Passive power factor correction(PPFC) and Active Power factor correction(APFC)

Both Passive Power Factor Correction(PPFC) and Active Power Factor Correction(APFC) are used to improve power factor and reduce reactive power, but they differ in complexity, cost, and performance.

Passive Power Factor Correction (PPFC)

Method: Uses passive components (capacitors, reactors, or filters) to compensate for reactive power.

Types of Passive PFC:

A. Capacitor Banks (Most Common)

• Used to compensate for lagging (inductive) power factor (common in motors, transformers).

• Fixed Capacitors:   Manually switched, best for stable loads.

• Automatic Capacitor Banks: Contactor Switched /TSC (Thyristor-Switched Capacitor) banks adjust based on load changes.

B. Harmonic Filters (LC Filters)

• Used when nonlinear loads (VFDs, SMPS) introduce harmonics.

• Tuned to block specific harmonic frequencies (e.g., 5th, 7th).

C. Synchronous Condensers

• Rotating machines that act as variable capacitors/inductors.

• Used in high-voltage transmission systems.

Advantages of Passive PFC:

• Low cost (simple capacitors are inexpensive).
•  High reliability (no active electronics).
• Easy maintenance (no complex control systems).

Disadvantages of Passive PFC:

• Fixed compensation (not ideal for rapidly changing loads).
• Risk of overvoltage/resonance (if not properly tuned).
• Cannot correct leading PF (only compensates lagging PF).

Active Power Factor Correction (APFC)

Method: Uses power electronics (IGBTs, PWM control) to dynamically adjust reactive power.

Types of Active PFC:

A. Active PFC in SMPS (Switched-Mode Power Supplies)

• Uses a boost converter to shape input current to match voltage (PF ≈ 0.99).

• Common in computers, LED drivers, and industrial power supplies.

B. Static VAR Generator (SVG)

• Use IGBT or Combines TSC (Thyristor-Switched Capacitors) and TCR (Thyristor-Controlled Reactors).

• Adjusts compensation in real-time for large industrial loads.

C. STATCOM (Static Synchronous Compensator)

• Voltage-Source Converter (VSC) generates reactive power dynamically.

• Faster than SVC, used in wind farms and smart grids.

Advantages of Active PFC:

•  Dynamic compensation (adjusts to load changes instantly).
• Wider correction range (can correct both lagging & leading PF)
•  Reduces harmonics (active filtering possible).

Disadvantages of Active PFC:

•  Higher cost (complex electronics, IGBTs, DSP control).
•  More maintenance (cooling, firmware updates).
•  Lower efficiency at light loads (switching losses).

Which One to Choose?

• Use Passive PFC if:

  • Load is stable (e.g., motors, HVAC).

  • Budget is limited.

  • No rapid load fluctuations.

• Use Active PFC if:

  • Load varies quickly (e.g., cranes, welding machines).

  • Harmonics are a concern (data centers, VFDs).

  • High precision is needed (smart grids, renewables).

Passive PFC is simple, cheap, and reliable but lacks flexibility.

Active PFC is advanced, fast, and versatile but more expensive.

Eng. Xu