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Current Harmonic Mitigation in Grid-tied Solar PV System

Current Harmonic Mitigation in Grid-tied Solar PV System

Understanding Harmonic Issues

When nonlinear loads, such as variable frequency drives or rectifiers, are connected to the grid-tied solar PV systems, they can introduce harmonics. These harmonics degrade the quality of the grid's current waveform, leading to inefficiencies and potential equipment damage.

Active Current Coefficient Control Concept

To mitigate these harmonic issues, grid-tied solar PV systems employ active current coefficient control. This technique involves measuring the load current and adjusting it based on specific coefficients derived from the active power requirements.



Components of the System

  1. PV Array

  • Consists of multiple solar panels arranged in series and parallel configurations.

  • Each panel has specific ratings for power output and voltage.

  1. Boost Converter

  • Positioned between the PV array and the voltage source inverter (VSI).

  • Regulates the voltage to optimize power extraction from the solar panels.

  1. Voltage Source Inverter (VSI)

  • Connected to both the grid and loads through a coupling inductor.

  • Utilizes active current coefficient control to manage harmonic currents.

Control Techniques

  1. Alpha-Beta Transformation

  • Converts phase voltages to alpha and beta components.

  • Facilitates easier harmonic filtering and control.

  1. ABC to Alpha-Beta Transformation

  • Converts ABC phase quantities back to alpha and beta components after processing through a bandpass filter.

  • Helps in extracting relevant harmonic components for mitigation.

  1. Hysteresis Controller

  • Regulates the VSI operation by generating pulse width modulation signals.

  • Ensures the grid current remains sinusoidal by compensating for harmonic distortions.

System Operations under Different Conditions

  1. No Solar Irradiation

  • When PV panels generate no power, the VSI acts as an active power filter.

  • It compensates for nonlinear loads, maintaining grid current quality.

  1. Changing Irradiation Levels

  • Varied solar irradiance affects PV power generation.

  • Active power from the VSI adjusts accordingly to supply both real and reactive power demands.

  1. Grid Voltage Distortion

  • Introducing voltage harmonics in the grid.

  • VSI compensates to keep grid current sinusoidal, even under distorted voltage conditions.

  1. Voltage Sag and Swell

  • Simulated voltage disturbances like sag (short-term voltage decrease) and swell (short-term voltage increase).

  • VSI adapts to maintain stable grid current, adjusting power supply based on load requirements.

Conclusion

Harmonic mitigation in grid-tied solar PV systems is crucial for maintaining grid stability and operational efficiency. By employing active current coefficient control and sophisticated control techniques, these systems ensure that grid currents remain within acceptable harmonic limits, benefiting both utilities and end-users.


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