Large DC Power Research Articles

Novel Halbach Permanent Magnet Solenoid Design using Finite Element Method

To generate the high axial field usually Electromagnetic Coils solenoid is used but it consumes large DC power supplies and cooling system and is not compact. The PM (Permanent Magnet) solenoid on the contrary can give fixed axial field profiles that are very compact and do not require any energy source as they are themselves energy sources. PM solenoids are usually designed using large radial and axial magnetized magnets. The drawback of such a design is using large radial magnets which are often unavailable with assembly problems. The paper discusses the novel Halbach solenoid configuration design and uses ref1 solenoid results to verify it. The finite element magneto static method is used to analyze the two models. The FEM magneto static analysis was done in Magnet Infolytica FEM magneto static analysis package.

Electricity ancillary service market model considering demand response of multi-energy load aggregators

Large-scale access of distributed generations, the increasing interconnection of large DC power grids and the demand fluctuation of loads caused by climate change put forward higher requirements for power system stability. The flexible resources on the demand side can respond quickly to meet the needs of power balance of the system. Under the background of the interconnection of multi-energy networks, multi-energy loads (MELs) have become excellent demand response (DR) resources. Firstly, MEL models are established in this paper, including the models for replaceable load, reducible load, transferable load and translational load. Moreover, considering that DR needs to be supported by the ancillary service market, an ancillary service market clearing model with DR provided by MEL aggregators is proposed. Finally, this paper summarizes and prospects the future development of DR with MEL.

Overview on critical heat flux experiment for the reactor fuel assemblies

The critical heat flux (CHF) experiment for the reactor fuel assemblies (FAs) is the most difficult and important one in the reactor thermo-hydraulic study. The FA CHF experiments are performed on the large scale thermo-hydraulic test facilities with large DC power suppliers, complicated test sections and rigid test process. The results are analyzed with subchannel codes to obtain the parameters at the CHF point. Based on the experimental data, the CHF correlation is derived as the tool for the reactor safety analysis and design. After many years’ work, the common understanding of the FA CHF was established and the method of the FA CHF experiment becomes similar. This paper reviewed the progress of the FA CHF experiments, analyzed the modeling of the test sections, introduced requirement of the test facilities, and discussed the hypothesis in the modelling. The benchmark qualification test adopted to verify the test method and test section used in the experiment are discussed in the paper, too.

Predicting Failure Cascades in Large Scale Power Systems via the Influence Model Framework

Large blackouts in power grids are often the consequence of uncontrolled failure cascades. The ability to predict the failure cascade process in an efficient and accurate manner is important for power system contingency analysis. In this paper, we propose to apply the influence model for the prediction and screening of failure cascades in large scale DC and AC power networks. Then, the trained influence model is applied to some large power grids with thousands of buses and transmission lines. The prediction performance is evaluated in four different aspects, from the global perspective of the overall failure size to the individual information regarding the link failure time. The results show that under limited training samples, the proposed framework is capable of predicting the failure cascade size with a 7% error rate, the final state of links with a 10% error rate, and the failure time within 1 time unit for both the DC and AC model. One major advantage of the proposed method is that it can reduce the computational time of the failure cascade prediction by a few orders of magnitude with limited compromise in accuracy, as compared to the power flow based contingency analysis. Another important feature of the proposed method is that the trained influence parameters can reveal the critical initial contingencies. This information is very helpful for identifying the worst contingency scenarios for system operators.

Multi‐tasking dc–dc and dc–ac converters for dc voltage tapping and power control in highly meshed multi‐terminal HVDC networks

this paper extends a recently proposed dc auto-transformer to a true multi-port converter that can function simultaneously as dc auto-transformer and a dc/ac converter for dc voltage matching and tapping, and power control in highly meshed multi-terminal dc grids. The presented multi-port converter can generate multiple adjustable dc voltages from a fixed or variable input dc voltage, or from an active ac grid. Theoretical discussions and simulations indicate that when the proposed multi-port converter is used as a hybrid dc and ac hub to manage congestions and resolve loop flow issues in a highly meshed multi-terminal dc network, large dc power can be fed to the lower dc terminal, without exposing the switching devices of the lower sub-converter to excessive current stress. Its increased control flexibility and response to dc faults at high and low dc terminals are validated using simulations and experiments.

Coherent Terahertz Emission of Intrinsic Josephson Junction Stacks in the Hot Spot Regime

We report on THz emission measurements and low temperature scanning laser imaging of ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8}$ intrinsic Josephson junction stacks. Coherent emission is observed at large dc input power, where a hot spot and a standing wave, formed in the ``cold'' part of the stack, coexist. By changing bias current and bath temperature, the emission frequency can be varied by more than 40%; the variation matches the Josephson-frequency variation with voltage. The linewidth of radiation is much smaller than expected from a purely cavity-induced synchronization. Thus, an additional mechanism seems to play a role. Some scenarios, related to the presence of the hot spot, are discussed.

Kink State in a Stack of Intrinsic Josephson Junctions in Layered High-T c Superconductors and Terahertz Radiation

A new family of dynamic states are found in a stack of inductively coupled intrinsic Josephson junctions in the absence of an external magnetic field. In this state, $(2m_l+1)\pi$ phase kinks with integers $m_l$'s stack along the c axis and lock neighboring junction together. Large dc power is pumped into plasma oscillation via kinks at the cavity resonance. The plasma oscillation is uniform along the c axis with the frequency satisfying the ac Josephson relation. Thus this state supports strong terahertz radiation and seems to be compatible with the recent experimental observations.

Probabilistic Models of Harmonic Currents Produced by Twelve-Pulse AC/DC Converters

The probabilistic approach is an efficient mean for harmonic prediction since it allows to take into account the randomly varying operating conditions of static converters. Although the six-pulse ac/dc converter has been the subject of probabilistic modeling, little consideration has been given to the 12-pulse ac/dc converter. In high-power applications, such as large rated dc power supplies and large rated dc and ac drives, 12-pulse ac/dc converters are usually preferred since they allow to reduce system disturbances due to harmonic currents. This paper presents an analysis of the random properties of harmonic currents produced by 12-pulse ac/dc converters that operate under random variations of their dc load and voltage unbalance. The probability density functions of the amplitudes and phase angles of the harmonic currents (of orders 12 k/spl plusmn/1 and 12 k-6/spl plusmn/1) are established and validated by results obtained from Monte Carlo simulations.

大型ヘリカル装置の超伝導システム 電源およびコイル保護システムの開発と製作

The LHD has 12 superconducting coils that generate 3T of magnetic field at the plasma center, and their stored energy becomes 1GJ. These coils require large current DC power supplies that have a 17-30kA class output current, small control error less than 0.04% and high reliability for quench protection. This section introduces a DC power system to drive these coils. First, we give a description of the specifications and structures of power supplies, that are thyristor rectifiers, a LC passive filter and a current dump circuit. Next, the quench protection system which uses a novel DC circuit breaker, is described.

Error analysis in pipeline A/D converters and its applications

The conversion error of a pipelined A/D converter using inaccurate comparators is analyzed. Error bounds are established, and it is shown that the error can be compensated using simple analog circuitry combined with some digital logic. The resulting system is especially useful for fast converters in which accurate compensators would require a large chip area and large DC power. Simulations are presented to verify the efficiency of the proposed error correction scheme. >

DC power interruption technology.

This report describes the newest technology for large DC pow er interruption of high voltage direct current (HVDC) transmission lines and thermonuclear fusion equipment power supply system. The main switching elements of DC interrupters are constructed by the most judicious use of VCB, ABB, or thyristor switch based on the individual devices. In particular, utilization of semiconductor switches is becoming more common in fusion equipment power supply system. The circuit interrupters based on this DC power interruption technology should be useful in future thermonuclear fusion equipment.