Fault Ride-through of Wind Parks with Induction Generators

This project deals with the design of the collector system for large wind parks and the study of reactive power compensation techniques to help the wind park meet grid code requirements, especially concerning fault ride-through. In this study, the wind turbine generators are selected to be fixed-speed induction generators without reactive power controllability. The studied wind park is made of one hundred and thirty 3MW wind turbine generators connected to a 20 kV collector system. This collector system is then connected to a 400 kV on-shore transmission grid through two 130 kV cables and transformers. In the first part of the project, the main design of the collector system was performed by first studying the system load flows using PowerWorld Simulator. From the results of load flows study, ratings and dimensionings of system components are then selected. Reactive power production and consumption of components are calculated and reactive power compensation has been applied in such a way that in steady-state, the reactive power exchange between the wind park and the transmission grid is kept as close to zero as possible. The second part of the project focuses on simulations of the wind park in PSCAD/EMTDC to study dynamic behavior of the wind park during disturbances (i.e., severe faults) in the connected grid. A study of the fault ride-through capability (FRT) of an induction generator has been conducted using the torque-speed curve approach. The influences of different parameters such as rotor inertia constant, short circuit ratio, and pre-fault operating point on the FRT have been investigated. Two aggregation methods for large wind farms have been studied and an error estimation has been made. It is shown that a two-machine model is the smallest one that gives an acceptable error in reactive-power flow. A single-machine model is not appropriate to assess fault-ride-through. FTR and grid code compliance of the wind park with and without additional reactive power support have been compared. The reactive power sources considered are: normal switched shunt capacitors (CAP), static var compensator (SVC), and static synchronous compensator (STATCOM). The simulation results have shown that either CAP, or SVC, or STATCOM would be a possible solution for the wind park meeting the Nordel grid code requirements on FTR. The needed reactive power support for the wind part is calculated to be 1.6 pu (on a 455 MVA base) for all supporting devices if they are installed at the 130 kV bus closest to the grid. If installed at the main 20 kV bus, the needed sizes could be reduced by 21% and by 38% for CAP/SVC and STATCOM, respectively. If the zero-voltage fault ride-through is not required, the needed size could be reduced significantly. In this case, the required reactive power support from CAP/SVC and STATCOM are found to be 1.00 pu and 0.56 pu, respectively to ride through 0.25 pu voltage dip for 250 ms