Contents I. Introduction
During the last two years, the installed capacity of wind generation is tripled while solar is quadrupled in the IPS of Ukraine [1]. Such rapid growth potentially could lead to the necessity to confine power output from traditional generation technologies, first of all, nuclear power plants due to physical impossibility operate nuclear units in the load-following mode according to their initial design and operational security requirements. One of the most reasonable ways to ensure the flexibility of the IPS of Ukraine in nearest future is to implement powerful BESS first of all because of the technical possibility to use this technology both as electricity storage and generator in a wide range of power consumption and output. The second reason for implementing BESS in the IPS of Ukraine is to keep in operation existing powerful NPPs that are not emitting GHG and hazardous pollutants into the atmosphere compared to coal-fired TPP. The required installed capacity of BESS depends on various factors but most important is the existing flexibility of the IPS of Ukraine which ensured by already existing HPSs, HPPSs, and some TPPs. As wind and solar generation are intermittent, the adequate modeling technique of dispatching the flexible types of generation is needed to continuously meet the demand for power. The most challenging issue is the accurate modeling of hydro units of national HPPS, which in the case of Ukraine are inflexible and operated only at stable levels of power consumption or generation. The paper is representing the formulation of the MILP model that includes new equations adequately and accurately describes operation modes of national HPPS hydro units for one typical day (24 hours) which is a common approach for analysis of IPS operation modes. Unlike the generally used approach for HPPS modeling [2]–[4] where the hydro units are treated as a flexible generation, could be operated in a wide range of installed capacity both in pumping and generating modes, and that is the usual case for the most countries of the world, the proposed approach is treating HPPS’ hydro units as an inflexible generation. Only stable levels of power consumption in a pumping mode or generation in generating mode are considered that is the actual state of Ukrainian HPPS’ hydro units. This feature requires a new formulation of the MILP model using binary variables. Due to the necessity of HPPS’ hydro units operate at stable levels the proposed model also accounts the time of operation and the number of starts of each hydro unit, that is not required if hydro units could be operated in flexible modes. Also, the model takes into account the necessity to limit the number of simultaneously starting the most powerful hydro units to avoid shocking changes in electricity consumption or generation by HPPS.
