Stability Design of Electric Springs in Power Grids

Yun Yang, Siu-Shing Ho, Siew-Chong Tan, Shu-Yuen Ron Hui
The University of Hong Kong

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 (ES) in large quantity over the power grids can also suffer from the same issue if specified design are not performed. Therefore, in our project, we find out a tuning method for K_p and K_i of the proportional-integral (PI) controllers of the ES to ensure the overall system stability of a weak grid based on the concept of relative stability. This global tuning method has been investigated and achieved through the aid of simulation on an extended low-voltage (LV) network of IEEE 13–node test feeder. Both simulation and experimental results have validated the proposed tuning method. This research work identifies that

1. As the number of ES in an isolated LV network (weak grid) increases, more stringent values of K_p and K_i are required to achieve system stability.
2. A hypothesis that if the optimal values of K_p and K_i are adopted, the maximum number of ES that can be stably installed over the entire grid is proposed.
3. It has been shown experimentally that by eliminating the instability of voltage fluctuation in a distribution network, the subsequent fluctuation of system’s frequency can also be eliminated.