Let us make a comparison of efficiency of alternator’s system and DC-DC converter system.
Alternator’s system has an efficiency of about 65% from the engine shaft to DC-load. The DC-
DC converter system has minimum efficiency of 82% from engine shaft to DC-load. We have a
minimum difference 17%. That means that we have additional 1.5kW power available or we can
save 1.5kW. For bus it means that the customer can save on average 0.1 mpg or 370 gallons
per year per bus. If the customer needs more power than 9kW, of course fuel saving will be
higher.We made a comparison between our topology and phase-shift topologies Fig.8 and Fig.9
which we call standard and improved. [6] We made this comparison with the assumption that all
topologies have the same efficiency, an output power and input and output voltage with output
current above 100A. Fig.10 The main advantages which help us achieve cost reduction are the
following: the power transformer works in optimal conditions, approximately a trapezoidal
waveform with roughly constant RMS voltage regardless of the input voltage. The current
carried by the winding is almost sinusoidal with a duty cycle of 90-95% and does not change
with the input voltage. This is an advantage when considering transformer losses, and along
with the fact that the new topology can reach a higher commutation frequency, significantly
helps to reduce the size of the transformer, decreases price, and increases the transformer’s
efficiency. When the topology operates under PWM control, it works like a current source,
because during this time the resonant inductor is discharging energy into the load via the
transformer (time period t3-t4, Fig.4c). This high impedance condition and strong control
through energy packets help when we parallel two or more of these power stages, it leads to
good sharing of current without any special current sharing control needed. This is convenient
when we use two or more converters in parallel connected to one load.