Optimized Control of LCL–VSC Converter With Refined s-Parameter

For the control of high-voltage dc (HVdc) systems, especially for that of the multiterminal HVdc (MTdc) systems, the voltage source converter (VSC) is a good option because of its high controllability. These days, different types of VSC converters have been realized such as the two/three level converter and modular multilevel converter. However, VSC converters are vulnerable against dc faults because the paralleled diodes may experience large fault currents. In order to maintain the sustainability of electricity delivery, efforts have been paid on protecting the HVdc networks, such as the novel converter topologies with the capability to tolerate faults and the dc circuit breaker. Among which, the concept of the inductor-capacitor-inductor circuit (LCL)-VSC converter aims at enhancing the ability of converter to ride through dc faults, which limits currents flowing from the ac side to dc side. The proposed method in this paper optimizes the control of LCL-VSC for partial load so that the power loss can be drastically decreased. In addition, the preferable working range for the LCL converter is introduced to guarantee the ability of restraining fault currents. The method is verified on the PSCAD/EMTdc platform.