Active power filter & harmonic cleanup

01

Live experiment

Educational example · phase RMS quantities · balanced three-phase system

Load

STATCOM

Grid

Active filtering

Passive RC filter

Filter capacitance50 µF

Source harmonic THD: 27.31 %
THD + switching noise: 27.31 %
50 Hz capacitor current: 0 A
Equivalent-circuit damping: —

02

Model & equations

The inverter injects the negative of 95% of the load harmonics. The remaining 5% represents imperfect tracking. Switching noise is modeled separately from low-order harmonic THD. Passive filtering can amplify harmonics near resonance.

i_h=i_{load}-i_1,\quad i_{inv}=-0.95i_h+i_{sw},\quad i_s=i_{load}+i_{inv}

Passive model: series coupling L and R, feeding a shunt series Rf–Cf branch. H(s) is the branch-node voltage transfer, used here as an illustrative attenuation model. It is not a complete closed-loop APF transfer function.

H(s)=\frac{1+sR_fC_f}{1+s(R+R_f)C_f+s^2LC_f},\quad\xi=\frac{R+R_f}{2}\sqrt{\frac{C_f}{L}}

I_{C_f,50}=2\pi f C_f V_g

03

Example parameters

Vg: 230 V RMS
f: 50 Hz
E: 750 V
Rcc: 0.05 Ω
Xcc: 0.1 Ω
R: 0.05 Ω
Rf: 0.6 Ω
P: 80 kW
cos φ: 0.74
fc: 10 kHz
L: 0.87 mH
Δt: 1 ms