Input capacitors are used to minimize the ripple voltage amplitude from the power source to the circuitry. This reduces the rms ripple current to a level that can be handled by bulk capacitors.
Ripple Voltage
Ripple Voltage is the difference in voltage between “peak” and “valley” from our DC power supply.
When the motor is at rest and there is no power being drawn, it has a resting voltage. When you load the DC supply, it sags in terms of the voltage, and this is going to be measured right at the input side - ripple voltage. The BLDC motor controller delivers the power to the motor at very high frequencies. What happens is that you get some power that is delivered from the battery pack to the motor controller, and it then turns a coil within the motor on and off in a split second. This process repeats itself numerous times within a one second time span. During this time, the battery is being loaded and unloaded at a very high rate. This is where we see ripple voltage occurring.
The maximum ripple voltage that we have within our controller is 10% of the nominal voltage.
Ripple Current