2.1. Non-isolated DC/DC¶
2.1.1. Converter definition¶
A non-isolated DC/DC converter performs bidirectional power conversion between two DC buses.
Since this conversion stage is current-bidirectional, there is no fixed ‘input’ or ‘output’ side. The structure, however, is not symmetric and there are distinct low-voltage (LV) and high-voltage (HV) sides that cannot be swapped around.
Both sides share the same voltage reference, i.e. the HV- and LV- terminals are connected.
A positive (HV→LV) power flow corresponds to step-down or buck operation and a negative (HV←LV) power flow corresponds to step-up or boost operation.
The reference power is defined on the LV side, hence total converter efficiency is computed by PowerForge as such:
if \(P_{LV}>0\) (buck) then \(η = \dfrac { |P_{LV}| }{ |P_{LV}| + P_{loss} }\)
if \(P_{LV}<0\) (boost) then \(η = \dfrac { |P_{LV}| - P_{loss} }{ |P_{LV}|}\)
A non-isolated DC/DC conversion stage is composed of several subsystems as shown below:
2.1.2. Sources modeling¶
2.1.2.1. Ideal DC sources¶
When using this operating point definition, the conversion stage’s HV and LV interfaces are both modeled as connected to an ideal DC source. The natures of these sources depend on the order of the corresponding filters.
At the HV interface:
odd order filters will be connected to a current source,
even order filters will be connected to a voltage source.
At the LV interface:
odd order filters will be connected to a voltage source,
even order filters will be connected to a current source.
Transferred power is specified by PLV, the power flowing out of the LV-side converter interface.