Integrating Flywheel Energy Storage System to Wind Farms-Fed HVDC System via a Solid State Transformer


As the power of wind farms (WFs) considerably proliferates in many areas worldwide, energy storage systems will be required to dynamically compensate the wind energy intermittency and increase power system stability. In this paper, a backup power conditioning strategy for wind energy-fed voltage source converter HVDC transmission systems is presented. An induction machine based flywheel energy storage systems (FESS) is integrated to the HVDC system via a solid state transformer (SST). The FESS is connected in parallel with the dc-link of the grid side converter; therefore, the excess wind energy can be stored in the flywheel and then restored during the energy shortage periods. The proposed system aims to compensate the power fluctuations caused by the intermittent nature of wind energy, levels the power-fed to the grid, and improves the quality of delivered power. The proposed system including FESS with an interfacing SST is modeled, simulated, and analyzed in MATLAB/SIMULINK environment. The results verify the effectiveness of the proposed system.



  1. HVDC
  2. Wind generation
  3. Storage system
  4. Smart grid
  5. Flywheel





Figure 1. The proposed system



Figure 2. Simulation results of power smoothing operation in pu (a) grid power, wind power, and flywheel power, (b) flywheel speed, (c) phase shift between two H-bridges of DAB, (d) HV dc link, (e) LV dc link.

Figure 3. Simulation results of HFT waveforms, in pu, employing soft switching using phase shift technique (a) positive power flow (from H2 to H1), (a)negative power flow (from H1 to H2).

Figure 4. Simulation results of power leveling operation in pu.



In this paper, a new strategy of improving the integration of large scale wind farms into HVDC transmission system using SST based FESS has been proposed to compensate for the wind power oscillations and to enhance the power profile at grid side. In the proposed technique a low speed induction machine based flywheel energy storage system is connected in parallel with the DC link of the grid side converter. Therefore, the excess wind power is stored in FESS and restored in case of wind power shortage and/or power demand increase preserving the grid power profile at its required value. The simulation results have demonstrated that the FESS compensates for power fluctuations caused by wind nature during different load conditions and exhibits good system performance with a relatively fast response and high dynamics.



  • Schettler, and H. Huang, N. Christl, “HVDC transmission systems using voltage sourced converters design and applications,” Power Engineering Society Summer Meeting, 2000. IEEE, vol.2, pp.715-720 vol. 2, 2000.
  • Long and S. Nilsson, “HVDC transmission: yesterday and today,” Power and Energy Magazine, IEEE, vol.5, no.2, pp.22-31, March-April 2007.
  • P. Bahrman and B.K. Johnson, “The ABCs of HVDC transmission technologies,” Power and Energy Magazine, IEEE, vol.5, no.2, pp.32- 44, March-April 2007.
  • M. Kirby, Lie Xu; M. Luckett, and W. Siepmann, “HVDC transmission for large offshore wind farms,” Power Engineering Journal, vol.16, no.3, pp.135-141, June 2002.
  • Jiancheng Zhang, “Research on Flywheel Energy Storage System Using in Power Network,” International Conference on PowerElectronics and Drives Systems, 2005. PEDS 2005, vol.2, no., pp. 1344- 1347, 28-01 Nov.2005.

A Two-Level 24-Pulse Voltage Source Converter with Fundamental Frequency Switching for HVDC System


This paper deals with the performance analysis of a two-level, 24-pulse Voltage Source Converters (VSCs) for High Voltage DC (HVDC) system for power quality improvement. A two level VSC is used to realize a 24-pulse converter with minimum switching loss by operating it at fundamental frequency switching (FFS). The performance of this converter is studied on various issues such as steady state operation, dynamic behavior, reactive power compensation, power factor correction, and harmonics distortion. Simulation results are presented for a two level 24-pulse converter to demonstrate its capability.



  1. Two-Level Voltage Source Converter
  2. HVDC
  3. Multipulse
  4. Fundamental Frequency Switching
  5. Harmonics





 Fig. 1 A 24-Pulse voltage source converter based HVDC system Configuration



Fig. 2 Synthesis of Stepped AC voltage waveform of 24-pulse VSC.



Fig. 3 Steady state performance of proposed 24-pulse voltage source Converter


Fig. 4 Dynamic performance of proposed 24-pulse voltage source converter



Fig. 5 Waveforms and harmonic spectra of 24-pulse covnerter i) supply voltage ii) supply current (iii) converter voltage


A two level, 24-pulse voltage source converter has been designed and its performance has been validated for HVDC system to improve the power quality with fundamental frequency switching. Four identical transformers have been used for phase shift and to realize a 24-pulse converter along with control scheme using a two level voltage source converter topology. The steady state and dynamic performance of the designed converter configuration has been demonstrated the quite satisfactory operation and found suitable for HVDC system. The characteristic harmonics of the converter system has also improved by the proposed converter configuration with minimum switching losses without using extra filtering requirements compared to the conventional 12-pulse thyristor converter.


[1] J. Arrillaga, “High Voltage Direct Current Transmission,” 2nd Edition, IEE Power and Energy Series29, London, UK-1998.

[2] J. Arrilaga and M. Villablanca, “24-pulse HVDC conversion,” IEE Proceedings Part-C, vol. 138, no. 1, pp. 57–64, Jan. 1991..

[3] Lars Weimers, “HVDC Light: a New Technology for a better Environment,” IEEE Power Engineering Review, vol.18, no. 8, pp. 1920-1926, 1989.

[4] Vijay K. Sood, “HVDC and FACTS Controller, Applications of Static Converters in Power Systems”, Kluwar Academic Publishers, The Netherlands, 2004.

[5] Gunnar Asplund Kjell Eriksson and kjell Svensson, “DC Transmission based on Voltage Source Converters, in Proc. of CIGRE SC14 Colloquium in South Africa 1997.

Analysis and Design of Three-Level, 24-Pulse Double Bridge Voltage Source Converter Based HVDC System for Active and Reactive Power Control


This paper deals with the analysis, design and control of a three-level 24-pulse Voltage Source Converter (VSC) based High Voltage Direct Current (HVDC) system. A three level VSC operating at fundamental frequency switching (FFS) is proposed with 24-pulse VSC structure to improve the power quality and reduce the converter switching losses for high power applications. The design of three-level VSC converter and system parameters such as ac inductor and dc capacitor is presented for the proposed VSC based HVDC system. It consists of two converter stations fed from two different ac systems. The active power is transferred between the stations either way. The reactive power is independently controlled in each converter station. The three-level VSC is operated at optimized dead angle (β). A coordinated control algorithm for both the rectifier and an inverter stations for bidirectional active power flow is developed based on FFS and local reactive power generation. This results in a substantial reduction in switching losses and avoiding the reactive power plant. Simulation is carried to verify the performance of the proposed control algorithm of the VSC based HVDC system for bidirectional active power flow and their independent reactive power control.



Voltage Source Converter (VSC), Three-level VSC, Fundamental Frequency Switching (FFS), HVDC System, Power Flow Control, Reactive Power Control, Power Quality, Total Harmonic Distortion (THD), Dead Angle (β).






Fig. 1 Three-level 24-pulse double bridge VSC based HVDC system




Fig. 2a Performance of rectifier station during reactive power control of three level 24-pulse VSC HVDC system


Fig. 2b Performance of Inverter station during reactive power control at rectifier station of three-level 24 pulse VSC HVDC system


Fig. 2c Variation of (δ) and (α) values for rectifier and inverter Stations for reactive power variation of a three-level 24-pulse VSC HVDC system


Fig. 3a Rectifier station during active power reversal of three-level 24-pulse VSC HVDC system


Fig. 3b Inverter station during active power reversal of three-level 24-pulse VSC HVDC system


Fig. 3c Variation of (δ) and (α) values during active power reversal of three level 24-pulse VSC HVDC system.



A new three-level, 24-pulse voltage source converter based HVDC system operating at fundamental frequency switching has been designed and its model has been developed and it is successfully tested for the independent control of active and reactive powers and acceptable level harmonic requirements. The reactive power has been controlled independent of the active power at both conditions. The converter has been successfully operated in all four quadrants of active and reactive powers with the proposed control. The reversal of the active power flow has been implemented by reversing the direction of dc current without changing the polarity of dc voltage which is very difficult in conventional HVDC systems. The power quality of the HVDC system has also improved with three-level 24-pulse converter operation. The harmonic performance of this three-level, 24-pulse VSC has been observed to an equivalent to two-level 48-pulse voltage source converter.



[1] “It’s time to connect,” Technical description of HVDC Light Technology, ABB HVDC Library.

[2] J. Arrillaga, “High Voltage Direct Current Transmission,” 2nd Edition, IEE Power and Energy Series 29, London, 1998.

[3] Vijay K. Sood, “HVDC and FACTS Controllers – Applications of Static Converters in Power Systems,” Kluwer Academic Publishers, Masachusetts, 2004.

[4] J. Arrillaga, Y. H. Liu and N. R. Waston, “Flexible Power Transmission- The HVDC Options,” John Wiley & Sons, Ltd, Chichester, UK, 2007.

[5] J. Arrillaga and M. E. Villablanca, “A modified parallel HVDC convertor for 24 pulse operation,” IEEE Trans. on Power Delivery, vol. 6, no. 1, pp. 231-237, Jan 1991.