New Multi-Port Non-Isolated DC-DC Converters Topologies for DC Microgrid Applications

Abstract

In this master's thesis, two new multiport non-isolated DC-DC converters are proposed for DC microgrid applications. The proposed converters mainly aim to present an alternative architecture for DC microgrid interfacing multiple sources and loads. Using less number of switches, diodes and passive elements, two novel five ports and four ports are developed reducing multiple redundant power conversion stages. Recently, DC microgrids have been gaining a substantial increasing interest over the past couple of years both in academia and industry because of its relevant merits compared to AC grids. Conventionally, dedicated DC converters have simple control; however, they lead to a high system cost and weight, more power loss. Hence, multi-port converters have recently attracted academia for developing new topologies for DC microgrid applications overcoming the aforementioned issues of the DC microgrid conventional architecture. A new five port DC-DC converter is proposed for DC Microgrid applications. The bidirectional buck-boost structure of the proposed topology allows an enhanced flexibility to connect sources and loads with different voltage and power levels. The control strategy is developed to achieve power control for renewable sources such as PV, in addition to a certain degree of resilience for DC sources availability maintaining boosted DC link voltage. A detailed steady state analysis is conducted to derive voltage relations between all ports. Additionally, small signal linear model is developed for the proposed converter to study the close loop control performance and stability. As the proposed system is multi-input multi-output system, a dual control feedback loops are used to control inductors currents and capacitors voltages achieving MPPT for PV and DC link voltage regulation. The proposed configuration has several benefits for the design and operation of DC microgrids such as reducing multiple power conversions, reduced number of elements, voltage boosting capability, and higher efficiency. A MATLAB/Simulink based simulation study is conducted to demonstrate the performance of proposed multiport converter topology under different operating conditions. A new non-isolated four port DC-DC converter is proposed for hybrid Microgrid application. Hybrid DC Microgrid where energy is optimally harvested from different kind of sources (PV/FC/Battery) is typical used in wide range of applications. By using four IGBT switches with their anti-parallel diodes and one additional diode, three different sources are interfaced to a boosted DC link. The new presented converter has two switches with reduced voltage stress compared with the ones proposed in the literature. Different operation modes of the new architecture are discussed and testified through simulation and experimentally. The buck-boost structure of the proposed topology allows an enhanced flexibility to integrate various sources with distinct voltage-current (V-I) characteristics while sharing load power among all ports. Average steady state analysis is performed to get voltage gains between all ports and to design the converter parameters. Additionally, the dynamics of the proposed converter is developed in mathematical model for the sake of stability analysis and controller design. The dynamic linearized model of the four port converter is obtained through out state space averaging followed by small signal modeling. Similar to five port converter, the proposed converter is derived from typical boost and buck-boost converters. The control strategy is developed to manage power flow between sources and load realizing MPPT in case when PV is available, otherwise, it controls the battery power. The DC link voltage is regulated in all modes of operations. The converter different operating conditions are testified through MATLAB/Simulink simulation platform and validated experimentally.

Date of Award	Dec 2021
Original language	American English