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When the inverter controlled as a virtual synchronous generator (VSG) is connected to the non-ideal grid, the grid current will be severely distorted, especially when the line impedance is relatively small. However, the commonly used voltage-type VSG at present cannot directly control the output current of the VSG. Thus, this paper presented a method of harmonic suppression based on the virtual harmonic impedance (VHI). By introducing the VHI to the voltage-current dual loop, the equivalent virtual resistor and inductor of each harmonic can be configured independently according to the actual situation. Accordingly, the attenuation ratio of each harmonic current can be adjusted equivalently. The effectiveness of the VHI are verified by simulation.
Yu,,Yaowei,Hong,,Suk-Ho,Yoon,,Si-Woo,Kim,,Kwang-Pyo,Kim,,Woong-Chae,Park,,Jae-Min,Oh,,Young-Suk,Na,,Hoon-Kyun,Bak,,Jun-Gyo,Chung,,Kyu-Sun Published jointly by The Institute of Physics and 2012 Plasma physics and controlled fusion Vol.54 No.10
<P>The first comprehensive particle balance study is carried out in the KSTAR 2010 campaign with a full graphite first wall and diverted plasmas. The dominant retention is observed during the gas puffing into the plasmas. Statistical analysis shows that deuterium retention is increased with the number of injected particles. Particle balance analysis in the whole campaign shows that the long-term retention ratio is ∼21%, and the retention via implantation can be partially recovered by He-glow discharge cleaning (GDC), while long-term retention via co-deposition. The wall pumping capability is decreased with the D<SUB>2</SUB> plasma due to fuel accumulation in the first wall, and He-GDC is effective in recovering the wall pumping. Boronization assisted by the D<SUB>2</SUB> glow discharge using C<SUB>2</SUB>B<SUB>10</SUB>H<SUB>12</SUB> strongly enhances the wall puffing and leads to negative retentions, but the wall pumping capability is recovered in 2–3 days by He-GDCs. Electron cyclotron resonance heating enhances wall outgassing during the discharge. During a diverted H-mode discharge, the retention rate decreases to a very low value, and a high divertor particle flux of ∼1.5 × 10<SUP>23</SUP> D s<SUP>−1</SUP> is observed indicating the strong recycling divertor. The amount of recovered deuterium after discharges mainly depends on the plasma–wall interaction when the plasma is terminated, and disruptive discharges release more particles from the first wall.</P>
Purpose: This study compared the changes in power and agility and muscle tone of the quadriceps and hamstring muscles after 10 weeks of plyometrics or weight training to strengthen the leg muscles. The following conclusions were obtained. Methods: Subjects were randomly assigned to a plyometrics group (n = 10) and a weight training group (n = 10) from male college students who did not recently participate in a regular exercise program. Plyometrics and weight training were performed three times a week for 10 weeks with 60 minutes a day. The exercise intensity was divided into 3 stages, and the weight training group and the plyometrics group performed 3 sets of 1 repetition maximum (RM) of 60, 70, 80%, and 10, 12, 15 repetitions (rep), respectively. Results: First, there was an interaction effect between the group and time period on power. The plyometrics group showed a greater increase in power than the weight training group. Second, there was an interaction effect between the group and time period on agility. While agility improved in the plyometrics group, no significant difference was observed in the weight training group. Third, there was an interaction effect between the group and time period on the muscle tones of the left and right quadriceps muscles. The muscle tone increased more in the weight training group than in the plyometrics group. Fourth, there was an interaction effect between the group and time period on the muscle tones of the left and right hamstring muscles. The muscle tone increased more in the weight training group than in the plyometrics group. Conclusion: The change in muscle tone value was found to have a significant relationship with the increase in muscle strength and power through plyometrics and weight training, and additional research should be conducted to investigate the relationship between exercise performance ability and muscle tone.
In this paper, a nonlinear adaptive damping controller based on radial basis function neural network (RBFNN), which can infinitely approximate to nonlinear system, is proposed for thyristor controlled series capacitor (TCSC). The proposed TCSC adaptive damping controller can not only have the characteristics of the conventional PID, but adjust the parameters of PID controller online using identified Jacobian information from RBFNN. Hence, it has strong adaptability to the variation of the system operating condition. The effectiveness of the proposed controller is tested on a two-machine five-bus power system and a four-machine two-area power system under different operating conditions in comparison with the lead-lag damping controller tuned by evolutionary algorithm (EA). Simulation results show that the proposed damping controller achieves good robust performance for damping the low frequency oscillations under different operating conditions and is superior to the lead-lag damping controller tuned by EA.
This paper presents an adaptive wide-area damping controller (WADC) based on generalized predictive control (GPC) and model identification for damping the inter-area low frequency oscillations in large-scale inter-connected power system. A recursive least-squares algorithm (RLSA) with a varying forgetting factor is applied to identify online the reduced-order linearlized model which contains dominant inter-area low frequency oscillations. Based on this linearlized model, the generalized predictive control scheme considering control output constraints is employed to obtain the optimal control signal in each sampling interval. Case studies are undertaken on a two-area four-machine power system and the New England 10-machine 39-bus power system, respectively. Simulation results show that the proposed adaptive WADC not only can damp the inter-area oscillations effectively under a wide range of operation conditions and different disturbances, but also has better robustness against to the time delay existing in the remote signals. The comparison studies with the conventional lead-lag WADC are also provided.
This paper studies the relations between ideals, filters, regular congruences and normal congruences in inclines. It is shown that for any incline, there are a one-to-one correspondence between all ideals and all regular congruences and a one-to-one correspondence between all filters and all normal congruences.
For a subset system M on any poset, M-Scott notions, such as M-way below relation,M-continuity,M-Scott convergence (of nets and filters respectively) and M-Scott topology are proposed Any approximating auxiliary relation on a poset can be represented by an M-way below relation such that this poset is M-continuous. It is shown that a poset is M-continuous iff the M-Scott topology is completely distributive. The topology induced by the M-Scott convergence coincides with the M-Scott topology. If the M-way below relation satisfies the property of interpolation then a poset is M-continuous if and only if the M-Scott convergence coincides with the M-Scott topological convergence. Also, M-continuity is characterized by a certain Galois connection.
We present hydrogen gas concentration data for drilling mud extracted during the Wenchuan Earthquake Fault Scientific Drilling (WFSD; holes 2 and 3), measured on-line during drilling in SW China. Hydrogen influx into the well at depth is largely dependent on lithology and fracture density. In hole WFSD-2, the average background concentration of hydrogen is lower in granitic rocks than in sedimentary formations. More than five major hydrogen influxes were detected while drilling through the sedimentary formations, and two hydrogen-rich zones were detected in the granite (1240–1243 m and 1383.5–1405 m depth). In hole WFSD-3, mud extracted from a tectonic breccia contains high hydrogen concentrations at depths of 600–1000 m depth, and relatively low concentrations below 1000 m depth. In both holes, we observe a lack of hydrogen in the center of the fault zone and high concentrations of hydrogen in fractured zones. Hydrogen concentration in both holes displays significant vertical heterogeneity, and is positively correlated with fracture density. Hydrogen was likely sourced from interaction between water and fresh silicate minerals surfaces that were exposed during faulting, from the mantle, and from faulting events. Fracture zones provide the main channels for the migration of hydrogen gas. The variations in background hydrogen concentrations relate to changes in porosity and permeability. The two hydrogen-rich zones (642.36–676.22 m, and 1383.5–1405 m) were likely caused by earthquake activity or far-field triggering during WFSD-2 drilling. The results of this study provide gas data that can be used to model fault activity. It is important to consider the relationship between hydrogen gas and the seismic cycle, and to use such data to identify seismic precursors.
The cascaded multilevel converter is widely adopted to medium/high voltage and high power electronic applications due to the small harmonic components of the output voltage and the facilitation of modularity. In this paper, the operation principle of a T-type H-bridge topology is investigated in detail, and a carrier phase shifted pulse width modulation (CPS-PWM) based control method is proposed for this topology. Taking a virtual five-level waveform achieved by a unipolar double frequency CPS-PWM as the output object, PWM signals of the T-type H-bridge can be obtained by reverse derivation according to its switching modes. In addition, a control method for the T-type H-bridge based cascaded multilevel converter is introduced. Then a single-phase T-type H-bridge cascaded multilevel static var generator (SVG) prototype is built, and a repetitive controller based compound current control strategy is designed with the DC-link voltage balancing control scheme analyzed. Finally, simulation and experimental results validate the correctness and feasibility of the proposed modulation method and control strategy for T-type H-bridge based cascaded multilevel converters.