Hybrid simulation for HVDC

Power system transient simulation is an important approach to study the system's dynamic behaviors and guide its daily operation schedule. It can be classified into the following two categories based on the different scales of time step: electromagnetic transient (EMT) simulation and transient stability analysis (TSA). EMT has time step in microseconds, uses instantaneous value of electrical variables, and studies the transient phenomena caused by the interaction between electrical and magnetic fields. EMT is able to present the detailed switch process of power electronic devices in HVDC, achieving very accurate simulation. However, generally it is not suitable for large-scale system simulation because of its large computational burden due to complicated model and small time step. EMT is commonly used in detailed study of HVDC system in a relatively small scale. Currently there are several commercial EMT tools, such as PSCAD/EMTDC, EMTP, MATLAB®/Simulink®, Real Time Digital Simulator (RTDS), HYPERSIM, and RT-LAB. Particularly, some EMT tools can achieve the so-called real-time simulation, such as RTDS, by parallel computation hardware. This capacity makes it possible to connect real control/protect devices via power amplifiers, implementing hardware in loop simulation, which is quite valuable for in-factory tests.