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

•Analyze the multi-retrofitted CHP units by utilizing both internal and external retrofit technologies including ZO-LPC, BCH and TES.•Present a two-stage day-ahead scheduling model based on the improved IGDT-stochastic method for the PHIES with HVDC infeed.•Formulate an annual system-wide benefits evaluation framework to compare the system gain value of different retrofit projects.•Discuss sensitivity analysis for diverse operation features of HVDC as well as different wind power installed capacity.