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Cascaded H-bridge multilevel inverter with isolated dc sources is a suitable choice as an interface between grid and distributed generation (DG) sources. The main duty of the interface inverter is to adapt voltage of the grid and DG source while active and reactive power exchange is also controlled by it. Conventional fundamental frequency switching methods have been studied so far only for quality improvement of the inverter output voltage. However, for the grid-connected applications, voltage quality at the point of common coupling (PCC) is more important than the inverter output voltage. This study presents a modified harmonic mitigation fundamental frequency switching method for the grid-connected cascaded H-bridge multilevel inverters. The goal is to calculate optimum switching angles of the inverter which satisfy the standard limits for the total harmonic distortion and harmonic contents of the voltage waveform at PCC considering specifications of the grid. This is also to be achieved with minimum required amount of the coupling impedance. Genetic algorithm optimisation program based on the modified switching method is employed for a sample system including a three-phase cascaded H-bridge seven-level inverter connected to a harmonic polluted grid. Computer simulation using Simulink/MATLAB is performed, the results of which confirm effectiveness of the proposed method.

Selective harmonic elimination PWM (SHEPWM) is a well-known fundamental frequency switching method for cascaded multilevel inverters. The main goal in the conventional SHEPWM is to eliminate some lower order harmonics of the output voltage while the fundamental component is satisfied. Thus, this method only regards the inverter output voltage quality, which is not sufficient in many applications. Different cells of the cascaded H-bridge multilevel inverter are supplied by isolated dc sources which may have different amounts of power. To deliver maximum power of these sources to a load or network, power should be properly shared among the cells. This study presents a modified SHEPWM method to control quality of the output voltage of the cascaded H-bridge five-level inverter in wide range of the modulation index while desired power sharing among the cells is also considered as the main priority in the whole range of the modulation index. The method forces new constraint in obtaining optimal switching angles and it may require additional switching. To study the problem, a genetic algorithm optimisation program, based on the modified method, is employed for a three-phase five-level inverter. Simulation and experimental results show the effectiveness of the proposed switching method.

In this paper, an innovative blind watermarking algorithm has been proposed for imagery applications. This algorithm has used the coefficients of the discrete wavelet transform of the host image in the form of super trees to embed the predefined binary watermark in the host image. In this scheme, a pseudo random sequence is generated to determine the exact wavelet super trees used for embedding procedure. In the next step, after choosing the maximum and second maximum amplitude coefficients of each super tree, the distance vector between two coefficients is computed. For embedding bit zero of the specified watermark, the values of the distance vector elements are decreased, while for embedding bit 1, those values will be increased based on the proposed formulas. The experimental results show that the proposed algorithm has significant robustness against image processing attacks, especially JPEG compression and also the PSNR value for the watermarked images generated by the proposed method is more than 42 dB. The watermark bits may be inserted into the host image either in spatial or in the transform domain. It is shown that hiding information in the transform domain will lead to a more robust watermarking system against most of the attacks (6). Among these methods, methods based on discrete wavelet transform (DWT) are of great renown. This is due to specific features of space-frequency localization, multi-resolution display, linear computational complexity and the excellent modeling related to Human Vision System

Objective: To determine the prevalence of HIV infection among homeless men and women and the related risk behaviors in Tehran, Iran. Methods: In 2007–2008, Tehran municipality stacked up 10672 homeless men and women for assessment of HIV and began collaboration with Iranian Research Center for HIV/AIDS (IRCHA) departments to conduct HIV infection prevalence surveys in homeless populations. The results were analyzed for associations with demographic information, family support, status of drug abuse and relation with family and friends. Results: Overall HIV prevalence was 1.7% (95% confidence interval 1.4–1.9). Factors independently associated with HIV infection included history of using drugs [AOR 8.15 (4.86–13.67)], older age [AOR 1.80 (1.08–2.99) for 40–55 yr], occupation [AOR 1.64 (1.19–2.24) for unemployed], and no relation with family [AOR 1.82 (1.30–2.54)]. Conclusions: This study supports the idea that injection drug use is contributing to the increased spread of HIV among Iranian homeless. Harm reduction programs should be expanded, particularly among homeless injection drug users.

This paper presents three-phase grid connected photovoltaic (PV) system that not only can inject active power to the grid but also can compensate harmonics and reactive power of nonlinear loads as a shunt active filter. A maximum power point tracking (MPPT) algorithm is used in order to obtain maximum power under different sun irradiance from PV; hence, in the darkness the system is used as an active filter and in the sunlight the system operates as both power conditioner and shunt active filter simultaneously. Control of the presented system is based on instantaneous power theory (p-q theory) and adaptive hysteresis band control (AHBC). Unlike conventional fix band hysteresis control in which instantaneous switching frequency is not constant, by changing hysteresis band in the AHBC method, instantaneous switching frequency will be constant with a little deviation. Simulation results using MATLAB/SIMULINK verifies effectiveness of the system in injecting of maximum power captured by the PV system to the grid and compensating of the harmonic currents and reactive power of the nonlinear load.

This paper proposes an efficient blind watermarking algorithm using distance vector for copyright protection. In this algorithm, the wavelet coefficients from various frequency locations have been grouped into a sequence and named as Group for invisible watermark embedding and extraction. In the next step, after choosing the maximum and second maximum amplitude coefficients of each Group, the distance vector between two coefficients is computed. For embedding bit zero and bit 1, values of the distance vector elements are decreased or increased, respectively. The proposed method, takes advantage of considerable robustness against prevalent attacks. Comparison analysis demonstrates that our method has better performance than the other watermarking schemes reported recently and also watermarked images do not suffer from obvious visual distortion.

This paper introduces a blind watermarking scheme based on remainder of distance vector between two wavelet blocks. In the proposed scheme, the wavelet coefficients from frequency sub-band LH3 and HL3 have been grouped into two blocks for invisible watermark embedding and extraction. In the next stage, the distance vectors between two blocks are computed and then remainder after division calculated. For embedding 0 and 1 bit, the remainder of distance vectors fixed up to specific values. By increasing divisor, it is possible to embed watermark bits in the host image with more energy; however, this will lead to PSNR reduction. The proposed method, takes advantage of considerable robustness against prevalent attacks and another profit have wide range trade off between watermark embedding energy and the quality of watermarked image with select suitable value of divisor. The experimental results show that the proposed algorithm is robust against image processing attacks and also the comparison analysis indicates that has better performance than the other blind watermarking methods.