High Efficiency Three-phase Power Factor Correction Rectifier using Wide Band-Gap Devices

Improving the conversion efficiency of power factor correction (PFC) rectifiers has become compelling due to their wide applications such as adjustable speed drives, uninterruptible power supplies (UPS), and battery chargers for electric vehicles (EVs). The attention to PFCs has increased even more since grid regulations have become stricter in terms of injected harmonic and power quality. Therefore, improving the efficiency and the power quality of PFCs are the main objectives of this PhD work.
New wide band gap (WBG) power switches have better switching characteristics in comparison with silicon power devices. Therefore, the PFC switching frequency using WBG devices can potentially be increased. This advantage helps the reactive components to be reduced in size. However, it also brings challenges such as identifying a proper material for inductive components that has lower loss and layout design that has lower parasitic elements. To fulfill the grid regulations (e.g. IEEE-519) high order filters are normally used. Achieving an optimum filter design is vital for having an efficient converter. Reducing low frequency harmonics can improve both the efficiency and also the power quality. Therefore, current controllers are also important to be investigated in this project.
In this PhD research work, a comprehensive design of a two-level three-phase PFC rectifier using silicon-carbide (SiC) switches to achieve high efficiency is presented. The work is divided into two main parts: 1) Optimum hardware design using WBG devices to improve the conversion efficiency and 2) Identifying the impact on the efficiency by current controller.
Part 1 is presented in Chapter ‎3. The converter topology is a two-level bidirectional boost voltage source converter (VSC). SiC devices (i.e. MOSFET and diode) are used for designing the converter. An analytical method for choosing the filter parameters to achieve an optimum design is presented. The method is based on the working principle of the converter. It focuses on analyzing the converter current and voltage for generalizing the filter design. The switching frequency which leads to the maximum converter efficiency is analyzed and selected. According to the selected switching frequency, an optimum LCL filter is designed and the layout is optimized for a 5 kW three-phase PFC using SiC MOSFETs.
The second part is presented in Chapter ‎4. It is focused on current controller and its impact on the efficiency. Two types of current controllers are studied: PI current controller in the rotational reference frame and proportional-resonant (PR) current controller in the stationary reference frame. For the PR controller, harmonic compensation is employed to improve the power quality. To have similar harmonic performance the PI controller needs larger filter in comparison with the PR controller. This eventually ends up with lower efficiency of the converter with the PI current controller.
In this thesis, two sets of experiments are carried out:
• Verification of the designed filter and the controllers performance in Chapter ‎3 and Chapter ‎4, respectively;
• Measurement and comparison of the converter efficiency for two types of controllers.
The highest efficiency is achieved at 50% of nominal load for the PR current controller. The measured efficiency is 99.1% at 50% of nominal load and 98.95% at full load. The converter with the PR controller is more efficient than the converter with the PI controller at low load.