How can differential mode filtering in a concentrator not affect data acquisition?

Adding differential-mode filtering (X capacitor and differential-mode inductor) to the power input of the concentrator may introduce phase shift and amplitude attenuation, affecting the accurate sampling of voltage and current waveforms by the power metering chip. Low-loss components and a reasonable cutoff frequency must be selected during the design. A CBB film capacitor is chosen for the X capacitor due to its low tanδ and stable capacitance. A high-permeability, low-coercivity core is selected for the differential-mode inductor PBZ3216E120Z0T to reduce hysteresis loss.

The filter's cutoff frequency fc should be much higher than the power frequency (50Hz) but lower than the main interference frequency (150kHz), typically set between 2-10kHz. For example, selecting a 0.22μF X capacitor and a 12μH differential-mode inductor results in fc of approximately 3kHz, with attenuation of less than 0.05% and phase shift of less than 0.05° for the 50Hz signal. A small capacitor (e.g., 100pF) of the same material as the X capacitor can be connected in parallel before the voltage sampling divider network of the metering chip to compensate for phase. After optimization, the additional error introduced by differential mode filtering can be controlled within 0.05%, meeting the accuracy requirements of Class 1 energy meters.