When multiple stable systems are combined into one system, the newly formed hybrid system has a certain possibility to be unstable. Such a natural phenomenon has been verified in the fields of chemistry and biology over the last century. The implementation of electric springs (ESs) in large quantity over the power grids can also suffer from the same issue if specified design are not performed. As an initial feasibility study of multiple ES in smart grids, in this paper, based on the concept of relative stability, a method of tuning Kpand Kiof the proportional-integral controllers of the ES to ensure the overall system stability of a weak grid is investigated and is achieved through the aid of simulation on an extended low-voltage (LV) network of IEEE 13-node test feeder. Both simulation and experimental results validate that as the number of ES in the isolated LV network (weak grid) increases, more stringent values of Kpand Kiare required to achieve system stability. Besides, a hypothesis that if the optimal values of Kp and Kiare adopted, a maximum number of ES can be stably installed over the grid is proposed. It is also shown experimentally that by eliminating the instability of voltage fluctuation in the distribution line, the subsequent frequency fluctuation of the power generation can also be eliminated.