Under the large-scale penetration of photovoltaic generation systems, the temperature constraints of transmission lines play a key role in the flexible operation of the power grid. In this paper, simplified line temperature constraints are derived from its physical model, and the strength and limitation of the proposed models are investigated from the viewpoint of robust model predictive control. The effect of ambient temperature prediction is discussed based on the simulations of photovoltaic battery systems with economic load dispatching control (EDC) and EDC recovering control.