Sufyan, Abu (2025) Improved power quality in grid-connected inverters using robust sliding mode control techniques. Masters thesis, Memorial University of Newfoundland.
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Abstract
Grid-connected inverters (GCI) play a crucial role in injecting DC power from renewable resources into the utility grid; moreover, the quality of the power transferred to the grid largely depends on the effectiveness of the adopted control strategy. This research proposed a novel super-twisting double integral sliding mode control (SMC) algorithm for a three-phase grid-connected inverter with an inductive-capacitive-inductive (LCL) filter. In this study, the control algorithm is first derived based on the system’s dynamic mathematical model. Then, extensive simulation studies are carried out in MATLAB and Simulink software to validate its performance. Furthermore, the controller effectiveness is rigorously assessed under challenging conditions, including a 400% grid impedance variation, a 66% system parametric variation, grid frequency variation, and higher-order grid harmonic components. In the worst-case scenario, the total harmonic distortion (THD) of the grid current stays below 2.6%, demonstrating the controller's effectiveness in enhancing the power quality supplied to the grid. In the second control technique a novel integral terminal sliding mode control (IT-SMC) for a grid-connected three-phase inverter is presented to overcome the adverse effects of external disturbances on the power being injected into the grid. The integral terminal SMC guarantees finite-time convergence, minimal overshoot, and chattering-free operation. In the mathematical design of the controller, a derivative term is introduced in the capacitor voltages to achieve a better damping effect and prevent overshoot. Additionally, the integral of the grid and inverter current error is incorporated into the sliding surface to achieve precise tracking of the current reference. A 3-kW system is designed using the MATLAB/Simulink tool to analyze the controller’s performance. The grid-current quality and the stability of the controller are analyzed under conditions of grid voltage distortions, impedance variations, and filter resonance frequency. Experimental results confirm that the designed controller ensures nearly zero steady-state error, low grid current harmonics, rapid dynamic response, and system stability under weak grid conditions, thereby significantly improving the power quality supplied to the grid. The third control method is constructed while integrating the sliding mode control (SMC) algorithm with proportional resonant harmonic compensators (PR-HCs) for a three-phase GCI with an LCL filter, offering a promising solution for injecting power generated from DC sources into the utility grid. The existing controllers exhibit a notable tendency toward GCI system instability when facing system with simultaneous occurrence of parameter mismatches, distorted grid voltage, and resonance frequency events. The proposed SMC+PR-HC method inserts a loop of PR-HCs in parallel with the SMC control loop, significantly suppressing unwanted grid current harmonic components. Furthermore, a combined SMC and PR-HC control law is appropriately derived to analyze system stability using linear control theory approach. The performance of the proposed control method is validated using MATLAB/Simulink platform while considering the grid impedance variation, grid voltage fluctuation, filter parametric change, and the resonance frequency of ƒₛ ̸ 6.Finally, experimental results demonstrate that the proposed controller ensures minimal steady-state error, low grid current harmonics, rapid dynamic response, and system stability, even under ultra-weak grid conditions, leading to significant power quality improvement.
| Item Type: | Thesis (Masters) |
|---|---|
| URI: | http://research.library.mun.ca/id/eprint/16938 |
| Item ID: | 16938 |
| Additional Information: | Includes bibliographical references -- Restricted until March 17, 2026 |
| Keywords: | grid-connected inverters, three-phase inverter, nonlinear control, sliding mode control, renewable energy |
| Department(s): | Engineering and Applied Science, Faculty of |
| Date: | May 2025 |
| Date Type: | Submission |
| Digital Object Identifier (DOI): | https://doi.org/10.48336/h401-4v83 |
| Library of Congress Subject Heading: | Electric inverters; Nonlinear control theory; Sliding mode control; Renewable energy sources |
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