Sometimes the grid constraints change unpredictably and a need arises to change the previously set unit commitments. This '''system redispatch''' change is controlled in real-time by the central operator issuing directives to market participants that submit in advance bids for the increase/decrease in the power levels. Due to the4the centralized nature of redispatch, there is no delay to negotiate terms of contracts; the cost incurred are allocated either to participants responsible for the disruption based on preestablished tariffs or in equal shares.<ref name="SongWang2003">{{cite book | editor1 = Yong-Hua Song | editor2 = Xi-Fan Wang | author = Yong-Hua Song | date = 31 July 2003 | title = Operation of Market-oriented Power Systems | publisher = Springer Science & Business Media | page = 150 | isbn = 978-1-85233-670-7 | oclc = 1112226019 | chapter = System Redispatch | chapter-url = https://books.google.com/books?id=sS33yLR0U7EC&pg=PA150}}</ref>
