Takami Sakai

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.

HVDC Transmission Control Equipment with High Reliability

A triplicated digital control equipment has been developed to improve reliability and performance of HVDC transmission. For improved reliability, DDC is used which is best suited to triplicated systems. The triplicated control equipment made up of three digital control equipments utilizes the self-diagnostic function of microcomputer to the maximum extent. It also employs an intermediate value selection as a signal selection method. The computation in the three control systems is performed in synchronism with the ac system to minimize signal transfer among the three systems and thereby facilitate maintenance. A new PLL circuit for synchronism detection is used to protect the HVDC transmission against ac system disturbances. An Operating System (OS) specially programed for HVDC transmission control is incorporated in the microcomputer to perform ac system control. The developed digital control equipment was tested in the simulated transmission facility. The simulation test showed that the control system has improved performance and reliability.

Consideration on self-commutated converter characteristics for DC power supply

A new DC power supply system is proposed based on the advanced current source type self-commutated convertor (ACSC). The ACSC is a network-friendly convertor and expected to achieve the high accuracy of 10/sup -5/ to 10/sup -6/ range of the DC current and required in the accelerator electromagnet application. The ACSC system performance is studied through digital simulation with the EMTDC (Electro Magnetic Transients program for Direct Currents transmission) and two control methods are discussed. A system consisting of the voltage source self-commutated convertor (VSC) and the choppers is also evaluated. Furthermore, characteristics of power conversion systems are discussed especially on the coordination between the convertor and the AC network. It is indicated that the convertor selection needs careful consideration on both the DC power quality requirements and the AC network conditions.