Forward-Flyback Converter With Cockcroft-Walton Voltage Multiplier in DCM: Averaged Small-Signal Modeling and Valley-Switching Control Design to Supply Electrohydrodynamic Devices

The Forward-Flyback converter with Cockcroft-Walton Voltage Multiplier (FFCWVM) operating in discontinuous conduction mode (DCM) is validated in Serrano-Vargas et al. (2021) as a suitable topology to supply novel cooling systems based in Electrohydrodynamic (EHD) technology. More details about the topology analysis, the steady-state operation and the whole design and optimization of the FFCWVM are given in Serrano Vargas (2022), where this converter is validated at different specifications. Since the conductivity of the EHD devices is reduced over time due to the erosion of the electrodes, the output voltage must be accurately controlled and the design of the control stage becomes essential, which is the main focus of this paper. The valley-switching control technique is proposed to optimize the performance of the FFCWVM under high voltage and very low power specifications due to its inherent resonant operation. In addition, the main functionalities required to control the FFCWVM while supplying the EHD devices are described. Then, the averaged modeling of the FFCWVM operating in DCM is achieved based on a first-order equivalent circuit approximation and considering the effect of the parasitic capacitances and the resonant currents in the circuit. As a result, two different averaged small-signal models (a simplified and a more accurate one) are accomplished, allowing for calculating the control-to-output transfer functions. Based on them, the most representative bode plots are highlighted and validated by means of simulations, and a suitable Type-II regulator is designed. Finally, a prototype is built and experimental results are presented, achieving a 94.07% global efficiency (96.03% open loop efficiency) and validating the proposed averaged modeling analysis and the implemented valley switching controller.