A Comparative Study of P-f Droop Control and Isochronous Control for Grid-Forming Inverters in Isolated Hybrid Power Systems

Abstract:
The proliferation of grid-forming (GFM) inverters has opened up new ways of operating power systems. Through isochronous control of the GFM inverters power systems are operated at fixed frequency instead of variable frequency through P-f droop control. In this paper, both control modes are compared for a real isolated hybrid power system con-sisting of volatile renewable energy resources, synchronous machines and a battery energy storage system (BESS). The results of 24 h simulations with a model predictive control-based energy management system and laboratory experi-ments in an adapted microgrid are evaluated in terms of the economic performance and the frequency dynamics of the power system. The economic evaluation shows that the BESS is used more in the isochronous control mode because it is solely responsible for balancing any power imbalances. Therefore, the BESS is expected to age faster. However, the frequency dynamics are significantly improved by the isochronous control. The frequency is kept at the nominal value throughout both, the 24 h simulations and the laboratory experiments.