Comparison of low voltage ride through capabilities of synchronous generator with STATCOM and DFIG based wind farms

Includes bibliography.Increase in wind generation and grid-integration of wind energy technologies has resulted from an increasing demand of cheap and clean electricity across the globe. Wind generators are available as small, medium and large scale electric generators, usually in the range of 1kW to 100MW and are usually installed in areas rich in wind resource which may or may not be located close to the load centres. Wind energy penetration has increased since the 1970s with the total worldwide capacity of installed wind power reaching about 282,275 MW. Apart from technical issues of grid-integration, research is also being done to investigate the participation of wind energy systems to enhance grid performance through fault ride-through capabilities, providing voltage control and power quality improvement etc. The goal of a Fault Ride Through (FRT) or Low Voltage Ride Through (LVRT) system is to enable a wind farm (WF) to withstand a severe voltage dip at the connection point and still stay connected to the power system as long as the fault persists. Wind turbine designs are required to incorporate LVRT capability as per Grid Code’s requirements only if they are technically needed for a reliable and secure power system operation. The basic requirement for LVRT is that the wind turbines must maximise their reactive power injections to the network without exceeding the turbine limits. The maximisation of reactive current must continue for at least 150msafter the fault clearance or until the grid voltage is recovered within the normal operation range. It is important here to discuss here the immediate impact of the voltage dip on the wind farm (WF) operation. During the voltage dip caused by the fault, the active power provided to the grid by the WF is instantaneously reduced. This power becomes at least temporarily lower than the mechanical power available at the rotor hence the rotor speed of the wind generator increases. It is required for the LVRT capability of the WF, that the wind generators of the WF must not disconnect from the grid during fault persistence, either due to over-speeding or under voltage protections. After the clearing of the fault that led to the voltage dip, the voltage at the wind turbine bus would increase. It is also required that the wind generators should resume their power supply to the network without losing stability