Suppression of Conducted EMI and Enhancement of Power Quality Using Digital Communication Modulation Technique in SMPS Applications

In SMPS applications DC-DC converters operate at high frequencies. It leads to a rise in EMI emission levels within the AC power source, consequently elevating the harmonic content in the current supply and deteriorating the quality of the grid power supply. The Frequency Hopping Spread-Spectrum (FHSS) modulation technique is implemented in SMPS to reduce Electro-Magnetic Interference (EMI) emission. The proposed method attenuates the peak EMI in the source side, by using a repeated switching of the carrier frequency. The modulated carrier signal hops between two switching frequencies within a specified band in a pseudo-random sequence, increasing the bandwidth of the carrier and thus reducing the EMI emission. The switching pulse for the DC-DC converter is obtained using Field Programmable Gate Arrays (FPGA). To prove the supremacy of the proposed FHSS modulation technique, the necessary power quality parameters namely source current THD and FFT spectrum, grid power factor and the peak value of the conducted EMI obtained are compared with the popularly used Random Pulse Width Modulation (RPWM). It is observed that by using the proposed FHSS modulation technique conducted EMI emission is reduced by 17 dBm in comparison with the RPWM technique.