A forensic acquisition and analysis system for IaaS

Cloud computing is a promising next-generation computing paradigm that offers significant economic benefits to both commercial and public entities. Furthermore, cloud computing provides accessibility, simplicity, and portability for its customers. Due to the unique combination of characteristics that cloud computing introduces (including on-demand self-service, broad network access, resource pooling, rapid elasticity, and measured service), digital investigations face various technical, legal, and organizational challenges to keep up with current developments in the field of cloud computing. There are a wide variety of issues that need to be resolved in order to perform a proper digital investigation in the cloud environment. This paper examines the challenges in cloud forensics that are identified in the current research literature, alongside exploring the existing proposals and technical solutions addressed in the respective research. The open problems that need further effort are highlighted. As a result of the analysis of literature, it is found that it would be difficult, if not impossible, to perform an investigation and discovery in the cloud environment without relying on cloud service providers (CSPs). Therefore, dependence on the CSPs is ranked as the greatest challenge when investigators need to acquire evidence in a timely yet forensically sound manner from cloud systems. Thus, a fully independent model requires no intervention or cooperation from the cloud provider is proposed. This model provides a different approach to a forensic acquisition and analysis system (FAAS) in an Infrastructure as a Service model. FAAS seeks to provide a richer and more complete set of admissible evidences than what current CSPs provide, with no requirement for CSP involvement or modification to the CSP’s underlying architecture

Liparis sanamalabarica (Orchidaceae): a new species from South Western Ghats, India

A new species of Liparis, L. sanamalabarica (Orchidaceae) is described based on specimens collected in the Wayanad Forests of southern Western Ghats, India. A line drawing, photographs of the new taxon, information about the habitat and its conservation status are also provided

Fuzzy-Genetic Algorithm-Based Direct Power Control Strategy for DFIG

Among a multitude of diverse control methods proposed for doubly fed induction generator (DFIG) based-wind energy conversion systems, direct power control (DPC) method has demonstrated superior dynamic performance and robustness in presence of disturbances. However, DPC is not a flawless method and shortcomings like necessity for high sampling frequency, high-speed sensors and less noise-affected sampling circuit need to be mitigated by utilizing fuzzy controllers. Parameter setting in a fuzzy controller plays a vital role, especially under non-ideal grid conditions. In this paper, a fuzzy-genetic algorithm-based direct power control (FGA-DPC) method is proposed for DFIG, while, the parameters of the fuzzy controller are optimized by genetic algorithm. The objective of the optimization is to minimize the stator active and reactive power errors to increase the precision of reference tracking. The objectives of the controller are also optimizing active power absorption based on the zone of operation and adjustment of reactive power according to grid requirements. The proposed method improves the overall precision and speed of transient response as well as significantly reducing power oscillations under non-ideal grid conditions. Finally, to demonstrate the effectiveness of the proposed method, extensive simulations are performed in Matlab/Simulink under different conditions

A New Pulsating Power Elimination Method for Single-Phase PWM AC/DC Converters with Minimum Voltage and Current Stress

An inherent problem of single-phase rectifiers is the existence of a pulsating portion in the input power, which pulsates at twice the grid frequency. If this pulsating power is transferred to the DC-link, it causes a significant amount of second-order harmonic at the output voltage. Since in many applications, such a high level of DC oscillation is not acceptable, so the pulsating power must be effectively filtered. A convenient solution to eliminate the output voltage oscillations is to use a capacitor with a relatively high capacity at the rectifier output. Due to the fact that the high capacity capacitors for this application usually have a short lifetime and occupy a lot of space, this solution cannot be considered as a proper one. In this paper, a new active method with the minimum of current and voltage stress is proposed to effectively eliminate the pulsating power and significantly reduce the required capacitance of the output filter. The proposed method is able to reduce the volume of the converter and increase its reliability and power density. The validity and effectiveness of the proposed method are confirmed by extensive simulations in the MATLAB/Simulink

A New Non-linear Control of the Four-Leg Inverter with Decoupled Model and Fast Dynamic Response for PV Generation Systems

Distributed generation (DG) will play an important role in future power generation systems, especially in stand-alone applications. Three phase four-leg inverter is a well-known topology which can be used as an interface power converter for DGs. Thanks to the fourth leg to provide the neutral path, the four-leg inverter is able to supply balanced loads as well as unbalanced loads. In this paper, the model of a three phase four-leg inverter with the fourth leg inductor in the αβγ reference frame is investigated thoroughly. Afterward, a decoupled model of the four-leg inverter is adopted to establish the proposed control method. Among non-linear control methods, pole-placement method is a famous solution to ensure fast transient response. Hence, in this paper, a pole-placement method via state feedback is proposed to control the output voltage of the four-leg inverter. Using this method, the transient performance of the system can be adjusted well. On the other hand, to guarantee good performance of the control system under steady state condition, a lead compensator is proposed to be used with the pole-placement method. Therefore, the proposed control system not only can provide fast dynamic response but also, it ensures very low steady state error. To validate the superior performance of the proposed control method, simulation and experimental results under various loading condition are provided based on a DSP-based digital control system

Space Vector Modulation Technique to Reduce Leakage Current of a Transformerless Three-Phase Four-Leg Photovoltaic System

Photovoltaic systems integrated to the grid have received considerable attention around the world. They can be connected to the electrical grid via galvanic isolation (transformer) or without it (transformerless). Despite making galvanic isolation, low frequency transformer increases size, cost and losses. On the other hand, transformerless PV systems increase the leakage current (common-mode current, (CMC)) through the parasitic capacitors of the PV array. Inverter topology and switching technique are the most important parameters the leakage current depends on. As there is no need to extra hardware for switching scheme modification, it's an economical method for reducing leakage current. This paper evaluates the effect of different space vector modulation techniques on leakage current for a two-level three-phase four-leg inverter used in PV system. It proposes an efficient space vector modulation method which decreases the leakage current to below the quantity specified in VDE-0126-1-1 standard. furthermore, some other characteristics of the space vector modulation schemes that have not been significantly discussed for four-leg inverter, are considered, such as, modulation index, switching actions per period, common-mode voltage (CMV), and total harmonic distortion (THD). An extend software simulation using MATLAB/Simulink is performed to verify the effectiveness of the modulation technique