In voltage source converter based HVDC transmission system the active power is controlled by changing
(A) phase angle of the converter ac input voltage
(B) supply frequency of the converter ac input voltage
(C) magnitude of the converter ac input voltage
(D) DC voltage at the inverter terminals
(A) phase angle of the converter ac input voltage
(B) supply frequency of the converter ac input voltage
(C) magnitude of the converter ac input voltage
(D) DC voltage at the inverter terminals