By Peter Matthews, Knowles
In electric vehicle (EV) applications, filter capacitors are a special type of component commonly used as input and output capacitors. Also known as noise suppression or electromagnetic interference (EMI) filters, these particular capacitors act to remove noise and other unwanted signals on the line. On the high voltage alternating current (AC) side of a system, the capacitors often provide EMI filtering, whereas on the direct current (DC) side of a subsystem, they serve to smooth ripple components of the AC and filter out noise.
When dealing with high-voltage EV subsystems, Class X and Class Y safety certified capacitors are chosen primarily for their extreme reliability and compliance with UL, TÜV, CSA, VDE, and other international safety specifications. Class X capacitors are placed between line and neutral and Class Y capacitors are placed between line and ground, with several subcategories for each class depending on their rated voltage and peak impulse voltage. For EV applications, we commonly recommend Class Y2/X1, X1, and X2 capacitors that are approved for mains AC voltages up to 250 Vac.