# Grid Code-Dependent Frequency Control Optimization in Multi-Terminal DC Networks

^{1}

^{2}

^{3}

^{4}

^{5}

^{6}

^{*}

^{†}

## Abstract

**:**

## 1. Introduction

## 2. Frequency Related Grid Code Requirements

#### 2.1. Regulation Levels

#### 2.2. Requirements for Power Plants Connected to HVDC Systems

- 50 Hz $\pm \phantom{\rule{4pt}{0ex}}2\%$ (49 Hz to 51 Hz) for $95\%$ of the week;
- 50 Hz $\pm \phantom{\rule{4pt}{0ex}}15\%$ ($42.5$ to $57.5$ Hz) $100\%$ of the time.

#### 2.3. Synthetic Inertia

#### 2.4. Requirements from Grid Codes

## 3. HVDC Modeling

#### 3.1. AC System Dynamics

#### 3.2. Converter and MTDC System Dynamics

#### 3.3. Converter Control

#### 3.4. Droop Control

#### 3.5. Phase-Locked Loop

## 4. Proposed Controller

#### 4.1. Optimal Performance Indicators

#### 4.2. Controller Optimization Using Particle Swarm Optimization

#### 4.3. Python-PSCAD Interface

## 5. Results and Discussion

- The $RoCoF$ should not be very steep according to the grid code requirements. If the $RoCoF$ is too steep, the converters would disconnect from the AC grid and could therefore no longer support it, thus provoking power imbalances;
- The $nadir$ should not drop below a specific value to ensure that the converter stays connected to the grid and follows the grid code limits;
- The settling time ${t}_{s}$ needs to be minimized to reach a stable operating state as quickly as possible, as an earlier recovery means less impact.

#### 5.1. Base Case Scenario

#### 5.2. Scenario A

#### 5.3. Scenario B

## 6. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

## References

- Strbac, G.; Konstantinidis, C.V.; Moreno, R.; Konstantelos, I.; Papadaskalopoulos, D. It’s All About Grids: The Importance of Transmission Pricing and Investment Coordination in Integrating Renewables. IEEE Power Energy Mag.
**2015**, 13, 61–75. [Google Scholar] [CrossRef] - Chamorro, H.R.; Ordonez, C.A.; Peng, J.C.; Ghandhari, M. Non-synchronous generation impact on power systems coherency. IET Gener. Trans. Distrib.
**2016**, 10, 2443–2453. [Google Scholar] [CrossRef] - Milano, F.; Dörfler, F.; Hug, G.; Hill, D.J.; Verbič, G. Foundations and Challenges of Low-Inertia Systems (Invited Paper). In Proceedings of the 2018 Power Systems Computation Conference (PSCC), Dublin, Ireland, 11–15 June 2018; pp. 1–25. [Google Scholar] [CrossRef][Green Version]
- Liu, X.; Lindemann, A. Control of VSC-HVDC Connected Offshore Windfarms for Providing Synthetic Inertia. IEEE J. Emerg. Select. Top. Power Electr.
**2018**, 6, 1407–1417. [Google Scholar] [CrossRef] - Cao, J.; Du, W.; Wang, H.F.; Bu, S.Q. Minimization of Transmission Loss in Meshed AC/DC Grids with VSC-MTDC Networks. IEEE Trans. Power Syst.
**2013**, 28, 3047–3055. [Google Scholar] [CrossRef] - Ordonez, C.A.; Puentes, A.; Chamorro, H.R.; Ramos, G. p-q theory for active compensation applied to supergrids and microgrids. In Proceedings of the 2012 Workshop on Engineering Applications, Bogota, Colombia, 2–4 May 2012; pp. 1–6. [Google Scholar] [CrossRef]
- Chamorro, H.R.; Ramos, G. Harmonic and power flow hybrid controller applied to VSC based HVDC stations. In Proceedings of the 2010 IEEE/PES Transmission and Distribution Conference and Exposition: Latin America (T D-LA), Sao Paulo, Brazil, 8–10 November 2010; pp. 245–250. [Google Scholar] [CrossRef]
- Litzenberger, W.; Mitsch, K.; Bhuiyan, M. When It’s Time to Upgrade: HVdc and FACTS Renovation in the Western Power System. IEEE Power Energy Mag.
**2016**, 14, 32–41. [Google Scholar] [CrossRef] - Yuan, Z.; You, S.; Liu, Y.; Liu, Y.; Osborn, D.; Pan, J. Frequency control capability of Vsc-Hvdc for large power systems. In Proceedings of the 2017 IEEE Power Energy Society General Meeting, Birmingham, UK, 10–12 February 2017; pp. 1–5. [Google Scholar]
- Zhou, H.; Su, Y.; Chen, Y.; Ma, Q.; Mo, W. The China Southern Power Grid: Solutions to Operation Risks and Planning Challenges. IEEE Power Energy Mag.
**2016**, 14, 72–78. [Google Scholar] [CrossRef] - Gemmell, B.; Korytowski, M. Refurbishments in Australasia: Upgrades of HVdc in New Zealand and FACTS in Australia. IEEE Power Energy Mag.
**2016**, 14, 72–79. [Google Scholar] [CrossRef] - Kim, S.; Kim, H.; Lee, H.; Lee, J.; Lee, B.; Jang, G.; Lan, X.; Kim, T.; Jeon, D.; Kim, Y.; et al. Expanding Power Systems in the Republic of Korea: Feasibility Studies and Future Challenges. IEEE Power Energy Mag.
**2019**, 17, 61–72. [Google Scholar] [CrossRef] - Irnawan, R.; Da Silva, F.F.; Bak, C.L.; Bregnhøj, T.C. An initial topology of multi-terminal HVDC transmission system in Europe: A case study of the North-Sea region. In Proceedings of the 2016 IEEE International Energy Conference (ENERGYCON), Leuven, Belgium, 4–8 April 2016; pp. 1–6. [Google Scholar] [CrossRef][Green Version]
- Pan, J.; Callavik, M.; Lundberg, P.; Zhang, L. A Subtransmission Metropolitan Power Grid: Using High-Voltage dc for Enhancement and Modernization. IEEE Power Energy Mag.
**2019**, 17, 94–102. [Google Scholar] [CrossRef] - Chamorro, H.R.; Riaño, I.; Gerndt, R.; Zelinka, I.; Gonzalez-Longatt, F.; Sood, V.K. Synthetic Inertia Control Based on Fuzzy Adaptive Differential Evolution. Int. J. Electr. Power Energy Syst.
**2019**, 105, 803–813. [Google Scholar] [CrossRef][Green Version] - Zhang, W.; Rouzbehi, K.; Luna, A.; Gharehpetian, G.B.; Rodriguez, P. Multi-terminal HVDC grids with inertia mimicry capability. IET Renew. Power Gener.
**2016**, 10, 752–760. [Google Scholar] [CrossRef][Green Version] - Andreasson, M.; Dimarogonas, D.V.; Sandberg, H.; Johansson, K.H. Distributed Controllers for Multiterminal HVDC Transmission Systems. IEEE Trans. Control Netw. Syst.
**2017**, 4, 564–574. [Google Scholar] [CrossRef][Green Version] - McNamara, P.; Milano, F. Model Predictive Control-Based AGC for Multi-Terminal HVDC-Connected AC grids. IEEE Trans. Power Syst.
**2018**, 33, 1036–1048. [Google Scholar] [CrossRef][Green Version] - Zhu, J.; Booth, C.D.; Adam, G.P.; Roscoe, A.J.; Bright, C.G. Inertia Emulation Control Strategy for VSC-HVDC Transmission Systems. IEEE Trans. Power Syst.
**2013**, 28, 1277–1287. [Google Scholar] [CrossRef][Green Version] - Zhu, J.; Guerrero, J.M.; Hung, W.; Booth, C.D.; Adam, G.P. Generic inertia emulation controller for multi-terminal voltage-source-converter high voltage direct current systems. IET Renew. Power Gener.
**2014**, 8, 740–748. [Google Scholar] [CrossRef][Green Version] - Ndreko, M.; Bucurenciu, A.; Popov, M.; Van der Meijden, M.A.M.M. On grid code compliance of offshore mtdc grids: Modeling and analysis. In Proceedings of the 2015 IEEE Eindhoven PowerTech, Eindhoven, The Netherlands, 29 June–2 July 2015; pp. 1–6. [Google Scholar] [CrossRef]
- Ye, Y.; Lu, Z.; Xie, L.; Qiao, Y. A Coordinated Frequency Regulation Strategy for VSC-HVDC Integrated Offshore Wind Farms. In Proceedings of the 2018 IEEE Power Energy Society General Meeting (PESGM), Portland, OR, USA, 5–10 August 2018; pp. 1–5. [Google Scholar]
- Papangelis, L.; Guillaud, X.; Cutsem, T.V. Frequency support among asynchronous AC systems through VSCs emulating power plants. In Proceedings of the 11th IET International Conference on AC and DC Power Transmission, Birmingham, UK, 10–12 February 2015; pp. 1–9. [Google Scholar]
- Jose, K.; Adeuyi, O.; Liang, J.; Ugalde-Loo, C.E. Coordination of fast frequency support from multi-terminal HVDC grids. In Proceedings of the 2018 IEEE International Energy Conference (ENERGYCON), Limassol, Cyprus, 3–7 June 2018; pp. 1–6. [Google Scholar]
- Kirakosyan, A.; El-Saadany, E.F.; El Moursi, M.S.; Salama, M. Selective Frequency Support Approach for MTDC Systems Integrating Wind Generation. IEEE Trans. Power Syst.
**2020**. [Google Scholar] [CrossRef] - Zhang, Q.; McCalley, J.D.; Ajjarapu, V.; Renedo, J.; Elizondo, M.; Tbaileh, A.; Mohan, N. Primary Frequency Support through North American Continental HVDC Interconnections with VSC-MTDC Systems. IEEE Trans. Power Syst.
**2020**. [Google Scholar] [CrossRef] - Adeuyi, O.D.; Cheah-Mane, M.; Liang, J.; Jenkins, N. Fast Frequency Response From Offshore Multiterminal VSC–HVDC Schemes. IEEE Trans. Power Deliv.
**2017**, 32, 2442–2452. [Google Scholar] [CrossRef][Green Version] - Ai, Q.; Liu, T.; Yin, Y.; Tao, Y. Frequency coordinated control strategy of HVDC sending system with wind power based on situation awareness. IET Gener. Trans. Distrib.
**2020**, 14, 3179–3186. [Google Scholar] [CrossRef] - Xiong, Y.; Yao, W.; Wen, J.; Lin, S.; Ai, X.; Fang, J.; Wen, J.; Cheng, S. Two-Level Combined Control Scheme of VSC-MTDC Integrated Offshore Wind Farms for Onshore System Frequency Support. IEEE Trans. Power Syst.
**2020**. [Google Scholar] [CrossRef] - Rouzbehi, K.; Miranian, A.; Luna, A.; Rodriguez, P. Optimized control of multi-terminal DC GridsUsing particle swarm optimization. In Proceedings of the 2013 15th European Conference on Power Electronics and Applications (EPE), Lille, France, 3–5 September 2013; pp. 1–9. [Google Scholar] [CrossRef]
- Namara, P.M.; Meere, R.; O’Donnell, T.; McLoone, S. Distributed MPC for Frequency Regulation in Multi-Terminal HVDC Grids. IFAC Proc. Vol.
**2014**, 47, 11141–11146. [Google Scholar] [CrossRef] - Wen, Y.; Zhan, J.; Chung, C.Y.; Li, W. Frequency Stability Enhancement of Integrated AC/VSC-MTDC Systems With Massive Infeed of Offshore Wind Generation. IEEE Trans. Power Syst.
**2018**, 33, 5135–5146. [Google Scholar] [CrossRef] - Papangelis, L.; Debry, M.; Panciatici, P.; Van Cutsem, T. Coordinated Supervisory Control of Multi-Terminal HVDC Grids: A Model Predictive Control Approach. IEEE Trans. Power Syst.
**2017**, 32, 4673–4683. [Google Scholar] [CrossRef] - Raza, A.; Yousaf, Z.; Jamil, M.; Gilani, S.O.; Abbas, G.; Uzair, M.; Shaheen, S.; Benrabah, A.; Li, F. Multi-Objective Optimization of VSC Stations in Multi-Terminal VSC-HVdc Grids, Based on PSO. IEEE Access
**2018**, 6, 62995–63004. [Google Scholar] [CrossRef] - Gonzalez-Longatt, F.M.; Acosta, M.N.; Chamorro, H.R.; Torres, J.L.R. Power Converters Dominated Power Systems; Springer: Cham, Switzerland, 2021; pp. 1–35. [Google Scholar] [CrossRef]
- COMMISSION REGULATION (EU) 2016/ 1447—of 26 August 2016—Establishing a Network Code on Requirements for Grid Connection of High Voltage Direct Current Systems and Direct Current-Connected Power Park Modules. p. 65. Available online: https://eur-lex.europa.eu/eli/reg/2016/1447/oj (accessed on 4 December 2020).
- Saborío-Romano, O. Connection of OWPPs to HVDC Networks Using VSCs and Diode Rectifiers: An Overview. p. 5. Available online: https://www.researchgate.net/publication/322571208_Connection_of_OWPPs_to_HVDC_networks_using_VSCs_and_Diode_Rectifiers_an_Overview (accessed on 4 December 2020).
- VDE/FNN. Technische Anschlussregeln für HGÜ-Systeme und über HGÜ-Systeme Angeschlossene Erzeugungsanlagen. Available online: https://www.vde.com/de/fnn/arbeitsgebiete/tar/tar-hgue (accessed on 4 December 2020).
- Winter, W.; Chan, D.; Norton, M.; Haesen, E.; Székely, Á. Towards a european network code for HVDC connections and offshore wind integration. In Proceedings of the 2015 50th International Universities Power Engineering Conference (UPEC), Stoke on Trent, UK, 1–4 September 2015; pp. 1–6. [Google Scholar]
- GmbH., T.T. Offshore-Netzanschlussregeln—O-NAR. 2017. Available online: https://docplayer.org/56149134-Offshore-netzanschlussregeln-o-nar-tennet-tso-gmbh.html (accessed on 4 December 2020).
- Rate of Change of Frequency (RoCoF) Withstand Capability—ENTSO-E Guidance Document for National Implementation for Network Codes on Grid Connection. Available online: https://eepublicdownloads.entsoe.eu/clean-documents/Network%20codes%20documents/NC%20RfG/IGD_RoCoF_withstand_capability_final.pdf (accessed on 7 December 2020).
- Need for Synthetic Inertia (SI) for Frequency Regulation—ENTSO-E Guidance Document for National Implementation for Network Codes on Grid Connection. Available online: https://eepublicdownloads.entsoe.eu/clean-documents/Network%20codes%20documents/NC%20RfG/IGD_Need_for_Synthetic_Inertia_final.pdf (accessed on 7 December 2020).
- Chamorro, H.R.; Sanchez, A.C.; Verjordet, A.; Jimenez, F.; Gonzalez-Longatt, F.; Member, S.; Sood, V.K. Distributed Synthetic Inertia Control in Power Systems. In Proceedings of the 8th International Conference on Energy and Environment: Energy Saved Today is Asset for Future, CIEM 2017, Bucharest, Romania, 19–20 October 2017; pp. 74–78. [Google Scholar] [CrossRef][Green Version]
- Chuquen, R.M.; Chamorro, H.R. Graph Theory Applications to Deregulated Power Systems; Springer Briefs in Electrical and Computer Engineering; Springer International Publishing: Berlin, Germany, 2021. [Google Scholar] [CrossRef]
- Saad, H.; Peralta, J.; Dennetiere, S.; Mahseredjian, J.; Jatskevich, J.; Martinez, J.A.; Davoudi, A.; Saeedifard, M.; Sood, V.; Wang, X.; et al. Dynamic Averaged and Simplified Models for MMC-Based HVDC Transmission Systems. IEEE Trans. Power Deliv.
**2013**, 28, 1723–1730. [Google Scholar] [CrossRef] - Cole, S.; Beerten, J.; Belmans, R. Generalized Dynamic VSC MTDC Model for Power System Stability Studies. IEEE Trans. Power Syst.
**2010**, 25, 1655–1662. [Google Scholar] [CrossRef][Green Version] - Haileselassie, T.M. Control, Dynamics and Operation of Multi-terminal VSC-HVDC Transmission Systems. 2012. Available online: https://ntnuopen.ntnu.no/ntnu-xmlui/handle/11250/257409 (accessed on 4 December 2020).
- Fahad, S.; Mahdi, A.J.; Tang, W.H.; Huang, K.; Liu, Y. Particle Swarm Optimization Based DC-Link Voltage Control for Two Stage Grid Connected PV Inverter. In Proceedings of the 2018 International Conference on Power System Technology (POWERCON), Guangzhou, China, 6–8 November 2018; pp. 2233–2241. [Google Scholar]

**Figure 2.**Requirements for the frequency-dependent power supply of generators connected via HVDC systems (based on [40]).

**Figure 4.**Methodology for the optimization of the AC grid stabilization using a PSCAD and Python interface.

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

$\frac{\left|\mathsf{\Delta}{P}_{1}\right|}{{P}_{max}}$ | 1.5–10% |

${t}_{1,\mathrm{inertia}}$ | $2\phantom{\rule{4pt}{0ex}}\mathrm{s}$ |

${t}_{1,\mathrm{no}\phantom{\rule{4pt}{0ex}}\mathrm{inertia}}$ | TSO |

${t}_{2}$ | $30\phantom{\rule{4pt}{0ex}}\mathrm{s}$ |

Iteration w | Settling Time (s) | Nadir (Hz) |
---|---|---|

$\mathrm{w}=1$ | $58.7967$ | $49.9624$ |

$\mathrm{w}$ = 2 | $59.0327$ | $49.9630$ |

$\mathrm{w}$ = 3 | $58.8410$ | $49.9636$ |

$\mathrm{w}$ = 4 | $58.8014$ | $49.9642$ |

$\mathrm{w}$ = 5 | $59.1660$ | $49.9658$ |

$\mathrm{w}$ = 6 | $58.9222$ | $49.9663$ |

$\mathrm{w}$ = 7 | $58.8060$ | $49.9676$ |

$\mathrm{w}$ = 8 | $59.3174$ | $49.9688$ |

$\mathrm{w}$ = 9 | $59.0327$ | $49.9697$ |

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. |

© 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**

Hoffmann, M.; Chamorro, H.R.; Lotz, M.R.; Maestre, J.M.; Rouzbehi, K.; Gonzalez-Longatt, F.; Kurrat, M.; Alvarado-Barrios, L.; Sood, V.K. Grid Code-Dependent Frequency Control Optimization in Multi-Terminal DC Networks. *Energies* **2020**, *13*, 6485.
https://doi.org/10.3390/en13246485

**AMA Style**

Hoffmann M, Chamorro HR, Lotz MR, Maestre JM, Rouzbehi K, Gonzalez-Longatt F, Kurrat M, Alvarado-Barrios L, Sood VK. Grid Code-Dependent Frequency Control Optimization in Multi-Terminal DC Networks. *Energies*. 2020; 13(24):6485.
https://doi.org/10.3390/en13246485

**Chicago/Turabian Style**

Hoffmann, Melanie, Harold R. Chamorro, Marc René Lotz, José M. Maestre, Kumars Rouzbehi, Francisco Gonzalez-Longatt, Michael Kurrat, Lazaro Alvarado-Barrios, and Vijay K. Sood. 2020. "Grid Code-Dependent Frequency Control Optimization in Multi-Terminal DC Networks" *Energies* 13, no. 24: 6485.
https://doi.org/10.3390/en13246485