Table 6 Overview of the characteristics of virtual inertia control strategy
Classification based on solution method | Types of control strategy/Topology | Characteristics | Merits | Demerit | Refs. |
|---|---|---|---|---|---|
Frequency-power response based topology:: | Virtual synchronous generator (VSG): and virtual synchronous control (VSYNC) | Utilizes a 1st-order model of a synchronous machine. It is a simplified approach to emulate system inertia. Inertia emulation method is based on the frequency response of synchronous generators Current controlled source method: A control signal is generated to inject the required amount of power from the storage units commensurate to the frequency deviation | Can provide fast frequency response in steady-state It has inherent overcurrent protection Simplified strategy for reducing frequency nadir in the modern power grid. Achieves better stability in weak power grid compared to the droop control method. | Frequency response is not as fast as SG Inaccurate frequency derivative data from phase-locked loop (PLL) Can be used only in grid-connected mode Prone to instability as a result of noise | |
Swing equation-based Topology | Synchronverter and Virtual Synchronous Machine (VISMA) | Inertia emulation is based on the exact dynamics of synchronous generators Frequency droop loop is used to regulate output power from converter Operation based on power angle control Operates on de-loaded RES Utilizes a 2nd, 5th, and 7th-order model of a synchronous machine It is a current-controlled voltage source method | Has small damping ratio with lower distortions.It can operate in both off-grid and on-grid mode Provides frequency and voltage regulation Phase-locked loop is not required. | Complex algorithms used may result in numerical instability. No inherent overcurrent protection hence external protection devices are required during transient conditions Difficult to implement in real life Lacks fault ride-through capability Presence of high-frequency noise due to converter switching | |
Synchronous Power Controller (SPC) | Gives an approximate emulation of the dynamic frequency response of the SG based on the conventional swing equation Utilizes a lower order model of a synchronous machine | It is simple to implement Can operate in island as well as grid-connected mode.•Has inherent overcurrent protection | Prone to numerical instabilities Difficulty in obtaining accurate control parameters may lead to unwanted oscillation | ||
Droop control | Virtual oscillator control (VOC) and:Inducverter | Inducverter is based on emulating the exact dynamics of inductor machines.:• Regulates active power based on frequency deviation using the virtual rotor inertia of the inverter | Phase-locked loop is not required Less prone to grid faults | Respond slowly to transients.:• Can operate in grid-connected mode only Prone to instability in weak grid Associated with high-frequency noise and vibrations |