Subsynchronous Impedance Measurement of a Megawatt-Level Grid-Tied Inverter Using Controller Hardware-in-the-Loop

The penetration of renewable energy sources into the power grid has increased considerably during the past few decades. Modern power systems may include a variety of power sources such as photovoltaic (PV), wind turbines, energy storage systems, in addition to the conventional power plants. Such systems require careful stability analysis to prevent stability issues that may cause damage. One important case is the subsynchronous resonance that appears due to the interaction between inverters and series compensated power lines, which has caused damage and power failure recently. Impedance stability analysis is a powerful tool that is used for this purpose. In this model, a power source is represented as current source in parallel with a Norton impedance. However, measurement of the equivalent impedance model can be a difficult task in practice, particularly for high capacity inverters. In this paper, controller hardware-in-the-loop (C-HIL) is used to measure the subsynchronous impedance of a 3.36 MW PV inverter. The results show that measurement with C-HIL provides a powerful and accurate solution for this purpose that precludes the need for full hardware testing. A simulation model using PSCAD software is also built and the impedance measurement results are compared with the experiment.