Wind power has become one of the major sources of electricity generation in Finland. Converter connected generation has already been feeding roughly 65 % of Finnish power system electricity at the peek hour and the number is expected to increase even more in upcoming years. The wind power is as well heavily concentrated to the west-coast of Finland whereas the large nuclear units are located in Southern and hydro power in Northern part of Finland. During this massive change in Finnish power system dynamics, the converter driven stability challenges has been emerging.

Fingrid, the Finnish transmission system operator (TSO), has been tackling the converter driven stability issues through various measures. These measures have included technical requirements for the customers such as fast initial voltage controlling capability for wind and solar power plants and grid forming requirements for battery energy systems (BESS). In addition to traditional short-circuit ratio (SCR) value, the customers have also been given equivalent short circuit ratio (ESCR) value along that considers the other converter connected power plants such as wind and solar. The customers have been also given electromagnetic transient (EMT) model called ESCR testbench that they can use to show their capability to operate in low ESCR environment. In practice, these measures have not alone been enough to ensure converter driven stability. Fingrid has also invested in total three synchronous condensers and one static synchronous condenser (STATCOM) with grid forming (GFM) controls to ensure the system stability. When the amount of wind and solar power increases more in upcoming years, more compensation investments will be needed for ensuring converter driven stability.

This paper will present the converter driven challenges through EMT simulations that has been observed in Finnish power system when the converter connected generation has been increasing. The paper will also discuss the expected development of wind and solar power in Finnish power system and how it is seen in ESCR values across the Finnish Power System. The converter driven stability can be enhanced through grid forming converter investments, such as E-STATCOM or BESS system, or through synchronous condensers. Impact of distributed compensation strategy based on grid forming BESS and centralized compensation strategy through E-STATCOM or synchronous condensers are discussed and compared through various aspects.