Analysis of the Reasons for Low Power Factor of Transformer PFC

Analysis of the Reasons for Low Power Factor of Transformer PFC
I, Load characteristic issues
1. Nonlinear loads: Modern devices such as switching power supplies, frequency converters, LED drivers, etc. use rectifier circuits, which cause distortion of current waveforms (including a large number of harmonics). Even if the active power is high, reactive power and harmonic components will reduce the power factor.
2. Low load rate: When the transformer operates under light load, the proportion of excitation current increases (inductive reactive power increases), resulting in a decrease in power factor.
II, harmonic interference
1. Harmonic current: Nonlinear loads generate harmonics such as 3rd, 5th, and 7th, which do not participate in active power transmission but increase apparent power, thereby reducing power factor.
2. Transformer harmonic losses: Harmonics may cause additional heating of the transformer core and winding, further affecting efficiency.
III. PFC circuit design or malfunction
1. Passive PFC defect: If a simple passive PFC (such as compensating capacitors) is used, it may not be able to dynamically adapt to load changes or resonate with the inductive components of the system.
2. Active PFC fault: If the control chip, MOSFET, or inductor of an active PFC circuit (such as Boost topology) is damaged, it will cause calibration failure and a significant decrease in power factor.
3. Parameter mismatch: The inductance, capacitance, or switching frequency of the PFC circuit are not properly designed to effectively correct the current phase.
IIII, Compensation capacitor issue
1. Insufficient or aging capacitor capacity: Compensating for the decay of capacitor capacity (such as electrolytic capacitor drying up) can lead to insufficient cancellation of inductive reactive power.
2. Overcompensation or Undercompensation: Unreasonable capacitor configuration may cause overcompensation (excess capacitive reactive power) or undercompensation (residual inductive reactive power), both of which affect power factor.
V, Abnormal system voltage
1. Voltage too high or too low: Input voltage deviation from the rated value may cause abnormal operation of the PFC circuit (such as uncontrolled duty cycle), or exacerbate distortion of the load current waveform.
VI, Transformer's own issues
1. Magnetic saturation: Improper transformer design or DC bias may lead to magnetic saturation, distortion of excitation current, introduction of harmonics and reactive power.
2. Winding or iron core loss: Insulation aging, loose iron core, etc. can increase reactive power loss.
VII, Measurement or control error
1. Sensor malfunction: Decreased accuracy or phase shift of current/voltage transformers can cause PFC control signal errors.
2. Control loop delay: The dynamic response speed of active PFC is insufficient to track load changes in real time.
VIII, solution proposal
1. Detecting harmonics: Use a power quality analyzer to measure THD (total harmonic distortion) and confirm the harmonic content.
2. Optimize PFC circuit: Active PFC requires checking the switching devices and driving signals; Passive PFC requires adjusting LC parameters to avoid resonance.
3. Dynamic compensation: Install APFC (Active PFC) or SVG (Static Var Generator) to achieve real-time calibration.
4. Capacitor maintenance: Regularly check the compensation capacitor group and replace aging components.
5. Load management: Avoid long-term light load operation of transformers and balance three-phase loads.