The principle of PFC power factor correction
Power factor correction (PFC) reduces reactive power and harmonic interference by adjusting the phase relationship and waveform matching between current and voltage, thereby improving energy utilization efficiency. The core principles can be divided into two categories:
1, Passive PFC (Passive Correction)
1. Compensate for phase difference
Using passive components such as inductors and capacitors to offset the phase shift of current caused by inductive/capacitive loads. For example, by connecting an inductor in series after a rectifier circuit and smoothing the current pulse through its "current non abrupt change" characteristic, waveform distortion can be reduced by 46.
Typical structure: A power frequency inductor is combined with a filtering capacitor to form an LC resonant network 46.
Effect: The power factor has been improved to 0.7-0.8, but harmonic 26 cannot be completely eliminated.
2. Limitations
Large size, significant low-frequency noise, and inability to dynamically adapt to load changes, only suitable for low-power sceneries.
2, Active PFC (Active Correction)
1. Dynamic current waveform control
By using high-frequency switching devices (such as MOSFETs) and closed-loop control circuits, the input current waveform is adjusted in real-time to be in the same frequency and phase as the input voltage.
Key topology: The Boost boost circuit is the core, which boosts the rectified pulsating DC power to a higher voltage, and controls the duty cycle of the switching transistor through PWM to force the current waveform to follow the voltage changes.
Control logic: Detect input voltage and current, and adjust them through a dual loop of voltage and current loops to ensure sinusoidal current and phase synchronization.
2. Advanced technology application
Multi level bridge free structure: such as Delta Electronics' patented solution, which suppresses zero crossing distortion and improves current quality through flying capacitor totem pole configuration and time-sharing drive switches.
Intelligent Multiphase Control: Adopting interleaved parallel technology to reduce current ripple and optimize the efficiency of low voltage output.
3. Performance advantages
The power factor can reach above 0.95, significantly reducing harmonic content (THD<5%), supporting a wide input voltage range, and suitable for medium to high power equipment.
3, Core Objectives and Effects
Phase synchronization: Eliminating current lag or lead phenomena and reducing reactive power components in apparent power.
Waveform shaping: Suppressing the pulse current generated by nonlinear loads (such as switching power supplies) and reducing harmonic pollution in the power grid.
Energy efficiency improvement: By reducing line and transformer losses, the efficiency of power transmission is improved to meet the mandatory energy efficiency standards for equipment above 75W.