  Combined heat and power dispatch promotes interactions and synergies between
electric power systems and district heating systems. However, nonlinear and
nonconvex heating flow imposes significant challenges on finding qualified
solutions efficiently. Most existing methods rely on constant flow assumptions
to derive a linear heating flow model, sacrificing optimality for computational
simplicity. This paper proposes a novel convex combined heat and power dispatch
model based on model simplification and constraint relaxation, which improves
solution quality and avoids assumptions on operating regimes of district
heating systems. To alleviate mathematical complexity introduced by the
commonly used node method, a simplified thermal dynamic model is proposed to
capture temperature changes in networked pipelines. Conic and polyhedral
relaxations are then applied to convexify the original problems with bilinear
and quadratic equality constraints. Furthermore, an adaptive solution algorithm
is proposed to successively reduce relaxation gaps based on dynamic bivariate
partitioning, improving solution optimality with desirable computational
efficiency. The proposed method is verified on a 33-bus electric power system
integrated with a 30-node district heating system and compared to nonlinear
programming solvers and constant-flow-based solutions.
