Quote:
Originally Posted by P-hack
That is what I was thinking when I saw 4 power sections 
the chunky prius booster switch has to carry the conversion current for all three phases, i.e. if the converter output is 150a @600v, and the input is 300a @ 300vish, the inductor sees 300a, the top diode sees 150a semi constant (depending on converter design) and the bottom switch swings/chops between 300a and zero. Meanwhile the inverter switches only have an average of 50a each to deal with. |
Yes - that is
definitely a serious issue.
The boost current is directly proportional to the difference in voltages. Essentially, the power output must be constant. As you state, amount of boost would be limited by the current handling capability of the boost stage. Another issue may be the resulting asymmetrical balance of current in the inverter - resulting in asymetrical capacitor loading and asymetrical thermal problems.
It may seem a bit of a cop-out, but I've convinced myself that it would still be useful for a less dramatic boost than the Prius sees. This would allow someone to use a 650V motor like a Prius or Highlander Hybrid motor with a battery pack with a less stratospheric voltage. This could significantly reduce the cost and weight of the battery pack.
Since the same controller runs all of this, it would be possible to adjust the amount of boost depending on conditions. Up to the point where the BEMF = battery voltage (or something close) the boost could be 1:1, requiring no extra work from the boost stage.
From what I've seen from various IGBT/Mosfet/SiC spec sheets, the TO-247 package can handle about 100A > 120A. ( Even though the manufactures claim over 200A for some models -
) A Correctly designed inverter would balance the design for a
PEAK 300A output of the boost stage. For example, a 75kW inverter controlling a 650V motor would be limited to a minimum battery voltage of 250V, assuming constant power, neglecting losses. I plan to use a Nissan Leaf pack, which has been tested to 360V nominal. Thus, the boost stage would be seeing something like 208A, or 70A per switch.
Another thing I'm playing with is a double H-bridge DC controller using this design. I'm building an electric snow-cat that could use this capability.
- E*clipse