Synchronization of a renewable energy inverter with the grid

The design, mathematical analysis, and testing results of the architecture of a new all-digital phase-locked loop system for synchronizing a voltage source DC-AC single-phase inverter with the low voltage utility grid are presented. The system which is based on the time-delay digital tanlock loop was simulated using MATLAB/ SIMULINK and was tested by subjecting the grid voltage to various perturbations similar to those which can occur in a real power system, such as voltage sags and nonlinear distortion of the grid voltage waveform. Results indicate that even in the presence of such perturbations the system achieved and/or re-gained synchronization within 100 ms. The proposed system is all-digital and can be readily implemented using a field programmable gate array and easily embedded into a power inverter

Rate-splitting multiple access for indoor visible light communication networks

Visible light communication (VLC) has been emerged as a technology that can increase the channel capacity in the next generations of wireless technologies by exploiting the largely unutilized, licence-free and huge visible light portion of the electromagnetic spectrum. In order to enable high-speed short-range wireless communications, VLC utilizes the installed high-switching rate light emitting diodes (LEDs) in the ceilings of indoor environments, which are primarily used for illumination, to modulate the signals into visible light intensity. However, VLC suffers from several limitations, such as the limited modulation bandwidth and the coverage area of LEDs that degrade the overall system spectral efficiency (SE). In this respect, the present contribution proposes rate splitting multiple access (RSMA) for multi-cell indoor VLC systems as a mean to enhance the overall system SE and energy efficiency (EE) as well as to provide ubiquitous indoor coverage and to address user mobility issues. Moreover, we utilize coordinated beamforming to design the precoders of the common and the private streams in each cell aiming to enhance the performance of cell-edge users. Finally, the formulated sum of the mean squared error optimization problem is solved sub-optimally using an alternating optimization approach. Extensive computer simulations demonstrate that RSMA improves the overall system performance in terms of the SE and EE compared to the recently used multiple access techniques, such as space division multiple access with coordinated beamforming which constitutes a special case of it.acceptedVersionPeer reviewe

Self-optimization of pilot power in enterprise femtocells using multi objective heuristic

Deployment of a large number of femtocells to jointly provide coverage in an enterprise environment raises critical challenges especially in future self-organizing networks which rely on plug-and-play techniques for configuration. This paper proposes a multi-objective heuristic based on a genetic algorithm for a centralized self-optimizing network containing a group of UMTS femtocells. In order to optimize the network coverage in terms of handled load, coverage gaps, and overlaps, the algorithm provides a dynamic update of the downlink pilot powers of the deployed femtocells. The results demonstrate that the algorithm can effectively optimize the coverage based on the current statistics of the global traffic distribution and the levels of interference between neighboring femtocells. The algorithm was also compared with the fixed pilot power scheme. The results show over fifty percent reduction in pilot power pollution and a significant enhancement in network performance. Finally, for a given traffic distribution, the solution quality and the efficiency of the described algorithm were evaluated by comparing the results generated by an exhaustive search with the same pilot power configuration

Performance evaluation of the time delay digital tanlock loop architectures

This article presents the architectures, theoretical analyses and testing results of modified time delay digital tanlock loop (TDTLs) system. The modifications to the original TDTL architecture were introduced to overcome some of the limitations of the original TDTL and to enhance the overall performance of the particular systems. The limitations addressed in this article include the non-linearity of the phase detector, the restricted width of the locking range and the overall system acquisition speed. Each of the modified architectures was tested by subjecting the system to sudden positive and negative frequency steps and comparing its response with that of the original TDTL. In addition, the performance of all the architectures was evaluated under noise-free as well as noisy environments. The extensive simulation results using MATLAB/SIMULINK demonstrate that the new architectures overcome the limitations they addressed and the overall results confirmed significant improvements in performance compared to the conventional TDTL system