Shoichi Irokawa

A New Control Method for Multiterminal HVDC Transmission Without Fast Communications Systems

A new control scheme (the 2-ACR method) for parallel multiterminal HVDC systems is proposed. The method does not require fast communication systems. Any terminal can be disconnected or connected to the system without power re-coordination, since a new stable operating point can be always determined automatically by control actions of each converter with two automatic current regulators and one constant voltage controller. A light duty dc circuit breaker can disconnect a fault line, and the remaining terminals can restore transmission power as fast as possible. The excellent performance of the proposed scheme has been demonstrated by digital simulations using EMTP.

Development of HVDC Circuit Breaker and its Interrupting Test

The authors have developed a DC circuit breaker (DCCB) which interrupts a DC current by injecting a high-frequency reverse current from a commutating capacitor to be superposed to DC current and forcibly creating a current zero point. A breaking part consists of a vacuum interrupters or a SF6 gas, interrupters of the most advanced design connected in series or in combination to attain a high interrupting capabilities. The commutating current is introduced into the interrupter through a pulse transformer so that DCCB can be conveniently used in the system. A 25OkV-3500A DCCB system with these features was designed, manufactured and tested with successful results.

A proposal of Modular Multilevel Converter applying three winding transformer

This paper proposes a new type of Modular Multilevel Converter (MMC) applying a three winding transformer. In general, MMC requires a buffer reactor in each arm, which increases number of components and converter footprint. The proposed MMC with three winding transformer does not require the buffer reactors. We describe mathematical properties of the proposed MMC. We also confirmed it operated as same as typical MMC (with reactor topology) by experimentation using a prototype 10kVA converters.

Simulation study of unified power flow controller

The increasing complexity of ac power networks requires a high-performance power flow control system in order to obtain the desired power flow and enhance static and dynamic stability. One of the most effective power electronic systems to satisfy these requirements is a UPFC (Unified Power Flow Controller) employing self-commutated converters. This paper presents basic control strategies and simulation results for the UPFC using the EMTP (Electromagnetic Transient Program). The simulations were carried out for start and stop operations, power flow change operations in normal system conditions, as well as operations during system fault conditions. Thyristor-based bypass switches are used for the protection of the series compensator of the UPFC from system fault currents, and satisfactory protection capability was confirmed.

A Voltage Control Method of Static Var Compensator for the Remote System Interconnected by Long Distance AC Cables

The voltage variation in the remote system is large when the system is connected by long distance AC cables due to the cable capacitance. In Japan, the longest 54km 66kV AC submarine cable interconnection between Kyushyu mainland and Goto-islands was commissioned in 2005. It is requested to mitigate the voltage variation caused by switching off and on of one circuit of AC cables out of two circuits when a fault occurs. Since the conventional voltage control methods such as transformer tap changer or shunt capacitor and reactor banks are not sufficient because of their slow response time, therefore an SVC (Static Var Compensator) was installed in Goto-islands. In such application, SVC control method should be developed not to override the existing voltage control systems. This paper describes the SVC control method developed for Goto-islands AC interconnection project, which can be applied to similar applications. The effectiveness of the control method was verified by effective-value-based simulation results and field test results of which implemented before SVC commissioning in 2007.