Performance Analysis of a Single-Stage Single-Phase Grid-Connected Photovoltaic System with Advanced Decoupling Control
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Abstract
This research evaluates the performance of a high-efficiency single-stage, single-phase grid-connected photovoltaic (PV) system utilizing an advanced synchronous frame control strategy. Unlike conventional multi-stage architectures, this single-stage configuration employs a centralized H-bridge inverter to execute both maximum power point tracking (MPPT) and DC-AC conversion, thereby reducing switching losses and system complexity. The control methodology integrates a Perturb and Observe (P&O) MPPT algorithm with a DQ-frame current regulator. To facilitate the DQ transformation in a single-phase context, an orthogonal signal generation (OSG) technique is utilized, ensuring precise decoupling of active and reactive power. The system was modeled for a 6.97 kW peak capacity and validated under dynamic irradiation steps between 500 W/m² and 1000 W/m². Simulation results demonstrate the controller's ability to maintain a stable 434 V DC-link voltage while managing bidirectional power flow. Specifically, the system successfully transitions from importing 1.6 kW from the grid to exporting approximately 1.97 kW, maintaining grid synchronization and high-power quality throughout transient events.
Keywords:
MPPT, DQ Control, Single-Phase Inverter, LCL Filter, MATLAB/Simulink, Orthogonal Signal Generation.
I. Introduction
The integration of solar energy into modern microgrids necessitates conversion architectures that maximize throughput while ensuring the highest possible reliability. Single-stage PV systems have emerged as a strategically important alternative to multi-stage topologies, as they eliminate the intermediate DC-DC boost stage, significantly attenuating conversion losses and reducing the component count. This efficiency gain is critical for enhancing the economic performance of residential and commercial distributed energy resources (DERs).
Despite these benefits, single-phase grid integration presents significant technical hurdles, primarily regarding grid synchronization and the mitigation of the stochastic nature of solar irradiance. Maintaining a stable DC-link voltage and ensuring the delivery of high-quality sinusoidal current requires sophisticated control to manage the second-order ripple inherent in single-phase systems. Furthermore, the control system must ensure seamless transition between grid-import and grid-export modes without violating power quality standards.
The objective of this study is to model and simulate a 6.97 kW-peak single-phase PV system that validates transient stability and robust power flow management under variable atmospheric conditions. By leveraging advanced DQ-frame decoupling, the proposed system aims to optimize the active and reactive power interface with the utility grid. The following sections outline the architectural configuration and the mathematical modeling of the control laws employed.
II. System Configuration and Proposed Methodology
The architecture of the proposed system is engineered for optimal energy harvest and robust grid compliance. A single-stage conversion topology was selected to streamline the power path, while an LCL filter was chosen for the grid interface to provide superior attenuation of high-frequency switching harmonics. While LCL filters introduce potential resonance challenges, the control strategy is designed to provide active damping through feed-forward compensation.
PV Array Configuration
The PV array is designed to match a target DC-link operating voltage of 434 V, which corresponds to the maximum power point voltage (Vmp) of the string configuration. The system utilizes modules with a peak rating of 249.86 W (Vmp = 31 V, Imp = 8.06 A). To achieve the system peak of 6.97 kW, the array is configured as a 14 × 2 matrix (two parallel strings of 14 modules in series), which yields a total Vmp of 434 V. This configuration aligns with the empirical characteristics observed in the source context, where a single string/array sub-unit generates approximately 696 W at lower intensities and scales to the 6.97 kW total system capacity at 1000 W/m².
Power Stage and Grid Interface
The power electronic stage is comprised of:
• DC-Link Capacitor: Sized to buffer the PV output and stabilize the DC voltage at the 434 V setpoint.• H-Bridge Inverter: A single-phase full-bridge converter utilizing high-frequency SPWM to synthesize the AC output.• LCL Filter: A third-order filter designed to minimize Total Harmonic Distortion (THD) and suppress switching noise before grid injection. • Utility Grid and Local Load: The system interfaces with a 230 V single-phase utility grid and a local load rated at 5 kW active power and 2 kVAr reactive power.
This setup enables the analysis of the system's ability to prioritize local load demand while managing the energy balance with the utility grid.
III. Control Strategy and Mathematical Modeling
The control system is the core component responsible for ensuring maximum energy extraction and grid-code compliance. The architecture utilizes a nested loop structure involving an MPPT-based voltage reference and a synchronous frame current controller.
Maximum Power Point Tracking (MPPT)
The MPPT algorithm processes the instantaneous PV voltage and current to track the maximum power point. The algorithm dynamically adjusts the operating point to generate the reference DC-link voltage (Vref). For the considered PV array, the MPPT maintains Vref near 434 V to ensure optimal carrier injection and modulation index for the inverter.
Inverter Control and DQ Transformation
For high-performance current regulation, the system employs DQ transformation. In single-phase systems, the DQ frame requires an orthogonal signal to represent the beta component. This is achieved via an Orthogonal Signal Generator (OSG), such as a Second-Order Generalized Integrator (SOGI), which creates a 90-degree phase-shifted version of the measured grid current. This allows the stationary frame signals to be mapped into a rotating DQ frame where AC quantities appear as DC values.
Current Controller and Feed-Forward Decoupling
A PI-based current controller regulates the d and q components of the inverter current. To mitigate the cross-coupling between the active and reactive axes caused by the LCL filter inductance, a feed-forward decoupling control law is implemented.
The control voltages are formulated as:
Vdcontrol = kp(Idref − Id) + ki ∫(Idref − Id) dt − ωL Iq + Vgridd
Vqcontrol = kp(Iqref − Iq) + ki ∫(Iqref − Iq) dt + ωL Id + Vgridq
Where ωL represents the cross-coupling reactance and Vgridd/q provides the grid voltage feed-forward to improve transient response.
Inverse Transformation and Pulse Generation
The control signals are transformed back to the stationary frame and processed by a Sinusoidal Pulse Width Modulation (SPWM) generator. This stage generates the gate pulses for the H-bridge, modulating the DC-link voltage into the required AC waveform.
IV. Simulation Model and Parameters
The dynamic performance was verified in the MATLAB/Simulink environment, which allows for the high-fidelity modeling of both the power stage and the discrete control logic.
Table 1: Simulation System Parameters
Parameter | Value |
PV Module Rating (Pmp) | 249.86 W |
Total PV System Peak (Ppeak) | 6970 W |
Grid Voltage (Vgrid) | 230 V (RMS, Single-Phase) |
Local Load (Pload, Qload) | 5 kW, 2 kVAr |
Solar Irradiation Steps | 500 W/m² to 1000 W/m² |
DC-Link Operating Voltage (Vdc) | 434 V (Referenced to Vmp) |
Filter Configuration | LCL Topology |
The simulation scenario subjects the system to a sharp step-change in irradiation to test the responsiveness of the MPPT and the stability of the decoupling control.
V. Results and Discussion
Analyzing the bidirectional power flow is critical for assessing the system's efficacy as a grid-connected DER. The results validate that the grid acts as a stiff buffer, ensuring load continuity regardless of PV production volatility.
Case 1: 500 W/m² Irradiation
Under 500 W/m² irradiation, the PV array generates 3486 W. As demonstrated in Figure 1, the MPPT maintains the DC-link at 434 V. Since the 5 kW local load exceeds the PV production, the control system draws the 1.6 kW deficit from the utility grid. This validates the system's ability to maintain power balance in grid-import mode.
Case 2: 1000 W/m² Irradiation
As irradiation increases to 1000 W/m², the PV power output rises to 6970 W. In this scenario, the system fulfills the 5 kW load requirement and exports the surplus power—approximately 1.97 kW—back to the utility grid. As illustrated in Figure 2 and Figure 3, the synchronization remains robust, with the inverter current amplitude increasing smoothly to accommodate the higher power throughput.
Waveform and Quality Analysis
The inverter output current remains in phase with the grid voltage, indicating unity power factor operation (unless reactive power compensation is commanded). The LCL filter effectively suppresses switching harmonics, and the DQ controller ensures that the DC-link voltage remains steady despite the step-change in current injection.
The system demonstrates a seamless transition between energy import and export, validating the advanced decoupling control logic.
VI. Conclusion and Future Scope
This study has successfully validated a single-stage, single-phase grid-connected PV system employing DQ-frame decoupling control. By integrating an OSG-based transformation, the system achieves precise active and reactive power management.
The simulation results confirm that the architecture maintains a consistent 434 V DC-link and manages bidirectional flows of 6.97 kW and 3.48 kW with high stability. The use of an LCL filter combined with feed-forward control ensures grid-compliant power quality even during rapid atmospheric transients.
Future research will focus on integrating Battery Energy Storage Systems (BESS) to mitigate the effects of extreme intermittent cloud cover and exploring active harmonic compensation algorithms to further reduce Total Harmonic Distortion (THD) under non-linear load conditions. This work provides a foundation for more resilient and efficient single-phase renewable energy integration.
VII. YouTube Video
VIII. Purchase link of the Model
SKU: 0018
https://www.lmssolution.net.in/product-page/single-stage-single-phase-grid-connected-solar-pv-system
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