A constrained sequential power flow algorithm for VSC-high voltage DC grids compensated by PFCs

Abstract

Upcoming HVDC systems will include multiple power flow controllers (PFCs). Frequent activation/deactivation of the PFCs will complicate the implementation of unified DC power flow (PF) algorithms; because, the DC system equations, variables, and the Jacobian matrix would be changed. To address these challenges, decoupled sets of equations are developed for the uncompensated HVDC grid and PFCs, and a sequential DC PF algorithm is proposed. The PF equations of the uncompensated HVDC grid are solved using the Newton-Raphson (N-R) method and the grid voltages are computed over the first sequence. The impacts of PFCs are proposed to be modeled through constant and artificially injected powers (AIPs) to the grid's buses. The computed system voltages are transferred to the second sequence to solve equations of each PFC, compute their variables (duty cycle and voltage of their intermediary capacitor), and update their associated AIPs. A modular method is also proposed to handle the system's technical limits by properly activating PFCs and altering system references. Several static and dynamic simulations are conducted to verify the accuracy, efficiency, and computational burden of the newly proposed AIPs, sequential algorithm, and handling method.