Analysis of Specific Reasons for Low Power Factor of Transformer PFC
I, The influence of transformer's own characteristics
1. Magnetic flux loss and copper loss
During the operation of transformers, eddy current losses (iron losses) caused by changes in iron core magnetic flux and copper losses caused by winding resistance result in differences between input and output power, reducing overall efficiency and deteriorating power factor.
2. Empty or light load operation
When the transformer is not fully loaded, the proportion of its excitation current (reactive power) to the total current increases significantly, and the power factor may drop below 0.2.
3. Design capacity mismatch
If the capacity of the transformer is much larger than the actual load demand, long-term light load operation will lead to an increase in reactive power consumption and a decrease in system power factor.
II, Load characteristics and operating environment
1. The proportion of inductive load is too high
Transformers often supply power to inductive loads such as motors and reactors, which require a large amount of reactive power to establish a magnetic field, resulting in an increase in the phase difference between voltage and current.
2. Input voltage fluctuation
When the input voltage increases, the excitation current of the transformer decreases, which may trigger the discontinuous conduction mode (DCM) of the PFC circuit, causing zero crossing distortion of the current waveform and further reducing the power factor by 8. For example, high input voltage can cause the interruption time of inductor current to be prolonged and the THD to increase.
III. Harmonic pollution
The harmonics generated by nonlinear loads (such as frequency converters and rectifiers) are coupled to the power grid through transformers, interfering with the correction of current waveforms by PFC circuits and causing abnormal power factor measurement values.
3, System matching and control issues
1. Insufficient reactive power compensation
If sufficient parallel capacitor banks or dynamic compensation devices (such as SVG) are not configured, it is impossible to offset the reactive power demand generated by transformers and loads.
2. Poor adaptability of PFC parameters
When PFC controller parameters (such as inductance and switching frequency) are not optimized according to transformer operating conditions, current tracking delay or abnormal capacitor charging and discharging may occur, exacerbating the decrease in power factor.
3. Temperature affects device performance
In high temperature environments, the capacity of filter capacitors decreases or the equivalent series resistance (ESR) increases, weakening the smoothing effect of PFC circuits on current waveforms and indirectly reducing power factor.
IIII, Typical improvement measures
1. Dynamic compensation optimization: using hybrid reactive power compensation (such as SVG+capacitor bank) to match the reactive power gap in real time;
2. Load rate management: To avoid long-term light load operation of transformers, optimize load distribution through parallel or graded switching;
3. Harmonic control: Install LC filters or active power filters (APF) to suppress the interference of harmonics on PFC circuits;
4. Parameter tuning: Adjust PFC inductance and switching frequency based on transformer operating conditions to ensure continuous conduction mode (CCM) covers a wider input range.