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Developments are aimed at significantly improving the durability
of the power semiconductor module relative to the number of load
cycles, even at higher chip temperatures, and achieving higher
switching frequencies. For example, attempts are being made to
achieve this through new manufacturing processes or new se-
miconductor material (SiC, GaN). Likewise, there are attempts to
further increase power density (for example, through a three-di-
mensional structure). However, there are also attempts to achieve
lower losses or to implement soft-switching topologies [De Donker
(2011)].
Currently the inverter is usually located in a separate housing. This
requires extensive effort for cabling and for the connections. High
costs and high weight are incurred due to the high currents and
the requirements imposed on insulation and shielding of the cable.
The plug connections too must satisfy high requirements. Conse-
quently, work is focused on adapting the inverter to the electric
motor. This could also reduce the intermediate circuit capacitance
and hence separate housing could be dispensed with; moreover
it would be possible to employ a common cooling system for the
inverter and the electric motor. However, in order to integrate the
control electronics in the E-propulsion system, first the inverter
components must reliably meet the requirements for robustness
against vibration and the effects of heat [Cebulski (2011)].
DIRECT CURRENT CONVERTER
In addition to the inverter, direct current converters (DC/DC con-
verters or converter modules) are also components for voltage ad-
aptation. The DC/DC converter generates a changed output volta-
ge from a variable input voltage with the aid of power electronics
elements. The most important criteria in this regard are the values
and the quality of the voltages and current used or that will be
generated [Cebulski (2011)].
A direct current converter, for example, is used to supply the 14 V
on-board electrical system from the high voltage on-board elec-
trical system of an electric vehicle. In addition, although a high-
voltage battery can be directly connected to the high-voltage on-
board electrical system, for a low-voltage battery an appropriate
voltage adaptation must be executed using a DC/DC converter, and
the battery voltage must be set to a higher voltage level (example
Toyota Prius from 202 V to 650 V) [Cebulski (2011); March (2011)].
CHARGER
In order to externally charge a battery electric vehicle - for examp-
le via, the national grid -, a charger is required. This unit adapts
the external voltage level to the voltage necessary for charging
the battery.
Fig. 15 shows a typical curve of the cell voltage [in volts], and the
current [in amperes] for the charge process for a lithium-ion batte-
ry, versus time. A sample discharge process is also illustrated. The
illustration also shows the state-of-charge (SOC) curve. It is clear-
ly evident in this respect that within a short time approximately 70
percent SOC is achieved; however, reaching the 100 percent mark
requires additional time and lower charge current intensity.
Fig. 14: Pulse inverter and its essential components
15
Fig. 14 shows the pulse inverter and its essential components in schematic
structure.
15 Authors’ own illustration I Image material: SIKRON 2011