Improved Decoupling Control Strategy of MMC-HVDC System Connected to the Weak AC Power Grid

In order to make full use of the regulation capabilities and avoid energy loss caused by coupling effect, a mathematical model of MMC-HVDC system was deduced. Subsequently, the coupling mechanism between the AC current and stations of the MMC system were analyzed via nonlinear equation. On the basis of mechanism analysis, the effects of inter-coupling in MMC-HVDC system connected to weak AC power grid were weakened by adding the dynamic feedforward compensation into the control system. In addition, to ensure the system stability and improve dynamic performance of the proposed controller, the control parameters design method was proposed based on the Hurwitz criterion and the time-domain mathematical calculations. By combining the two parts of the control system, an improved decoupling control strategy applicable to MMC system was proposed. Taking MMC-HVDC system as an example, the simulation based on PSCAD/ EMTDC verified the effectiveness of the proposed method.