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.
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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