Re: topology suggestions for 3.5kW batt charger?

On 30 jun, 23:06, "Tesseract" <u35475@uwe> wrote:
Greetings all - just found this site while searching for "boost pfc" and
noticed that Winfield Hill has posted here before so I figure the site can't
be all that bad ;)

I'm just throwing this out as a sort of curiosity-type question. I have
designed quite a few switchmode power supplies over the years but nothing
even approaching this power level (600W is the previous maximum). A friend of
a friend has one of 492 electric chevy S-10 pickups, and the onboard charger
has lost its magic smoke. Frankly, the design of this charger/motor drive
pretty much blows, ihmo, so I'm toying around with the idea of whipping up
something new. "Toying" because there is little financial motivation for
doing this. However, it is an interesting project and that is motivation
enough, sometimes.

There are two banks of batteries in the pack, each containing 26 12V/42Ah
batteries. The manufacturer, Genesis, recommends charging them at the 0.4C
rate up to a maximum of 2.4V/cell (with -20mV/C of compensation). As this
comes out to a rather onerous 6.3kW, I'll either have to go with a less-
ambitious charge rate or force the guy to unplug the range every time he
needs to plug in (or, of course, have a dedicated 40A. circuit installed). As
of now he does have a 240V/20A circuit for this purpose which, if we adhere
to the NEC, gives us *just* enough continuous amperage to charge each bank at
0.25C (10.5A) . This means both banks can be sequentially charged in about 8
hours, which is tolerable.

A linear and/or design using 60Hz magnetics is totally out of the question -
you won't be able to move the thing around without a forklift. The next
simplest thing I can imagine, then, is to use the output of a boost PFC more
or less directly. This has some serious safety issues, but it ain't like I'm
going to be submitting it for UL approval any time soon. So, these are the
various factors/ideas I am contemplating:

quasi-resonant (soft) switching; ZVS or ZCS?
IGBTs or advanced MOSFETs
Boost PFC + full-bridge or some combo to provide isolation

Current mode control is a natural, here. Voltage regulation needs to be
accurate but there's no need for a lot of loop bandwidth (ie - fast transient
response not required). Ideas welcome!

-Jeff

Hello Jeff,

When a switching topology is a mandatory, mi first thoughts go to a
full bridge forward converter with zero voltage switching where the
current limit is determined by the leakage inductance of the
transformer (probably a very large set of U cores). This is inherently
short circuit proof and you have plenty of time to shut it down. The
voltage waveform at the bridge is trapezoidal. dV/dt at the switches
is limited by the external capacitors.

Instead of one unit, I would use (depending on components available) 2
or three units. In that case, main charging is done by (for example) 3
units in parallel. As the voltage reaching final level, one or two
units are switched of. When you can make one, you can also make three
units.

Main advantage for a full bridge circuit is the ripple current in both
the primary rectifier and secondary rectifier. There is also efficient
utilization of the semiconductors. High dI/dt is avoided because of
the leakage inductance of the transformer. The transformer design is
somewhat tricky. You might use a separate coil for dI/dt limiting.

Because of the required large sized magnetics, you are limited in
maximum operating frequency because of risk on bad flux distribution
due to field propagation issues inside the magnetics.

You can drive the IGBT's or MOSFETs with one transformer (with 4
secondary windings).

Best regards,

Wim
PA3DJS
www.tetech.nl

.

Relevant Pages

  • Re: Calculating DC Output Current From Unregulated AC Transformer
    ... example context of it being a typical E-core transformer and basic ... Next, figure the ripple voltage, Vr. ... This is what the example circuit would need at a bare minimum by ...
    (sci.electronics.basics)
  • Re: Low Voltage to High Voltage/Low Current
    ... high voltage like +1 KV with very low current. ... this circuit as small as possible. ...  If the transformer has fairly high ...
    (sci.electronics.design)
  • Re: Calculating DC Output Current From Unregulated AC Transformer
    ... example context of it being a typical E-core transformer and basic ... First, with a bridge rectifier and capacitive filter, ... based on worst case line voltage and worst case Vsec sag under load. ... This is what the example circuit would need at a bare minimum by ...
    (sci.electronics.basics)
  • Re: Coupling coefficient of industrial transformers
    ... using the simulation to avoid destroying expensive IGBTs. ... By doing this, how will it not destroy the transformer, ... unless you use lower voltage than its nominal voltage. ... circuit voltage at the other, ...
    (sci.electronics.design)
  • Re: 11V to 15V AC/DC switching power supply?
    ... power) switching power supply? ... circuit possibilities? ... front of, and its meant to be adjustable in my voltage output range, ... which are reference circuits for each of their switching ...
    (sci.electronics.design)