Takaaki Ohishi

Dr. Takaaki Ohishi


Research Focus & Metrics

Academic Career Length

5Years (2022-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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28 December 2022 in Energies
Verified
Journal Article
Open access
PDF file
MMMax Olinto Moreira
Max Olinto Moreira
BKBetânia Mafra Kaizer
Betânia Mafra Kaizer
TOTakaaki Ohishi
Takaaki Ohishi
Benedito Donizeti BonattoBenedito Donizeti Bonatto
Benedito Donizeti Bonatto
Antonio Carlos Zambroni de SouzaAntonio Carlos Zambroni de Souza
Antonio Carlos Zambroni de Souza
PBPedro Balestrassi
Pedro Balestrassi
Electric power systems have experienced the rapid insertion of distributed renewable generating sources and, as a result, are facing planning and operational challenges as new grid connections are made. The complexity of this management and the degree of uncertainty increase significantly and need to be better estimated. Considering the high volatility of photovoltaic generation and its impacts on agents in the electricity sector, this work proposes a multivariate strategy based on design of experiments (DOE), principal component analysis (PCA), artificial neural networks (ANN) that combines the resulting outputs using Mixture DOE (MDOE) for photovoltaic generation prediction a day ahead. The approach separates the data into seasons of the year and considers multiple climatic variables for each period. Here, the dimensionality reduction of climate variables is performed through PCA. Through DOE, the possibilities of combining prediction parameters, such as those of ANN, were reduced, without compromising the statistical reliability of the results. Thus, 17 generation plants distributed in the Brazilian territory were tested. The one-day-ahead PV generation forecast has been considered for each generation plant in each season of the year, reaching mean percentage errors of 10.45% for summer, 9.29% for autumn, 9.11% for winter and 6.75% for spring. The versatility of the proposed approach allows the choice of parameters in a systematic way and reduces the computational cost, since there is a reduction in dimensionality and in the number of experimental simulations.

22 May 2025 in Energies
Verified
Journal Article
Open access
PDF file
José OsculloJosé Oscullo
José Oscullo
NONathaly Orozco
Nathaly Orozco
HCHenry Carvajal
Henry Carvajal
Diego EcheverriaDiego Echeverria
Diego Echeverria
JSJosé David Vega Sánchez
José David Vega Sánchez
TOTakaaki Ohishi
Takaaki Ohishi
The growing complexity and uncertainty in modern power systems—driven by increased integration of renewable energy sources and variable loads—underscore the need for robust tools to assess dynamic stability. This paper presents an enhanced methodology for modal analysis that combines Adaptive Variational Mode Decomposition (A-VMD) with Prony’s method. A novel energy-based selection mechanism is introduced to determine the optimal number of intrinsic mode functions (IMFs), improving the decomposition’s adaptability and precision. The resulting modes are analyzed to estimate modal frequencies and damping ratios. Validation is conducted using both synthetic datasets and real synchrophasor measurements from Ecuador’s national power grid under ambient and disturbed operating conditions. The proposed approach is benchmarked against established techniques, including a matrix pencil, conventional VMD-Prony, and commercial tools such as WAProtector and DIgSILENT PowerFactory. The results demonstrate that A-VMD consistently delivers more accurate and robust performance, especially for low signal-to-noise ratios and low-energy ambient conditions. These findings highlight the method’s potential for real-time oscillation mode identification and small-signal stability monitoring in wide-area power systems.

17 July 2024 in Energies
Verified
Journal Article
Open access
PDF file
José OsculloJosé Oscullo
José Oscullo
HCHenry Carvajal
Henry Carvajal
NONathaly Orozco
Nathaly Orozco
JSJosé David Vega Sánchez
José David Vega Sánchez
TOTakaaki Ohishi
Takaaki Ohishi
Ensuring a balance between supply and demand is critical within electricity grids, requiring a supply composition that guarantees consistent service provision in the short and medium term. Between 2008 and 2017, Ecuador’s electricity generation capacity expanded significantly, with an investment of approximately USD 8150 million into harnessing the potential energy of water. This led to the construction of five high-capacity hydroelectric projects by 2017, contributing 33.4% of the sector’s energy output by 2023. However, it is important to note that if installed hydroelectric projects operate as run-of-river plants, with limited reservoir capacity, they can only regulate water use for electricity generation on an hourly basis. As of 2023, these run-of-river plants represent 68.8% of Ecuador’s total hydroelectric capacity within the National Interconnected System (SNI). Consequently, during periods of low inflows, supplementary energy from other power generation plants is necessary to prevent energy crises. This paper addresses the impact on energy storing for electricity generation resulting from the evolution of hydroelectric power plant entry from 2006 to 2023. This aspect has not been thoroughly examined in hydrothermal systems, which primarily focus on potential energy obtained from dams. Our approach involves a statistical analysis of hydroelectric dam reservoir operational levels. We further explore the influence on demand service within Ecuador’s electricity system, particularly during observed energy crises towards the end of 2023.

31 October 2025 in Energies
Verified
Journal Article
Open access
PDF file
José OsculloJosé Oscullo
José Oscullo
LSLuis Fernando Salazar
Luis Fernando Salazar
NONathaly Orozco
Nathaly Orozco
HCHenry Carvajal
Henry Carvajal
JSJosé David Vega Sánchez
José David Vega Sánchez
TOTakaaki Ohishi
Takaaki Ohishi
Modal analysis is essential for evaluating the small-signal stability of power systems by identifying poorly damped oscillatory modes. This paper introduces an automated framework for residue computation directly within DIgSILENT PowerFactory, exploiting its internal state-space matrices and scripting environment. Unlike traditional approaches that rely on external data processing, the proposed method enables a fully integrated, repeatable, and scalable workflow for residue-guided control design. The framework automatically extracts and computes modal residues, quantifying both controllability and observability to identify the most effective control locations. Its application to benchmark systems demonstrates accurate detection of critical modes and effective damping enhancement through residue-based tuning. This integration of automated residue analysis into PowerFactory bridges theoretical modal analysis with practical implementation, offering a novel and efficient tool for oscillatory stability assessment in modern power grids.

10 June 2026 in Energies
Verified
Journal Article
Open access
PDF file
LSLuis Fernando Salazar
Luis Fernando Salazar
Josua Oña AráuzJosua Oña Aráuz
Josua Oña Aráuz
José OsculloJosé Oscullo
José Oscullo
NONathaly Orozco
Nathaly Orozco
HCHenry Carvajal
Henry Carvajal
TOTakaaki Ohishi
Takaaki Ohishi
Hybrid transmission corridors combining overhead lines and underground cables introduce impedance discontinuities that significantly modify electromagnetic transient behavior. These discontinuities generate traveling-wave reflections, waveform distortions, and high-frequency components at relay measurement locations during the first microseconds following disturbance inception. This paper presents a waveform-level electromagnetic transient (EMT) analysis of overhead–cable transition effects using detailed EMTP-RV simulations including frequency-dependent line and cable models, tower representations, grounding systems, and instrument transformers within a differential protection measurement framework. The results show that overhead–cable transitions produce transient waveform modifications characterized by reflections, attenuation, dispersion, and temporary current imbalance mechanisms associated with traveling-wave propagation and cable capacitive effects. The analysis also demonstrates the transient evolution of instantaneous waveform-derived (EMT-derived) differential and restraining current quantities, defined as combinations of terminal current signals obtained directly from EMT waveforms. These quantities do not represent final phasor-domain operating values of practical numerical relays, but provide insight into the transient electromagnetic environment preceding conventional filtering and phasor estimation. The study contributes to a clearer physical interpretation of transient phenomena in hybrid transmission systems and supports EMT-based evaluation of signals relevant to differential protection applications.

9 May 2024
Verified
Conference Paper
Open access
PDF file
RGRodrigo Luiz Gigante
Rodrigo Luiz Gigante
AAAnibal Tavares de Azevedo
Anibal Tavares de Azevedo
TOTakaaki Ohishi
Takaaki Ohishi
Rapid availability of ambulance services is crucial to saving lives in medical emergencies. The strategic location of ambulance bases plays a fundamental role in the efficiency and speed of service. This paper proposes an approach based on clustering methods to determine the optimal location of ambulance bases. The study uses clustering techniques to identify the best location for the bases using historical data on emergency calls and their geographic characteristics. The results demonstrate that the clustering approach can improve the allocation of bases and, therefore, improve coverage for the population. Ambulance bases are then positioned in central locations within each cluster, maximizing coverage and minimizing response times. This study highlights the possibility of using clustering methods to determine the optimal location of ambulance bases. By considering spatial patterns and demand for services, the proposed methodology can improve the efficiency of the emergency care system, resulting in shorter response times. The application of this methodology can guide urban planning decisions and resource allocation strategies in health systems, ensuring an efficient distribution of emergency services and, consequently, saving lives.