PCS vs BMS vs EMS
These three acronyms are constantly mixed up. They are three different jobs.
PCS — Power Conversion System
The hardware that moves power: a bidirectional inverter converting battery DC to grid/load AC (and back when charging). It follows setpoints; it does not decide strategy. See ESS architecture.
BMS — Battery Management System
The safety and cell layer: measures every cell, balances them, and cuts off on over/under-voltage, over-current or over-temperature. It reports SoC/SoH to everything above it. See the BMS guide.
EMS — Energy Management System
The brain for strategy: decides when to charge/discharge for peak shaving, time-of-use arbitrage, backup or frequency response, and sends setpoints to the PCS.
Why the distinction matters
If you spec a BMS expecting it to do EMS dispatch, or an EMS that cannot talk to the PCS, the site will not behave. Keep the layers clean: BMS protects, PCS converts, EMS decides.