IEEE Smart loads associated with electric springs (ES) have been used for fast demand-side management for smart grid. While simplified dynamic ES models have been used for power system simulation, these models do not include the dynamics of the power electronic circuits and control of the ES. This paper presents a dynamic and modular ES model that can incorporate controller design and the dynamics of the power electronic circuits. Based on experimental measurements, the order of this dynamic model has been reduced so that the model suits both circuit and system simulations. The model is demonstrated with the radial chordal decomposition controller for both voltage and frequency regulation. The modular approach allows the circuit and controller of the ES model and the load module to be combined in the d-q frame. Experimental results based on single and multiple smart loads setup are provided to verify the results obtained from the model simulation. Then the ES model is incorporated into power system simulations including an IEEE 13 node power system and a three-phase balanced microgrid system.