Modelling and Interference Analysis of AC-DC Converters for Immunity to Voltage Disturbances up to 150 kHz

Sammanfattning: The function of electrical and electronic equipment is challenged by the high frequency emission originated from the more use of switching-based power electronic equipment and Power line communication (PLC) signaling. Investigations have shown that interferences occur in the frequency range between 2 kHz and 150 kHz, e.g., error in smart meter reading, audible noises, performance degradation and even malfunction of the equipment. This study aims to model and analyze the interference mechanism and gain the knowledge of equipment behavior/immunity under voltage disturbance from 2 kHz up to 150 kHz, so called “Supraharmonics.”Experimental studies were conducted on different type of AC-DC converters, LED drivers, computer power supplies, Active Power Factor Correction (APFC) circuits (pre-regulator), single stage and double stage converters such as flyback and buck topologies. AC-DC converters were exposed to Supraharmonics (SHs) according to IEC 61000-4-19. Interferences, that occur in the input voltage/current and dc-link, were observed and analyzed through a mathematical model of converter circuit. When the AC-DC converter is exposed to SHs, three phenomena occur that 1) the conduction and blocking time of the diodes, in the bridge rectifier circuit, are deviated, 2) intermittent conduction takes places in the beginning and of diodes conduction, 3) reverse-recovery of the diodes happen that impact the dc-link voltage of the converter. Those behaviors are verified in a functional model and validated through the experiments. It is also shown that dc-link voltage metrics, peak-to-peak and average value, are impacted when SHs are present at the terminal of the converter. Further, it is revealed that if the SHs are nonsynchronized to the power system frequency, the converter due to uneven deformation of the diode conduction /blocking time generates interharmonic currents. The generated interharmonic frequency can be precisely determined by using frequency modulation equation. Result shows that generated interharmonic magnitudes are negligible if the applied SH frequency is above 16 kHz. In order to quantify the impact of SHs on dc-link capacitor, an immunity model that links the intermittent conduction and the dc-link capacitor current is established, analytically. By this means, it is ensured to avoid the degradation of the dc-link capacitor’s lifetime by defining the SHs voltage limits.The analysis and modelling studies proves that SHs at the AC-DC converter terminal can cause deviations in the function of equipment both in short term and long term., e.g., increased light intensity in LED drivers, reduced peak-to-peak voltage in dc-link, interharmonic injection and reduced estimated lifetime of the dc-link capacitor. Those impacts originates from the reaction of the diodes and non-linear circuit configuration. Functional models presented in this study are able to express the reasoning and occurrence of the impacts. Established immunity model analytically gives guidance on how immune converters can be achieved in the design stage of power electronic circuits. This study provides deep insight on how AC-DC converters behaves under SH emission. Standard committees and converter manufacturer, to achieve immune and reliable power system and equipment for the future’s systems, can use this knowledge.