A Virtual Impedance Based Grid Emulator for the Performance Analysis of Distributed Generations

This paper presents a virtual impedance-based grid emulation technique to evaluate the performance of distributed generations connected to a grid/micro-grid. A two-level voltage source converter (VSC) with an output LC filter is used to emulate the grid. In the emulation, the grid is represented as a voltage source behind a virtual series impedance, where the impedance can be an inductor, a resistor, a capacitor or a combination of all the three. A simple estimator based active damping technique is proposed to damp out oscillations associated with the output LC filter of the VSC. A detailed time domain analysis is carried out in PSCAD/EMTDC to study the transient response of the emulator. A hardware prototype is developed to verify the performance of the emulator experimentally.