09-01-2012, 05:05 PM
A SINGLE PHASE POWERFACTOR CORRECTION CONVERTER
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1. INTRODUCTION
In recent years, the power electronic systems and devices, which are used more frequently, create harmonics current and pollute the electricity network. Harmonics have a negative effect on the operation of the receiver, which is fed from the same network. Nowadays, engineers design all the electronic devices to meet the harmonic standards.
AC–DC converters have drawbacks of poor power quality in terms of injected current harmonics, which cause voltage distortion and poor power factor at input ac mains and slow varying ripples at dc output load, low efficiency, and large size of ac and dc filters . These converters are required to operate with high-switching frequencies due to demands for small converter size and high-power density. High-switching frequency operation, however, results in higher switching losses, increased electromagnetic interference (EMI), and reduced converter efficiency. To overcome these drawbacks, low harmonic and high-power factor converters are used with soft-switching (SS) techniques. High-switching frequency with SS provides high power density, less volumes and lowered ratings for the components, high reliability, and efficiency.
In principle, the switching power losses consist of the current and voltage overlap loss during the switching period, power diode’s reverse recovery loss and discharge energy loss of the main switch parasitic capacitance. SS with pulse width modulation (PWM) control has four main groups as zero-voltage switching (ZVS), zero-current switching (ZCS), zero-voltage transition (ZVT), and zero-current transition (ZCT). ZVS and ZCS provides a SS, but ZVT and ZCT techniques are advanced, so switching power loss can be completely destroyed or is diverted to entry or exit.
In the converter submitted in, ZVT turn ON and ZVS turn OFF together are provided for the main switch, while ZVS turn ON and ZCS turn OFF together are provided for the main diode, respectively. Also, ZCS turn ON and turn OFF together are provided for the auxiliary switch. The energy of the parasitic capacitor of the main switch is transferred to the output capacitor by the coupling inductance in the ZVT process. Although ZVT turn ON improves the efficiency of the converter, there is additional voltage stresses on the main switch and the main diode. Also, there are additional current stresses on the main and the auxiliary switches. In this converter, the auxiliary switch is used to provide ZVT turn ON only for the main switch.
In the converter submitted in, ZVT turn ON and ZVS turn OFF together are provided for the main switch, while ZVS turn ON and ZCS turn OFF together are provided for the main diode, respectively. Also, ZCS turn ON and turn OFF together are provided for the auxiliary switch. Although, there are no additional current stresses on the main switch, there are additional current stresses on the auxiliary switch. Furthermore, discharge energy loss of the parasitic capacitance of the main switch is not recovered. In this converter, the auxiliary switch is used to provide ZVT turn ON only for the main switch.
In this study, to eliminate drawbacks of the power factor B correction (PFC) converters, which are presented earlier, a new active snubber circuit is proposed. The proposed circuit provides perfectly ZVT turn ON and ZCT turn OFF together for the main switch, and ZCS turn ON and turn OFF for the auxiliary switch without an important increase in the cost and complexity of the converter. There are no additional current or voltage stresses on the main switch. A part of the current of the auxiliary switch is diverted to the output with the coupling inductance, so better SS condition is provided for the auxiliary switch. The D2 diode is added serially to the auxiliary switch path to prevent extra current stress for the main switch. The aim of this proposed converter is to achieve high efficiency and high-switching frequency PFC converter with sinusoidal current shape and unity power factor at universal input. The steady-state operation of the new converter is analyzed in detail, and this theoretical analysis is verified exactly by a prototype of a 300Wand 100 kHz boost converter.
