16 research outputs found
Composite power semiconductor switches for high-power applications
It is predicted that 80 % of the world’s electricity will flow through power electronic based converters by 2030, with a growing demand for renewable technolo gies and the highest levels of efficiency at every stage from generation to load. At
the heart of a power electronic converter is the power semiconductor switch which
is responsible for controlling and modulating the flow of power from the input to
the output. The requirements for these power semiconductor switches are vast,
and include: having an extremely low level of conduction and switching losses;
being a low source of electromagnetic noise, and not being susceptible to external
Electromagnetic Interference (EMI); and having a good level of ruggedness and
reliability. These high-performance switches must also be economically viable
and not have an unnecessarily large manufacturing related carbon footprint.
This thesis investigates the switching performance of the two main semiconductor switches used in high-power applications — the well-established Silicon
(Si)-Insulated-Gate Bipolar Transistor (IGBT) and the state-of-the-art Wide-Bandgap (WBG) Silicon-Carbide (SiC)-Metal–Oxide–Semiconductor Field-Effect
Transistor (MOSFET). The SiC-MOSFET is ostensibly a better device than
the Si-IGBT due to the lower level of losses, however the cost of the device is
far greater and there are characteristics which can be troublesome, such as the
high levels of oscillatory behaviour at the switching edges which can cause serious Electromagnetic Compatibility (EMC) issues. The operating mechanism of these devices, the materials which are used to make them, and their auxiliary
components are critically analysed and discussed. This includes a head-to-head
comparison of the two high-capacity devices in terms of their losses and switching
characteristics. The design of a high-power Double-Pulse Test Rig (DPTR) and
the associated high-bandwidth measurement platform is presented. This test rig
is then extensively used throughout this thesis to experimentally characterise the
switching performance of the aforementioned high-capacity power semiconductor
devices.
A hybrid switch concept — termed “The Diverter” — is investigated, with
the motivation of achieving improved switching performance without the high-cost of a full SiC solution. This comprises a fully rated Si-IGBT as the main
conduction device and a part-rated SiC-MOSFET which is used at the turn-off.
The coordinated switching scheme for the Si/SiC-Diverter is experimentally examined to determine the required timings which yield the lowest turn-off loss and
the lowest level of oscillatory behaviour and other EMI precursors. The thermal stress imposed on the part-rated SiC-MOSFET is considered in a junction
temperature simulation and determined to be negligible. This concept is then
analysed in a grid-tied converter simulation and compared to a fully rated SiC-MOSFET and Si-IGBT. A conduction assistance operating mode, which solely
uses the part-rated SiC-MOSFET when within its rating, is also investigated.
Results show that the Diverter achieves a significantly lower level of losses compared to a Si-IGBT and only marginally higher than a full SiC solution. This is
achieved at a much lower cost than a full SiC solution and may also provide a
better method of achieving high-current SiC switche