Two types of new inverters with high frequency resonant AC link and current sourced DC link

Abstract

In this thesis, two types of new inverters are proposed. One is the series resonant inverter with high frequency AC resonant link for he constant voltage and constant frequency (CVCF) application. Other is the current sourced inverters for the variable voltage and variable frequency (VVVF) application. The detailed operations of the proposed inverters are given for each inverter types. And the mathematical modeling and the commutation mode analyses are given for the system control and the commutation circuit design, respectively. The operations of the proposed inverters are verified through the computer simulation and the experiment. In case of CVCF application, a new series resonant inverter (SRI) controlled by the estimation concept is proposed. The proposed inverter has the power circuit of the conventional series resonant converter (SRC) with the modification, so that the output voltage of SRC can swing from the negative value to the positive value by replacing the diodes in the output rectifier with the bidirectional switches. Besides the circuit modification, new control scheme is developed to overcome the demerits of the conventional control methods. Since the proposed inverter is operated at constant resonant frequency, zero switching condition is always guaranteed. Also the bidirectional switches of the SRI are in synchronization with the current zero crossing points and have the fixed switching pattern to obtain the high frequency isolation. Therefore the switching stress and the switching loss are considerably low and the device capability can fully be utilized with the high frequency operation. In addition, the magnetic opponents and capacitors can be reduced in size and weight owing to the constant switching frequency and the independence of the load condition. Even though the switching instants of the SRI are fixed at the current zero crossing points, it is possible to control the resonant tank energy by the appropriate resonant mode selections. S...