Hybrid shifted frequency analysis-electromagnetic transients multirate simulation of power systems

Traditional power systems have high inertia, and disturbances can be represented with relatively large discretization steps. However, power electronic interfaced generation requires time steps, at least two orders of magnitude smaller to represent the switching operations. In addition, the increased penetration of these devices reduces the total inertia of the system, and a single-time step size transient stability (TS) solution that considers the details of the power electronic devices would take two orders of magnitude longer (that is, electromagnetic transients (EMT) simulators time step sizes). Hybrid TS-EMT simulators aim at using large time steps for the traditional (slow) part of the system and small time steps for the power electronic devices. However, in the current state-of-the-art, the proposed hybrid solutions are limited in a number of ways. Most of them introduce a one TS time step interfacing delay between solutions, which reduces accuracy and can create numerical oscillations. Other approaches use the travelling time of transmission lines to tear the system and interface the solutions, but this limits the flexibility of connecting power electronic components anywhere in the system. The hybrid solution presented in this work combines a Shifted Frequency Analysis (SFA) solution that is more accurate than traditional phasor solutions to follow transient stability trajectories in lower inertia systems with the traditional EMT solution for the fast power electronic converters. In order to interface the SFA and EMT solutions, a new hybrid protocol has been developed that overcomes the disadvantages of the current hybrid solutions. The two subsystems are joined using the Multi-Area Thévenin Equivalent (MATE) solution framework, and introducing the novel concept of employing a second parallel EMT simulation. Illustrative examples demonstrate the validity and accuracy of the SFA-EMT multirate protocol. The new protocol achieves significant computational savings when compared with an all-EMT solution. A simulator operating with the proposed protocol will allow improved accuracy when conducting power system transient studies with high penetration of renewable generation without considerably increasing the computational time.Applied Science, Faculty ofElectrical and Computer Engineering, Department ofGraduat