With the nonlinear and unbalanced loads and high penetration of distributed generations connected into the power distribution network, some deteriorative influences such as poor power quality and stability issues have been caused. Static synchronous compensator (STATCOM) and another custom power device, electric spring (ES) are competent for solving these problems. This paper provides a general comparative analysis of STATCOM and ES on fundamental principles, control strategies and power quality improvement functions including reactive power compensation capacities and voltage regulation capabilities. Necessary mathematical derivations supporting the theoretical framework of the principle and the final conclusion are detailed in the paper.

With the high penetration of distributed generations (DGs) have been connected into the local power distribution network, it will result in some deteriorative influences such as poor power quality and stability issues. And power distribution network itself with problems of power system nonlinear characteristic, power system faults and nonlinear loads makes this issue more severe. Meanwhile, in order to restraint the large output power fluctuation caused by great many DGs, enough power support, which can be implemented by energy storage technology, is needed. Thus, for solving the voltage problems in power distribution network with the high penetration of DGs, a novel Unified Power Quality Conditioner (UPQC) based on fast energy storage is introduced in this paper. Then the structure principle and the control strategy were explained at length. At last the practicality of the device was determined successfully by simulation and experiment research.