oa A new normalized digital feedback control for grid connected distributed generation system

Background & Objectives Distributed Generation systems such as fuel cells, solar, and wind play a crucial role in producing energy with low or zero CO2 emissions and are explored for various stand-alone and grid connected applications. Inverters (conditioners) play an important role in interfacing the DG sources to the grid as they link them with controlling the power flow. Therefore, control techniques for inverters should achieve high performance not only during normal operating conditions of the grid, but also under fault conditions. This work proposes a newly designed Real Time Digital Feedback Controller for a grid connected PV system. A multilevel Flying Capacitors Inverter along with inductor and step-up transformer is used as an interface between the PV system and grid. The proposed controller is Deadbeat type controlling simultaneously the grid current and capacitor voltages variables using a weighting factor to ensure a proper balancing among the controlled variables. Furthermore, the proposed approach is offering the possibility of duty cycles normalization when the reference is not achievable within the sampling period. The newly designed controller transfers the power to the grid even under voltage fluctuations resulting from grid faults. This Voltage Ride Through capability is made possible without any noticeable current overshoot, while maintaining unity power factor and low harmonic distortion. Methods: In this work, a new normalized Deadbeat control technique with VRT capability is proposed to transfer power to the grid with unity power factor. Unlike other control techniques, the proposed control is based on a hybrid model taking into consideration duty cycles, state variables, and external disturbances (voltage sags). Furthermore, a normalization of the control vector is presented when the calculated duty cycles do not satisfy the physical condition. The validated approach consists of a serial of mathematical calculations (min, max) in order to ensure the generation of duty cycles within the physical domain. Results & Conclusion: An experimental power conditioning unit was developed to transfer the power from a DG system to the grid. Simulation and experimental results obtained on 1kW prototype validate the high performance of the proposed control under grid voltage sag. Smooth transition between normal and faulty operation is achieved. Keywords: Normalized Deadbeat Controller, Voltage Ride Through Capability, Grid connection, Unity power factor, Solar Energy Interfacing.