In brief
Low-voltage ride-through (LVRT) is the requirement that grid-connected equipment stays online and behaves predictably during short voltage dips instead of tripping off. HVRT extends the same rule to overvoltage events, and ZVRT to faults where voltage collapses to zero. Grid codes define ride-through profiles — voltage-versus-time envelopes — that inverters, PCS, UPS and other converters must survive to connect, often while actively supporting the grid during the event itself.
Key takeaways
- Ride-through exists because mass disconnection during a fault turns a local disturbance into a regional one — the grid needs its converters to hold on, not flee.
- An LVRT curve is an envelope in voltage-versus-time space: stay connected anywhere above the line, and behave as specified while you do.
- Where the applicable code and assigned category require it, ride-through includes dynamic support during the event and controlled recovery — not only remaining connected.
- ZVRT is often among the most demanding cases: at commanded zero residual voltage, normal terminal-voltage reference is absent and recovery must remain controlled.
- Requirements differ meaningfully by jurisdiction and equipment class — always test against the specific code and edition your project connects under.
Why do grids demand ride-through at all?
The requirement was born from a failure mode. Early grid-tied inverters were programmed defensively: at the first sign of abnormal voltage, disconnect and protect yourself. Individually sensible; collectively dangerous. A transmission fault depresses voltage across a wide area for a few hundred milliseconds — and if every inverter in that area interprets the dip as its cue to leave, the grid loses a large block of generation at precisely the moment it is already stressed. The local fault has now been amplified into a regional generation deficit, with frequency and further voltage consequences cascading outward.
As inverter-based resources grew, grid codes increasingly required equipment to ride through defined disturbances — stay connected, remain controlled and, where the applicable rules say so, provide dynamic support while the fault is cleared. Ride-through is therefore not a nuisance test bolted onto certification; it is part of the connection behaviour that must be mapped clause by clause. The companion grid-code compliance guide explains how requirements, test procedures and acceptance roles remain separate.
What does an LVRT curve look like?
| Envelope segment | What it defines | What the test record should show |
|---|---|---|
| Pre-event dwell | Nominal voltage, frequency, operating point and settling time | Stable initial conditions and the device configuration under test |
| Entry edge | How quickly voltage reaches the specified residual or overvoltage level | Delivered edge timing, phase behaviour and current response on one timebase |
| Event dwell | Required depth or height and the time for which it is sustained | Connection status, reactive-current behaviour, protection states and limit flags |
| Recovery boundary | The permitted trajectory back toward the continuous operating region | Voltage tracking, resynchronisation, active-power restoration and any overshoot |
| Post-event observation | The period in which delayed trips or unstable recovery can appear | Continued operation, settled power and a complete event log |
Read the envelope in four segments. The depth is how far voltage falls — profiles range from moderate sags to full collapse, with the deepest cases handed to ZVRT. The duration is how long the depressed voltage persists before clearance; grid faults are typically cleared within a few hundred milliseconds, and the profiles reflect that. The recovery boundary defines how voltage returns toward nominal, and equipment must tolerate the trajectory — including the awkward partial-voltage region on the way back up. Throughout the shaded region, the applicable behavioural clause determines what the converter must do. Depending on the code and assigned category, that can include dynamic reactive-current support during the event and a defined active-power recovery after voltage returns.
That behavioural clause is what makes ride-through a control-system test rather than a robustness test. Remaining connected may be necessary, but the campaign also examines whether the measured current response, timing and recovery meet the criteria assigned to the device under test.
HVRT and ZVRT: the other two letters
HVRT mirrors the logic upward. Overvoltage events arise from load rejection, capacitive effects on lightly loaded lines and fault-recovery transients, and equipment that trips on a brief swell can create the same collective risk as equipment that trips on a dip. HVRT profiles therefore define an overvoltage trajectory and a time for which the assigned equipment class must remain controlled. For the test bench this has a hard implication: voltage headroom must be specified at the required load and duration, not inferred from a nominal rating. Released MVGS data identifies an optional high-voltage configuration, but the usable HVRT envelope must be confirmed for the quoted system.
ZVRT is the extreme case of LVRT: the commanded profile reaches zero at the test boundary. The converter temporarily loses its normal voltage reference and must follow the connection rule’s specified state and recovery behaviour when voltage returns. The source must deliver the commanded residual voltage and recovery at the DUT without transformer, control or load effects silently reshaping the event. That is one reason the distinction between front-end and back-end isolation matters when the test architecture is selected.
How do requirements differ by grid code?
The ride-through concept is widespread; the parameters are not. Depth, duration, recovery shape, the reactive-support formula and the equipment classes covered all vary by jurisdiction and by edition. The table maps the frameworks structurally — deliberately without quoting curve parameters, because standards revise and the only safe source for numbers is the current official text of the code your project connects under.
| Framework | Region | Ride-through scope | Verification note |
|---|---|---|---|
| IEEE 1547-2018 (with IEEE 1547.1 procedures) | United States (DER; adoption-specific) | LVRT and HVRT by abnormal-performance category | Category assignment and the adopting jurisdiction drive the applicable curves |
| AS/NZS 4777.2 | Australia / New Zealand (inverters) | Voltage ride-through with regional settings | Large-scale plant additionally faces NER / AEMO performance standards |
| EU Requirements for Generators (national implementations) | Europe | Fault ride-through by generating-module type | Parameters and procedures are completed by national implementation |
What belongs in the test matrix?
Translate the governing document into controlled test rows before programming the source. Each row should identify not only a voltage level and duration, but the complete basis that makes the result reproducible and reviewable.
| Matrix field | What to freeze before execution | Why it changes the result |
|---|---|---|
| Code basis | Document, edition, amendment, clause, assigned category and regional setting | A familiar profile from the wrong category is still the wrong test |
| DUT identity | Model, hardware, firmware, parameter set and protection configuration | Evidence is valid only for the configuration actually exercised |
| Operating point | Active and reactive power, current limit, DC-side or load condition and pre-event dwell | Converter response and source headroom vary with the starting point |
| Delivered event | Residual or overvoltage trajectory, phase selection, entry, dwell and recovery measured at the DUT terminals | Programmed setpoints can be reshaped by the source, transformer, cables and load |
| Required response | Connection state, support current, protection behaviour and post-event recovery rule | “Did not trip” may be necessary but may not be the complete obligation |
| Evidence package | Repetition ID, common timebase, raw waveforms, status logs, uncertainty and deviation record | Reviewers need a traceable decision, not only a screenshot |
This matrix also exposes scope early. If a required waveform cannot be measured at the DUT boundary, or the opposite-side operating point cannot be held through the event, the gap belongs in the bench design and quotation rather than in a deviation written after testing.
How is ride-through actually tested?
A ride-through test is the controlled reproduction of the envelope: the source executes the programmed voltage trajectory — dip or swell, at the specified depth, duration and recovery — while instrumentation captures the device under test’s voltage, current, operating state and support response. Three properties decide whether the result is usable. First, dynamic performance must be verified at the DUT terminals, at the declared load and with adequate measurement bandwidth; a catalogue rise/fall figure alone does not prove the delivered event. Second, trajectory accuracy must cover the entry, dwell and recovery segments rather than only a setpoint snapshot. Third, repeatability and evidence must share configuration identity and a common timebase so each required repetition can be traced to raw waveforms, status logs and the programmed profile. The grid-simulator fundamentals guide describes the source boundary; the compliance plan decides the pass/fail rule.
Can ride-through be tested at reduced voltage scale? Partially. Control logic — state machines, support algorithms and fault recovery — can be exercised on simulation, hardware-in-the-loop and low-voltage benches early in development. Those methods do not reproduce the complete medium-voltage insulation, protection, current and thermal boundary. The required final evidence and test voltage come from the applicable conformity or connection process, so the test-method mix should be agreed before the campaign rather than labelled “certification grade” by the source supplier.
Product fit
Where the MVGS fits
Executing MV-class ride-through profiles is a core workload of the XGY MVGS medium-voltage grid simulator. Released product data lists direct medium-voltage output, LVRT/HVRT/ZVRT functions and a rise/fall-time specification below 1 ms for the product family; the delivered edge at the DUT, usable overvoltage headroom, event sequence, load condition and evidence format remain configuration- and programme-specific. Those conditions are reviewed against the target grid code and test boundary at quotation.
FAQ
Frequently asked questions
What is the difference between LVRT and anti-islanding?
They pull in opposite directions, deliberately. LVRT requires equipment to stay connected through a grid disturbance; anti-islanding requires it to disconnect when the grid is genuinely gone and the equipment would otherwise energise an island. Compliance testing verifies both behaviours and, critically, that the equipment distinguishes the two situations correctly.
Does ride-through apply to energy storage and UPS, or just solar inverters?
It applies to grid-connected converters generally. Energy-storage PCS face ride-through requirements in both charge and discharge directions, and grid-interactive UPS architectures inherit the requirements of their connection class. The specific curves depend on the code and equipment category your project connects under.
Why is ZVRT often considered especially demanding?
At commanded zero residual voltage, the converter has no normal terminal-voltage reference while its required state and recovery still have to remain controlled. The exact obligation comes from the applicable rule, and the test source must demonstrate the delivered residual voltage and recovery at the DUT boundary rather than rely on programmed setpoints alone.
Can I take ride-through curve parameters from this article?
No — deliberately. Depth, duration and support requirements vary by jurisdiction, equipment class and standard edition, and they change on revision. Take parameters only from the current official text of the code your project connects under, and have the applicable category confirmed as part of the compliance plan.
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