Simplified Grid Emulator for Testing Grid-Connected Power Electronic Converters

Power grid emulator is used extensively for the testing and validation of the hardware and control of PWM rectifiers and grid-tied inverters. The grid emulators are required to produce practical grid voltage disturbances such as unbalance, harmonic distortion, sag and swell. Conventionally, grid emulators are realized through voltage source inverters (VSIs) and passive LC filters. The voltage across the filter capacitor is controlled using a closed-loop feedback controller to track the emulated grid voltage reference. Apart from cost and size implications, the LC filter requires well-designed closed loop control, and is certainly a limitation on the bandwidth of the grid emulator. A VSI based grid emulator is proposed in this paper which does not utilize any passive filter. Such an emulator is controlled by an open-loop feed forward controller. The elimination of passive filter and closed-loop controller makes the emulator cost-effective, compact, efficient, fast and easy to implement. The effectiveness of the proposed grid emulator is demonstrated by testing a PWM rectifier load under practical grid conditions including voltage sag and unbalance. Simulation and experimental results are provided.