A novel virtual synchronous machine implementation and verification of its effectiveness to mitigate renewable generation connection issues at weak transmission grid locations

Large-scale penetration of renewable resource based generation will displace conventional synchronous machine-based power generation. This will lower the overall system inertia and will result in lower short circuit levels at point of connection (POC) of renewable resources. Renewable resources such as wind and solar photovoltaic (PV) are interfaced to the power system via power electronic inverters. Operation of inverter-based equipment under low inertia and low short circuit conditions is challenging. Specific challenges include fault recovery response, unstable oscillatory interactions, and impact on torsional oscillations of thermal generating units. In this paper, the effectiveness of inverters, controlled as a virtual synchronous machine (VSM), to overcome some of these issues is investigated. A battery energy storage system (BESS) inverter is controlled as a VSM. The input signals provided to the BESS inverter are derived from solving the time domain equations of a synchronous machine. The response of exciter, governor, and power system stabilizer (PSS) are also included in the VSM strategy. The dynamic characteristics of the proposed VSM are verified using a single machine infinite bus (SMIB) test model. The effectiveness of the proposed VSM approach to mitigate specific technical challenges is verified by performing dynamic response studies on two test systems. The two test systems represent selected regions of practical power systems with high renewable penetration. The VSM response is compared with a conventional synchronous machine response in all test cases, to demonstrate the close correlation of dynamic response. The simulation results demonstrate that the VSM's response is as expected and is capable of mitigating stability-related issues due to low system inertia and low short circuit strength.