Mixed H2/H∞ Optimal Voltage Control Design for Smart Transformer Low-Voltage Inverter

The smart transformer has been widely applied for the integration of renewables and loads. For the smart transformer application, the voltage control of low-voltage inverter is important for feeding the load. In this paper, a multi-objective optimization control design approach which comprehensively considers all aspects of indexes, such as linear quadratic (LQ) index, H∞ norm, and closed-loop poles placement, is proposed based on the linear matrix inequality (LMI) solution. The proposed approach is able to alleviate the weight of the designer from the tedious design process of the multiple resonant controllers and the selection of the weighting matrix for the LQ control. Besides that, some excellent performances such as fast recovering time, low total harmonic distortion (THD) and high robustness are achieved by the proposed approach. The THD are 0.5% and 1.7% for linear and non-linear loads, respectively. The voltage drop for linear load step is reduced to 10 V. The proposed approach is applied to a 5 kVA three-phase inverter to yield an optimal control law. Results from the simulation and experiment presented herein will illustrate and validate the proposed approach.

Reliability Metrics for Generation Planning and the Role of Regulation in the Energy Transition: Case Studies of Brazil and Mexico

In recent years electricity sectors worldwide have undergone major transformations, referred to as the “energy transition”. This has required energy planning to quickly adapt to provide useful inputs to the regulation activity so that a cost-effective electricity market emerges to facilitate the integration of renewables. This paper analyzes the role of system planning and regulations on two specific elements in the energy market design: the concept of firm capacity and the presence of distributed energy resources, both of which can be influenced by regulation. We assess the total cost of different regulatory mechanisms in the Brazilian and Mexican systems using optimization tools to determine optimal long-term expansion for a given regulatory framework. In particular, we quantitatively analyze the role of the current regulation in the total cost of these two electricity systems when compared to a reference “efficient” energy planning scenario that adopts standard cost-minimization principles and that is well suited to the most relevant features of the new energy transformation scenario. We show that two very common features of regulatory designs that can lead to distortions are: (i) renewables commonly having a lower “perceived cost” under the current regulations, either due to direct incentives such as tax breaks or due to indirect access to more attractive contracts or financing conditions; and (ii) requirements for reliability are often defined more conservatively than they should be, overstating the hardships imposed by renewable generation on the existing system and underestimating their potential to form portfolios.

Assessment of Renewable Electricity Policy for Sustainable Electricity Generation in Nigeria

Nigeria commits to fast track the integration of renewables in electricity generation by enacting a 2015 National Renewable Energy and Energy Efficiency Policy (NREEEP). Thus, this policy briefing assesses the effect of the policy, and other socioeconomic factors, on the deployment of renewable electricity generation. The preliminary findings show that renewable energy policy has little effect in facilitating renewable electricity integration in Nigeria due to lack of political will and its adverse effect evident in the non-implementation of incentives like feed-in-tariffs and a zero import duty waiver. Second, increased fossil fuel consumption impedes the deployment of renewable electricity due to the hydrocarbon endowment and its subsidization. The domestic financial market development in Nigeria does not also support the deployment of renewable electricity that requires long-term finance. It requires a political will to strengthen the legal and institutional framework for a sustainable electricity generation deployment. It is also pertinent to consider the total removal of fossil fuel subsidies for renewable electricity integration.

A Multi-Factorial Review of Repowering Wind Generation Strategies

The integration of renewables into power systems is a key transformation for mitigating climate change and reducing fossil-fuel dependence. Among the different resources, wind participation has become crucial in recent decades—both onshore and offshore wind power plants. However, assuming the useful life of the wind turbines at approximately 20 years, different solutions should be discussed to overcome the turbine’s aging problem. In the coming years, some countries within the wind sector will face the decision of partially or totally repowering or dismantling their turbines. This paper reviews different repowering strategies and contributions from a multifactorial perspective. A set of categories is defined by the authors and those multifactorial parameters are then classified according to such categories: technical, economic, environmental, social, and political. From each category, the most relevant factors to be considered for repowering decision-making purposes are identified and discussed. According to the specific literature, more than 90% of the reviewed contributions are focused on onshore wind power plant repowering actions. This percentage is in line with onshore and offshore wind generation units installed in recent decades. The reviewed studies show that Germany has a major number of contributions. Regarding offshore repowering strategies, all contributions propose a multifactorial analysis, in contrast to onshore repowering strategies where only 68% of the authors carry out a multifactorial analysis. The revised repowering methodologies and the categorization of factors can also be used by the repowering market, as a useful tool in the near future.

Shedding Light on the Factors That Influence Residential Demand Response in Japan

Residential demand response empowers the role of electricity consumers by allowing them to change their patterns of consumption, which can help balance the energy grid. Although such type of management is envisaged to play an increasingly important role in the integration of renewables into the grid, the factors that influence household engagement in these initiatives have not been fully explored in Japan. This study examines the influence of interpersonal, intrapersonal, and socio-demographic characteristics of households in Yokohama on their willingness to participate in demand response programs. Time of use, real time pricing, critical peak pricing, and direct load control were considered as potential candidates for adoption. In addition, the authors explored the willingness of households to receive non-electricity related information in their in-home displays and participate in a philanthropy-based peer-to-peer energy platform. Primary data were collected though a questionnaire survey and supplemented by key informant interviews. The findings indicate that household income, ownership of electric vehicles, socio-environmental awareness, perceived sense of comfort, control, and complexity, as well as philanthropic inclinations, all constitute drivers that influence demand flexibility. Finally, policy recommendations that could potentially help introduce residential demand response programs to a wider section of the public are also proposed.

Risk-Benefit Assessment Scheme for Renewable Solar Solutions in Traditional and Historic Buildings

Within the framework of IEA-SHC Task 59, a multidisciplinary team of experts from around the world has come together to investigate current approaches for energy retrofit of the built heritage with energy efficiency conservation-compatible measures, in accordance with cultural and heritage values, and to check and adapt the new standard EN-16883:2017 for historic buildings. This paper introduces activities within IEA-SHC Task 59 (Subtask C) focused on retrofit solutions with high impact on sustainability, energy efficiency, and the integration of renewables, which is the main goal of the solar group, focused on the integrated solar systems for historic buildings. Relying on an extensive, detailed, and accurate collection of case studies of application of solar photovoltaic and thermal systems in historic buildings, the assessment criteria of the standard have been reviewed and tailored for better solar implementation evaluation in a heritage context. All this is studied based on technical compatibility, the heritage significance of the building and its settings, the economic viability, the energy performances and indoor environmental quality and use, as well as the impact on the outdoor environment of solar renewables.