Parallel operation of virtual synchronous machines with frequency droop control

Studies had shown that the transient stability of a PV-Hydro micro-grid could be improved using a virtual synchronous machine (VSM), by injecting virtual inertia into the system. In the case of an interconnected system with multiple numbers of PV-Hydro micro-grid, a number of VSMs need to be operated in parallel. The parallel operated VSMs shall share the transient load in proportion to their respective capacities. Otherwise, the storage battery of one VSM will discharge more and other storage battery will be less discharged. This paper presents a control logic for parallel operated VSMs so that they share the transient load in proportion to the capacity of respective VSMs. Frequency droop control approach is used in the control logic to ensure proper load sharing. The control logic is simulated in MATLAB\ Simulink and results show that the frequency droop control approach is good enough for parallel operation of VSMs.