This thesis concerns with improving the efficiency of high-current low-voltage rectifiers. High-current low-voltage rectifiers have a widespread usage in the industry especially in the field of electroplating processes. These rectifiers have certain challenges and limitations. The topology of a rectifier has direct impact on its performance. The comparison of different topologies based on different criteria such as the conduction losses of semiconductor switches and the size of the transformer are addressed in this thesis. Among various topologies, the six-phase topology with interphase transformer is adopted since it has the lowest conduction losses. Most high current rectifiers must have the ability to control output voltage/current. The conventional method of controlling the power of these rectifiers is to use a controlled semiconductor switch, such as a thyristor, at the load side of the transformer. However, in high current applications, the higher voltage drop of controlled switches leads to higher conduction losses and lower efficiency. In this thesis, a thyristor-based AC voltage controller is employed at the high-voltage and low-current side of the transformer, resulting in lower conduction losses. By changing the firing angle of the thyristors, the rectifier output power can be continuously controlled. Another approach for reducing conduction losses in high current rectifiers is replacing the diodes with MOSFET switches. Such rectifiers are sometimes called synchronous rectifier as the switching command of power MOSFETs must be synchronous with the line voltage. Replacing diode with a suitable MOSFET can significantly reduce conduction losses. In this thesis, various synchronous rectification methods are reviewed. A driving method for is presented in which by inserting a proper dead-time in MOSFET gating pattern, the short circuit condition is avoided. Simulations are carried out to verify the function of the proposed synchronous rectifier and the driving method. Simulation results show that the amount of synchronous rectifier losses is significantly lower than that of a diode type. In order to verify the simulation results, a laboratory prototype of a six-phase synchronous rectifier with IPT with an AC voltage controller at the input are implemented. It is observed that the practical results match the simulation results. Key Words:High-power Rectifier, High-current Rectifier, Controllable Rectifier, Synchronous Rectifier (SR)
