Phase Control Scheme Research Articles

An Application of Two-Phase Resonant Inverter System to Generate Rotating Magnetic Field for Plasma Instability Control in a Tokamak

Rotating magnetic field (RMF), which interacts with plasma through electromagnetic force, is increasingly used for plasma instability control in magnetic confinement fusion experiment devices. In general, energizing magnetic field coils to obtain the desired RMF requires multiphase currents with an amplitude of up to several kiloamperes at a frequency ranging from a hundred hertz to several kilohertz. In this paper, we propose a two-phase ac power supply (ACPS) system based on full-bridge resonant inverters as an extension of the application of multiphase resonant converters. A novel phase control scheme for the two-phase resonant inverter system using a digital phase-locked loop is also proposed to synthesize RMF with enough spectral purity. The completed power system consists of two units. Each unit can supply a load with a rated output power of 1200 kW and a sinusoidal current in the frequency range of 1-5 kHz. The proposed ACPS can effectively cope with the physical requirements.

Piezoelectric actuator based phase locking system to improve the dynamics of the control scheme for a heavy ion superconducting linac

The superconducting heavy ion linear accelerator at Inter-University Accelerator Centre Delhi has been in operation since 2007. Initially, the superconducting niobium Quarter Wave Resonators (QWRs) in the linac were phase locked using a combination of electronic and mechanical controls which operated in fast (~10μsec) and slow (~sec) time scales respectively. In this scheme, fast control was achieved through dynamic phase control whereas slow control of the frequency was done through the niobium tuner bellows installed at the drift tube end of the resonator and flexed using helium gas to change the resonance frequency. In order to improve the dynamics of this control system, an alternate scheme using piezoelectric actuator, instead of helium gas, to flex the same niobium bellows, has been implemented in the QWRs of the second and third accelerating modules of the linac. The piezoelectric actuator is used in closed loop along with the fast dynamic phase control scheme. The feedback loop of the piezoelectric control includes a dual control scheme - an integral control loop to arrest the slow drift, and the positive position feedback (PPF) based control loop to damp the microphonics. This control scheme has been found to arrest slow drifts in the resonator frequency more tightly along with damping of low frequency microphonics (~few tens of Hz) picked up by the resonator from its surrounding environment. This has substantially eased the load from the fast electronic control, resulting in the reduction of the radio frequency (RF) power requirement during operation. In addition, it has improved the stability of phase and amplitude of the QWRs. The details of the new scheme along with results obtained during the online run of the linac for beam acceleration are presented.

Bismuth ferrite as low-loss switchable material for plasmonic waveguide modulator.

We propose new designs of plasmonic modulators, which can be used for dynamic signal switching in photonic integrated circuits. We study performance of a plasmonic waveguide modulator with bismuth ferrite as a tunable material. The bismuth ferrite core is sandwiched between metal plates (metal-insulator-metal configuration), which also serve as electrodes. The core changes its refractive index by means of partial in-plane to out-of-plane reorientation of ferroelectric domains in bismuth ferrite under applied voltage. As a result, guided modes change their propagation constant and absorption coefficient, allowing light modulation in both phase and amplitude control schemes. Due to high field confinement between the metal layers, existence of mode cut-offs for certain values of the core thickness, and near-zero material losses in bismuth ferrite, efficient modulation performance is achieved. For the phase control scheme, the π phase shift is provided by a 0.8-μm long device with propagation losses 0.29 dB/μm. For the amplitude control scheme, up to 38 dB/μm extinction ratio with 1.2 dB/μm propagation loss is predicted.

Phase Characterization of Reconfigurable Reflectarray Antennas

The design and performance optimization of X-band reconfigurable reflectarray antennas have been discussed in this paper concentrating mainly on the phase characteristics. Liquid crystals based substrates and slot embedded patch elements have been proposed as two different techniques for the design of reflectarrays with frequency tunability characteristics. Reflectarray patch elements constructed on anisotropic liquid crystal substrate are proposed to be employed as a dynamic phase control strategy for terrestrial systems. A detailed analysis of dynamic phase range and frequency tunability with respect to dielectric anisotropy is presented for two different anisotropic liquid crystal substrate materials. The investigated liquid crystals substrates provided a maximum reduction of 14.1% in volume for reflectarray design at 10 GHz. Moreover rectangular slots on the patch elements are shown to offer a maximum frequency tenability of 1.7GHz. The Finite Integral Method (FIM) validated by waveguide scattering parameter measurements demonstrated a dynamic phase range of 314° and a volume reduction of up to 24.36%.

The phase-controlled Raman effect.

Unlike spontaneous Raman effect, nonlinear Raman scattering generates fields with a well-defined phase, allowing Raman signals from individual scatterers to add up into a highly directional, high-brightness coherent beam. Here, we show that the phase of coherent Raman scattering can be accurately controlled and finely tuned by using spectrally and temporally tailored optical driver fields. In our experiments, performed with spectrally optimized phase-tunable laser pulses, such a phase control is visualized through the interference of the coherent Raman signal with the field resulting from nonresonant four-wave mixing. This interference gives rise to Fano-type profiles in the overall nonlinear response measured as a function of the delay time between the laser pulses, featuring a well-resolved destructive-interference dip on the dark side of the Raman peak. This phase-control strategy is shown to radically enhance the coherent response from weak Raman modes, thus helping confront long-standing challenges in nonlinear Raman imaging and microspectroscopy.

A Drive Control Scheme Based on Phase-control for Silicon Micromechanical Gyroscopes

A drive control scheme based on phase-control for silicon micromechanical gyroscopes (SMG) is studied and implemented. By analyzing the dynamical characteristics of the drive mode, the elementary principle of phase control scheme upon which the control loop is built is described and the stability of the loop is presented using the theory of self-sustained oscillation. The phase model of the loop is modeled where a special factor is introduced to realize the conversion from phase-error to frequency-error which is the difference between current working frequency and the resonance-frequency of the drive mode. By building the frequency closed-loop corresponding to the phase-control loop, we find that the order of the loop-filter is just one when considering loop-filter as a first-order-model, which is different from the general phase locked loop (PLL) that is second-order. Elaborate design of the digital phase-control circuit is carried out based on the FPGA platform where a linear phase-detector is applied. Aided by an amplitude control loop, a double-closed-loop drive control circuit is realized. Results show that the drive control loops work precisely.

다중 송신안테나 통신시스템에서 송신 안테나의 위상 조절 기법

Two phase control (PC) schemes using limited feedback are proposed for multiple-input single-output (MISO) systems. One PC scheme cophases channel gains with respect to the first transmit antenna channel gain, and the other PC scheme cophases channel gains by positioning all the channel gains into a fixed sector. We analyze the combined channel gain for both PC schemes, and find that the PC scheme that cophases with respect to the first transmit antenna channel gain provides 1.2 dB power gain over an orthogonal space-time block code (OSTBC) when the number of transmit antennas is four and the number of feedback bits is three.

Design of a Microwave Applicator for Water Sterilization Using Multiobjective Optimization and Phase Control Scheme

This paper presents a methodology based on multiobjective evolutionary optimization and a phase control scheme to design a microwave heating applicator for water sterilization. The optimization problem is formulated in terms of two objective functions: one to maximize the amount of water and the other to minimize the energy spent. The device is modeled as a lossy dielectric multilayer irradiated by two microwave sources. The phase control is done by allowing one of the sources to move. By applying the developed methodology, an efficient applicator is obtained.

Phase control strategy for a wave energy hyperbaric converter

Oscillating bodies represent an important class of wave energy converters (WECs). In these systems, the steps of converting wave energy into electricity usually employ a floating body that is either connected to a hydraulic system and a turbine (or motor) coupled to an electric generator or connected directly to a linear electric generator. The improvement of the efficiency of the extracted energy from these systems is closely related to different control strategies. Currently, the reactive control and the phase control by latching are the most analyzed control strategies used for this purpose. This paper proposes a strategy based on phase control concepts for a hyperbaric wave energy converter—a WEC with an oscillating body linked to a hyperbaric chamber through a lever arm. A proportional–proportional integral (P–PI) cascade controller is adopted to regulate the position of a sliding mass, which is used to change the inertia of the floating body. The analysis of the body motion in regular waves is also presented. Simulation results that consider both the regular and irregular waves illustrate the performance of the proposed control scheme.

Novel bioconversion of wheat straw to bio-organic fertilizer in a solid-state bioreactor

In order to increase the eco-efficiency and overall availability of naturally renewable resource, the novel bioconversion of steam-exploded wheat straw to bio-organic fertilizer containing N(2)-fixer, P and K solubilizers was investigated. The conversion was performed in solid-state fermentation (SSF) with periodic air-forced pressure oscillation (PAPO). The results showed that SSF-PAPO was competitive with the conventional solid-state fermentation (cSSF) in biomass accumulation and wheat straw digestion. With solid-liquid ratio 1:3, microbial biomass production at 72 h was high up to 2 x 10(11) cfu g(-1), nearly twice as that in cSSF. The degradation rate of cellulose, hemicellulose and lignin after fermentation in SSF-PAPO reached 48.57 +/- 10.66, 84.77 +/- 2.75 and 2.15 +/- 10.11, respectively, which was greater than that of 29.30 +/- 10.28%, 33.47 +/- 4.85% and 0.53 +/- 9.07% in cSSF, correspondingly. The SSF-PAPO system displayed unique advantage, by a novel gas phase control strategy on gas concentration and heat gradient, on the bioconversion of wheat straw to the bio-organic fertilizer.

Phase control for resonant DC-DC converter with class-DE inverter and class-E rectifier

In this paper, a phase control scheme for Class-DE-E dc-dc converter is proposed and its performance is clarified. The proposed circuit is composed of phase-controlled Class-DE inverter and Class-E rectifier. The proposed circuit achieves the fixed frequency control without frequency harmonics lower than the switching frequency. Moreover, it is possible to achieve the continuous control in a wide range of the line and load variations. The output voltage decreases in proportion to the increase of the phase shift. The proposed converter keeps the advantages of Class-DE-E dc-dc converter, namely, a high power conversion efficiency under a high-frequency operation and low switch-voltage stress. Especially, high power conversion efficiency can be kept for narrow range control. We present numerical calculations for the design and the numerical analyses to clarify the characteristics of the proposed control. By carrying out circuit experiments, we show a quantitative similarity between the numerical predictions and the experimental results. In our experiments, the measured efficiency is over 84% with 2.5 W output power for 1.0-MHz operating frequency at the nominal operation. Moreover, the output voltage is regulated from 100% to 39%, keeping over 57% power conversion efficiency by using the proposed control scheme.

Power injection model of STATCOM with control and operating limit for power flow and voltage stability analysis

This paper presents a power injection model (PIM) of STATCOM for power flow and voltage stability analysis. In this model, PWM control and phase control strategies of STATCOM are handled, and the operating limit is enforced. The NR formulation has the same structure before and after the limit enforcement, and the Jacobian matrix adds only one dimension. This model can also take into account the steady-state losses of STATCOM if desired, and hence more accurately predict the active and reactive power injections. The singular value decomposition (SVD) based method is then extended to study the effect of STATCOM on power systems voltage stability. IEEE 300-bus and 30-bus systems are used to verify the effectiveness and performance of this model and the effect of load changes at all the buses simultaneously on voltage stability has also been studied with the STATCOM.

Variable phase control of wing rock

This paper addresses a variable phase control issue for suppressing wing rock with hysteresis. In free-to-roll tests, as the angle of attack (AOA) is increased, the roll angle versus the rolling moment indicates hysteresis and provides clues about where wing rock motion is being driven and where the motion is being damped. We present the analysis method of wing rock energy to explain the mechanism of wing rock and the formation of hysteresis, and then develop a variable phase control (VPC) scheme to compensate the phase and magnitude distortions. The effectiveness and robustness of the proposed scheme are demonstrated by suppressing wing rock phenomenon at various AOA and any initial conditions.

Stochastic chaos in a Duffing oscillator and its control

Stochastic chaos discussed here means a kind of chaotic responses in a Duffing oscillator with bounded random parameters under harmonic excitations. A system with random parameters is usually called a stochastic system. The modifier ‘stochastic’ here implies dependent on some random parameter. As the system itself is stochastic, so is the response, even under harmonic excitations alone. In this paper stochastic chaos and its control are verified by the top Lyapunov exponent of the system. A non-feedback control strategy is adopted here by adding an adjustable noisy phase to the harmonic excitation, so that the control can be realized by adjusting the noise level. It is found that by this control strategy stochastic chaos can be tamed down to the small neighborhood of a periodic trajectory or an equilibrium state. In the analysis the stochastic Duffing oscillator is first transformed into an equivalent deterministic nonlinear system by the Gegenbauer polynomial approximation, so that the problem of controlling stochastic chaos can be reduced into the problem of controlling deterministic chaos in the equivalent system. Then the top Lyapunov exponent of the equivalent system is obtained by Wolf’s method to examine the chaotic behavior of the response. Numerical simulations show that the random phase control strategy is an effective way to control stochastic chaos.

A Comparative Study of AC/DC Converters for High-Power DC Arc Furnace

Today, dc arc furnaces are supplied by thyristor rectifiers. Because of the phase control strategy on the rectifiers, the arc voltage swings induce large reactive power variations on the power network and a static VAr compensator (SVC) or a static synchronous compensator (STATCOM) is always added to avoid flicker effect. In this paper, the authors present a new control strategy which suppresses the flicker effect and increases the furnace productivity. To supply the dc arc furnace, the ac/dc converter is based on diode rectifiers and choppers with a constant power control strategy. Consequently, the ac/dc converter can operate without a STATCOM or an SVC. To evaluate the gain in flicker and furnace productivity, simulations are done with Matlab software. These simulations take into account arc voltage measurements on a 100-MW dc arc furnace and allow for comparison of the different solutions.

Prediction of the solubility of 6APA in aqueous phase and optimum control scheme for batch crystallization process through pH variation

Solubilities of 6APA in water at different pH and temperatures are measured. A three parameter model is proposed for predicting the aqueous solubility of this amino acid. Predicted values are in good agreement with the experimental data. The model may be used for quick and accurate evaluation of the aqueous solubility of other simple ampholytes. The proposed correlation is combined with the population balance and kinetic equations for predicting the optimum pH profiles required to maintain a constant supersaturation in a batch crystallizer. The suggested policy leads to a more uniform crystal size distribution for 6APA with C.V of 23%.

Influence of pH conditions on metabolic regulations in serine alkaline protease production by Bacillus licheniformis

The effects of the controlled and uncontrolled pH conditions, as well as of the value of initial pH in the range of 7–7.5, on serine alkaline protease (SAP) production by Bacillus licheniformis were investigated on a defined medium with the single carbon source glucose in batch bioreactors. Besides uncontrolled pH operations, growth phase, production phase, and entire process control strategies were also applied. The concentrations of the product (SAP) and by-products, i.e. neutral protease, amylase, amino acids, and organic acids were determined in addition to SAP activities. For SAP production, uncontrolled pH operation was more favourable than the controlled pH operations; and pH 0=7.25 was optimum for SAP production where maximum enzyme activity was obtained as 390 U cm −3, while, the highest cell concentration was obtained at pH 0=7 in uncontrolled operation. Thereafter, by using the experimental data obtained at pH 0=7, 7.25 and 7.5 uncontrolled pH operations, perturbation effects of pH on the intracellular flux distributions were investigated for the growth (0< t<20 h) and SAP production (20< t≤43 h) periods. In the growth phase the fluxes of the glycolysis pathway and the TCA cycle increased with the increase in pH 0; further, due to the difference in proton electrochemical gradients generated, the lowest and the highest energies were produced at pH 0=7 and 7.5 conditions, respectively. In the SAP production period, at pH 0=7.5 and 7 the glycolysis pathway fluxes were, respectively, the lowest and the highest. However, the TCA cycle fluxes, amino acid synthesis fluxes and SAP synthesis flux were the highest at pH 0=7.25 condition. The diversions in the pathways and certain metabolic reactions and potential strategies for improving SAP production are also discussed.

A new synthetic loading for large induction machines with no feedback into the power system

Full-load testing of large induction machines is constrained by the limitations in the power-supply and loading equipment of the manufacturer's facilities, resulting in costly set up time. A new synthetic loading method is proposed based on a bang-bang phase control strategy. The rated power oscillation created is routed to an auxiliary system and the source hydro has to provide only the total losses of the system, without seeing the excessive power swings observed in other synthetic loading techniques. In this technique, only induction machines are used which would enable motor manufacturers to build the test rig in-house. The control stage is very simple to implement and requires only unregulated DC supplies for the excitation windings. The method is suitable for any induction machine and does not requires any set up time. It is possible to strictly maintain constant DEFINE RMS voltage and current at rated values for the duration of the heat runs.

A New Synthetic Loading for Large Induction Machines with No Feedback into the Power System

Full load testing of large induction machines are constrained by the limitations in the power supply and loading equipment of the manufacturer's facilities resulting in costly set-up time. A new synthetic loading method is proposed based on a bang-bang phase control strategy. The rated power oscillation created is routed to an auxiliary system and the source hydra has to provide only the total losses of the system, without seeing the excessive power swings observed in other synthetic loading techniques. In this technique, only induction machines are used, which would enable motor manufacturers to build the test rig in house. The control stage is very simple to implement and requires only unregulated dc supplies for the excitation windings. The method is suitable for any induction machine and requires no set-up time. It is possible to strictly maintain constant RMS voltage and current at rated values for the duration of the heat runs.

The effect of coupled nonreactive modes on laser control of quantum wave packet dynamics

The laser control of reactions in solution has recently been a topic of growing interest. The theoretical possibility for such control has now been established. This paper investigates two closely related issues regarding potential practical implementation of condensed phase control schemes. A previous study from our group was able to demonstrate control assuming that a laser field coupled only to a reaction coordinate. The assumption that the laser will not couple to the condensed phase environment is a drastic simplification, and we investigate in this paper how relaxing this simplification may affect the possibility of control. To investigate this phenomenon, we study two cases: that of a laser coupled only to a reaction coordinate which is in turn coupled to a “bath” mode, as compared to the case in which the laser is coupled both to the reaction coordinate and the environmental mode. In another closely related investigation, we study the effect of uncertainty introduced into the controlling pulse. The exact potential of a chemical reaction in solution cannot be known to perfect accuracy. Our results give insights into the challenges which will face attempts at condensed phase chemical reaction control, and point strongly to the need for adaptive algorithms for laser control pulse generation.