Power Quality Enhancement of a Grid-Connected PV–WECS Hybrid Energy Storage System Using Fuzzy Logic Controller and Dynamic Voltage Restorer

Abstract

The increasing penetration of renewable energy resources into modern power systems has introduced significant challenges related to voltage regulation, harmonic distortion, renewable intermittency, and grid stability. This paper presents an intelligent grid-connected photovoltaic (PV) and wind energy conversion system (WECS) integrated with a Hybrid Energy Storage System (HESS) for enhancing power quality under varying operating conditions. The proposed system employs a Fuzzy Logic Controller (FLC) to regulate the DC-link voltage and control the Voltage Source Converter (VSC), thereby providing superior dynamic performance compared with conventional control approaches. A Dynamic Voltage Restorer (DVR) is incorporated at the Point of Common Coupling (PCC) to compensate voltage sag, voltage swell, and severe grid disturbances, ensuring continuous and reliable power delivery to sensitive loads. The coordinated operation of PV, WECS, HESS, FLC, and DVR significantly improves voltage stability, reduces Total Harmonic Distortion (THD), enhances renewable energy utilization, and strengthens fault ride-through capability. The complete system is developed and analysed in the MATLAB/Simulink environment under nonlinear loading conditions and grid disturbances. Simulation results demonstrate that the proposed intelligent control strategy effectively minimises harmonic distortion, maintains stable DC-link voltage, improves transient response, and delivers superior power quality while satisfying IEEE-519 harmonic standards for modern smart grid applications.

Introduction

This work proposes a Fuzzy Logic Controller (FLC)-based grid-connected hybrid renewable energy system integrating Photovoltaic (PV), Wind Energy Conversion System (WECS), Hybrid Energy Storage System (HESS), and Dynamic Voltage Restorer (DVR) to improve power quality, voltage stability, harmonic suppression, and Low Voltage Ride Through (LVRT) capability under normal and fault conditions.

Introduction

The increasing demand for electricity, depletion of fossil fuels, and environmental concerns have accelerated the adoption of renewable energy sources. Photovoltaic (PV) systems are widely used because of their clean and cost-effective operation; however, their intermittent nature causes voltage fluctuations and power instability. Combining PV with WECS provides complementary power generation, improving energy availability, while Hybrid Energy Storage Systems (HESS) consisting of batteries and supercapacitors smooth renewable power fluctuations and maintain continuous power supply.

Despite these advantages, power electronic converters introduce power quality issues such as:

• Harmonic distortion,
• Reactive power imbalance,
• Voltage sag and swell,
• Transient instability at the Point of Common Coupling (PCC).

To address these problems, the study integrates a Fuzzy Logic Controller (FLC) with a Dynamic Voltage Restorer (DVR). The FLC adaptively regulates converter operation and DC-link voltage, while the DVR compensates voltage disturbances during grid faults, improving voltage quality and system reliability.

Literature Survey

Previous research has shown that:

• Hybrid PV–WECS systems improve renewable energy availability.
• Hybrid Energy Storage Systems enhance dynamic energy management and reduce renewable intermittency.
• Conventional PI controllers suffer from slow response and reduced performance under nonlinear and rapidly changing operating conditions.
• Intelligent controllers, particularly Fuzzy Logic Controllers, provide:
  • Better DC-link voltage regulation,
  • Faster transient response,
  • Lower steady-state error,
  • Reduced harmonic distortion.
• DVRs effectively compensate voltage sag, swell, and transient disturbances, improving fault ride-through capability.

However, coordinated control of PV, WECS, HESS, FLC, and DVR for simultaneous renewable energy management and power quality enhancement remains an active research area. The proposed system addresses this gap.

Methodology

The proposed microgrid consists of:

• Photovoltaic (PV) array,
• Wind Energy Conversion System (WECS),
• Hybrid Energy Storage System (battery + supercapacitor),
• Voltage Source Converter (VSC),
• Dynamic Voltage Restorer (DVR),
• Fuzzy Logic Controller (FLC).

The operating process includes:

• PV generates DC power through a boost converter.
• WECS generates AC power, which is rectified to DC.
• Both renewable sources share a common DC-link.
• HESS absorbs excess renewable energy and supplies power during generation deficits, maintaining DC-link voltage stability.
• The FLC continuously processes the DC-link voltage error and its rate of change using fuzzy membership functions to generate the reference direct-axis current.
• A Phase-Locked Loop (PLL) synchronizes the controller with the utility grid.
• The VSC injects balanced sinusoidal currents while maintaining unity power factor.
• During voltage sag, swell, or severe Three-Line-to-Line-to-Ground (LLLG) faults, the DVR injects compensating voltage to restore the PCC voltage.

The coordinated operation improves:

• Voltage regulation,
• Harmonic suppression,
• DC-link stability,
• Renewable energy utilization,
• Fault ride-through capability,
• Compliance with IEEE-519 power quality standards.

Simulation Results

The proposed system was implemented in MATLAB/Simulink and evaluated under nonlinear loading and severe fault conditions.

Compared with the conventional PI controller, the FLC:

• Responds much faster to changing operating conditions.
• Produces smoother converter switching.
• Maintains stable DC-link voltage.
• Improves PCC voltage and current quality.
• Reduces converter oscillations.
• Coordinates effectively with PV, WECS, HESS, and DVR.

During severe LLLG faults:

• The DVR rapidly restores the PCC voltage.
• The FLC minimizes voltage recovery time and suppresses transient oscillations.
• Continuous power delivery to sensitive loads is maintained.
• The hybrid renewable system satisfies Low Voltage Ride Through (LVRT) requirements.

The coordinated control also:

• Improves renewable energy utilization.
• Reduces battery stress.
• Maintains stable active and reactive power exchange.
• Enhances overall microgrid reliability and resilience.

Performance Comparison

The conventional PI-controlled system exhibits poor performance during fault conditions:

• Voltage THD = 45.71%
• Current THD = 40.93%

These values greatly exceed IEEE-519 harmonic limits, indicating severe waveform distortion and poor fault performance.

The proposed FLC-DVR-based hybrid system significantly suppresses harmonics, restores PCC voltage and current, enhances converter stability, and maintains uninterrupted operation under severe grid disturbances.

Conclusion

This studyrepresents a grid-connected photovoltaic (PV) and Wind Energy Conversion System (WECS) integrated with a Hybrid Energy Storage System (HESS) employing a Fuzzy Logic Controller (FLC) and a Dynamic Voltage Restorer (DVR) to enhance power quality and system reliability. The coordinated integration of multiple renewable energy sources with intelligent control effectively addressed the challenges associated with renewable intermittency, voltage fluctuations, harmonic distortion, and grid disturbances. The FLC provided adaptive DC-link voltage regulation by generating appropriate converter control signals without requiring an accurate mathematical model, thereby offering faster dynamic response and superior robustness under varying operating conditions. Simultaneously, the HESS maintained power balance by compensating renewable energy fluctuations, while the DVR mitigated voltage sag, voltage swell, and fault-induced disturbances at the Point of Common Coupling (PCC), ensuring continuous power supply to sensitive loads. MATLAB/Simulink results demonstrated that the proposed system significantly reduced Total Harmonic Distortion (THD), improved voltage regulation, enhanced transient response, and maintained stable converter operation during both steady-state and fault conditions. Furthermore, the proposed control strategy improved renewable energy utilization, minimized DC-link voltage ripples, and achieved effective active and reactive power management while satisfying IEEE-519 harmonic standards. Therefore, the proposed intelligent PV–WECS–HESS system represents an efficient and reliable solution for future smart grid applications requiring high renewable energy penetration, improved power quality, and enhanced operational stability.

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Copyright

Copyright © 2026 Dr. S. Jagadish Kumar , Soppari Nithin . This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.