Separate control of active and reactive power of Doubly-Fed Induction Generators (DFIG) Based on Wind Turbines at Unbalanced network Voltage Conditions
Pages : 536-548Download PDF
In order to convert wind energy into electric one, several generators are being used in connection with multiple structures of power electronic tools. Today, Doubly-Fed Induction Generators are used as the most common energy converter system. Depending on DFIG field of use, electric system is analyzed separately from or in connection with mechanical system. In the present paper, electrical system has been analyzed and investigated separately from mechanical system, considering changes in speed. From another point of view, wind turbine systems are investigated in two forms; in connection with multi-bus network or infinite bass. At the first state, the connection between DFIG system and network as well as its effect on several modes such as stability in multi-bus system is analyzed. But in order to investigate the DIFG system individually and apply modern control methods on it, the system is considered to be in connection with infinite bus. So in this study, we have applied this mode, considering the topic in question. According to the procedure used in this study, the coiled rotor will be fed using infinite bus of inductive machine stator. Rotor of the machine is fed using Back-to-Back configuration, and maximum external power will be received from the stator for applying several torques. For this purpose, active and reactive powers have been controlled separately by introducing a new control method. Imbalance in network voltage will result in fluctuation in electromagnetic torque and non-sinuous changes in the current injected to the system. In the present paper, we have investigated the system when being faced to normal network voltage conditions as well as to imbalance in voltage, indicating preservation of stability of the system as well as its acceptable output when being under modern control.
Keywords: active, reactive, Wind Turbines