Application of Integrated Magnetics and Discontinuous Conduction Mode to Multi-port DC-DC Power Conversion for integrating PV panels with storage

Abstract

Multi-port converter design and analysis presents one of the most intriguing challenges in the incorporation of renewables in the power grid. Choice of topology is of paramount importance to improve the power conditioning. To this eect, the Cuk topology can be a suitable candidate : low Electromagnetic Interference (EMI), low component count, simplied Maximum Power Point Tracking (MPPT) and power management, reduction of lter capacitor requirement, high eciency. This thesis revisits the concept of integrated magnetics in the Cuk topology and uses it judiciously to achieve the aforementioned requirements, by generating ripple-free currents at two terminals, independent regulation of two outputs in addition to magnetic integration. However, till date, no completely deterministic method has existed to design the integrated magnetic version of the Cuk converter. Two dierent methods, adopted from the area-product and the Kg (geometrical constant) methods are explored to design the two-port version of this converter. The area-product method is validated by means of experimental results on a 250W prototype. The ideas are then extended to a three-port version, but with the addition of another feature: independent regulation of two output ports. This is achieved by means of a combined Continuous Conduction Mode (CCM)-Discontinuous Conduction Mode (DCM) operation, but without sacrificing the ripple-free nature of currents on two of the ports. The non-isolated version of this converter, meant for modular use in a microconverter architecture, is validated by means of simulation and experimental results on a 150W prototype. A soft-switching scheme has also been demonstrated for a three-port converter with integrated magnetics. This has an active-clamp Zero-Voltage Switching (ZVS) turn-on circuit with the addition of a Zero-Current Switching (ZCS) turn-o. The design of the external components and simulation results for the same are presented as well. Finally, with the ever-increasing adoption of wide bandgap devices and planar magnetics in power electronics, it makes sense to get rid of the isolation transformer altogether for PV-to-grid applications, since isolation is not an imposed standard in PV power systems. Two Cuk converter based topologies are proposed which are hybrid charge-pump/inductive converter circuits. Simulation results are presented for the same.