CO2 emissions DC grid HVAC systems History of engineering & technology Levenberg-Marquardt method Nash equilibrium TSTTC of transmission lines combined heat and power system commercial buildings damping torque day-ahead thermal generation scheduling dissemination distributed energy systems double-layer optimal scheduling dynamic market economic environmental dispatch eigenvalue analysis electric boiler emission abatement strategies energy flexibility energy system analysis enhance total transfer capability estimation of thermal demand flexibility optimization flexibility quantification flexibility scheduling flexible demand gas distribution grid expansion planning heat pumps