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The electromagnetic transient simulation of a power system with nonlinear characteristics is very time-consuming due to numerous inversion calculations of the admittance matrix. To speed up the simulation of the power system with nonlinear characteristics, a multi-rate and parallel electromagnetic transient simulation method is proposed. Firstly, a Multi-Area Thevenin Equivalents (MATE)-based parallel algorithm considering nonlinear characteristics of the power system is proposed. This method guarantees the admittance matrix is constant by considering changing branches as link current without dividing the subnet again. Secondly, considering the differences of the time constant of the AC/DC subnet, different simulation steps are used for these subnets. The Lagrange interpolation method is used for calculating the Thevenin voltage of the AC subnet in non-synchronous time. Calculation methods of the DC subnet Thevenin voltage is proposed by considering the simulation results during the entire large simulation step. Finally, the simulation process is optimized for improving the simulation efficiency further. The simulation results show that the proposed method could greatly improve the simulation efficiency without losing simulation accuracy too much compared with the traditional method. [ABSTRACT FROM AUTHOR]

In order to improve the simulation speed of the AC/DC hybrid grid, the inductance/capacitance (L/C) switch model for line-commutated converter of high-voltage direct current (LCC-HVDC) is presented in this study. The time domain modeling method is used to analyze the circuit of L/C switch model for the six-pulse system in LCC-HVDC in a switching period. A parameter setting method of L/C switch model is proposed considering the transient response, the steady state performance, switching losses and simulation error of the switch. The inductance/capacitance (L/C) switch model for LCC-HVDC has the advantage of keeping the admittance matrix unchanged regardless of the change of switching state, which improves the simulation efficiency. Finally, the validity of the parameter setting method is verified. Compared with the test results of PSCAD/EMTDC, the accuracy of the proposed LCC-HVDC simulation model is proved. The model is suitable for real-time or offline simulation of AC/DC hybrid grid. [ABSTRACT FROM AUTHOR]