vehicle.

In order to explore the influence of voltage deviation on the loss of permanent magnet synchronous motor (PMSM), a 50kW PMSM was taking as an example. The finite element method was taken for the numerical calculation and analysis of its rated load in voltage deviation situation by frequency converter power supply. The magnetic flux density of stator core, rotor core and air gap were analyzed. The fundamental and harmonic component of winding current were analyzed as well. The distribution characteristic of stator corn loss, rotor corn loss, winding loss and permanent magnet eddy loss were obtained. Phase A current was selected to simulate and compared with experimental result. As indicated by the result: With the increase of voltage, stator core loss, rotor core loss, permanent magnet eddy loss and winding loss all raised. The numerical calculation result was matched to the experimental data, which verified the correctness of research method. It can provide some reference for the motor design and optimization.

Permanent magnet (PM) machines possess the merits of high torque density and high efficiency which is very suitable for some applications such as electric vehicles (EVs) [1]-[4]. Over the years, the surface PM and interior PM types, have been extensively studied and developed. The 2004 prius interior PM machine with the advantages of high torque density and wide speed range has been built and applied successfully in hybrid EVs. Recently, PM vernier (PMV) machines derived from magnetic gears are acknowledged that it can offer higher torque density than conventional one [4]-[6]. Unfortunately, similar to conventional PM machines, the PMV ones also suffer from relatively low flux adjusting efficiency and poor performance at high speed range due to the uncontrollable PM magnetic field. A flux controllable PMV machine has been proposed to improve these problems by the introduction of DC field excitation windings [6]. Although the flux controllable PMV machine definitely combines the merits of high torque density and wide speed range, its flux adjustment capability is still limited because the flux by the field excitation windings goes through the high magnetic reluctance of PMs. In addition, it suffers from the problems of mechanical integrity and thermal instability since the PMs are located on the rotor. To solve these problems in the existing flux controllable PMV machine, two novel hybrid excitation PMV machines with surface and V shape PMs, termed as the hybrid excitation surface PM vernier (HE-SPMV) and hybrid excitation V shape interior PM vernier (HE-VIPMV) machines, will be proposed in this paper.

This paper analytically derives the optimal third harmonic current to improve the output torque in five-phase surface-mounted permanent magnet (SPM) machines under the constraints of the same peak/rms value. The relationship between the output torque and the third harmonic current is established and its optimal value for maximizing the output torque is derived. It is found that the optimal third harmonic current is dependent on the ratio of the third harmonic back electromotive force (EMF) to the fundamental one but it is not 1/6 of the fundamental one as pulse width modulation in an inverter. In order to improve the output torque by increasing the fundamental and third harmonic winding factors and the third harmonic airgap flux density, the unequal width tooth and permanent magnet (PM) segmentation are employed in the 10-slot/8-pole five-phase SPM machine. The optimal unequal tooth dimensions and the number of PM segmentations are analyzed for maximizing the output torque. The airgap flux density, back EMF, cogging torque, and output torque of the machine with equal/unequal tooth width and unsegmented/segmented PM are compared. Finally, the experiments on the prototype 10-slot/8-pole PM machine with unequal tooth width and segmented rotor are given to verify the analytical and finite element analyses.