LQR-Based Current Controller for Three-Phase Inverters with Asymmetric Loads

Three-phase inverters play an important role in renewable energy systems, as they are capable of supplying active and reactive power according to the demand, and can operate as voltage sources, imposing the frequency and amplitude of the system’s voltage in grid-forming microgrids. To ensure proper operation, the control system must be capable of regulating all of the system’s variables, even under non-ideal conditions, such as voltage sags or asymmetrical loads, guaranteeing robustness under these scenarios. A vast majority of prior works focused on current control under unbalanced grid conditions, primarily aiming at suppressing oscillations in the active and reactive power, as well as eliminating the negative sequence component of the current. However, most of these studies overlook the zero-sequence current control and the impact of asymmetrical line impedances. This paper presents a current controller in the dq frame for three-phase inverters operating under asymmetrical loads, based on optimal control. The proposed controller was tested using a TI control card connected to a HIL emulator, and the results were compared with the traditional PI approach, exhibiting a faster and more efficient response.