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.

The distribution network (DN) reconfiguration is a well-known optimal power flow (OPF) problem. However, with the transition of DN from “passive” to “active”, new technical challenges arise in DN reconfiguration. This paper addresses two key issues in this regard. Firstly, the integration of local renewable generation (LRG) introduces uncertainty into the system-wide power flow of the DN. Secondly, the coupling between DN and the external power grid (EPG) affects the determination of DN root voltage. Consequently, a novel DN reconfiguration approach is proposed in this paper. To begin with, an explicit mixed-integer convex OPF model is constructed that incorporates both the EPG and DN sides. Notably, the OPF model embeds the function of local droop control that is provided by LRG. Subsequently, the original OPF model is decomposed, and the distributed optimization methods based on the augmented Lagrangian relaxation are employed. The paper comprehensively discusses parallel processing and asynchronous implementation as parts of the distributed optimization procedure. Furthermore, to address the uncertainty related to LRG integration, the extreme scenario method is used to provide a robust decision regarding DN reconfiguration. The application of the extreme scenario method in the distributed OPF model concerning DN reconfiguration is successively developed. Finally, numerical results are presented to demonstrate the acceptable performance of the distributed optimization methods, in terms of optimality and convergence. Also, these are validated that the proposed DN reconfiguration approach exhibits robustness to LRG integration, the system-wide voltage profile is improved, and the active power loss is effectively reduced using the proposed DN reconfiguration approach.

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.

Reference network model determines the optimal transmission line capacities by minimizing the generation cost and investment cost of transmission lines, in which line flow constraints under contingency events should be respected. However, the number of these constraints is tremendous and this makes the impediment when reference network model is applied for real large power systems. In this paper a new method is proposed to solve reference network efficiently based on line outage distribution factor (LODF). Firstly, the power flow without contingency events is calculated. Next, the line flow under contingency events is calculated based on LODF. For each contingency event, the line flow constraint which possesses the most severe overload level is added into the reference network model. The optimization procedure proceeds until all the overload flows are eliminated. The efficiency and validity of the proposed method is verified by IEEE test systems and a real large power system.

Z-source converters have been used in new energy sources because of their advantages. These converters have attracted considerable attention under high-frequency conditions given their high power density and high conversion efficiency. However, the stability of a system of ultra-high frequency Z-source converters are likely to be affected because of the inappropriate selection of parameters or the interference of weak signals in the process of the system. These factors will render such converters unable to work properly. The chaotic bifurcation behavior of Z-source converters based on peak current control mode is analyzed in this study. A precise discrete iterative mapping model for such converters is established, and the regional stability of a system is determined based on the characteristic value of changes in the Jacobian matrix. Finally, the bifurcation and chaos phenomena in a high-frequency Z-source converter and the accuracy of the aforementioned analysis are verified via experiments. The conclusion drawn from this study does not only can provide a reference for the stable operation of ultra-high frequency Z-source converters, but also presents a theoretical basis for optimizing system parameters and improving control performance.