Three-phase AC-to-DC soft-switching HF transformer isolated converters with power factor correction and low harmonic distortion
Date
2017-11-30
Authors
Hamdad, Fatemeh Soheila
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Abstract
This thesis presents new configurations for three-phase AC-to-DC single-stage, softswitched, high frequency (HF) transformer isolated converters with power factor correction (PFC) and low harmonic distortion. Four different configurations are presented. Topology of all these four configurations is based on integration of a front-end DCM boost with a soft switching HF transformer isolated DC-to-DC PWM converter with fixed frequency. DCM operation of the front-end boost provides natural PFC with low total harmonic distortion (THD) and the DC-to-DC HF transformer isolated soft switching PWM converter with an appropriate gating scheme provides output voltage regulation.
A double switch AC-to-DC converter is presented in Chapter 2. Due to unsymmetrical gating scheme, DC blocking capacitors are required to avoid transformer saturation. To reduce this problem, a new gating scheme is proposed in Chapter 3, which can be used in full bridge converters providing ZVS. This gating scheme is first used in a DC-to-DC bridge converter. In the next three chapters, this new gating scheme is applied to three different types of single-stage AC-to-DC boost integrated fixed-frequency bridge converters. These configurations are: (i) boost integrated single inductor linear current DC-to-DC PWM bridge converter, (ii) boost integrated series resonant DC-to-DC bridge converter and (iii) boost integrated parallel resonant DC-to-DC bridge converter.
The steady state operation of each converter and modes of operation are explained with equivalent circuits for each interval of HF cycle. The general solutions for all the intervals are derived and design curves are obtained based on steady state relations. The design procedure is illustrated with a design example. Detailed PSPICE simulation results and experimental results obtained from a laboratory prototype model are given for all the converters to verify the theory and analysis. THD of the line current without any complex control circuit remains in a reasonable range of 8% to 13% for the total range of operation. Input line current waveforms for all suggested converters shows a low harmonic distortion similar to a single 3-Φ DCM boost. The difference would be in increase or decrease of DC bus voltage in each case, which can affect THD of the boost converter. Three switches in the full bridge converter operate with zero-voltage switching (ZVS) while the main switch operates with ZVS at full load, minimum line voltage and with ZVT at lower loads conditions. Soft switching of all the switches helps in lower loss. Chapter 6 presents the contributions of this thesis, summarizes the advantages and disadvantages of each configuration and gives some suggestions for future work.
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Keywords
Electric transformers, Electric current converters