Voltage sag compensation with minimum energy injection by use of a micro‐SMES

This paper presents a method to compensate voltage sags with minimum energy injection for a series‐connected voltage restorer using a micro‐SMES. A circuit for extracting the fundamental symmetrical components from sag voltages and a minimum energy injection algorithm is described. Simulations of voltage sag compensation have been carried out using PSCAD/EMTDC for various faults. The simulation results confirm the validity of the proposed method and show the possibility of reducing the size of energy storage devices. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(3): 70–80, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10047     

Quantitative evaluation of generator power control effect of FACTS controllers for power system stabilization

The advancement of power electronics technologies has significantly developed the power system stabilizing controllers. Quantitative as well as qualitative evaluation of their effectiveness in power systems is a matter of great importance for the feasibility investigation of these apparatus. In this paper, the possible control region of FACTS controllers with series and/or shunt configuration in a single machine to infinite bus system is formulated in the powerangle curve with a set of algebraic equations. The effectiveness of TCPST (Thyristor‐Controlled Phase Shifting Transformer), SSSC (Static Synchronous Series Compensator), and TCSC (Thyristor‐Controlled Series Compensator) for the improvement of the transient stability is evaluated quantitatively as a numerical example. The correctness of the proposed method has been confirmed by analysis based on the electromagnetic transients simulation with a detailed system model. © 2001 Scripta Technica, Electr Eng Jpn, 138(3): 43–51, 2002     

Anionic polymerization of styrene in 2-methyltetrahydrofuran: temperature dependence of the field effect

Kinetics of living anionic polymerizations of styrene was investigated for lithium, sodium, and potassium salts in 2-methyltetrahydrofuran at 35, 25, 0, and ?70°C in the presence and absence of a high intensity electric field. At 35 and 25°C, a field acceleration effect was observed whereas no effect was found at 0 and ?70°C. The propagation rate constant of ion pairs was almost independent of gegen ions and their temperature dependence was smaller than that of free anions. The free ions seem to be more strongly solvated as the temperature decreases.     

Stabilization of a Power System Including Inverter‐Type Distributed Generators by a Virtual Synchronous Generator

The capacity of distributed generators (DGs) connected to the grid by inverters is growing year after year. The inverters are generally controlled by a phase locked loop (PLL) in order to achieve synchronization with the power system frequency. Power systems may become unstable as the capacity of the inverter‐type DGs continues to increase, because the inverter frequency is controlled just to follow the frequency determined by other synchronous generators. It has been suggested that inverters be controlled to behave like a synchronous generator. This concept is referred to as the virtual synchronous generator (VSG). In this paper, a control scheme for a VSG is presented, and the design method for the required energy storage and the capacity for grid stabilization control by a VSG is investigated by computer simulations.     

A circulating current control scheme for multiple three‐level NPC inverter systems

In recent years, motor drive systems for steel rolling mills have been steadily increasing in capacity. In particular, the development of three‐level NPC (Neutral Point Clamped) inverters is now focusing on the replacement of cycloconverters. In order to satisfy such a requirement, in this paper a multiple three‐level NPC inverter system is proposed. The configuration consists of two three‐level NPC inverters with the same configuration connected in parallel by current limiting reactors. In this case, the circulating current flowing between the two three‐level NPC inverters must be controlled to prevent a decrease in the maximum output capacity. In particular, a new method for control of the circulating current is a major topic of discussion. The method is based on space voltage vector‐based PWM (Pulse Width Modulation) control for the three‐level NPC inverters and the circulating current is controlled by adjusting the output durations of the respective space voltage vectors. In this method the circulating current controller can be decoupled from the motor current controller. Therefore, it is possible to design the different controllers independently. In addition, the experimental results obtained using an induction motor show that the circulating current can be reduced to within 2% of the rated motor current when the motor current response exceeds 1000 rad/s. © 2001 Scripta Technica, Electr Eng Jpn, 136(2): 38–48, 2001     

An autopsy case of cytokeratin 7-positive minute adenocarcinoma of the lung with systemic metastases

We describe a 60-year-old woman with leg pain. Although metastatic bone tumor and atypical cells mimicking signet-ring cells in the bone marrow picture were observed, systemic survey revealed no primary lesion. The patient died two months after admission from systemic progress of the disease. Autopsy revealed a small focus of adenocarcinoma within the right upper lobe of the lung and systemic metastases without any particular changes in the gastrointestinal tract. The tumor cells of the lung were diffusely positive for cytokeratin 7, whereas cytokeratin 20 immunoreactivity was weak and focal, and that supported the lung origin of the present tumor. Moreover, the tumor cells in the bone marrow showed a similar pattern in immunoreactivity. These findings suggest that cytokeratin 7 and cytokeratin 20 immunoreactivity is helpful for the premortem diagnosis of the metastatic tumor of unknown origin.     

The concept of distribution flexible network PV system

In stand-alone photovoltaic (PV) systems, when the battery is fully charged, the excess generated power is wasted. To solve the problems of wasted excess power, a distributed flexible network photovoltaic (DFNPV) system is studied. It incorporates many PV subsystems each consisting of PV panel, DC/DC converter, and load, and are connected to each other with shared batteries. The excess generated power of the subsystem is transferred between PV subsystems to compensate the lack of power in other subsystems.The control method of transferring power is based on simple voltage control of the subsystems. The output voltage in a given subsystem decreases if a transient excessive load is larger than the generated power; as a result excess power is transferred from another subsystem that has sufficient power and higher voltage output. In this study, this proposed operation method is demonstrated by simulation of power transfer between two subsystems and among four subsystems. Furthermore, to estimate the size of the DFNPV system within an acceptable voltage drop, the relationships between cable length, power loss, and cable types are discussed.