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Simulation of sizeable hydro-thermal power systems, such as Northern Europe or larger, requires several extensive simplifications and model reductions to decrease simulation time. Such reductions for hydrosystems are often called Equivalent models. Their purpose is to mimic a more detailed hydropower model while decreasing computation time. Both aspects are vital for accurate and useable simulation results. Here, different Equivalent models for hydropower have been developed together with a new function for adaptive Equivalent inflow based on local inflows to the detailed system. The models were computed via a bilevel optimization problem factoring in the novel adaptive inflow. Based on this, the new function for adaptive inflow was calculated using regression. The Equivalents have then been evaluated in a case study of hydropower systems in Northern Sweden regarding accuracy in hourly and total power generation, revenue estimation, and relative computation time. For all Equivalents, the computation time is decreased by ¿96%. Further, the Equivalents demonstrate improved performances in hourly and total power production and revenue estimations. The best hourly power difference was 9.2%, and the best revenue estimation was 5.9%. Especially notable is the low total power production difference of ¡0.5% compared to the more detailed model. [ABSTRACT FROM AUTHOR]

• Linear hydropower Equivalent models computed from a nonlinear hydropower model. • Significant reduction in computation time. • Case study for the electricity trading area SE1 in northern Sweden. • Qualitative analysis of multi-scenario Equivalent hydropower models. Simulations and analysis of large hydro-thermal power systems easily become computationally heavy without simplifications of the system at hand. Hydropower, in particular, presents a challenge as complex river systems add a large amount of variables and linked constraints to the analysis. A possible simplification is to use aggregated Equivalent models for different parts of the hydrosystem which give similar results, with respect to e.g. power production, as a more detailed description of the Original system. In this paper, novel linear multi-scenario Equivalent models for hourly simulations of nonlinear hydropower systems are developed and their performance investigated. The new models consider multiple scenarios for inflow, price and start resp. end content in the reservoirs as well as reserves for balancing capacity. The performance analysis is based on case studies over Swedish hydropower systems located in the electricity trading area SE1. The average relative error in power production is 9–15% and the computation time is reduced from 9 hours to between 0.4 and 36 seconds. [ABSTRACT FROM AUTHOR]