Analysis and Impacts of Implementing Droop Control in DFIG-Based Wind Turbines on Microgrid/Weak-Grid Stability
Wind energy is going to be a significant part of electric energy generation in the very near future. However, in addition to its intermittent nature that could lead to major difficulties for power system reliability and stability, the conventional control applied to wind turbines and their generators, usually doubly-fed induction generators (DFIGs), does not allow them to participate in frequency regulation, whether short or long term. Moreover, the use of wind generators for autonomous frequency regulation is becoming an essential objective in power grids with reduced inertia and isolated microgrid operation. While droop-control is suggested by many researchers to solve these problems, detailed analysis of droop-controlled DFIG units in microgrids has been reported in this project.
In the grid-connected mode, many grid codes have changed to allow or even force wind power generation to participate in primary frequency regulation. Significant part of research efforts is devoted to the use of wind turbine rotating mass, whereas several proposals are made to provide this energy by deviating from maximum power extraction point. Interestingly, the use of frequency deviation, i.e., frequency droop method, instead of frequency derivative, conventional inertia emulation, or at least a combination of both is proposed. It is reported that this method has more advantages; however, detailed analysis was not provided to prove these arguments. It may be worthy to mention that in all of these works, a secondary, usually dispatchable, source of energy was employed to restore the frequency to its nominal value
In this project, it is shown that the employment of conventional power-droop in non-dispatchable wind power generation could result in problems which could not be observed and even discussed in conventional dispatch able distributed generation (DG) units. The paper also shows that the simple yet effective method of torque-droop could solve these problems. On the contrary, such a method could not be applied to conventional inverter- based dispatchable DG units.
The torque- and power-droop, as two easily-achievable methods to implement droop-control in DFIG-based wind power generation units, were analyzed and compared in this paper. Small-signal analysis showed why under-speeding should be avoided and how variance of effective torque-droop could yield higher stability margins as compared to the power-droop method.
TOOLS AND SOFTWARE USED:
- MP LAB
Mohammadreza F. M. Arani, Student Member, IEEE, and Yasser Abdel-Rady I. Mohamed, Senior Member, IEEE, “Analysis and Impacts of Implementing Droop
Control in DFIG-Based Wind Turbines on Microgrid/Weak-Grid Stability”, IEEE TRANSACTIONS ON POWER SYSTEMS, VOL. 30, NO. 1, JANUARY 2015.