# Dynamic Voltage Support of Converters during Grid Faults in Accordance with National Grid Code Requirements

^{*}

## Abstract

**:**

## 1. Introduction

#### 1.1. Requirements and Relevant Standards for the Behavior of Converters during Grid Faults

#### 1.1.1. LVRT

#### 1.1.2. Dynamic Voltage Support during Grid Faults

#### 1.2. Current Limitation

## 2. Simulation

#### 2.1. Description of the Model

Algorithm 1: Implementation of a current limitation according to Section 1.2 |

#### 2.2. LC-Filter Design Considerations and Tuning of the Inverter Current Control

#### 2.3. Application of the Model

## 3. Conclusions

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## Appendix A. Calculation of the Positive- and Negative-Sequence Voltages in the Sequence Analyzer

## Appendix B. List of Symbols

${\mathbf{i}}_{t}$ | normalized instantaneous current vector |

${i}_{L1,t}$ | instantaneous value of the current in phase L1 |

${i}_{L2,t}$ | instantaneous value of the current in phase L2 |

${i}_{L3,t}$ | instantaneous value of the current in phase L3 |

${\widehat{i}}_{max}$ | peak value of the current capability |

${\underline{i}}_{S}$ | current space vector in the $\alpha \beta $-plane |

${\underline{i}}_{S,dq}$ | current space vector in the dq-plane |

${\underline{i}}_{S,d{q}_{1+}}$ | positive-sequence component of the current space vector |

${\underline{i}}_{S,d{q}_{1-}}$ | negative-sequence component of the current space vector |

${i}_{S,{d}_{1+},ref}^{\prime}$ | reference value of the direct/active, positive-sequence component of the normalized current space vector |

${i}_{S,{q}_{1+},ref}^{\prime}$ | reference value of the quadrature/reactive, positive-sequence component of the normalized current space vector |

${i}_{S,{d}_{1-},ref}^{\prime}$ | reference value of the direct/active, negative-sequence component of the normalized current space vector |

${i}_{S,{q}_{1-},ref}^{\prime}$ | reference value of the quadrature/reactive, negative-sequence component of the normalized current space vector |

${i}_{S,{d}_{1+},ref}$ | limited reference value of the direct/active, positive-sequence component of the normalized current space vector |

${i}_{S,{q}_{1+},ref}$ | limited reference value of the quadrature/reactive, positive-sequence component of the normalized current space vector |

${i}_{S,{d}_{1-},ref}$ | limited reference value of the direct/active, negative-sequence component of the normalized current space vector |

${i}_{S,{q}_{1-},ref}$ | limited reference value of the quadrature/reactive, negative-sequence component of the normalized current space vector |

${i}_{S,{d}_{1+}}$ | direct/active, positive-sequence component of the normalized current output space vector |

${i}_{S,{q}_{1+}}$ | quadrature/reactive, positive-sequence component of the normalized current output space vector |

${i}_{S,{d}_{1-}}$ | direct/active, negative-sequence component of the normalized current output space vector |

${i}_{S,{q}_{1-}}$ | quadrature/reactive, negative-sequence component of the normalized current output space vector |

$\mathbf{U}$ | phase-to-phase root-mean-square voltage vector |

${U}_{n}$ | nominal phase-to-phase voltage |

$\mathbf{u}$ | normalized phase-to-phase root-mean-square voltage vector |

${u}_{12}$ | normalized phase-to-phase root-mean-square voltage between L1-L2 |

${u}_{23}$ | normalized phase-to-phase root-mean-square voltage between L2-L3 |

${u}_{31}$ | normalized phase-to-phase root-mean-square voltage between L3-L1 |

${\mathbf{u}}_{N,t}$ | normalized phase-to-neutral instantaneous voltage vector |

${\mathbf{u}}_{N,t,ref}$ | normalized phase-to-neutral instantaneous reference voltage vector |

${u}_{1N,t}$ | normalized phase-to-neutral instantaneous voltage in L1 |

${u}_{2N,t}$ | normalized phase-to-neutral instantaneous voltage in L2 |

${u}_{3N,t}$ | normalized phase-to-neutral instantaneous voltage in L3 |

${\underline{u}}_{S,dq}$ | normalized voltage space vector in the dq-plane |

${u}_{S,{d}_{1+}}$ | direct/active, positive-sequence component of the normalized voltage output space vector |

${u}_{S,{q}_{1+}}$ | quadrature/reactive, positive-sequence component of the normalized voltage output space vector |

${u}_{S,{d}_{1-}}$ | direct/active, negative-sequence component of the normalized voltage output space vector |

${u}_{S,{q}_{1-}}$ | quadrature/reactive, negative-sequence component of the normalized voltage output space vector |

${u}_{S,{d}_{1+},ref}$ | reference value of the direct/active, positive-sequence component of the normalized voltage output space vector |

${u}_{S,{q}_{1+},ref}$ | reference value of the quadrature/reactive, positive-sequence component of the normalized voltage output space vector |

${u}_{S,{d}_{1-},ref}$ | reference value of the direct/active, negative-sequence component of the normalized voltage output space vector |

${u}_{S,{q}_{1-},ref}$ | reference value of the quadrature/reactive, negative-sequence component of the normalized voltage output space vector |

${\underline{u}}_{1+}$ | complex value of the normalized positive-sequence voltage |

${\underline{u}}_{1-}$ | complex value of the normalized negative-sequence voltage |

${u}_{1+}$ | magnitude of the normalized positive-sequence voltage |

${u}_{1+}$ | magnitude of the normalized negative-sequence voltage |

$\theta $ | angle of the normalized positive-sequence voltage |

${\phi}_{\pm}$ | angle between the positive- and negative sequence voltage |

${\overline{u}}_{1min}$ | 1-minute average of the mean value of the phase-to-phase voltages |

${U}_{DCL}$ | DC-link voltage |

${u}_{LC1N,t}$ | instantaneous phase-to-neutral voltage in L1 at the inverter output |

${u}_{LC2N,t}$ | instantaneous phase-to-neutral voltage in L2 at the inverter output |

${u}_{LC3N,t}$ | instantaneous phase-to-neutral voltage in L3 at the inverter output |

${T}_{gf}$ | starting time of a grid fault |

p | normalized active power output of the converter |

q | normalized reactive power output of the converter |

${p}_{ref}$ | reference value of the active power |

${q}_{ref}$ | reference value of the reactive power |

$\omega $ | angular frequency |

${\omega}_{n}$ | nominal angular frequency |

L | inductance of the LC-filter |

l | normalized inductance of the LC-filter |

R | resistance of the LC-filter |

C | capacitance of the LC-filter |

${\tau}_{i}$ | time constant of the current control loop |

${K}_{P}$ | proportional controller gain of the current control loop |

${K}_{I}$ | integral controller gain of the current control loop |

${k}_{1+}$ | proportional factor of the reactive current injection in the positive-sequence system |

${k}_{1-}$ | proportional factor of the reactive current injection in the negative-sequence system |

${f}_{sw}$ | switching frequency of the switching control |

${S}_{n}$ | nominal apparent power of the converter |

$\Delta {I}_{rip}$ | maximum current ripple at the converter output |

${R}_{I}\left(s\right)$ | transfer function of the current controller |

${G}_{I}\left(s\right)$ | process transfer function of the current control loop |

${L}_{I}\left(s\right)$ | loop gain of the current control loop |

## References

- Erlich, I.; Neumann, T.; Shewarega, F.; Schegner, P.; Meyer, J. Wind turbine negative sequence current control and its effect on power system protection. In Proceedings of the 2013 IEEE Power & Energy Society General Meeting, Vancouver, BC, Canada, 21–25 July 2013; pp. 1–5. [Google Scholar]
- VDE. VDE-AR-N 4110: Technische Regeln für den Anschluss von Kundenanlagen an das Mittelspannungsnetz und deren Betrieb (TAR Mittelspannung). 2017. Available online: https://www.vde.com/de/fnn/arbeitsgebiete/tar/tar-mittelspannung-vde-ar-n-4110 (accessed on 9 May 2020).
- E-Control. Technische und organisatorische Regeln für Betreiber und Benutzer von Netzen: TOR Erzeuger: Anschluss und Parallelbetrieb von Stromerzeugungsanlagen des Typs B. 2019. Available online: https://www.e-control.at/documents/1785851/1811582/TOR+Erzeuger+Typ+B+V1.0.pdf/a9a7e5ae-5842-caa9-d2c0-93be4b6e0802?t=1562757801048 (accessed on 9 May 2020).
- Castilla, M.; Miret, J.; Sosa, J.L.; Matas, J.; de Vicu na, L.G. Grid-fault control scheme for three-phase photovoltaic inverters with adjustable power quality characteristics. IEEE Trans. Power Electron.
**2010**, 25, 2930–2940. [Google Scholar] [CrossRef] - Chaudhary, S.K.; Teodorescu, R.; Rodriguez, P.; Kjaer, P.C.; Gole, A.M. Negative sequence current control in wind power plants with VSC-HVDC connection. IEEE Trans. Sustain. Energy
**2012**, 3, 535–544. [Google Scholar] [CrossRef] - Mortazavian, S.; Shabestary, M.M.; Mohamed, Y.A.R.I. Analysis and dynamic performance improvement of grid-connected voltage–source converters under unbalanced network conditions. IEEE Trans. Power Electron.
**2016**, 32, 8134–8149. [Google Scholar] [CrossRef] - Camacho, A.; Castilla, M.; Miret, J.; Borrell, A.; de Vicu na, L.G. Active and reactive power strategies with peak current limitation for distributed generation inverters during unbalanced grid faults. IEEE Trans. Ind. Electron.
**2014**, 62, 1515–1525. [Google Scholar] [CrossRef][Green Version] - Teodorescu, R.; Liserre, M.; Rodriguez, P. Grid Converters for Photovoltaic and Wind Power Systems; John Wiley & Sons: Hoboken, NJ, USA, 2011; Volume 29. [Google Scholar]
- Jia, J.; Yang, G.; Nielsen, A.H. Investigation of grid-connected voltage source converter performance under unbalanced faults. In Proceedings of the 2016 IEEE PES Asia-Pacific Power and Energy Engineering Conference (APPEEC), Xi’an, China, 25–28 October 2016; pp. 609–613. [Google Scholar]
- Du, X.; Wu, Y.; Gu, S.; Tai, H.M.; Sun, P.; Ji, Y. Power oscillation analysis and control of three-phase grid-connected voltage source converters under unbalanced grid faults. IET Power Electron.
**2016**, 9, 2162–2173. [Google Scholar] [CrossRef] - Rodriguez, P.; Timbus, A.V.; Teodorescu, R.; Liserre, M.; Blaabjerg, F. Flexible active power control of distributed power generation systems during grid faults. IEEE Trans. Ind. Electron.
**2007**, 54, 2583–2592. [Google Scholar] [CrossRef] - López, M.A.G.; de Vicu na, J.L.G.; Miret, J.; Castilla, M.; Guzmán, R. Control strategy for grid-connected three-phase inverters during voltage sags to meet grid codes and to maximize power delivery capability. IEEE Trans. Power Electron.
**2018**, 33, 9360–9374. [Google Scholar] [CrossRef][Green Version] - Shin, D.; Lee, K.J.; Lee, J.P.; Yoo, D.W.; Kim, H.J. Implementation of fault ride-through techniques of grid-connected inverter for distributed energy resources with adaptive low-pass notch PLL. IEEE Trans. Power Electron.
**2014**, 30, 2859–2871. [Google Scholar] [CrossRef] - Göksu, Ö.; Teodorescu, R.; Bak, C.L.; Iov, F.; Kjær, P.C. Impact of wind power plant reactive current injection during asymmetrical grid faults. IET Renew. Power Gener.
**2013**, 7, 484–492. [Google Scholar] [CrossRef] - Taul, M.G.; Wang, X.; Davari, P.; Blaabjerg, F. Current reference generation based on next generation grid code requirements of grid-tied converters during asymmetrical faults. IEEE J. Emerg. Sel. Top. Power Electron.
**2019**. [Google Scholar] [CrossRef][Green Version] - Wurm, M. 110-und 30-kV-Netzkurzschlussversuche mit einem 2, 2-MWh-Batteriespeicher. E I Elektrotechnik Und Inf.
**2019**, 136, 21–30. [Google Scholar] [CrossRef] - European Union. Commission Regulation (EU) 2016/631; Establishing a Network Code on Requirements for Grid Connection of Generators (RfG). 2016. Available online: http://data.europa.eu/eli/reg/2016/631/oj (accessed on 9 May 2020).
- IEC 60909-0:2016. Short-Circuit Currents in Three-Phase a.c. Systems—Part 0: Calculation of Currents. 2016. Available online: https://webstore.iec.ch/publication/24100 (accessed on 9 May 2020).
- Beres, R.N.; Wang, X.; Liserre, M.; Blaabjerg, F.; Bak, C.L. A review of passive power filters for three-phase grid-connected voltage-source converters. IEEE J. Emerg. Sel. Top. Power Electron.
**2015**, 4, 54–69. [Google Scholar] [CrossRef][Green Version] - Yazdani, A.; Iravani, R. Voltage-Sourced Converters in Power Systems: Modeling, Control, and Applications; John Wiley & Sons: Hoboken, NJ, USA, 2010. [Google Scholar]
- Marchgraber, J.; Gawlik, W.; Wurm, M. Modellierung der dynamischen Netzstützung von über Umrichter angebundenen Erzeugungsanlagen und Speichern. E I Elektrotechnik Und Inf.
**2019**, 136, 31–38. [Google Scholar] [CrossRef][Green Version] - FGW. Technische Richtlinien für Erzeugungseinheiten und -anlagen; Teil 3 (TR3); Bestimmung der elektrischen Eigenschaften von Erzeugungseinheiten und -anlagen am Mittel-, Hoch- und Höchstspannungsnetz. 2017. Available online: https://wind-fgw.de/wp-content/uploads/2018/10/FGW/Teil3/Rev25/preview/180901-1.pdf (accessed on 9 May 2020).

**Figure 1.**LVRT-curve for Type B non-synchronous power-generating modules (power park modules) in Austria [3]. The minimum phase-to-phase voltage at the PCCR is relevant to the decision of whether a module is allowed to disconnect or not. The LVRT-curve is valid both for symmetrical as well as asymmetrical grid faults. The starting point of the LVRT-curve is defined as ${T}_{gf}$, which is described in Equation (6).

**Figure 2.**Vector diagram to derive the calculation for the current limitation (valid only for $\omega t=0$).

**Figure 4.**“Inverter current control”-block of Figure 3, using a double synchronous reference frame (DSRF) with notch filters (NF) based on [8]. The current limitation implements the explanations in Section 1.2 (R of Equation (25) is neglected).

**Figure 5.**Single-line diagram of the short-circuit location from which measurements are used for simulation.

Parameter | Value |
---|---|

${U}_{n}$ | 550 $\mathrm{V}$ |

${S}_{n}$ | 650 kVA |

${U}_{DCL}$ | 900 $\mathrm{V}$ |

${f}_{sw}$ | 8 $\mathrm{k}$$\mathrm{Hz}$ |

L | 280 $\mathsf{\mu}$$\mathrm{H}$ |

R | 1 $\mathrm{m}$$\mathsf{\Omega}$ |

C | 342 $\mathsf{\mu}$$\mathrm{F}$ |

${\widehat{i}}_{max}$ | $1.1$ pu |

${\tau}_{i}$ | 20 $\mathsf{\mu}$$\mathrm{s}$ |

${K}_{P}$ | 14 pu |

${K}_{I}$ | 50 pu |

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

Marchgraber, J.; Gawlik, W. Dynamic Voltage Support of Converters during Grid Faults in Accordance with National Grid Code Requirements. *Energies* **2020**, *13*, 2484.
https://doi.org/10.3390/en13102484

**AMA Style**

Marchgraber J, Gawlik W. Dynamic Voltage Support of Converters during Grid Faults in Accordance with National Grid Code Requirements. *Energies*. 2020; 13(10):2484.
https://doi.org/10.3390/en13102484

**Chicago/Turabian Style**

Marchgraber, Jürgen, and Wolfgang Gawlik. 2020. "Dynamic Voltage Support of Converters during Grid Faults in Accordance with National Grid Code Requirements" *Energies* 13, no. 10: 2484.
https://doi.org/10.3390/en13102484