Modern power systems, integrated with microgrids and Distributed Energy Resources (DERs), have shifted their operational mechanisms from centrally-dominated architectures to complex, inter-coupled ecosystems. In these systems, numerous inverters interfacing renewable sources must be precisely synchronized and harmonized to ensure grid stability.

Then the fundamental question emerges: Who commands the grid’s key metrics like voltage and frequency – and among the interconnected sources who is tasked with comply with the collective pulse?

What underpins the balancing among sub-systems on the grid is the coordination of grid-forming and grid-following controls, which defines the grid’s resilience from micro-level harmonic suppression to system-level inertia support and black-start capability.

Why Grid-Forming vs. Grid-Following are Critical for Modern Power Systems?

To understand the roles of Grid-Forming and Grid-Following technologies, one must revisit the foundational distinction between how power is controlled and injected into a system — transitioning from voltage source behaviour to current source behaviour.

Grid-Following Operation is in Nature a Current Source

A current source is an electronic device or circuit that delivers a constant, fixed amount of electric current to a load, regardless of the voltage across it.

Inverters interfacing renewable energy with the grid generally operate as followers that synchronize to the grid’s pre-defined voltage and frequency via PLL. In the event of outages, these systems cannot sustain operation independently.

Grid-Forming Operation Sustains Power System as a Voltage Source

A voltage source provides a constant electrical potential difference to drive current through a circuit.

Grid-forming technology allows inverters to act as independent voltage sources, sustaining the grid even without external reference while emulating inertia and damping of traditional generators.

Key Operation Differences between Grid-Forming vs. Grid-Following Inverters against Grid Disturbances

Extending the topic from the above clarification regarding the nature of grid-forming and grid-following operations, their stability, and resiliences against certain variety of grid anomalies and disturbances such as voltage sags, frequency deviations, weak-grid oscillations, and grid restoration events.

The following table specifies several common scenarios and explains how each control strategy responds.

	Grid-Following	Grid-Forming
Voltage Sag & Fault Ride-Through (LVRT)	PLL-Dependent Current Control: Operates as a current source synchronized by PLL. Deep voltage sags or phase jumps may cause PLL loss of lock, leading to unstable current control or protective tripping.	Voltage Source Behaviour: Maintains an internal voltage reference and injects reactive current according to the PCC voltage deviation. Phase reference remains stable during deep sags, enabling effective voltage support.
Weak Grid Conditions (Low SCR)	Stability Limited by Grid Impedance: Strong coupling between PCC voltage and current control loop. Low SCR conditions may trigger PLL-induced oscillations, particularly when multiple units operate in parallel.	Voltage Reference Establishment: Forms a controlled voltage source through power synchronization control. Provides damping to voltage oscillations and maintains stable operation in very low SCR networks.
Frequency Disturbance & Power Imbalance	Frequency Tracking: Follows grid frequency through PLL. Power response depends on external commands and delayed measurements, providing limited inertial response during disturbances.	Inertia Emulation: Implements swing-equation-based control to adjust frequency according to active power imbalance. Provides virtual inertia and damping to limit ROCOF and frequency nadir.
Blackstart & Grid Restoration	Grid Reference Required: Requires an existing voltage vector for PLL synchronization. Cannot energize a dead bus or establish system voltage and frequency independently.	Autonomous Grid Establishment: An internal oscillator defines voltage magnitude and phase during the blackstart. Capable of energizing a dead bus and providing the voltage-frequency reference during system restoration.