Virtual Inertia And System Damping Control For Variable Speed Wind Turbines

Both the system inertia and the power oscillation damping in the regional network will be reduced by the integration of large scale wind power generation, and thus the stability of the network under high wind power penetration level is more serious than that of the traditional grid. In this paper, the dynamic model of the variable speed wind turbine is established firstly, in order to analyze the impact of the wind generation on the system inertia and the power oscillation damping. Then, based on the conventional maximum power point tracking (MPPT) control, the virtual inertia control strategy by improving the MPPT control, the active power and the reactive power damping control strategies are proposed, respectively. Finally, the integrated control of the variable speed wind turbine for the dynamic frequency support and the power oscillation damping is further presented, so as to enhance the frequency and the power angle stability of the regional network with high wind power penetration during active power disturbances. The main research results are as follows:(1) The dynamic model of the variable speed wind turbine is established, include: doubly fed induction generator model, permanent magnet synchronous generator model, converter and its control system model, wind turbine and variable pitch control system model, which are used to analyze the impact of the large scale wind generation on the system inertia and the power oscillation damping.(2) The differences of the virtual inertia, the nature inertia of synchronous generators and variable speed wind turbines are discussed. The inertia concept of the grid with wind farms is redefined as well. Following that, a novel virtual inertia control strategy is proposed by improving the MPPT control. In this scheme, the controllable inertia response can be achieved for the grid dynamic frequency support and the safe operation is also ensured during the inertia control process.(3) The impact of the integration of variable speed wind turbines on the system damping is analyzed by the infinitesimal perturbation analysis in a simple network. The principles of the enhancement of the system damping by the active power and the reactive power regulation are discussed respectively in theory. Then, the fault ride through capability of the wind turbine with the proposed damping control schemes is further discussed, in order to ensure not only the safety of the wind turbine during grid faults, but also the improvement of the system damping.(4) The regulating characteristics of the proposed virtual inertia control and the active power damping control for the wind turbine’s electromagnetic power is analyzed. Then, the integration of the inertia control with the active power damping control is achieved in the wind turbine’s active power control loop. Furthermore, the system damping is further enhanced by the addition of the reactive power damping control and within the reactive power capacity of the wind turbine. Following that, the impacts of the wind turbine with the proposed virtual inertia control, the active power and the reactive power damping control on the grid security are also considered, and thus the integrated PSS control aim of the variable speed wind turbine is finally achieved by resolving the contradictions of these control schemes.