Power Factor Correction (PFC)

Power Factor Correction (PFC) What is power factor? Power factor (PF) is a measure of how effectively electrical power is being used. It compares real power (P), which does useful work, to apparent power (S), which is the combination of real power and reactive power (Q) drawn from the supply. PF is defined as PF = P / S = cos(phi), where phi is the phase angle between voltage and current. A PF of 1 (or 100%) means all the current does useful work. In practice, many loads—especially motors and power supplies with capacitive or inductive components—draw reactive power, causing a lag or lead between voltage and current and a PF less than 1. Why PF matters - Energy efficiency and cost: Utilities may charge penalties for poor PF because it means more current is required to deliver the same real power. Improving PF reduces current, lowers losses in wiring, and can reduce electricity bills. - Equipment and voltage quality: Lower current for the same power reduces voltage drop in cables, reducing heating and wear on components and improving voltage regulation. - Capacity and sizing: With better PF, a facility can get more usable capacity from existing transformers and distribution panels. How PFC works PFC aims to minimize reactive power so that the current waveform more closely follows the voltage waveform. This is typically done by supplying or absorbing reactive power to counteract the load’s reactance. - Passive Power Factor Correction: Uses passive components (capacitors and/or inductors) to neutralize the reactive power. It’s simple and inexpensive but typically cannot achieve a PF very close to 1 across all operating conditions, especially at low or highly dynamic loads. - Active Power Factor Correction: Uses power electronics (such as a controlled rectifier or boost converter) to shape the input current so it remains in-phase with the input voltage. Active PFC can achieve high PF (often > 0.95) across a wide range of loads and is common in switched-mode power supplies, computers, and LED drivers. When to use PFC - Light commercial and industrial loads with many non-linear devices (DC power supplies, computer equipment, LED lighting). - Equipment with high instantaneous power demands or variable loads where PF varies significantly. - Systems requiring compliance with standards for power quality and harmonics (for example, IEC/IEEE standards and certain utility tariffs). Benefits and considerations - Reduced line losses and smaller conductor sizes. - Improved voltage regulation and less heat in electrical equipment. - Potentially lower utility charges and better power quality. - Design considerations: Active PFC offers best performance but adds cost and complexity; passive PFC is simpler but less capable at maintaining high PF across all conditions. Harmonics and interference can also affect PFC performance, so harmonic filters may be needed in some installations. Example (conceptual) Suppose a 1 kW load has a PF of 0.6. It draws S = P / PF = 1 kW / 0.6 ≈ 1.67 kVA, with Q ≈ 1.33 kVAR. By adding PFC to raise PF toward 0.95, the reactive portion drops to about 0.33 kVAR, dramatically reducing current and losses. Bottom line Power Factor Correction helps make electrical systems more efficient, cost-effective, and reliable by reducing reactive power and improving the alignment between voltage and current. For many modern electronic and lighting loads, both passive and active PFC solutions are practical paths to better power quality. If you’re considering PFC for a specific installation, a professional assessment can determine the best approach and sizing.