A Review of System Strength and Inertia in Renewable-Energy-Dominated Grids: Challenges, Sustainability, and Solutions
Abstract
:1. Introduction
- An analysis of recent events and SO market intervention in the deregulated and weakly interconnected electricity markets of Australia, Ireland, and Texas.
- A critical review of current mitigation techniques including synchronous condensers and ancillary services.
- An evaluation of research gaps in system strength and inertia estimation methods, high-IBR grid modelling, and non-linear GFMI output current control techniques.
2. Understanding System Strength and Inertia
2.1. Definitions and Key Concepts
2.2. Impact of IBR Generation
3. System Strength and Inertia Challenges
3.1. System Strength Issues
Voltage Stability
- IBRs cause a drop in SCR making the node voltage more susceptible to rapid current changes caused by transient conditions.
- GFLI algorithms demonstrate suboptimal performance under faulted conditions. IBR plant tripping during faulted conditions is a significant problem as shown by the examples provided in Section 4.3.
- The tripping in item 2 can lead to further voltage instability and entire plant tripping.
3.2. Inertia Issues
3.2.1. Frequency Stability
3.2.2. Angle Stability
3.2.3. Emerging Stability Categories
- Resonance stability, related to the impact of HVDC and FACTS devices.
- Converter stability, relating to the impact of GFLI (both current and voltage source).
4. Case Studies from Regions with High Renewable Energy
4.1. IBR Penetration Levels
4.2. System Operator Interventions
- Maximum system non-synchronous penetration (SNSP) limit of 75%.
- A minimum number of conventional units on (MUON) of seven units.
4.3. System Strength and Inertia Events
5. Mitigation Strategies
5.1. Synchronous Condensers
5.2. Flexible AC Transmission Systems
5.3. Grid-Forming Inverters
5.4. Ancillary Services
6. Future Research Direction
6.1. Improve System Strength and Inertia Evaluation Methodology
6.1.1. System Strength
Method | Formula | Contribution | Ref |
---|---|---|---|
SCRPOC | Commonly used metric. Suitable for single inverter connection at POC. | [104,105] | |
WSCR-MW | Considered N IBRs in the locality and provided a weighted value. | [104,105] | |
WSCR-MVA | As per WSCR-MW but considered IBR reactive power capability. | [104] | |
CSCR | Created composite bus and provides an average SCR. Assumes perfect bus coupling. | [104,107] | |
ESCR | Enhanced SCR by including shunt reactive compensation. | [108] | |
IILSCR | Used power tracing to reflect bus interactions | [106] |
6.1.2. Inertia
6.2. Improved Grid Modelling
6.3. Advanced GFLI/GFMI Control
6.3.1. Droop Control
6.3.2. Virtual Synchronous Machine
- The energy storage ramp rate impact on VSM stability requires further study. Research is required before the integration and impact of energy storage for VSM systems is clear.
- The transient stability issue remains for VSM. This is due to the use of linear control techniques, such as PI, in many current implementations. Issues such as energy storage ramping and filter parameter changes have also been shown to impact stability. Non-linear techniques, SMC and MPC, have demonstrated increased stability margin and robustness for VSM, but research and real-world implementation remain limited.
- Smart-grid technologies like VSM involve the use of communications and can be computationally expensive. As VSMs are a critical power grid infrastructure, further research is required in this area to ensure that new solutions are secure, cost-effective, and implementable on existing inverter technology.
6.3.3. Dispatchable Virtual Oscillator Control
6.3.4. GFMI Fault Current
6.3.5. Swing Equation Derivation from Energy
7. Discussion
Benefit to Planetary Health
8. Conclusions
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
References
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- THE 17 GOALS | Sustainable Development. Available online: https://sdgs.un.org/goals (accessed on 5 February 2025).
Grid System | System Operator | Platform | Action | Outcome |
---|---|---|---|---|
NEM | AEMO | NEM Dispatch Engine (NEMDE) | Network curtailment Economic constraint | 9.44% of solar in the NEM was curtailed during October 2023 [56]. |
SEM | EirGrid/SONI | SEMOpx | SNSP limit of 75% MUON of 6 SGs Dispatch down instruction | 1795 GWh of RESs was curtailed in 2023 [54]. |
ERCOT | ERCOT | Security-Constrained Economic Dispatch (SCED) | GTCs | Almost 6000 h of GTC-based curtailment in 2023 [57]. |
Plant Category | Plant Loss (MW) |
---|---|
SG | 884 |
IBR | 1771 |
Service | GFLI | GFMI | Synchronous Machine |
---|---|---|---|
Inertia | - | Virtual | Physical |
Damping | Limited | Virtual | Physical |
Fault current | - | 1.2–1.5 p.u. | 6–8 p.u. |
Voltage/reactive power support | Yes | Yes | Yes |
System strength support | - | Yes | Yes |
Phase jump support | - | Yes | Yes |
Primary frequency response | Yes | Yes | Yes |
Fast frequency response | Yes | Yes | - |
Service Provider | Locations | Capacity |
---|---|---|
Enel-X | NSW, SA, QLD, VIC | 134 MW |
Grid Beyond | SA, VIC, NSW | 145 MW |
VIOTAS | SA, VIC, NSW, QLD, TAS | 53 MW |
Simulation Category | Complexity | Computational Demand | Fidelity | Application | Assumptions | Domain |
---|---|---|---|---|---|---|
Phasor Based (RMS) | Low | Low | Low | Long-term dynamic analysis such as load flow and stability analysis. | Linearity, stable, and pure system frequency | Frequency |
Positive Sequence | Low | Low | Medium | Stability analysis. | Balanced system | Steady state |
Electromagnetic Transient (EMT) | High | High | High | Analysing EMT phenomena such as switching, IBR dynamics, and protection system operation. | None | Time |
Ref. | Method | Research Contribution | Limitation |
---|---|---|---|
[103,105,107,109,110] | Improved system strength metrics | Research has developed new metrics that better reflect the reactive power control capabilities of IBRs. | Proposed methods such as QESCR are not yet sufficiently studied to gain widespread industry adoption by SOs. |
[113,114,115,116,117,118] | Improved inertia estimation | Significant research has been conducted to obtain real-time online estimates of grid inertia. Notably, refs. [104,105] consider virtual inertia contribution. | SOs take a conservative approach in the absence of accurate real-time inertia estimates. More research is required to develop solutions that can be widely adopted. |
[121,122,123,124,125,126,127,128] | EMT grid modelling | Advancements have been made, notably with hybrid modelling techniques. | Further research is required to develop modelling techniques with required EMT level fidelity to represent IBR dynamics while adhering to reasonable computational requirements. Modelling for grid connection approvals remains a bottle neck as noted in Section 5.3. |
[131,133,134,135,136] | Droop control | Droop control aims to emulate governor control in a steam turbine. Improved concepts such as adaptive droop control and blending non-linear techniques, such as fuzzy logic, have been made. | Droop controllers generally rely on PLLs for synchronisation. Droop is a measured and control response and, therefore, limited to primary frequency control. This is a valuable service in declining inertia. |
[130,131,136,138,139,140,141,144,145,146,147,148,149,150,151,153,154,155,156,157,158,159,160,161,163,164,165,167,168,169,170,171,172,173,176,182,183] | Virtual synchronous machine | VSM can replace declining inertia with a virtual form by emulating the swing equation for SGs. Non-linear control methods such as SMC and MPC are gaining traction with improved transient stability and recovery characteristics. | Energy storage requirements and integration techniques for inertia provision has limited research. VSM transient stability remains a problem in strong grids. Fault current provision remains a limitation as most proposed research solutions involve performance compromises. Communication and computational requirements need to be carefully managed. |
[85,152,177,178,179,180,181,183] | Dispatchable Virtual Oscillator Control | Like non-linear VSM, dVOC is emerging as a solution in the literature for fast transient response for inverters and reliable recovery from faulted conditions. | dVOC techniques struggle to provide good system strength due to its time-domain-based control. dVOC experiences 3rd order harmonics that require new solutions to meet grid requirements. dVOC is not as active in the research as VSM; as a result, development appears slower. |
Theme 1. Addressing system strength decline | ||
Recommendation | Commentary | Paper section reference |
Improved system strength metrics. | Seek new methods of system strength evaluation, beyond SCRPOC, that appropriately recognise the reactive power control capability of IBRs. This is important to avoid unnecessary curtailment of RESs and delay of RES projects. The QESCR method is of particular interest to achieve this goal. | Section 6.1.1 |
Voltage and frequency support requirements. | Droop control algorithms can increase the primary control effectiveness of IBRs in providing both voltage and frequency support to the grid. Clearly quantified SO requirements for frequency and voltage support will greatly aid researchers in further developing solutions. | Section 6.3.1 |
Theme 2. Compensation for falling inertia | ||
Recommendation | Commentary | Section reference |
Demand side solutions. | Demand response, often used for peak demand reduction, can also provide valuable primary frequency control services. These services support declining inertia. Demand response is low cost, quick to implement, and effective. SOs should consider demand response as a key component of their primary frequency control strategy. | Section 5.4 |
Improved inertia estimation. | Accurate dispatch of inertia supporting services becomes critical in high-IBR grids. SOs require accurate real-time inertia data to determine ancillary service requirements. Joint research and development with academia is highly recommended. | Section 5.4 and Section 6.1.2 |
Theme 3. Market incentives | ||
Recommendation | Commentary | Section reference |
Market-based incentives for advanced GFLI/GFMI asset investments. | Market incentives to compensate for both GFMI and RESs for providing voltage, frequency, and inertia support. Provision of these services will come at an opportunity cost for plant operators; compensation will be required. A market-based approach can provide a low-cost path but requires more development. Incentives should consider industry and academic partnership approaches. | Section 4.1, Section 5.3, Section 5.4, and Section 6.3.1 |
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Moore, P.; Alimi, O.A.; Abu-Siada, A. A Review of System Strength and Inertia in Renewable-Energy-Dominated Grids: Challenges, Sustainability, and Solutions. Challenges 2025, 16, 12. https://doi.org/10.3390/challe16010012
Moore P, Alimi OA, Abu-Siada A. A Review of System Strength and Inertia in Renewable-Energy-Dominated Grids: Challenges, Sustainability, and Solutions. Challenges. 2025; 16(1):12. https://doi.org/10.3390/challe16010012
Chicago/Turabian StyleMoore, Paul, Oyeniyi Akeem Alimi, and Ahmed Abu-Siada. 2025. "A Review of System Strength and Inertia in Renewable-Energy-Dominated Grids: Challenges, Sustainability, and Solutions" Challenges 16, no. 1: 12. https://doi.org/10.3390/challe16010012
APA StyleMoore, P., Alimi, O. A., & Abu-Siada, A. (2025). A Review of System Strength and Inertia in Renewable-Energy-Dominated Grids: Challenges, Sustainability, and Solutions. Challenges, 16(1), 12. https://doi.org/10.3390/challe16010012