In this paper, the stability analysis of a gridconnected voltage source inverter with an LCL filter is presented. The Poincaré map is used to analyze the stability of the system from a geometric point of view and provides a better understanding of the system performance. In addition, a composite nonlinear feedback (CNF) control is proposed in order to improve the transient and steady-state performance of the control system. Simulation and experimental analysis verify the validity of the analysis and also show the superiority of the CNF-based controller compared to the conventional proportional-resonant controller during transients and steady-state operation.Index Terms-DC/AC inverter, nonlinear control, observer, proportional-resonant (PR) controller, pulsewidth modulation (PWM), renewable energy, state feedback.

This paper presents a very fast DC-bus voltage controller for a single-phase grid-connected Voltage Source Inverter (VSI) with an LCL output filter used in renewable energy applications. In single-phase grid-connected inverters, the design of the DC-bus voltage control scheme is very challenging due to the presence of a second harmonic ripple across the DC-bus voltage. The proposed DC-bus voltage control scheme is able to address the difficulties introduced by the second harmonic ripple. The DC-bus voltage controller is based on an adaptive droop control technique, which is able to provide a very fast transient response for the closed-loop system and ensures the optimal operation of the VSI during steady-state conditions. Also, the simple structure of the controller makes it very practical for grid-connected VSIs used in renewable energy power conditioning systems. Theoretical analysis and experimental results demonstrate the superior performance of the proposed control approach compared to conventional DCbus voltage control schemes.

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This paper presents an advanced current controller for grid-connected bi-directional AC/DC converters used for Energy Storage Systems (ESSs). The proposed control scheme is designed to incorporate both the time-domain and frequencydomain dynamics to achieve superior transient and steady-state performance. The advanced current controller can overcome the various challenges faced by the conventional current controllers used in this application, which lead to sluggish transients and steady-state errors when tracking the sinusoidal reference for the grid current. Combining the time-domain dynamics with the frequency-domain dynamics creates a more intelligent controller compared to existing methods, which only consider the dynamics of one domain. The proposed controller is able to eliminate steady-state error by adaptively changing the controller coefficients in the frequency-domain according to the current error. In the time-domain, the control scheme minimizes the derivative of a defined energy function in order to optimize the transient performance. Simulation and experimental results obtained from a 3.3kW grid-connected AC/DC converter demonstrate its superior performance.

This paper presents a new active/reactive power closed-loop control system for a hybrid renewable energy generation system used for single-phase residential/commercial applications. The proposed active/reactive control method includes a hybrid estimator, which is able to quickly and accurately estimate the active/reactive power values. The proposed control system enables the hybrid renewable energy generation system to be able to perform real-time grid interconnection services such as active voltage regulation, active power control, and fault ride-through. Simulation and experimental results demonstrate the superior performance of the proposed closed-loop control system.

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