There is an increasing need to perform real-time simulation of power plant performance behavior using Hardware-in-the-loop (HiL) and/or Software-in-the-loop (SiL), particularly for HDVC grid connected wind power plants. Real-time simulation based on HiL/SiL can help mitigating grid connection challenges by allowing for a more realistic testing of the target system under different grid, weather and operational conditions, which is either impossible or costly to do on-site; hence, HVDC and wind power plants can be largely de-risked before connecting to the grid and start of operation. In this paper, the methods to develop source code based SiL models (same control code as in real products, such as Wind Turbine Generator) are investigated. Two main real-time simulation platforms are considered, i.e., RTDS and OPAL-RT. A common SiL execution platform based on IntervalZero is introduced, which can interface with both RTDS and OPAL-RT and thus, largely improve the interoperability and scalability of the SiL models. In the end, a comparison between HiL and SiL models and between the SiL and PSCAD (offline) models are presented, including discussions about the intended use scenarios of real-time and offline simulation models.