Aggregate modelling of wind farms containing full-converter wind turbine generators with permanent magnet synchronous machines: transient stability studies

When the transient interaction between a large wind farm and a power system is to be studied, there are two possible approaches to wind farm modelling. It can be modelled as one or more equivalent wind turbine generators (aggregate modelling) or each wind turbine generator (WTG) can be modelled separately (detailed modelling). When a power system with many wind farms is to be simulated, the aggregate approach becomes especially attractive. A successful aggregate model will reduce the simulation time without significantly compromising the accuracy of the results in comparison to the detailed model. Here, the aggregate modelling options for a wind farm with 5 MW full-converter WTGs (FCWTGs) using permanent magnet synchronous machines are presented. A braking resistor in the DC circuit of the FCWTG´s converter system is employed as a means of satisfying the latest grid code requirements. It will be shown that with a braking resistor implemented in the FCWTG there is scope for significant model simplifications, which is particularly relevant for transient stability studies of large-scale systems.