H bridge cascaded chain STATCOM can be used for reactive power compensation in the high voltage（10 kV or 35 k V） systems. When the traditional SPWM modulation method is used

the disadvantage is low utilization rate of device’s DC voltage

and it needs multiple cascaded H bridges which causes high cost and low reliability. Space vector modulation（SVPWM） technology has the advantage of improving the utilization ratio of voltage and effectively reducing the number of H bridge

but it’s too complicated for computation when the level number is large. Therefore

this paper proposes a simplified SVPWM algorithm which applies to the star connection chain STATCOM. What’s more

the SVPWN algorithm combines the two level space vector modulation technique with carrier phase-shifted modulation technology together

which effectively improves the utilization rate of DC voltage and reduces the complexity of calculation. On this basis

in order to realize stability and balance of voltage of DC side in each H bridge

this paper puts forward a hierarchical control strategy of DC voltage. Simulation model is built in the simulation software PSCAD

which verified the feasibility and accuracy of modulation algorithm and control strategy of the DC voltage.