PRC-029-1 and Inverter-Based Resources: New Challenges for Frequency and Voltage Ride-Through Compliance

Unlike traditional synchronous generators, IBRs rely on power electronics and manufacturer-specific controls, which can behave differently under voltage and frequency disturbances. The PRC-029-1 standard establishes Frequency and Voltage Ride-Through (FVRT) requirements to ensure grid stability. The unique characteristics of IBRs, including fast switching, limited current capability, and sensitivity to phase angle changes, present new challenges for compliance. Understanding these challenges is essential for grid operators, engineers, and regulators to maintain reliable and secure power system operations in an evolving energy landscape.

Understanding PRC-029-1

The Reliability Standard PRC-029-1 addresses Inverter-Based Resource (IBR) disturbance Ride-through performance criteria. This standard is a consequence of both the different natures of synchronous and inverter-based generation resources and several recent events exhibiting significant IBR Ride-through deficiencies. PRC-029-1 aligns with certain Ride-through requirements of IEEE 2800-2022, but is structured to follow the FERC Order No. 901.

The lack of standardization in IBR technology (equipment/controller behavior) has created reliability challenges in the interconnection of IBR facilities to the power grid. The nature of the rapid switching in power electronics for IBR generation and the electronic interface to the transmission system means that disturbance Ride-through behavior is largely determined by manufacturer-specific equipment and control system designs.

Challenges of Inverter-Based Resources for FVRT Compliance

IBRs introduce several technical and operational challenges when meeting the FVRT requirements outlined in PRC-029-1. These challenges arise from fundamental differences between IBRs and synchronous machines, the diversity of inverter technologies, and past disturbance events in which IBRs failed to ride through system conditions as expected.

1. Limited Current Capability and Fast Power-Electronic Switching

Maximum current limits, short-duration current capabilities, and fast electronic switching characteristics constrain IBRs. These constraints make it difficult for many IBRs to sustain current injection during voltage dips or frequency excursions, which is essential for compliance with PRC-029-1. The combination of limited current capacity and rapid switching behavior creates operational challenges during system disturbances.

2. Sensitivity to Phase Angle Jumps and PLL Instability

A significant challenge for FVRT compliance is the Phase-Lock Loop (PLL), which synchronizes the inverter to the grid voltage. Significant phase angle jumps, which frequently occur during faults or switching events, can cause PLL desynchronization, loss of control stability, and inadvertent tripping. To address this, PRC-029-1 requires IBRs to withstand at least 25° electrical phase-angle jumps and requires that protection functions not cause tripping within the defined ride-through region.

3. Momentary Cessation in Low-Voltage Conditions

Many legacy inverter controls historically entered momentary cessation during low-voltage events to protect equipment. PRC-029-1, however, mandates that IBRs must not cease operation within the Ride-through zone and must rapidly return to regular current exchange within five cycles after voltage recovery.

4. Reactive Current Prioritization and Voltage Recovery

Some plants face difficulty because of faster response settings. They can cause controller instability, whereas slower settings can delay voltage recovery, both of which pose compliance risks during voltage disturbances.

5. Reduced System Inertia and Higher ROCOF Exposure

IBRs must sustain Ride-through during these rapid and large frequency swings, which can challenge controller settings and legacy frequency protections that may trip too quickly. PRC-029-1 requires IBRs to ride through specified ROCOF conditions, including rates up to 5 Hz/sec under defined scenarios, and operate across a wider frequency range than synchronous machines, highlighting the importance of robust design and tuning for modern IBRs.

6. Highly Diverse and Non-Standardized Control Designs

IBRs generate short-circuit currents that are much lower than those of conventional synchronous machines. This low current can delay or prevent traditional overcurrent relays from detecting faults. This introduces challenges in fault detection and clearing times, potentially threatening system stability.