Analysis and design of electronic transformer for electric power distribution and utility interface of power electronic systems

In electric power distribution and power electronics applications, a transformer is an indispensable component and performs many functions. However, at low frequencies, it is one of the most bulky and expensive components.; In this dissertation, the concept of electronic transformer is proposed which results in a considerable reduction in the size and weight of the transformer. 4-quadrant converters are employed to change the operating frequency from low frequency into higher frequency. The concept is applied to both single and three-phase transformers and several possible topologies are proposed. For higher voltage system, a series connected building block approach is proposed. Voltage sharing of the series connected electronic transformer blocks is guaranteed due to converter operation and magnetic coupling. Also, a four step switching strategy is proposed which enables snubberless operation of the converter blocks. Both simulation and experimental results illustrate the advantages of the proposed approach.; In the next study, the proposed electronic transformer is applied to three-phase multi-pulse diode rectifier systems, which are primarily used to reduce utility input current THD by canceling low order harmonics. The proposed polyphase electronic transformer along with dc-side magnetic components is small in size and weight due to higher frequency operation. Further, the switching frequency components are neutralized in the utility input current which enhances the EMI performance of the proposed approach. Both 12 and 24-pulse polyphase electronic transformers are studied. Simulation and experimental results are shown.; Finally, a High Frequency Harmonic Subtractor (HFHS) concept is proposed to improve utility input current THD of two independent 6-pulse rectifier loads. The HFHS is an auto-connected high frequency transformer powered by a static converter and delivers power to two separate 6-pulse diode rectifier loads. The system shows robust harmonic subtracting capability under both equal and unequal loading conditions. The proposed HFHS suitably alters the harmonic characteristics of two 6-pulse rectifiers to 12-pulse and achieves cancellation of 5th and 7th harmonics. In addition, 11th and 13th harmonic magnitudes are also significantly reduced. The cancellation of 5th and 7th harmonics is achieved via open loop and no measurements and feedback control are necessary. Extensive simulation results and selected experimental results are presented.