A Reconfigurable Current-Fed LLC Resonant Converter With Circulant PWM Control and Wide Gain Range

In this article, a reconfigurable current-fed LLC resonant converter based on two series-connected voltage source submodules (VSMs) with wide voltage gain is proposed. By circulant PWM (CPWM) control strategy, the output voltage can be regulated. Since, the switching patterns of the power devices are reconfigured under this modulation scheme, the resonant tank can operate in three-level or two-level modes. Therefore, two operation modes are obtained, ensuring that it can work over a wide voltage range while realizing zero-voltage switching (ZVS) for all switches. In addition, self-balancing of VSM capacitor voltages and high-efficiency are achieved. Compared with existing resonant topologies, the proposed solution not only has a smaller number of devices, but also the voltage stress on the input-side switches is lower than the input voltage for the entire wide voltage range. Therefore, primary switches with lower voltage ratings can be applied, which can further reduce device costs and improve efficiency. The working principle and circuit characteristics of the converter are elaborated on. Finally, a 250W prototype with 75-300 V input and 200 V output for space electric propulsion systems is developed and tested to confirm the theoretical analysis and validity of the proposed converter.