UL 1741 and Its SA and SB Supplements: Empowering Distributed Energy Resources (DER) Grid Connectivity

In the dynamic landscape of renewable energy, the seamless integration of distributed energy resources (DER) into the grid is paramount. As solar panels, wind turbines, and energy storage systems proliferate, ensuring their safe and efficient connection becomes a critical task. Let’s delve into the world of UL 1741, its SA and SB supplements, and their impact on DER grid connectivity.

UL 1741: The Foundation

UL 1741 serves as the bedrock standard for grid-connected inverters. Here’s what you need to know:

1. Definition: Underwriters Laboratories (UL): a respected certification body, developed UL 1741 to ensure the safety and reliability of inverter-based devices.
2. Safety Assurance: UL 1741 encompasses rigorous safety tests beyond the IEEE 1547 conformance requirements.
3. Inverter Compliance: It certifies that inverters adhere to safety standards, allowing them to connect to the grid.

The Challenge with Previous Standards

Before UL 1741, the older standard (UL 1537) compelled wind and solar inverters to disconnect during grid instability. The rationale was to let utility-scale power electronics stabilize the grid. However, unintended consequences emerged:

●      Supply Reduction: Disconnecting productive renewable energy sources during high demand periods reduces overall supply.

●       Cascading Blackouts: Regions with substantial renewable energy penetration experienced cascading blackouts during grid fluctuations.

Updates: UL 1741SA and SB

1. UL 1741SA (Supplement A):

The purpose of this supplement is to improve DER grid support capabilities through below main modifications:

• Continuous Connection: Inverters must remain connected during grid fluctuations.
• Expanded Frequency Range: Inverters stay connected down to around 57 Hz.
• Grid Support Functions: 

           ▪   Anti-islanding: Prevents inverter operation independently during grid outages.

           ▪   Low/High-Voltage Ride-Through (L/HVRT): Allows ride-through during voltage fluctuations.

           ▪   Frequency Ride-Through (FRT): Ensures stability during frequency deviations.

           ▪   Volt-Watt (V-W) and Volt-Var (V-V) Control: Adjusts power output based on grid conditions.

           ▪   Dynamic Volt-Ampere Reactive (D-VAR) Control: Regulates reactive power.

2. UL 1741SB (Supplement B):

• DER Communication: Addresses communication protocols between DER and the grid.
• Grid Services: Enables DER to provide ancillary services (e.g., frequency regulation, voltage support).
• DER Integration: Facilitates seamless DER integration into grid operations.

DER Grid Connectivity

DER encompasses a decentralized approach to energy production, including solar, wind, and battery storage. UL 1741SA and SB directly impact DER by:

●      Active Grid Support: Inverters actively stabilize the grid during fluctuations.

●      Enhanced Reliability: DER becomes a reliable component of our energy landscape.

In summary, UL 1741, along with its SA and SB supplements, ensures that modern inverters stay connected, contribute to grid stability, and enhance our renewable energy infrastructure. Circuit Energy ensures our offerings are all code compliant and safe to operate.