A PRC-PI APF control method for improving power quality and harmonic suppression in substations

Introduction Nonlinear loads in substations cause current distortion, increased harmonics, and reactive power, leading to power quality degradation and energy inefficiency. Traditional PI control lacks steady-state accuracy for AC signals, while conventional repetitive control (RC) suffers from slow transient response due to its inherent one-cycle delay. Methods This paper proposes a dual-loop proportional repetitive control-proportional integral (PRC-PI) strategy. An improved PRC with a proportional bypass term ( k prc ) is used in the outer loop to ensure multi-harmonic accuracy and improve transient recovery, while a high-bandwidth PI inner loop provides rapid current regulation. A decoupled double synchronous reference frame phase-locked loop (DDSRF-PLL) is also integrated to enhance phase tracking under unbalanced grid conditions. Results Simulation results show that the PRC-PI strategy reduces grid current Total Harmonic Distortion (THD) to 2.16%, significantly lower than traditional PI (8.54%) or RC-PI (3.80%) schemes. Experimental verification on an APF prototype confirms that Phase A grid current THD drops from 28.83% to 4.02%, and the system recovers to steady state within approximately one fundamental cycle (20ms) during load changes. Discussion The "precise outer loop and fast inner loop" structure effectively balances steady-state compensation accuracy with dynamic response speed. By significantly suppressing low-order harmonics and improving power quality, this strategy enhances the operational safety and reliability of substation equipment.