Autonomous synchronizing and frequency response control of multi-terminal DC systems with wind farm integration

Recent analyses have shown that the grid-integration of offshore wind farms through MTDC systems has brought low inertia and small-signal stability issues, in which the dynamics of phase-locked-loop (PLL) play a crucial role. To address this issue, this paper proposes a control strategy for the multi-terminal VSCs aiming at PLL-less synchronization and autonomous frequency response of the MTDC system. One of the significant features of the proposed control is that the deviation of the grid frequency can be instantaneously reflected on the deviation of the DC voltage without ancillary control. Based on this feature, a fast inertia response and primary frequency regulation among wind farms and AC systems interconnected by the MTDC system can be achieved. A small-signal model is established to evaluate the overall system stability using the proposed control. Finally, comparative studies of this proposed control with the conventional PLL-based vector control are conducted in PSCAD/EMTDC based on a practical MTDC system in China, the Zhangbei four-terminal HVDC transmission system. The analysis shows that the proposed control exhibits advantages in weak grid operation and autonomous frequency respons

Homodyne coherent detection of ASK and PSK signals performed by a subcarrier optical phase-locked loop

Optical transmission systems based on homodyne coherent detection of 2-ASK and pilot carrier 2-PSK signals have been implemented. ASK data has been transmitted at 2.5 Gbps, while 2.5 Gbps and 10 Gbps PSK systems have been tested. The proposed architecture is based on a new optical phase locked loop founded on sub-carrier modulation and leads to new compact integrated receivers and new transmission formats, thus opening new opportunities for future optical systems

Optical Phase Locking techniques: an overview and a novel method based on Single Side Sub-Carrier modulation

A short overview on Optical Phase locking techniques and a detailed description of the Phase Locking technique based on Sub-Carriers modulation is presented. Furthermore, a novel Single Side Sub-Carrierbased Optical Phase Locked Loop (SS-SC-OPLL), with off the shelf optical components, is also presented and experimentally demonstrated. Our new method, based on continuous wave semiconductor lasers and optical single side sub-carrier modulation using QPSK LiNbO3 modulator, allows a practical implementation with better performance with respect to the previously proposed OPLL circuits, and permits an easy use in real time WDM signal coherent demodulation

The PLL

В статье приведены результаты исследований системы фазовой автоподстройки частоты с учетом и без учета аддитивных помех, сопровождающих эталонный сигнал. Использованием метода теории выбросов проведен теоретический анализ зависимости вероятности срыва слежения (синхронизации) за заданное время наблюдения от отношения мощностей сигнала и помехи в канале эталонного сигнала. Для получения более точных результатов разработана имитационная модель системы в пакете динамических систем «Simulink» в среде Matlab, с использованием которой получены основные характеристики системы

Frequency and fundamental signal measurement algorithms for distributed control and protection applications

Increasing penetration of distributed generation within electricity networks leads to the requirement for cheap, integrated, protection and control systems. To minimise cost, algorithms for the measurement of AC voltage and current waveforms can be implemented on a single microcontroller, which also carries out other protection and control tasks, including communication and data logging. This limits the frame rate of the major algorithms, although analogue to digital converters (ADCs) can be oversampled using peripheral control processors on suitable microcontrollers. Measurement algorithms also have to be tolerant of poor power quality, which may arise within grid-connected or islanded (e.g. emergency, battlefield or marine) power system scenarios. This study presents a 'Clarke-FLL hybrid' architecture, which combines a three-phase Clarke transformation measurement with a frequency-locked loop (FLL). This hybrid contains suitable algorithms for the measurement of frequency, amplitude and phase within dynamic three-phase AC power systems. The Clarke-FLL hybrid is shown to be robust and accurate, with harmonic content up to and above 28% total harmonic distortion (THD), and with the major algorithms executing at only 500 samples per second. This is achieved by careful optimisation and cascaded use of exact-time averaging techniques, which prove to be useful at all stages of the measurements: from DC bias removal through low-sample-rate Fourier analysis to sub-harmonic ripple removal. Platform-independent algorithms for three-phase nodal power flow analysis are benchmarked on three processors, including the Infineon TC1796 microcontroller, on which only 10% of the 2000 mus frame time is required, leaving the remainder free for other algorithms

Attosecond Precision Multi-km Laser-Microwave Network

Synchronous laser-microwave networks delivering attosecond timing precision are highly desirable in many advanced applications, such as geodesy, very-long-baseline interferometry, high-precision navigation and multi-telescope arrays. In particular, rapidly expanding photon science facilities like X-ray free-electron lasers and intense laser beamlines require system-wide attosecond-level synchronization of dozens of optical and microwave signals up to kilometer distances. Once equipped with such precision, these facilities will initiate radically new science by shedding light on molecular and atomic processes happening on the attosecond timescale, such as intramolecular charge transfer, Auger processes and their impact on X-ray imaging. Here, we present for the first time a complete synchronous laser-microwave network with attosecond precision, which is achieved through new metrological devices and careful balancing of fiber nonlinearities and fundamental noise contributions. We demonstrate timing stabilization of a 4.7-km fiber network and remote optical-optical synchronization across a 3.5-km fiber link with an overall timing jitter of 580 and 680 attoseconds RMS, respectively, for over 40 hours. Ultimately we realize a complete laser-microwave network with 950-attosecond timing jitter for 18 hours. This work can enable next-generation attosecond photon-science facilities to revolutionize many research fields from structural biology to material science and chemistry to fundamental physics.Comment: 42 pages, 13 figure