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

Abstract

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 Parks 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 with a low computational burden in the implementation. Furthermore, better transient stability performance is presented when no PLL and Park’s transformation exists. To derive the findings and evaluate the validity and effectiveness of the proposed new control strategy for the VSC-HVDC system under various grid states and fault scenarios to ensure its dynamic stability, experimental tests were carried out using the STM32F407 microcontroller, which demonstrated that the experimental results closely matched the theoretical predictions.