How does the circulating current of a PCS (Power Control System) in parallel cause EMC (Electronic Content Computing) issues?

Circulating current generated during parallel operation of PCS (Precast Conversion System) modules is not only a current sharing and loss issue, but can also directly cause EMC (Electronic Compatibility) problems. Circulating current is essentially an undesirable differential-mode or common-mode current between modules. Its mechanisms for causing EMC problems include:

1. As a noise source: Circulating current is an additional current that may contain high-frequency components. It generates changing magnetic fields on parallel busbars and connecting cables, leading to increased radiated emissions.

2. Modulation interference: Circulating current may disturb the modulation process of a single PCS, distorting its switching waveform and introducing new switching harmonic noise.

3. Ground loop common-mode noise: If there is a potential difference between the grounding reference points of each PCS, circulating current may form a loop through the ground wire, converting into common-mode noise current and exacerbating conducted common-mode EMI.

4. Filtering stress: Circulating current may flow through the output common-mode inductor, causing its core to become magnetized, reducing its high-frequency impedance and saturation margin, and weakening the filtering effect. Therefore, suppressing circulating current is also an important part of EMC design for parallel systems.