Power factor correction using SEPIC converter

Power factor correction using SEPIC converter

Introduction to Power Factor Correction

Power factor correction is crucial for enhancing the efficiency of electrical systems. Non-linear loads, such as diode rectifiers, can cause significant reactive power draw, leading to a non-sinusoidal source current. This increases THD and reduces power factor, leading to inefficiencies and potential penalties from utility companies. By implementing power factor correction, we aim to align the source current with the source voltage, improving the system's overall power quality.

Open-Loop Control

Let’s start by examining the open-loop control model for power factor correction:

1. System Components:

• AC voltage source

• Diode bridge rectifier

• SEPIC (Single-Ended Primary Inductor Converter)

• Load

1. Non-Linear Load Effect:

• The diode bridge rectifier acts as a non-linear load, causing the source current to be non-sinusoidal and drawing more reactive power from the source.

1. Simulation Results:

• Without control, the source current is non-sinusoidal.

• The THD of the source current is around 66.24%, which is significantly higher than the acceptable standard of less than 5% as per IEEE and IEC standards.

These results highlight the inefficiencies caused by non-linear loads, emphasizing the need for effective power factor correction.

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Closed-Loop Control

To address the inefficiencies observed in the open-loop system, we implement a closed-loop control strategy using both voltage and current control loops.

1. Control Strategy:

• Outer Loop (Voltage Control): Compares the load voltage with a reference voltage and processes the error through a PI controller, generating a reference current in DC form.

• Inner Loop (Current Control): Converts the reference current to AC form using the measured input AC voltage to find the unit voltage vector template. The AC reference current is then compared with the actual source current, and the error is processed through another PI controller. The resulting signal is used to generate the pulse for the IGBT in the SEPIC converter.

1. Simulation Results:

• The closed-loop control successfully makes the source current sinusoidal.

• The load voltage is regulated to the reference value (e.g., 100V).

• The THD of the source current is reduced to 3.72%, meeting the IEEE and IEC standards.

• Source voltage and source current are in phase, indicating an improved power factor close to unity.

These improvements demonstrate the effectiveness of the closed-loop control in correcting the power factor and reducing THD.

Conclusion

By implementing a closed-loop control strategy, we significantly improve the power factor and reduce THD in systems with non-linear loads. The use of semiconductor devices like SEPIC converters, along with PI controllers for both voltage and current control, ensures efficient and reliable power delivery.