Analysis of the reasons for the decrease in power factor on the power supply side after the AHF only performs harmonic filtering:
I. Increased total apparent power naturally leads to a decrease in the overall power factor.
Power factor λ = P/S. Active power P is determined only by the fundamental active power; harmonics do not contribute. After filtering, the fundamental reactive power remains unchanged, but harmonic currents are only transferred to the AHF and circulating with the load, leaving a small amount of residual harmonic current on the power supply side.
Total current = fundamental current + harmonic current. The total apparent power S increases, while active power remains unchanged, resulting in a lower overall power factor.
II. Harmonic filtering only, without fundamental reactive power compensation.
The AHF only activates harmonic mode and does not compensate for inductive/capacitive fundamental reactive power:
1. Existing inductive reactive power from motors, transformers, etc., is fully retained, and the fundamental reactive power itself has a low cosφ.
2. If there is a fixed capacitor bank on site, there is no offsetting effect for capacitive leading reactive power, and the fundamental reactive power defect remains unchanged.
III. Active Power Losses of the AHF System Itself
The IGBTs, reactors, heat sinks, and control boards continuously consume a small amount of active power, while the grid supplies an additional portion of this lost active power. Compared to the load's active power ratio, this slightly decreases, resulting in a minor drop in the power factor.
IV. Reactive Power Components Introduced by Harmonics
Harmonic currents and harmonic voltages have a phase difference, generating harmonic reactive power. This reactive power does not contribute to active power but only occupies grid capacity, further lowering the overall power factor.
V. Poor Capacitor Cabinet Coordination Exacerbates the Deterioration
The existing LC capacitor compensation cabinet has low impedance to harmonics. After filtering, the circulating harmonic current impacts the capacitors, generating circulating harmonic reactive power. The fundamental reactive power ratio is unbalanced, with leading/lagging reactive power superimposed, worsening the power factor.
In short: Simply eliminating harmonics without adjusting fundamental reactive power, combined with the apparent increase in harmonics, device losses, and harmonic reactive power, actually lowers the power factor on the power supply side compared to before the AHF system was implemented.
