Soft-switching High Frequency AC Link Buck-Boost DC-DC Converters

AC link universal power converters are a relatively new class of power converters with numerous advantages. The reason they get the universal power converters name is that inputs and outputs of these converters can be either dc or ac; therefore, they can be configured as dc-dc, dc-ac, ac-dc, or ac-ac. Also, input and output can be multi-phase or single-phase. The ac link universal converters can be widely and efficiently used in numerous applications from small electronics device to high power renewable energy systems, such as solar and wind power generation. The ac link universal converters can benefit from soft-switching with a small modification in the configuration and control. Switches in the modified configuration will benefit from zero-voltage turn on and soft turn off. Compared with hard-switching converters, power dissipation is greatly reduced in soft-switching ac link converters. In this thesis, the dc-dc ac link universal converter will be studied in detail. At the same time, some modified configurations that require fewer switches are introduced in this thesis. Soft-switching ac-link universal converter have a relatively complex control algorithm; therefore, in most cases digital control methods are used in these converters. Digital control can be implemented through microcontrollers or FPGAs. Use of microcontrollers limits the link frequency due to long microcontroller execution time and delays. FPGA is faster; however, it is more expensive compared with analog controllers. In this thesis, two new control methods that can be implemented by analog circuits are proposed for regulating the voltage in these converters. One of these methods uses PI controller along with PWM; thus switching frequency is fixed. The other control method uses a PI controller for generating the reference of the link peak current, and operates with variable switching frequency. Control schemes proposed in this thesis are simplified, and can be implemented through analog circuit.