How to avoid resonance problems in intelligent controllers (PACs)?

The filtering circuit of the intelligent controller PAC may resonate due to improper matching of inductor and capacitor parameters, amplifying noise at specific frequencies. Methods to avoid this include: firstly, using SPICE tools to analyze the impedance curve of the LC filter during the simulation phase to ensure there are no peak resonance points within the target frequency band (e.g., 150kHz-30MHz); secondly, selecting high-Q, wide-bandwidth components, such as CMZ series common-mode inductors and low-ESR ceramic capacitors; and thirdly, for multi-stage filtering, adjusting the cutoff frequencies of each stage to be staggered by at least one octave, for example, the first stage cutoff...

The frequency was set to 100kHz, and the second stage was set to 1MHz. In the PCB layout, the area of the filter loop was reduced to avoid resonance between parasitic inductance and capacitance. For existing resonances, a damping resistor (such as 10Ω) can be connected in parallel or a ferrite bead (such as PBZ2012E600Z0T) can be connected in series to suppress them. After testing with an impedance analyzer, the optimized filter network showed flat impedance in the 10kHz-100MHz frequency band with fluctuations of less than 3dB, effectively avoiding resonance peaks and enabling the PAC system to pass the IEC61000-4-7 harmonic current test.