Synchronous Condenser vs GFM Inverter — PatSnap Eureka
Synchronous Condenser vs Grid-Forming Inverter for Inertia Emulation
As synchronous generators retire, two competing technologies step in to stabilise low-carbon grids: rotating synchronous condensers delivering physics-based inertia, and grid-forming inverters emulating it algorithmically. Drawing on 50+ patents and peer-reviewed studies, this analysis reveals how they differ — and when to deploy each.
How Each Technology Delivers Inertia to the Grid
The displacement of synchronous generators by converter-interfaced renewables creates a deficit of inertia, leading to higher RoCoF, deeper frequency nadirs, and elevated risk of cascading failures. Two technology families respond differently.
Physics-Based Inertia: Rotating Mass Coupled to Grid Frequency
Synchronous condensers are rotating electrical machines — essentially synchronous generators operated without a prime mover — that exchange reactive power with the AC grid and contribute genuine kinetic energy stored in their rotating masses. Because the rotor is physically coupled to the grid frequency, the inertial response is instantaneous and requires no measurement, communication, or control delay. This physics-based behaviour is the defining advantage of synchronous condensers for system strength provision.
Instantaneous · No control delay · High short-circuit currentAlgorithmic Inertia: Swing Equation Implemented in Software
Grid-forming (GFM) inverters are voltage source converters (VSCs) controlled to behave as voltage sources with an internal frequency governed by a swing equation — directly emulating the electromagnetic and mechanical dynamics of a synchronous generator. Unlike grid-following inverters, which rely on a PLL to track grid voltage, GFM inverters form a voltage phasor internally and exhibit an inherent inertial response to frequency deviations. As documented by Fraunhofer IEE (2020), GFM inverters are capable of operating AC grids with or without rotating machines and inherently deliver momentary reserve.
Programmable · PLL-free · Adaptive inertia constantEnergy-Limited and Capital-Intensive Rotating Machinery
The key technical limitation of synchronous condensers is their inability to produce real power on a sustained basis — they consume real power to cover losses. While flywheels extend the kinetic energy reserve, inertia provision from a synchronous condenser remains energy-limited and cannot be dynamically reprogrammed over wide ranges. Their capital cost, installation footprint, and maintenance requirements for rotating machinery also represent disadvantages compared to static power-electronic alternatives. ABB's patent documentation warns that auxiliary synthetic inertia added to a synchronous condenser can excite sub-synchronous oscillations if the signal is delayed by 180 degrees relative to the rotor swing.
High capex · Maintenance burden · Fixed H constantOscillatory Instability at Higher Emulated Inertia Values
A key stability concern for GFM inverters is that increasing the emulated moment of inertia can make the system oscillatory. Universidad Carlos III de Madrid (2022) showed that stability analysis of GFM converter synchronization via active power control reveals oscillatory behaviour at higher inertia values, requiring a novel compensation mechanism to damp oscillations, with real-time hardware-in-the-loop validation confirming the approach. Furthermore, Tomsk Polytechnic University (2023) demonstrated that in converter-dominated systems with continuously changing renewable generation share, a fixed virtual inertia is inadequate and adaptive VSG control must respond to real-time changes in inertia requirements imposed by grid codes on RoCoF and frequency nadir.
Oscillation risk · Adaptive control required · Hardware-in-loop validatedInertia Technology Landscape: Key Metrics at a Glance
Derived from patent and literature analysis of 50+ sources. All data points sourced directly from the studies cited.
GFM Inverter Control Architecture Distribution
VSG/VSM dominates the patent and literature landscape, followed by adaptive virtual inertia strategies, synchronverter, and DC-link capacitor approaches.
Energy Storage Technologies for GFM Virtual Inertia
GFM inverters must dispatch real power during inertia emulation. The storage medium chosen determines response speed, duration, and system cost.
From VSG to Synchronverter: The GFM Inverter Control Taxonomy
Multiple control variants have been developed and commercialised for grid-forming inverters. The Virtual Synchronous Generator (VSG) / Virtual Synchronous Machine (VSM) approach explicitly implements the swing equation of a synchronous generator in the inverter control loop. As documented by National Institute of Technology Silchar (2020), the VSG emulates both the mechanical inertia and damping characteristics (virtual inertia emulation, VIE) and the excitation system behaviour (virtual excitation emulation, VEE) to control both AC frequency and voltage profiles — mimicking the synchronous generator swing equation so the inverter output responds to frequency deviations as a physical machine would.
Hitachi Energy's VSM patent (EP, 2023) processes measured converter power through a differential equation of angular velocity to obtain a phase angle control contribution, while monitoring the converter's ability to act as a virtual synchronous machine and adjusting the control contribution based on that monitored ability — introducing an adaptive mechanism absent in physical synchronous condensers. Hitachi's earlier distributed power source controller (EP, 2021) extends this to calculate a virtual inertia value based on the specification and operational state of the distributed power source, or set it to a value required by a grid operator — providing a programmable inertia capability fundamentally impossible with a rotating mass.
The Synchronverter concept (Zhejiang University, 2019) implements a complete mathematical model of a synchronous generator including electromagnetic torque and magnetic flux in the converter controller, enabling self-synchronization without a PLL while providing inertia and reactive power support. The DC-link capacitor approach (University of Alberta, US patent 2019) implements rotor inertia using the intermediate DC-link capacitor of a double-stage inverter — simulating rotor speed from the measured DC-link voltage and mapping the changing voltage into the inverter as an internal frequency, eliminating the need for a separate external energy storage system. Learn more about power electronics innovation intelligence at PatSnap.
General Electric Renovables has filed patents across multiple jurisdictions for operating asynchronous inverter-based resources as virtual synchronous machines with coupled storage (US, 2022), applicable to wind and hybrid resources. According to WIPO data, GFM inverter patent filings have accelerated significantly since 2019 as grid codes have tightened.
Synchronous Condenser vs Grid-Forming Inverter: 11 Technical Dimensions
Based on the RTE comparison study (2021) — the most authoritative direct head-to-head evaluation — and corroborated by 50+ additional sources in the dataset.
Explore RTE's Definitive Head-to-Head Study
The RTE comparison (2021) is the most authoritative source comparing both technologies at equivalent apparent power and inertial reserve.
Key Players and Their Patent Strategies
Analysis of the patent and literature dataset reveals distinct clusters of innovation activity across industry leaders and academic institutions.
General Electric / GE Renovables
The most patent-prolific entity in this dataset, with filings on the Hybrid High-Inertia Synchronous Condenser Facility (2015), Systems and Methods for Controlling an Inertia of a Synchronous Condenser (2012–2017), and multiple EP, US, and IN filings for operating asynchronous inverter-based resources as virtual synchronous machines with storage (2022). GE thus covers both physical synchronous condenser improvement and GFM inverter VSM emulation for wind assets. See PatSnap customer case studies for energy sector applications.
ABB / Hitachi Energy
ABB's hybrid SC + power-electronics synthetic inertia architecture (WO 2020, GB 2022) and Hitachi Energy's VSM converter control patent (EP 2023) and distributed power source virtual inertia controller (EP 2021) reflect a strategy of bridging physical and electronic inertia provision. ABB's documentation explicitly warns that if the synthetic inertia signal is delayed by 180 degrees relative to the rotor swing, the electronic output can operate in complete anti-phase to the synchronous machine, exciting sub-synchronous oscillations.
Where Each Technology is Deployed — and Why
Transmission-level system strength restoration: Synchronous condensers are favoured where physical short-circuit current and genuine synchronous inertia are required. The RTE study (2021) is the most directly comparative source in this dataset. It evaluates both technologies for equivalent apparent power and inertial reserve, using time-domain simulations and concluding that both technologies provide grid-forming functions but with distinct behavioural profiles — synchronous condensers provide instantaneous, physics-driven short-circuit current while GFM VSCs require appropriate control and energy storage coupling to match this capability.
Offshore wind and HVDC integration: The coordinated strategy described by China Energy Engineering Group Zhejiang (2019) places synchronous condensers in conjunction with DFIG wind turbines and VSC-HVDC links, assigning each resource a distinct role in a wide-area control scheme. This reflects the practical reality that synchronous condensers serve as backup inertia and voltage support while power-electronic resources handle dynamic active power modulation. ENTSO-E grid code requirements are increasingly driving this hybrid deployment model.
Microgrid and weak grid applications: GFM inverters dominate microgrid deployment. Kyushu University (2023) documents that GFM control is preferred over grid-following control for providing system control and stability in converter-dominated grids, addressing low inertia, reduced power quality, fault-ride-through capability, and reduced stability margins. In stand-alone microgrids, Incheon National University (2017) demonstrated that VSG control inheriting the transient characteristics of synchronous generators substantially improves voltage and frequency transient response compared to conventional droop controllers.
System-level carbon and cost benefits: Flensburg University (2022) found that energy system models which represent only synchronous inertia from fossil-fuel plants significantly overestimate CO2 emissions and system costs, since synthetic inertia from wind turbines and battery storage can substitute for must-run fossil capacity. This finding directly motivates replacing synchronous condensers with GFM inverter-coupled storage where technically feasible, reducing both cost and carbon footprint. Explore PatSnap's energy transition intelligence solutions for deeper sector analysis.
For energy storage sizing, Gannon University (2022) presents an empirical model for sizing Battery Energy Storage Systems required for virtual inertia emulation, noting that VSG-based distributed energy resources exhibit inertia, droop, and damping behaviour similar to synchronous generators but do not optimally solve frequency stability without proper storage capacity. The IEA has highlighted energy storage sizing as one of the critical barriers to widespread GFM inverter adoption in national grid decarbonisation plans.
Technology Suitability Across Six Grid Scenarios
Qualitative suitability scores derived from RTE (2021), Kyushu University (2023), Flensburg University (2022), and TU Wien (2020) assessments in the dataset.
Synchronous Condenser vs GFM Inverter: Suitability by Grid Scenario
Radar comparison across six key grid scenarios. Scores reflect qualitative assessments from peer-reviewed sources — not vendor claims. Higher score = more suitable for that scenario.
Synchronous Condenser vs Grid-Forming Inverter — key questions answered
Synchronous condensers are rotating electrical machines that provide genuine physical inertia through kinetic energy stored in their rotating masses — the inertial response is instantaneous and requires no measurement, communication, or control delay. Grid-forming inverters are voltage source converters controlled to behave as voltage sources with an internal frequency governed by a swing equation, directly emulating synchronous machine behavior algorithmically. GFM inverters form a voltage phasor internally and exhibit an inherent inertial response to frequency deviations, but this response depends on measurement, computation, and control bandwidth.
Yes. Because GFM inverters implementing virtual inertia must actually dispatch real power to emulate the inertial response, the energy storage device must be sized accordingly. Battery Energy Storage Systems (BESS), supercapacitors, or superconducting magnetic energy storage (SMES) are required to deliver real power during the inertial response period. The University of Alberta patented an approach using the DC-link capacitor of a double-stage inverter as the inertia storage medium, eliminating the need for a separate external energy storage system.
For synchronous condensers with auxiliary synthetic inertia, ABB's patent documentation warns that if the synthetic inertia signal is delayed by 180 degrees relative to the rotor swing, the electronic output can operate in complete anti-phase to the synchronous machine, exciting sub-synchronous oscillations and degrading network stability. For GFM inverters, Universidad Carlos III de Madrid (2022) showed that increasing the emulated moment of inertia can make the system oscillatory, requiring a novel compensation mechanism to damp oscillations.
Synchronous condensers provide naturally high short-circuit current and inherently enhance system strength. GFM voltage source converters require specific control design to provide short-circuit current and generally provide lower levels than synchronous condensers. The RTE comparison study (2021) established that both technologies fulfill grid-forming functions but with distinct inertial response profiles and short-circuit current contributions at equivalent capacity ratings.
Coordinated hybrid deployment — synchronous condensers for system strength and short-circuit support combined with GFM inverters for flexible, programmable inertia — represents the emerging best practice. The German inertia dispatch modelling study (Flensburg University, 2022) demonstrated that including wind turbine and battery synthetic inertia in energy models reduces must-run fossil capacity, CO2 emissions, and system costs, but the RTE study (2021) confirms that GFM VSCs require adequate coupled energy storage to match the synchronous condenser's inertial reserve at equivalent capacity ratings.
Adaptive virtual inertia strategies allow real-time adjustment of the emulated inertia constant based on operating conditions. Tomsk Polytechnic University (2023) demonstrated that in converter-dominated systems with continuously changing renewable generation share, a fixed virtual inertia is inadequate, and adaptive VSG control must respond to real-time changes in inertia requirements imposed by grid codes on RoCoF and frequency nadir. This programmability is fundamentally impossible with a rotating mass.
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References
- Performance Assessment of Synchronous Condensers vs Voltage Source Converters Providing Grid-Forming Functions — Réseau de Transport d'Électricité (RTE), Paris, France, 2021
- Hybrid High-Inertia Synchronous Condenser Facility — General Electric Company, US Patent, 2015
- Systems and Methods for Controlling an Inertia of a Synchronous Condenser — General Electric Company, EP, 2012/2017
- Synthetic Inertia Provided Based on Synchronous Machine — ABB Schweiz AG, WO, 2020; ABB Power Grids Switzerland AG, GB, 2022
- Power Supporting Arrangement for a Power Grid Operated as a Virtual Synchronous Machine — Hitachi Energy Switzerland AG, EP, 2023
- Control Device for Distributed Power Source — Hitachi Ltd., EP, 2021
- Grid-Supporting Inverters with Significantly Reduced Storage Requirements — The Governors of the University of Alberta, US, 2019/2021
- System and Method for Operating an Asynchronous Inverter-Based Resource as a Virtual Synchronous Machine with Storage — General Electric Renovables España S.L., US, 2022
- Overview on Grid-Forming Inverter Control Methods — Fraunhofer IEE, 2020
- Adaptive Inertia and Damping Control Strategy Based on Enhanced VSG Model — Tomsk Polytechnic University, 2023
- Improving the Inertial Response of a Grid-Forming Voltage Source Converter — Universidad Carlos III de Madrid, 2022
- Power System Inertia Dispatch Modelling in Future German Power Systems — Flensburg University of Applied Sciences, 2022
- Grid-Forming Control: Advancements towards 100% Inverter-Based Grids — A Review — Kyushu University, 2023
- Sizing of Energy Storage System for Virtual Inertia Emulation — Gannon University, 2022
- Applying Virtual Inertia Control to SMES Systems — Kyushu Institute of Technology, 2019
- A Fuzzy Logic-Based Emulated Inertia Control to a Supercapacitor System — Vellore Institute of Technology, 2022
- Applying Synchronous Condenser for Damping Provision in Converter-Dominated Power System — Danmarks Tekniske Universitet, 2021
- Wide-Area Synthetic Inertia Control of Multiple Resources — China Energy Engineering Group Zhejiang Electric Power Design Institute, 2019
- Comparison of Control Strategies to Realise Synthetic Inertia in Converters — TU Wien, 2020
- Isochronous Control of a Virtual Synchronous Generator Using Inertia and Excitation Emulations — National Institute of Technology Silchar, 2020
- WIPO — World Intellectual Property Organization — Patent filing trend data
- ENTSO-E — European Network of Transmission System Operators for Electricity — Grid code requirements
- IEA — International Energy Agency — Energy storage and grid decarbonisation analysis
All data and statistics on this page are sourced from the references above and from PatSnap's proprietary innovation intelligence platform.
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