Performance Analysis and Control of a 30 MW Grid-Connected Solar Photovoltaic System using P&O MPPT and DQ Transformation
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Abstract
This study provides a rigorous performance evaluation of a utility-scale 30 MW grid-connected solar photovoltaic (PV) system. Given the inherent non-linearity of PV source characteristics, a dual-stage power conversion architecture is employed to maximize energy yield and ensure grid stability. The system integrates a DC–DC boost converter utilizing a Perturb and Observe (P&O) Maximum Power Point Tracking (MPPT) algorithm with a three-phase, three-level Voltage Source Inverter (VSI) governed by Synchronous Reference Frame (SRF) current control. High-fidelity MATLAB/Simulink simulations were conducted to evaluate the system’s dynamic response under varying irradiance profiles. Results demonstrate that the control framework effectively maintains the PV array at its 5,000 V optimal terminal voltage and the DC link at a stable 20 kV. Performance analysis confirms high-quality power injection into the 11 kV grid, with Total Harmonic Distortion (THD) levels consistently remaining below 1%, well within the IEEE 519 standard. This architecture proves to be a robust solution for large-scale renewable energy integration.
Keywords:
Photovoltaic Systems, P&O MPPT, Grid Integration, Power Electronics, THD Analysis, Three-Level Inverter.
I. Introduction
The escalating integration of large-scale (30 MW) solar photovoltaic systems into modern power grids is a strategic necessity for transitioning toward sustainable energy infrastructures. To ensure these multi-megawatt installations contribute effectively to grid reliability, sophisticated power electronic interfaces are required. Specifically, the conversion stages must maximize power extraction from the fluctuating DC source while providing sufficient voltage headroom through a 20 kV DC link to maintain inverter linear modulation during 11 kV grid interfacing.
The primary challenge in PV systems is the nonlinear I–V and P–V characteristics of solar arrays. The electrical power generated by a PV array is expressed as
where
= PV array voltage = PV array current
The maximum power point (MPP) varies with solar irradiance and temperature. If the system fails to track this operating point, considerable energy losses may occur.
Furthermore, injecting large power into an 11 kV, 50 Hz grid requires strict harmonic regulation and accurate synchronization. The inverter must ensure unity power factor operation and minimal harmonic distortion.
The objective of this research is to model and validate a 30 MW grid-connected PV system using MATLAB/Simulink. The model evaluates transient stability, MPPT convergence, and harmonic performance under rapid environmental changes.
II. System Configuration and Design Methodology
The proposed PV system consists of three main subsystems:
1. PV Array
2. DC–DC Boost Converter
3. Three-Level Voltage Source Inverter
The boost converter increases the PV terminal voltage from 5 kV to 20 kV according to the following relation:
where
= DC link voltage = PV array voltage = duty cycle
The design of the boost converter components depends on the switching frequency, inductor current ripple, and capacitor voltage ripple.
Inductor Design
Capacitor Design
where
= switching frequency = inductor current ripple = capacitor voltage ripple
A three-phase three-level VSI is selected to reduce harmonic distortion and handle high DC voltage levels efficiently.
An L-type filter is installed between the inverter and the grid to suppress switching harmonics.
Table 1
System Design Parameters
Parameter | Value |
PV Array Capacity | 30 MW |
PV Terminal Voltage at MPP ( ) | 5000 V |
DC Link Voltage ( ) | 20,000 V (20 kV) |
Inverter Topology | Three-Phase Three-Level VSI |
Grid Voltage / Frequency | 11 kV / 50 Hz |
Design Criteria (L & C) | , % Ripple , % Ripple |
III. Control Strategy and Mathematical Modeling
The control strategy consists of two stages:
1. DC Stage Control (MPPT)
2. AC Stage Control (Grid Synchronization)
A. Perturb and Observe (P&O) MPPT
The P&O algorithm continuously adjusts the duty cycle of the boost converter to track the maximum power point.
The power change is calculated as
The operating rules are:
• If and → decrease duty cycle• If and → decrease duty cycle• If and → increase duty cycle• If and → increase duty cycle
The duty cycle is constrained by
to prevent instability.
B. Inverter Control Mechanism
The inverter uses Synchronous Reference Frame (SRF) control with Park Transformation.
The abc currents are converted to dq components using
The inverse Park transformation is given by
The control loops operate as follows:
Voltage Control Loop
Current Control Loop
For unity power factor operation
IV. Simulation Model and Parameters
The complete system is implemented in MATLAB/Simulink using the following blocks:
• PV Array block• Boost Converter with PWM switching• Three-Level VSI• SRF-based controller• Grid model
To evaluate the system response, a dynamic irradiance profile was applied.
The irradiance variation is defined as
Time (s) | Irradiance |
0 – 0.5 s | 1000 W/m² |
0.5 – 1 s | 100 W/m² |
1 – 2 s | 1000 W/m² |
This scenario evaluates:
• MPPT tracking speed• DC link voltage stability• Grid current quality
V. Results and Discussion
The simulation results confirm stable system operation.
Under 1000 W/m² irradiance, the PV system generates:
When irradiance drops to 100 W/m², the power decreases proportionally, but the DC link voltage remains stable at 20 kV due to the voltage control loop.
Power quality analysis was performed using FFT analysis with a 50 Hz fundamental frequency.
Table 2
Grid Current THD Analysis
Time | Operating Condition | THD |
0.5 s | Irradiance Transition | 0.81 % |
1.2 s | Low Irradiance | 0.86 % |
1.8 s | Irradiance Recovery | 0.47 % |
The results confirm that harmonic distortion remains well below the IEEE 519 limit of 5%.
The use of a three-level inverter combined with an L-filter significantly improves waveform quality.
VI. Conclusion and Future Scope
This study validates the performance of a 30 MW grid-connected PV system using a dual-stage conversion architecture.
The P&O MPPT algorithm successfully maintains the PV array at its 5000 V maximum power point, while the DQ-based SRF controller ensures synchronized power injection into the 11 kV grid.
The system maintains a stable 20 kV DC link voltage even during rapid irradiance variations. The measured THD remains below 1%, confirming excellent power quality and compliance with IEEE standards.
Future work will investigate the Incremental Conductance MPPT method to reduce steady-state oscillations around the maximum power point. Additionally, the integration of Battery Energy Storage Systems (BESS) will be explored to improve grid stability and provide energy buffering during solar intermittency.
The results confirm that the proposed architecture is a robust and scalable solution for utility-scale solar power integration.
VII. YouTube Video
VIII. Purchase link of the Model
SKU: 0193
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