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This paper describes a new control scheme of grid connected inverter of DG (distributed generation) under unbalanced grid voltage. In this paper, the proposed scheme of synchronous reference frame (SRF) controller can reduce the influence of unbalanced grid voltage, which is mainly caused by unbalanced distribution of single-phase and non-linear loads, etc. In order to realize the control goal, a positive SRF which rotates counterclockwise and a negative SRF which rotates clockwise are used to control the positive sequence current and negative sequence current, separately. According to PF =1 of grid side and average output active power is constant, the positive sequence reference current and negative sequence reference current are obtained. The positive sequence ac link feedback current is derived through a notch filter to eliminate the 100Hz negative sequence in the positive SRF. The same as the negative sequence ac link feedback current. The effectiveness of the proposed scheme has been demonstrated through computer simulation.

Bibliography: p. 84-93

As one kind of renewable energy sources, photovoltaic is gaining more importance and popularity in the recent years. Photovoltaic power system can operate in parallel to the grid or in island. Traditionally, DR often works in current mode during connected to the main grid, while intentional islanding demand which operating in voltage mode in case of utility faults, power-quality events and schedule maintenance. During the switch from current mode to voltage mode, uncontrolled and unpredictable transient process may appear on the output terminal voltage of grid-connected inverter. This paper proposes a control algorithm to maintain seamless transfer on the output voltage across critical and sensitive loads during intentional islanding, meanwhile a reasonable output filter topology between inverter and the grid is presented. The algorithm is implemented on a voltage source inverter (VSI) platform using a DSP. Simulation and experiments proved the feasibility of this control scheme.

In order to improve the dynamic performance of the grid-connected PV inverter control system, reduce the hardware and software cost of inverter control design, in view of grid-connected inverter non-linear mathematical model, this paper proposes the design of single-phase current closed loop grid-connected PV inverter control system using the Exponential Sliding Mode Control of the modern control theory. Theory testify of the Exponential Sliding Mode Approach Law applied in the grid-connected inverter is completed, and system stability was proven using Lyapunov theorem. In view of the question of chosen Sliding Mode Approach Law existence the non-linearity possibly to cause system buffeting, used the unit to control continuous method, it can enable smooth after the control having high gain characteristic nearby the cut surface, and it has the resistance disturbance and parameter perturbation ability. Compared with the conventional control system, the result had proven proposed the control strategy accurate, and the system has a good control precision and followed characteristic.

Proceedings of DIS 2007, p.735-738, ISBN 978-3-935702-23-2, ISSN 1435-8077

We propose to measure azimuthal correlations of heavy-flavor hadrons to address the status of thermalization at the partonic stage of light quarks and gluons in high-energy nuclear collisions. In particular, we show that hadronic interactions at the late stage cannot significantly disturb the initial back-to-back azimuthal correlations of DDbar pairs. Thus, a decrease or the complete absence of these initial correlations does indicate frequent interactions of heavy-flavor quarks and also light partons in the partonic stage, which are essential for the early thermalization of light partons.

We propose to measure correlations of heavy-flavor hadrons to address the status of thermalization at the partonic stage of light quarks and gluons in high-energy nuclear collisions, shown on the example of azimuthal correlations of D-Dbar pairs. We show that hadronic interactions at the late stage can not disturb these correlations significantly. Thus, a decrease or the complete absence of these initial correlations indicates frequent interactions of heavy-flavor quarks in the partonic stage. Therefore, early thermalization of light quarks is likely to be reached. PACS numbers: 25.75.-q

Unprecedented pressure on the physical, chemical and biological systems of the Earth results in environment problems locally and globally, therefore the detection and understanding of environmental change based on long-term environmental data is very urgent. In developing countries/regions, because the natural resources are depleted for development while environmental awareness is poor, environment is changing faster. The insufficient environmental investment and sometimes infeasible ground access make the environment information acquisition and update inflexible through standard methods. With the main advantages of global observation, repetitive coverage, multispectral sensing and low-cost implementation, satellite remote sensing technology is a promising tool for monitoring environment, especially in the less developed countries. Multi-sensor satellite images may provide increased interpretation capabilities and more reliable results since data with different characteristics are combined and can achieve improved accuracies, better temporal coverage, and better inference about the environment than could be achieved by the use of a single sensor alone. The objective of this thesis is to demonstrate the capability and technique of the multi-sensor satellite data to monitor the environment in developing countries. Land cover assessment of Salonga national park in the democratic republic of Congo of Africa, desertification monitoring in North China and tropical/boreal wildland fire detection in Indonesia/Siberia were selected as three cases in this study for demonstrating the potential of multi-sensor application to environment monitoring. Chapter 2 demonstrates the combination of Landsat satellite images, Global Position System (GPS) signals, aerial videos and digital photos for assessing the land cover of Salonga national park in Congo. The purpose was to rapidly assess the current status of Salonga national park, especially its vegetation, and investigated the possible human impacts by shifting cultivation, logging and mining. Results show that the forests in the Salonga national park are in very good condition. Most of the area is covered by undisturbed, pristine evergreen lowland and swamp forests. No logging or mining activity could be detected. Chapter 3 demonstrates the one full year time series SPOT VEGETATION with coarse resolution of 1 km and the ASTER images with higher resolution of 15 meters as well as Landsat images for land cover mapping optimised for desertification monitoring in North-China. One point six million km2 were identified as risk areas of desertification. Results show within a satellite based multi-scale monitoring system SPOT VEGETATION imagery can be very useful to detect large scale dynamic environmental changes and desertification processes which then can be analysed in more detail by high resolution imagery and field surveys. Chapter 4 demonstrates the detection of tropical forest fire and boreal forest fire. Firstly, the ENVISAT ASAR backscatter dynamics and ENVISAT full resolution MERIS characteristics of fire scars were investigated in Siberian boreal forest, and results show these two sensors are very useful for fire monitoring and impact assessment. Secondly, the general capability and potential of ENVISAT multi-sensor of MERIS, AATSR, ASAR as well as NOAA-AVHRR and MODIS for tropical forest fire event monitoring and impact assessment in tropical Indonesia were investigated, and results show the capability of ENVISAT to acquire data from different sensors simultaneously or within a short period of time greatly enhances the possibilities to monitor fire occurrence and assess fire impact. Finally, the multi-sensor technology was applied to the disastrous boreal forest fire event of 2003 around East and West Lake Baikal in Siberia, and results show that 202,000 km2 burnt in 2003 within the study area of 1,300,000 km2, which is more than the total burnt area between 1996-2002. 71.4% of the burnt areas were forests, and 11.6% were wetlands or bogs. In total 32.2% of the forest cover has been burnt at least once from 1996 to 2003, 14% of the area has been affected at least twice by fire. These demonstrations show that in spite of the two disadvantages of indirect satellite measurements and the difficulty of detecting the cause of environment change, multi-sensor satellite technology is very useful in environment monitoring. However more studies on multi-sensor data fusion methods are needed for integrating the different satellite data from various sources. The lack of personnel skilled in remote sensing is a severe deficiency in developing countries, so the technology transfer from the developed countries is needed.