Real time power factor correction and active power factor correction

While the terms are sometimes used interchangeably, there's a key conceptual difference between Real-Time Power Factor Correction and Active Power Factor Correction.

1. Real-Time Power Factor Correction (PFC)

This is a functional description. It describes any power factor correction system that can dynamically adjust its compensation in response to changes in the load.

• Goal: To maintain a power factor as close to 1.0 (unity) as possible at all times, regardless of how the electrical load changes.

• How it Works: A controller continuously monitors the system's power factor (or more precisely, the reactive power - kVAr). It then switches compensation devices (like capacitor banks) in and out of the circuit in real-time to match the exact amount of reactive power required by the load at that moment.

• Key Technology: Typically uses Thyristor-Switched Capacitors (TSC) or, more commonly, Capacitor Banks with Contactor Switches. The "real-time" capability comes from the fast switching of these components based on the controller's commands.

• Analogy: Imagine a thermostat and an air conditioner. The thermostat (controller) measures the temperature (power factor) and turns the AC (capacitors) on or off as needed to maintain the set temperature. It's reactive and discrete.

Pros:

• Highly effective for large, variable industrial loads (e.g., factories with large motors cycling on and off).

• More cost-effective than active PFC for high-power applications.

• Preuces power factor penalty charges from utility companies.

Cons:

• Can only provide step-wise, not perfectly smooth, correction.

• Risk of introducing system resonance with harmonic distortions already present in the network.

• Can be susceptible to wear and tear from switching transients.

2. Active Power Factor Correction (Active PFC)

This is a technical design description. It refers to a specific method of power factor correction using active, switched-mode electronics (like IGBTs) instead of passive components (like capacitors) alone.

• Goal: To force an electrical load (often a single device) to appear resistive to the power grid, thereby achieving a near-unity power factor.

• How it Works: An Active PFC circuit is built into a device (e.g., a power supply). It uses a boost converter circuit controlled by a microprocessor. This circuit actively shapes the input current to be a perfect sine wave that is in phase with the input voltage waveform. It does this by drawing current continuously over the entire AC cycle.

• Key Technology: A switched-mode power supply (SMPS) design featuring:

  • Controller IC

  • Inductors

  • Power semiconductors (MOSFETs, IGBTs)

  • Fast-recovery diodes

  • Capacitors

• Analogy: Imagine a skilled artist (the Active PFC circuit) who can perfectly redraw a distorted image (the distorted current draw) into a perfect copy of the original (the voltage sine wave). It's proactive and continuous.

Pros:

• Provides near-perfect power factor (often >0.99).

• Dramatically reduces Total Harmonic Distortion (THDi) in the current.

• Provides stable DC bus voltage for the device.

• Works over a wide range of input voltages.

• Immune to resonance issues because it doesn't rely on passive LC networks.

Cons:

• Increases the cost and complexity of individual devices.

• Primarily implemented at the device level, not for whole buildings.

How They Work Together

The beauty of modern electrical systems is that these two technologies work together from different ends:

1. Device Level (Source of the Problem): Non-linear devices like computer servers, VFDs, and LED lights traditionally had poor power factors and generated harmonics. Active PFC is now mandated in many regions (e.g., EN 61000-3-2 standard) for new equipment. This solves the problem at the source.

2. System Level (Cleaning Up the Mess): Even with Active PFC in some devices, a large industrial facility will still have older equipment, massive motors, and other loads that create a poor, variable power factor. A Real-Time PFC system (a capacitor bank) is installed at the main service entrance to correct the overall power factor of the entire facility, minimizing energy waste and utility penalties.

So,

• Active PFC is a technology used inside equipment to make itself efficient.

• Real-Time PFC is a function performed by a system to make an entire building or facility efficient.