Dynamic simulation on the frequency regulation ability enhancement with energy stored in steam distribution system for a combined heat and power unit

With high penetration of renewable energy, thermal power plants play a key role in peak shaving and frequency regulation for the power grid. In this study, the feasibility of combined heat and power (CHP) unit frequency regulation assisted by steam distribution system (SDS) is evaluated. Based on time scale analysis of CHP unit's devices, dynamic models of the CHP unit integrated with the SDS are developed. When the SDS assisting to frequency regulation for the reference 1000 MW CHP unit, the maximum power increment is 33.63 MW, and the CHP unit can generate peak power of 301.16 kWh. The influences of parameters on frequency regulation are analyzed. Results show that reducing the extraction valve closing/opening time can improve the load cycling rate of CHP unit. The CHP unit maximum extra cumulative power increases with the SDS size. The power increment of CHP unit is restricted by SDS mass flow rate of supply steam. The transfer functions for predicting the pressure variation are developed based on the mechanism model. The time for simulation sharply decreases significantly, and the error of results is within 1.5 %. The study may provide some guidance for the flexibility enhancement of CHP units.