###### Abstract  
This paper presents a stationary reference frame grid current control algorithm for a grid-connected inverter (GCI) to improve command tracking performance and resilience in response to disturbances, i.e., a grid voltage incident in a GCI current control system. In the proposed algorithm, disturbance rejection is applied to reduce the overcurrent at the GCI in response to a grid fault. Disturbances to the GCI current control system are estimated using a grid current observer, and the estimate applied to the grid current controller to activate the disturbance rejection. The stationary reference frame current of a GCI system is also controlled to avoid cross-coupling issues at a synchronous reference frame model, reference transformation and dependency to phase locked loop (PLL) performance. However, the phase lead or lag and steady-state response error, which are drawbacks of AC signal control based on stationary reference frame proportional-integral (PI) controller, must be eliminated in order to secure competition with the synchronous reference PI (SRFPI) controller that was mainly used in the GCI system. Hence, to compensate for command tracking the AC current, such as steady-state response error and phase lead or lag, command feedforward control is applied in the proposed control system. The theory behind the proposed GCI current control algorithm is analyzed, and the proposed algorithm is tested via simulation and experimentation. g 2020 10 8642 10.3390/app10238642 10.3390/app10238642 10. In a synchronous reference frame PI (SRFPI) control system, DC signals are controlled, and phase lag or steady-state error with respect to frequency can be negligible. However, the phase angle information of the grid voltage is required for reference frame transformation. For that reason, SRFPI current control systems should be implemented with a phase locked loop (PLL). In a stationary reference frame control system, reference frame transformation, PLL implementation, and cross-coupling between the d and q axes can be avoided. In such a system, however, command tracking performance, which are frequency-related phase lag and steady state errors, is degraded because AC signals are controlled in the stationary reference frame control system. In an effort to compensate for this drawback and improve command tracking performance, a command feedforward control (CFFC) has been applied. In [12; 13], CFFC is applied to a PI controller to compensate the drawbacks of controlling AC signals, but it was used for voltage control for in a single-phase Uninterruptible Power System (UPS) system. The CFFC is applied to the stationary reference PI controller to improve transient dynamic performance of a GCI current control system but it is limited to a single-phase system [14]. Model predictive control (MPC) are applied for GCI current control systems in [15; 16]. By using MPC, optimization objectives such as minimization of losses or total harmonic distortion (THD) can be achieved but implementation of the control algorithm is relatively complicated and is limited by performance of a signal processor due to heavy computation loads. Along with command tracking performance, resilience in the face of disturbances is an important aspect of control system performance. In a grid-connected current control system, grid voltage is treated as a disturbance to the system. When a grid fault, including a line-to-ground or line-to-line fault, occurs, overcurrent may damage the electrical circuit or its components. Accordingly, commercial GCIs are tripped when 200-225% of its rated current occurs [17; 18]. Tripping a GCI disconnects it from a grid, which may result in an unstable system. Disturbance observer-based control (DOBC) and active disturbance rejection control (ADRC) algorithms have been developed in an effort to improve these aspects of system resilience.