What are the differences in EMC between PCS islanded operation and grid-connected operation of energy storage systems?

The EMC characteristics of a PCS differ between islanded (independent load) and grid-connected operation modes, primarily due to variations in operating conditions and load characteristics.

1. Noise Source Differences: In grid-connected mode, the PCS operates in current-source mode, with switching frequency harmonic currents directly injected into the grid. In islanded mode, it operates in voltage-source mode, requiring a stable sinusoidal voltage to the load. The design focus and control algorithm of its output filter may differ, affecting internal switching noise.

2. Load Influence: The type (resistive, inductive, capacitive, nonlinear) and size of the load in islanded operation directly determine the PCS's operating point, potentially leading to an EMI spectrum different from the grid-connected rated load. Nonlinear loads (such as rectifiers) can reflect harmonics, potentially triggering resonance.

3. Grounding and Reference Point: In grid-connected mode, there is a defined grid ground as a reference. In islanded mode, the system's grounding method may differ, affecting the common-mode noise path. Therefore, for PCS capable of dual-mode operation, its EMC performance must be evaluated separately in both modes to ensure compliance with requirements.