Frequency-Adaptive Repetitive Control for Three-Phase Four-Leg V2G Inverters

Three-phase four-leg inverters with an LCL filter are employed as onboard vehicle to grid (V2G) inverters due to their advanced features-high utilization of the dc bus voltage, counteraction of unbalanced voltages, and so on. Repetitive control (RC) can exactly track periodic signals with known frequency, which offers a simple high-accuracy current tracking and harmonic suppression solution for three-phase four-leg inverters. However, the conventional RC (CRC) offers slow dynamic responses due to the embedded delay element, and grid frequency fluctuation would cause significant performance degradation of CRC controllers in V2G applications. Moreover, the three-order LCL filter often causes complexity in developing good performance feedback control schemes for the inverters, especially for complex three-phase four-leg ones. To address these problems, an easy-for-implementation hybrid control scheme that combines a frequency-adaptive RC (FARC) controller with a deadbeat (DB) controller is proposed to obtain fast and accurate control of feed-in grid current for the onboard three-phase four-leg V2G inverters with an LCL filter in the presence of grid frequency variation and load changes. The fast-response DB control scheme is based on a simplified first-order model of an LCL filter. The FARC controller is immune to grid frequency fluctuation. Simulations and experiments have been done to prove that the DB plus FARC control strategy can provide an excellent current control solution for the three-phase four-leg V2G inverters.