Elhassan, Garba (2023) Modelling and simulation of multi-sampling deadbeat current controller with time-delay compensation for grid-connected inverter. Doctoral thesis, Universiti Tun Hussein Onn Malaysia.

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Abstract

Digital controller realisations suffer from a phase lag induced by time delay. This phase lag makes it hard for inverter controller to maintain stability and robustness, especially during grid-impedance perturbations. This research aims at mitigating the inherent one-sampling-period delay associated with deadbeat current control without requiring an anti-aliasing filter. First, a deadbeat current controller was modelled with the right tuning polynomial and with the caution of not cancelling the poles and zeroes to improve the performance of the system, as well as its resilience against parameter variation. The designed controllers were tested using Nyquist and Bode plots, and their responses were acceptable with the control margin stability. In the second part, time delay condition has been added to the model to mimic the real delay and a quadruple-sampling deadbeat current controller was modelled, which reduced the one-sampling-period delay of the traditional deadbeat current controller to 14 sampling period. This time-delay mitigation improved the bandwidth of the controller, as well as reduced the total harmonics injected into the grid. In the last part, a comparison between the performances of the proposed quadruple-sampling deadbeat current controller and the conventional proportional-integral controller was intuitively carried out using the same simulation setup. The proposed method achieved an improvement of 120 μs from that of the Proportional Integral (PI) current controller. In terms of Total Harmonic Distortion (THD), the quadruple-sampling design method exhibited 1.01% in THD current and 0.12% in THD voltage as compared to the PI controller with 4.03% and 0.18% in current and voltage THDs, respectively. Finally, the two controllers were compare subjected to grid parameter variation of 40% and 80% and from the results obtained, the quadruple-sampling design method displayed good current tracking, improve time-delay compensation, and robustness against parameter variation

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