A doubly-fed induction machine and energy storage system for wind power generation

Wind power has become a very important source of renewable energy, and has been shown to complement central generation effectively. However, good power quality from distributed generators is vital, and hence independent control of the real and reactive power is desirable. Also, there has been an increasing demand for alternative energy sources to behave like conventional generators, whereby their output power is deterministic. Wind energy is an inherently stochastic system and, therefore, external measures must be used to overcome the fluctuations in the generator´s energy production. The paper deals with the modeling and simulation of a doubly-fed induction machine as a wind power generator. The ability of the system to provide independent control of the real and reactive power is demonstrated. The incorporation of a battery or other energy storage device in the DC link enables temporary storage of energy and, therefore, the ability to provide smooth output power which is both deterministic and resistant to wind speed fluctuations. Power electronic converters directly control the machine and act as the interface between the storage system and the grid. This allows full control over voltage characteristics as well as real power generation. Simulations of the system in EMTP-RV show that the design is feasible.