Kaoru Koyanagi

Trade-off analysis of autonomous microgrid sizing with PV, diesel, and battery storage

This paper introduces a trade-off analysis on the sizing of microgrid equipment aimed at autonomous application in remote regions. The microgrid includes a diesel engine, solar photovoltaic (PV) panels, and a battery storage. The performance of the microgrid is measured by environmental impact (CO2 emission), and frequency stability. The sizing of the battery storage is analyzed when the load is supplied mainly by the diesel engine. From the simulation analysis, it was shown that there exists a certain front of trade-off between the battery size and other performance indices due mainly to the dynamic performance of the battery storage and to the variation of PV output under different weather conditions.

The role of battery systems and expandable distribution networks for smarter grid

Renewable energies such as wind power and PV energy sources are valuable energy resources which can contribute to improvement of self-sufficiency rate of energy and can be used to reverse global warming. However, when there is a large amount of penetration of renewable energy generations into a grid, some problems will arise in the present distribution power network, due to instability of power output and large reverse power flow caused by the renewable energy generation. In researches on recent new electricity supply system, there is a way of thinking of local production for local consumption by the so-called micro-grid and smart-grid which supply the area demand by the area electric power resources, and several demonstrations have been performed also in Japan. From the viewpoint of local production for local and its consumption of electric power energy, a new type of expandable distribution network is proposed to meet regional expansion of the areas electricity demand and supply by the addition of electricity-cluster. The role and operation of battery energy storage system (BESS) in the expandable distribution networks are also discussed. Dynamical models of the expandable network and BESS for computer simulations are developed by MATLAB/Simulink, and the dynamic properties to maintain frequency and voltages in the cluster by appropriate operations of BESS are presented.

Field Tests of a Microgrid Control System

A microgrid control system using multi-agent technologies is proposed. In this control system, operation planning is realized based on generation and load forecasting by using artificial neural network and fuzzy systems. Unit commitment of generations includes start/stop of power generations and energy storages. Load following function is accomplished by an adaptive control system based on conventional PI control scheme. To include, in a flexible manner, new generations or loads into the microgrid, multi-agent technologies might be applied. In this paper, at first proposed microgrid control system is outlined and then field tests outline is stated

BCU-guided time-domain method for energy margin calculation to improve BCU-DSA system

On-line dynamic security assessment offers several significant engineering and financial benefits. However, Current EMS systems can not perform online dynamic security assessment (DSA) to ensure the ability of the power system to withstand some contingencies. We have designed and implemented a reliable and effective system, called BCU-DSA, for online dynamic security assessments and energy margin calculations of practical power systems. BCU-DSA system achieves high level of reliability and accuracy by effective exploration of the merits of both the improved BCU classifiers and the detailed time-domain simulation program. The system has been evaluated on practical power system models with promising results. The BCU-DSA system gives exact stability/instability assessments and accurate energy margin for every contingency of practical power systems.

The development and the application of fast decoupled load flow method for distribution systems with high R/X ratios lines

An improved Fast Decoupled Load Flow calculation method for distribution systems with high R/X ratio is proposed. This method is based on a coordinate transformation in Y-matrix for Jacobian matrix in the load flow method. The biggest advantage of so-called Fast Decoupled Load Flow(FDLF) method over the conventional Newton-Raphson method is the short computation time for large power systems which is achieved by the reduced size of Jacobian matrix. However, it is said to worsen convergence characteristics for distribution systems with lines of high R/X ratios compared to the conventional Newton-Raphson method. In order to overcome the problem, the authors employed a coordinate transformation in Y-matrix of the Fast Decoupled method. Better convergence processes in the improved Fast Decoupled method are demonstrated and some discussions are given in case of the analysis of the distribution systems with high R/X ratio lines.

Dynamic characteristic of frequency control by rotary frequency converter to link wind farm and power system

This work proposes an application of rotary frequency converter for a wind farm system. Wind power is getting attention for prospective renewal energy sources, and introduction of wind farm generation will solve environmental matters and energy exhaust problem. However, the quality of power system frequency will be degraded as the capacity of wind power generator increases. Attenuation of mismatch between the served power and load demand is most important problem in order to increase number of wind generators. Here, a large rotary frequency converter is proposed as a buffer to connect the wind farm and the power system. This provides energy storage function of the output power associated with irregular wind power. The converter has a synchronous generator and a doubly-fed machine. The synchronous motor is connected to the wind farm to supply AC voltage for induction generators of wind power generation units. The shaft of the doubly-fed machine is mechanically jointed to the synchronous motor, and rotates together. Tuning the current of the secondary winding supplied by cycloconverter or self-corn mutated inverter controls the output power. At present, doubly-fed machine is commonly used in pumped storage hydraulic power plants recently constructed. The proposed scheme is an expansion from the present application. For the evaluation of the proposed scheme, two simulation tests are carried out. One is load reference setting test for discussion of the power exchange response to a power grid. Other is load frequency control test in order to discuss required capacity for the rotary frequency converter to improve the frequency quality.

Development of an integrated power system analysis package

With the present de-regulation in the electric power market, powerful analytical tools are required for the planning and evaluation of feasibility of wheeling of electrical power. A major role for power system engineers is confirming the stable operation of power systems in order to maintain dynamic stability voltage stability, etc. under a wide variety of constraints. Conventional computer software used in power system analysis is, however, not convenient or friendly because it requires that data be input in text form, including even the data for modeling generators, their controllers, loads and so on. In this paper, the authors present a new integrated power system package named Impact (Integrated and Multi-purpose Package of Advanced Computational Tools for power system engineering). This package was developed to provide a fully graphical user interface (GUI). Impact is a package of several useful integrated analytical applications. Users can easily handle bus configurations from the powerful GUI. The power of the GUI coupled with full integration of the application is demonstrated in many attractive themes.

Analytical studies on power system dynamic stability enhancement by doubly-fed adjustable speed machine

Doubly-fed adjustable-speed pumped storage generating systems of large capacity have been newly installed in power systems with technologies of power electronics. These new generating systems contribute not only to frequency regulation of power system at nights by means of input power change as results of rotor speed control, but also to enhancement of power system stability by fast control of voltage and power. New analytical method based on extended Heffron-Phillips model was developed in order to support design of a power system stabilizer which is used to improve dynamic stability of the synchronous generators located in the vicinity of the doubly-fed generating system. A systematic approach based on the new analytical method is shown with numerical examples, explaining how to design the additional power system stabilizing controller of the doubly-fed generating system.

Autonomous Distributed Control of Micro Grid with Diesel Generator

Recently, solar energy generation and wind power generation have been introduced to electric power system. But, as for this natural energy, influence such as frequency fluctuation is exerted on electric power system, which is a fundamental problem in operation of a small grid system such as micro-grid. These systems should provide appropriate power quality compared to a large grid. However, using the telecommunication line for monitoring and controlling the system devices is costly, as an alternative method, autonomous distribution control that enables local power supply and demand control is also required in design and operational stage. This paper discusses benefits of these methods conducting cost evaluation

PADES: an analytical tool for designing power system stabilizer for cross-compound unit

In this paper, an analytical method for design of power system stabilizers (PSS) that will be equipped in cross-compound units is proposed, and a simple and practical design tool based on a frequency response method is presented. An extended Heffron-Phillips model which has been developed for two machines-to-infinite-bus power system model is employed for dynamic stability analysis. The effects of PSS on damping of both inter-area and inter-machine electromechanical modes are described.