B. UL 1741 Certification Requirement Decision for Power Control Systems
It is expected that the PCS tests currently found in the CRD will be incorporated directly into UL 1741, likely before the end of 2022. In addition to general export limiting capability, PCS may control export for various commands and functions defined in IEEE 1547, as explained in full below. These include the limit maximum active power command (IEEE 1547 subclause 4.6.2) or the voltage-active power function (IEEE 1547 subclause 5.4). IEEE 1547.1 type test 5.13 (Limit Active Power) notes that PCS tested to the UL 1741 Power Control Systems test procedure may be utilized, and the time to reach steady state should be recorded. IEEE 1547.1 type tests 5.14.9 (test for voltage-active power (volt-watt) mode) and 5.14.10 (test for voltage-active power (volt-watt) mode with an imbalanced grid) could also be used with PCS equipment to determine it can provide the voltage-active power response.
Where such controls are used, the manufacturer should document the device’s capabilities, technical requirement documents should convey related requirements, and customers should identify the devices in the interconnection application.
- To ensure PCS controls are appropriately addressed, any performance capability should align with or reference UL 1741 (e.g., as is done in Chapter III.E.2 with new section 184.108.40.206.1). Since the PCS testing requirements are yet to be published in UL 1741, requirements should note that in the interim period, listing and certification can be fulfilled per the UL CRD for PCS.
- To ensure that the interconnection procedures require certified equipment, they should require PCS to be certified. SGIP requires certification of the interconnecting devices, which likely includes PCS. However, some states’ interconnection procedures instead require inverter certification (such as in a Simplified process); those rules should be updated to be inclusive of PCS or any interconnection equipment.
- To ease the evaluation of PCS during interconnection, manufacturers should list the following in equipment documentation (note that the interconnection process cannot ensure that this is implemented by manufacturers, other than creating a market driver to provide this information):
- Supported exporting and importing modes (unrestricted, export only, import only, no exchange, export limiting from all sources, export limiting from ESS, import limiting to ESS)
- Support for export control of the limit maximum active power command
- Support for export control of the voltage-active power (volt-watt) command
4) Revise the interconnection application form to ask whether or not a Power Control System is included in the DER system design. If so, require identification of such on the submitted one-line diagram, as follows:
Does the DER include a Power Control System? [yes / no] (If yes, indicate the Power Control System equipment and connections on the one-line diagram)
What is the PCS maximum open loop response time? _____
What is the PCS average open loop response time? _____
When grid-connected, will the PCS employ any of the following? [Select all that apply]
- Unrestricted mode
- Export only mode
- Import only mode
- No exchange mode
- Export limiting from all sources
- Export limiting from ESS
- Import limiting to ESS