TJ - 120 Amps RMS - that is exotic.
I have ordered some film caps from china (mentioned in other threads) for Richo and myself.
I was sizing them conservatively, based on the maximum average IGBT current in the controller (300Amps)
The caps are coming from (EACO capacitor through Yesiya in Shenzhen - SHD caps) 390uF at 900 Volts ans 51 Amps RMS. These have really low ESR at 3mR and tremendous pulse capabilility -- shoud be able to take the corner off a screwdriver!
I am intending using 6 for a total of 2340uF and ~300 Amps RMS. The ESR should be in the 500 (micro) R territory, giving an ESR-induced ripple of about 0 Volts. The ripple will be almost entirely derived from the capacitance, estimated at about 20 Volts, worst case.
I would expect that because the ESR is in the order of 10% of an equivalent electrolytic capacitor network, the heating should be corrrespondingly much lower.
Some other advantages are:
The overall capacitance is low so that not so much energy is needed to pre-charge the caps at startup.
Dry film capacitors don't have electrolyte problems and are rated for times like 100,000 hours at 70 deg.C
The caps are rated for 900V, so no series-parallel network needed.
EACO is reasonably priced at about $50 each for the above type.
Epcos caps are blue because that's the colour you become when the supplier tells you the price
The capacitors buffer the motor current each time the power transistors switch. This varies with the motor torque primarily.
At low speed and high acceleration this will be very high, but reduce greatly at cruise.
[edit: Add]
At low speed (high motor current and low battery current) the diodes conduct most of the time.
