Kiyoshi Takenaka

Development of static and simulation programs for voltage stability studies of bulk power system

In the analysis and evaluation of power system voltage stability, it is necessary to accurately identify the stability margin at each load point under specific system configuration or power balance condition. The voltage stability margin can be basically identified by the multi-solution load flow calculation method. When predicted by this static analysis that voltage instability may occur, time domain simulation will be required which includes the models of various control equipment related with power system voltage profile. To deal with this, the following two analytical computer codes were developed: (1) a voltage stability static analysis computer code employing a new load flow calculation method; and (2) a time-domain long-term simulation computer code for voltage stability. These computer codes can also calculate the voltage stability index at each load point which is based on the margin to the stability power limit at each load point. The practicality of these codes developed were verified by applying to the IEEE-118 test system.

Enhancement of continuous operation performance of HVDC with self-commutated converter

This paper describes a converter control scheme to enhance continuous operation performance of HVDC system with voltage source type self commutated (SC) converter. The continuous operation of SC converter can be achieved by suppressing converter overcurrents and AC overvoltages in the case of AC line faults including phase failure. Development of a new control scheme has been accomplished by experiment using an AC/DC power system simulator in CRIEPI and the EMTP (Electro Magnetic Transients Program) analysis. At first, we show that converter overcurrents and AC overvoltages are caused by lack of control information to static limiter and insufficient control performance to negative-sequence current of SC converter. Next, an adequate converter control scheme is proposed which is composed of an ACRs (automatic current legulator) adjustable dynamic limiter to suppress the converter overcurrents, and the limit logic of SC converter to suppress AC overvoltages during phase failure.

Control and protection scheme of HVDC system with self-commutated converter in system fault conditions

For extending self-commutated converter application to future trunk power systems, it is important to develop a stable operation scheme as well as to realize substantial cost reduction through coordinated system and control design. Suppression controls of converter overcurrent and dc overvoltage in various system fault conditions are essential in order to ensure stable operation and cost reduction of HVDC systems with voltage source type self-commutated converters. Converter control and protection schemes which include such suppression controls have been developed, employing CRIEPIs ac/dc Power System Simulator test and EMTP analysis. This paper first discusses the cause of converter overcurrent at ac system faults, considering the effect of PWM pulse number and converter control speed. Continued operation has been achieved by adding a new overcurrent suppression scheme to the converter control. In the case of a dc line grounding fault, the selection of the grounding circuit constant and the adoption of a high-speed converter control practically ensure the reduction of dc overvoltage while suppressing converter overcurrent. The converter block and restart sequence after a dc fault, which is coordinated with dc circuit breaker operation, enables stable recovery of HVDC transmission as fast as the usual line-commutated HVDC system.

Voltage Control Performance of Typical Wind Farm Grid Connection Schemes

A lot of wind farms has been promoted from the viewpoint of the global environmental problem in Japan. These are introduced at the end of transmission line at middle voltage system because the wind blows considerably only in the limited place. Therefore, it is necessary to examine how one wind farm can be introduced to one site in power system from the viewpoint of the voltage and power flow. This paper shows the voltage control performance of typical wind farm grid connection schemes such as AC link type and AC-DC-AC link type with the wind farm introduction place as a parameter to clarify the reasonable grid connection

Study of coordinate Control method to Improve Stability on Multi -Infeed HVDC system

Recently, in particular, many of the coming hydro power projects in China are located far away from the load centers. As the use of HVDC transmission continues to develop situations have arisen where multiple HVDC links terminate in close proximity in a common AC system area. This paper refers to the methods to improve the stability of voltage on multi-infeed HVDC system, and using CRIEPIs transient stability simulation tool (CAPT). Through the simulations, this paper find the better measurement to solve those faults cases. Make a model multi- infeed system base on the China Southern Power Grid for system. We focused of the inverter side voltage, and compared this traditional control method with the rapid restart control methods results. The control of constituent HVDC subsystems can be better coordinated by the consideration of the time of rapid restart control at inverter side.

Transport Characteristics and AC Losses in YBCO Toroidal Coils for DC Reactor With Harmonic Current of Three-Phase Converter

In plant and industrial complex, further energy saving can be realized by DC interconnection between the ends of AC radial distribution system. We fabricated a power system simulator to verify that the DC interconnection is effective for energy saving in the distribution system. An YBCO toroidal coil composed of eight double pancake coils was fabricated and adopted in the simulator as a DC reactor. Harmonic current with DC-offset component were observed in the YBCO toroidal coil and the frequency component ratio of harmonic current depended on the inductance of the toroidal coil. Energy loss in the YBCO toroidal coil during the DC interconnection in the power system simulator decreased with the inductance of the YBCO toroidal coil because the magnitude of harmonic current component decreased with the inductance. To clarify the loss characteristics in the YBCO toroidal coil, we investigated influence of the magnitude of harmonic-frequency component and DC-offset component on the transport current loss in YBCO tape conductor. The transport current lose was independent of the magnitude of DC-offset component. The energy loss characteristics in the YBCO toroidal coil were closely related to the transport current loss in the YBCO tape conductor with harmonic current.