Adaptive In-Phase Quadrature LMS (IPQ-LMS)-Based Reference Current Generator for Grid-Connected DSTATCOM

Abstract

This paper proposes an In-Phase and Quadrature Least Mean Square (IPQ-LMS)-based control strategy for grid-connected DSTATCOM under three-phase nonlinear load and unbalanced load conditions. The controller adaptively extracts the fundamental component of the load current using orthogonal reference signals derived from the phase angle of the grid voltage. A proportional-integral (PI) regulator is employed to maintain the DC-link voltage at 700?V, ensuring effective active power injection. To improve current symmetry under load imbalance, an averaged adaptive weight vector is used across all three phases. The reference current thus generated ensures balanced grid injection and reduced harmonic content. The proposed control strategy is implemented in MATLAB/Simulink, and performance is validated under various dynamic load switching scenarios. Simulation results demonstrate that the proposed method achieves effective harmonic mitigation, voltage regulation, and current balancing, thereby improving overall power quality in compliance with IEEE-519 and IEEE-1547 standards.

Introduction

Power quality in distribution systems is increasingly degraded due to the widespread use of nonlinear and unbalanced loads (e.g., rectifiers, speed drives, computing systems), which inject harmonics and reactive power, leading to voltage distortion, unbalanced currents, and low power factor.

Solution: DSTATCOM

A Distribution Static Compensator (DSTATCOM) is employed as a shunt-connected device that uses a Voltage Source Inverter (VSI) to:

• Inject compensating currents,

• Reduce harmonics,

• Supply/absorb reactive power,

• Balance load currents at the Point of Common Coupling (PCC).

Control Strategy Evolution

Traditional control methods (SRF, IRPT) depend on Phase-Locked Loops (PLLs) and Low-Pass Filters (LPFs), which cause delays and degrade performance under dynamic/unbalanced conditions.

To address these limitations, adaptive signal processing techniques like the Least Mean Square (LMS) algorithm are used due to their:

• Simplicity,

• Low computational load,

• Independence from PLLs/LPFs.

However, conventional LMS algorithms often treat each phase separately, leading to reduced performance under unbalance.

Proposed Method: In-Phase and Quadrature LMS (IPQ-LMS) Algorithm

This study proposes an enhanced IPQ-LMS algorithm for DSTATCOM that:

• Uses orthogonal (sine and cosine) components of the grid voltage to estimate the fundamental load currents,

• Adapts filter weights across all phases and averages them for balanced reference current generation,

• Integrates a PI controller to regulate the DC-link voltage.

Benefits:

• Effective in mitigating harmonics,

• Handles nonlinear and unbalanced loads,

• Operates directly in the time-domain (abc frame),

• Does not require coordinate transformation.

System Configuration

The test system consists of:

• A three-phase grid,

• VSI-based DSTATCOM,

• Interfacing inductors, RC filters,

• Nonlinear and unbalanced loads at the PCC.

Sensors monitor grid/load currents and DC-link voltage for feedback control.

Key Parameters (Table I):

• Supply Voltage: 415 V

• DC-link Voltage: 700 V

• DC Capacitance: 13000 µF

• Interfacing Inductor: 5 mH

• Filter Capacitance: 10 µF

• Loads: 50 kVA (unbalanced), 16 kW (nonlinear)

Results and Validation

• Simulation in MATLAB/Simulink under varying load and disturbance conditions confirms the effectiveness of IPQ-LMS.

• Achieves balanced and sinusoidal source currents, harmonic suppression, and stable DC voltage.

Contributions

• Introduced a novel IPQ-LMS based control algorithm for DSTATCOM.

• Demonstrated its superiority under nonlinear and unbalanced loading conditions.

• Validated its application for power quality (PQ) improvement in low/medium voltage distribution systems.

Conclusion

The proposed In-Phase Quadrature Least Mean Square (IPQ-LMS) control algorithm has been effectively implemented in a DSTATCOM system to enhance power quality under two critical load conditions: nonlinear and unbalanced loading. Under nonlinear load conditions, the algorithm significantly mitigates current distortion by accurately extracting and compensating the harmonic components of the load current. This leads to a substantial reduction in THD of the source current, achieving a value of 4.85%, which complies with the IEEE-519 standard (limit < 5%). In the case of unbalanced loading, the IPQ-LMS algorithm dynamically adjusts the reference source currents to maintain balance across all three phases, thereby achieving nearly symmetrical grid current profiles despite the unbalanced nature of the load. This results in improved the profile of voltage and current waveform PCC.

References

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Copyright

Copyright © 2025 Mritunjaiya Mani Tripathi, Kuldeep Sahay. 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.