Emission control in UPS system — A systematic approach to achieve EMI compliance

Any switched mode power supply is a source of EMI that can interfere with the operation of the coexisting electronic/electrical equipments by conduction and/or by radiation. To minimise such interferences to accepted levels, the EMC standards specify the limits for the emission spectrum emanating from the power sources. This paper discusses a case study how a commercially available Uninterrupted Power Supply is made to comply with the international EMC standards for the conducted and radiated emission measurements. The noise sources were identified and minimised the noises with EMI fixes. The effect of these fixes on conducted and on radiated emission patterns are demonstrated.