• Energy Research

Inertia emulation is claimed to play a decisive role in the regulation and management of frequency in modern electrical systems. The support offered by renewable energy power plants and distributed generators is key to diminish the rate of change of frequency (RoCoF), as many synchronous generators are being replaced all around the globe. It is a reality that the implementation of the swing equation in the power converter control has been the core of several proposals on grid-forming controllers to emulate inertia. This kind of controller has been heavily studied and integrated in some demonstrators around the world during the last years, providing dynamic inertia support functionalities. However, the need to modify the synchronization strategy in already deployed power units has been one of the key opposition factors on industry, leading to a severe shortcoming on the integration. In contrast to the traditional swing equation implementation this paper presents a lightweight inertial phase-locked loop (IPLL) able to take the most of inertial features introducing minor changes on classical power converter control and synchronization structures. As shown in this work, the straightforward implementation significantly reduces the technological and computational effort compared to other synchronous emulation proposals. Moreover, it integrates not only dynamic inertial response to the converter, but also all grid-forming capacities to the power conversion unit. This modification on the synchronization structure enables the converter to work in grid-following mode in grid-tied applications, and grid-forming in islanded ones. The integration of the proposed IPLL, the stability analysis and a sample of its performance in HIL and experimental environments will be presented in this paper. This work was supported by the Margarita Salas Program promoted by the Spanish Ministry of Universities under Grant GA 94126. Peer Reviewed

Inertia emulation is claimed to play a decisive role in the regulation and management of frequency in modern electrical systems. The support offered by renewable energy power plants and distributed generators is key to diminish the rate of change of frequency (RoCoF), as many synchronous generators are being replaced all around the globe. It is a reality that the implementation of the swing equation in the power converter control has been the core of several proposals on grid-forming controllers to emulate inertia. This kind of controller has been heavily studied and integrated in some demonstrators around the world during the last years, providing dynamic inertia support functionalities. However, the need to modify the synchronization strategy in already deployed power units has been one of the key opposition factors on industry, leading to a severe shortcoming on the integration. In contrast to the traditional swing equation implementation this paper presents a lightweight inertial phase-locked loop (IPLL) able to take the most of inertial features introducing minor changes on classical power converter control and synchronization structures. As shown in this work, the straightforward implementation significantly reduces the technological and computational effort compared to other synchronous emulation proposals. Moreover, it integrates not only dynamic inertial response to the converter, but also all grid-forming capacities to the power conversion unit. This modification on the synchronization structure enables the converter to work in grid-following mode in grid-tied applications, and grid-forming in islanded ones. The integration of the proposed IPLL, the stability analysis and a sample of its performance in HIL and experimental environments will be presented in this paper. This work was supported by the Margarita Salas Program promoted by the Spanish Ministry of Universities under Grant GA 94126. Peer Reviewed

Global warming is already having significant and costly effects on our communities, our health, and our climate. Nowadays, In developing countries (G20) around the world, decisions are being considered and a shifting of our dependence from fossil fuels to renewable energy sources (RES). Among RES solar energy, specially photovoltaic system (PV) play a key role in this challenge, thus, this paper provides a comparative study on the performances of three transformer-less inverters for photovoltaic applications (H-Bridge, H5, HERIC and NPC inverters) in terms of power losses, considering the use of different kinds of switches. Silicon (Si) and Silicon Carbide (SiC) diodes have been combined with two topologies of IGBTs in the performed tests. Simulation results have been obtained for each of the systems in different operating conditions by using PLECS software. Power losses and European Efficiency (EE) have been calculated for all the topologies, taking into account the real characteristics of the switches by using the thermal models provided by the software library. Peer Reviewed

Global warming is already having significant and costly effects on our communities, our health, and our climate. Nowadays, In developing countries (G20) around the world, decisions are being considered and a shifting of our dependence from fossil fuels to renewable energy sources (RES). Among RES solar energy, specially photovoltaic system (PV) play a key role in this challenge, thus, this paper provides a comparative study on the performances of three transformer-less inverters for photovoltaic applications (H-Bridge, H5, HERIC and NPC inverters) in terms of power losses, considering the use of different kinds of switches. Silicon (Si) and Silicon Carbide (SiC) diodes have been combined with two topologies of IGBTs in the performed tests. Simulation results have been obtained for each of the systems in different operating conditions by using PLECS software. Power losses and European Efficiency (EE) have been calculated for all the topologies, taking into account the real characteristics of the switches by using the thermal models provided by the software library. Peer Reviewed

The development and implementation of energy storage solutions is essential for the sustainability of renewable energy penetration in the electrical system. In this regard, power-to-gas technologies are useful for seasonal, high-capacity energy storage. Bioelectrochemical systems for electromethanogenesis (EMG-BES) represent an additional power-to-gas technology to the existing chemical and biological methanation. EMG-BES process can be retrofitted in traditional anaerobic digesters, with advantages in terms of biologic process stability and high-quality biogas production. Nowadays, there are no reported studies of scaled-up EMG-BES plants for energy storage. The present work describes the setup and operation of a medium-scale EMG-BES prototype for power-to-gas, storing energy in the form of biomethane. The prototype was built by stacking 45 EMG-BES cells, accounting for a total volume of 32¿L. It was continuously fed with 10¿L¿day-1 municipal wastewater, and it was long-term operated at different voltage and temperature ranges. A steady-state current density demand of 0.5¿A¿m-2 was achieved at 32¿°C while producing 4.4¿L¿CH4¿m-2¿d-1 and removing 70% of the initial organic matter present in wastewater. Microbial competition between electro-active bacteria and acetoclastic methanogens was observed. Energy storage efficiency was estimated around 42–47%, analyzing surplus CH4 production obtained when applying voltage to the stack. A first order electric model was calculated, based on the results of a series of electrical characterization tests. The model may be used in the future to design the converter for EMG-BES plant connection to the electrical grid. The obtained results show that energy storage based on EMG-BES technology is possible, as well as its future potential, mixing renewable power overproduction, biomethane generation and wastewater treatment under the circular economy umbrella. Peer Reviewed

The development and implementation of energy storage solutions is essential for the sustainability of renewable energy penetration in the electrical system. In this regard, power-to-gas technologies are useful for seasonal, high-capacity energy storage. Bioelectrochemical systems for electromethanogenesis (EMG-BES) represent an additional power-to-gas technology to the existing chemical and biological methanation. EMG-BES process can be retrofitted in traditional anaerobic digesters, with advantages in terms of biologic process stability and high-quality biogas production. Nowadays, there are no reported studies of scaled-up EMG-BES plants for energy storage. The present work describes the setup and operation of a medium-scale EMG-BES prototype for power-to-gas, storing energy in the form of biomethane. The prototype was built by stacking 45 EMG-BES cells, accounting for a total volume of 32¿L. It was continuously fed with 10¿L¿day-1 municipal wastewater, and it was long-term operated at different voltage and temperature ranges. A steady-state current density demand of 0.5¿A¿m-2 was achieved at 32¿°C while producing 4.4¿L¿CH4¿m-2¿d-1 and removing 70% of the initial organic matter present in wastewater. Microbial competition between electro-active bacteria and acetoclastic methanogens was observed. Energy storage efficiency was estimated around 42–47%, analyzing surplus CH4 production obtained when applying voltage to the stack. A first order electric model was calculated, based on the results of a series of electrical characterization tests. The model may be used in the future to design the converter for EMG-BES plant connection to the electrical grid. The obtained results show that energy storage based on EMG-BES technology is possible, as well as its future potential, mixing renewable power overproduction, biomethane generation and wastewater treatment under the circular economy umbrella. Peer Reviewed