Flexible operation of integrated energy system with HVDC infeed considering multi-retrofitted combined heat and power units

For the coal-dominated power system, facilitating the thermo-electric decoupling of combined heat and power (CHP) units through flexibility retrofit technologies is an effective approach to strengthen the peak-shaving capacity of the system and promote wind accommodation. This paper focuses on exploiting the flexible regulation potential of the large-scale CHP units in the power and heat integrated energy system (PHIES) with high voltage direct current (HVDC) transmission infeed, in order to well deal with the dual peak-shaving pressure arising from the HVDC delivery power and the high share of fluctuant wind power. The internal and external retrofit technologies including zero output of low-pressure cylinders (ZO-LPC), bypass compensation heating (BCH), and thermal energy storage (TES) are adopted for CHP units as retrofit options. Firstly, the PHIES including multi-retrofitted CHP units, HVDC transmission systems, and a high share of wind power is described and modeled. Then, a two-stage day-ahead scheduling model based on the improved information gap decision theory (IGDT)-stochastic method is proposed considering the probability distribution information of uncertain variables. Finally, an annual system-wide benefits evaluation framework is formulated to assess the economic and environmental benefits of multi-retrofitted CHP units and compare the system gain value of different retrofit projects. Numerical results indicate that the thermo-electric feasible operating regions of CHP units can be comprehensively expanded with the cooperation of the proposed retrofit technologies, so as to greatly relieve wind curtailment and reserve risk of the whole system. Moreover, sensitivity analysis for diverse operation features of HVDC and different wind power installed capacity is illustrated to further verify the robust adaptability and effectiveness of multi-retrofitted CHP units in the PHIES with HVDC infeed.