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A new interleaved two-phase quasi three-level DC-DC modular multilevel converter (MMC) with coupled inductors is presented in this paper, which can be used in high-power applications. Compared with the existing quasi three-level output MMC, the proposed converter adopts a paralleled two-phase structure. By controlling the switching sequences of the arms with the N-type interleaving operation, the output current ripple can be effectively reduced. Meanwhile, the converter can operate in buck mode or boost mode to achieve the bidirectional power flow. This paper presents the structure of the proposed converter and analyzes its operation principles in detail. Finally, the performance of the proposed converter is verified by the simulations.

A new multi-port power electronic transformer (PET) for distribution grid is presented in this paper. The proposed PET includes high voltage stage, isolation stage and low voltage stage, which can provide high voltage DC port, high voltage AC port, low voltage DC port and low voltage AC port. The high voltage stage adopts three-phase four arms Modular Multilevel Converter (MMC) structure, which can reduce the number of sub-modules and associated elements compared with three-phase six arms MMC. The third phase of three-phase four arms MMC consists of batteries in order to achieve energy storage capability.

The infant period before the age of 6 is the key period for each person's growth and development in his life. At this stage, infants' intelligence, physical strength, and psychological development are the fastest, and family education is an indispensable and important link. However, due to irresistible factors such as going out to work, many parents accompany their children for a very limited time or even cannot live together. However, the lack of accompanying children's soul will be hurt, and even affect early education. Therefore, this paper takes "parent-child accompanying reading" software as a case study, and proposes a mobile digital early education model based on the Internet and cloud platform, especially for the long-term and short-term left-behind children to provide them with parents' long-distance accompanying reading early education platform. With the rapid development of mobile client and Internet technology, the platform can easily record, broadcast and manage the audio materials of parents' original reading picture books. The purpose of the platform is to effectively alleviate the psychological trauma of children who lack the care of escort, and gradually cultivate children's early reading habits and promote their mental development.

This paper proposes a passive transient current balancing method for multiple paralleled SiC-MOSFET half-bridge modules. The transient currents of the paralleled SiC-MOSFETs could be significantly different from each other because of the parameters mismatch, which induces significantly uneven switching losses distributions among the paralleled SiC-MOSFETs. Therefore, a passive transient current balancing method is proposed to deal with this issue. The proposed method does not rely on sensors and feedback control, so it is simple and easy to implement. Moreover, the proposed method can be easily extended to any number of paralleled SiC-MOSFET half-bridge modules. The operation principles and the parameters design of the proposed method are analyzed and presented in this paper. The performance of the proposed transient current balancing method is evaluated on an experimental set-up with three paralleled 1700V/300A SiC-MOSFET half-bridge modules.

In view of the limitations of the traditional Modular Multilevel Converter (MMC) in the prior art, a novel quasi three-level hybrid MMC is proposed in this paper. This novel topology inherits the advantages of the quasi two-level MMC's modularity, easy expansion, common DC bus and high efficiency. Meanwhile, the output voltage levels are increased up to three. Consequently, the harmonics of output voltage are reduced, so the required inductance and capacitance of the output filter can also be reduced. The structure and the operation principles of the proposed topology are presented and investigated in detail and a simulation model is built in order to verify the performance of the proposed topology.

The mathematical model of isometric polygonal curve was analyzed. To predigest the construct of isometric polygonal profile, and the realization on engineering application and the favorable of NC machining being taken into account, the practical isometric polygonal curve was put forward. The mathematical model of practical isometric polygonal was analysed, and the 2D model and solid machining process simulation were put forward. At the same time, the experiment of practical isometric-trilateral profile shaft was carried out. The results of simulation and experiment showed that the derivation of isometric polygonal curve equation and the establishment of mathematical model were correct, the NC milling program generated by MasterCAM 9.1 can be used process after little modification, and the isometric polygonal profile can be high-precision, high-efficiency and high-flexibility machining by the method of NC milling.