Effect of sudden variation of grid voltage in primary frequency control application using converter based energy storage systems for weak grid systems

One of the main revenue streams of the power system industries is provide a stable frequency all the time. Energy storage systems are well suited for the purpose because of their bidirectional capabilities. Recently converter based energy storage system has been gaining interests for providing frequency response replacing traditional generator based solutions due to the speed of the power electronic converters. One of the emerging problems has been how to control the converter or ride-through when there is a fault or sudden variation in grid voltage and what could be the possible impact on frequency. This paper analyses the effect of variation of grid voltage on the frequency control through the dynamics of the phase locked loop. The paper brings in a unique issue arises in frequency control structure especially under sudden grid voltage variation/fault conditions. It has been found that the frequency may undergo some unwanted oscillations during fault duration and the converter may be unstable. The detailed analysis of the frequency control stability issue under weak grid scenario is presented followed by a brief solution of the problem is discussed through comprehensive simulation studies.