Stability analysis of VSC-HVDC system based on new phase-locked-loop less voltage oriented control method

Voltage Source Converters-based High Voltage Direct Current (VSC-HVDC) systems are generally implemented to transmit power across long distances due to their low cost and flexibility. This paper will discuss a new simple and low-computational-burden phase-locked loop less voltage-oriented control strategy (PLL-less-VOC strategy) for controlling and synchronizing a VSC-HVDC system in a synchronous rotating frame (dq frame). The proposed method is used not only to control the VSC-HVDC but also to obtain the mathematical model of both VSCs-based HVDC systems in the dq frame using the basics of the direct instantaneous power control theory (DPC) without using PLL and Park transformations. The proposed PLL-less-VOC strategy is equivalent to the conventional VOC strategy for steady-state stability, but it has the benefit of both conventional VOC and DPC, better transient stability performance, and low computational burden in the implementation. The experimental tests using STM32F407G microcontroller demonstrate that the proposed control strategy has better dynamic stability under certain exceptional conditions such as step changes on DC-link voltage change, powers change, and three-phase fault.