Dynamic characteristics analysis and instantaneous value control design for buck-type power electronic transformer (PET)

Detail dynamic characteristics analysis of buck-type PET under general load condition was accomplished and the study showed that: under general inductive load condition, the open-loop system is marginally stable and serious output voltage oscillation can be provoked by any random disturbance upon input voltage, control signal or output current. Therefore, in order to ensure the out power quality, we must find out a suitable close-loop regulator. In this paper, we employed the classical PID control algorithm to instantaneously control output voltage following the pre-setting signal. The close-loop system was stable and had good dynamic response characteristic. In addition, during one switching period, the line-frequency input/output voltage and output impedance were treated as constants, and a parameter-gamma, which is related to load feature, was introduced to simplify the modeling and analyzing process, it is a valid method for small-signal modeling and system dynamic analysis of the PET