Converter-Based Damping of Low Frequency Oscillations in Mixed-Source Microgrids

This paper uses a combination of state space modeling and real-time hardware-in-the-loop simulations to compare the suitability of grid forming inverse-droop controls with virtual synchronous machine (VSM) controls for mitigation of frequency oscillations in islanded mixed-source microgrids. A linearized state space model is produced around an analytically determined equilibrium of the microgrid, which allows the electrical and mechanical dynamics of the microgrid to be investigated. Participation factor analysis is used to identify poorly damped low frequency system modes excited by each control techniques. Real-Time hardware-in-the-loop experimentation is conducted to verify this stability conclusions. using a PLECS Real-Time (RT) Box as the real-time digital simulator. Through study of a system containing two controlled converters and one rotating generator, the impact of control choice on the inter-converter and converter-generator power flow is shown. It is convincingly demonstrated that the grid forming inverse droop topology provides superior damping of frequency oscillations by eliminating poorly damped oscillatory modes that exist when VSM controls are used.