Frequency Control Strategies of Power System with Renewable Generation Integration

Pengfei Li

Research output: Book/ReportPh.D. thesisResearch

Abstract

Frequency is a considerable indicator of power system operation and power quality. Meanwhile, its stability is very essential to the power system. For the traditional interconnected power systems, if the backup of active power is sufficient and the power system has the strong anti-disturbance capability, the system could generally ensure the frequency stability. However, with the increasing complexity of the power system, especially the continuous grid-connection renewable energy sources and storage systems, such as wind power, tidal power and electric vehicles, the nonlinear degree and uncertainty of the system are greatly increased, and frequency instability accidents are likely to occur, which could seriously threaten the safe and stable operation of the power systems.
Although the renewable energies integrate into power grid will relieve the energy crisis and environmental pollution problems, its strong fluctuation may seriously affect the power quality and the stable operation of power systems. Especially, the generators of renewable energy plants do not have such inertia response features as conventional generators do. When an impact load disturbance occurs in a power system with large-scale wind power or a microgrid with electric vehicles, their outputs are volatile and uncertain. Thus, those generators may not have fast response to meet frequency regulation requirements of the power grid. Furthermore, to ease the bottleneck of integrating intermittent power sources and improve frequency indices, it is necessary to introduce new supplementary means of the frequency by its rapid response feature.
This PhD project proposes the novel frequency regulation methods and advanced control strategies for renewable energies integrated into power grid and microgrid in different operating conditions. The capability of wind power plant and electric vehicles could be taken full advantages by these strategies, it could also enhance the stability of power system, reduce the pressure of traditional power plant and ensure the reliability of power grid. Therefore, the contribution of this Ph.D. project includes three parts:
1) Wind power plants participate into frequency regulation in a large wind speed range under the power constraints. A novel de-loading operation strategy is designed that combines with over-speed control and pitch control to achieve the de-loading strategies for different types of VSWTs. The WPP is allowed not only to store reserved power to meet the restricted requirements from power grid, but also contribute to PFR. The proposed control strategy can adjust the calculated droop value and active power scheduling strategy to improve the characteristics of PFR and alleviate the pressure of conventional power plant.
2) A novel integrated control strategy, which includes virtual inertia control of wind turbine with DFIG, could achieve frequency control of power system. The designed control strategy uses the Cp-λ-β operating characteristics to calculate the reserved capacity for de-loading strategy, achieve the controllable inertia response by virtual inertia control and analyze the droop value for modifying the pitch angle and static characteristics of power-frequency. Furthermore, the integrated control strategy could and decrease the frequency deviation and achieve the PFC in steady state.
3) EVs with V2G (vehicle to grid) control strategy to participate into frequency regulation of the microgrid. Electric vehicle as a mobile energy storage device, after it is accessed to the microgrid, it could provide reserve capacity of frequency regulation for the microgrid when the microgrid works in the independent mode. EV could reduce the demand for frequency regulation resources of microgrid and brings the obvious economic benefits. Based on the VSG control technique, a charging control method for EV with inertia/damping simulation and auxiliary frequency adjustment is designed.
Finally, all the proposed control strategies and methodologies are compared with traditional control methods. Meanwhile, the simulation results are verified and show the effectiveness of these proposed strategies.
Original languageEnglish
Publication statusPublished - 2019
SeriesPh.d.-serien for Det Ingeniør- og Naturvidenskabelige Fakultet, Aalborg Universitet
ISSN2446-1636

Bibliographical note

Dissertation not published.

Keywords

  • Frequency control
  • Renewable Energy Integration
  • Wind Power
  • Electric Vehicle (EV)
  • Virtual inertia
  • V2G vehicle to grid

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