Universitat Rovira i Virgili
Campus of International Excellence Southern Catalonia
Group of Automatic Control and Industrial Electronics

PROJECTS IN PROGRESS

PROJECTS IN PROGRESS

There are currently four projects being developed by GAEI:

Ultrafast Charging of Electric Vehicles

The main goal of the project is to propose solutions to the problems caused by the absence of fast charging infrastructure for electric vehicles of battery.

In particular, the project aims to perform a study of realistic scenarios to implement fast charging stations that (i) can be easily integrated in the medium voltage (MV) or low voltage (LV ) networks , (ii) allow the inclusion of energy storage (iii) permit the insertion of renewable energy and (iv) will be capable to supply simultaneously several vehicles.

Complementarily, as a proof of concept, we will implement a reduced scale demonstrator of an ultrafast battery charger that will be supplied by a hybrid microgrid of modular type.

The study of different scenarios for a fast charging station design will be carried out at real scale and the design will be performed with the existing technology, namely, low-frequency magnetic transformers and commercial converters and fast chargers. The multiplicity of scenarios should lead to consider MV or LV connection, different types of energy storage systems as well as the insertion of PV and/or wind energy.

In the demonstrator design, a microgrid of modular type will be implemented, so the addition of an important number of similar microgrids like the one of the demonstrator would be equivalent to a commercial fast charger in terms of power and current. The scale factor of the microgrid will be related to the number of modules required to provide the power and current features of a commercial charger. In the demonstrator the battery charging should be faster than that of a commercial charger.

Intelligent Active Damping in Microgrids and Electric Vehicles

The main goal of the project is stabilizing the power distribution system in microgrids and electric vehicles EVs using a new active approach based on the concept of Loss Free Resistor (LFR) without compromising the efficiency. The project aims at the implementation and the use of LFRs for Intelligent Active Damping System (IADS) in microgrids and EVs in which the LFR can be connected as an auxiliary power stage. The LFR-based IADSs can be synthesized by using suitable power converters under sliding mode control (SMC). New solutions for the stabilization of power distribution systems using IADSs will be proposed. Specifically, the design of IADSs will be addressed to stabilize the power train of EVs operating in constant power regime and microgrids with tightly regulated load converters acting as CPL for the source converters. To achieve this goal, some open problems must be addressed; the most important ones are listed below:

Modular Prototype for Ultrafast Charging of Electric Vehicles

The goal of this project is implementing a small-scale demonstrator for ultrafast (UF) charging of the battery of an electric vehicle using a LV three-phase AC grid as a primary source. The electrical architecture of the demonstrator will be made up of two conversion stages in cascade connection, namely an isolated three-phase rectifier with power factor correction and a unidirectional modular non-isolated DC-DC switching converter loaded by the electric vehicle battery. While existing solutions will be used for the rectifier, the research will be concentrated in the design and implementation of the second stage because it constitutes the bottleneck of UF charging.

First of all, conventional topologies for unidirectional power flow will be investigated in hard-switching and resonant modes regarding their capability of association. Then, they will be compared with other solutions based on paralleling canonical elements for power processing such as loss-free resistors or gyrators. Special emphasis will be given to the control strategy to ensure both the stable association of the modules for the UF charger assembling and an appropriate power sharing among them. A hierarchical control strategy will be subsequently introduced to supervise the interaction between the battery and the converter, and ad-hoc communications functions will be implemented in the digital devices of the hardware set-up.

Circuit boards, electric elements and protections corresponding to the three-phase rectifier, the modular unidirectional converter plus local and supervisory controllers would be embedded in a transportable box that could eventually be plugged to a 50 Hz LV three-phase AC grid with enough power capacity for UF charging.

Universal On-Board Battery Charging Platform for Electric Vehicles

The aim of the project is to facilitate the integration of electric vehicles (EVs) in a more sustainable and respectful with the environment transportation system by improving the performance (efficiency) of two-stage isolated on-board charger of electric vehicles. Usually, two-stage on-board chargers are composed by a PFC stage (AC/DC conversion) connected to the grid and cascaded with a second stage (DC/DC converter), which is responsible to manage the energy flow towards the battery in charging mode (grid to vehicle, G2V) or from it in discharging mode (vehicle to grid, V2G). This second converter also guarantees galvanic isolation between the battery and the first stage and, ultimately, the grid.

The converter topologies most used in the isolated DC-DC conversion role are the resonant LLC converter and the phase-shifted full-bridge converter. According to the literature, both converters offer less power efficiency when they operate with large variations in their input-output voltage ratios, which result in switching frequencies away from the resonant frequency and/or the loss of soft switching (ZVS). We pretend to improve the system efficiency by substituting the first stage step-up converters used to maintain a fixed dc-link voltage value and to guarantee good power factor correction (PFC). These converters will be replaced by step up/down converters providing a variable dc-link voltage that could be smaller than the peak grid voltage. In this way, the second stage DC/DC converter would operate around its most efficient working point while guaranteeing good PFC.

A study will be carried out on step up/down structures and their performances as PFC rectifiers so that the most suitable ones for the considered power levels (3,6 kW and 11 kW) can be selected. Also, the necessary digital control loops that will allow the system to operate as PFC, regulating at the same time their output voltage to track a variable reference, must be designed. This implies obtaining a good dynamic model of the system.

In order to evaluate the global efficiency of the two-stage system, the second stage isolated DC/DC converter and its respective control loops must be also designed. The final goal is to obtain a bidirectional 11-kW two-stage on-board charger for EVs.

Control-oriented Design Methodologies for Extending the Stability Margin of Hybrid Microgrids at Different Timescales

Hybrid microgrids that utilize several forms of energy carriers, multiple energy storage systems (ESSs), local distributed generation (DGs) and a multiple demanding loads form a complicated system that needs to be accurately modelled and controlled. One fundamental difference between traditional power networks and today's microgrids is the local generation, storage and consumption of energy that forces us to use multiple power electronic circuits (e.g., converters, inverters) that are required in order to connect the local sources to the dc and ac bus or grid within the network. Due to the introduction of power electronic circuits which operate at high switching frequency (e.g., 20-100 kHz), the modelling, design, and analysis of the overall system is different than the modelling of traditional power system. Traditionally, these power electronic switching circuits are modelled using simple averaged models that are easy to use but they completely ignore the switching action. While for simple cases this may be adequate, for microgrid applications the effect of the high frequency switching events can play a major role especially as more complicated, multilevel, interleaved, fault tolerant converters are utilized. In this project, a novel method will be used in order to properly model these new complicated converter topologies that employ state of the art control strategies and then it will propose a supervising control approach that greatly increases the grid's stability and reliability. The proposed method is generalized in the sense that it can handle the addition and removal of the sources and loads to the overall system. Moreover, the method is systematic and accurate because it is based on switched nonlinear model. Therefore, the purpose of this project is to develop generalized control-oriented design methodologies for modelling, stability analysis and control of hybrid microgrids where power electronic circuits are used for optimum and efficient energy management. The proposed analytical method will be tested on the overall system both in time-domain as well as in frequency-domain. Based on the generalized method, the design of supervising controllers for the microgrid, to control real and reactive power of power electronic circuits interfaced DGs will be done. The controller parameters will be selected based on small-signal and dynamic stability analyses to regulate voltage and frequency of the system. It will ensure stability during steady state operation and transition from one mode of operation to another. The proposed control method will be experimentally validated on a small-scale prototype in the laboratory.