Principle and Topology Synthesis of Integrated Single-input Multi-output and Multi-input Single-output DC-DC Converters

Abstract

Renewable energy sources (RESs) such as Photovoltaic (PV) and wind dominate total renewable power generation. Since both sources are intermittent in nature, effective solutions are needed for reliable operation. However, due to the erratic nature of RESs, a battery and grid are always incorporated with the RES system to maintain an uninterruptable power supply to load and improve system reliability. Conventionally, separate DC-DC converters are connected among RESs and batteries to the DC bus and load. However, using several SISO converters increases the overall system component count, size, and implementation cost. Therefore, this work has introduced a topology synthesis technique to reduce the costs of synthesizing an integrated three-port converter with a reduced component count. The principle of topology synthesis states that an integrated three-port converter can be easily developed from a conventional SISO converter by replacing a diode with a basic cell inclusive of an additional bidirectional port. This three-port converter is compared with the conventional strategy, which employs two separate DC-DC Cuk converters to generate dual-output voltages. The three-port converter can operate in three operating modes: single input dual output (SIDO), dual input single output (DISO), and SISO, depending on the power transfer among the three ports. The MIMO converter controller structure has multiple interacting control loops to maintain the power balance between source and load demand. With multiple control loops, it is challenging to design closed-loop control algorithm for individual output ports without a proper decoupling method. Therefore, this thesis presents a detailed approach by utilizing the state-space averaging method to obtain the converter model under different modes of operation. Then a decoupling network is introduced to allow separate controller designs. The proposed control structure is composed of a decoupling network to address the inevitable cross-coupling effect of multiport converters present due to various interacting control loops. In addition, a PI-Lead compensator is designed to achieve improved steady-state and transient performance in each operating mode of the three-port Cuk Converter (TPCC). Furthermore, an autonomous mode selection (AMS) technique is proposed to achieve a seamless transition between different operating modes. The AMS technique automatically shifts the operating modes of TPCC by comparing the availability of instantaneous power at each port to maintain an uninterruptable power supply to the load. The proposed TPCC uses to interface solar, EV and utility grid. This system comprises two major parts. The first one is TPCC, which is connected to Solar PV generation, Electric vehicles and DC links. The second one is the secondary side of the DC link, which is connected to the utility grid with the help of a single-phase voltage source converter (VSC). This VSC is a bidirectional converter allowing power flow between the grid and TPCC. An ANF-based phase error minimization technique is implemented to improve system reliability during grid synchronization. Moreover, Power sharing among solar, EV and grid effectively handles both grid-connected and islanded modes. The TPCC controller controls the charging of the EV from PV and the grid. Finally, the feasibility and effectiveness of the proposed control algorithm are validated with the help of a laboratory prototype.