How can a three-level energy storage system (PCS) reduce radiated EMI?

Compared to two-level PCS (such as NPC and T-type), three-level PCS (such as NPC and T-type) can effectively reduce radiated EMI, especially in the high-frequency range. The principle is as follows:

1. Voltage step halved: The output voltage change with each switching action is only half that of the DC bus voltage, significantly reducing dv/dt, thereby reducing common-mode current and high-frequency radiated energy generated by dv/dt excitation.

2. Improved harmonic spectrum: The output waveform is closer to a sine wave, with lower high-frequency harmonic content, and the energy distribution of the radiated spectrum is concentrated at lower frequencies. To fully utilize this advantage and further reduce radiated EMI, the following measures are also needed: optimize the driving timing of multi-level circuits to avoid unnecessary narrow pulses; design low parasitic inductance layouts and buffer circuits for each level's switching unit; although common-mode noise is reduced, common-mode inductors are still required, but their requirements for inductance and saturation current may be relatively reduced.