Digital Conversion of SOGI-PLL for Enhance PLL Performance of Vienna Rectifiers under Weak-Grid Conditions

Most rectifiers that operate with AC grid voltages assume that the voltage is ideal and free from distortion. However, in high-power systems, such as water electrolysis system, the effect of grid impedance is significant, as it can distort the grid voltage. These conditions are referred to as a weak grid. In a weak grid, the p oint of the common coupling voltage can be further distorted because of the how PWM switching frequency of high-power rectifiers. This distortion may cause phase errors in voltage measurements, hindering accurate voltage detection. Two common methods can be used to mitigate distortion. The first method uses a hardware low-pass filter (LPF) to reduce high-frequency switching noise. The second method uses a phase-locked loop (PLL) based on the second-order generalized integrator (SOGI) to separate the distortion components. Although these two methods are widely used, their performance can vary depending on how they are applied. In this study the size and phase error compensation of the hardware LPF caused by the low PWM switching frequency of high-power converters and the voltage error generated in digitally implemented SOGI-PLLs are comparatively analyzed according to discrete implementation methods. The validity of their designs is verified via hardware-in-the-loop simulation experiments.