In view of the problem that the traditional decoupling control system only ensures the flexible DC transmission system to transmit active power and reduce the harmonic signal in the AC current but not compensates the series circuit

a kind of feedforward decoupling control system with harmonic and reactive power compensation capability is proposed. The system is based on the mathematical model of modular multilevel converter

the detected reactive current is fed back to the feed-forward decoupled reactive inner loop as a reference value to achieve reactive power compensation and the harmonic component detected by the high pass filter is fed back to the feedforward decoupling reactive inner loop as reference value to achieve harmonic compensation. The simulation and test results show that the proposed reactive power compensation system can reduce the phase current of the THD of high-voltage DC transmission of the test system from 18.92% to 7.22% and

at the same time

it can not only compensate for the harmonics and reactive power for the supplier and receiver

but also has ability to transmit active power and DC expansion.