Research On Hybrid Cascade STATCOM Control Strategy Of NPC And CHB

The static synchronous compensator is an important reactive power compensation device in the power grid,and the cascade structure is mainly used in the medium and high voltage power grid.Compared with the H-bridge cascaded multi-level structure,the hybrid cascaded topology can reduce the number of required power cells,effectively reduce switching losses and increase the power density of the device.Firstly,to reduce the number of CHB power cells,hybrid cascade static synchronous compensator(HC-STATCOM)with neutral-point clamped(NPC)three-level power cell and H-bridge cascade(CHB)power cell is proposed.The modulation method is designed.The neutral-point voltage of the NPC three-level power cell is analyzed.The mathematical relationship between the DC voltage of NPC three-level power cell and the utilization rate of the HC-STATCOM modulation voltage is established.The influence curve of the DC voltage of NPC three-level power cell on the utilization rate of the HCSTATCOM modulation voltage is obtained.Compared with the HC-STATCOM composed of two-level power cell and H-bridge cascade power cell,which shows that the number of CHB cascade cell of the HC-STATCOM based on NPC three-level power cell can be reduced by 30%.Secondly,to achieve cluster voltage balancing under unbalanced grid voltage,the CHB power cell in the HC-STATCOM needs to inject zero-sequence voltage.The zerosequence voltage injection affects the value of the HC-STATCOM DC side voltage.The proportion of the CHB power cells output fundamental voltage and the zero-sequence voltage to be injected under the unbalanced grid voltage are derived.With the grid voltage peak value as the constraint,the correspondence between unbalanced grid voltage and the DC voltage value of HC-STATCOM is analyzed.Taking 6k V static synchronous compensator as an example,the DC voltage required by the conventional H-bridge cascade STATCOM and HC-STATCOM during unbalanced grid voltage is compared.Showing that HC-STATCOM requires lower DC voltage during unbalanced grid voltage.Finally,the control scheme of the HC-STATCOM DC voltage is constructed,and the parameters of the 6k V/3Mvar HC-STATCOM main circuit are selected.The effectiveness of the theoretical analysis is verified by the Matlab/Simulink simulation platform.There are 30 pictures,3 tables,and 76 references in the article.