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The torque density is a key factor for magnetic gears. To obtain maximum torque density, the design principle of magnetic gears is proposed and the maximum transmitting torque is investigated under different combinations of the inner and outer permanent magnets (PM) rotor pole pairs. The research proves that the maximum transmitting torque and the minimum torque ripple can be obtained only when the ratio of the outer and inner PM pole pair numbers is fractional. Then, the optimal selection of the span ratio and thickness of magnetic blocks in the stationary modulating ring is investigated to obtain the maximum torque. Meanwhile, analyses of the losses of various parts in the magnetic gear show that the loss of the PMs is about 70% of the total losses. Therefore, the method of dividing the PM into several pieces along the circumferential direction is employed to reduce the PM loss, which makes the PM loss reduced by 73%. Additionally, the transient behavior of the magnetic gear is analyzed, indicating that the lower torsional stiffness is the main reason for oscillations during transient changes in speed and load. To suppress oscillations due to transients, damper windings are employed and the transient time and the maximum oscillation amplitude are reduced by 25% and 20%, respectively.

The less-rare-earth interior permanent-magnet synchronous machines (LRE-IPMSMs), which have the advantages of high power density, high efficiency, and low cost, are promising candidates for electric vehicles (EVs). In this paper, the equivalent magnetic circuit (EMC) of LRE-IPMSM is established and analyzed to investigate the machine design principles, and then the performance of an optimized machine is analyzed. Firstly, the equivalent magnetic circuits of the LRE-IPMSM are established by taking the saturation effect into consideration. Secondly, the effects of geometric parameters, such as the permanent-magnet (PM) width, the PM thickness, the flux barrier thickness, the flux barrier span angle, and the bridge width, on no-load flux, q-axis flux, and d-axis flux are investigated, respectively. The results calculated by the EMC method and finite-element analysis (FEA) are analyzed and compared, which proves the effectiveness of the EMC method. Finally, an optimized design of LRE-IPMSM obtained by the magnetic circuit analyses is proposed. The electromagnetic performances and mechanical strength of the optimized LRE-IPMSM are analyzed and verified, respectively.

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A single-phase oscillating permanent-magnet (PM) alternator is proposed for free-piston stirling engines. According to its sinusoidal kinetic characteristic, the design principle of this machine is proposed. On this basis, the finite-element model is built. Since the no-load back EMF and no-load thrust are two key indexes for the single-phase oscillating PM machine, the influence of PM thickness on the no-load back EMF and no-load thrust is further investigated. Then an optimal scheme of single-phase oscillating PM machine is obtain. Because this machine has two working modes, the electromagnetic performance of two working modes is analyzed. In the generator mode, no-load and load back EMF, voltage harmonics distortion ratio, the voltage regulation ratio and kinetic characteristics are deeply analyzed. Then in the motor mode, the electromagnetic force versus current is investigated. That proves the electromagnetic thrust per current can reach 35.7 N/A.

The magnetic-field-modulated brushless double-rotor machine (MFM-BDRM), composed of a stator, a permanentmagnet rotor and a modulating ring rotor, is a novel machine used for hybrid electric vehicles (HEVs). As a three-port machine, the energy transfer relations among three ports of the MFM-BDRM are complicated. Furthermore, the special operating principle of the MFM-BDRM, the magnetic field modulation principle, is quite different from that of traditional machines. Therefore, investigating the design method of MFM-BDRM is valuable for its applications. First, the power flow of the MFM-BDRM system is analyzed on the base of the HEV background. Then different working modes of the MFM-BDRM are obtained. By analyzing the speed and torque relations among three ports, the design principle of the MFM-BDRM is proposed. In the design process, the analytical methods of the fundamental flux, stator frequency and q-/d-axis inductance, which are different from traditional machines, are proposed. The influence of some key parameters, like combinations of PMs and magnetic blocks, the span and thickness of magnetic blocks, on the electromagnetic performance is discussed. Finally, a favorable solution with the higher power density and the lower torque ripple is determined.

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