Effect of device models on the multiobjective optimal operation of CCHP microgrids considering shiftable loads

Based on the importance of device modelling for the optimal operation of combined cooling, heating and power (CCHP) microgrids and load shifting for the demand-side response, the partial load ratio (PLR) and constant efficiency (CE) models of the main devices on the system operation are studied. Nonlinear PLR models of gas turbines, boilers and chillers are constructed. A piecewise least squares linearization method is proposed. Shiftable load models of cooling, heating and electricity are established, and load shifting is carried out. System optimization models with multiple optimization objectives are constructed and solved by a CPLEX solver. To compare the effects of different equipment models on the optimal operation under load shifting, different targets and heat-to-electricity ratios are given. The results show that compared with the segment broken-line linearization and least squares linearization method, the proposed method reduces the standard error of the performance curve by at least 20.97% and 75.49%, respectively. With different optimization objectives, the positive advantage of load shifting is related to the heat-to-electricity ratio. Using different heat-to-electricity ratios, the sensitivity of the optimization results of the PLR models to the heat-to-electricity ratio is higher than that of the CE models. The optimal operational effect of load shifting on different objectives of the PLR model is significantly better than that of the CE model. The model selection of the gas turbine, heating recovery steam generator and electric chiller with either the PLR or CE model demonstrates a considerable impact on the system operational results.