Virtual impedance adaptation in a load emulator device for laboratory PV inverter testbed

The paper presents an adaptive virtual impedance for load emulator control to be used in an emulator-based laboratory testbed. The target platform aims to investigate the impact of nonlinear local loads on PV systems and local storage systems as solution for higher integration of PV systems into existing low-voltage networks. The platform is equipped with PV inverter with unknown LCL filter parameters and industrial grid emulator. These devises as well as the load emulator are connected to a Point of Common Coupling (PCC) via LCL filters. Their parallel operation can lead to some instability. In this paper, authors propose a simple and fast method for instability detection by defining a residual giving a low value under normal operation and higher values when instability occurs. Virtual impedance is then introduced in the load emulator control to suppress these instabilities. Its value is tuned gradually till the residual value returns lower than the threshold defined in normal conditions. This method can be applied to any LCL type inverter with proportional resonant controller. A PSIM software platform model is established and simulation results are carried out to demonstrate the effectiveness of the method.