Abstract
M.Ing. (Electrical & Electronic Engineering)
Switching losses in power electronic converters can be reduced by using
snubbers, or resonant circuits.
Simple snubbers can be implemented without much effort, but then energy is still
dissipated, which reduces the efficiency of the converter. Regenerative snubbers
are known, but these usually require complicated additional circuits. The use of
nonlinear capacitors as turn-off snubbers has been investigated, and proved
profitable. The main reason for this is the much smaller amount of energy which is
stored in the the nonlinear capacitors, compared to linear capacitors.
Resonant circuits reduce switching losses by allowing switchings to occur when
the voltage across the switching device, or the current through the switching
device is zero. This effect is called soft-switching and to obtain this, resonance
between an inductor and capacitor is usually involved. Resonant circuits have the
disadvantage that the installed switching power cannot be used optimally. This
drawback has been reduced by using a saturable inductor in the resonant circuit.
This thesis considers the use of both nonlinear capacitors and nonlinear inductors
in a resonant phase arm. It was found that the nonlinear resonant elements lead to
very low overdimensioning of the switching devices, and minimal switching losses
in such a phase arm. Very few additional components are used, which keeps the
cost of the converter down.
A 1.5kW converter was constructed in which the double nonlinear resonant phase
arm was implemented. This converter was investigated both experimentaly, and by
means of computer simulations. The converter is also compared with the current
state of the art.
It is concluded that resonant phase arms with both. nonlinear inductors and
nonlinear capacitors can function effectively in power electronic converters. Some
important advantages are also assosiated with the use of the double nonlinear
resonant circuit.