Power-flow initialization of fixed-speed pump as turbines from their characteristic curves using unified Newton-Raphson approach

Recently, fixed-speed pumps as turbines (FSPATs) have become more attractive to be used in small hydropower plants as distributed generation (DG) to the grid at distribution-level voltages. Since growing FSPAT integration influences power-system dynamic behavior, an accurate dynamic assessment of the distribution and transmission system, including the FSPAT, is necessary. To obtain suitable initial conditions for a dynamic simulation, an appropriate initialization is required. Nevertheless, the initialization of FSPAT using a traditional power-flow approach is not straightforward due to an inevitable discrepancy between the predefined reactive power from power-flow calculation and the actual ones. To address this issue, this dissertation presents an expanded unified Newton-Raphson (NR) power-flow technique to enhance the dynamic initialization of FSPATs. The conventional NR power-flow algorithm is expanded to simultaneously solve the PAT and network variables by combining them in a single frame-of-reference. Additionally, the power-flow calculation integrates the PATs characteristic curves to obtain a correct steady-state solution in conformity to their actual behavior. A comparison between the traditional and proposed initializing methods is carried out to emphasize the superiority of the proposed approach in eliminating the problem of reactive mismatch. The robustness of the modified NR approach is confirmed through tests on various standard networks (distribution 15-bus, 69-bus, IEEE 30-bus, and 118-bus networks). The results exhibit that the proposed technique not only establishes superiority over existing methods in achieving accurate steady-state solutions without reactive-power discrepancy but also maintains quadratic convergence.In addition, the comparative dynamic simulation results between the traditional and proposed initializing procedures are presented. According to the study results, the proposed technique provides exact steady-state solutions for conducting the dynamic simulation by eliminating an oscillatory response at beginning of dynamic simulation. The obtained steady-state operating points give a precise dynamic assessment since any artificial shunt compensator is not required in the dynamic simulation.