Fig. 1. Structure of star-connected STATCOM and individual H-bridge cell
Fig. 2. CHB based STATCOM control system composed of three loops, i.e., cluster voltage control loop (outer loop),current control loop (inner loop) and individual DC voltage balancing loop
Fig. 3. Power loss model of the cell
Fig. 4. Sketch of the software-based DC voltage balancingstrategy
Fig. 5. Power loss model of the cell at zero current mode
Fig. 6. Power losses under different DC voltages in zerocurrent mode
Fig. 7. Equivalent resistors under different DC voltages inzero current
Fig. 8. Equivalent circuit of the cascaded chain at zerocurrent mode
Fig. 9. The schematic of the module in the cell-controllerboard
Fig. 10. Impact of the adaptive load with different ratedpowers on the Hbridge cell and its local supplyconverter in the controller board
Fig. 11. The layout of the module in the cell-controllerboard
Fig. 12. 12-cell-cascaded 10 kV STATCOM
Fig. 13. Basic operating conditions of the STATCOM atzero current mode
Fig. 14. DC voltage divergency and the effection ofproposed module
Fig. 15. DC voltgae divergency when the power lossdeviation exceeds the ability of the adaptive load
Fig. 16. Other two hardware based individual DC voltagebalancing methods, i.e., (a) a single parallelresistor and (b) a parallel branch composed of aresistor and a switch in series
Fig. 17. H-bridge cell with a parallel resistor on the DC bus
Table 1. parameters of the tested H-bridge cell
Table 2. Power loss deviation at zero current mode
Table 3. Paramiters of the fly-back converter
Table 4. Parameters of the proposed module
Table 5. Comparison of the three hardware based methods
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