Analytical Modeling and Comparison of EMI pre-filter Noise Emissions of Three-Phase Voltage and Current DC-Link Converters

Three-phase power-factor-correction rectifiers (PFC) or motor drive inverters can be realized using two dual converter topologies featuring either a voltage dc-link (voltage source) or a current dc-link (current source). This article presents a generic comparison of the pre-filter differential-mode (DM) and common-mode (CM) electromagnetic interference (EMI) noise emissions of these two topologies (considering only the switching stage), which serve as indicators for the required EMI filter attenuation and, hence, EMI filter realization effort. In contrast to the voltage dc-link topology, the DM pre-filter noise of the current dc-link topology is primarily attributed to the current pulses generated by its switching stage, resulting in high-frequency voltage drops across the 50-
$\Omega$
measurement resistor employed in line-impedance stabilization networks (LISNs) as defined by, e.g., the CISPR 11 standard. Addressing this aspect, low-complexity analytical expressions for approximating the envelopes of the pre-filter DM and CM noise amplitude spectra are derived and experimentally verified using 400 V (line-to-line rms), 10 kW voltage and current dc-link ac/dc converter demonstrator systems. The DM pre-filter noise of current dc-link converters is lower than that of the voltage dc-link converters if the equivalent ac resistance the converter represents to the mains is higher than the LISN's 50-
$\Omega$
measurement resistor. On the other hand, the current dc-link converter's CM pre-filter noise is, in typical cases, lower than the voltage dc-link converter's; current dc-link converters are thus an interesting choice for motor drive inverter applications.