Ramp-down Rates Research Articles

Control of supercritical CO2 Brayton cycle for fast and efficient load variation processes

The supercritical carbon dioxide (S-CO2) cycle is considered a promising power conversion system due to its high efficiency and flexibility. This work presents a dynamic model of a 600 MWe S-CO2 recompression Brayton cycle (RBC) and validates it at both component and system levels. To ensure the safety and stability of the S-CO2 RBC during wide-load operation, some necessary control strategies are designed, including minimum pressure and temperature control, split ratio control, turbine inlet temperature control, and anti-surge control. Moreover, an innovative valve-inventory joint control method is proposed, coupled with an improved inventory tank layout, to achieve both fast and efficient load variation processes. Compared to the control strategy before improvement, the ramp-up and ramp-down rates are significantly increased by 2.65 and 2.24 times, respectively. In addition, the values of key parameters suitable for wide-load operation of the S-CO2 RBC are determined to maximize the cycle efficiency under off-design conditions. The results show that the split ratio should be dynamically adjusted to determine the optimal value that varies with the load, which can improve the cycle efficiency by a maximum of 1.13 %. Finally, the dynamic performance of the S-CO2 RBC is studied during load ramp changes and real-time microgrid load, and the variations in heat exchange, pressure, temperature, and mass flow rate of key components are revealed. Comparative analysis with previous literature demonstrates that the proposed control method provides a wider load regulation range, an increase of 7.78 % in cycle efficiency, and a reduced maximum generation frequency deviation of 0.696 Hz. There is no overpressure or compressor surge risk, and the maximum temperature change rate is only 1.3 ℃·min−1.

Scenario optimization for the tokamak ramp-down phase in RAPTOR: Part B. safe termination of DEMO plasmas

An optimized plasma current ramp-down strategy is critical for safe and fast termination of plasma discharges in a tokamak demonstration fusion reactor (DEMO), both in planned and emergency scenarios, avoiding plasma disruptions and excessive heat loads to the first wall. Plasma stability limits and machine-specific technical requirements constrain the stable envelope through which the plasma must be navigated. Large amounts of auxiliary heating are required throughout the ramp-down phase, to avoid a radiative collapse in the presence of intrinsic tungsten and seeded xenon impurities, as quantitatively estimated in this work. As the plasma current is reduced, the current density becomes increasingly peaked, reflected by a growing value of the internal inductance ℓi3 , resulting in reduced controllability of the vertical position of the plasma. The feasibility of different plasma current ramp-down rates is tested by applying an automated optimization framework embedding the RAPTOR core transport solver. Optimal time traces for plasma current Ip(t) and plasma elongation κ(t) are proposed, to satisfy an Ip -dependent upper limit on the plasma internal inductance, as obtained from vertical stability studies using the CREATE-NL code, as well as a constraint on the time evolution of q 95, to avoid an ideal MHD mode. A negative current density near the plasma edge is observed in our simulations, even for the most conservative Ip ramp-down rate, indicating significant transient dynamics due to a large resistive time.

Scenario optimization for the tokamak ramp-down phase in RAPTOR: Part A. Analysis and model validation on ASDEX Upgrade

We discuss how the combination of experimental observations and rapid modeling has enabled to improve understanding of the tokamak ramp-down phase in ASDEX Upgrade. A series of dedicated experiments has been performed, to disentangle the effect of individual actuators like plasma current, auxiliary heating and plasma shaping. Optimized discharge termination strategies with increased margin with respect to radiative and vertical stability limits are proposed and tested in experiment. Radiative collapse of the edge Te profile after the HL back-transition is avoided by initially maintaining auxiliary heating during L-mode, showing beneficial effects even after the auxiliary heating is turned off. The capability of the RAPTOR code to model the time evolution of the internal inductance has been validated, including the effect of a change in the Ip ramp-down rate and the HL transition timing. The reduction of caused by rapid compression of the plasma cross-section has been quantitatively recovered in simulations. Successful modeling of the time evolution is essential to optimize ramp-down scenarios for future fusion reactors, for which vertical stability and power balance control will be more challenging.

Electric water heater flexibility potential and activation impact in system operator perspective – Norwegian scenario case study

Simultaneous activation of demand side flexibility on thermostatically controlled loads will cause adverse impacts later in the form of rebounds. Distribution system operators must know the characterisation of the impact, as they are responsible for voltage quality of power delivery and suffer the loss of lifespan of network components due to overloading. In this paper, characterising parameters for flexibility activation on electric water heaters (EWHs) are proposed and flexibility potentials are computed considering smart activation methods for the Norwegian scenario. The proposed parameters are rebound percentage, delay, ramp rates, second peak distance, activation error, flexible power, and temperature deviation. Four scenarios with different levels of flexible power and activation time are developed in the Norwegian context for quantification of the flexibility potentials and the parameters. The highest average flexible power potential is 53.9% at 8:00 a.m. for a duration of 61 min. EWHs flexibility activation can serve as Frequency Containment Reserves (FCR) at peak demand hours with high ramp-up and ramp-down rates of 48.5% and 23.8% per minute and as Frequency Restoration Reserves (FRR) during non-peak hours.

Information gap decision theory (IGDT)-based robust scheduling of combined cooling, heat and power energy hubs

Energy hubs (EHs) are units wherein multiple energy carriers can be converted, stored and conditioned to simultaneously supply different energy demands. In this paper, a new model is proposed for unit commitment in renewable EHs with electric, thermal and cooling demands, different storage systems, combined heat and power (CHP) unit, boiler, electric chiller, absorption chiller, PV module, wind turbine and battery charging station (BCS). Using information gap decision theory (IGDT), day-ahead EH scheduling is done from risk-neutral, risk-averse and risk-seeking perspectives, considering the uncertainties of electric demands, BCS demands, heat demands, cooling demands, PV and wind power and electricity prices. Comprehensive models are used for storage systems considering their degradation, charging loss, discharging loss and storage loss; the ramp-up and ramp-down rate limits, start-up and shut-down costs of CHP, boiler and cooling components are considered. The effect of risk as well as effect of critical cost deviation factor and target cost deviation factor on EH operation cost and schedule of EH components is investigated. The findings indicate that the sensitivity of EH operation cost may be very different with respect to different sets of uncertain input data. The findings also show the significant effect of risk-awareness on schedule of EH components and its operation cost.

Effects of inversed-delta injection rate on late combustion and soot emissions from diesel combustion in a constant-volume chamber

The aim of this study is to clarify the effect of an inversed-delta injection rate, which is a ramp-down injection rate achieved with a tandem injector, on the late combustion period, which affects thermal efficiency and soot emissions. Diesel combustion was simulated in a constant-volume chamber combined with a rapid compression machine. Two types of injection rate profile, namely rectangular and ramp-down, were tested in our experimental trials. To eliminate the significant effect of the maximum injection rate on mixture formation, we compared the results for the two types of injection rate profile under a given rail pressure. The time histories of the heat release rate demonstrated that the ramp-down fuel injection profile shortened the late combustion period by 0.2 ms. As a result, combustion was maintained despite the longer injection duration. The non-dimensional fuel consumption rate, defined in terms of the heat release rate and the fuel injection rate, revealed that high fuel consumption in the injection period reduced the quantity of fuel carried over to the late combustion period, resulting in a short duration of late combustion. When the ramp-down injection profile was employed, the temporal variation of total soot (spatially integrated KL factor) exhibited a rapid decrease after the end of injection. This is due to the abundant oxygen in soot regions that originated from the significant quantity of ambient air entrained into the spray during the injection period. This result indicates that ramp-down injection may reduce engine-out soot emissions.

Addressing Abrupt PV Disturbances, and Mitigating Net Load Profile’s Ramp and Peak Demands, Using Distributed Storage Devices

At high penetration level of photovoltaic (PV) generators, their abrupt disturbances (caused by moving clouds) cause voltage and frequency perturbations and increase system losses. Meanwhile, the daily irradiation profile increases the slope in the net-load profile, for example, California duck curve, which imposes the challenge of quickly bringing on-line conventional generators in the early evening hours. Accordingly, this paper presents an approach to achieve two objectives: (1) address abrupt disturbances caused by PV generators, and (2) shape the net load profile. The approach is based on employing battery energy storage (BES) systems coupled with PV generators and equipped with proper controls. The proposed BES addresses these two issues by realizing flexible power ramp-up and ramp-down rates by the combined PV and BES. This paper presents the principles, modeling and control design aspects of the proposed system. A hybrid dc/ac study system is simulated and the effectiveness of the proposed BES in reducing the impacts of disturbances on both the dc and ac subsystems is verified. It is then shown that the proposed PV-BES modifies the daily load profile to mitigate the required challenge for quickly bringing on-line synchronous generators.

A Finite Horizon Markov Decision Process Based Reinforcement Learning Control of a Rapid Thermal Processing system

Manufacture of ultra large-scale integrated circuits involves accurate control of a challenging nonlinear Rapid Thermal Processing (RTP) system. Precise control of temperature profile and rapid ramp-up and ramp-down rates demanded by a RTP system cannot be achieved with conventional control strategies due to nonlinear and multi time-scale effects. In this paper the control of a RTP system is reformulated as an optimal multi-step sequential decision problem using the framework of finite horizon Markov decision processes and solved using a Reinforcement Learning (RL) algorithm. Three increasingly complex RL based control strategies are explored and compared with the existing state-of-the-art approach for controlling RTPs. Simulation results indicate that the approach proposed in this paper achieves superior control of the temperature profile and ramp-up and ramp-down rates for the RTP system.

The time-dependent simulation of CFETR baseline steady-state scenarios

One of the key issues to achieve the phase I mission of China fusion engineering test reactor (CFETR) is steady-state operation with a modest fusion power up to 200 MW. To study this feasibility, time-dependent modeling of CFETR baseline scenario is performed. The time-dependent scenario design examines actual discharge features, including auxiliary heating and current drive scheme, equilibrium, transport, PF coil systems and plasma control system during the plasma evolution. During plasma current ramp-up, 10 MW of EC or LH heating is used to effectively save volt–second consumption to a reasonable level within magnet coil capability and to reduce li for better plasma control. Three reference scenarios are designed to target full non-inductive operation with different external heating and current drive (H&CD), which are NB + EC, NB + LH, and LH + EC, respectively. Two scenarios with neutral beams reach the required fusion power of CFETR phase I target, while for LH + EC scenario the fusion power and confinement is somewhat lower. A reversed magnetic shear with is sustained with off-axis current drive and bootstrap current for all cases examined. Ideal MHD analysis shows that both large toroidal mode number n ballooning mode and low n kink mode are stable in the three reference cases independent of whether the current is totally relaxed or not. The L mode and H–L back transition ramp-down are designed to successfully reduce the plasma current to 2 MA and keep li below 2 with ramp-down rate of 80 kA s−1. The H–L back transition ramp-down yields improvements in the power transfer and coil current evolution as well as the li evolution. The heating and current drive characteristics of three auxiliary heating sources are indicated by scanning studies. A 2D scan of NB energy and tangency radius indicates the features of NB power deposition, current drive, torque and shine through issue. Both ramp-up and flattop are considered in the scanning of radio frequency parameters. For EC waves, the ramp-up phase constrains the parameter space more. The 2D scan of EC launch angle shows that EC waves launched above the midplane yield a better CD efficiency than using a midplane launcher. Specifically, 10 MW of EC waves launched from LFS above the midplane yield a maximum on axis driven current of about 0.55 MA, while waves launched from top yield a maximum near edge driven current of about 0.45 MA in the region of . Scanning of in LH spectrum shows that should be set around 1.7 to get enough penetration (inside ) for current drive and avoid strong accessibility problem. It is found that LH waves launched from HFS drives more current than that launched from LFS when is small. The maximum LH driven current reaches 1.1 MA with 10 MW of LH power launched from HFS.

Impacting Factors and Improvement for Within-Shot IDSAT Uniformity

This paper studies the root causes of the impacting factors for within-shot Idsat uniformity (IDU) improvement, and presents a model to characterize the impact factors. RTA process is one of main factors leading to high IDSAT non-uniformity within-shot because its initial temperature, ramp-up rate, peak temperature and ramp-down rate can affect the amount of thermal absorption and thermal distribution in the chip. Therefore the optimized RTA process can improve the thermal distribution in the chip, hence the IDU across the wafer. We also study the correlation of the transmission rate pattern density and the equivalent reflectivity to the device performance. Based on the model simulation results, we can modify the chip arrangement within the Multi-Project Wafer (MPW) shot in the way that can optimize the RTA process and improve both NMOS and PMOS the Idsat uniformity about ~20%. The use of this model can help to provide the guideline for the optimized arrangement of multiple chips within the shot to achieve better IDU performance

강풍 시 전력망 연계기준을 만족하는 해상풍력발전단지 강제종료 방법

A wind turbine (WT) should be shut down as fast as possible to minimize its own damage in a storm-driven situation. Shutdown of a large wind farm requires a power grid to have a ramp-up capability large enough to balance between generation and consumption of electrical energy. This paper proposes a supervised shutdown algorithm of a wind farm to meet a required ramp-down rate in a grid code in the case of a storm-driven situation. The information on the speed and the direction of wind is measured at a wind mast (WM) installed around a wind farm. If the wind speed exceeds a cut-out speed, the number of WTs to be shut down simultaneously is decided to meet a required ramp-down rate of a grid-code. Arrival times to each WT from the WM are calculated and sorted in the order of time. Then a sequence of groups is generated. The shutdown start/end times of each group are decided to avoid superposition between adjacent two groups. The performance of the proposed shutdown algorithm is verified under various storm scenarios. Results indicate that the proposed algorithm can not only protect the wind farm in the case of a storm-driven situation but also meet the required ramp-down rate. In addition, the algorithm can produce more energy than that of a conventional shutdown algorithm.

Analysis of the Reversal Flow Phenomenon of Supercritical Helium Due to AC Losses in the KSTAR PF Magnets at the Low Current

Superconducting magnets of the Korea Superconducting Tokamak Advanced Research (KSTAR) are cooled by supercritical helium with 4.5 K, which was supplied and recovered by the 9 kW of the Helium Refrigerator System (HRS). While current is being charged, the supercritical helium expands to both side of the helium inlet and the outlet of the magnets due to the generated AC losses. To maintain the pressure gradient, both the supply and the return pressures of the HRS are increased at the same time and the differential pressure of the HRS was reduced after the event. However, the pressure rising in the magnets may block the helium flow or create reversal flow of the helium. During unipolar experiment of PF1 magnet up to 2 kA with 1 kA/s of ramp-up rate, the mass flow rate was decreased at the PF1 cooling tube (manifold) in the helium distribution system (HDS), whereas the pressure is increased and the temperature is to be increased or decreased according to compression and expansion of the heated helium in the magnets. For the bipolar experiment of PF1 up to ±2 kA with 1 kA/s ramp-up rate and 2 kA/s ramp-down rate, the conditions in the helium flow were drastically changed, especially the mass flow rate was measured to be maintained at zero for a few second (more than 4 s). This behavior could decisively affect the cryogenic stabilities in the magnet, and may impose a major limit on the long pulse operation of KSTAR. In this paper, we investigated this behavior and analysed by using 1-dimentional thermo-hydraulic code, GANDALF.

Frictional aging, de-aging, and re-aging in a monolayer-coated micromachined interface

Measurements on monolayer-coated polycrystalline silicon surfaces have shown that the static friction coefficient ${\ensuremath{\mu}}_{s}$ strongly depends on loading parameters including hold time and normal hold force by Corwin and de Boer [J. Microelectromech. Syst. 18, 250 (2009)]. In that work, ${\ensuremath{\mu}}_{s}$ was measured by keeping the tangential force constant and lowering normal force until motion occurred. Results indicated that ${\ensuremath{\mu}}_{s}$ also depends strongly on normal force ramp-down rate. Here, we postulate that if the normal load is lowered instantaneously, the time for the block to begin moving, the ``release time'' ${t}_{r}$, will be greater than the inertial response time, which is on the order of $5\text{ }\ensuremath{\mu}\text{s}$. We measure the release time and find that it spans nearly six decades from less than $100\text{ }\ensuremath{\mu}\text{s}$ to almost 50 s. Release time depends on the loading and unloading history through all three of the parameters varied: hold time, hold force, and release force. An empirical model incorporating all three of these parameters fits the release time data over the full range. Release time decreases after the contacting surfaces are held together at increasing hold force levels and this qualitatively explains a previous observation that static friction aging is suppressed with increasing normal force at a fixed tangential load in this interfacial system. We further quantitatively relate the previous ${\ensuremath{\mu}}_{s}$ loading dependence on all three parameters to the release time model established here by introducing a ``re-aging'' parameter. This work firmly establishes that release time is a more fundamental parameter than the static friction coefficient and is the origin of static friction coefficient dependencies in this micromachined interface.

Experimental simulation of ITER rampdown in DIII-D

Because of the high value of the stored energy in planned ITER plasmas, the safe and controlled termination of ITER discharges is an important aspect of ITER operation. In a series of experiments on the DIII-D tokamak, we have simulated the proposed ITER rampdown for the 15 MA baseline operating scenario. These scaled discharges match the reference scenario (including scaled time dependence) with regard to key parameters such as scaled current, poloidal beta, elongation and internal inductance. The scaled plasma current is reduced to the equivalent of less than 1 MA, well below the 1.4 MA specified for ITER as the maximum allowable for disruptive termination. The plasma shape and position are controlled during rampdown so that the high heat flux zones near the strike points of the separatrix are held within the equivalent of the armoured zones of the ITER divertor; the regulation of the strike-point location is an order of magnitude better than required. Scans of the current rampdown rates indicate that a more rapid rampdown than the ITER reference case may be needed to avoid excessive current in the ITER central solenoid. Rampdown with a full-size plasma was studied, but was found to be unsuitable for ITER because of transitions to ELM-free H-mode with a consequent lack of density control, as well as large excursions in poloidal beta and internal inductance. We find that ELMs play an important role during the H-mode phase of the rampdown, helping to reduce the density as the current is reduced.

최적 증착 속도로 형성된 MgO를 갖는 인-라인 진공 실장된 플라즈마 디스플레이 패널의 방전 특성에 관한 연구

AC PDP with MgO protective layer coated with the optimum evaporation rate of can generate more enhanced efficiency through the vacuum in-line sealing process. However, the optimized process conditions still require the optimum driving scheme on the ramp-up and ramp-down slope of the reset waveform for enhancing the efficiency. In this paper, for the in-situ vacuum sealed PDP with the optimum evaporation rate of MgO protective layer, the address delay time was investigated with various slopes of ramp waveform during a reset ramp-up and ramp-down period. In this study, the minimum statistical delay time was obtained at the ramp-up rate of and the ramp-down rate of of the reset waveform.

Implant Annealing – An Evolution from Soak over Spike to Millisecond Annealing

This work presents a summary on the use of rapid thermal processing for implant annealing. It gives a short historical overview of rapid thermal processing systems and the first implant anneal processes on these newly developed tools. We then looked in detail on the soak anneal and spike anneal processes and the influence of certain process parameters. For the soak anneal influences of the ambient, either oxidizing or nitriding, were evaluated. The results of spike anneal processes are influenced by the pre-stabilization temperature, ramp-up and ramp-down rate, peak temperature, and gaseous ambient. The need for shallow, abrupt and highly activated junctions leads to co-implantation of species like fluorine or carbon in conjunction with pre-amorphization. Nowadays, combinations of spike and millisecond annealing as well as millisecond annealing alone are in the focus.

Reliability improvement of rapid thermal oxide using gas switching

The instantaneous switch-off of the gas precursors during the ramp-down cycle in a spike ramp process is demonstrated to be an effective method to enhance the reliability of rapid thermal oxide. Due to the slow ramp-down rate (60/spl deg/C-90/spl deg/C/s) of a rapid thermal process, the oxidation during the slow ramp-down cycle may produce the inferior oxide, especially for ultrathin oxide. To avoid the oxidation in the slow ramp-down cycle, the oxidation precursor (oxygen) is switched off during the ramp-down cycle. The reliability of resulting oxide without oxidation during the ramp-down cycle is enhanced as compared with the conventional oxide, which is still oxidized during the ramp-down cycle.

Ultra Shallow Junction Formation with High Process Controllability Using Optimized Rapid Thermal Anneal Process

Implant and rapid thermal annealing (RTA) are investigated for a source/drain (S/D) formation process. Optimization of RTA conditions is the key for ultra shallow junction formation. This paper describes the ultra shallow junction formation using RTA. We investigate the effects of thermal budget such as ramp-up rate and ramp-down rate, oxygen content and cap films during the RTA process for achieving a shallow junction and low sheet resistance. In addition, we investigate the effects of these parameters on process controllability and on the combination of complementary metal-oxide-semiconductor (CMOS) fabrication. Using optimized RTA technology, shallow junctions with low sheet resistance and good process controllability for early 100 nm technology nodes can be achieved, even though problems remain with process controllability for wafers of various structures and with the trance enhanced diffusion (TED) effect of gate side-wall spacers.

Dynamical study of remanent magnetization in nanoparticles

For collections of noninteracting nanoparticles, we study the reduced static remanent magnetization, m R, produced by the removal of a saturating magnetic field. We show that, except for special cases such as easy uniaxial anisotropy, m R depends on both the ramp-down rate of the field and the energy dissipation rate of the spin dynamics. Using the Landau–Lifshitz equation, we illustrate this result with explicit dynamical calculations of m R for cubic and for mixed cubic–uniaxial anisotropies.

A novel illuminator design in a rapid thermal processor

The instantaneous insertion of an opaque shutter between the lamp arrays and the wafer in a rapid thermal processor can significantly increase the ramp-down rate from 90 to 400/spl deg/C/s during the cooling period. This shutter can prevent the residual heating of lamp filament as well as the self-heating from the reflector due to the mirror image of the wafer. To compensate for the weak irradiation intensity close to the edge of the linear lamps, a multiplane reflector design is used to increase the uniformity of irradiation intensity in the direction along the linear lamps. The distance between the reflector plane and the linear lamp is designed to be smaller at the edge, as compared to the center, of the linear lamp. Together with two oblique reflectors at the ends of the linear lamps, a typical three-plane reflector design can increase the uniformity by 60% in a typical lamp configuration.