Combined error adaptive fuzzy-PI for reducing DC voltage ripple in three-phase SPWM boost rectifier under unbalanced DGs system

Boost rectifiers are commonly used as the input for power inverters. The output voltage of the boost rectifiers should have high quality and precise value to enable the power inverters to achieve maximum performance. However, the grid occasionally supplied unbalanced voltage and current to the boost rectifiers so that the performance of the rectifiers is impaired. When unbalanced AC voltages occurred, the frequency of DC voltage ripples may become two times higher than the AC voltage frequency. The unbalance voltage and current may occur when the grid is supplied by several single-phase Distribution Generators (DGs) with varied capacities. This condition becomes more complicated if the DG is renewable energy in which the output power is intermittent. This study proposes a novel three-phase pulse-width modulated (PWM) boost rectifier control using Voltage Oriented Control (VOC) with a Combined error adaptive fuzzy-PI (CEAF). CEAF is a combination of the Delta error adaptive fuzzy (DEAF) and the Absolute error adaptive fuzzy (AEAF). DEAF is a self-tuning fuzzy-PI method that is generally used as an adaptive fuzzy controller with inputs of errors e(t) and delta error de(t). As for AEAF, it is a modified DEAF of which the inputs are the absolute values of e(t) and de(t). This adaptive Fuzzy-PI is used to determine K_p and K_i values that suit the needs, especially when the sources are fluctuating or unbalanced. The performance of the proposed controller is then compared with a conventional DEAF and with a well-adjusted PI controller. Based on the simulation in Matlab/Simulink, the proposed method would result in a significant reduction in DC voltage ripples and DC steady-state error when fluctuating, unbalanced voltages occur. The resulted ripple voltage decreases from 0.16% to become 0.12%. The steady-state error decreases from 0.27% to become 0.19%.