Improved Ramping and Reserve Modeling of Combined Heat and Power in Integrated Energy Systems for Better Renewable Integration

With the largest installed capacity of wind power and solar PV in the world, China is experiencing an approximately 10% curtailment in major northern provinces. The combined heat and power (CHP) units account for over 50% of the local thermal generation capacity, hardly making contributions to ancillary services due to complex coupling of heat and power constraints, and thus are the major barriers for renewable energy integration. This paper explores opportunities for increasing the flexibility of CHP units by improving modeling of ramping and reserve constraints. Reformulated ramping constraints are proposed via analyzing the internal mechanical structure and introducing the regulation of heat exchange rate controlled by heating butterfly valve. A reformulated available reserve capacity model is put forward based on heating compensation mechanism between CHP units and heat storages. The reformulated models are examined in a 6-bus test system and the results show that the reformulated ramping constraint model improves notably the ramping capability of CHP units, especially operating in parallel with heat storages, facilitating the renewable integration during morning hours; whereas the reformulated reserve constraints release the hidden capability of heat storages to supply power reserves, enabling the system integration of additional renewable energy.