To decrease direct serial number and switching frequency of electronic devices
and simplify the main circuit topology
a module-cascade based BTB HVDC-flexible system is proposed.The converter module operates with a fairly low switching frequency
and thus the low-switching power electronic device IGCT is selected due to its high power and low conducting loss.A mathematical model is developed for the multi-module-converter based HVDC-flexible system
and a controller is designed for the HVDC-flexible system based on the model.Performance of the HVDC-flexible system and effectiveness of the designed controller are verified via digital time-domain simulations with the software MATLAB.