occur, which causes the low-voltagemonitor of the driver to trip. As a counter measure
either a large bootstrap capacitor should be provided or an alternativeway to supply the
driver has beused.
Because of the mentioned relationship that the output frequency equals the switching
frequency of the power semiconductors, especially at low frequencies in the range of
some 100Hz, there is a requirement for low conduction losses. Accordingly, in the
selection of IGBTs and diodes one has to pay attention to lowest U
Furthermore, the diodes have to be of a more rugged design than the associated
IGBTs, as they bear the full load in normal operating mode and show higher junction
temperatures due to the (generally) higher thermal resistance. Also, the diodes are
heavily stressed in this operating point, especially with drives showing a regenerative
loadprofile. Applications include drives inelectric buses or trucks (hybrid systems).
Switching states of theSRMdrive
Inverters for drive (motor) applications operating at high voltages of several kV, also
referred to as "Medium-VoltageDrives" ormore seldom "High-VoltageDrives", are often
built as cascaded inverters as well as the previously described three-level or multi-level
circuits. Typically 1.2kV or 1.7kV IGBTmodules are used in an H-bridge circuit (chapter
then configured as a cascade
. The DC-bus circuits are supplied via
a transformer which supplies a partial voltage to each cascade or power cell. The sum
of all output voltages of the series connected power cells with their own partial output
voltages results in the total output voltage, which is then available to the electricmotor.
This topology is now widespread and is found in applications such as: Pumps, fans,
drives and compressor motors for the oil and gas industry, water treatment, power