Yoshiki Nakachi

A multi-agent cooperative voltage control method

This paper presented a method for the coordinated control of voltage and reactive power employing multiple agents. In this system, agents installed in sub-stations exchange information with each other through the network and attempt to reduce the overall number of actions needed to control network conditions. In order to verify the performance of the proposed method, it has been applied to the model network system. The simulation results showed that the system provided equal control performance with fewer control steps than conventional systems.

A Hybrid Genetic Algorithm for Service Restoration Problems in Power Distribution Systems

This paper proposes a hybrid genetic algorithm (GA) for addressing service restoration problems in power distribution systems. The authors have already proposed a GA-based algorithm, called the two-stage GA, and this algorithm has been shown to perform well for small systems. However, it is difficult to apply to large systems from the viewpoint of computation time. To improve the time performance of the algorithm, the authors introduce three kinds of speedup strategy: a local search procedure, greedy algorithm, and efficient maximum flow algorithm. Computational results with several test systems show that the proposed hybrid algorithm can dramatically reduce the computation time compared with the two-stage GA, and can be applied to real-scale systems.

Fast optimization method for service restoration in sub-transmission systems with priority loads

This paper proposes a new optimization method for service restoration in sub-transmission systems. The proposed method has some functions to ensure feasible switching operations and to speed up the optimization process. To adequately assess the unrestored total power after network switching operation, we model it as a restoration priority constrained maximum subset-sum problem. Moreover, the method uses only three promising candidates for the final radial configuration to speed up the process. Computational results with a test sub-transmission system show that the proposed method can find better solutions faster than the existing method.

Short circuit current estimation using PMU measurements during normal load variation

This paper purposes a short circuit current estimation method using phasor measurement unit (PMU) measurements (synhcrophasors, hereafter called as phasors) of voltages and currents obtained during normal load variation. The method follows the basic concept of representing the source side of power system by an equivalent circuit with a voltage behind back impedance and employs a set of voltage and current phasors measured at substations over a certain period. In order to improve an accuracy of the proposed estimation method, the concept of using a difference between the two consecutive phasors is introduced. Furthermore, to make the method applicable to a real world system, the estimation process is augmented by implementing a reference phasor concept to remove the effects of system wide frequency variations and a filtering process to filter out the outlier phasors. Finally, the validity and effectiveness of the purposed methods were checked and confirmed using field tests.

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.

Application of Decision Tree Classification to the Probabilistic TTC Evaluation

AbstractTotal transfer capacity (TTC) is an index used to provide the system operators with key information necessary for the transmission network security and energy trading management. In contrast to deterministic methods, probabilistic methods are justified since they can effectively deal with the uncertainty associated with the system parameters and conditions. In addition, they are also able to cope with wind power generation which has uncertain and fluctuating power output characteristics. In this paper, the TTC is computed using Monte Carlo simulation with transient stability consideration. To alleviate the computational burden due to the addition of the transient stability constraint, decision tree classification is used as a prediction tool for the transient stability assessment during the TTC evaluation. The effectiveness of the proposed method is demonstrated through a numerical example conducted on the modified IEEE 30-bus test system integrated with wind power.

Calculation of transformer saturated leakage inductance based on field test data

In a black start of a power system, at times, an overvoltage could be caused by core saturation on the energization of a transformer with residual flux. Such an over-voltage might damage some equipment and delay power system restoration. Through an actual field test and EMTP simulations, we have found that such phenomena cannot be accurately simulated using a normal transformer model with inductance data measured during the factory test. This paper proposes a new calculation scheme of transformer inductance by using actual field test data in order to grasp the saturated transformer characteristics accurately. We also show an analytical scheme for calculating the leakage inductances from shunt currents in delta windings that give extensive influence to over-voltage under flux saturation