Stability of FPGA Based Emulator for Half-Bridge Inverters Operated in Stand-Alone and Grid-Connected Modes

In this paper, we present stability of a field programmable gate array (FPGA)-based emulator for single-phase half-bridge inverters operated in stand-alone and grid connected modes. The emulator is not only sufficiently accurate to emulate the characteristic behavior of the inverters, but also is sufficiently simple to be implementable on limited FPGA resources. This implementation enables the inverter developers to evaluate the FPGA-based high-speed controller in the early process by a real-time simulator system, which is unable for offline commercial simulation software packages. The discrete-time models, which are implementable on FPGA, are derived by discretizing the continuous-time models of the inverter using the forward-difference method. The stability analysis for the proposed inverter models showed that the quite small values of internal resistances of the inductors may have a serious effect on the stability, which is one of the most important properties of the inverter mathematical model. The experimental results show that the proposed emulator yields voltage, and current responses, which match with that of the real inverter circuit almost exactly under the same digital controller. The results also show that the responses of the emulators are consistent with the stability analysis for the inverter models.