Improved Frequency Divider Based on Frequency Response Model of Grid-Following VSC

Frequencies at different buses in power system are different during a dynamic process. A large number of power electronic devices are connected to power system through grid-following voltage source converters (GFL-VSCs), which use phase-locked loop (PLL) to realize synchronization with the system. It is generally thought that GFL-VSC does not modify the frequency at their point of connection. However, this paper finds that GFL-VSC also affects terminal frequency in dynamic process and then the conventional frequency divider formula is improved to estimate frequency distribution based on a frequency response model of GFL-VSC. The main idea is to express terminal frequencies by both magnitude and frequency of VSC internal voltage and allowing the bus to be a new frequency boundary, thus reformulating the original frequency divider. Now all bus frequencies can be estimated only by the information of the rotor speeds of synchronous generator, magnitude and frequency of VSC internal voltage and the system admittance matrix. The correctness of this method is verified in a system with high proportion GFL-VSC in matlab.