Research on DC-link Capacitor Voltage Control Strategies of the Cascaded STATCOM

The cascaded STATCOM has been widely used in various STATCOM prototypes and projects due to its advantages such as low loss,high efficiency,little harmonic content in output voltage,easy modularization,and so on.However,this kind of STATCOM structure contains inherent unbalance capacitor voltage in the DC-link,which may lead to abnormal running of STATCOM.This paper analyzes various factors which may influence this unbalance capacitor voltage,and considers parallel connection loss,mixed loss and pulse delay as the main influence factors.It sums up four common control strategies as viewed from energy balance,and three common control strategies as viewed from control variable.In addition,this paper introduces a novel DC-link capacitor voltage control strategy with convenient software implementation,and offers some recommendations.Its work can be helpful to the STATCOM designers.