How does the di/dt ratio of PCS switching devices in an energy storage system affect EMC?

The di/dt (rate of change of current) of switching devices is one of the key factors affecting the EMC performance of PCS. A high di/dt will generate induced voltage spikes (V=L*di/dt) on the parasitic inductance of the power loop. These spikes are rich in high-frequency harmonics and are a significant source of conducted and radiated EMI.

Specific effects include: increased differential-mode noise voltage; larger common-mode current through parasitic capacitance coupling; and strong near-field radiation due to the corresponding rapidly changing magnetic field.

To improve EMC, measures need to be taken to reduce the effective di/dt or absorb its energy, such as: optimizing the drive resistor to smooth the switching speed; using magnetic rings or power beads on the current path to suppress high-frequency currents; adopting low parasitic inductance busbar layouts and device packages; and designing effective snubber circuits.