Application of Single-to-Single Phase Matrix Conversion in Conventional Rectifier-Inverter

The principle of single to single phase matrix electric power conversioin is further studied and the conversioin switch function is introduced into conventional rectifier inverter, thus a general character of the two conversion techniques is discovered. It is characteristic of the switch functiion to follow mains voltage distortion and mains frequency drift. By utilizing the merit, unidirectional switch duty rations of the inverter follow the variation of DC link voltage automatically, thus the size of DC link electrolytic capacitor can be reduced considerably, bringing about improved mains side power factor. Corresponding topologies and theoretical and theoretical derivations are given, and so are the simulation results, based on which it is confirmed that the single to single phase matrix conversion technique is potentially useful in large scale production, and the introduction of switch function can yield good economic returns.

Emotional State Transition Model Based on Stimulus and Personality Characteristics

In order to use mathematical methods to study how cognitive reappraisal strategies affect the output state of emotions,Gross's cognitive reappraisal strategy is transformed into a quantitative parameter which is proposed to describe the general perception of emotional events on the basis of the emotion regulation.According to Gross's emotional regulation model,the Finite State Machine(FSM) model is used for describing the process of emotional state transition and the Likert 5 grading scale is introduced to study the level of an individual's reappraisal according to the participant's self-evaluation.The experimental results verify that the algorithm can effectively describe the relationship between the reappraisal strategy,emotional events and an emotiongenerative process.There are multiple dimensions of a human's emotional state.Thus,in the field of human-computer interaction,further research requires the development of a specific algorithm which can be implemented by a computer for the emotion regulation process.

Bézier representation of geometrically continuous splines

As an intrinsic measure of smoothness, geometric continuity is an important problem in the fields of computer aided geo- metric design. It can afford more degrees of freedom for manipulating the shape of curve. However, piecewise polynomial functions of geometrically continuous splines are difficult to be constructed. In this paper, the conversion matrix between geometrically con- tinuous spline basis functions and Bezier representation is analyzed. Based on this, construction of arbitrary degree geometrically continuous spline basis functions can be translated into a solution of linear system of equations. The original construction of geomet- rically continuous spline is simplified.

具有多重时滞的中立型反馈系统的稳定性

本文结合Ｌｙａｐｕｎｏｖ泛函和差分算子稳定性的结果，采用常数变易法，给出了一类具有多重时滞的中立型反馈系统一致渐近稳定的充分条件．

Land cover dynamics of different topographic conditions in Beijing,China

Topographic conditions play an important role in controlling land cover dynamic processes.In this study,remotely sensed data and the geographic information system were applied to analyze the changes in land cover along topographic gradients from 1978 to 2001 in Beijing,a rapidly urbanized mega city in China.The study was based on five periods of land cover maps derived from remotely sensed data:Landsat MSS for 1978,Landsat TM for 1984,1992,1996 and 2001,and the digital elevation model(DEM)derived from 1:250,000 topographic map.The whole area was divided into ten land cover types:conifer forest,broadleaf forest,mixed forest,shrub,brushwood,meadow,farmland,built-up,water body and bare land.The results are summarized as follows.(1)Shrub,forest,farmland and built-up consist of the main land cover types of the Beijing area.The most significant land cover change from 1978 to 2001 was the decrease of the farmland and expansion of the built-up area.Farmland decreased from 6354 to 3813 km^(2)in the 23 years,while the built-up area increased from 421 to 2642 km^(2).Meanwhile,the coverage of forest increased from 17.2%to 24.7%of the total area.The conversion matrix analysis indicated that the transformation of farmland to the built-up area was the most significant process and afforesta-tion was the primary cause of the replacement of shrub to forest.(2)Topographic conditions are of great importance to the distribution of land cover types and the process of land cover changes.Elevation has an intensive impact on the dis-tribution of land cover types.The area below 100 m mostly consists of farmland and built-up areas,while the area above 100 m is mainly covered by shrub and forest.Shrub has the maximum frequency in areas between 100 and 1000 m,while forest has dominance in areas above 800 m.According to the analysis of land cover changes in different ranges of elevation,the greatest change below 100 m was the process of urbanization.The process of the main land cover change occurred above 100 m was the transformation from shrub to forest.This result was consistent with the vertical change of natural vegetation distribution in Beijing.(3)Slope has a great influence on the distribution of land cover.Farmland and built-up areas are mostly distributed in flat areas,while shrub and forest occupy steeper areas compared with other land cover types.Forest frequency increased with the increas-ing slope.Land cover changes differed from the slope gradients.In the plain area,the land cover change occurred as the result of urbanization.With the increasing of the slope gradient,afforestation,which converts shrub to forest,was the process of the primary land cover change.

Dynamic Modeling and Closed-loop Control of Hybrid Grid-connected Renewable Energy System with Multi-input Multi-output Controller

In this study, a novel approach for dynamic modeling and closed-loop control of hybrid grid-connected renewable energy system with multi-input multi-output(MIMO) controller is proposed. The studied converter includes two parallel DC-DC boost converters, which are connected into the power grid through a single-phase H-bridge inverter. The proposed MIMO controller is developed for maximum power point tracking of photovoltaic(PV)/fuel-cell(FC) input power sources and output power control of the grid-connected DC-AC inverter. Considering circuit topology of the system, a unique MIMO model is proposed for the analysis of the entire system. A unique model of the system includes all of the circuit state variables in DCDC and DC-AC converters. In fact, from the viewpoint of closed-loop controller design, the hybrid grid-connected energy system is an MIMO system. The control inputs of the system are duty cycles of the DC-DC boost converters and the amplitude modulation index of DC-AC inverters. Furthermore, the control outputs are the output power of the PV/FC input power sources as well as AC power injected into the power grid. After the development of the unique model for the entire system, a decoupling network is introduced for system input-output linearization due to inherent connection of the control outputs with all of the system inputs. Considering the decoupled model and small signal linearization, the required linear controllers are designed to adjust the outputs. Finally, to evaluate the accuracy and effectiveness of the designed controllers, the PV/FC based grid-connected system is simulated using the MATLAB/Simulink toolbox.