At first we need to calculate Ripple Current for one of switched motor phases using following formula:
In our design Ripple Current has a value of ~48.41A. When selecting capacitors we need to make sure that the
capacitor bank has Irms greater than this value. Another important factor is a Ripple Voltage. We wanted Ripple Voltage to have a value less than 1% of Vbus voltage. Using following formula we calculated minimal capacitance of DC Link Capacitor bank:
In our application the minimum capacitance of the bank has a value of ~66,7uF. We want our Capacitor bank to
have a capacitance greater than this value. As a result of calculations we decided to use two C4AQIEW6100A3BJ KEMET capacitors with 100uF capacitance and 40,6A I_RMS each. It makes our DC Link Capacitor Bank small, light and still a bit overparameterizedfor safety reasons.
To ensure high precision and consistent spacing between high voltage elements we decided to use a PCB as a template for all components. Some PCB manufacturers, like JLCPCB give the ability to order high quality PCBs for low price. To make connection to IGBT transistors even better we soldered laser-cutted copper terminals. They are making resistance between terminals and capacitors much much lower.
Manufacturing is done by JLCPCB you just need to drag your Gerber file .zip into the ‘Add gerber file’ slot and press ‘Instant quote’(useful links below). All further steps are pretty self explanatory - if you are not sure about something you can click on a question mark to learn more. We choose 1oz, 1.6mm thick FR-4 PCB, with a Blue solder mask(the base settings are a ‘good to go’ in most cases).
As you can see, the boards are really affordable. The above price is not for a single PCB, but for five(minimal quantity) which makes it even a greater deal. Standard build time is 1-2 days, in our case due to non-standard solder mask color it is extended to 3 days.