Modelling of Single Stage Three Level Resonant AC/DC Converters Operating with Variable Frequency Phase Shift Modulation

This paper presents a state space modelling approach for a single stage three level resonant power factor correction converter operating with variable frequency phase shift control in discontinuous conduction mode. Modelling is achieved using a combined averaging and multiple-frequency approach. The model gives good prediction of both the transient and steady state operations of the converter. The dynamics of the output filter can also be represented as well as the influence of parasitic parameters such as the capacitor equivalent series resistance (ESR). This method also allows the separation of both the frequency and duty cycle as the control variables. All state variables are broken down into their frequency components, including high and low frequency components (the high frequency components being in the order of the switching frequency and the low frequency components being in the order of power line frequency) and the amplitudes of the frequency components are used as the new state variables. As a result a model is obtained that has the switching frequency as well as the required duty ratio for the phase-shift-modulation as separated control input variables, which facilitates controller design. The developed model is verified on a 2.3 kW, 48 V, input voltage 90-265 V_rms.