Hiroo Konishi

Nonlinear optimal control applied to STATCOM for power system stabilization

This paper presents the results of simulator test for improvement of power system stability by applying a nonlinear optimal control to a static synchronous compensator (STATCOM). The STATCOM using the self-commutated converter was selected for this study among FACTS devices, and the power system oscillation damping control and voltage control were designed by using the approach of nonlinear optimal control based on the differential geometry theory. The capability of STATCOM supplies the reactive power at low voltage is larger than conventional SVC, and reactive power of STATCOM can be controlled continuously at high speed. The stabilizing control system was investigated supposing that STATCOM is used in the nonlinear operating points. Specifically, the stabilizing effects by nonlinear control theory were compared with the effects by linear control theory. It was confirmed that nonlinear control was more effective compared with linear control. Moreover, system conditions where nonlinear control operates effectively were clarified.

Power system transient stability enhancement by STATCOM with nonlinear control system

A nonlinear control approach is applied to static synchronous compensator (STATCOM), which is one of the FACTS devices. Here, the nonlinear controller is designed locally based on mathematical models of one of the generators, STATCOM and transmission lines in a multi-machine system. The influence of the proposed controller, which controls the terminal voltage of STATCOM, on the power system stability is tested by digital dynamic simulations. As a result of the simulation, it has been made clear that the STATCOM can improve the transient stability in the 3-machine loop system. In the case of the IEEJ West 10-machine system, the effectiveness is also discussed.

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.

Five-year's verification test results in Hokuto mega-solar system

The New Energy and Industrial Technology Development Organization (NEDO) advertised for consignment research business called “Verification of Grid Stabilization with Large-scale Photovoltaic Power Generation Systems” in 2006. Two sites were selected for the verification tests, which were Hokuto City in Yamanashi Prefecture and Wakkanai City in Hokkaido. Mega-solar system (Large-scale photovoltaic system) of about 2MW and about 5MW was constructed each. Five-years verification test results of grid stabilization and PV characteristics evaluation in Hokuto mega-solar system are discussed in this paper.

Simulation study of power quality compensation system using EDLC for distribution systems

Power quality problems such as voltage sags, voltage distortions, voltage interruptions and frequency or phase variations In distribution systems are serious concerns, especially for semiconductor manufacturing companies, paper mill companies and so on. We have been studying a power quality compensation (PQC) system using electric double-layer capacitors (EDLCs) for distribution systems, which compensates not only reactive powers but active powers for a short period to the systems. It has large capacitors on the DC side. There are two methods for the PQC system, a series connection type and a parallel connection type for loads. We compared them on needed capacities, the compensation ability and so on. Based on the comparison, we selected the parallel connection type for future development. A control system of the PQC system was developed to deliver power to the loads. Finally, detailed digital simulations of the PQC system were carried out and the behaviors were confirmed.

A study of large-scale PV system design considering PV generation distribution

In Japan, attractive system of Feed-in Tariff (FIT) was started from last July. However it is still important to design large-scale PV (LSPV) systems reasonably in order to return high investment as soon as possible. To design LSPV systems with the whole PV capacity that we can install is not reasonable from this point of view. We propose the design method of cost-effective LSPV systems which can utilize facilities effectively, the first. It is based on statistical and individual data of PV generation distribution which are issued by the association of weather etc. The specification of the LSPV system capacities is decided considering the PV generation distribution. The system specifications are decided through comparing the reduced equipment cost with the selling of electricity income that we lost by the reduced equipment. Next, we propose a configuration of large-scale power conditioners (LS-PCSs) to get an efficiently dynamic performance from the test results of shade of the modules. We propose how to connect an optimal number of strings to the LS-PCSs in consideration of imbalance of modules.

Verification test of grid stabilization and evaluation of PV module characteristics for large-scale PV generation system

About 2MW PV system was constructed in Hokuto city of Yamanashi Prefecture in Japan for verifying grid-stabilization control methods and evaluation of various kinds of PV module characteristics for construction of future large-scale PV systems. Five-year tests were finished in March last year. The test results are summarized in this paper and discussed.

Development of power quality controller connected in parallel to dispersed generations

The dispersed generations (DGs) are expected to increase. The output power of DGs fluctuates, making AC system interconnection problematic. As DC-to-AC converters of DGs generates harmonics, the harmonics lead to degradation of power quality, too. We have developed a power quality controller with built-in electric double-layer capacities (EDLCs)