because the inductors are bulkier and heavier than the DC link capacitor in low and
medium power converters.
An alternative solution to a frequency converter with voltage source inverter is the
solution with PWM current source inverter (CSI), presented in Fig. 2.5 [34, 59]. The
CSI produces sinusoidal supply current waveforms similar to the back-to-back VSI.
The CSC contains a DC link inductor, which is generally larger and heavier than the
link capacitor in voltage source converters. In the CSI, a source filter is also required.
This is a low-pass LC-type filter, and the physical size of CSI source filter is smaller
than used in a B2B VSI. Furthermore, the CSI usually requires series-connected
diodes with every IGBT. This increases semiconductor conduction losses and the
complexity of the main circuit.
The DC energy storage in the presented indirect frequency converters is a bulky
component. In the solution with VSI the DC link capacitors are relatively large
compared to the size of the rectifier and inverter semiconductor components, at the
same time reducing the speed of response. Electrolytic capacitors typically occupy
from 30 to 50% of the total volume of the converter for power levels greater than a
few kWand in addition to this they are a component with a limited lifetime. It should
be noted that the electrolytic capacitor has by far the shortest lifetime of any element,
active or passive, used in power electronic converters. In addition, the presence of the
capacitor significantly limits the power converter to high temperature applications