Accurate simulation models are becoming increasingly important tools to secure wind farm integration into power grids in accordance with the requirements.
As we have seen in our previous blog posts, power grids are regulated by a variety of different standards and grid code requirements at both national and international levels. To ensure that wind farms comply with the relevant requirements, there is a growing need for accurate simulation models. Many grid codes even include a clause that requires new wind farms to provide validated simulation models as part of their compliance with connection conditions.
Grid operators typically require models that represent wind park performance with sufficient accuracy, and support simulations for extensive power grids with a large number of network elements. Study cases include the transient stability of the power system in response to grid faults, and voltage control stability in conjunction with wind parks.
In many cases, quasi-stationary (or ‘RMS’) models of the wind park are aggregated from models on wind turbine level. RMS models run in larger time steps of the order of milliseconds and are validated against measurements from the wind turbine. A recent trend in this area is the use of ‘generic’, open ‘glass-box’ models in accordance with IEC Standard 61400-27-1 Ed1, which was published in February, 2015. These standardized models merely require a wind turbine specific parameterization of otherwise commonly defined functional blocks. They are available as library modules on popular power system simulation platforms, thus reducing development efforts and increasing transparency of modelling.
By contrast, grid integration studies carried out in North America often require very detailed electromagnetic transient (EMT) models in which all controls of the converter software are accurately represented. Typical study cases involve integration of wind parks with serially compensated transmission lines which pose the risk of sub-synchronous resonances (SSR). These models are ‘black-box’ and run in much smaller time steps, of order of ten(s) of microseconds, and are also validated against measurements from the wind turbine. ABB can meet these requirements with EMT models that are derived directly from the actual converter software and are thus highly accurate in their modelling of the controls.
Project developers also aim to eliminate (or reduce) the cost of filters to mitigate harmonic resonances when connecting wind parks. For this purpose ABB can provide validated models of harmonic emissions of the converter, allowing the developer to assess harmonic voltages at the PCC under a variety of impedance conditions.
In addition to grid operator requirements, wind turbine manufacturers themselves often require a high degree of modelling accuracy: this enables them to mitigate the risks of drive train stresses and assess the actual wind farm electrical performance under a variety of grid conditions. In particular, risks to voltage control stability under certain grid resonance conditions can be detected and eliminated as early as in the project planning phase. Highly accurate EMT models, directly derived from the actual converter software and available on popular simulation platforms, are an ideal match for this need.