Reliable Modular Multilevel Converters (MMCs) for High -Voltage Direct-Current (HVDC) Transmission

1. Reliable Modular Multilevel Converters (MMCs) for High-Voltage Direct-Current (HVDC) Transmission Fujin Deng Department of Energy Technology Aalborg University, Denmark fde@et.aau.dk

2. HVDC Transmission Technology Advantages: • Low losses & Small footprint • Long-distance power transmission • Active and reactive power individual control • No reactive power and frequency regulation issue • Power transmission between different AC grids (different voltage or frequency)

3. 3 Outline Basics of MMC-HVDC Fault Detection Method Fault Localization Method Fault Tolerant Control

4. I. Basics of MMC based HVDC MMC Advantages: • Modularity • Scalability • High reliability • Multi-level • High power quality • Low switching frequency SM F. Deng and Z. Chen, 2015, “Voltage-balancing method for modular multilevel converters under phase-shifted carrier-based pulse-width modulation,” IEEE Transactions on Industrial Electronics, vol. 62, no. 7, pp. 4158-4169.

5. SM equivalent model: F. Deng and Z. Chen, “A control method for voltage balancing in modular multilevel converters,” IEEE Transactions on Power Electronics, vol. 29, no. 1, pp. 66-76, 2014

6. II. Fault Detection for MMCs Switch open-circuit fault in SM unit Kalman Filter Method with Method: Detecting fault based on inner difference current idiff_j. Phase A Phase B Phase C Three-phase MMCs

7. Kalman Filter (KF) for estimating inner difference current idiff_j Fault detection method F. Deng, Z. Chen, M. R. Khan, and R. Zhu, “Fault detection and localization method for modular multilevel converters,” IEEE Transactions on Power Electronics, vol. 30, no. 5, pp. 2721-2732, 2015.

8. IV. Fault Localization for MMCs (1) Conclusion: Normal Fault Capacitor voltage uc in faulty SM would be increased. (2) Normal Fault Conclusion: Capacitor voltage uc in faulty SM would be increased. F. Deng, Z. Chen, M. R. Khan, and R. Zhu, “Fault detection and localization method for modular multilevel converters,” IEEE Transactions on Power Electronics, vol. 30, no. 5, pp. 2721-2732, 2015.

9. (3) Conclusion: Capacitor voltage uc in faulty SM would be increased. Normal Fault Normal Fault Fault localization method

10. Experimental Studies Experimentalsetup: • kW prototype • 4 cells per arm • Dspace controller

11. Normal Operation Estimated value = Measured value

12. Top IGBT Fault in Cell21

13. Buttom IGBT Fault in Cell21

14. V. Fault Tolerant Control Equivalent circuit: Result in fundamental component in

15. Control for eliminating fundamental component in inner difference current of phase A Control for eliminating fundamental component in inner difference current of three-phase MMCs

16. Experimental Studies Experimentalsetup: • kW prototype • 4 cells per arm • Dspace controller Phase A Phase B Phase C

17. Phase A Phase B Phase C No control with control No control with control No control with control

18. 18 Thanks !