This paper provides an overview of the design and analysis of high-speed PM motors by focusing on prominent issues such as motor losses, temperature rise, rotor strength and vibration. The design challenges of high-speed PM motors are briefly described, and the application of various stator and rotor structures and materials is presented in electromagnetic design. Combined with the temperature distribution of the motor, various heat dissipation measures to suppress the temperature rise are summarized. Strength and dynamics analysis of the rotor are outlined with respect to the safety of rotor operation. The current status of coupled multi-physics domain design used to improve the comprehensive design capability of high-speed PM motors is reviewed. Future directions of technologies related to the design of high-speed PM motors are pointed out.

Both the spectral analysis and the closed‐form root‐mean‐square (RMS) equations are widely used to determine the three‐phase inverter dc‐link current for capacitor rating proposed. However, the analytical models of the dc‐link currents have rarely been reported for applications like the active power filter, where ac currents are mostly low‐order harmonics (LOHs). This paper first derived expressions for each dc‐link LOH current, in order to compute the capacitor losses for each LOH frequencies. Then, it is shown that the derivation of the dc‐link switching harmonic current (SHC) RMS equation is very much complicated when LOHs are present in the ac currents. Hence, new set of generalised RMS equations were successfully derived and simplified into one equation to facilitate the worst case design. The design case of the dc‐link current is demonstrated with the proposed equations. A flexible grid‐tied inverter lab prototype is developed to inject arbitrary combinations of LOH currents of different orders, sequences, amplitudes and angles into the grid. Good match between the computational and experimental results validates the proposed methods.

This paper investigates the dc-link current to facilitate the dc-link capacitor sizing for the single phase H-bridge inverter under harmonic ac currents. As the capacitor equivalent series resistance (ESR) varies significantly until the frequency is higher than 1kHz, the expressions of the dc-link current individual low order harmonics (LOHs) and the switching harmonic currents (SHCs) root mean square (RMS) value are derived respectively to accurately evaluate the dc capacitor losses. The dc-link LOH expressions reveal that each harmonic ac current induces two harmonic currents in the dc-link. When the ac current has multiple combinations of LOHs, the dc-link current envelopes take infinite possible unusual forms, so after somewhat complicated derivation, the SHCs RMS equations are successfully derived and further simplified into one equation for easy worst case design as demonstrated by the actual case study. A single phase H-bridge inverter lab prototype is developed to inject arbitrary combinations of harmonic currents of different orders, amplitudes and angles into the grid. The good match between the computational, simulation and experimental results validate the effectiveness of proposed method. Particularly, the worst case analysis is verified by the experiment and the differences between the experiment and computation results are formulated and explained definitely.

Supercapacitors (SCs) are widely used as energy storage devices in many practical applications of wireless power transfer. However, the modeling and analysis of a wireless power transfer system are seldom based on SC load; thus, the effects of the charging process on the wireless power transfer system cannot be analyzed clearly. In this paper, a variable-resistance-based method is proposed for the modeling and analysis of the process of constant current charging. First, how to make an SC equivalent in variable resistance is described, and the relationship between SC and variable resistance is considered. Next, the charging process, including charging current, voltage, power and transfer efficiency, is analyzed in detail. Furthermore, the effects of transmitting side voltage and frequency offset on this system are studied, and the optimal design method for an SC-load WPT system is provided on a preliminary basis. Finally, the theoretical derivation and analysis are verified by means of simulations and experiments.

Since the capacitor equivalent series resistance (ESR) above 1kHz almost stays constant, dc-link current root-mean-square (RMS) closed form equation is an easy way to evaluate the capacitor losses from the switching harmonic currents (SHCs). But when the ac current contains multiple low order harmonics (LOHs), their impacts on the dc-link has not been systematically studied. In this paper, a straightforward instant power based method is first proposed to derive the general expressions of the dc-link low-order harmonics (LOHs) for the single phase H-bridge inverter. Each low order harmonic (LOH) in the dc-link current is computed separately as the capacitor ESR varies with the frequencies less than 1kHz and each harmonic ac current corresponds to two dc-link harmonics. It is further revealed in this paper that the conventional switching harmonic current (SHC) RMS equation derivation process is no longer applicable when ac output current has the low order harmonics (LOHs). Hence, new switching harmonic currents (SHCs) RMS equations were derived. The good match between the computational, simulation and experimental results validate the effectiveness of proposed methods.

The dc-link voltage ripple plays an important role in dc capacitor design for three-phase voltage source converters (VSCs). However, the analytical models of the dc-link voltage ripple have rarely been reported for VSCs with nonlinear output current. This paper first derived the LOH voltages expressions in the dc-link. It reveals that each LOH component in ac current would induce two dc-link LOH voltages. Then the switching frequency harmonic voltages (SHVs) and their envelope expressions are formulated. Moreover, the proposed analytical models could be very much simplified when applied to special cases in the previous literature. Finally, an easy to design dc capacitor equation under nonlinear output current is also derived. Both simulation and experimental results validate the proposed method.