electrolytic capacitors whilst the resistance of the electrolyte sets the lower limit. With
decreasing temperature the ESR (Equivalent Series Resistance
rises. The limits of
the ambient temperature are likely to cause reduced capacitance and require a
de-rating. The input rectifier causes the ripple current on the one hand and on the other
hand the switching of the output power semiconductors. ThisAC current passes through
the DC-bus capacitors and heats them up. Operation near or above themaximum core
temperature of the capacitor can cause early failure. Manufacturers of DC-bus
capacitors now offer a variety of tools to calculate the lifetime of the capacitors and to
make anappropriate selectionaccording to the specific application.
Calculation/simulation software of variousmanufacturers on the Internet
When connecting the DC-bus to the output circuit with its power semiconductors, it is
important to keep the stray inductance as low as possible. On the one hand, the
mechanical construction determines this; on the other hand it is the ESL (Equivalent
of the DC-bus capacitors. Therefore, keep the area that is enclosed
by the DC+ and DC- conductors as small as possible and also, the selected capacitors
should have a lowESL value. A preferable design of the DC-bus is the implementation
of laminated copper or aluminium sheets (sheet bus). The parallel sheets should
connect the capacitors and the power electronic components of the inverter in the
shortest possible way. The implications of too high stray inductance of the DC-bus are
discussed ina number of other chapters in this book andwill not be covered here.
heavier the oxide layer. The oxide layer then determines the rated voltage and themaximum operating voltage of
The equivalent series resistance ESR combines the ohmic conduction losses and the dielectric reversal charge
losses of the capacitor.
ESL is the equivalent series inductanceof a capacitor. It combines all parasitic inductances of the capacitor.