Improved power quality buck boost converter for SMPS

樊涵宇

INTRODUCTIONAt present Electronic gadgets like Personal Computer (PC), Laptop, mobile, etc., play a major role in human life. But these gadgets introduce harmonics in the distribution system which pollutes and degrades the PQ of the electric supply system. SMPS supplies multiple DC output voltages to various accessories like mouse, keyboard, touch pad etc., in PC application. These SMPS draw highly distorted sinusoidal current from input ac mains and thereby increase the THD of source current, reduce the PF at the source side and decrease the overall performance of the system. Based on the literature survey, the conventional SMPS has THD of the source current about 81.2% and PF around 0.4 [1]. Thus the conventional SMPS violates the IEC and IEEE-519 standards of PQ [2]. Single stage SMPS is preferred in many PC applications for PQ improvement and power conversion. But it suffers from major drawbacks like increased stress across the switch and degradation of output voltage. To improve the performance of the single stage SMPS, PFC converters are implemented in the front stage which improve the PF and PQ. The buck and boost converters are not preferred for PC application where the input ac main voltage varies from 170 V to 270V. For an ac voltage of 230 V, the output of the uncontrolled bridge rectifier is about 320 V and thus the boost and buck converter cannot control the output voltage below 350V. To overcome the above deficiency, BBC is preferred for PC application which can operate with a nominal ac voltage of 220V and improve the PQ with a Diode Bridge Rectifier (DBR) at front end [3], [4].The Power Factor Correction (PFC) converters are operated in two different modes of operation i.e., a) Discontinuous conduction mode (DCM) and b) Continuous Conduction Mode (CCM). The DCM of operation is preferred in PFC converters since it reduces the size of the inductor. The BBC with different configurations and two switches is proposed by chen et al [4]. A. Abramovitz et al [5] designed a BB   ISSN: 2088-8708Int J Elec & Comp Eng, Vol. 9, No. 2, April 2019 : 789 - 801790converter configuration which mitigates the sudden inrush currents, protects against short circuit and improves PQ for a wide variation of ac main voltages. In [6], various bridgeless BB converter topologies are analyzed and in [7] higher order low power BB converter is analyzed for continuous current but the number of component required is high in both analysis when compared to conventional one. Hence the selection of converter is a trade-off between the source current waveform and number of components. In SMPS application, to have minimum switching stress, improved utilization of core and lesser voltage ripple at the output a half bridge Voltage Source Inverter (VSI) is preferred [8]-[12]. This paper deals with NN based SMPS having an ac-dc converter at the front end to improve the PQ in terms of THD and PF and with tight voltage regulation at the output for wide variation of source and load conditions.