Synchronization of Power Inverters in Islanded Microgrids Using an FM-Modulated Signal

A microgrid can operate in island mode, isolated from the main grid during certain time intervals. When operated in island mode, the electronic converters of the microgrid must keep the voltage and frequency of the microgrid inside the desired range. The converters of a microgrid can be classified into three groups: 1) grid-feeding; 2) grid-supporting; and 3) grid-forming power converters. The grid-forming converters operate as a voltage source, and require an external synchronization signal provided by the microgrid central controller. Both the noise and the delay in the synchronization signals received by the grid-forming converters are critical issues, which deteriorate the quality of the microgrid voltage and may overload those converters. The synchronization signals must be robust and suitable for operating in noisy environments. In this paper, the synchronization signal is frequency-modulated to be transmitted, being robust against noise. The transmission is done through an industrial RS-485 line with a low delay. The demodulation is performed with a low computational load by the control processors of the grid-forming power converters.