Network integration of wind power - Wind Power Integration: Connection and System Operational Aspects - page 126

complexity without materially affecting its validity. SVC models have been devel-
oped for standard network analysis programmes. The issue is to ensure that the
control is properly modelled. In the final analysis, the performance of the model
should be verified against the as-built device.
The issue of dynamic models is similar to that stated above for power elec-
tronic devices. Manufacturers have produced models in reduced-order industry-
standard formats for many devices, but many of these are unverified against actual
wind farm performance. Utilities, installers and manufacturers need to work toge-
ther to create an archive of performance data in real network environments.
An issue for utility managers has been that many turbine manufacturers believe
that their control systems are of proprietary value and therefore they are reluctant to
provide the detail of models. Under pressure and surrounded by data confidentiality
provisions, versions of the models have been made available in assembled code for
proprietary power system analysis software. However, as the power system soft-
ware undergoes version change the assembled code may no longer function. For
this reason utilities have reacted by providing rules for models which they will
accept. Typically the models need to be in source code, e.g. Fortran or DSL, and
accompanied with IEEE-type descriptions. 'Black box' models are no longer
acceptable. The models may be required for individual turbines and for the lumped
arrangements for the entire wind farm, and would need to incorporate any time
delays resulting from the wind farm park control arrangements. They need to show
the response of the WTG, park controller, reactive control systems and tap-chan-
gers, and take into account the properties and characteristics of all electrical
equipment including lines/cables and transformers. The following is typical of the
features required by models:

the electrical characteristics of the plant and apparatus ●

the separate mechanical characteristics of the turbine and the generator and the
drive train between them

●

variation of power coefficient with pitch angle and tip speed ratio ●

blade pitch control ●

converter controls ●

reactive compensation ●

protection relays ●

In order to facilitate commissioning tests the models need to include the
facility to inject:

step changes to the voltage set point ●

step changes and linear ramps to the frequency set point ●

step changes to the reactive power set point ●

step changes to the power-factor set point ●

step changes to the active power set point ●

The first stage of compliance tests is carried out using models and then, to the
extent possible, the as-built wind farm is assessed against grid code requirements
and the performance expected as a result of modelling. If the wind farm is code