The World Energy Council, in its 2019 World Energy Scenarios Report, advised policymakers to identify innovative opportunities for the integration of renewable energy resources into existing electrical power systems to achieve a fast and affordable solution. However, large-scale industries with cogeneration units are facing problems in handling the higher penetration levels of intermittent renewable energies. This paper addresses large-size photovoltaic power integration problems and their optimal operation. This work considers the case of a chemical industry having both cogeneration power and solar photovoltaics. Here, a modified firefly algorithm and a hybrid power resource optimization solver are proposed. The results of the proposed method are compared with other benchmark techniques, to confirm its advantages. The proposed techniques can be used in industries having cogeneration power plants with photovoltaics for better optimization and to meet the guidelines specified in IEEE 1547. The voltage ramp index is proposed to determine the voltage ramp up and down with intermittent solar irradiance. Additionally, a machine learning technique is used to predict the cogeneration plant efficiency at different loads and the solar irradiance under varying weather conditions. Finally, this paper proposes the effectiveness of the modified heuristic technique and certain guidelines, including solvers for industrial use.

Optimal Operation of a Photovoltaic Integrated Captive Cogeneration Plant with a Utility Grid Using Optimization and Machine Learning Prediction Methods

This paper proposes a new approach to estimate the inertia of the 60 Hz Japanese power system from the background signals of phasor measurement units. Regarding the constraint boundaries, the entire system is divided into two control areas, which can be represented by an equivalent two-generator model based on small-signal stability analysis. The ambient inertia of each area, including both generation and demand sides can be estimated by measuring the corresponding phase difference and interchange power with respect to the extracted proportions of the frequency response, inter-area oscillation, and synchronizing power. Then, the sum of the estimated inertia for each area gives the total inertia of the entire 60 Hz system. The method was validated on the benchmark model of the Japan transmission network, and its sensitivity is evaluated by conducting various system operations on generator control effects. The efficiency and robustness were verified through real measurements under diverse system conditions. The results confirm that the developed approach can accurately estimate the system inertia during normal operation, enabling nearly continuous inertia tracking trajectory. 

Inertia Estimation of the 60 Hz Japanese Power System From Synchrophasor Measurements

This paper proposes a new approach to estimate the inertia of the 60 Hz Japanese power system from the background signals of phasor measurement units. Regarding the constraint boundaries, the entire system is divided into two control areas, which can be represented by an equivalent two-generator model based on small-signal stability analysis. The ambient inertia of each area, including both generation and demand sides can be estimated by measuring the corresponding phase difference and interchange power with respect to the extracted proportions of the frequency response, inter-area oscillation, and synchronizing power. Then, the sum of the estimated inertia for each area gives the total inertia of the entire 60 Hz system. The method was validated on the benchmark model of the Japan transmission network, and its sensitivity is evaluated by conducting various system operations on generator control effects. The efficiency and robustness were verified through real measurements under diverse system conditions. The results confirm that the developed approach can accurately estimate the system inertia during normal operation, enabling nearly continuous inertia tracking trajectory.

Distributed energy resources (DERs) play an indispensable role in mitigating global warming. The DERs require flexibility owing to the uncertainty of their power output when connected to the power grid. Recently, blockchain technology has actualized peer-to-peer (P2P) energy markets, promoting efficient and resilient flexibility in the power grid. This study aimed to extract insights about the contribution of the P2P energy markets to ensuring flexibility through analyzing transaction data. The data source was a demonstration project regarding the P2P energy markets conducted from 2019 to 2020 in Urawa-Misono District, Japan. The participants in the project were photovoltaic generators (PVGs), convenience stores (CSs), and residences equipped with battery storage as the only flexibility in the market. We quantitatively analyzed the prices and volumes ordered or transacted by each participant. The execution prices purchased by the residences were lower than those purchased by CSs; the differences between execution prices and order prices of the residences were narrower than those of PVGs and CSs; the lower state-of-charge (SoC) in the storage battery induced the higher purchasing prices. Thus, P2P energy markets, where holding flexibility resulted in the advantageous position, can promote installing flexibility through market mechanisms.

Feasibility Conditions for Demonstrative Peer-to-Peer Energy Market

Currently, the substantial renewable penetration brings a low inertia issue to the Japanese power system, threatening stability and resiliency than ever. The inertia estimation based on transient events provides a reliable basis for system control and operation. However, the poor rate of change of frequency extraction from different types and locations of phasor measurement units (PMUs) could significantly lead to inertia estimation errors. As a remedy with a lesson learned, this paper analyzes effective inertia estimations based on transient measurements of the Japanese wide-area monitoring in both distribution and transmission levels. Due to the longitudinally interconnected configuration of the 60 Hz Japanese power system, the polynomial approximation technique is proposed to restrain the strong effect of oscillatory components. To enhance the estimation performance considering an existing center of inertia, the comprehensive mode-shape analysis is performed via geographical measurement locations, indicating sufficient PMUs with precise estimation. The effectiveness of inertia estimation techniques is verified through actual system events corresponding to various transient sites. The numerical results demonstrate that recent inertia of the 60 Hz Japanese system with existing renewables ranges around 7.12 - 8.13 s in its system load base.

https://ieeexplore.ieee.org/ielx7/6287639/6514899/09802111.pdf

Inertia Assessment From Transient Measurements: Recent Perspective From Japanese WAMS

Japan has been experiencing a rapid deployment of photovoltaics (PVs) since the Feed-In Tariff (FIT) Scheme for Renewable Energy was launched in July 2012 . The increasing penetration levels of variable renewable generation, especially PVs and wind, have been affecting power system operations in each of Japan's 10 balancing areas. To accommodate this rapid growth in variable generation, the government established the Working Group on Grid Connection of Renewable Energy in 2014 to continually discuss and make timely decisions about these operational issues, including capacity connections, operation enhancement and asset improvement in each balancing area, and inevitable curtailment procedures for renewable generation.

Hiroshi Wani

Papers

Making Renewables Work: Operational Practices and Future Challenges for Renewable Energy as a Major Power Source in Japan