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The variable voltage and variable frequency voltage source converter (VVVF-VSC) has recently received wide attention for its capability to offer continuously adjustable frequency and amplitude. However, it is a challenge to design the controller for providing the precise tracking of the voltage references, since the voltage reference of VVVF-VSC is variable in a wide frequency band, and the existing controllers usually rely on a specific control frequency or frequency band. To cope with the issue, a new feedforward compensation control is proposed for VVVF-VSC, which is based on inversion-based feedforward theory. With the method, the controller can achieve the zero steady-state error control for the variable voltage reference in a wide frequency range. And, the proposed method is simple in implementation. Finally, the experimental results are presented to validate the proposed method.

GNSS-R (Global Navigation Satellite System-Reflectomery) has emerged as a new and promising remote sensing techniques. In the recent two years, several airborne experimental campaigns have been carried out to demonstrate the possibility of wetland monitoring by GNSS-R. However, to our knowledge, there are no theoretical models for this new application. As for GNSS-R, whose working mode is an essential bistatic radar, the received power is DDM (Delay Doppler Map). A wetland GNSS-reflections simulator is presented. This model is based on the integral bistatic radar equation by taking into consideration the wetland, system impulse responses and geometry observation system. The wetland parameters affect the DDM waveforms through the BRCS (bistatic radar cross sections), which is a function of soil (surface roughness, soil moisture, soil freeze/thaw state) and vegetation parameters (vegetation moisture, biomass and growth). The simulator contains the inundated wetlands including two kinds of Aspen, whose effects on the final GNSS reflected power (DDM) can be predicted by the simulator. The developed simulator can assist as mechanism tools for wetland monitoring with GNSS-R technique, and this model can provide theoretical backup for wetland mapping, data analysis and experiment design.

We study the problem of searching a circular corridor with three flashlights, a variation of the 1-searcher problem in a circular corridor. A circular corridor is a polygon with one polygonal hole such that its outer and inner boundaries are mutually weakly visible. A flashlight is considered as a 1-searcher who has a flashlight and can see only along the ray of the flashlight emanating from his position. In the searching process, each 1-searcher can move on the boundary or into the circular corridor, the beam of his flashlight must be irradiated on the inner boundary. This paper proves that a given circular corridor can always be cleared by at most three flashlights (1-searchers), and a search schedule can be reported in O(m) time, where m?n2 denotes the walk instructions reported, and n denotes the total number of vertices of the outer and inner boundaries.

We designed a cryptographic algorithm to fit the wireless micro sensor network in this paper. The coupled extended integer tent maps, which to generate the key sequence, one byte plain text block, one byte Feistel structure, and bit confusion are used to construct the algorithm. Since It has not only the time pad property but also the high speed confusion and diffuse, the security capability of the algorithm is excellent. Moreover, there will not be multiplication, division or floating-point calculation in the computation process of the algorithm, it's suitable for the application in the WSN nodes, of which the computing power is limited.

THA(Tent map-based Hash Algorithm)-256 is a dedicated hash function with output length of 256 bits. “Tent map-based” means that message expansion of the algorithm is realized through the rolled-out and folded-over of the integer tent maps and the algorithm combines integer tent maps with traditional logic functions as major nonlinear component of compression function. Compared with SHA-256, THA-256 has ideal properties of diffusion and confusion, and improves the computation efficiency. In addition, the parallel iteration structure is adopted in the compression functions of THA-256?which is advantag-eous to high speed parallel operation of software and hardware. Preliminary security testing indicates that, THA-256 has a high degree of security, and it can be realized easily with great rapidity. Therefore, it is an ideal substitution for conventional Hash function.

This paper deals with the application of evolutionary computational methods to a problem in fluidpower engineering. An evolutionary algorithm is used here to search for an optimal spatial configuration of fluidpower valves on a valve-stand that reduces pressure drop in the system thereby leading to conservation of energy. The results of our algorithm are very satisfactory. If chosen for the spatial arrangement of the valves, the reduction in pressure drop can reduce operational costs that accrue during the continuous function of a system. The results also indicate cuts in direct and indirect costs. Pointers are provided for enhancements to this work.