The design of cascaded DC-DC converters with single-switch PWM and PFM for standalone PV power applications

摘要

This paper proposes a design of cascaded DC-DC converters for transferring energy from solar panels to loads in standalone cases. The storage units are connected to the proposed system via the converters to solve the instability of the renewable power source. The voltage levels of the power supply, storage and the load are different to each other in the design. Single-switch simplification is utilised to reduce the number of switches in the topology. The control circuit of the system is developed based on the conventional cascaded converters. Resettable integrators are introduced in the control circuit to perform Pulse Frequency Modulation (PFM) to regulate one of the converters. The ramp signal from the integrator is used to achieve Pulse Width Modulation (PWM) simultaneously. The advantages of the proposed design include the fewer components, the smaller size and more control freedom than the conventional converters for PV power system. In this paper, the design process of the proposed converters is introduced with the operation principles in different situations. Moreover, the design of the control circuit is illustrated as well as the operation of PWM and PFM. Last, the proposed design is verified by the simulation and experimental results.