Advanced Automotive System based on Modular Multilevel Converter

Battery packs in recent electric vehicles (EVs) have high energy and high power densities which exerts a strong thermal stress upon them. This means that the individual battery cells are more prone to decline away and eventually fail early because of an excessive loss of capacity and an increase of internal resistance caused by accelerated aging. Moreover, for electromechanical reasons, each cell is totally unbalanced in operating mode. Unfortunately, most of the published literatures are carelessly emphasizing the fault ride-through capabilities of actual automotive battery packs. Therefore, for safety, efficiency and flexibility reasons, this presentation proposes a new concept for packaging EVs battery based on Configurable Modular Multilevel Converter (CMMC). In addition, EVs owners are confronted by the limited compatibility of available charging infrastructures. Hence, the CMMC is designed for a large range of charging infrastructure; from AC household basic supply to AC or DC ultrafast charging infrastructure. The CMMC proposes an intelligent control for power quality in EV application. The concept is proposed for universal and flexible EV charger and it is based on the MMC. It aims to use the existing motor winding as current filter during charging mode and the traction converter like charger converter. It distributes also the conventional battery pack into multilevel module, which increases the fault ride-through capabilities of the EV battery against thermal runaway. The electrical motor is fed by multilevel voltages which also increases the motor efficiency. In fact, the switching mode is controlled by a shifted angle between the upper-arm and lower-arm currents. This new concept allows interfacing EV to worldwide charging infrastructure which increases the flexibility of EV owner.

Contribution to the Ultra-Fast Charging of Electric Vehicles

Rosa Martel Danoary Tsirinomeny

It is generally agreed that one of the drawbacks of a conventional vehicle is the inability to always reach the best operating point of the engine and the inability to regenerate the kinetic energy. Meaning, even with the help of the gearbox or automatic transmission, there is no way to reach more efficient operating points without increasing the power and then there is nowhere to store the excess of the energy converted. Electric vehicles (EVs) offer an opportunity for intelligent motion by working at the best operating point during driving mode, as well as a smart energy management during charging mode. However, it is well-known that the EV has been criticised due to its range anxiety, its limited compatibility with various charging points, its high cost, as well as its limited capability to ride-through a thermal runaway, etc. Today, the range anxiety seems to be resolved by the fact that a significate development is foreseen in the field of the battery cells market for portable equipment such as cell phones, pads, laptops, etc; the same battery technology can be deployed for EVs. Actually, battery packs in EVs tend to have high energy and power densities which will exert a strong thermal stress upon them. This means that individual battery cells are more prone to decline away and eventually fail early because of an excessive loss of capacity and an increase of the internal resistance caused by accelerated aging. Moreover, for electromechanical reasons, each cell is totally unbalanced in operating mode. Therefore, a suitable battery management system should be installed and the capability of the EV to ride-through thermal runaways must be guaranteed. Furthermore, in order to overcome the difference between AC and DC charging station standards, the EV on-board charger has to be flexible for various levels of charging modes (from AC household basic supply to AC or DC ultrafast charging). In order to meet the EV requirements, an advanced power converter which driven efficiency, power density is required. Therefore, the configurable modular multilevel converter (CMMC) has been introduced. It is part of a family of modular multilevel converters, also known as MMC, M2C or DSCC. Hence, its heritage allows bringing the whole advantages to EV applications. In addition it carries the surname of configurable because the converter plays a double role: in fact, it merge the traction converter and the bidirectional charger as well as the battery balancer converter, which not only increases the modularity and the scalability of the power modules but it reduces the cost, condenses the volume. In detail, the concept is linked to the idea of replacing the branch inductance of the standard MMC by the tapped stator windings of the traction motor itself. This allows operating the stator windings as current filter during charging mode. In addition, the famous EV battery pack is split into the MMC submodule. This will increase the fault ride-through capabilities of the Flex-EV battery against thermal runaways, by increasing the capability of the system to work under fault condition. In addition, states of charge (SoC) balancing are implemented at the level of modulation in order to balance that submodule battery state of charge. This is based on a selecting and sorting algorithm, which connect and disconnect the batteries submodules actively according to the sign of the generated AC current wave form and the SoC of the submodules batteries.

EPFL2016

Electric Vehicle Driving and Fast Charging System based on Configurable Modular Multilevel Converter (CMMC)

Alfred Rufer, Rosa Martel Danoary Tsirinomeny

Electric Vehicles (EVs) owners are challenged by the limited flexibility of the actual EVs on-board charger according to the available charging station. This paper proposes a new concept of a Unified Converter (UC) for EVs based on the Configurable Modular Multilevel Converter (CMMC), which uses only one converter for fast charging and for driving system. In fact, the motor winding is used as filter during charging operation and the battery pack is split into submodules in order to modularize the battery subsystem. The concept enables an adaptation of the on-board standalone fast charger for different kinds of power sources (AC or DC, normal or fast). In addition, the CMMC itself can play the role of ancillary services during the interconnection with the Distributed Generation (DG). Furthermore, its implementation is pratically simple because it is based on well-known threephase control [1]. However, the CMMC requires an open-end AC machine with common middle points.

2013

Contribution to the Ultra-Fast Charging of Electric Vehicles

Rosa Martel Danoary Tsirinomeny

EPFL2016