LiFePo Batteries High Voltage

Hi, here is a question that one asked in a forum, i dont know the answer, but perhaps one of you guys can help . This type of battery is interesting for safety, some of its drawbacks are being lessned with nannos i understand. Thank you quote: Thank you for all the helpful tips on the batteries. The A123 20Ah Pouch cells look really good, since we anyway decided to switch to LiFePo. And they are also not that expensive actually. http://shop.lipopower.de/A123-Systems-AMP20M1HD-A-20Ah-Folienzelle, just 50€ each. We really would like to stick to the tip Quote: Try to use a single string of higher capacity cells in series because it will be cheaper and easier to design around as well as increase cell life and simply BMS cost and wiring. But since we don't want to go with less than 8kwh, this would mean that we need 121 cells, which is 400V nominal or 435V maximum, although our motor only needs less than 200V RMS. on the phases. When I asked at the manufacturer of our controllers, UNITEK I was told that this voltage would be too high, since we would not be able to use all the energy if we use such a high voltage. But I don't understand this. The input voltage of the controller is 400 or 700 Volts depending on the exact model. By PWM they make a sinusoidal at the outputs. I thought that when the voltage is higher, then the "on-pulses" of the PWM are a little bit shorter for the same output and therefore it should draw less current from the battery for the same output, if the battery has a higher voltage. So why can't we use all of the energy? If it was possible to use this voltage, we would be very interested to do so, because the a123 pouch cells are the most lightweight solution in LiFePo we have found and at the same time very affordable. For example the a123 cylindrical cells with 2.3 Ah would be more than 10kg more, a few thousand euros more and a lot more mess with 1000+ cells... Or does anyone happen to know a similar pouch cell but with a little bit more capacity, like 24 Ah? Can anyone explain me if or why my thoughts to justify the high voltage are incorrect?