FPGA-based Real-Time Simulation for LLC Resonant Converter Prototyping

LLC converters are a very commonly used topology in electric vehicles and in electric aircrafts, because of their high energy density, high efficiency due to natural zero-voltage-switching (ZVS) capabilities, and operation at a voltage gain less than, equal to or more than unity. This paper demonstrates a verification method of a designed resonant LLC converter using real-time hardware-in-the-loop simulation (HiL). The main advantage of this method is that a designed power converter can be tested and verified in real time prior to building a hardware prototype. This enables us to validate, debug and tune converter parameters without the experimental setup in a safe and hazard-free environment and with no risk of damage to expensive hardware. After a successful HiL simulation, it will be safe and cost-efficient to continue or implement the system in real hardware. However, real-time simulation of high-frequency LLC converters is very challenging due to the requirements for a very small simulation time step, even beyond hardware capabilities. In this paper, a 3.0 kW LLC converter is designed based on first harmonics approximation and time-domain simulation. Afterward, the designed converter is simulated in a real-time (RT) system equipped with an FPGA-based electrical solver that employs oversampling of switching signals. Finally, the results from the RT system are compared to experimental data from the hardware prototype to assess the performance of the simulation with respect to the actual results.