Enhancing PLL performance in weak grids: a comparative analysis of backward and bilinear ADC with SOGI-PLL

Most rectifiers using AC grid voltage assume that the voltage is ideal and has no distortion. However, in high-power systems such as water electrolysis, the grid voltage can be distorted. This situation is called a weak grid. In weak grids, the switching of rectifiers causes voltage distortion. Distorted voltage causes phase errors during observation, so it is important to measure voltage without distortion. There are two common methods to reduce errors during observation. One is using a hardware Low-Pass Filter (LPF) to reduce high-frequency switching distortion. The other is using a Second-Order Generalized Integrator (SOGI) Phase-Locked Loop (PLL) to separate the distorted component. Both methods are commonly used, but their performance changes depending on how they are applied. This paper compares the distortion reduction of the hardware LPF and the error caused by the digital method of the SOGI-PLL. Simulation results show that the hardware LPF reduces distortion by about 75 %, and the SOGI-PLL can have up to 6.7 % error depending on the digital method. These results are verified through PSIM simulation.