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A Novel Frequency and Voltage Controller for Parallel Voltage Source Converters and Synchronous Generators Coexisting in Islanded Microgrids

In low-inertia microgrids (MGs), one of the major challenges is the large frequency drop in case of active load increment. There has been presented an appropriate approach to tackle this issue, which is the virtual synchronous generator (VSG) control method for inverters. This presented method, however, needs a phase-locked loop (PLL) to estimate the frequency of the power grid. This paper proposes a method for controlling the voltage source converters (VSCs), leading to a fast frequency restoration for the grid without using any PLL. Moreover, the proposed method eliminates the need for the secondary frequency control and voltage control loop of the synchronous generator (SG). In other words, the VSC is responsible for regulating the frequency of the grid and the load voltage. Simulation results show that the grid frequency is restored to its nominal value once the VSC is connected to the grid. In addition, thanks to the presence of VSC, the load voltage returns to its nominal value when a reactive load is connected to the load bus.