Kazuya Yokoyama

Application of single DC reactor type fault current limiter as a power source

This paper presents an application of single DC reactor type fault current limiter (FCL) with a gate turnoff (GTO) thyristor bridge as an emergency power source. A DC reactor type FCL stores electrical energy in a superconducting coil at a steady state. When a power transmission stops due to line faults, the FCL supplies stored energy to the load. This conception can be realized by operating the GTO thyristor bridge as an inverter. On the other hand, the function of fault current limitation is possible by keeping all GTO thyristors turned-on. The proposed FCL is numerically tested in a three-phase distribution system.

A single DC reactor type fault current limiting interrupter for three-phase power system

The authors propose a single DC reactor type fault current limiting interrupter (FCLI) for a three-phase power system. The device uses a single high temperature superconducting (HTS) coil that operates in conjunction with a modified half control bridge composed of thyristors and diodes connected to a transformers secondary windings. One variety is an automatic interrupter, which automatically blocks fault current through the application of DC bias current to the bridge. Another is a gate interrupter, which does the same thing by locking the thyristors gate pulses. The authors examine the results of various simulations on a new device that both limits and interrupts fault current in a three-phase power system.

Study of single dc device type FCL for three-phase power system

Various types of fault current limiters (FCLs) that use superconducting element are proposed and are under development, but there are many technical issues: their cost, fault current limiting ability, etc., so at present are far from commercialization. The purpose of this work is to study single dc device type FCL for three-phase power system. The device uses single high temperature superconducting coil that is operated in the diode bridge connected to transformers secondary windings. The bias power supply is required in the bridge for a rectification type limiter to avoid the distortion of load currents. This bias power supply requires the ability to supply at least the load currents in the steady state in the power system. Also the ability that many times of rated line currents can flow in the bias power supply at the time of a fault is required. In this paper, we study technical items that are demanded on this bias power supply and provide the optimal constitution of simple dc device type FCL for three-phase power system.

Reachability of the sliding mode control for multimachine power systems

This paper presents conditions of reachability of a switching plane for the sliding mode control of phase shifters in multimachine power systems. Sliding mode controllers are usually synthesized so as to satisfy only the existence condition of a sliding mode. However, there is the border of an asymptotically stable region and a system state cannot reach a switching plane unless a state at the beginning of control (initial state) exists in that region. Hence, reachability is defined as an asymptotic stability of the initial state. A sufficient condition to reach onto a switching plane is given by an energy-type Lyapunov function. It is described by control parameters that are introduced to find required control gains rather than feedback gains themselves. This allows us to straightforwardly evaluate an asymptotic stability. A phase-shift control system is numerically tested in a 2-machine 1-infinite-bus power system. The simulation results show that the improved control system offers faster transient stability and achieves the reachability of a switching plane.