Phase Control System Research Articles

Electromechanical modelling and design for phase control of locked modes in the DIII-D tokamak

A basic nonlinear electromechanical model is developed for the interaction between a pre-existing near-saturated tearing-mode, a conducting wall, active coils internal to the wall, and active coils external to the wall. The tearing-mode is represented by a perturbed helical surface current and its island has a small but finite moment of inertia. The model is shown to have several properties that are qualitatively consistent with the experimental observations of mode-wall and mode-coil interactions. The main purpose of the model is to guide the design of a phase control system for locked modes (LMs) in tokamaks. Such a phase controller may become an important component in integrated disruption avoidance systems. A realistic feedback controller for the LM phase is designed and tested for the electromechanical model. The results indicate that a simple fixed-gain controller can perform phase control of LMs with a range of sizes, and at arbitrary misalignment relative to a realistically dimensioned background error field. The basic model is expected to be a useful minimal dynamical system representation also for other aspects of mode-wall-coil interactions.

DC MOTOR DISCRETE CONTROL TECHNIQUE

The technique of the discrete control of a continuous object is considered by the example of a DC motor. The proposed method can simplify the procedure of selecting the desired properties of the synthesized control system, and reduce the control identification to a standard problem on the linear equation system solution with regard to the inequality constraints at each sample spacing. The desired properties of the synthesized system are specified through the reference transient. The quadratic performance criterion that characterizes the deviation of the transition process from the reference at the equally separated moments of time is applied. This approach allows a real-time control of the object with account to the restrictions of both to the controlling action, and to the phase control system coordinates. Thus, it is possible to achieve absence of overshoot and oscillability.

Integration of distributed generation in the power distribution network: The need for smart grid control systems, communication and equipment for a smart city — Use cases

Abstract The exploitation of renewable energy resources poses great challenges regarding the manner in which they can be integrated into the modern electrical distribution infrastructure. To understand the difficulties of integration of Distributed Generation (DG) in electricity distribution network, the analyses and result of the effects on aspects of power quality are provided, as can be the problem of failure defects in networks and how DG grid connection affects voltage control at both medium-voltage (MV) and low-voltage (LV) levels. Results demonstrated that there was a communication system between all generators protective systems, a selective protective system, a tracking of perturbations system to isolate failure defects, and a phase control system between the generators and the network. Also synchronizing voltage regulation is crucial for guaranteeing the quality of the power supply. Currently, recent and modern technologies allow different services to share a single communications infrastructure while guaranteeing the required levels of security, reliability, and efficiency. This paper aims to provide a Smart City (SC) project, implemented in the city of Malaga, Spain, where the integration of the applications of Smart Grid (SG) and the Use Cases (UCs) for the different functionalities of SG has been developed. The SC architecture proposed envisions a hierarchical, distributed, and autonomous structure to address the challenge of smart distribution grids. As a result of this project, new levels of standardization of languages and protocols and new interconnection functions will be required. These functions will allow smart devices to recognize each other so that they can reconnect in case of failure regardless of the state of the network topology. In conclusion, renewable energy sources (RES) can be optimally integrated into the distribution grid. Generation can approach consumption through the installation of photovoltaic (PV) panels and mini-wind generators, with the reuse of electrical infrastructure.

Precision phase control for the radio frequency system of K500 superconducting cyclotron at Variable Energy Cyclotron Centre, Kolkata

Variable Energy Cyclotron Centre (VECC) has commissioned K500 Superconducting cyclotron (SCC) based on MSU and Texas A&M university cyclotrons. The radio frequency (RF) system of SCC has been commissioned with the stringent requirement of various RF parameters. The three-phase RF system of Superconducting cyclotron has been developed in the frequency range 9-27 MHz with amplitude and phase stability of 100 ppm and ±0.1°, respectively. The phase control system has the option to change the relative phase difference between any two RF cavities and maintain the phase stability within ±0.1° during round-the-clock cyclotron operation. The said precision phase loop consists of both analogue In-phase∕Quadrature modulator to achieve faster response and also Direct Digital Synthesis based phase shifter to achieve wide dynamic range as well. This paper discusses detail insights into the various issues of phase control for the K500 SCC at VECC, Kolkata.

Target-in-the-loop coherent beam combination of 100 W level fiber laser array based on an extended target with a scattering surface

Target-in-the-loop coherent beam combination (TIL CBC) of a 100 W level fiber laser array has been demonstrated. In the experiment, the beams from nine 10 W level fiber amplifiers achieve a scattering surface target after transmitting 10 m in free space. When the phase control system goes into close loop, atmosphere turbulence could be effectively compensated and a stable fringe pattern could be obtained on the scattering surface with 85% fringe contrast. To our best knowledge, this is the TIL CBC with the highest output power and the largest number of laser beams. Additionally, the effect of atmosphere turbulence on the backward paths on TIL CBC has been studied experimentally.

Coherent beam combining of fiber amplifier based on adaptive polarization and active phase control

Coherent beam combining (CBC) of a polarization-maintaining fiber amplifier and a non-polarization-maintaining fiber amplifier is presented. The experiment is based on adaptive polarization control and active phase control. The stochastic parallel gradient decent (SPGD) algorithm is used for the adaptive polarization control in the non-polarization-maintaining fiber amplifier and the active phase control is realized by single frequency dithering (SFD) algorithm. When the adaptive polarization control system and the phase control system go into closed loop, the fringe contrast of far-field intensity pattern is improved to more than 87.7%. A scalable architecture for CBC of two styles fiber amplifiers is also proposed.

A coherent beam combination system based on double PZT phase modulators

A novel coherent beam combination system based on double piezoelectric ceramics transducer (PZT) phase modulators is presented and demonstrated for the first time. In this system, two different PZT phase modulators are used for high frequency phase modulation and low frequency phase control, respectively, while in previous demonstrated system, LiNbO3 phase modulators are often employed. The inherent low insert loss and high laser-induced damage threshold of the PZT phase modulator makes the new proposed system more compact and stable. By the way, the experiment of coherent beam combination of two 5-W fiber laser beams based on double PZT phase modulators is done. In the experiment, the PZT phase modulator with 500-kHz frequency response point made in home is used for high frequency phase modulating and another one with 0∼30-kHz linear frequency response range for phase controlling. When the phase control system is in the closed loop, the fringe contrast of far-field intensity pattern is improved to be more than 90 % from 5 % in open loop.

Detection of Acoustic Emission (AE) from Zinc Emibrittlement Cracking During Welding Using Optical Fiber AE Monitoring System

We have developed an optical fiber acoustic emission (AE) monitoring system equipped with phase and polarization control systems. The phase control system has an integration-type feedback loop with a phase lead process that maintains the phase difference between the sensing and the reference beam at π/2 and compensates for environment noise in the frequency range of less than one hundred hertz. Additionally, we controlled the polarization of the sensing beam corresponding with the reference beam to keep the system highly sensitive. We applied the developed system to the detection of zinc embrittlement cracking in an AISI type 304 plate during a simulated welding process (melt-run) at elevated temperatures. We succeeded in detecting a significant amount of AE from the cracking during welding process.

Analysis of the compensation algorithm stability of disturbance for the phase control systems

The main component of error of phase control systems of drivers is a periodic component caused by external disturbances. This error can be reduced using compensation principle. In fact, the compensation is a positive feedback and thus the setting of control parameters is very parameters sensitive. The paper deals with setting conditions, which guarantee the convergence of compensation process of control error. The result of the presented analysis is a setting technique of phase control systems.

Fermi chopper developed at KEK

Abstract We developed a Fermi chopper by modification of a turbo molecular pump with a magnetic bearing system, and the actual device, rotating at f =100–600 Hz using a rotation system similar to the turbo molecular pump, was successfully produced for inelastic neutron scattering experiments at the Japan Proton Accelerator Research Complex (J-PARC). We assumed a phase control accuracy of Δ τ ≤ 0.3 μ s , i.e., a frequency resolution of Δ f ≤ 0.01 Hz at a rotational frequency of f =600 Hz, as the specification for the development. The phase control system was developed using a direct digital synthesizer (DDS) system with a frequency control unit of 0.00058 Hz at f =600 Hz. The phase control accuracy in the produced Fermi chopper was observed to be Δ τ = 0.08 μ s at f =600 Hz, well within the specification parameters. After mounting the produced Fermi chopper on the High Resolution Chopper Spectrometer (HRC) at J-PARC, the energy resolution for an incident neutron energy E i =206 meV was observed to be identical to the designed standard resolution of Δ E / E i = 2.5 % . We were able to produce a state-of-the-art Fermi chopper.

Application of the method of Lyapunov periodic functions

The paper is concerned with asymptotic behavior of continuous and discrete phase control systems involving periodic differentiable nonlinear vector functions and featuring nonunique equilibrium state.

Active phase locking of fiber amplifiers using sine–cosine single-frequency dithering technique

The sine-cosine single-frequency dithering technique for active phase locking of fiber amplifiers is presented for the first time to our knowledge. It has twice the phase control speed as the single-frequency dithering technique. Detailed theoretical development has been presented and the relevant experiment has been done. In the experiment, nine 10 W level fiber amplifiers are tiled into 3×3 array and the total output power is about 100 W. The sine-cosine single-frequency dithering algorithm is run on a signal processor based on a field-programmable gate array for phase control on the fiber amplifiers. When the phase control system is in a closed loop, the fringe contrast of far-field intensity pattern is improved by more than 90% from 21% in an open loop, and the residual phase error is less than λ/20.

Stable single-photon interference in a 1 km fiber-optic Mach–Zehnder interferometer with continuous phase adjustment

We experimentally demonstrate stable and user-adjustable single-photon interference in a 1 km long fiber-optic Mach-Zehnder interferometer, using an active phase control system with the feedback provided by a classical laser. We are able to continuously tune the single-photon phase difference between the interferometer arms using a phase modulator, which is synchronized with the gate window of the single-photon detectors. The phase control system employs a piezoelectric fiber stretcher to stabilize the phase drift in the interferometer. A single-photon net visibility of 0.97 is obtained, yielding future possibilities for experimental realizations of quantum repeaters in optical fibers and violation of Bell's inequalities using genuine energy-time entanglement.

Coherent beam combination of 137W fiber amplifier array using single frequency dithering technique

Abstract We demonstrate coherent beam combination of 137 W fiber amplifier array using single frequency dithering technique. Four polarization-maintained fiber amplifiers are tiled into 2×2 array and the output power of each amplifier is about 35 W. Single frequency dithering algorithm is run on a signal processor based on field programmable gate array (FPGA) for phase control on the fiber amplifiers. When the phase control system goes into closed-loop, the fringe contrast of far-field intensity pattern is improved by more than 87% from 0 in open-loop, and the residual phase error is less than λ/20.

Coherent beam combination of 108 kW fiber amplifier array using single frequency dithering technique

Coherent beam combination of a 1.08 kW fiber amplifier array has been demonstrated for the first time, to our knowledge. In the experiment, nine fiber amplifiers are tiled into a 3×3 array, and the output power of each amplifier is approximately 120 W. A single frequency dithering algorithm is used to compensate the phase noises between the elements, which runs on a signal processor based on field programmable gate array for phase control on the fiber amplifiers. When the phase control system goes into closed loop, the fringe contrast of the far-field intensity pattern is improved to more than 85%, and the residual phase error is less than λ/15.

Coherent Beam Combining with Second-Harmonic Generation Optimized with Adaptive Phase Control

A theoretical and experimental study of phase-controlled beam combining based on noncollinear frequency doubling is described. Optimized second-harmonic power and improved output intensity distribution are simultaneously achieved by a closed-loop phase control system via an adaptive algorithm. It is shown that the profile of the combined beam at the second-harmonic with 12 noncollinear frequency inputs can be shaped to a near-fundamental Gaussian mode, with a power enhancement of more than two orders of magnitude, compared to the second-harmonic signal generated with a single beam.

Coherent beam combination of two thulium-doped fiber laser beams with the multi-ditheringtechnique

Coherent beam combination of two thulium-doped fiber laser beams using a multi-dithering technique is presented for the first time. In the experiment, two fiber lasers centered at 1948.6 nm are coherently combined, and a phase modulator based on piezoelectric ceramics transducer is connected in one beam path to compensate for the phase errors between the two beams. When the phase control system is closed loop, the fringe contrast of the far-field intensity pattern is improved to be more than 75%, from 15% in open-loop, and the residual phase error is less than λ/20. The experimental results show that the performance of the phase control system is robust and the control bandwidth is more than 1 kHz, which indicates that the above approach can be scaled to facilitate the coherent beam combination of kilo-watt level thulium-doped fiberlaser.

Synchrophasor Broadcast Over Internet Protocol for Distributed Generator Synchronization

Synchronous islanded operation involves continuously holding an islanded power network in virtual synchronism with the main power system to aid paralleling and avoid potentially damaging out-of-synchronism reclosure. This requires phase control of the generators in the island and the transmission of a reference signal from a secure location on the main power system. Global positioning system (GPS) time-synchronized phasor measurements transmitted via an Internet protocol (IP) are used for the reference signal. However, while offering low cost and a readily available solution for distribution networks, IP communications have variable latency and are susceptible to packet loss, which can make time-critical control applications difficult. This paper investigates the ability of the phase-control system to tolerate communications latency. Phasor measurement conditioning algorithms that can tolerate latency are used in the phase-control loop of a 50-kVA diesel generator.

Coherent beam combination with single frequency dithering technique

The single frequency dithering technique for coherent beam combination with one single modulation frequency and without a reference beam is presented for the first time to our knowledge. Coherent beam combination of four fiber amplifiers is successfully demonstrated by using the single-dithering technique. When the phase control system is in the closed loop, the fringe contrast of far-field intensity pattern is improved by more than 85% from 8% in open loop, and the residual phase error is less than lambda/20. Experimental results reveal that the single-dithering technique has great potential in scaling to a large number of beamlets with a simple phase control system and low cost.

Efficient Phase Locking of Fiber Amplifiers Using a Low-Cost and High-Damage-Threshold Phase Control System

We propose a low-cost and high-damage-threshold phase control system that employs a piezoelectric ceramic transducer modulator controlled by a stochastic parallel gradient descent algorithm. Efficient phase locking of two fiber amplifiers is demonstrated. Experimental results show that energy encircled in the target pinhole is increased by a factor of 1.76 and the visibility of the fringe pattern is as high as 90% when the system is in close-loop. The phase control system has potential in phase locking of large-number and high-power fiber laser endeavors.