Voltage control performance enhancement by adding energy storage to shunt connected voltage source converters

Shunt-connected voltage controllers such as a STATCOM can only provide reactive current to the power system. This paper investigates the potential benefits from adding significant energy storage capability to such devices, thus enabling their real power capability. A steady-state analysis of a remote fault on a sample distribution system with heavy induction motor loading is presented. It provides insight into the two problems of supporting the load voltage during moderate voltage sags and mitigating voltage collapse after the fault has been cleared. Real and reactive power required from the compensator for those tasks are given. Additional results from a transient EMTDC simulation show good agreement with the steady-state assessment. It is concluded that real power is necessary only for very low X/R ratios, even for a severe decrease in motor speed during the fault. However, the analysis also shows a reduced reactive power requirement when energy storage is added.