Modeling and Dynamics of a Single-Stage Three-level Resonant AC/DC Converter Operating with Combined Variable Frequency & PWM Control

This paper presents a state space model based on a combined averaging and multiple frequency models suitable for the prediction of the performance of a single stage three level resonant AC/DC converter operated with variable frequency pulse width modulation control to regulate the output voltage, shape the input current as well as to control the dc bus voltage. The pulse width modulation aims to regulate the input current shape as well as the level of the dc-bus voltage; whereas, the variable frequency provides a tightly regulated output voltage. Using two control variables reduces the frequency range required to give the required output voltage over the whole loading and input voltage (90-265Vrms) ranges, in addition to that it reduces to a great extent the sensitivity of the output voltage these variations due to the faster dynamics of the output control loop. This converter, therefore, gives high efficiency and low voltage stresses across its switches and Zero Voltage Switching is achieved over a very wide range of loading and input voltage variations. The proposed model gives very good performance prediction under transient and steady state conditions and facilitates a better controller design.