Power factor correction (PFC) is a set of techniques used to improve a system’s power factor (PF) by reducing reactive power and/or shaping current draw so it aligns more closely with the supply voltage. The goal is to deliver the same useful real power (kW) with lower apparent power (kVA) and lower current.
In EV charging, PFC is most relevant in DC fast chargers and in other power-electronics-based equipment connected to the grid.
Why PFC Matters in EV Charging
Good PFC improves efficiency, reduces stress on electrical infrastructure, and supports grid compliance. It helps:
– Reduce current draw for the same charging power (lower cable and transformer heating)
– Increase usable capacity within a site import capacity or kVA limit
– Reduce reactive power charges or penalties (market-dependent)
– Improve power quality by reducing harmonic distortion (depending on PFC type)
– Support compliance with grid and EMC requirements for large charger deployments
How PFC Works
PFC works by controlling how current is drawn from the grid:
– Without PFC, some power supplies draw current in uneven “pulses,” creating harmonics and lowering true PF
– With PFC, the input stage shapes current to be smoother and more in-phase with voltage
– The system reduces both phase shift (reactive power) and distortion-related PF losses
Main Types of PFC
Passive PFC
Uses fixed components such as inductors and capacitors to improve PF:
– Simpler and lower cost
– Can be bulky and less effective over varying load conditions
– Can interact with harmonics and resonance if not designed carefully
Active PFC
Uses controlled power electronics to shape input current dynamically:
– High PF (often close to 1.0 under normal load)
– Better performance across wide load ranges
– Can reduce input current harmonics and improve true PF
– More complex and typically used in modern high-power systems
PFC in EV Charger Architectures
In DC fast chargers, PFC is often integrated into the AC→DC rectifier stage:
– The rectifier converts AC to a DC link while maintaining high PF and low harmonics
– Multiple power modules can share PFC functions or each module can include PFC
In AC chargers, the main AC→DC conversion is in the vehicle’s onboard charger (OBC), which typically includes its own PFC behavior (vehicle-dependent).
Benefits
– Higher true power factor and lower kVA for the same kW output
– Reduced losses and heat in upstream equipment
– Improved power quality and reduced harmonic emissions (when well-designed)
– Better scalability for multi-charger sites without early grid upgrades
– Supports compliance expectations in commercial and public deployments
Limitations and Practical Considerations
– Active PFC adds complexity, cost, and additional components that need cooling
– PF can still vary at very low loads or during transients
– Harmonics can come from other site loads; PFC in chargers doesn’t fix everything
– Site-wide PF and THD should be checked at the PCC for large deployments
– Poorly tuned external capacitor banks can conflict with harmonic-rich environments
Related Glossary Terms
Power Factor (PF)
Reactive Power
Apparent Power (kVA)
Harmonic Distortion
Total Harmonic Distortion (THD)
Power Quality
Rectifier Stage
Power Conversion Stage
K-rated Transformers
Point of Common Coupling (PCC)