New-type power system stability testing evaluates the capability of power-electronics-dominated grids with high shares of wind, solar, and energy storage to maintain frequency stability, voltage stability, and wide-band oscillation stability under disturbances. This technical article covers the scope of stability testing, representative equipment samples, key testing items, industry-standard methodologies, and typical engineering applications.
Technical Overview
A new-type power system is characterized by a high penetration of renewable generation, extensive use of power electronic converters, growing energy storage capacity, and reduced synchronous inertia. While this architecture enables deep decarbonization, it fundamentally changes the dynamic behavior of the grid: the rotating mass of conventional generators is progressively replaced by converter-interfaced resources whose control loops interact across a wide frequency range, from a few hertz to several kilohertz.
As a result, stability assessment must extend beyond the traditional categories of rotor-angle, frequency, and voltage stability. Modern frameworks, such as GB 38755 and IEEE stability definitions for converter-dominated systems, introduce additional categories including resonance stability and converter-driven stability, which manifest as sub-synchronous oscillation (SSO), super-synchronous oscillation, and high-frequency oscillation. New-type power system stability testing is the systematic verification, through measurement and simulation, of how individual devices and aggregated plants behave under these conditions, ensuring that grid-connected resources do not destabilize the wider network.
Testing is typically performed by accredited third-party laboratories or grid operator test facilities, covering device-level certification, plant-level commissioning tests, and electromagnetic transient (EMT) model validation. The objectives are to demonstrate compliance with interconnection codes, confirm the accuracy of simulation models used in stability studies, and quantify the contribution of converter-based assets to frequency support, voltage regulation, and oscillation damping.
Testing Samples
Wind Turbines and Wind Farm Components
Both doubly-fed induction generator (DFIG) and full-converter permanent magnet synchronous generator (PMSG) wind turbines are tested, along with their main circuit components, crowbar and chopper protection, and turbine-level controllers. Wind farms connected near series-compensated lines or weak grid points are priority samples for sub-synchronous oscillation evaluation, in accordance with IEC 61400-21-1 and national grid codes.
Photovoltaic Inverters and PV Power Stations
String and central PV inverters, station-level power plant controllers, and aggregated PV plants are tested for power quality, fault ride-through, frequency response, and broadband impedance characteristics. Verification follows IEC 62116, IEC 61000 series requirements, and applicable national photovoltaic grid-connection standards.
Energy Storage Converters and Hybrid Stations
Power conversion systems (PCS) for battery energy storage, as well as wind-solar-storage hybrid stations, are tested for bidirectional power capability, fast frequency response, virtual synchronous machine behavior, grid-forming control performance, and black start capability.
Flexible Transmission and Compensation Equipment
Voltage source converter HVDC (VSC-HVDC) terminals, static var generators (SVG), static var compensators (SVC), and other flexible AC/DC transmission equipment are tested for dynamic reactive support, control interaction, and wideband impedance behavior across their operating envelopes.
Grid-Forming Converters and Microgrid Systems
Grid-forming inverters, virtual synchronous generators, and islanded microgrid systems are evaluated for autonomous voltage and frequency establishment, seamless transition between grid-connected and islanded modes, and fault current contribution.
Testing Items
Depending on the sample type and applicable grid code, a new-type power system stability test program generally includes the following items:
- Power quality testing: harmonic and interharmonic distortion, flicker, three-phase voltage unbalance, voltage deviation, and frequency deviation, measured per IEC 61000-4-7, IEC 61000-4-15, and IEC 61000-4-30.
- Frequency stability testing: primary frequency response droop and deadband, fast frequency response activation time, virtual inertia emulation, rate-of-change-of-frequency (RoCoF) withstand capability, and frequency ride-through envelope verification.
- Voltage stability testing: reactive power capability curves (P-Q envelopes), dynamic reactive response time, automatic voltage control (AVC) tracking accuracy, and voltage ride-through performance.
- Fault ride-through testing: low-voltage ride-through (LVRT), high-voltage ride-through (HVRT), continuous operating voltage and frequency ranges, and reactive current injection during faults.
- Wide-band oscillation testing: frequency-domain impedance characterization, sub-synchronous and super-synchronous oscillation damping, control interaction with series compensation and weak grids, and high-frequency resonance screening.
- Anti-islanding testing: detection of unintended islanding conditions and disconnection within specified time limits per IEC 62116.
- Grid-forming function testing: black start and self-excitation, voltage source behavior under grid disturbances, transient current limiting, and multi-converter parallel stability.
- Model validation: verification of EMT and RMS simulation models against field or laboratory measurements, including active/reactive power response, ride-through trajectories, and impedance-frequency curves.
Testing Methods
Stability testing combines field measurement, controlled disturbance injection, laboratory testing, and simulation-based verification. The principal methods are described below.
- Field measurement and monitoring: Class A power quality analyzers and dedicated wideband oscillation monitoring devices record voltage, current, power, frequency, and spectral content over extended periods at the point of interconnection, capturing real disturbance events and natural oscillations.
- Controlled disturbance testing: mobile fault generators, grid simulators, and voltage source amplifiers apply voltage dips, swells, phase jumps, and frequency ramps to the device under test, verifying ride-through and response characteristics against grid code envelopes.
- Impedance scanning and frequency sweeping: a broadband perturbation signal is injected (series or shunt injection) while the device operates at defined setpoints, extracting the impedance-frequency characteristic used to assess resonance risk and control interaction.
- Hardware-in-the-loop (HIL) and power hardware-in-the-loop (PHIL) testing: the physical converter or its controller is coupled with a real-time simulator to evaluate behavior in synthetic but realistic grid scenarios, including weak grid, islanding, and fault conditions that are impractical to create in the field.
- EMT simulation and model validation: measured disturbance waveforms from field or laboratory tests are replayed in electromagnetic transient simulation platforms, and simulated versus measured responses are compared using standardized accuracy criteria for active power, reactive power, voltage, and current.
- Aggregation and screening studies: validated device models are aggregated at plant level to perform small-signal and time-domain stability screening, identifying potential sub-synchronous or high-frequency oscillation modes across the operating envelope.
All test procedures should be executed under documented test plans with calibrated instrumentation, traceable measurement chains, and uncertainty evaluation, and the results are compiled into test reports suitable for grid code compliance submission.
Applications
New-type power system stability testing supports multiple engineering and regulatory applications:
- Grid code compliance certification for wind farms, PV stations, and storage plants prior to connection, including ride-through and power quality verification.
- Sub-synchronous oscillation risk assessment for renewable clusters located near series-compensated transmission corridors or operationally weak grid areas.
- Acceptance testing and commissioning of energy storage and grid-forming projects, including fast frequency response, black start, and islanding transition performance.
- EMT model bank development for grid operators and dispatch centers, enabling accurate stability studies in high-renewable-penetration systems.
- Post-event analysis following oscillation incidents, voltage excursions, or ride-through failures, providing root cause identification and corrective action verification.
- Equipment development support, allowing converter manufacturers to validate control firmware upgrades, grid support functions, and damping strategies before deployment.
FAQ
Q: Why is stability testing different for a new-type power system compared with a conventional grid?
A: In a converter-dominated system, stability is governed not only by electromechanical dynamics but also by fast control loops of power electronic converters, which introduce broadband interaction risks, reduced inertia, and altered fault behavior. Testing therefore must cover wide-band impedance characteristics, grid support functions, and converter-driven stability phenomena that traditional stability assessment did not address.
Q: Which standards are most relevant to new-type power system stability testing?
A: Commonly applied references include IEC 61400-21-1 for wind turbine electrical characteristics, IEC 62116 for islanding prevention, the IEC 61000 series for power quality measurement, IEEE 1547 and IEEE 2800 for inverter-based resource interconnection, and national grid codes such as GB 38755 for power system security and stability together with the corresponding wind and PV grid-connection standards.
Q: How is sub-synchronous oscillation risk evaluated in practice?
A: A combination of field oscillation monitoring, impedance-frequency scanning of the connected converters, and electromagnetic transient simulation is used. If the measured impedance characteristics of the device interact adversely with the grid impedance at sub-synchronous frequencies, mitigation measures such as control parameter retuning or supplementary damping are verified through retesting.
Q: Can stability tests be performed without interrupting plant operation?
A: Many assessment activities, such as power quality monitoring, natural disturbance recording, and passive impedance measurement, can be performed online. Ride-through and controlled disturbance tests, however, require scheduled outages or dedicated test windows because they intentionally apply voltage and frequency excursions to the equipment.
Q: How long does a typical stability testing program take?
A: The duration depends on scope. Device-level certification testing in a laboratory may take several weeks, while a full plant-level program, including field commissioning tests, wideband monitoring, and EMT model validation, typically spans several months to align with construction schedules and grid connection milestones.
