Symmetrical angle switched single-phase and three-phase rectifiers: application to micro hydro power plants

Micro-size hydro power plants are commonly used at remote areas to supply islanded AC microgrids. A typical way to control grid frequency is to manipulate active power dissipated in ballast loads by AC/AC converters. However, these asymmetrically switched thyristor controlled converters consume reactive power degrading the power factor at the generator output. In this paper the operation of a symmetric angle switched, bridged three-phase rectifier and three single-phase rectifiers connected in series with ballast load, are studied to improve the power factor of the system. As a consequence, the objective is to evaluated the use of the three and single-phase rectifiers switched with symmetrical angle to improve the power factor, by reactive power compensation, at the output terminal of the electric generator of µHPPs that use ballast load to regulate frequency.Postprint (published version

Scenarios for future power system development in Finland

This paper demonstrates how various part-solutions can be combined in different scenarios for a more climate-neutral electric energy system. The case study is the Finnish electric energy system. Four scenarios are discussed. A base scenario for 2030 consists of already agreed future investments in new energy production facilities by 2022 supplemented by additional consumption and a moderate increase in renewable energy generation. Alongside the base scenario 2030, two scenarios with more ambitious renewable energy targets and flexibility issues are examined. The fourth scenario is for year 2050 analyzing the operational properties of the system with high share of variable renewable generation, flexible loads, and high-capacity energy storages. These scenarios help to assess how, for example, investing in wind or solar production, heat pumps on a large scale or the battery storage of electric vehicles influences the other components of the system and the implications for emissions.publishedVersionPeer reviewe

Evaluation of the symmetrically-switched converter structures on the frequency regulation of standalone micro hydro power plants

Micro hydro power plants (¿HPP) are typically used to supply electric energy to microgrids outside the national power grids taking care of the frequency control of the isolated system. A conventional way to maintain the load balance in the system is to use thyristor switched AC-AC converters controlled dump loads. A disadvantage of the AC-AC converters is their reactive power consumption decreasing the power factor at the generator output. To avoid this problem the authors have earlier proposed two converter topologies utilizing symmetrical switching scheme resulting to zero reactive power consumption. The objective of this paper is to evaluate the frequency regulation loop performance of the dump load controlled single generator system by using the symmetrically switched converter structures. Evaluation is carried out by analyzing the performances of different converter structures in a simulator representing the operation of a Cuban ¿HPP “Los Gallegos”. The results showed that the frequency regulation loop performance using each proposed converter structure satisfied the Cuban standard of frequency regulation, but with the symmetrically switched structures reactive power consumption was reduced resulting to reduced losses and improved effective current delivery capacity of the generator.Postprint (published version

Symmetrical angle switched single-phase and three-phase rectifiers: application to micro hydro power plants

Micro-size hydro power plants are commonly used at remote areas to supply islanded AC microgrids. A typical way to control grid frequency is to manipulate active power dissipated in ballast loads by AC/AC converters. However, conventional asymmetrically switched thyristor controlled converters consume reactive power degrading the power factor at the generator output and transmission efficiency. In this paper the operation of a symmetric angle switched, bridged three-phase rectifier and three single-phase rectifiers connected in series with ballast load, are studied to improve the power factor of the system. The objective is to evaluate the characteristics of these two configurations to improve the power factor of the system.Peer ReviewedPostprint (published version

Evaluation of the symmetrically switched converter structures on the frequency regulation of standalone micro hydro power plants

Micro hydro power plants (µHPP) are typically used to supply electric energy to microgrids outside the national power grids taking care of the frequency control of the isolated system. A conventional way to maintain the load balance in the system is to use thyristor switched AC-AC converters controlled dump loads. A disadvantage of the AC-AC converters is their reactive power consumption decreasing the power factor at the generator output. To avoid this problem the authors have earlier proposed two converter topologies utilizing symmetrical switching scheme resulting to zero reactive power consumption. The objective of this paper is to evaluate the frequency regulation loop performance of the dump load controlled single generator system by using the symmetrically switched converter structures. Evaluation is carried out by analyzing the performances of different converter structures in a simulator representing the operation of a Cuban µHPP “Los Gallegos”. The results showed that the frequency regulation loop performance using each proposed converter structure satisfied the Cuban standard of frequency regulation, but with the symmetrically switched structures reactive power consumption was reduced resulting to reduced losses and improved effective current delivery capacity of the generator.Postprint (published version

Solar microsystem modeling and simulation: photovoltaic inverter control based on energy technical product quality criteria

In this work an analysis of the quality of electric power in off-grid solar photovoltaic microsystems is carried out. Applied to an existing case study in an island developing country like Cuba, the purpose is to control the bridge inverter to reduce the effect of harmonics. The tripping of the switches is controlled by pulse width modulation (PWM). The design is computer aided with Simulink / Matlab. The testing of different control strategies in these systems resulted proposing the design method of a Proportional - Resonant controller control system. The results with an isolated single-phase system with a residential load reveal the reduction of the total harmonic distortion (THD) in the voltage at the output of the solar PV inverter filter to the AC load.publishedVersionPeer reviewe

Possibilities and challenges of developing a 100% renewable electricity system in Cuba

The use of renewable energy sources (RES) has increased exponentially worldwide as an alternative to the indiscriminate use of fossil fuels and to mitigate their effect on the environment. Unfortunately, around 95% of electricity production in Cuba is based on fossil fuels. However, the Cuban government has planned a change in the energy matrix and made the most of the renewable resources available at the national level. Recently, the Cuban authorities have discussed different possibilities and ways to develop a 100% renewable electricity system. This article analyzes possible scenarios in Cuba to achieve a 100% renewable electricity system by 2050. The fundamental emphasis is on building electricity consumption scenarios for different sectors of the national economy and creating retrospective electricity supply scenarios, complying with the objectives of increasing the participation of renewable energies in the electricity production mix. The results were obtained using the CubaLinda model

Optimized utilization of groundwood lines with single layer grinding surfaces for pulp production and electrical grid stabilization

The climate change is forcing the power production from controllable fossil-based combustion to intermittent renewable resources like wind and solar power. The power production and consumption must be equal at all moments to stabilize the power system. This has traditionally been achieved with controllable production but the new situation with intermittent production requires new solutions. One solution is demand response that means flexible consumption to achieve balance between production and consumption in the power system. This paper analyzes the techno-economical possibilities for groundwood lines with single layer grinding surfaces to both produce pulp and to participate in electrical grid stabilization. Thanks to the on/off nature of the batch processing and the fast-loading response in wood grinding the process is suitable also for more valuable reserve markets. Based on the measured loading response, reserve requirements and marketplace prices investments for participation in Frequency containment reserve for normal operation (FCR-N) and Fast frequency reserve (FFR) have a payback time shorter than 10 months that is attractive for forest industry. After payback the annual earnings are significant.acceptedVersio

Electricity supply with renewable energy sources and the Cuban electricity system: Challenges of supply-demand balance Suministro de electricidad con fuentes renovables de energía y el sistema eléctrico cubano: Desafíos del equilibrio generación-demanda

The article describes possible scenarios for the future development of the Cuban electricity system. The plans of increasing electricity supply from intermittent energy source like solar PV and wind power create challenges in balancing the supply-demand in the context of varying load curve. Different scenarios for future electricity demand are constructed based on different potential paths for economic development and technological changes in the consumption side. In addition, different scenarios for electricity supply are constructed to reflect potential differences in the construction of renewable electricity supply capacity. Also the potential use of energy storage, in the form of pumped hydro capacity, is analysed. The storage capacity can reduce the demand for peak power capacity. It can also reduce the required ramping rates for the fossil fuel power plants for balancing supply and demand. Scenarios are constructed using CubaLinda model having hourly production and consumption calculations up to 2050. The model produces information of fuel demand and the CO2 emissions related to the different scenarios as well as the costs of electricity production.</p