Low Voltage Ride Through (LVRT) Testing for Energy Storage Systems

Low voltage ride through (LVRT) testing verifies that a grid-connected energy storage system can remain connected, inject reactive current, and resume normal power exchange when the grid voltage dips during a network fault. This article explains LVRT requirements for battery energy storage systems (BESS), the applicable standards such as GB/T 36547, IEC 62933, and IEEE 1547, the samples and items covered by testing, laboratory and field test methods, and typical pass criteria for grid interconnection compliance.

Technical Overview

Low voltage ride through (LVRT), also referred to as fault ride through (FRT), is the capability of a grid-connected energy storage system to remain electrically connected and continue operating when the voltage at the point of common coupling (PCC) drops to a low value for a short, defined period. Voltage dips are typically caused by short circuits, lightning strikes, ground faults, or the starting of large loads elsewhere on the network. If a large-scale battery energy storage system (BESS) were to trip and disconnect during such a disturbance, the sudden loss of generation or load would further depress or destabilize the grid, potentially triggering cascading disconnections.

Because modern energy storage systems increasingly provide frequency regulation, peak shaving, voltage support, and renewable energy smoothing, transmission and distribution system operators require them to support the grid during faults rather than disconnect. An LVRT test therefore verifies that the energy storage system, and in particular its power conversion system (PCS), can tolerate a defined voltage-versus-time profile without tripping, inject reactive current to assist voltage recovery, and restore active power charging or discharging promptly after the fault is cleared.

LVRT requirements are normally expressed as a boundary curve of residual voltage versus duration. Above the curve, the system must ride through the event; below it, disconnection is permitted. Typical requirements include riding through a zero-voltage condition for approximately 150 ms and residual voltages of around 20% of nominal for roughly 625 ms, although the precise boundaries depend on the applicable grid code, the connection voltage level, and the size of the installation. Reactive current support requirements commonly demand additional quadrature current proportional to the voltage drop, established within a few tens of milliseconds.

Testing is generally carried out by accredited third-party laboratories against standards and grid codes such as GB/T 34120, GB/T 36547, the IEC 62933 series, IEEE 1547-2018, UL 1741 SB, and EN 50549, together with the specific interconnection rules of the relevant system operator. Key behaviors verified during LVRT testing include:

• Continuous connection and synchronized operation throughout the voltage dip, without protective tripping or islanding
• Adequate reactive current injection with the required magnitude, direction, and dynamic response time
• Controlled active power behavior during the dip, including current limitation and DC bus stability
• Rapid and stable recovery of pre-fault active power exchange after voltage restoration
• Coordination between PCS protection settings and the mandatory ride-through envelope

Testing Samples

Power Conversion Systems (PCS) and Grid-Connected Inverters

The PCS is the primary object of LVRT type testing because it directly controls the grid-side current response. A representative production unit of a defined rated power class is tested, connected on the AC side to a programmable grid simulator or voltage dip generator and on the DC side to a battery pack or a battery simulator. The firmware version, control parameters, and undervoltage protection settings must be identical to the commercial configuration intended for deployment.

Integrated and Containerized Battery Energy Storage Systems

For grid-scale projects, complete containerized or skid-mounted BESS units may be tested, including battery racks, the battery management system (BMS), the PCS, the step-up transformer, and the local control and monitoring layer. Testing at this level verifies that supervisory control, BMS communication, and thermal management do not initiate spurious shutdowns during grid faults.

Converters for Other Storage Technologies

Grid-connected converters for flywheel, supercapacitor, and hybrid energy storage systems are also subject to LVRT verification, since grid codes generally apply fault ride through obligations by connection point and rated capacity rather than by storage technology.

Operating Points and Sample Conditions

The sample must be tested at multiple operating points to demonstrate behavior independent of power flow direction. Typical conditions include rated discharging, rated charging, and partial load operation, at state-of-charge levels that allow sustained power delivery or absorption throughout each test sequence.

Testing Items

LVRT test programs are constructed from combinations of fault type, residual voltage depth, and dip duration selected along and above the applicable boundary curve. The core test items are summarized below.

Symmetrical and Asymmetrical Voltage Dip Tests

• Three-phase (symmetrical) voltage dips at residual voltage levels typically including 0%, 20%, 40%, 60%, 75%, and 90% of nominal voltage
• Dip durations at each level, commonly spanning 150 ms to several seconds, corresponding to the points defined by the applicable grid code curve
• Two-phase and single-phase (asymmetrical) fault emulation, including phase-to-phase and phase-to-ground conditions, which produce negative-sequence voltage components that stress the current controller differently than balanced faults
• Zero-voltage ride through (ZVRT) verification, in which the residual voltage approaches 0% for the maximum mandatory duration
• Repetition of selected dips during both charging and discharging operation

Reactive Current Support Verification

During each dip, the reactive current injected by the storage system is measured and compared with the required characteristic. Many grid codes, for example, require additional reactive current of at least 1.5 per unit multiplied by the voltage deviation, established within roughly 30 ms of fault inception. The test evaluates the magnitude, polarity, dynamic response time, and steady-state accuracy of the injected current.

Post-Fault Recovery Verification

After voltage restoration, the system must return to its pre-fault active power exchange within a defined recovery time and ramp rate, without oscillation, overshoot beyond allowable limits, or a second trip. Recovery behavior is assessed from recorded active power and current waveforms following fault clearance.

Complementary Checks

• Verification that no protective relay, BMS alarm chain, or supervisory controller initiates disconnection during or between dips
• Assessment of fault current magnitude and duration to confirm compliance with current limitation requirements
• Optional high voltage ride through (HVRT) testing, which is frequently combined with LVRT since grid codes define both over- and under-voltage envelopes
• Observation of harmonic distortion and current quality during the transient recovery period

Testing Methods

Test Equipment

Laboratory testing employs a voltage dip generator or a four-quadrant power-electronic grid simulator capable of producing controlled, repeatable dips down to near-zero residual voltage with defined phase angles. Common dip generation techniques include impedance-based solutions using series reactors with fast bypass switches, transformer-based solutions with switched secondary windings, and full power-amplifier-based simulators that also allow frequency and phase-jump emulation. The DC side is supplied by a real battery or a battery emulator. Measurements are taken with calibrated voltage and current transducers, power analyzers, and a high-speed data acquisition system, typically sampling at several kilohertz or higher, so that the sub-cycle dynamic response can be resolved accurately.

Laboratory Test Procedure

The test sequence begins with establishment of the steady-state operating point, followed by application of each voltage dip defined in the test plan at the machine terminals or simulated PCC. The dip is held for the specified duration and then removed, restoring nominal voltage. Throughout the event, the system records AC voltages and currents, active and reactive power, DC-side quantities, contactor and breaker status signals, and controller fault flags. Sufficient time is allowed between consecutive dips for the system and battery to stabilize. Each combination of depth, duration, fault type, and power direction is documented with synchronized waveform captures that form the objective evidence of compliance.

Field and On-Site Testing

For installed systems, on-site LVRT verification can be performed using transportable dip generation equipment or, where permitted by the system operator, staged network switching operations. Field measurements should follow good power quality measurement practice, for example in line with IEC 61000-4-30, and should account for the influence of the actual grid impedance, transformer configuration, and background distortion at the connection point. Field tests are commonly used for commissioning acceptance, whereas full type testing is usually completed in the laboratory.

Assessment Criteria

The sample is deemed to pass when, for every test point, the system remains continuously connected and synchronized, does not trip any protection that is required to be coordinated with the ride-through envelope, injects reactive current within the tolerance band of the required characteristic and response time, limits fault currents as specified, and recovers active power within the permitted time and ramp rate after voltage restoration. The final report issued by the accredited third-party laboratory includes the test setup, instrumentation and uncertainty statement, waveform records for each dip, and a compliance matrix mapping each result to the corresponding clause of the applicable standard or grid code.

Applications

LVRT testing is an essential compliance gateway for any energy storage project or product that connects to a public electricity network. Typical applications include:

• Certification of PCS and BESS products for grid interconnection in markets governed by GB, IEC, IEEE, UL, and EN requirements
• Type testing and design validation by manufacturers during product development and before market release
• Commissioning and acceptance testing of utility-scale storage plants, including solar-plus-storage and wind-plus-storage hybrid facilities
• Compliance demonstrations required by transmission and distribution system operators during connection agreements
• Supporting documentation for grid code compliance audits, periodic re-verification after firmware upgrades, and bidding qualifications for storage tenders
• Research and benchmarking use, comparing the dynamic fault response of different converter control strategies

FAQ

What is the difference between LVRT and HVRT?

LVRT evaluates behavior when the grid voltage drops below nominal during a fault, while HVRT evaluates behavior when the voltage rises above nominal, typically after load rejection or fault clearing. Most modern grid codes define both envelopes, and the two tests are frequently performed together using the same grid simulation equipment.

What is zero-voltage ride through (ZVRT)?

ZVRT is the most severe LVRT case, in which the residual voltage at the connection point falls to essentially 0% of nominal for a short mandatory period, commonly around 150 ms depending on the grid code. Passing ZVRT demonstrates that the converter can maintain a controlled current contribution even during the deepest bolted faults close to the connection point.

Which standards govern LVRT testing of energy storage systems?

Frequently referenced standards and codes include GB/T 34120 and GB/T 36547 for electrochemical storage systems connected to the Chinese grid, the IEC 62933 series for electrical energy storage systems, IEEE 1547-2018 and UL 1741 SB for North American interconnection, and EN 50549 for European generator connection. The specific interconnection rules of the local system operator must always be checked, as they may impose stricter curves.

Should testing be performed in a laboratory or in the field?

Formal type testing is normally conducted in an accredited third-party laboratory, where grid simulators provide repeatable, precisely controlled dips down to zero voltage. Field testing with portable dip equipment is used for commissioning, acceptance, and re-verification of installed systems, and must account for real network impedance and background distortion.

How long does an LVRT test campaign take?

A complete LVRT campaign for a PCS or integrated BESS, covering multiple residual voltage levels, durations, symmetrical and asymmetrical faults, and both charging and discharging directions, typically requires several working days of laboratory time in addition to setup, calibration, and report preparation. The exact duration depends on the scope defined in the applicable standard and grid code.

What are the typical pass criteria?

The system must remain connected and synchronized for the full duration of every dip on or above the boundary curve, inject reactive current meeting the required magnitude and response time, avoid protection trips or supervisory shutdowns, and recover pre-fault active power within the specified time and ramp rate after voltage restoration. All evidence is documented in waveform records and a clause-by-clause compliance matrix in the final test report.