Quick DC Charging Architecture

[ted.lowe]

Hi Rich C et al, i misspoke last night when you were discussing DC quick charging.  i thought the EV would only have the DC/DC and control stages, but after more thought, i realized the EV doesn't even have the DC/DC stage anymore.   This image illustrates the high-level architecture as i understand it:



The DC Quick Charger has all the high power conversion and adjustment stages and just listens to the EV (via CHAdeMO protocol (CAN-like)) to tell it what voltage and current to generate.  i understand the EV must send a message to the charger every 20 milliseconds with the wanted power levels or the charger will suspend power (safety timeout).

So onboard the EV is a much simpler (TINY!) device that monitors the battery pack voltage and sends power level control messages to the off-board DC quick charger.   It's not a charger per se, but a battery charge controller.  It will resemble the LTC4009 chip (but must be able to handle much higher voltages):

http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1003,C1037,C1078,C1089,P85071,D26456

The battery voltage monitor/balancer circuit could use a chip like the MAX11068:

http://www.maxim-ic.com/datasheet/index.mvp/id/5523/t/al

Todd Dore's 48-cell pack would require only 4 of these chips!  i've requested samples from Maxim (twice) but have received nothing yet (others seeing same shortages/non-response).

Good info and links at:

http://en.wikipedia.org/wiki/Charge_station
http://en.wikipedia.org/wiki/CHAdeMO

[ted.lowe]

snip

Todd Dore's 48-cell pack would require only 4 of these chips!  i've requested samples from Maxim (twice) but have received nothing yet (others seeing same shortages/non-response).

i've since received the max11068 samples (twice, since i reordered thinking they lost the first order).  However, i think reception of the samples now is because Maxim has just introduced their 2nd-gen IC (the max17830) that more or less obsoletes the max11068.   The max17830 is listed as a future product (yet, i've requested samples already):

http://www.maxim-ic.com/datasheet/index.mvp/id/7114

In the meantime, Linear has just introduced their 2nd-gen chip, the LTC6803.  Here's the press release:

http://www.linearnews.com/press/LTC6803/LTC6803.html?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+LinearTechnology+%28Linear+Technology%29&utm_content=Google+Reader

What i take away from this is that the electronics manufacturers GET IT about electric vehicles and our needs for such IC's to enable our development!  i'll try to sample the LTC6803 and see if/when i get it (probability looks poor since it's predecessor the LTC6802 was never really available for experimenter-types).  

The 2nd-gen chips offer higher voltage (more cells handled per chip), more accurate readings (maxim 0.1%, linear 0.25%), faster measurements (100hz for whole pack), parallel and serially cascade-able processor interfaces (to support multiple and/or parallel battery packs), and one of the coolest things, support for external higher-power balancing MOSFETS (the internal balancing MOSFETS are fine for level-1/level-2 charging, but inadequate for rapid DC charging).   You can almost read the future of EV technology by seeing what these chips can do (and visa versa)!

i forecast that EVentually each battery cell has it's own high-current controller (like a miniature version of our EV controllers) to control the power going in (regen/charging) and out (acceleration/balancing).   We've come a long way folks... :-)
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