MMIC development for millimeter-wave space application

The latest millimeter-wave monolithic-microwave integrated-circuit (MMIC) developments and technologies at the Mitsubishi Electric Corporation, Kanagawa, Japan, concerning high power amplifiers, low-noise amplifiers and phase shifters have been summarized. It has been shown that high-efficiency, low-noise, and low-loss performance for millimeter-wave space applications can be achieved by employing pseudomorphic high electron-mobility transistor (p-HEMT) MMIC technology. The investigation for gamma-ray irradiation hardness has cleared that millimeter wave p-HEMT MMICs have over a 100 years of life against gamma-ray irradiation in the space environment     

Balancing control method by dispersed generators based on H∞ control theory in DC power feeding system

Recently, dispersed generators have been installed in distribution network to supply power to commercial facilities. Renewable energy generation contains output power fluctuations and distributed generator produces sluggish response for power demand. In order to overcome these problems, an ultra capacitor energy storage system is used for compensating the instantaneous power imbalance. However, use of a large capacity ultra capacitor energy system increases system cost. In addition, PPSs (Power Producer and Supplier) that own these generators are supposed to achieve 30-min balancing control for stable supply of electric power. This paper proposes a control system to achieve both 30-min balancing control and interconnection point power flow control by using a fuel cell and an ultra capacitor based on the H_∞ control theory. Besides, remaining storage energy of the ultra capacitor is controlled to be constant to maintain compensation capability. Effectiveness of the proposed control system is verified by using simulation results.     

Granularity and Surface Structure of Ground Granulated Blast-Furnace Slags

Ground granulated blast-furnace slags (GGBS) show improved hydration reactivity when granularity fineness increases, but the reason for the improvement in reactivity is still unknown. GGBS specimens with Blaine surface areas of 4680, 6470, and 8050 are analyzed, but the conventional reactivity criteria, such as degree of vitrification, basicity, and mineralogical composition, of the GGBS show no significant differences. X-ray photoelectron spectroscopic analysis, however, successfully distinguishes and identifies SiO₂ gels as well as glassy phases of CaO-SiO₂ and Al₂O₃-SiO₂ in the slag surfaces, where, with an increase in the Blaine surface area of the slag, CaO-SiO₂-type glass becomes dominant and contributes to the evolution of hydration, determined in terms of silicate anion morphology by the trimethylsilylation (TMS) method.     

Effect of Treatment of Reactive Aggregate by H2O2 on the Alkali-Silica Reaction

A method of controlling the alkali-silica reaction by treating a reactive aggregate with a solution of hydrogen peroxide was investigated. Mortar bars made using the hydrogen peroxide-treated aggregate exhibited no expansion after 12 months, indicating that the alkali-silica reaction was suppressed. Study of the state of bonding of Si in the aggregate using XPS showed that the Si-O bond energy indicating glassy SiO₂ (102.7 eV) before treatment had changed to crystalline SiO₂ (103.2 eV) after hydrogen peroxide treatment. This indicates that the strong oxidizing potential of hydrogen peroxide stabilizes the silica in the reactive aggregate and thus suppresses the alkali-silica reaction.     

Low-loss HVDC transmission system with self-commutated power converter introducing zero-current soft-switching technique

In recent years, application of self turn-off devices for the HVDC transmission system is very important for flexible and high efficient power transport and supply. However, for self turn-off devices that are applied to high-power system, excessive switching losses due to voltage/current surges occurred on hard switching and the current tail characteristics on turn-off lead to the considerable switching loss. Therefore switching-loss reduction by using a soft-switching technique is very effective for improvement of the considerable switching losses. A self-commutated HVDC circuit topology with soft-switching characteristics is discussed. The proposed topology is able to achieve a zero-current switching in self-commutated power converters. In order to examine the effectiveness of the proposed system, the system is analysed in terms of the characteristics of switching losses through a theoretical approach and computer simulations.     

Reaction mechanism of methane activation using non-equilibrium pulsed discharge at room temperature

The reaction mechanism of methane activation using non-equilibrium pulsed discharge was largely clarified from the emission spectroscopic study and experiments with higher hydrocarbons and some kinds of isotopes. The strong emission of atomic carbon and C₂ swan band system was observed as well as H Balmer series emission. This indicates that methane was highly dissociated into C and H by electron impact, which is consistent with the result of high C₂D₂ composition in produced acetylene when the mixture of CH₄ and D₂ was fed into discharge region. High electron energy contributed to produce atomic carbon directly from methane, and high electron density promoted the dehydrogenation from CH₃, CH₂ and CH to produce atomic carbon consecutively. The reason for the high selectivity to C₂H₂ was the high concentration of CH or C₂ formed from atomic carbon, and the repetition mechanism of decomposition and recombination among C, CH, C₂ and C₂H₂.     

Smoothing of Wind Power Fluctuations for Permanent Magnet Synchronous Generator-Based Wind Energy Conversion System and Fault Ride-through Consideration

Due to the increment of penetration level of wind power generation, output power fluctuation is one of the most important issue's that can destabilize the power system operation. This article mainly deals with the smoothing of the output power fluctuations of a wind energy conversion system based permanent magnet synchronous generator and fault ride-through enhancement during a grid fault. The concerned wind energy conversion system based permanent magnet synchronous generator adopts an AC-DC-AC converter system. The proposed control method limits the wind energy conversion system output power by adjusting the pitch angle of the wind turbine blades when wind speed is above the rated wind speed. In the grid-side converter, a fuzzy logic controller is used to determine the torque reference for which the kinetic energy stored by the inertia of wind turbine can smooth the output power fluctuations of the permanent magnet synchronous generator. Also, the DC-link voltage, controlled by the grid-side inverter, is adjusted in accordance with the output power fluctuations of the permanent magnet synchronous generator using a voltage smoothing index. Moreover, in this aticle, the proposed method ensures that the wind turbine stays operational during grid faults and provides fast restoration once the fault is cleared. To show the effectiveness of the proposed method, simulations under different conditions have been performed by using MATLAB/Simulink® (The Math Works, Natick, MA, USA).     

Optimal configuration of power generating systems in isolated island with renewable energy

In isolated islands, usually diesel generators supply electric power. However, there are problems, e.g., a lack of fossil fuel, environmental pollution etc. So, isolated island, e.g. Miyako island, installs renewable energy power production plants. However, renewable energy power production plants are very costly. This paper presents an optimal configuration of power system in isolated island installing renewable energy power production plants. The generating system consists of diesel generators, wind turbine generators, PV system and batteries. Using the proposed method, operation cost can be reduced about 10% in comparison with diesel generators only from simulation results.     

A fuzzy control strategy for power smoothing and grid dynamic response enrichment of a grid‐connected wind energy conversion system

This paper concentrates on the output power smoothing and the grid dynamic response enhancement of a grid‐interactive MW‐class permanent magnet synchronous generator‐based wind energy conversion system (WECS). A simple fuzzy controller method is applied to improve the overall performance of the WECS. The proposed method can retrieve the storing kinetic energy from the inertia of a wind turbine, perfectly. As a result, it can ensure a proficient power smoothing of the variable speed WECS. On the other hand, the grid side inverter is controlled by the fuzzy controller. This approach can reduce the fluctuation of DC link voltage and can deliver a smooth power to the power grid. The proposed method is compared with two other methods such as the maximum power point tracking control method and the without fuzzy controller method. A simple shunt circuit also includes in the DC link circuit. Therefore, during the system fault condition, the WECS can perform a stable operation. Effectiveness of the proposed method is verified by numerical simulations. Copyright © 2013 John Wiley & Sons, Ltd.     

Optimum configuration for renewable generating systems in residence using genetic algorithm

Photovoltaic power generation and wind power generation have an advantage that energy is clean and infinite, but they have a disadvantage in that electrical output energy is unstable, and initial and maintenance costs are expensive. This paper presents an optimal configuration for renewable generating systems in residence using a genetic algorithm (GA). We define that the objective function is the total cost, where the total cost is the sum of initial cost, an operation cost, and a maintenance cost. We determine an optimal configuration of renewable generating systems, where total cost is more reasonable using GA. The simulation using this technique is shown.