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MIMO SAR Waveform Diversity and Design
Published in Wen-Qin Wang, Multi-Antenna Synthetic Aperture Radar, 2017
RSF waveforms are generated by using a random frequency on each subpulse. It is common to represent the frequency ordering using a time-frequency grid. The grid is divided into N2 regions of size Br/N×Tp/N. Figure 5.3 shows a single random frequency ordering, where the actual frequency values which are transmitted during a particular subpulse are shown. Only a single frequency is transmitted during each subpulse.
Permutation Entropy Thresholding: A Non-Linear Signal Processing Method for Islanding Detection
Published in IETE Journal of Research, 2023
Sindhura Rose Thomas, Bindu M. Krishna, Usha Nair
The performance of the proposed method in islanding detection is evaluated by simulation on a general case of inverter-based DG system and more realistic complex PV system model in single as well as multi-DG structures. The systems are modeled in MATLAB/SIMULINK software environment. The inverter-based DG model considered for the general analysis consists of a DG source with a PWM controlled Voltage Source Inverter, a three-phase RLC load and the grid is shown in Figure 4. All the components of the system are connected to Point of Common Coupling (PCC). The terminal voltage of DG is 415 V. The grid parameters like line to line voltage frequency grid resistance and inductance are 415 V, 50 Hz, 0.015 Ω and 0.2 mH respectively. The R, L and C parameters of the load are chosen such that the quality factor is 1. Different testing conditions like of active and reactive power mismatches, ΔP and ΔQ, various load quality factors, other transient disturbances are used for testing the effectiveness and the detection times taken by the system.
Comparison of Cost, Power Consumption, and Spectrum Utilization in Protected Fixed- and Flexi-Grid Optical Networks
Published in IETE Journal of Research, 2018
Sridhar Iyer, Shree Prakash Singh
In view of satisfying demand(s) of the various heterogeneous services having different applications and varied bandwidth requirements, architectures of the optical transport networks (OTNs) have evolved from the fixed-grid wavelength-switched optical networks (WSONs) towards flexi-grid elastic optical networks (EONs) technology [1,2]. In WSONs, a particular transceiver type is assumed, and only a single demand serving method exists, which fixes, bit-rate, transmission reach (TR), and spectrum utilization [3]. However, WSONs are required to admit all the channels within a fixed frequency grid which may not be adequate for high-speed channels, and may also under-utilize the spectrum for low bit-rate requests. Hence, for future OTNs, it is essential to resort to EON technology in which (1) on the basis of requirement(s), wider channels are created by combining spectrum units (or frequency slots), and (2) use of multiple subcarrier(s) ensures that the wavelength capacity can be zoned into finer granularities, hence provisioning an increased flexibility in capacity allocation to heterogeneous demands. The other main features of EONs include the (1) use of different modulation formats (MFs) differing in both, the spectral efficiency (SE) and the TR, (2) signal regeneration execution ability with modulation conversion [4], and (3) transmission of super channel(s) (or multiple carrier(s)) [5].
Autonomous Operation of Grid Synchronizing Breakers with Low Voltage Ride Through (LVRT) Capabilities
Published in Electric Power Components and Systems, 2020
Liu Zhang, Shaohua Ma, Yiqi Liu, Yi Zhao
It is noteworthy that there could be multiple grid conditions that an interface inverter should be accommodated. In normal operation mode, the voltage and current are normal and the control objective of an interface inverter is to maintain the required grid-connected current following the designed control diagram. Meanwhile, as some ad hoc functions, grid-connected converters can also be used to compensate for the harmonics in grid-connected current and thereby maintain converter operation stability [7]. On the other hand, in autonomous operation mode, it should be mentioned that the grid voltage is influenced by faults, and there could be unbalanced or even oscillations in grid voltage at the PCC. Therefore, the interface inverter should ensure reliable and stable operation under these grid faults [8]. Among common grid faults, both balanced and unbalanced faults should be considered, including balanced three-phase faults, unbalanced two-phase faults, and single-phase to ground faults. The power electronic interface converters should be designed to mitigate the faults or ride through the faults and maintain the required grid operation condition [9]. Among different types of converter operation modes under fault conditions, low-voltage ride-through (LVRT), which is similar to high-voltage ride through (HVRT), is a common control function that needs to be achieved. Especially for single-phase low-voltage ride through, it is necessary to suppress oscillations in grid voltage and frequency that is induced by unbalanced grid voltage. Meanwhile, line-frequency grid-connected current should also be maintained to support basic operation [10, 11].