While conventional PI controllers operate optimally under stationary DC conditions, tracking AC signals inherently introduces steady-state tracking errors and delayed phase responses. This technical note covers the operating principles and design methodology of vector current control (or dq current control) for three-phase grid-tied converters. By deploying synchronous reference frame transformations (Clarke and Park projections), alternating three-phase quantities are mapped into direct and quadrature DC elements, enabling flawless tracking with zero steady-state error. The document models the system-level cross-coupling terms introduced by the grid frequency and outlines decoupling strategies. Finally, comparative simulation and hardware benchmarks are detailed using imperix B-Box and B-Board controllers programmed via C/C++ and Simulink/PLECS toolchains.