Development of AC/DC and DC/DC Converters Applied to DC Power Supply with Wide Range of Input Voltage
A Dissertation Submitted to the School of Electrical and Electronic Engineering and the Graduate School of Yonsei University in partial fulfillment of the requirements for the degree of Doctor of Philosophy
TaeHo Bang
December 2018
Abstract
This dissertation presents development of AC/DC and DC/DC converters applied to a DC power supply used for various electric devices from home appliances to electric vehicles. In general, the DC power supply consists of electromagnetic interference (EMI) filter for reducing the EMI noise, AC-DC converter to rectify the AC grid voltage into DC voltage and DC-DC converter to supply the power with the suitable voltage level for each device. The EMI filter is essential part of power supply because high speed switching of the converter devices causes undesirable EMI noise. The boost power factor correction (PFC) has widely used for the AC-DC converter because of its simple structure and low cost. In addition, the ability to cope with various AC grid voltages and conditions in different countries is becoming important for PFC converter topologies from the industrial point of view. Meanwhile, full-bridge DC-DC converter is one of the most frequently used topologies in electric vehicle when electrical isolation is required. Isolated DC-DC full-bridge converters are suitable for low DC-DC converter (LDC) which converts high input voltage of the battery into low output voltage level for suppling the power to load of the electrical vehicle. The efficiency of DC-DC converter in electric vehicle are highly related with overall performances including range distance, weight and charging time. Then, improving efficiency without much additional component becomes very important in converter topologies used in electric vehicle. The buck cascaded buck-boost (BuCBB) PFC converter and isolated full-bridge (FB) converter are studied in this dissertation, respectively.
First, the BuCBB PFC converter which operates in wide input voltage range to cope with various grid conditions is developed. The converter can operate in buck or boost mode according to the peak value of input voltage. The converter parameters are properly determined to endure voltage and current stress in all operating ranges. In addition, the EMI filter is used to reduce the high frequency switching noise and guarantee continuous input current in buck mode operation. In addition, switching loss is reduced in all operation range by applying zero-voltage-transient pulse-width-modulation (ZVT-PWM) method. In particular, the power factor (PF) depending on the operation modes of the PFC converter including EMI filter is derived with associated mathematical equations in buck and boost mode, respectively. The performances of proposed PFC converter with wide range of input voltage are evaluated by the simulation and experimental test including PF and input current harmonics in all operating ranges. Finally, the efficiency of proposed PFC converter is compared with that of a conventional buck cascaded buck-boost PFC converter in various conditions. And then, a novel control method for FB converter by using the combined phase-shifted and asymmetric pulse-width-modulation (APWM) method is proposed. It reduces the peak and DC offset values of the input-side current of converter. Then, the overall efficiency is consequently improved by reduced the switching losses in its input-side. Moreover, the zero-voltage switching (ZVS) conditions of switches are satisfied in all operating ranges. The phase-shifted duty ratios corresponding to the output currents of converter are optimally selected based on the loss model analysis. Also, the operational features characterized by the proposed phase-shifted asymmetric pulse-width-modulation (PS-APWM) method are investigated under both the continuous and discontinuous current modes of converter. Then, the effectiveness of proposed PS-APWM method is verified with the simulation and practical hardware experimental results. In particular, the experimental test is carried out in a light load condition. Finally, the efficiency of FB converter controlled by the proposed PS-APWM method is compared with that by the conventional phase-shifted or APWM method, which has been separately applied.
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