Low-Voltage Ride-Through

Low-voltage ride-through (LVRT) is a solar inverter’s ability to remain connected to the electricity grid during a temporary fall in grid voltage, rather than immediately switching off. More precisely, it must withstand voltage dips within a prescribed voltage-time envelope, while meeting applicable requirements for current injection and recovery after the disturbance.

What the inverter must do

A fault on the electricity network can briefly depress voltage even at solar installations that are not themselves faulty. LVRT distinguishes a disturbance that the inverter should withstand from a condition requiring protective disconnection.

• The voltage-time curve specifies the combinations of voltage depth and duration for which the inverter must remain connected; deeper dips generally have shorter required withstand periods.
• Remaining connected does not necessarily mean maintaining full active-power output. The inverter’s response is constrained by the available voltage, its current rating and the applicable grid requirements.
• Where required by the grid code, the inverter must provide reactive-current support during the disturbance to help voltage recovery.
• After the disturbance clears, the inverter must restore its output in accordance with the specified recovery requirements.

Why this capability matters

If many solar inverters disconnect simultaneously during a temporary voltage dip, the grid loses generation just when it is already disturbed. LVRT helps prevent this collective loss of generation and supports power-system stability.

• Reactive-current injection can support grid voltage during a fault, although it does not replace the network protection needed to clear that fault.
• As inverter-based generation increases, its coordinated response to disturbances becomes increasingly important for maintaining reliable electricity supply.
• LVRT addresses voltage disturbances; it should not be confused with frequency ride-through, which concerns remaining connected during specified frequency deviations.

Grid-code requirements and protection limits

In India, the relevant Central Electricity Authority connectivity standards provide the regulatory framework for fault ride-through requirements where applicable. The precise obligation must be checked against the installation’s category and applicable connectivity provisions, rather than assuming one numerical threshold for every rooftop inverter.

• LVRT is a bounded requirement, not an instruction to remain connected under every fault or indefinitely low voltage.
• Anti-islanding protection serves a different purpose: it prevents an inverter from continuing to energise an unintentionally isolated portion of the network. LVRT must be coordinated with this and other protection functions.