Discrete-time dynamic systems demonstrate quite exciting possibilities from the perspective of control as compared with the continuous-time counterpart. Interesting properties of discrete-time dynamic systems include the possibility to algebraically determine previously unknown system parameters by simply measuring the present inputs and outputs of the system. Additionally, achieving a finite settling time with zero steady-state error is only achievable in discrete-time dynamic systems. Deadbeat current control (DBCC) has been used to achieve a finite settling time, especially in grid-connected inverter applications. However, there is no comprehensive study on reviewing or evaluating existing control approaches, to the authors' best knowledge. This paper systematically examined the existing methods by paying attention to four key research issues: 1) research evidences indicating the adoption of DBCC in grid-connected inverter applications (GCIAs), 2) the types of deadbeat control approaches adopted in GCIAs, 3) the best approach in terms of stability especially regarding grid-impedance variation, and 4) the barriers that might prevent the wide adoption of DBCC in GCIAs. Finally, this paper presents a hypothesis based on the simulated results on which approach is superior at present to give readers a direction for further research classification on deadbeat control.INDEX TERMS Deadbeat control, grid-connected inverter, current control, renewable energy sources.
The control of grid‐connected inverters is recently executed with digital microprocessors due to the advances in digital signal processing technology. However, the digital realisation has a drawback of the phase lag induced by the time‐delay. This phase lag challenges the stability and robustness of the controller of the inverters. In view of the challenge, this paper presents a comprehensive review of time‐delay compensation techniques employed in both model‐free (MF), and model‐based (MB) controls of an inverter in grid connection. MF techniques mainly use proportional‐integral, and proportional resonance controllers with some techniques to reduce time‐delay. Meanwhile, for MB, this paper discusses the commonly used control techniques, which are the Smith predictor, modified Smith predictor, deadbeat controller and model predictive controller. Several related techniques from the literature that have been adopted to mitigate the delays are tabulated comprehensively, and critical issues regarding the MF and MB techniques are also discussed. Finally, this paper presents a hypothesis on which technique is superior at present and suggests a hybrid technique from the MF and MB techniques to give readers a direction for further research.
The current paradigm in integrating intermittent renewable energy sources into microgrids presents various technical challenges in terms of reliable operation and control. This paper performs a comprehensive justification of microgrid trends in dominant control strategies. It covers multilayer hierarchical control schemes, which are able to integrate seamlessly with coordinated control strategies. A general overview of the hierarchical control family that includes primary, secondary, tertiary controls is presented. For power sharing accuracy and capability, droop and non-droop-based controllers are comprehensively studied to address further development. The voltage and frequency restoration techniques are discussed thoroughly based on centralized and decentralized method in order to highlights the differences for better comprehend. The comprehensive studies of grid synchronization strategies also overviewed and analyzed under balanced and unbalanced grid conditions. The details studies for each control level are displayed to highlight the benefits and shortcomings of each control method. A future prediction from the authors’ point of view is also provided to acknowledge which control is adequate to be adopted in proportion to their products applications and a possibility technique for self-synchronization is given in this paper.
<a name="_Hlk16093850"></a><span>Droop control technique is one of the renowned techniques which does not need any communication connection between Distibuted Generations (DG), hence the cost, as well as the reliability of the microgrid (MG) system can be reduced. MG is operated in two modes as their functionality and structure is concern. These are the grid connected or islanded (stand-alone) mode. DGs operating values may have different ratings of voltage, power and line impedance. The power sharing in these operatng conditions is not shared equally by all DGs connected in the system and also during load changes conditions power sharing accuracy is difficult to achieve. In this paper, a droop power control is used to balance the power sharing in islanded mode. As from the results, the active power sharing is equally shared from all DGs connected in the microgrid system. However, reactive power sharing accuracy always disturbed when there is impedance mismatch among the different DG feeders. The accuracy is done by monitoring the effects when load changes for low load to high load or vice versa. The Proportional Integral (PI) controller has been used to minimize the reactive power errors. At the end, the power droop is capable to share power accurately and results prove the stability and reliability of the proposed technique.</span>
The control of voltage source converters (VSCs) is now implemented on digital microprocessors. This digitalization has the drawback of time delay in the control loop. The goal of this research work was to investigate improvements that can be obtained from the combination of model-based and model-free time-delay compensation approaches. Deadbeat control (DBC) from model-based techniques and the method of moving the control variable's sampling instants, or the pulse-width modulation (PWM) updating instants, from model-free time-delay compensation techniques, were put together as the proposed new method of time-delay compensation in this study. These controllers were thoroughly examined in terms of control algorithm design, system stability analysis, and sensitivity analysis of plant parameter perturbations. In addition, thorough Simulink-based computer simulations were conducted in this work to assess the performance of each controller. The proposed method compensated about 80 µs as compared with the time delay compensated by the conventional single-sampling method. This research work was limited to simulations only; hence, conducting experiments to further validate this research work could be a direction for further research.
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