Review of ImpedanceBased Analysis Methods Applied to GridForming Inverters in InverterDominated Grids
Abstract
:1. Introduction
2. GridForming Control
 They control voltage source inverters as dispatchable voltage sources with independent control of voltage and frequency. The output current is then determined by the system loading conditions and the inverter current limits. Their ability to function as an “infinite bus” is limited by the size and strength of the DC source.
 Since they do not rely on a stiff grid for synchronism, gridforming inverters impose the grid voltage frequency and phase angle reference through their own controls and are capable of blackstart operation without a dedicated phaselocked loop (PLL).
 Gridforming inverters are voltagecontrolled and have a smaller output impedance compared to gridfollowing inverters, which makes them suitable for weak AC grids.
3. ImpedanceBased Analysis for Controller Design
3.1. DCSide Stability
3.2. ACSide Stability
3.3. Load Disturbance Compensation
3.4. CrossCoupling in Different Domains
3.5. Improved Power Sharing
3.6. Synchronization Stability
3.7. Harmonic Stability
4. Application of Impedance Analysis to Droop Control
5. Conclusions
 1.
 The input impedance should not behave as a negative resistance and remain in the passive region.
 2.
 The output impedance should also be passive to prevent resonant oscillations in the AC output.
 3.
 The output impedance should be small enough to not only reduce circulating currents and improve power sharing accuracy but to also reduce the effect of gridside/load disturbances.
 4.
 The impact of synchronization control on inverter impedances should be included for a comprehensive analysis.
 5.
 Couplings among paralleled inverters which create resonant interactions should be compensated.
Funding
Institutional Review Board Statement
Informed Consent Statement
Conflicts of Interest
References
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Control Method  Features 

Droop Control [33] 

Virtual Synchronous Generator [5] 

Synchronverter [6] 

Direct Vf regulation [34] 

Virtual Oscillator Control [7] 

Matching control [8] 

Inducverter [35] 

Parameter  Value 

Nominal AC voltage: ${V}_{ac}$  294 V (peak) 
Nominal AC current: ${I}_{od}$, ${I}_{oq}$  26.7 A, 0 A 
Nominal DC voltage: ${V}_{dc}$  400 V 
Nominal DC current: ${I}_{dc}$  15 A 
DClink capacitor: C  5 mF 
Lfilter inductor: ${L}_{f}$  0.575 mH 
Lfilter resistor: ${r}_{f}$  0.2 $\Omega $ 
Nominal frequency: ${f}_{s}$  60 Hz 
Switching frequency: ${\omega}_{sw}$  10 kHz 
Current controller gains: $k{i}_{p}$, $k{i}_{i}$  0.105, 35 
Voltage controller gains: $k{v}_{p}$, $k{v}_{i}$  0.008, 40 
Droop coefficients: ${m}_{p}$, ${m}_{q}$  0.001, 0.001 
Sampling period: ${T}_{s}$  100 s 
Filter frequency: ${\omega}_{f}$  1500 Hz 
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Ray, I. Review of ImpedanceBased Analysis Methods Applied to GridForming Inverters in InverterDominated Grids. Energies 2021, 14, 2686. https://doi.org/10.3390/en14092686
Ray I. Review of ImpedanceBased Analysis Methods Applied to GridForming Inverters in InverterDominated Grids. Energies. 2021; 14(9):2686. https://doi.org/10.3390/en14092686
Chicago/Turabian StyleRay, Ishita. 2021. "Review of ImpedanceBased Analysis Methods Applied to GridForming Inverters in InverterDominated Grids" Energies 14, no. 9: 2686. https://doi.org/10.3390/en14092686