Power factor correction using SEPIC converter
- lms editor
- 20 hours ago
- 3 min read
Modern electrical systems frequently encounter non-linear loads such as diode rectifiers, LED drivers, and switched-mode power supplies. These loads distort the input current, increase total harmonic distortion (THD), and lower the power factor. As a result, energy efficiency decreases, components heat up, and utility penalties may apply.To overcome these issues, Power Factor Correction (PFC) techniques are essential—and one effective solution is using a SEPIC (Single-Ended Primary Inductor Converter) with closed-loop control.
In this blog, we explore how SEPIC-based PFC improves current quality, reduces THD, and brings the power factor close to unity.
🔌 Introduction to Power Factor Correction
Power factor is a measure of how effectively electrical power is being utilized. For ideal conditions, a power factor of 1 (unity) means the source voltage and current are perfectly in phase, resulting in maximum efficiency.
However, non-linear loads—especially rectifiers—cause the input current to become distorted and non-sinusoidal. These distortions introduce:
High reactive power
Increased current harmonics
Reduced power factor
Higher losses and stress on components
Utility standards such as IEEE-519 and IEC-61000 recommend maintaining current THD below 5%, making active PFC essential for modern power electronics.
🔍 Open-Loop System Analysis
Let’s first examine the system without control, where the SEPIC converter operates in open loop.
System Components
AC voltage source
Diode bridge rectifier
SEPIC converter
Resistive load
Impact of Non-Linear Load
The diode rectifier introduces significant distortion:
Source current becomes non-sinusoidal
Reactive power increases
Harmonics penetrate back to the supply
Open-Loop Simulation Results
Input current is highly distorted
THD ≈ 66.24%, far above standard limits
Poor power factor
Load voltage is unregulated
These inefficiencies highlight the need for closed-loop control to improve power quality and system stability.
⚙️ Closed-Loop Power Factor Correction Using SEPIC
To correct the distortion and regulate the load voltage, a closed-loop control strategy is implemented using two PI controllers.
1️⃣ Outer Loop – Voltage Control
Measures the load voltage
Compares it with the reference value (e.g., 100 V)
The PI controller generates a DC reference current
This ensures stable and regulated load voltage
2️⃣ Inner Loop – Current Control
Uses the measured AC input voltage to generate a unit voltage template
Converts the DC reference current into an AC reference current aligned with the input voltage
Compares the reference current with the actual source current
A PI controller minimizes the error and generates the control signal
PWM pulses are produced to switch the IGBT of the SEPIC converter
This dual-loop architecture ensures both voltage regulation and current shaping.
📈 Closed-Loop Simulation Results
After applying the control strategy, the system performance improves significantly:
✔ Sinusoidal Input Current
The source current closely follows the source voltage waveform.
✔ Regulated Load Voltage
The output voltage settles at the desired reference value (e.g., 100 V).
✔ Improved Power Factor
Source voltage and current are perfectly in phase, indicating a power factor near unity.
✔ THD Reduction
THD is reduced from 66.24% to 3.72%, meeting both IEEE and IEC standards.
These results show that SEPIC-based PFC provides strong harmonic suppression and ensures high-quality power delivery.
🏁 Conclusion
Power factor correction is essential for improving the efficiency and reliability of electrical systems. Using a SEPIC converter with a robust closed-loop control strategy significantly improves system performance by:
Reducing harmonic distortion
Regulating load voltage
Aligning source current with voltage
Achieving a power factor close to unity
The combination of outer voltage PI control and inner current PI control produces a highly effective active PFC solution. This approach is widely applicable in LED drivers, EV chargers, SMPS systems, and renewable energy converters—where power quality is a critical requirement.
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