With the continuous expansion of renewable energy installations and the deepening digital transformation of power systems, traditional grid operation methods are undergoing profound changes. To address declining grid stability and regulation capabilities, an innovative control technology known as the Virtual Synchronous Generator (VSG) has emerged. This paper explores VSG concepts, technical principles, and their integration with energy storage systems.

I. Background to VSG Technology  

In conventional centralised power systems, synchronous generators served as the ‘central nervous system’ maintaining grid frequency and voltage stability. Speed governors controlled mechanical rotation to stabilise frequency, while excitation systems regulated current to maintain voltage, ensuring seamless grid operation.

However, the large-scale integration of renewable energy sources such as wind and solar power has altered this paradigm. These renewable generation methods predominantly utilise power electronic interfaces, lacking the inertia and regulation capabilities of traditional synchronous generators. Consequently, the grid becomes more susceptible to frequency and voltage fluctuations when subjected to disturbances.

Simply increasing the installed capacity of renewable energy and energy storage cannot fundamentally resolve this issue. For energy storage to genuinely assume the role of a ‘generator,’ it must possess frequency and voltage regulation capabilities—precisely where VSG technology comes into play.

II. Operating Principles of VSG

The core concept of VSG technology involves utilising power electronic devices and advanced control algorithms to enable inverters to ‘mimic’ the mechanical and electromagnetic dynamic characteristics of synchronous generators. Through this approach, power electronic equipment can provide inertia support and regulation capabilities to the grid, akin to conventional generators.

Primary functions include:

1.  Simulated Inertia Response: During rapid grid frequency fluctuations, VSGs employ control strategies to provide virtual inertia, mitigating frequency deviation.
2.  Frequency Regulation: VSGs automatically adjust active power output in response to frequency changes, performing frequency regulation akin to generators.
3. Voltage Regulation: By controlling output voltage magnitude and phase angle, the VSG maintains voltage stability within localised grid sections.
4. Power Modulation: The VSG flexibly allocates active and reactive power, dynamically responding to system conditions.

Based on control architecture, VSGs are categorised into voltage-controlled and current-controlled configurations to suit diverse application scenarios.

III. Integration of VSG with Electrochemical Energy Storage  

Energy storage systems, particularly lithium-ion battery systems, offer rapid response times and high control precision, making them ideal carriers for VSG functionality. VSG technology endows storage systems with ‘generator attributes’, enabling synchronous power generation characteristics within the grid.

Within microgrids, each power conversion system (PCS) can emulate synchronous generator operation through VSG algorithms:

A ‘virtual governor’ manages frequency control;

A ‘virtual exciter’ maintains voltage stability.

When multiple VSG energy storage systems operate in parallel, they function akin to synchronous generators rotating in unison, forming a stable virtual synchronous network that provides reliable power supply to regional or isolated grids.

IV. Advantages and Application Prospects of VSG Energy Storage Systems  

The deep integration of VSG with electrochemical energy storage not only enhances the value of energy storage systems but also offers novel approaches to grid stability and renewable energy integration. Key advantages include:

1. Ultra-fast response: Battery storage can respond to VSG commands within milliseconds, providing instantaneous power support to the grid.
2. Intelligent Energy Management: VSG control strategies optimise battery charge/discharge profiles, extending system lifespan and enhancing efficiency.
3. Enhanced Renewable Integration: Dynamic voltage and frequency support facilitates smoother grid integration of intermittent sources like wind and solar power.
4. Market Participation Potential: VSG-enabled storage systems can engage in ancillary service markets (frequency regulation, peak shaving) to generate additional economic returns.

The advent of Virtual Synchronous Generator (VSG) technology transforms energy storage systems from mere ‘power reservoirs’ into vital ‘virtual generators’ sustaining grid stability. As renewable energy penetration continues to rise, the integration of VSG with energy storage will become a core enabling technology within future smart grids and microgrid systems, providing critical assurance for achieving high-penetration clean energy integration.