Application of STATCOM for the Mitigation of Disturbance and Stability of Wind Farm Connected to Weak Grid

Abstract

This thesis describes the impact of Static Synchronous Compensator (STATCOM) on stability of the wind farms based on double fed induction generators (DFIG) and fixed speed induction generators (FSIG) which are connected to power system, after a severe disturbance occurrence. Because of asynchronous characteristic of fixed speed induction generators, the instability in wind farms based on FSIG is severally created by the extreme reactive power absorption by FSIG after fault. This phenomenon is a result of rotor slip of FSIG increase during the fault, and during steady state condition when the induction generator operates, it has variation in slip and speed. So during no load condition and slip is near to zero, less reactive power absorbed by machine but when the load and power generation is increased, results in the rotor slip and the reactive power absorption rises. The reactive power is mainly compensated per turbine level in the wind farms i.e., when the power output is increased, a number of power factor capacitor (PFC) are gradually connected to induction generator terminal through mechanical switches. However, this system can only generate steady state compensation and cannot be an effective compensating tool during transient conditions. During normal operation, the electric torque is equal to the mechanical torque and the FSIG is in steady state condition. When a system fault happens, a sudden drop in the AC voltage is created and it causes the FSIGs electrical torque reduction and consequently, the consumption of reactive power is raised. So the performance of the wind farm equipped by STATCOM to improve the wind farm stability during and after fault. This thesis discusses the problems and implications of wind integration in the network. As a corrective measure, the application of the Static Synchronous Compensator (STATCOM) will be investigated to improve the dynamics of the hybrid wind farm DFIG and FSIG connected to the grid. The STATCOM control strategy has been developed to improve the stability of dynamic wind turbine power. STATCOM provides voltage support by providing or receiving reactive power in the event of fault. The simulation results show that STATCOM can enhance the system stability during and after disturbance, especially when the network is weak.