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This paper proposes an improved parallel control strategy which suits for the auxiliary inverter under different working conditions in metro. Firstly, differential droop coefficient and virtual impedance are introduced to improve the stability and dynamic response of the system. Meanwhile, the proportional-resonant control is introduced to enhance the ability of the auxiliary inverter under the sudden load change condition or with the non-linear load. Furthermore, mathematical modeling of the auxiliary inverters is carried out in the system. Finally, the improved droop control, virtual impedance and current resonant control strategies are applied to two paralleled inverters test platform of 120kVA. The experimental results show that the proposed control algorithm can greatly improve the voltage waveform and dynamic response of the parallel inverters, and improve the ability of the system under non-linear loads.

In this paper, the relationship between the resonant control and repetitive control (RC) are investigated. Then through the experiment these two control methods are compared by using them in the constant-voltage constant-frequency (CVCF) inverter. Both the static and the dynamic performances are compared for the two control strategies.

Aiming at the needs for using map tiles and creating map tiles in web map applications, this study puts forward a practical coding algorithm for digital map tiles. Based on the map tile algorithm, a program of creating digital map tiles for ArcGIS mxd map documents was implemented, which can produce seamless map tiles at any scale in any extent.

Starting from the definition of fractal dimension, this paper presented the correction calculation model of curve fractal dimension which was adaptive to the interval fractal dimension. The calculation example of some actual curves'fractal dimensions which was carried out by programming showed that the correction model not only enriched and improved the theory of curve fractal dimension calculation, but also solved the calculation problem of curve fractal dimension, thus laying a theoretical and methodological foundation for the application of curve fractal dimension.

Reviewed relevant theories, we proposed an enterprise integration strategy and competitive advantage model. In the context of globalization and transition economy, some industries are characterized by industrial growth stage, so enterprises can implement horizontal and vertical integration strategies to achieve economies of scale and economies of scope, lower transaction costs, and on the basic of the above, enterprises must have a strong resource integration ability, then integrate enterprise resources by using country-specific advantages as to form firm-specific advantages, then it can build competitive advantage. In this paper, we took Baosteel for example, discussed the path of its competitive advantage formation.

Ground fissures often appear to be linear cracks on the earth's surface, but spatial curved surfaces cutting through the superficial stratum in the longitudinal direction beneath the ground. How to express such kind curved surface in digital form is unprecedented. But certainly, the digital models of ground fissures' spatial curved surfaces will undoubtedly affect and even directly determine the process and degree of the research work on the ground fissure hazard in digital environment. Base on the linear ground fissures data, and the top TIN and the bottom TIN of the Coarse Strata generated from boreholes, as well as a number of boundary conditions, this paper, for the first time, applied the TIN modeling technology to create and express ground fissures' spatial continuous curved surfaces, which run through the Coarse Strata and can carry out seamless integration, providing conditions for the creation and integration of geological 3D models and also offering reference to complex geological modeling. The digital presentation of ground fissures has two levels such as reappearance and simulation. This study shows that the digital model of ground fissures not only lays the foundation for reappearance, but also provides the possibility for simulation. Therefore, the digital model of ground fissures is the necessary premise for further probing into the ground fissure hazard by means of virtual reality technology.

To transmit real-time traffic in mobile ad hoc networks, a combined design of TDMA MAC and routing protocol was proposed. Most approaches proposed recently applied schemes in the routing protocol to provide QoS and paid no attention to the MAC design. Actually, the ability to provide QoS heavily depends on how well the resources are managed in the MAC layer. In our work, we try to focus on the design of MAC protocol and combine it with AODV to provide QoS. The QoS requirement of a certain session can be satisfied if all nodes in the route reserve slots with the corresponding frame length. It is convenient to manage slot assignment information and select a slot with a certain frame length in a binary tree structure. Simulation results are presented to verify the performance of the combined design.

To realize time division multiple access (TDMA) in ad hoc networks, a new slot synchronization scheme based on frequency hopping (FH) synchronization was proposed. In this scheme, every node in the network uses a slot counter to position slots. By compensating the time when the separator is detected with the estimated delays, the receiver's slot counter can synchronize to the sender's. Guard intervals are used in nodes to avoid collisions caused by the synchronization error. As the proposed scheme can avoid transmitting concrete time information in the network, the channel utilization can be improved. Simulation results show that the channel utilization of the proposed scheme is higher than other schemes. Moreover, this scheme has a small synchronization error and only needs a short time period to realize the initial slot synchronization. Therefore, it can be applied to real ad hoc networks

An on-demand and dynamic slot assignment (ODSA) protocol for ad hoc networks is proposed. The protocol assigns slots for nodes basing on information in their two-hop neighborhood, which can be collected by listening before slot assignment. In ODSA, a slot is divided into several mini-slots, and the reservation procedure is realized in the selected idle slot by message exchanging. ODSA can adapt to variations of application and network topology. Furthermore, it can ensure the time delays of nodes owning slots. ODSA has been studied in different network situations, and the results show that ODSA has smaller average access delay and higher channel utilization compared with FPRP.

In wireless sensor networks, efficient usage of energy helps in improving the network lifetime. Many power saving MAC schemes based on TDMA have been proposed in recent years, but none of them particularly discuss the problem of time synchronization. As there are many time synchronization algorithms have been proposed, but they can't be applied to these TDMA MAC schemes directly. In this paper, a lightweight and energy efficient time synchronization (LEETS) scheme that can be applied to all kinds of TDMA power saving MAC schemes was proposed. In the scheme, nodes compete the first slot of each time frame to broadcast local time information, which can be used to realize whole network synchronization. And guard interval is inserted in two consecutive slots to avoid collision may be caused by synchronization errors. The scheme has been simulated and the results show LEETS needs less message exchanges to realize synchronization than other time synchronization schemes. So, It is lightweight and energy efficient.