As the global energy landscape transitions toward renewable sources, maintaining grid stability while integrating variable renewable energy (VRE) systems—such as solar photovoltaics (PV) and wind turbines—has become increasingly important. One essential feature that ensures the resilience of these systems during disturbances is Low Voltage Ride-Through (LVRT) capability.
What is LVRT?
Low Voltage Ride-Through (LVRT) refers to the ability of a power generating unit to stay connected to the grid during short-term voltage sags caused by faults or other disturbances. Rather than disconnecting from the grid, a VRE system with LVRT continues to operate and helps support voltage recovery.
Why is LVRT Important?
1. Prevents Mass Disconnection
During faults, significant voltage dips can cause large numbers of generators to disconnect if not equipped with LVRT. This simultaneous disconnection can severely destabilize the grid and potentially lead to widespread blackouts.
2. Supports Grid Recovery
Generators with LVRT capabilities can inject reactive power during faults, aiding voltage recovery and enabling the grid to return to a stable operating condition more quickly.
3. Regulatory Compliance
Most grid operators around the world now mandate LVRT as a precondition for interconnecting renewable energy systems. Compliance with these grid codes ensures system reliability and market participation.
4. Facilitates High Renewable Penetration
Without LVRT, utilities would limit the amount of VRE that can be connected to the grid. Implementing LVRT capabilities allows higher levels of renewable integration while maintaining system security.
International Standards and Grid Code Requirements
To ensure consistent LVRT performance, various national and international standards define minimum capabilities for different generator types:
| Region / Body | Standard / Grid Code | LVRT Requirements |
|---|---|---|
| IEC | IEC 61400-21 (Wind), IEC 62817 (PV) | Performance metrics under voltage disturbance conditions |
| USA (NERC) | NERC PRC-024-2 | Specifies voltage/time curves for ride-through behavior |
| Europe (ENTSO-E) | EU RfG | Requires LVRT for Type C and D generation units |
| India (CEA) | CEA Grid Code | VRE must remain connected during voltage dips of specified severity |
| Australia (AEMO) | Generator Performance Standards | Inverters must ride through faults and support the grid |
| China | GB/T 19964 (PV systems) | National technical specification for LVRT in PV systems |
How to Achieve LVRT in VRE Systems
Achieving LVRT compliance requires a combination of hardware design, inverter control algorithms, and protection coordination. Key methods include:
1. Advanced Inverter Control
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Fast fault detection via DSPs or microcontrollers.
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Reactive current injection to stabilize voltage during faults.
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PLL decoupling to maintain synchronization even under distorted voltages.
2. DC-Link Voltage Management
During a fault, the inverter’s power output path may be blocked, causing DC-link voltage to rise. Solutions include:
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Energy storage integration
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Dynamic braking resistors
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Crowbar circuits
3. Grid-Side Support Devices
Devices like STATCOMs or SVCs can provide additional reactive support to help meet LVRT requirements in weak grid scenarios.
4. Protection System Coordination
Protection relays must be set to allow inverters to remain online during the duration of the voltage sag as specified by the grid code. This involves:
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Adjusting undervoltage, overcurrent, and anti-islanding settings.
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Using ride-through curves from grid code standards to set relay thresholds.
5. Testing and Certification
Type-testing using voltage sag simulators and grid simulators is essential to demonstrate compliance with LVRT requirements. Certified testing laboratories typically verify performance against IEC or national grid standards.
Conclusion
As VRE penetration continues to grow worldwide, LVRT is no longer optional—it is essential. It ensures that renewable energy sources can contribute to grid stability rather than compromise it during transient events. By complying with international standards and employing robust inverter controls, energy developers and operators can ensure the seamless, resilient integration of renewables into modern power systems.