Efficient technique for suppression of motor transient voltage

This paper presents a design consideration for the effects of long feeding cables in pulsewidth modulation (PWM) voltage-fed drive. The focus is mainly the overvoltage transient presented in the motor. Theoretical analysis has been achieved based on the transmission line traveling wave theory. Factors contributing to the motor transient overvoltage including typically < 2 pu (per unit) bus voltage or especially the > 2 pu case are described both in theory and by experiment. An improved simple filter structure with low power loss has been proposed. Case study for an adjustable speed ac motor drive is demonstrated by means of prototype experiment to prove its performance and effectiveness.     

A Contention-Based TDMA Technique for Data Transmissions through Satellite

The performance of a contention-based time-division multiple access (TDMA) technique is studied. Time axis of the channel is organized into frames. Each frame consists of three parts: minislot subframe, fixed subframe, and variable subframe. Users are partitioned into groups. Each group is given a data slot in the fixed subframe. A collision occurs when more than one user in the samegroup tries to access the same slot. The minislot subframe is used to identify the users involved in a collision. Each of these colliding users will be given a data slot in the variable subframe. Results obtained include average queue length and average delay, etc. The validity of analyses is also verified by computer simulations.     

High-frequency AC power distribution in Space Station

A utility-type, 20-kHz, AC power distribution system for the space station employing resonant power-conversion techniques is presented. The system converts raw DC voltage from photovoltaic cells or three-phase, low-frequency AC voltage from a solar dynamic generator into a regulated, 20-G kHz AC voltage for distribution among various loads. Operations of the components of the system such as driver inverter, DC receiver, bidirectional receiver, and three-phase AC receiver are discussed. EASY5 computer modeling and simulations were performed to study the local and global performance of the system. Simulation results show that the system has fast response and good transient behavior. The AC bus voltage is effectively regulated using the phase-control scheme, which is demonstrated with both line and load variations. The feasibility of paralleling the outputs of driver modules is illustrated with the driver modules synchronized and sharing a common feedback loop. A high-frequency, sinusoidal AC voltage is generated in the three-phase, AC input case, when the driver modules are phased 120° away from one another and their outputs are connected in series     

Charge equalization for series-connected batteries

A novel nondissipative charge equalization circuit is proposed for charge equalization control of series-connected batteries. Each battery associates with a subcircuit, which is essentially a buck-boost converter acting as a current diverter to redistribute the excessive energy from more affluent batteries to the hungry ones. By dynamically redistributing the charging current, charge equalization can be achieved more quickly and efficiently. The applicability of this approach is confirmed by experiments.     

SiC_P/Al复合材料界面反应动力学研究

用复合铸造法制备的SiC_μ/Al复合材料,加热到一定温度并保温不同时间以改变其界面反应程度,通过确定复合材料中的分含量及其与温度和时间之间的相互关系,对界面反应动力学进行了研究,并导出动力学方程,由此求出反应动力学的参数。     

LY-12铝合金应变疲劳性能和疲劳位错结构

系统研究了LY-12铝合金自然时效及240℃人工时效试样的应变疲劳性能和疲劳位错结构。通过疲劳位错组态、位错的滑移特征以及位错同微观组织相互作用的研究,解释了该种实际合金的疲劳性能。     

Crosslink slot assignment in LEO networks

The problem of crosslink time slot assignment in low Earth orbiting (LEO) satellite networks is addressed. A crosslink channel connects two neighboring satellites through half-duplexed directional antennas. Coordination among the crosslinks between a satellite and all its neighbors in a dynamic LEO network is a delicate problem and rarely addressed in the literature. The problem is solved here using bipartite graphs. Two versions of slot assignment algorithm are given: distributed and centralized.     

Interleaved buck converters with a single-capacitor turn-off snubber

This paper proposes interleaved buck converters with a single-capacitor snubber to smooth out switch turn-off transition. The single-capacitor snubber is used to limit rising rate of drain-source voltage of the metal-oxide-semiconductor field-effect transistor (MOSFET) switch in the converters to reduce turn-off loss. In addition, the converters are operated at the boundary of continuous and discontinuous conduction modes (CCM), (DCM) to reduce turn-on loss, and in an interleaving fashion to reduce output current ripple. As compared with the counterparts of conventional converter topologies, the proposed converters have the merits of less component count, higher efficiency over a certain load range, smaller size, and they are easier to implement. Hardware measurements obtained from experimental prototypes have verified these merits.