Yoshifumi Zoka

FACTS Devices Allocation With Control Coordination Considering Congestion Relief and Voltage Stability

This paper presents an optimal allocation method for flexible ac transmission system (FACTS) devices for market-based power systems considering congestion relief and voltage stability. The purpose of the FACTS devices installation is to provide benefit for all entities accomplished by both minimizing annual device investment cost and maximizing annual benefit defined as difference between expected security cost (ESC) with and without FACTS devices installation. Different from previous approaches, the proposed method accurately evaluates the annual cost and benefits obtainable by FACTS devices installation by formulating a large-scale optimization problem that contains power flow analyses for a large number of system states representing annual power system operations. In addition, dynamic state transitions caused by specified contingencies are also simulated in the optimization problem to evaluate the effect of FACTS control actions as well as the other coordinated controls. The expected cost consists of operating cost under normal and contingency states along with their related probabilities to occur. Maximizing social welfare is the objective for normal state while minimizing compensations for generations re-scheduling and load shedding as well as maximizing social welfare are the objectives in case of contingency. Although installation cost of FACTS devices is required, they are useful as cost free means, which can reduce effectively the annual costs for generations re-scheduling and load shedding.

An interaction problem of distributed generators installed in a MicroGrid

This paper investigates an interaction problem that might be induced from various kinds of distributed generators installed in a MicroGrid. One of the most important features of MicroGrid is islanding operation. MicroGrid does not include large central generators and all distributed small generators have to share all loads existing in the MicroGrid. In this case, undesirable mutual oscillation problem might appear when MicroGrid goes into islanding mode. In this paper, MicroGrid itself and several types of distributed generator are modeled by using Matlab/Simulink. A typical case is simulated and examined by using the developed model.

High-Speed Real-Time Dynamic Economic Load Dispatch

A large amount of renewable energy penetration may cause a serious problem in load dispatch in the future power system, where the amount of controllable generators will decrease while disturbances increase. Therefore, a new economic load dispatch (ELD) method is required in order to make the best use of the ramp-rate capability of existing generators to cope with the disturbances caused by loads as well as by renewable energy generations. This paper proposes a new dynamic ELD method to meet the general requirements for real-time use in a future power system, where load following capability is critically limited. The method is also satisfactory from an economical point of view, and is suitable for high-speed online application due to fast and steady computation time. The proposed method has been successfully tested on several systems supplying a typical morning to noon demand profile.

A Study on the Effect of Generation Shedding to Total Transfer Capability by Means of Transient Stability Constrained Optimal Power Flow

In nowadays deregulated market, total transfer capability (TTC) calculation, which is the basis for evaluating available transfer capability (ATC), has been becoming more significant. During the last decade, transient stability constraints have been included in the optimal power flow approach to maximize TTC. However, no previous work on investigating the effect of generation shedding action to TTC has been reported. Therefore, in this paper, we propose a TTC maximization by means of transient stability constrained optimal power flow considering the generation shedding action. Proper selection of the generator to shed is based on its Lagrange multiplier value of transient stability constraint. Our simulation results show how TTC can be increased to anticipate possible generation shedding.

Application of metaheuristic methods to reactive power planning: a comparative study for GA, PSO and EPSO

This paper proposes the application of metaheuristic methods to Reactive Power Planning (RPP). RPP involves optimal allocation of reactive sources to satisfy voltage constraints during normal and contingency states. The main objective of the proposed RPP is to make a trade-off between economy and security by determining the optimal combination of fast and slow controls (load shedding, new slow and fast VAR devices). The overall problem is formulated as a large scale mixed integer nonlinear programming problem. The proposed RPP problem is a combinatorial optimization problem, which cannot be solved easily by conventional optimization methods. Metaheuristic methods are reported to be efficient to solve combinatorial optimization problems. Among the well-known metaheuristic methods, this paper discovers the efficiency of Genetic Algorithm (GA), Particle Swarm Optimization (PSO) and Evolutionary PSO (EPSO) in solving the proposed RPP problem. The proposed approaches have been successfully tested on IEEE 14 bus system and a comparative study is illustrated.

Sensitivity Analysis to Operation Margin of Zone 3 Impedance Relays With Bus Power and Shunt Susceptance

Zone 3 impedance relays are sensitive to power-flow distribution due to their overreaching property, and may undesirably operate in stressed system conditions with reactive power shortages or neighboring faults. In this paper, the distance of the apparent impedance to the protection boundary on the R-X plane is defined by the operation margin, which is expressed as the function of bus voltages. The sensitivities of the operation margin to bus voltages, bus powers, and shunt susceptances quantify the influence of various disturbances on the relay performance. The numerical results show: (1) the operation margin is quantified by the sensitivities with satisfying accuracy and less computation effort compared with power-flow schemes; (2) the variation of bus powers and shunt susceptances at different locations may improve or decrease the operation margin; and (3) the variation of active and reactive powers at the same bus may yield opposite effects on the operation margin.

An optimal deployment of fuel cells in distribution systems by using genetic algorithms

A fuel cell has been expected to be a very energy efficient and clean device and has been technologically matured to a stage of practical use. In consideration of its relatively small generation capacity, a fuel cell may be installed in a distribution network. This paper presents the framework of a method of introducing fuel cells into a radial distribution system. According to this framework, an optimal deployment problem of fuel cells is formulated as a combinatorial optimization problem. Since this problem has nonlinear objective function to be minimized, the optimal solution could be obtains only through an exhaustive search, which is susceptible to combinatorial explosion for large scale systems. Hence, a genetic algorithm (GA) must be an adequate method to obtain a solution within reasonable computation time. Further, several kinds of techniques to improve GA performance have been introduced in this paper. The proposed algorithm has been applied to test distribution systems of 69 and I I1 nodes with successful results.

An Optimal Autonomous Decentralized Control Method for Voltage Control Devices by Using a Multi-Agent System

Impact of increasing penetration of photovoltaic (PV) generation is expected in Japan in the near future; thus a new voltage control scheme is required in order to improve the operation of distribution networks. We propose a new voltage control scheme for distribution networks based on a multi-agent system. The large voltage fluctuations caused by PV generations are effectively regulated by adjusting the conventional types of tap-changing controllers. We achieved an optimal control performance by developing a new optimal control law applicable to decentralized autonomous control. The autonomy is accomplished by using a multi-agent system. The proposed method is applicable to general distribution network and highly efficient for popular radial networks under certain approximations. The effectiveness of the proposed scheme is demonstrated through numerical simulations of radial 6.6-kV test system with successful results.

An Application of Critical Trajectory Method to BCU Problem for Transient Stability Studies

This paper proposes a new method for obtaining controlling unstable equilibrium point (CUEP) for transient stability analysis in electric power systems. A minimization problem is formulated to attain CUEP by applying the critical trajectory (CTrj) method to the boundary controlling unstable equilibrium point (BCU) method. CTrj method is a unique approach proposed by the authors to obtain critical condition for transient stability problem. The Proposed method simultaneously computes a trajectory on the stability boundary starting from the exit point reaching CUEP. The effectiveness of the method is demonstrated through simulations for various systems.

An application of robust power system security to power system operation for high-penetration of PV

This paper proposes a method of analyzing the N-1 security under the circumstances of PV penetration. The concept of Robust Power System Security (RS) proposed by the authors is used to evaluate the N-1 security quantitatively. It is shown that (1) the relationship between PV penetration and the N-1 security results in a clear trade-off, (2) installation of storage batteries is effective to enhance the N-1 security and (3) power system operators will be able to monitor the N-1 security condition directly by visualizing the security regions gained from the concept of RS. The effectiveness of the proposed method is demonstrated through simulations using a three machine system.