Dynamic Variable Time-Stepping Schemes for Real-Time FPGA-Based Nonlinear Electromagnetic Transient Emulation

Electromagnetic transient (EMT) simulation of nonlinear elements in power systems is a particular challenge due to the requirements of an accurate representation and an efficient solution. The existing real-time simulators utilize a piecewise linear representation along with a fixed time step for the solution of nonlinear elements. This paper proposes the detailed methodologies for applying variable time stepping to real-time EMT simulation to improve the simulation accuracy and efficiency. The challenges, the feasible solutions, and corresponding restrictions of applying various variable time-stepping schemes along with nonlinear element solution methods in real time are discussed. The offline simulation and the real-time hardware emulation of two case studies, a full-bridge diode circuit and a power transmission system, are presented. The case studies were implemented on the field-programmable gate array device (Xilinx Virtex-7 XC7VX485T) in real time using high-level synthesis tool to achieve a parallelized and pipelined hardware design with minimum coding effort. The real-time emulation results captured by an oscilloscope are validated against the offline simulation on Saber and PSCAD/EMTDC software tools.