Research

All SEA-UNIOVI activities are focused on the study of efficient electrical energy conversion and, more specifically, on power electronic converters designed to supply different types of loads. However, the diversity of types of loads, input and output voltages, power handled, dynamic specifications and types of electronic devices used, means that the different projects presented are grouped together. The following is an attempt to reflect the lines of work and research on which the members of the SEA-UNIOVI have habitually worked and continue to work over the last 5 years.
 
Electronic circuits for powering LED lighting diodes (LEDs)
In this line, research is carried out into the power supply of LED diodes, which are DC loads, from AC electrical power distribution systems (single-phase and three-phase) and from very low DC voltages (1.5 V and lower). In recent years, research has focused on the elimination of electrolytic capacitors, with the aim of extending the lifetime of the entire lighting system. Another sub-line which has produced very good results in recent years is the analysis of DC/DC converters with very high efficiency as second stages.
 
Domestic direct current (DC) distribution
The aim of this line is to verify, in a real situation, the advantages and limitations of the use of DC in a future distribution of electrical energy in households. It is well known that an important part of the loads connected to domestic networks are DC loads (LED lighting, multimedia consumer electronics, battery chargers, etc.) and another important part are not DC loads, but the energy that feeds them is converted from AC to DC at some point before acquiring its final form (actuators of various types of AC motors, for example). For this reason, DC distribution can have significant advantages in terms of saving power electronic converters to carry out the electrical energy transformations (which saves energy), but on the other hand it requires that alternatives be determined.
 
This is the focus of the work in this line and, as a starting point, a "bus provider" platform for an original DC power distribution system has been developed.
 
Use of Modular Converters (MOD)
In general, standardisation saves design time and leads to better products. This extends to power electronics, but the disparity of situations with regard to power ratings and voltages to be handled poses an additional difficulty. Fortunately, modularisation helps to overcome this problem, since the grouping of several power electronic converters makes it possible to multiply the capacity to handle power, to accept input voltages and to generate output voltages.
The research in this case focuses on determining the topologies, operating modes and controls that are best for the converter "cell" and the strategy of operating all cells together.
 
Characterisation and use of silicon carbide and gallium nitride electronic devices in power electronic converters (SiC and GaN) 
Electronic devices based on gallium nitride (GaN) have been used for many years in radio spectrum or RF oriented applications. However, their use in electrical power conversion applications is relatively recent. As they are not MOSFET transistors, but of the High-Electron-Mobility Transistors (HEMTs) type, their use in power electronic converters is not without difficulties, which has delayed their application. The particularities of the governance of these devices (as they are in some cases "normally closed" switches), the location of applications in which their advantages compensate for their higher cost and the search for specific topologies for them is, and will continue to be, the subject of research at SEA-UNIOVI.
Power electronic devices based on silicon carbide (SiC) have much higher electric breakdown fields than silicon (Si) (between 7 and 10 times higher), which makes them very suitable for working at high voltages. The thermal conductivity of SiC is 3 times higher than that of Si. This fact, together with the previous one, determines that the field of application of SiC will be towards high power electronic devices, where thermal management and switching at high voltage levels and high frequencies is feasible, which is not currently the case with Si. The SEA-UNIOVI group is studying the possibility of using these devices in on-board applications (the most electric aircraft, the electric train and the electric vehicle), solid-state transformers, integration of renewable energies, smart grids, etc.
 
Very fast response converters for envelope tracking applications in power amplifiers and for visible light communications (ET and VLC)
These are 2 research topics in which SEA-UNIOVI has developed a very relevant and original activity in the last 15 years. In both cases, the aim is to develop power electronic converters with extraordinarily fast dynamic response, which requires new devices and new topologies (in the latter field, SEA-UNIOVI has been particularly active). The difference between the two cases (Envelope Tracking or ET, and Visible Light Communications or VLC) is the load connected to the output of the converters: in the first case it is a radio frequency power amplifier or RFPAs, for example, the amplifier that in a repeater station raises the level of mobile phone signals to the appropriate value to provide coverage to an area, while in the second case they are LED lighting diodes with which the dual function of illuminating and transmitting information is to be carried out.
The particularity represented by the 2 types of load mentioned above makes it possible to develop new topologies of power electronic converters that are particularly interesting for these applications. In this line, the evaluation of the use of GaN-based power electronic devices (HEMTs) plays a very relevant role. 
 
Characterisation and use of new silicon (Si) power electronics devices
Although the technology of Si-based power electronic devices is mature, there are research niches in behavioural modelling and the application of these models to power loss assessment and reliability estimation of power electronic converters. SEA-UNIOVI continues to focus on the study of the application of Si-based power electronic devices developed by different companies in real and massively used power electronic converters.
 
Study of new converters for satellite power management (ESA)
For the last 7 years, work has been carried out on various projects consisting of looking for alternatives to the electronic power converters currently used in the electrical energy distribution system in satellites. The objectives are the general objectives of power electronics in terms of improving performance, weights, costs and dynamic responses, adding in this case the particularities of redundancy and reliability of equipment which, due to its location, cannot be repaired (although it can be reconfigured on the basis of an order received from the ground or generated in the satellite itself). It is very important to highlight the particularity that this entire system depends on the satellite's mission (it must be custom-designed for the mission), which makes it more expensive and more difficult to design.
 
Power electronic converters for integration in solid-state transformers (SSTs)
This line is an extension of what has been defined as MOD to the particular case of solid state transformers or SSTs. The activity to be developed aims to continue exploiting the possibility of applying power electronics to electrical energy distribution systems, specifically to SSTs. The main objective of SSTs is to replace the traditional 50/60 Hz power transformer using high switching frequency conversion techniques with power electronic converters. The main motivation for the research and development of this technology is to provide a significant reduction in transformer volume and weight, as well as to provide distribution intelligence.
 
Converters to improve the quality of the power grid (LQ)
The activity in this line focuses on the development of active reactive power compensators based on electronic power converters for households. As the title of the line clearly reflects, the singularity of the power electronic converters to be developed lies in the fact that they are for a single-phase installation (with the problems of total pulsed power that this implies) and that they must fit into the domestic environment, where size and safety conditions are more restrictive than in the industrial context. Future work in this line of research is oriented towards compliance with the aforementioned specifications in the domestic environment.
 
Converters for on-board systems (EMB)
For some years now, on-board electronic systems in different types of transport (air, sea and land) have been evolving and increasing day by day. The objectives of this line are the general objectives of power electronics in terms of improved performance, cost, dynamic response, reliability, size, weight and cost. The last three are the main priorities in the design of the power electronic converters that make up the power supply systems of these applications: the electric train, the electric car, the more electric or fully electric aircraft and the more electric ship.
 
Other lines in which research work has been carried out:
  • Uninterruptible power supply systems
  • Converters for powering LED diodes
  • Magnetic components
  • Multiport power supplies for renewable energies
  • Dynamic modelling of converters
  • Synchronous rectification
  • Power Factor Correction
  • Low and medium power AC/DC and DC/DC converters
  • Battery chargers
  • Examples of prototypes linked with some research lines:

  •                 Prototypes linked with the research line of converters for space applications

  • Prototype linked to the research of converters for on-board systems

  • Prototype linked to the research line of converters for electric vehicles

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    • Prototypes linked to the research line of converters for visible light communications (VLC)

      • Prototype linked to the research line of converters for solid-state transformers

      •    Prototypes linked to the research line of power supplies design. In this case, it was a colaboration with Marshall

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