Akademik Veri Yönetim Sistemi
IET RENEWABLE POWER GENERATION, cilt.19, sa.1, ss.1-14, 2025 (SCI-Expanded)
This study proposes an efficiency-oriented control approach for an LLC resonant converter-based high-frequency-link grid-connected inverter. The proposed topology has two stages. In the first stage, the LLC resonant converter generates a rectified sinewave output synchronized with the grid voltage. However, achieving zero gain under this operating condition is a challenge for theLLC resonant converter. To address this, a combination of phase-shift modulation and pulse-frequency modulation is employedwithout relying on a topology-morphing strategy. This approach enables both zero gain and a wide gain range for the LLC resonantconverter. However, integrating two different modulation strategies introduces another challenge. Multiple combinations of phase-shift angles and switching frequency values can yield the same gain. Effectively managing this is crucial to ensure both accurategain control and optimal system efficiency. Therefore, in the proposed system, a PI controller generates the phase-shift angle valuebased on the current error. Then, the PSO algorithm dynamically finds the optimal switching frequency value for any instant tomaximize efficiency according to the predetermined cost function. This novel efficiency-oriented approach effectively enhancesthe performance of LLC resonant converters. In the second stage, an unfolder inverter operating at the grid frequency generates asine wave from the LLC output to achieve grid connection. Since the unfolder operates at the grid frequency, its switching losses arenegligible. Experimental results demonstrate that the proposed system successfully tracks reference signals, even under abruptchanges, while maintaining high efficiency under various operating conditions. Additionally, the output current THD remainswithin internationally specified limits, ensuring compliance with relevant standards.