Chen Junling

Capacitor voltage balancing control of cascaded multilevel inverter for high-power active power filters

High-power applications of cascaded multilevel inverter to active power filters (APF) is hindered by the problem of keeping capacitor voltage balance while retaining good filtering performances. This paper proposes a novel capacitor voltage balance control technique with closed-loop harmonic compensation for the cascaded multilevel inverter used in high- power APF. The proposed control method not only maintains capacitor voltage balance but also has good filtering performances, which suits for APF based on five-level and more level cascaded inverters. The steady state and dynamic experiment waveforms obtained from a prototype APF using cascaded multilevel inverter are presented to verify the validity and effectiveness of the proposed control methods.

A closed-loop selective harmonic compensation with capacitor voltage balancing control of cascaded multilevel inverter for high-power active power filters

This paper proposes a closed-loop selective harmonic compensation with capacitor voltage balancing control of cascaded multilevel inverter for high-power active power filters (APF). Firstly, the sum of each phase capacitor voltage is built through absorbing the fundamental active power current from the power system. Further, the capacitor voltage regulation method is presented to balance the voltages of flying capacitor of each cascaded cell in the same phase. Secondly, the selective compensation currents are injected into the power system to provide high power quality at the point of common coupling of a power system. Finally, a prototype APF, rated at 40 kVA based on cascaded multilevel inverter is described and the proposed method is implemented with a digital signal processors (DSP) control system. The steady state and dynamic experimental waveforms show that good filtering characteristics and fast responses of the APF are achieved and the each capacitor voltage is also controlled and balanced by using the proposed control methods, which can also be used in high-power applications of more than five-level cascaded inverter for active power filters.

Design, Analysis and R&D of the EAST In-Vessel Components

In-vessel components are important parts of the EAST superconducting tokamak. They include the plasma facing components, passive plates, cryo-pumps, in-vessel coils, etc. The structural design, analysis and related R&D have been completed. The divertor is designed in an up-down symmetric configuration to accommodate both double null and single null plasma operation. Passive plates are used for plasma movement control. In-vessel coils are used for the active control of plasma vertical movements. Each cryo-pump can provide an approximately 45 m3/s pumping rate at a pressure of 10−1 Pa for particle exhaust. Analysis shows that, when a plasma current of 1 MA disrupts in 3 ms, the EM loads caused by the eddy current and the halo current in a vertical displacement event (VDE) will not generate an unacceptable stress on the divertor structure. The bolted divertor thermal structure with an active cooling system can sustain a load of 2 MW/m2 up to a 60 s operation if the plasma facing surface temperature is limited to 1500 °C. Thermal testing and structural optimization testing were conducted to demonstrate the analysis results.

Evaluation of The Thermal Performance of Multi-Element Doped Graphite under Steady-State High Heat Flux

Multi-element doped graphite, GBST1308 has been developed as a plasma facing material (PFM) for high heat flux components of the HT-7U device. The thermal performance of the material under steady-state (SS) high heat flux was evaluated under actively cooling conditions, the specimens were mechanically joined to copper heat sink with supercarbon sheet as a compliant layer between the interfaces. The experiments have been performed in a facility of ACT (actively cooling test stand) with a 100 kW electron gun in order to test the suitability and the loading limit of such materials. The surface temperature and bulk temperature distribution of the specimens were investigated. The experimental results are very encouraging that when heat flux is not more than 6 MW/m2, the surface temperature of GBST1308 is less than 1000 °C, which is the lowest, compared with IG-430U and even with CX-2002U (CFC); The primary results indicate that the mechanically-joined material system by such as a proper design as thin tile, super compliant layer, GBST as a PFM and copper-alloy heat sink, can be used as divertor plates for HT-7U in the first phase.

A Novel Combined System Using Cascaded Active Power Filter and Static Var Compensator for High-Power Applications

As a compromise between economy and good performance, this paper adopts the combined system using cascaded active power filter (APF) and static var compensator(SVC) to compensate reactive power and harmonic currents simultaneously for high-power applications. The SVC is constructed by fixed capacitor (FC) and thyristor controlled reactor (TCR), and the APF is constructed by a cascaded multi-level voltage source converter and its filter reactor. SVCacts as a classic reactive power compensator for load balancing and power factor correction, and APF is used to compensate the harmonic current. Firstly, the circuit topology and the principle of the combined system are introduced in detail. Then filtering characteristics using the novel control method are analyzed. Furthermore, the steady state and dynamic waveforms show that good performance and system stability of the combined system are achieved.

Studies of a scintillator-bar detector for a neutron wall at an external target facility

To achieve a better time resolution of a scintillator-bar detector for a neutron wall at the external target facility of HIRFL-CSR, we have carried out a detailed study of the photomultiplier, the wrapping material and the coupling media. The timing properties of a scintillator-bar detector have been studied in detail with cosmic rays using a high and low level signal coincidence. A time resolution of 80 ps has been achieved in the center of the scintillator-bar detector.

Thermal Performance Study of VPS-W Coatings on CuCrZr Under High Heat Flux

Three tungsten coatings with a thickness of 250 μm, 600 μm and 220 μm, respectively, were deposited on a CuCrZr substrate by the vacuum plasma spraying technology. In order to study the thermal performance of the coatings, heat load limit, thermal fatigue lifetime and thermal response tests were performed by means of the electron beam irradiation with a heat flux from 0 MW/m2 to 10 MW/m2. Experimental results indicated that tungsten coatings on CuCrZr with a titanium or tungsten/copper interlayer could expel heat flux timely and had good thermal fatigue properties. Titanium was a promising compliant layer which provided a reliable way to join tungsten onto the CuCrZr heat sink, even suffering from a heat flux of 10 MW/m2 or withstanding 54 cycles of fatigue tests under 5 MW/m2. However, the better quality of tungsten coating itself was necessary because its surface temperature was higher than that of the sample with a tungsten/copper interlayer.

Structure and Properties of W-Cu/AlN Composites Prepared via a Hot Press-Sintering Method

Abstract W-30wt% Cu nano-crystalline powder was prepared by high-energy ball-milling, and then different mass fractions of AlN nanoparticles were added to the powder via the ball-milling. Finally W-30Cu/x% AlN composites were obtained by hot press-sintering process. The microstructures, the physical and mechanical properties of as-sintered composite samples were studied. The results indicate that the W-30Cu/x% AlN composites possess denser and more uniform microstructure. Moreover, the degree of refinement of W particles and the hardness of the composites increase with the addition of AlN, but the bending strength decreases with increasing of AlN nanoparticles due to the nanoparticles excessive distribution on the grain boundaries of the matrix. It is beneficial to increase thermal conductivity of W-Cu composites, when the content of AlN nanoparticles is ≤1%. Resistivity of the composites increases with increasing the amount of AlN nanoparticles, but the conductivity of the composites declines.

Influence of Erosion and Deposition on Metallic First Mirror in HT-7 Tokamak

Dedicated experiments in the HT-7 tokamak were performed to investigate the influence of erosion and deposition on the mirror samples. The first mirror (FM) samples made of polycrystalline (PC) stainless steel (SS), molybdenum (Mo) and tungsten (W) were fixed on a holder at an angle of 45° with respect to the horizontal plane and set at different locations with different connection lengths along the magnetic field. The optical reflectivity of the first mirror was measured by a spectrophotometer before and after plasma exposure. It was found that the surface morphology and specular reflectivity of the mirror samples after the exposure were different with respect to the different distances from the mirror surface to the last closed flux surface (LCFS) of the plasma in the tokamak. It was also found that shortening the connection length before the mirror surface would weaken the influence of the plasma erosion and impurity deposition on the mirror surface. In order to maintain the optical characteristics of the mirror surface, it is necessary to adopt the in-situ cleaning and mirror protection techniques.

Analysis of Residual Thermal Stress in CVD-W Coating as Plasma Facing Material

Chemical vapor deposition-tungsten (CVD-W) coating covering the surface of the plasma facing component (PFC) is an effective method to implement the tungsten material as plasma facing material (PFM) in fusion devices. Residual thermal stress in CVD-W coating due to thermal mismatch between coating and substrate was successfully simulated by using a finite element method (ANSYS 10.0 code). The deposition parametric effects, i.e., coating thickness and deposition temperature, and interlayer were investigated to get a description of the residual thermal stress in the CVD-W coating-substrate system. And the influence of the substrate materials on the generation of residual thermal stress in the CVD-W coating was analyzed with respect to the CVD-W coating application as PFM. This analysis is beneficial for the preparation and application of CVD-W coating.