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Appendix B: Multi-mode transfer / bypass relay operation
The Evolve Hub and Evolve PCS within the Evolve line of energy storage systems provides fully automated multi-mode
operation, including utility interactive and backup (off-grid) operating modes. The diagram below highlights the three main
relay controls used to transfer the backup panel supply source and island the Evolve PCS to a micro-grid during a grid
outage. The battery portion of the Evolve ESS / LFP is not shown.
Note: while the EMS is responsible for monitoring PCS states and controlling the battery discharge / charge rates, the PCS
is responsible for the relay controls, and thus does not rely on EMS communication for transfer of the backup panel source.
Figure 25: Evolve Hub and Evolve PCS relay protection definitions in an AC coupled solar plus storage installations.
There are three main protection relays within the complete system, defined below, all of which have internal fail-safe fault
verification circuitry to prevent an unsynchronized PCS load to grid output connection.
Kx: Evolve Hub bypass / transfer relay
The Evolve Hub bypass / transfer relay ensures the backup panel is connected to the main panel with or without an
operating Evolve ESS / LFP system. When standalone, the Kx relay bypasses the energy storage system to power the
backup panel from the main supply. It remains in the NC or bypass state until powered up with the Evolve ESS / LFP
initialized and ready for control. Once the energy storage system’s PCS is in a “ready” mode, the PCS will take over control
of the backup supply source by transferring Kx to NO, and closing K3 for an uninterrupted transfer. Kx will revert to an NC
state with or without a valid grid if the PCS reports a critical service state which prevents it from safely operating the K3
transfer relay.
Fail-safe: Critical failure of the Kx relay will prevent PCS operation and will result in loss of power to the backup panel.
K3: PCS transfer relay
This relay operates with Kx as defined above when the Evolve ESS / LFP is in a “ready” state. See the table below for a
complete list of PCS states. This relay opens upon a grid outage to island the backup panel from the main panel. This relay
acts as the PCS grid timing / synchronization grid connect relay when the grid supply returns from an outage, allowing
seamless connection of the battery system and the backup panel circuits to the grid.
Fail-safe: Critical failure of the K3 relay will prevent operation of the PCS, but will allow the backup panel to be supplied by
the main panel via the Evolve Hub.