December 29, 2018

To whom it may concern:

The PWS1, PWS2 series PCS are certified to be in full Conformity to UL 1741 (Second Edition, Revision September 7, 2016) includes compliance with applicable requirements of IEEE 1547.1-2005(R2011), California Rule 21(SRD) and UL 1741 Supplement A. This certification requires that the system disconnect when connected grid voltage drops below the ride-through thresholds defined there-in, and remain disconnected until grid voltage is back to service.

In this mode of operation the inverter injects current into the grid based on the capability of the connected battery storage.

The PWS1, PWS2 series PCS DO have off-grid operation capability, allowing operation as a stand-alone voltage source;

However, to operate in this mode it would have to start in a voltage mode (aka stand-alone or off-grid mode) instead of grid-interactive mode.

• For systems intended to operate in stand-alone (off-grid) mode, an automatic transfer switch must be employed to isolate the de-energized grid circuitry from the output of the inverter so as to prevent system discharge into a dead grid circuit.
• The BMS auxiliary power that operates the system logic would need to be fed into the PWS1, PWS2 series PCS, when the grid lost power to the BMS, the BMS will trip after the UPS drained out and no power will be applied on the PCS
• The ability to start-up instand-alone (off-grid) mode is controlled by a screen on PWS1, PWS2 series. If nobody intends to modify the setting, the PCS will NOT go into off-grid mode.

The lack of access to the screen and need for different physical wiring excludes the ability of non-authorized personnel to do change the operational mode of the system.

There is NO need for software patch that can be employed to eliminate this toggling. But a patch is also available.

Ran Gao
Product Engineer
Sinexcel inc