How to calculate the differential mode filter parameters of a frequency converter?

Calculating the differential-mode filter parameters for a frequency converter requires consideration of the target attenuation, noise source impedance, and load impedance. Differential-mode filtering typically consists of an L-type or π-type circuit composed of a differential-mode inductor and an X-type capacitor. The calculation steps include: First, determining the noise frequency f and amplitude A to be attenuated through conducted emission pre-testing or estimation based on the switching frequency. Then, setting the required insertion loss IL at that frequency f. For an L-type filter, its corner frequency f_c = 1/(2π√(L_dm * C_x)) should be lower than the noise frequency f. The inductive reactance X_L = 2πfL_dm, and the capacitive reactance X_C = 1/(2πfC_x). At f, the filter attenuation is approximately 20log10(|(Z_s + jX_L) / (Z_s + jX_L - jX_C)|), where Z_s is the source impedance, which is usually complex but can be approximated. In practical design, initial values for inductors and capacitors are typically selected based on experience, such as tens to hundreds of μH for differential-mode inductors and a few tenths to a few μF for the X capacitor. Optimization is then achieved through iterative testing. The rated current and saturation current of the inductor, and the withstand voltage and surge current of the X capacitor need to be calculated. For π-type filters, the calculations are more complex and can be aided by simulation software. Yinte Electronics can provide filter parameter calculation support based on specific customer operating conditions to help determine the optimal differential-mode filtering scheme.