Sizing decoupling capacitor for a 3-ph inverter bridge.

Thread Starter


Joined Jan 25, 2012

I'm in the process of building a three phase bridge for driving my E-bike.

Sizing the decoupling capacitor proves to be a big challenge. Some of the people I've been talking to says motor inductance and resitance has little to say for the decoupling capacitor. For calculations I've been using a 170 uH, 0.1 ohm resistance - phase to phase.

Switching frequency is 20kHz, but I've been thinking about increasing it around 50% duty cycle if current ripple is very high here.

The battery imagined is a 1kWh, 10kW burst, 66v. Burst amperage (battery side) is 115 A (200A phase amps). Imagined battery resistance is 40mOhm, and inductance 1-2uH.

Low ESR is a must, going MLCC therefore seems like viable solution. The problem is enough capacitance. For 40 dollars (the amount I'll spend on capacitors), this will buy me ~250uF.

If anyone have any pointers to how to attack this problem, I would be very grateful :)