Overall, the so-called energy shield can be understood as magnetism; once any energy approaches, it is directly repelled. If it's a physical object that's flying towards it, the repulsive force creates a reaction force, weakening the intensity of the physical attack.
However, if the physical attack is strong enough, the effect is minimal. Take Luo Fu as an example. Once he gets close, with a single slash of his Thousand Feather Greatsword, no matter how strong your repulsive force is, can it be greater than the force of his slash? If it really were that strong, that would be invincible! Even the Taiji Diagram doesn't have that effect, let alone it being a common ability of all dragons.
